Journal articles: 'Iridium catalysts'

1

Siebert, Max, Golo Storch, Frank Rominger, and Oliver Trapp. "Temperature-Controlled Bidirectional Enantioselectivity in Asymmetric Hydrogenation Reactions Utilizing Stereodynamic Iridium Complexes." Synthesis 49, no. 15 (June 20, 2017): 3485–94. http://dx.doi.org/10.1055/s-0036-1588861.

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Stereochemically flexible 2,2(-bis(diphenylphosphino)biphenyl (BIPHEP) ligands were modified with chiral α-substituted carboxylic acid auxiliaries in the 3- and 3′-position. The resulting central-to-axial chirality transfer to the stereochemically flexible chiral axis of the BIPHEP core was investigated as well as complexation of these diastereomeric ligands to iridium(I). Solid-state structures of both ligand diastereomers and a diastereomerically pure iridium(I) BIPHEP complex were obtained. Thermal equilibration of the resulting iridium(I) complexes was studied to investigate the stereodynamic properties of the BIPHEP ligands. The iridium(I) complexes without and after pre-catalysis warming in solution — which induces a shift of the diastereomeric ratio — were applied for asymmetric hydrogenation of a prochiral α-substituted acrylic acid, resulting in temperature-controlled bidirectional enantioselectivity of iridium catalysts for the first time. In both cases, enantioenriched (R)-naproxen as well as (S)-naproxen — after re-equilibration of the catalyst at elevated temperatures — was obtained by using the same catalyst.

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Lukey, CA, MA Long, and JL Garnett. "Aromatic Hydrogen Isotope Exchange Reactions Catalyzed by Iridium Complexes in Aqueous Solution." Australian Journal of Chemistry 48, no. 1 (1995): 79. http://dx.doi.org/10.1071/ch9950079.

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Sodium hexachloroiridate (III) and sodium hexachloroiridate (IV) have been used as homogeneous catalysts for hydrogen isotope exchange between benzenoid compounds and water. The ideal solvent consisted of 50 mole % acetic acid/water, and the optimum temperature was found to be 160°C. Under these conditions the rate of incorporation of deuterium into benzene was significant (typically 15% D in 6 h), and reduction to iridium metal was minimized. The active catalytic species was identified as a solvated iridium(III) species, which is also postulated to be the active catalyst in solutions containing hexachloroiridate (IV). The kinetics of exchange in benzene catalysed by sodium hexachloroiridate (III) were elucidated, and found to be more complex than for the corresponding sodium tetrachloroplatinate (II) catalysed exchange, in that a two-term rate dependence was found for catalyst concentration and the reaction was inversely dependent on hydrogen ion concentration. The reaction was found to be independent of chloride ion concentration, this confirming that the active catalyst is a solvated species. Isotopic labelling in all compounds was confined to the aromatic ring, and most substituted benzenes exhibited deactivation of the ortho positions, indicating that a dissociative π-complex exchange mechanism was operating. This was confirmed by exchange into naphthalene, where it was found that labelling was predominantly in the β position. Facile exchange into nitrobenzene provided good evidence of homogeneous catalysis, and not catalysis by precipitated metal.

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Frety, R., P. N. Da Silva, and M. Guenin. "Supported iridium catalysts." Applied Catalysis 57, no. 1 (January 1990): 99–103. http://dx.doi.org/10.1016/s0166-9834(00)80726-5.

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Yoo, Dalsan, Jaegyu Woo, Seolyeong Oh, and Jong-Ki Jeon. "Performance of Pt and Ir Supported on Mesoporous Materials for Decomposition of Hydroxylammonium Nitrate Solution." Journal of Nanoscience and Nanotechnology 20, no. 7 (July 1, 2020): 4461–65. http://dx.doi.org/10.1166/jnn.2020.17598.

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The catalytic decomposition of hydroxylammonium nitrate (HAN) was investigated using a series of platinum and iridium supported on mesoporous materials. In this study, MMZY, KIT-6, and SBA-15 were used as supports. The effects of the active metal and the pore structure of the catalysts on decomposition of HAN solution were studied. The activity of the platinum catalysts supported on mesoporous material is much superior to that of the iridium catalysts on the same support. The Pt(10)/SBA-15 catalyst showed excellent decomposition activity and was the best among the catalysts tested here, which seemed to be because of the pore structure of Pt(10)/SBA-15. Because the pore size of Pt(10)/SBA-15 is larger than that of Pt(10)/MMZY and Pt(10)/KIT-6, it is more advantageous for diffusion of reactant and product gas. The activity of the catalyst increased as the amount of Pt loaded on the SBA-15 support increased.

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Amirsardari, Zahra, Akram Dourani, Mohamad Ali Amirifar, Nooredin Ghadiri Massoom, and Rahim Ehsani. "Development of novel supported iridium nanocatalysts for special catalytic beds." Journal of Nanostructure in Chemistry 10, no. 1 (December 26, 2019): 47–53. http://dx.doi.org/10.1007/s40097-019-00327-8.

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Abstract In the present paper, an experimental study of the catalytic decomposition of hydrous hydrazine was investigated on the different structural forms of the catalyst. The synthesized iridium catalysts have been usually used directly and have not been evaluated in the laboratory reactor. This study includes the preparation of iridium-based catalysts supported on spherical (alumina), honeycomb monoliths (cordierite) and foams (alumina) for the evaluation of catalytic activity in the laboratory reactor. The characterizations of these catalysts were evaluated by the TGA, FESEM and BET analysis. The result of the catalytic characterization of monolithic support was shown a homogeneous distribution of active metal without any problem of sintering (average size 25 nm) on the support surface. While the surface of the spherical and foam supports were shown non-uniform distribution of nanoparticles on the support skeleton (average size 55 nm). The monolithic catalyst exhibits higher decomposition rate and H2 selectivity than other supports due to uniform in shape and particle size distribution. Graphic abstract

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Jiménez, M. Victoria, Ana Ojeda-Amador, Raquel Puerta-Oteo, Joaquín Martínez-Sal, Vincenzo Passarelli, and Jesús Pérez-Torrente. "Selective Oxidation of Glycerol via Acceptorless Dehydrogenation Driven by Ir(I)-NHC Catalysts." Molecules 27, no. 22 (November 8, 2022): 7666. http://dx.doi.org/10.3390/molecules27227666.

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Iridium(I) compounds featuring bridge-functionalized bis-NHC ligands (NHC = N-heterocyclic carbene), [Ir(cod)(bis-NHC)] and [Ir(CO)2(bis-NHC)], have been prepared from the appropriate carboxylate- or hydroxy-functionalized bis-imidazolium salts. The related complexes [Ir(cod)(NHC)2]+ and [IrCl(cod)(NHC)(cod)] have been synthesized from a 3-hydroxypropyl functionalized imidazolium salt. These complexes have been shown to be robust catalysts in the oxidative dehydrogenation of glycerol to lactate (LA) with dihydrogen release. High activity and selectivity to LA were achieved in an open system under low catalyst loadings using KOH as a base. The hydroxy-functionalized bis-NHC catalysts are much more active than both the carboxylate-functionalized ones and the unbridged bis-NHC iridium(I) catalyst with hydroxyalkyl-functionalized NHC ligands. In general, carbonyl complexes are more active than the related 1,5-cyclooctadiene ones. The catalyst [Ir(CO)2{(MeImCH2)2CHOH}]Br exhibits the highest productivity affording TONs to LA up to 15,000 at very low catalyst loadings.

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Kumar, Prashant, Torsten Irrgang, George E. Kostakis, and Rhett Kempe. "Phosphine-free chiral iridium catalysts for asymmetric catalytic hydrogenation of simple ketones." RSC Adv. 6, no. 45 (2016): 39335–42. http://dx.doi.org/10.1039/c6ra04524c.

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Phosphine free iridium catalysts with simple structures show efficient enantioselectivities and activities in the asymmetric hydrogenation of simple ketones by using chiral iridium catalysts to chiral alcohols with up to 96% ee.

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8

Espinosa-Moreno, Francisco, Putrakumar Balla, Wenjie Shen, Juan Chavarria-Hernandez, Miguel Ruiz-Gómez, and Saúl Tlecuitl-Beristain. "Ir-Based Bimetallic Catalysts for Hydrogen Production through Glycerol Aqueous-Phase Reforming." Catalysts 8, no. 12 (December 3, 2018): 613. http://dx.doi.org/10.3390/catal8120613.

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Iridium, Iridium-Nickel and Iridium-Copper catalysts were prepared by incipient wetness impregnation and evaluated in the aqueous-phase reforming of glycerol using La2O3 or CeO2 as supports. The catalysts were characterized by N2 physisorption, XRD, H2-TPR, XPS, and EDS. The reactions were carried out in a fixed bed reactor feeding a solution of glycerol (10 wt %) in water, at 270 °C and 58 bar. All IrNi catalysts showed higher activity than Ir and IrCu, and in general, La2O3 catalysts showed a better performance when compared to CeO2 catalysts. The highest hydrogen production yield was reached by bimetallic IrNi catalysts with over 250 µmol min−1 gcat−1 for La2O3 and 150 µmol min−1 gcat−1 for CeO2.

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9

Pham, Pierce, and Christian Hilty. "Tunable iridium catalyst designs with bidentate N-heterocyclic carbene ligands for SABRE hyperpolarization of sterically hindered substrates." Chemical Communications 56, no. 98 (2020): 15466–69. http://dx.doi.org/10.1039/d0cc06840c.

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A series of iridium catalysts provides NMR sensitivity enhancement using para-hydrogen. The substrate exchange rate can be tuned for optimal polarization by the choice of an aryl and a nucleophilic moiety in the catalyst.

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10

Slavcheva, Evelina P. "Magnetron sputtered iridium oxide as anode catalyst for PEM hydrogen generation." Macedonian Journal of Chemistry and Chemical Engineering 30, no. 1 (June 15, 2011): 45. http://dx.doi.org/10.20450/mjcce.2011.69.

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Thin films of iridium oxide are deposited by reactive magnetron sputtering. The influence of oxygen partial pressure in the sputtering plasma on the composition, surface structure and morphology of the films has been studied by XRD, SEM, AFM and XPS analysis. An optimal combination of sputtering parameters yields stable microporous amorphous films with highly extended fractal surface. The electrochemical properties of these films are investigated in view of their application as catalysts for PEM water splitting, using the electrochemical techniques of cyclovoltammetry and steady state polarization. A morphology factor assessing the catalyst active surface for a series of sputtered samples with varying thickness/loading is determined and correlated to the catalytic efficiency. It has been proven that iridium oxide is a very efficient catalyst for oxygen evolution reaction (OER). The best performance with anodic current density of 0.3 A cm–2; at potential of 1.55 V (vs. RHE) shows the 500 nm thick film containing 0.2 mg cm-2; catalyst. These results combined with the established long-term mechanical stability of the sputtered iridium oxide films (SIROFs) prove the advantages of the reactive magnetron sputtering as simple and reliable method for preparation of catalysts with precisely controlled composition, loading, and surface characteristics.

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11

Lu, Sheng-Mei, Zhijun Wang, Jijie Wang, Jun Li, and Can Li. "Hydrogen generation from formic acid decomposition on a highly efficient iridium catalyst bearing a diaminoglyoxime ligand." Green Chemistry 20, no. 8 (2018): 1835–40. http://dx.doi.org/10.1039/c8gc00495a.

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A new iridium catalyst bearing a dioxime derived ligand has been developed for aqueous formic acid (FA) dehydrogenation in the absence of any additives. These catalysts can work at high temperature or room temperature with high efficiency and stability.

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12

Ding, Shengtao, and Weiwei Gao. "Progress on Iridium-Catalyzed Hydrosilylation of Alkenes and Alkynes." Synthesis 52, no. 23 (August 18, 2020): 3549–63. http://dx.doi.org/10.1055/s-0040-1707239.

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Hydrosilylation of multiple carbon–carbon bonds is a well-known process for the construction of organosilicon compounds. Nowadays, precious metal catalysts, especially platinum complexes, still occupy dominant positions in such processes. However, one important member of the precious metal family, iridium, is less used in this field. As early research mainly focused on developing stable and effective iridium catalysts, recent advances have disclosed the specific efficiency of simple iridium catalytic systems in the synthesis of functional organosilicon compounds. This short review summarizes the utilization of iridium complexes for the hydrosilylation of alkenes and alkynes, with an emphasis on the recent advances published in the last decade.1 Introduction2 Iridium-Catalyzed Hydrosilylation of Alkenes3 Iridium-Catalyzed Hydrosilylation of Alkynes4 Conclusions and Perspectives

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13

Stoltz, Brian, Samantha Shockley, and J. Hethcox. "Intermolecular Stereoselective Iridium-Catalyzed Allylic Alkylation: An Evolutionary Account." Synlett 29, no. 19 (August 15, 2018): 2481–92. http://dx.doi.org/10.1055/s-0037-1610217.

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Our lab has long been interested in the development of methods for the creation of enantioenriched all-carbon quaternary stereocenters. Historically, our interest has centered on palladium-catalyzed allylic alkylation, though recent efforts have moved to include the study of iridium catalysts. Whereas palladium catalysts enable the preparation of isolated stereocenters, the use of iridium catalysts allows for the direct construction of vicinal stereocenters via an enantio-, diastereo-, and regioselective allylic alkylation. This Account details the evolution of our research program from inception, which focused on the first iridium-catalyzed allylic alkylation to prepare stereodyads containing a single quaternary stereocenter, to our most recent discovery that allows for the synthesis of vicinal quaternary centers.1 Introduction2 Synthesis of Vicinal Tertiary and All-Carbon Quaternary Stereocenters via Enantio- and Diastereoselective Iridium-Catalyzed Allylic Alkylation2.1 Cyclic Nucleophiles2.2 Acyclic Nucleophiles2.3 Alkyl-Substituted Electrophiles3 Umpoled Iridium-Catalyzed Allylic Alkylation Reactions3.1 Tertiary Allylic Stereocenters3.2 Quaternary Allylic Stereocenters4 Synthesis of Vicinal All-Carbon Quaternary Centers via Enantioselective Iridium-Catalyzed Allylic Alkylation5 Summary and Future Outlook

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14

López, Óscar, and José M. Padrón. "Iridium- and Palladium-Based Catalysts in the Pharmaceutical Industry." Catalysts 12, no. 2 (January 28, 2022): 164. http://dx.doi.org/10.3390/catal12020164.

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Transition metal catalysts play a vital role in a wide range of industrial organic processes. The large-scale production of chemicals relying on catalyzed organic reactions represents a sustainable approach to supply society with end products for many daily life applications. Homogeneous (mainly for academic uses) and heterogeneous (crucial in industrial processes) metal-based catalysts have been developed for a plethora of organic reactions. The search for more sustainable strategies has led to the development of a countless number of metal-supported catalysts, nanosystems, and electrochemical and photochemical catalysts. In this work, although a vast number of transition metals can be used in this context, special attention is devoted to Ir- and Pd-based catalysts in the industrial manufacture of pharmaceutical drugs. Pd is by far the most widely used and versatile catalyst not only in academia but also in industry. Moreover, Ir-based complexes have emerged as attractive catalysts, particularly in asymmetric hydrogenation reactions. Ir- and Pd-based asymmetric reductions, aminations, cross-coupling reactions, and C–H activation are covered herein in the production of biologically active compounds or precursors; adaptation to bulk conditions is particularly highlighted.

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15

Allebrod, Frank, Maximilian Bernt, Jan Byrknes, Christian Eickes, Hany A. El-Sayed, Matthias Felix Ernst, Mohammad Fathi Tovini, et al. "(Invited) Design, Performance Characterization, and Durability of an Iridium-Based OER Catalyst for PEM Water Electrolysis." ECS Meeting Abstracts MA2022-01, no. 33 (July 7, 2022): 1339. http://dx.doi.org/10.1149/ma2022-01331339mtgabs.

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One of the building blocks to transition to a fully renewable energy supply is the utilization of hydrogen as a replacement of fossil fuels and as a chemical energy storage/carrier medium. This requires the economical and sustainable generation of hydrogen by water electrolysis, whereby proton exchange membrane (PEM) water electrolyzers would enable much higher power densities compared to conventional electrolyzers based on liquid alkaline electrolytes [1]. However, one of the short-comings of PEM water electrolyzers (PEMWEs) is the need for expensive and resource-limited iridium based catalysts for the oxygen evolution reaction (OER), so that the large-scale global deployment of PEMWEs would require a substantial reduction of the iridium loading from currently ~1-2 mgIr/cm2 elelctrode to below ~0.05 mgIr/cm2 elelctrode [2]. In this contribution, we will discuss the technical challenge to reduce the iridium loading using currently employed iridium catalysts, which is related to the high iridium packing density in the electrode (in units of gIr/cm3 electrode), so that for iridium loadings below ~0.4 mgIr/cm2 the electrode becomes too thin to allow for a homogenous electrode with sufficient in-plane electrical conductivity [3]. We will then present a catalyst concept that results in much lower iridium packing densities and that thus enables lower iridium loadings [4]. While such a catalyst exhibits a lower electrical conductivity than a currently employed benchmark catalyst, this drawback can be mitigated by utilizing porous transport layers at the anode that have a highly conductive coating [4]. The long-term stability of this novel type of iridium based OER catalyst will be examined in a 30 cm2 active area short-stack over ~3700 h; comparing the evolution of the OER mass activity and of the high frequency resistance corrected cell voltage with that of a benchmark catalyst that is evaluated in the same short-stack, which allows for mechanistic insights into the observed degradation rates [5]. References: [1] A. Buttler, H. Spliethoff; "Current status of water electrolysis for energy storage, grid balancing and sector coupling via power-to-gas and power-to-liquids: A review"; Renewable and Sustainable Energy Reviews 82 (2018) 2440. [2] M. Bernt, A. Weiß, M. Fathi Tovini, H. El-Sayed, C. Schramm, J. Schröter, C. Gebauer, H. A. Gasteiger; "Current Challenges in Catalyst Development for PEM Water Electrolyzers"; Chem. Ing. Tech. 92 (2020) 31. [3] M. Bernt, A. Siebel, H. A. Gasteiger; "Analysis of Voltage Losses in PEM Water Electrolyzers with Low Platinum Group Metal Loadings"; J. Electrochem. Soc. 165 (2018) F305. [4] M. Bernt, C. Schramm, J. Schröter, C. Gebauer, J. Byrknes, C. Eickes, H. A. Gasteiger; "Effect of the IrOx Conductivity on the Anode Electrode/Porous Transport Layer Interfacial Resistance in PEM Water Electrolyzers"; J. Electrochem. Soc. 168 (2021) 084513. [5] M. Möckl, M. Ernst, M. Kornherr, F. Allebrod, M. Bernt, J. Byrknes, C. Eickes, C. Gebauer, A. Moskovtseva, H. A. Gasteiger; "Durability investigation and benchmarking of a novel iridium catalyst in a PEM water electrolyzer at low iridium loading"; manuscript to be submitted. Acknowledgements: This work was conducted within the framework of the Kopernikus P2X project funded by the German Federal Ministry of Education and Research (BMBF).

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16

Apple, David C., Karen A. Brady, Jeffrey M. Chance, Nina E. Heard, and Terence A. Nile. "Iridium complexes as hydrosilylation catalysts." Journal of Molecular Catalysis 29, no. 1 (February 1985): 55–64. http://dx.doi.org/10.1016/0304-5102(85)85130-0.

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17

Willemsen, Jorgen S., Jan C. M. van Hest, and Floris P. J. T. Rutjes. "Aqueous reductive amination using a dendritic metal catalyst in a dialysis bag." Beilstein Journal of Organic Chemistry 9 (May 17, 2013): 960–65. http://dx.doi.org/10.3762/bjoc.9.110.

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Water-soluble dendritic iridium catalysts were synthesized by attaching a reactive metal complex to DAB-Am dendrimers via an adapted asymmetric bipyridine ligand. These dendritic catalysts were applied in the aqueous reductive amination of valine while contained in a dialysis bag. Comparable conversions were observed as for the noncompartmentalized counterparts, albeit with somewhat longer reaction times. These results clearly show that the encapsulated catalyst system is suitable to successfully drive a complex reaction mixture with various equilibrium reactions to completion.

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18

Britton, Luke, Jamie H. Docherty, Andrew P. Dominey, and Stephen P. Thomas. "Iron-Catalysed C(sp2)-H Borylation Enabled by Carboxylate Activation." Molecules 25, no. 4 (February 18, 2020): 905. http://dx.doi.org/10.3390/molecules25040905.

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Arene C(sp2)-H bond borylation reactions provide rapid and efficient routes to synthetically versatile boronic esters. While iridium catalysts are well established for this reaction, the discovery and development of methods using Earth-abundant alternatives is limited to just a few examples. Applying an in situ catalyst activation method using air-stable and easily handed reagents, the iron-catalysed C(sp2)-H borylation reactions of furans and thiophenes under blue light irradiation have been developed. Key reaction intermediates have been prepared and characterised, and suggest two mechanistic pathways are in action involving both C-H metallation and the formation of an iron boryl species.

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Mantilli, Luca, David Gérard, Sonya Torche, Céline Besnard, and Clément Mazet. "Highly enantioselective isomerization of primary allylic alcohols catalyzed by (P,N)-iridium complexes." Pure and Applied Chemistry 82, no. 7 (May 4, 2010): 1461–69. http://dx.doi.org/10.1351/pac-con-09-09-10.

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The catalytic asymmetric isomerization of allylic amines to enamines stands out as one of the most accomplished and well-studied reactions in asymmetric catalysis as illustrated by its industrial application. In contrast, the related asymmetric isomerization of primary allylic alcohols to the corresponding aldehydes still constitutes a significant challenge in organic synthesis. Herein, we show that under appropriate reaction conditions, iridium-hydride catalysts promote the isomerization of primary allylic alcohols under very mild reaction conditions. The best catalysts deliver the desired chiral aldehydes with unprecedented levels of enantioselectivity and good yields. Mechanistic hypotheses have been drawn based on preliminary investigations.

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20

Delgado, Sofia, Paranjeet Lakhtaria, Eva Sousa, Tiago Lagarteira, K. A. Friedrich, and Adélio Mendes. "Towards stable and highly active IrO₂ catalysts supported on doped tin oxides for the oxygen evolution reaction in acidic media." E3S Web of Conferences 334 (2022): 03001. http://dx.doi.org/10.1051/e3sconf/202233403001.

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Iridium oxide is the preferred catalyst for water oxidation but it is required to maximize its utilization to deploy Proton Exchange Membrane Water Electrolyzers (PEMWEs) into the large-scale applications panorama. A promising pathway for dispersing this precious catalyst is on an electric conductive and stable support. However, there is a lack of understanding how the support-catalyst interactions affect the stability/activity of the electrocatalyst under anodic conditions. This work discloses a modified, easy-scalable, polyol synthesis protocol to produce a highly active and stable iridium-based catalyst, supported on metal-doped tin oxides. The loading of Ir was reduced 30 wt.% compared to the reference IrO2, and dispersed on Sb-SnO2 (IrOx/ATO), In-SnO2 (IrOx/ITO) and SnO2 supports. All synthesized electrocatalysts not only surpassed the OER-mass activity of a commercial catalyst (IrO2) – reference – but also reached higher electrochemical active surface areas and enhanced stability under the OER conditions. The highest performance was achieved with Ir NPs supported on ITO (176 A/gIr vs. 15.5 A/gIr for the reference catalyst @ 1.51 V vs. RHE) and both IrOx/ITO and IrOx/SnO2 catalysts demonstrated remarkable stability after cycling the electrode and performing long-term chronopotentiometry. ITO is, therefore, an auspicious support to serve Ir-based catalysts as it favors a good bargain between activity and stability, while drastically reducing the amount of noble metal.

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Stollenwerk, Manfred, Tobias Schäfer, Johannes Stadtmüller, Thorsten Döhring, Dominic Freudenmann, and Nicole Röcke. "Sputtered highly effective iridium catalysts: a new approach for green satellite propulsion." Journal of Materials Science 56, no. 16 (March 1, 2021): 9974–84. http://dx.doi.org/10.1007/s10853-021-05897-z.

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AbstractThis work demonstrated the large potential of sputtered iridium metal for catalytic reactions shown by the example of decomposition of hydrogen peroxide (H2O2) for space propulsion systems. For this purpose, iridium was coated onto Al2O3 pellets by a sputter process under varied process parameters. Depending on previously selected parameters, the obtained metal-loaded pellets offer closed- and/or open-shell structures. Catalytic productivity of these first-generation iridium-sputtered catalysts was estimated in laboratory experiments and compared to platinum-loaded pellets. Under optimized sputter-process conditions, the reactivity is significantly improved compared to the platinum-impregnated pellets. The better catalytic productivity can be explained by the increased active surface area of the iridium layers on the pellets. The surface morphology and the microstructure of the iridium coating can be actively controlled by the sputter pressure. The results are in accordance with the sputtering process pressure tendency described by the Thornton Structure–Zone Model. Graphical abstract

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Zhang, Qiaoqiao, Zhiyao Duan, Yin Wang, Lina Li, Bing Nan, and Jingqi Guan. "Atomically dispersed iridium catalysts for multifunctional electrocatalysis." Journal of Materials Chemistry A 8, no. 37 (2020): 19665–73. http://dx.doi.org/10.1039/d0ta05750a.

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23

Corre, Y., W. Iali, M. Hamdaoui, X. Trivelli, J. P. Djukic, F. Agbossou-Niedercorn, and C. Michon. "Efficient hydrosilylation of imines using catalysts based on iridium(iii) metallacycles." Catalysis Science & Technology 5, no. 3 (2015): 1452–58. http://dx.doi.org/10.1039/c4cy01233j.

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Ir(iii) metallacycles were applied as catalysts for the hydrosilylation of ketimines and aldimines by using sodium tetrakis[(3,5-trifluoromethyl)phenyl]borate, NaBArF₂₄, as an additive. By using a slight excess of the organosilane reagent, the reactions proceeded rapidly and efficiently, at low catalyst loadings and at room temperature.

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Da Silva, P. N., M. Guenin, C. Leclercq, and R. Frety. "Metallic area of supported iridium catalysts." Applied Catalysis 54, no. 1 (September 1989): 203–15. http://dx.doi.org/10.1016/s0166-9834(00)82365-9.

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Kanki, Keiji, Yoshihiko Misumi, and Toshio Masuda. "Polymerization of phenylacetylene by iridium catalysts." Journal of Polymer Science Part A: Polymer Chemistry 40, no. 8 (March 7, 2002): 1075–80. http://dx.doi.org/10.1002/pola.10184.

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26

Conk, Richard J., Steven Hanna, Jake X. Shi, Ji Yang, Nicodemo R. Ciccia, Liang Qi, Brandon J. Bloomer, et al. "Catalytic deconstruction of waste polyethylene with ethylene to form propylene." Science 377, no. 6614 (September 30, 2022): 1561–66. http://dx.doi.org/10.1126/science.add1088.

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The conversion of polyolefins to monomers would create a valuable carbon feedstock from the largest fraction of waste plastic. However, breakdown of the main chains in these polymers requires the cleavage of carbon–carbon bonds that tend to resist selective chemical transformations. Here, we report the production of propylene by partial dehydrogenation of polyethylene and tandem isomerizing ethenolysis of the desaturated chain. Dehydrogenation of high-density polyethylene with either an iridium-pincer complex or platinum/zinc supported on silica as catalysts yielded dehydrogenated material containing up to 3.2% internal olefins; the combination of a second-generation Hoveyda-Grubbs metathesis catalyst and [PdP( t Bu) 3 (μ-Br)] 2 as an isomerization catalyst selectively degraded this unsaturated polymer to propylene in yields exceeding 80%. These results show promise for the application of mild catalysis to deconstruct otherwise stable polyolefins.

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27

Fathi Tovini, Mohammad, Ana Marija Damjanovia, Hany A. El-Sayed, Franziska Friedrich, Benjamin Strehle, Jozsef Speder, Alessandro Ghielmi, and Hubert Andreas Gasteiger. "Irreducible IrO₂ Anode Co-Catalysts for PEM Fuel Cell Voltage Reversal Mitigation and Their Stability Under Transient Operation Conditions." ECS Meeting Abstracts MA2022-01, no. 35 (July 7, 2022): 1466. http://dx.doi.org/10.1149/ma2022-01351466mtgabs.

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The cell voltage reversal that can occur during the transient operation of a proton exchange membrane fuel cell (PEMFC) stack leads to a substantial degradation of the anode catalyst. During cell reversal, the anode potential increases (>>1 V vs. the reversible hydrogen electrode potential (RHE)), causing severe oxidation of the anode catalyst carbon support, which leads to a collapse of the anode catalyst layer and to cell failure. One strategy to mitigate the damages of H2 starvation is the addition of a co-catalyst to the anode electrode, which catalyzes the oxygen evolution reaction (OER), so that the non-damaging OER rather than the damaging carbon oxidation reaction (COR) takes place. A commonly used anode co-catalyst to favor the OER over the COR during cell reversal events is iridium oxide (IrO2).1 Recent findings show that the near-surface layer(s) of IrO2 can be completely reduced to metallic Ir upon exposure to H2, e.g., under the operating conditions of a PEMFC anode.2, 3 Such alteration of the near-surface layer(s) of IrO2 drastically affects its stability during the anode potential transients that occur during start-up/shut-down (SUSD) events, where our recent study showed that the dissolution of metallic Ir and crossover of the dissolved Irn+ species through the membrane to the cathode electrode cause iridium deposition on the Pt/C cathode catalyst.3 Such iridium-based contamination on the cathode catalyst surface deteriorates the oxygen reduction reaction (ORR) activity of Pt and results in a significant performance loss during the normal operation of the fuel cell. At the same time, SUSD transients also cause an OER activity loss of the anode co-catalyst, which was shown to be mainly due to the redeposition of Pt dissolved from the anode hydrogen oxidation reaction (HOR) catalyst onto the reduced IrO2 anode co-catalyst, blocking its OER active sites.3 Since these degradation mechanisms are caused by the chemical reduction of the typically employed IrO2 anode co-catalysts in the PEMFC anode, a reduction-resistant OER catalyst would be required. In this contribution, we introduce an unprecedented approach to synthesize IrO2 catalysts that are not reduced in the PEMFC anode environment. The preparation of such irreducible IrO2 (Irr-IrO2) catalysts is based on an industrially scalable procedure consisting of a high-temperature (650-1000 ᵒC) heat treatment step followed by a deagglomeration step and a post annealing step to prepare catalyst powders with specific surface areas of ~25 m2/g. Figure 1 shows the thermogravimetric analysis (TGA) according to our previously proposed evaluation protocol3 under 3.3 vol.% H2/Ar of an as-received commercial benchmark catalyst (IrO2/TiO2 (Umicore)), a self-made IrO2 catalyst heat-treated near the conventional temperature of 500 °C (IrO2-500 °C), and a stabilized IrO2 catalyst prepared by a procedure introduced in this contribution (Irr-IrO2). It can be seen that the temperature that corresponds to the reduction of 20% of the IrO2 phase (α = 20%) of the Irr-IrO2 catalyst is ~38 °C and ~53 °C higher than those of the IrO2-500 °C and the IrO2/TiO2 (Umicore) catalysts, respectively. Considering the fact that all of these catalysts have a specific surface area of ~25 m2/g, the observed reductive stability improvement of Irr-IrO2 catalyst is due to its intrinsic structural distinctions from the typically synthesized IrO2 and the commercial benchmark IrO2 catalysts. As will be shown, this higher stability is reflected by the observation that SUSD cycling of MEAs with the Irr-IrO2 as anode co-catalyst does not result in iridium dissolution and the associated iridium poisoning of the ORR activity of the cathode catalyst. Furthermore, while its OER activity is lower than that of conventional IrO2 catalysts, it still dramatically increases the cell reversal tolerance time of a conventional Pt/C anode. References T. R. Ralph, S. Hudson, and D. P. Wilkinson, ECS Transactions, 1 (8), 67-84 (2006). P. J. Rheinländer and J. Durst, Journal of the Electrochemical Society, 168 (2), 024511 (2021). M. Fathi Tovini, A. M. Damjanovic, H. A. El-Sayed, J. Speder, C. Eickes, J.-P. Suchsland, A. Ghielmi, and H. A. Gasteiger, Journal of The Electrochemical Society, 168 (6), 064521 (2021). Figure 1. TGA (5 K min-1) experiments under 3.3 vol.% H2/Ar with the as-received IrO2/TiO2 (Umicore), the IrO2-500 °C, and the Irr-IrO2 catalyst powder samples (following a drying/cleaning step; see Ref. 3 for further details). The y-axis represents the fraction of the IrO2 phase in the catalyst powder samples that is reduced to metallic Ir (α). The black horizontal dashed line illustrates a reaction extent of α= 20%, to compare the stability of different samples in a H2-containing atmosphere. Figure 1

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Zieliński, Michał, Monika Kot, Mariusz Pietrowski, Robert Wojcieszak, Jolanta Kowalska-Kuś, and Ewa Janiszewska. "Studies of New Iridium Catalysts Supported on Modified Silicalite-1—Their Structure and Hydrogenating Properties." Materials 14, no. 16 (August 9, 2021): 4465. http://dx.doi.org/10.3390/ma14164465.

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This paper investigates the catalytic properties of the iridium catalysts supported on modified silicalite-1. Post-synthesis modification of silicalite-1, with solutions of ammonium compounds (NH4F and NH4OH), appeared to be an efficient method to generate the acidic sites in starting support. The modification of support led not only to changes in its acidity but also its porosity—formation of additional micro- and mesopores. The novel materials were used as supports for iridium. The iridium catalysts (1 wt.% Ir) were characterized by N2 adsorption/desorption measurements, temperature-programmed reduction with hydrogen (TPR-H2), H2 chemisorption, transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (TPD-NH3), X-ray photoelectron spectroscopy (XPS) and tested in the hydrogenation of toluene reaction. The catalytic activity of iridium supported on silicalite-1 treated with NH4OH (higher porosity of support, better dispersion of active phase) was much higher than that of Ir supported on unmodified and modified with NH4F silicalite-1.

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Sévery, Laurent, Sebastian Siol, and S. Tilley. "Design of Molecular Water Oxidation Catalysts Stabilized by Ultrathin Inorganic Overlayers—Is Active Site Protection Necessary?" Inorganics 6, no. 4 (September 29, 2018): 105. http://dx.doi.org/10.3390/inorganics6040105.

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Anchored molecular catalysts provide a good step towards bridging the gap between homogeneous and heterogeneous catalysis. However, applications in an aqueous environment pose a serious challenge to anchoring groups in terms of stability. Ultrathin overlayers embedding these catalysts on the surface using atomic layer deposition (ALD) are an elegant solution to tackle the anchoring group instability. The propensity of ALD precursors to react with water leads to the question whether molecules containing aqua ligands, such as most water oxidation complexes, can be protected without side reactions and deactivation during the deposition process. We synthesized two iridium and two ruthenium-based water oxidation catalysts, which contained an aqua ligand (Ir–OH2 and Ru–OH2) or a chloride (Ir–Cl and Ru–Cl) that served as a protecting group for the former. Using a ligand exchange reaction on the anchored and partially embedded Ru–Cl, the optimal overlayer thickness was determined to be 1.6 nm. An electrochemical test of the protected catalysts on meso-ITO showed different behaviors for the Ru and the Ir catalysts. The former showed no onset difference between protected and non-protected versions, but limited stability. Ir–Cl displayed excellent stability, whilst the unprotected catalyst Ir–OH2 showed a later initial onset. Self-regeneration of the catalytic activity of Ir–OH2 under operating conditions was observed. We propose chloride ligands as generally applicable protecting groups for catalysts that are to be stabilized on surfaces using ALD.

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Zhang, Yajing, Qian Wang, Zongsheng Yan, Donglai Ma, and Yuguang Zheng. "Visible-light-mediated copper photocatalysis for organic syntheses." Beilstein Journal of Organic Chemistry 17 (October 12, 2021): 2520–42. http://dx.doi.org/10.3762/bjoc.17.169.

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Photoredox catalysis has been applied to renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are widely investigated, because they are abundant and less expensive. This review discusses the scope and application of photoinduced copper-based catalysis along with recent progress in this field. The special features and mechanisms of copper photocatalysis and highlights of the applications of the copper complexes to photocatalysis are reported. Copper-photocatalyzed reactions, including alkene and alkyne functionalization, organic halide functionalization, and alkyl C–H functionalization that have been reported over the past 5 years, are included.

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Murawski, James, Shuaihang Yin, Christopher Zalitis, James Stevens, Katie Rigg, Mark Clapp, Graham Smith, Jonathan Sharman, Gareth Hinds, and Ifan Erfyl Lester Stephens. "Oxygen Evolution Reaction Catalyst Development: Benchmarking IrO_x Catalyst Activity and Stability." ECS Meeting Abstracts MA2022-01, no. 34 (July 7, 2022): 1367. http://dx.doi.org/10.1149/ma2022-01341367mtgabs.

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While PEM electrolyser catalyst cost may not be a significant portion of system costs1 it does represent a bottleneck for the ability to generate TW level of H2. This is primarily because of the reliance on IrOx as a stable oxygen evolution catalyst in order to meet future green H2 needs either replacement or reduction of iridium loading of at least 50 times is needed while maintaining a high level of stability2. IrOx based materials are the only oxygen evolution catalysts combining activity and stability under PEM electrolysis conditions; even so, they are insufficiently stable. In the current work, we tailored the activity of IrOx catalysts synthesised by a variant of the Adams fusion reaction3 using decomposition of Iridium nitrate and varying temperature of synthesis to generate a series of catalysts with differing crystallinity and surface area. We benchmarked their stability using both accelerated degradation electrochemical measurements (30k cycles 1.2-1.7VRHE @ 500 mV s-1) and inductively coupled plasma-mass spectrometry(ICP-MS), both in rotating disk electrode(RDE) measurements and in a single cell PEM electrolyser. We have compared several different methods for probing electrochemical surface area, including BET, double layer capacitance from cyclic voltammetry, adsorption capacitance using impedance spectroscopy and CO stripping using ultrasensitive on chip electrochemical mass spectrometry. The results from the RDE measurements are shown in figure 1; they show that while the high surface area amorphous IrOx catalysts demonstrate higher activity normalised to geometric area, when normalised to specific activity the difference is insignificant. In addition to electrochemical performance losses, the amorphous IrOx shows an order of magnitude increase in iridium dissolution, determined via ICP-MS. Future studies will look at the ability to overcome the limitations of aqueous model studies for stability testing and utilising testing to select OER catalyst candidates that meet both activity and stability required for long term operation in PEM electrolyser systems. 1 L. Bertuccioli, A. Chan, D. Hart, F. Lehner, B. Madden and E. Standen, Study on development of water electrolysis in the EU, Fuel Cells and hydrogen Joint Undertaking, 2014, vol. 1. 2 P. S. Alexis Grimaud, Jan Rossmeisl, Research nees towards sustainable production of fuels and chemicals, Section 1: Water splitting and sustainable H2 Production, 2019. 3 D. F. Abbott, D. Lebedev, K. Waltar, M. Povia, M. Nachtegaal, E. Fabbri, C. Copéret and T. J. Schmidt, Chem. Mater., 2016, 28, 6591–6604. Figure 1

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Schafer, Andrew G., and Simon B. Blakey. "Ir-Catalyzed enantioselective group transfer reactions." Chemical Society Reviews 44, no. 17 (2015): 5969–80. http://dx.doi.org/10.1039/c5cs00354g.

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Foster, Daven, Pengchao Gao, Ziyun Zhang, Gellért Sipos, Alexandre N. Sobolev, Gareth Nealon, Laura Falivene, Luigi Cavallo, and Reto Dorta. "Design, scope and mechanism of highly active and selective chiral NHC–iridium catalysts for the intramolecular hydroamination of a variety of unactivated aminoalkenes." Chemical Science 12, no. 10 (2021): 3751–67. http://dx.doi.org/10.1039/d0sc05884j.

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Amourizi, Fereshteh, Kheibar Dashtian, and Mehrorang Ghaedi. "Developing a new colorimetric bioassay for iodide determination based on gold supported iridium peroxidase catalysts." New Journal of Chemistry 44, no. 14 (2020): 5588–97. http://dx.doi.org/10.1039/c9nj06310b.

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Prössl, Carolin, Markus Kübler, Mohammad Ali Nowroozi, Stephen Paul, Oliver Clemens, and Ulrike I. Kramm. "Investigation of the thermal removal steps of capping agents in the synthesis of bimetallic iridium-based catalysts for the ethanol oxidation reaction." Physical Chemistry Chemical Physics 23, no. 1 (2021): 563–73. http://dx.doi.org/10.1039/d0cp04900j.

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Nikolaraki, Ersi, Grammatiki Goula, Paraskevi Panagiotopoulou, Martin J. Taylor, Kalliopi Kousi, Georgios Kyriakou, Dimitris I. Kondarides, Richard M. Lambert, and Ioannis V. Yentekakis. "Support Induced Effects on the Ir Nanoparticles Activity, Selectivity and Stability Performance under CO2 Reforming of Methane." Nanomaterials 11, no. 11 (October 28, 2021): 2880. http://dx.doi.org/10.3390/nano11112880.

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The production of syngas (H2 and CO)—a key building block for the manufacture of liquid energy carriers, ammonia and hydrogen—through the dry (CO2−) reforming of methane (DRM) continues to gain attention in heterogeneous catalysis, renewable energy technologies and sustainable economy. Here we report on the effects of the metal oxide support (γ-Al2O3, alumina-ceria-zirconia (ACZ) and ceria-zirconia (CZ)) on the low-temperature (ca. 500–750 ∘C) DRM activity, selectivity, resistance against carbon deposition and iridium nanoparticles sintering under oxidative thermal aging. A variety of characterization techniques were implemented to provide insight into the factors that determine iridium intrinsic DRM kinetics and stability, including metal-support interactions and physicochemical properties of materials. All Ir/γ-Al2O3, Ir/ACZ and Ir/CZ catalysts have stable DRM performance with time-on-stream, although supports with high oxygen storage capacity (ACZ and CZ) promoted CO2 conversion, yielding CO-enriched syngas. CZ-based supports endow Ir exceptional anti-sintering characteristics. The amount of carbon deposition was small in all catalysts, however decreasing as Ir/γ-Al2O3 > Ir/ACZ > Ir/CZ. The experimental findings are consistent with a bifunctional reaction mechanism involving participation of oxygen vacancies on the support’s surface in CO2 activation and carbon removal, and overall suggest that CZ-supported Ir nanoparticles are promising catalysts for low-temperature dry reforming of methane (LT-DRM).

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Steinbach, Andrew, Andrew Haug, Fuxia Sun, Krzysztof A. Lewinski, Hui Xu, Natalia Macauley, Shuo Ding, Elliot Padgett, Shaun M. Alia, and David A. Cullen. "(Invited, Digital Presentation) Nanostructured Thin Film (NSTF) Iridium Catalyst Powder for Proton Exchange Membrane Water Electrolyzers." ECS Meeting Abstracts MA2022-01, no. 33 (July 7, 2022): 1340. http://dx.doi.org/10.1149/ma2022-01331340mtgabs.

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Proton exchange membrane water electrolyzers (PEMWEs) are electrochemical devices which generate hydrogen (H2) gas from water and electrical energy feedstocks. PEMWEs produce H2 renewably and carbon-free when the electricity is from renewable sources, and are a pathway to enable deep decarbonization across multiple industrial and energy sectors[1]. However, commercial deployment of PEMWEs is currently limited to megawatt-scale due to relatively higher H2 production costs and capital costs than hydrocarbon reforming [2]. The higher costs are due in part to the use of significant quantities of expensive materials (Pt and Ir electrocatalysts and perfluorinated ionomers), insufficient operating performance and durability, and high manufacturing costs. Additionally, commercial PEMWEs additionally use high Ir loadings [3] for the oxygen evolution reaction (OER), and the limited abundance of Ir [4] may limit PEMWE annual deployment of those technologies to gigawatt (GW) scale. 3M Nanostructured Thin Film (NSTF) PEMWE OER powder catalysts and electrodes are a unique approach to address the cost and Ir utilization barriers noted above. NSTF catalysts [5] are comprised of nm-scale catalyst metal thin films on a high aspect ratio inert support (Fig. A). NSTF Ir OER catalysts enable high efficiency and high durability due to high OER mass activity and intrinsic resistance to dissolution, imparted by the unique agglomerated thin film catalyst structure. NSTF OER electrodes [6] consist of a dispersed matrix of NSTF catalyst powder particles within a perfluorosulfonic acid (PFSA) ionomer binder (Fig. B), which have high catalyst utilization due to the high electronic conductivity of the primary catalyst particles. One of the key challenges associated with development of OER catalysts and electrodes is the lack of qualified accelerated stress tests (ASTs) to enable rapid assessments of durability under conditions relevant for end-use. The challenge is in part magnified by the long lifetime requirements of 80,000 hours and low required decay rates of single microvolts per hour, which traditionally has required long testing times and multiple replicates to obtain needed statistical significance. Additionally, evaluations of durability have often occurred under steady state testing with fixed current densities, which do not reflect anticipated use profiles when integrated with renewables such as wind and solar with significant power production variability over time. Lastly, operation at increased stack power densities is considered a key strategy to reduce stack capital costs and Ir requirements on a gram per kW basis. In this paper, we will report recent work on our durability assessment of NSTF OER powder catalysts and electrodes under aggressive testing protocols with low catalyst loadings relevant for PEM electrolyzers at large scale. Assessments included steady state durability tests, an accelerated stress test, and a protocol intended to simulate integration with a wind variable renewable energy (VRE) load profile. An example of results from the wind VRE protocol are summarized in Figs. C and D. The wind VRE protocol generated by Alia et al. [7] was modified from voltage control to current control and the maximum current density was scaled to 4.5A/cm2. The protocol was applied to a 3M laboratory CCM comprising a 0.20 mg/cm2 of 78wt% Ir/NSTF powder catalyst OER electrode, 0.09 mg/cm2 of 78wt% Pt/NSTF powder hydrogen evolution reaction (HER) electrode, and a 100 micron thick PEM (800EW 3M PFSA). After 500 hours of the wind VRE protocol, the cell performance was essentially unchanged (1mV voltage decrease at 2A/cm2). S. Dept. of Energy “H2@Scale”, https://www.energy.gov/eere/fuelcells/h2scale. S. Dept. of Energy H2USA Model, Current Forecourt Hydrogen Production v. 3.101. Ayers et al., Catalysis Today 262 121-132 (2016). Babic et al., Electrochem. Soc. 164 F387 (2017). Debe et al., ECS Trans. 45(2) 47-68 (2012). Steinbach et al., 2019 U.S. DOE Annual Merit Review, Project ta026. Alia et al., Electrochem. Soc. 166 F1164 (2019). Figure 1

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Messerle, Barbara A., and Khuong Q. Vuong. "Synthesis of spiroketals by iridium-catalyzed double hydroalkoxylation." Pure and Applied Chemistry 78, no. 2 (January 1, 2006): 385–90. http://dx.doi.org/10.1351/pac200678020385.

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A highly efficient approach to the synthesis of spiroketals involves the double cyclization of alkynyl diols using transition-metal catalysts. The iridium complex [Ir(PyP)(CO)2]BPh4 where PyP = 1-[(2-diphenylphosphino)ethyl]pyrazole is an effective catalyst for promoting the formation of spiroketals via this double hydroalkoxylation reaction. The complex promotes the formation of a series of spiroketal products from alkynyl diol starting materials such as 3-ethynylpentane-1,5-diol and 2-(4-hydroxybut-1-ynyl)benzyl alcohol. Stereoselective cyclization occurs for 3-ethynylpentane-1,5-diol, 3-ethynylhexane-1,6-diol. The cycloadditions occur in all but one case with quantitative conversion in under 24 h at 120 °C.

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Feiters, Martin, A. Engwerda, B. van Weerdenburg, N. Eshuis, M. Tessari, A. Longo, D. Banerjee, C. Fonseca Guerra, F. M. Bickelhaupt, and F. Rutjes. "EXAFS and DFT studies on iridium catalysts for SABRE." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C958. http://dx.doi.org/10.1107/s205327331409041x.

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Since it was first developed, Nuclear Magnetic Resonance (NMR) has become a powerful analytical tool that is now used widely in the fields of chemistry, materials science, and medicine. One way to overcome the intrinsic insensitivity of NMR is to use hyperpolarization techniques to produce non-Boltzmann spin-state distributions. One of these techniques is Signal Amplification By Reversible Exchange (SABRE),[1] in which hyperpolarization is achieved by the temporary association of parahydrogen and a substrate in the coordination sphere of a transition metal. The polarization can be transferred from the parahydrogen-derived hydride ligands to the bound substrate via scalar coupling, followed by dissociation of the hyperpolarized substrate into the bulk solution. We have investigated the efficiency of various iridium NHC complexes with aliphatic and aromatic R groups as SABRE catalysts.[2] The used metal centre is a six-coordinate iridium N-heterocyclic carbene complex, with three substrates and two hydrides, in which the exchange rate of substrate and parahydrogen at the metal centre determines the efficiency of the hyperpolarization. As solvent molecules compete with pyridine for coordination to iridium, the sensitivity of SABRE can be enhanced by displacement of solvent molecules by cosubstrates, i.e. proton-poor ligands such as methyltriazole.[3] In this exchange process, several mixed iridium complexes can be considered to exist, which were not all observed by NMR. Therefore, Density Functional Theory (DFT) calculations were performed on these complexes to better understand this phenomenon. While NMR itself is the best source of information on protons and dynamic processes involved in SABRE, we have found that Extended X-ray Absorption Fine Structure (EXAFS) studies in organic solutions provide interesting complimentary information on the complexes involved.

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Manguin, Romane, Delphine Pichon, Robert Tarrieu, Thomas Vives, Thierry Roisnel, Vincent Dorcet, Christophe Crévisy, et al. "A kinetic resolution strategy for the synthesis of chiral octahedral NHC–iridium(iii) catalysts." Chemical Communications 55, no. 43 (2019): 6058–61. http://dx.doi.org/10.1039/c9cc02434d.

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The transmetalation reaction of a chiral-bidentate NHC–silver complex to racemic [lr(μ-Cl)(ppy)₂]₂ operates with kinetic resolution leading to chiral octahedral NHC–iridium(iii) complexes and enantio-enriched bis-cyclometalated iridium(iii) complexes.

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Ferner, Kara, Janghoon Park, Zhenye Kang, Scott A. Mauger, Michael Ulsh, Guido Bender, and Shawn Litster. "High Resolution Characterization of Proton Exchange Membrane Water Electrolysis Anodes." ECS Meeting Abstracts MA2022-02, no. 44 (October 9, 2022): 1647. http://dx.doi.org/10.1149/ma2022-02441647mtgabs.

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The current use of expensive and geographically-limited precious metal catalysts, typically iridium, in proton exchange membrane water electrolyzer (PEMWE) anodes is necessary to accelerate the sluggish oxygen evolution reaction (OER). However, high loadings of iridium catalyst drastically increase the capital costs of PEM electrolysis, while low loadings of iridium lead to a significant decline in the efficiency of hydrogen production. Thus, PEMWE anode fabrication methods must be optimized to achieve the highest performance with lower iridium loadings. Using high resolution characterization methods, we show nanoscale differences in anode morphology between different IrO2 anode fabrication methods, such as spray coated versus blade coated anodes. We also explore the evolution of the electrode morphology throughout its fabrication and testing lifetime. The characterization methods used in this work include high resolution nanoscale X-ray computed tomography (nano-CT) as well as plasma-focused ion beam cross-sectioning and scanning electron microscopy (pFIB-SEM). Additionally, we present quantitative data such as solid particle and pore size distributions as well as pore network extractions derived from our image-based characterizations to elucidate the morphological differences between IrO2 anodes. This conference presentation was developed based upon funding from the Alliance for Sustainable Energy, LLC, Managing and Operating Contractor for the National Renewable Energy Laboratory for the U.S. Department of Energy.

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Kot, Monika, Robert Wojcieszak, Ewa Janiszewska, Mariusz Pietrowski, and Michał Zieliński. "Effect of Modification of Amorphous Silica with Ammonium Agents on the Physicochemical Properties and Hydrogenation Activity of Ir/SiO2 Catalysts." Materials 14, no. 4 (February 18, 2021): 968. http://dx.doi.org/10.3390/ma14040968.

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The modification of commercial silica with solutions of NH4F or NH4Cl salts, followed by thermal treatment, enabled generation of the acidic sites in SiO2 and changed its textural properties. The use of ammonium salts solution also caused the generation of additional porosity. Using NH4F solution caused significant decrease in the specific surface area and the increase in the average pore diameter. The number and strength of resulting acid sites depend on the nature of anion in the applied ammonium salt and the concentration of salt solution. It has been found that the sample treated with NH4F presented higher total acidity (TPD–NH3) and the amount as well as the strength of acid sites increased with the concentration of the used modifier. As modified amorphous SiO2 materials used as a support for iridium (1 wt %, Ir(acac)3) nanoparticles permitted to obtain highly active catalysts for toluene hydrogenation under atmospheric pressure. The highest activity (expressed as the apparent rate and TOF) was obtained for iridium catalysts supported on silica modified by NH4F with the highest acidity. The modification of silica with NH4F favors the generation of centers able to adsorb toluene, which results in higher activity of this catalyst.

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Xu, Guoqiang, Tijs Lammens, Qiang Liu, Xicheng Wang, Linlin Dong, Aldo Caiazzo, Nadim Ashraf, Jing Guan, and Xindong Mu. "Direct self-condensation of bio-alcohols in the aqueous phase." Green Chem. 16, no. 8 (2014): 3971–77. http://dx.doi.org/10.1039/c4gc00510d.

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Manas, Michael G., Jesús Campos, Liam S. Sharninghausen, Elisa Lin, and Robert H. Crabtree. "Selective catalytic oxidation of sugar alcohols to lactic acid." Green Chemistry 17, no. 1 (2015): 594–600. http://dx.doi.org/10.1039/c4gc01694g.

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Kovalenko, Oleksandr O., and Ola F. Wendt. "An electron poor iridium pincer complex for catalytic alkane dehydrogenation." Dalton Transactions 45, no. 40 (2016): 15963–69. http://dx.doi.org/10.1039/c6dt01816e.

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Alt, Helmut G, and Ingrid K Böhmer. "Catalytic Dehydrogenation of Isopentane with Iridium Catalysts." Angewandte Chemie International Edition 47, no. 14 (March 25, 2008): 2619–21. http://dx.doi.org/10.1002/anie.200704856.

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Brunen, Sebastian, Yvonne Grell, Philipp S. Steinlandt, Klaus Harms, and Eric Meggers. "Bis-Cyclometalated Indazole and Benzimidazole Chiral-at-Iridium Complexes: Synthesis and Asymmetric Catalysis." Molecules 26, no. 7 (March 24, 2021): 1822. http://dx.doi.org/10.3390/molecules26071822.

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A new class of bis-cyclometalated iridium(III) catalysts containing two inert cyclometalated 6-tert-butyl-2-phenyl-2H-indazole bidentate ligands or two inert cyclometalated 5-tert-butyl-1-methyl-2-phenylbenzimidazoles is introduced. The coordination sphere is complemented by two labile acetonitriles, and a hexafluorophosphate ion serves as a counterion for the monocationic complexes. Single enantiomers of the chiral-at-iridium complexes (>99% er) are obtained through a chiral-auxiliary-mediated approach using a monofluorinated salicyloxazoline and are investigated as catalysts in the enantioselective conjugate addition of indole to an α,β-unsaturated 2-acyl imidazole and an asymmetric Nazarov cyclization.

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Cano, Israel, Luis M. Martínez-Prieto, Pier F. Fazzini, Yannick Coppel, Bruno Chaudret, and Piet W. N. M. van Leeuwen. "Characterization of secondary phosphine oxide ligands on the surface of iridium nanoparticles." Physical Chemistry Chemical Physics 19, no. 32 (2017): 21655–62. http://dx.doi.org/10.1039/c7cp03439c.

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Ooka, Hideshi, Toshihiro Takashima, Akira Yamaguchi, Toru Hayashi, and Ryuhei Nakamura. "Element strategy of oxygen evolution electrocatalysis based on in situ spectroelectrochemistry." Chemical Communications 53, no. 53 (2017): 7149–61. http://dx.doi.org/10.1039/c7cc02204b.

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Ajakaiye Jensen, Lucy Idowu, Sara Blomberg, and Christian Hulteberg. "Effect of Pd and Ir as Promoters in the Activity of Ni/CeZrO2 Catalyst for the Reverse Water-Gas Shift Reaction." Catalysts 11, no. 9 (September 7, 2021): 1076. http://dx.doi.org/10.3390/catal11091076.

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Catalytic conversion of CO2 to CO using reverse water gas shift (RWGS) reaction is a key intermediate step for many CO2 utilization processes. RWGS followed by well-known synthesis gas conversion may emerge as a potential approach to convert CO2 to valuable chemicals and fuels. Nickel (Ni) based catalysts with ceria-zirconia (Ce-Zr) support can be used to tune the metal-support interactions, resulting in a potentially enhanced CO2 hydrogenation rate and elongation of the catalyst lifespan. The thermodynamics of RWGS reaction is favored at high temperature for CO2 conversion. In this paper the effect of Palladium (Pd) and Iridium (Ir) as promoters in the activity of 10 wt%Ni 2 wt%Pd 0.1wt%Ir/CeZrO2 catalyst for the reverse water gas shift reaction was investigated. RWGS was studied for different feed (CO2:H2) ratios. The new active interface between Ni, Pd and Ir particles is proposed to be an important factor in enhancing catalytic activity. 10 wt%Ni 2 wt%Pd 0.1 wt%Ir/CeZrO2 catalyst showed a better activity with CO2 conversion of 52.4% and a CO selectivity of 98% for H2:CO2 (1:1) compared to the activity of 10%Ni/CeZrO2 with CO2 conversion of 49.9% and a CO selectivity of 93%. The catalytic activity for different feed ratios using 10 wt%Ni 2 wt%Pd 0.1 wt%Ir/CeZrO2 were also studied. The use of palladium and iridium boosts the stability and life span of the Ni-based catalysts. This indicates that the catalyst could be used potentially to design RWGS reactors for CO2 utilization units.

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Journal articles on the topic 'Iridium catalysts'

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