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Articoli di riviste sul tema "Reductive dehydroxylation"

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Autore: Grafiati

Pubblicato: 20 luglio 2024

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1

Gräwert, Tobias, Ingrid Span, Adelbert Bacher e Michael Groll. "Reductive Dehydroxylation of Allyl Alcohols by IspH Protein". Angewandte Chemie International Edition 49, n. 47 (4 ottobre 2010): 8802–9. http://dx.doi.org/10.1002/anie.201000833.

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2

Mostinski, Yelena, David Lankri, Yana Konovalov, Riva Nataf e Dmitry Tsvelikhovsky. "Proline-promoted dehydroxylation of α-ketols". Chemical Science 10, n. 40 (2019): 9345–50. http://dx.doi.org/10.1039/c9sc02543j.

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A new single-step proline-potassium acetate promoted reductive dehydroxylation of α-ketols is reported. We introduce the unexplored reactivity of proline and, for the first time, reveal its ability to function as a reducing agent.

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3

Abdel-Azeim, Safwat, Abdesslem Jedidi, Jorg Eppinger e Luigi Cavallo. "Mechanistic insights into the reductive dehydroxylation pathway for the biosynthesis of isoprenoids promoted by the IspH enzyme". Chemical Science 6, n. 10 (2015): 5643–51. http://dx.doi.org/10.1039/c5sc01693b.

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4

Kim, Sunggak, Li Chan e Jazreel Lim. "Iron-Catalyzed Reductive Dehydroxylation of Benzylic Alcohols Using Polymethylhydrosiloxane (PMHS)". Synlett 2011, n. 19 (9 novembre 2011): 2862–66. http://dx.doi.org/10.1055/s-0031-1289857.

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5

Graewert, Tobias, Ingrid Span, Adelbert Bacher e Michael Groll. "ChemInform Abstract: Reductive Dehydroxylation of Allyl Alcohols by IspH Protein". ChemInform 42, n. 6 (13 gennaio 2011): no. http://dx.doi.org/10.1002/chin.201106274.

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6

Boll, Matthias, e Georg Fuchs. "Unusual reactions involved in anaerobic metabolism of phenolic compounds". Biological Chemistry 386, n. 10 (1 ottobre 2005): 989–97. http://dx.doi.org/10.1515/bc.2005.115.

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AbstractAerobic bacteria use molecular oxygen as a common co-substrate for key enzymes of aromatic metabolism. In contrast, in anaerobes all oxygen-dependent reactions are replaced by a set of alternative enzymatic processes. The anaerobic degradation of phenol to a non-aromatic product involves enzymatic processes that are uniquely found in the aromatic metabolism of anaerobic bacteria: (i) ATP-dependent phenol carboxylation to 4-hydroxybenzoate via a phenylphosphate intermediate (biological Kolbe-Schmitt carboxylation); (ii) reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA; and (iii) ATP-dependent reductive dearomatization of the key intermediate benzoyl-CoA in a ‘Birch-like’ reduction mechanism. This review summarizes the results of recent mechanistic studies of the enzymes involved in these three key reactions.

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7

Szewzyk, Ulrich, Regine Szewzyk e Bernhard Schink. "Methanogenic degradation of hydroquinone and catechol via reductive dehydroxylation to phenol". FEMS Microbiology Letters 31, n. 2 (aprile 1985): 79–87. http://dx.doi.org/10.1111/j.1574-6968.1985.tb01134.x.

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8

Zhang, Jie, Hong-Kui Zhang e Pei-Qiang Huang. "Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A". Beilstein Journal of Organic Chemistry 9 (5 novembre 2013): 2358–66. http://dx.doi.org/10.3762/bjoc.9.271.

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A concise enantioselective synthesis of the advanced intermediate 5 for the synthesis of pumiliotoxins (Gallagher’s intermediate) is described. The synthesis started from the regio- and trans-diastereoselective (dr = 98:2) reductive 3-butenylation of (R)-3-(tert-butyldimethylsilyloxy)glutarimide 14. After O-desilylation and Dess–Martin oxidation, the resulting keto-lactam 10 was subjected to a highly trans-stereoselective addition of the methylmagnesium iodide to give carbinol 11 as sole diastereomer. An efficient ring closure procedure consisting of ozonolysis and reductive dehydroxylation provided the indolizidine derivative 5, which completed the formal enantioselective total synthesis of pumiliotoxins 251D and 237A.

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9

Chan, Li Yan, Jazreel Seh Kai Lim e Sunggak Kim. "ChemInform Abstract: Iron-Catalyzed Reductive Dehydroxylation of Benzylic Alcohols Using Polymethylhydrosiloxane (PMHS)." ChemInform 43, n. 15 (15 marzo 2012): no. http://dx.doi.org/10.1002/chin.201215029.

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10

Boll, Matthias, Bernhard Schink, Albrecht Messerschmidt e Peter M. H. Kroneck. "Novel bacterial molybdenum and tungsten enzymes: three-dimensional structure, spectroscopy, and reaction mechanism". Biological Chemistry 386, n. 10 (1 ottobre 2005): 999–1006. http://dx.doi.org/10.1515/bc.2005.116.

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Abstract The molybdenum enzymes 4-hydroxybenzoyl-CoA reductase and pyrogallol-phloroglucinol transhydroxylase and the tungsten enzyme acetylene hydratase catalyze reductive dehydroxylation reactions, i.e., transhydroxylation between phenolic residues and the addition of water to a triple bond. Such activities are unusual for this class of enzymes, which carry either a mononuclear Mo or W center. Crystallization and subsequent structural analysis by high-resolution X-ray crystallography has helped to resolve the reaction centers of these enzymes to a degree that allows us to understand the interaction of the enzyme and the respective substrate(s) in detail, and to develop a concept for the respective reaction mechanism, at least in two cases.

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11

Holland, Herbert L., Ronald W. Ninniss e Frances M. Brown. "Stereochemistry of hydrogen loss during C-21 dehydroxylation of tetrahydrodeoxycorticosterone by Eubacteriumlentum". Canadian Journal of Chemistry 67, n. 10 (1 ottobre 1989): 1590–95. http://dx.doi.org/10.1139/v89-242.

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The loss of hydrogen from the C-21 position of 5β-pregnane-3α,21-diol-20-one (tetrahydrodeoxycorticosterone, THDOC) during reductive removal of the 21-hydroxy group by the anaerobic bacterium Eubacteriumlentum has been shown to be selective for the pro-S position by the use of THDOC labelled with deuterium at the C-21 pro-S and C-21 pro-R positions. The labelled substrates were obtained by using the bacterium Clostridiumparaputrificum to reduce chemically prepared C-21 labelled samples of pregn-4-en-21-ol-3,20-dione (deoxycorticosterone, DOC) at C-3 and C-4 (5). The stereochemistry of deuterium label introduced by chemical means at C-21 of DOC was determined by comparison with a sample of 21-(R)-DOC-21-d1 produced by reduction of the corresponding aldehyde pregn-4-en-21-al-3,20-dione, 21-d by the enzyme 21-hydroxysteroid NAD oxidoreductase from beef liver. Keywords: Eubacterium, Clostridium, steroids, tetrahydrodeoxycorticosteroids.

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12

Becker, Jennifer G., David A. Stahl e Bruce E. Rittmann. "Reductive Dehalogenation and Conversion of 2-Chlorophenol to 3-Chlorobenzoate in a Methanogenic Sediment Community: Implications for Predicting the Environmental Fate of Chlorinated Pollutants". Applied and Environmental Microbiology 65, n. 11 (1 novembre 1999): 5169–72. http://dx.doi.org/10.1128/aem.65.11.5169-5172.1999.

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ABSTRACT Biotransformation of 2-chlorophenol by a methanogenic sediment community resulted in the transient accumulation of phenol and benzoate. 3-Chlorobenzoate was a more persistent product of 2-chlorophenol metabolism. The anaerobic biotransformation of phenol to benzoate presumably occurred via para-carboxylation and dehydroxylation reactions, which may also explain the observed conversion of 2-chlorophenol to 3-chlorobenzoate.

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13

Gasser, U. G., E. Jeanroy, C. Mustin, O. Barres, R. Nüesch, J. Berthelin e A. J. Herbillon. "Properties of synthetic goethites with Co for Fe substitution". Clay Minerals 31, n. 4 (dicembre 1996): 465–76. http://dx.doi.org/10.1180/claymin.1996.031.4.03.

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AbstractIsomorphic substitution in goethites is common in nature and the properties of goethites generally change as a function of the degree of substitution (e.g. Al-goethites). In synthetic goethites, substitution by other elements such as Co is also known. Recent literature indicates that the influence of Al and Co on the unit-cell dimensions of goethite is similar. In contrast to Al-goethites, however, little is known about other properties of Co-goethites and in this study some properties of synthetic Co-goethites were investigated by XRD, IR, TEM, TGA and reductive dissolution techniques. Eight goethite samples (S1 to S8) with varying Co concentrations were synthesized from mixed alkaline solutions of Fe(III) nitrate and Co(II) nitrate, aged at 63°C and ambient pressure. The goethites contained up to 9.5 mol.% Co. Their redness increased with Co concentration, e.g. 0.5 Y 6.0/6.4 for S1 and 6.4 YR 3.3/3.2 for S8. Surface area ranged from 46 to 88 m2/g. Unit-cell parameters a, b, c and v all showed a negative linear dependency on the Co concentration of the goethites. Transmission and diffuse reflectance IR spectrometry showed the presence of strong bands which were interpreted as v-OH, δ-OH and γ-OH vibrations. The δ-OH and γ-OH band positions showed a positive linear dependency on the Co concentration of the samples. Dehydroxylation occurred between 280 and 315°C and dehydroxylation peak positions tended to decrease with increasing Co concentrations. As with Al-goethites, Co-goethite reductive dissolution rates decreased parabolically with increasing substitution. X-ray diffraction and IR analyses, TGA and congruent reductive dissolution suggest the existence of single phases, i.e. Co-goethites of varying degrees of isomorphic substitution.

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14

Hashimoto, Toru, Takushi Shiomi, Jun-ichi Ito e Hisao Nishiyama. "Asymmetric synthesis of α-chiral dihydrocinnamates by catalytic reductive aldol coupling and subsequent dehydroxylation". Tetrahedron 63, n. 52 (dicembre 2007): 12883–87. http://dx.doi.org/10.1016/j.tet.2007.10.055.

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15

Glöckler, Rainer, Andreas Tschech e Georg Fuchs. "Reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA in a denitrifying, phenol-degradingPseudomonasspecies". FEBS Letters 251, n. 1-2 (17 luglio 1989): 237–40. http://dx.doi.org/10.1016/0014-5793(89)81461-9.

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16

Gorny, Norbert, e Bernhard Schink. "Hydroquinone degradation via reductive dehydroxylation of gentisyl-CoA by a strictly anaerobic fermenting bacterium". Archives of Microbiology 161, n. 1 (gennaio 1994): 25–32. http://dx.doi.org/10.1007/bf00248890.

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17

Gorny, N., e B. Schink. "Hydroquinone degradation via reductive dehydroxylation of gentisyl-CoA by a strictly anaerobic fermenting bacterium". Archives of Microbiology 161, n. 1 (1 gennaio 1994): 25–32. http://dx.doi.org/10.1007/s002030050018.

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18

Jiang, Li-Jiao, Bo Teng, Jian-Feng Zheng, Jian-Liang Ye e Pei-Qiang Huang. "Bis-Lewis acids-catalyzed highly diastereoselective one-pot reductive dehydroxylation of chiral N,O-acetals". Tetrahedron 66, n. 1 (gennaio 2010): 172–75. http://dx.doi.org/10.1016/j.tet.2009.11.003.

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19

Wang, Yu-Huang, Wei Ou, Linfeng Xie, Jian-Liang Ye e Pei-Qiang Huang. "Towards Reaction Control:cis-Diastereoselective Reductive Dehydroxylation of 5-Alkyl-4-Benzyloxy-5-Hydroxy-2-Pyrrolidinones". Asian Journal of Organic Chemistry 1, n. 4 (6 novembre 2012): 359–65. http://dx.doi.org/10.1002/ajoc.201200113.

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20

Shadakshari, Uma, e Sandip K. Nayak. "Reductive dehydroxylation of Baylis–Hillman adducts with low-valent titanium reagent: syntheses of stereoselective trisubstituted alkenes". Tetrahedron 57, n. 21 (maggio 2001): 4599–602. http://dx.doi.org/10.1016/s0040-4020(01)00333-7.

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21

Jobelius, Hannah, Gabriella Bianchino, Franck Borel, Philippe Chaignon e Myriam Seemann. "The Reductive Dehydroxylation Catalyzed by IspH, a Source of Inspiration for the Development of Novel Anti-Infectives". Molecules 27, n. 3 (21 gennaio 2022): 708. http://dx.doi.org/10.3390/molecules27030708.

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The non-mevalonate or also called MEP pathway is an essential route for the biosynthesis of isoprenoid precursors in most bacteria and in microorganisms belonging to the Apicomplexa phylum, such as the parasite responsible for malaria. The absence of this pathway in mammalians makes it an interesting target for the discovery of novel anti-infectives. As last enzyme of this pathway, IspH is an oxygen sensitive [4Fe-4S] metalloenzyme that catalyzes 2H+/2e- reductions and a water elimination by involving non-conventional bioinorganic and bioorganometallic intermediates. After a detailed description of the discovery of the [4Fe-4S] cluster of IspH, this review focuses on the IspH mechanism discussing the results that have been obtained in the last decades using an approach combining chemistry, enzymology, crystallography, spectroscopies, and docking calculations. Considering the interesting druggability of this enzyme, a section about the inhibitors of IspH discovered up to now is reported as well. The presented results constitute a useful and rational help to inaugurate the design and development of new potential chemotherapeutics against pathogenic organisms.

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22

Shadakshari, Uma, e Sandip K. Nayak. "ChemInform Abstract: Reductive Dehydroxylation of Baylis-Hillman Adducts with Low-Valent Titanium Reagent: Syntheses of Stereoselective Trisubstituted Alkenes." ChemInform 32, n. 35 (24 maggio 2010): no. http://dx.doi.org/10.1002/chin.200135028.

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23

Chandrasekhar, S., G. Chandrashekar, K. Vijeender e M. Srinivasa Reddy. "Synthesis of trisubstituted alkenes by reductive dehydroxylation of Baylis–Hillman adducts using polymethylhydrosiloxane (PMHS) and catalytic B(C6F5)3". Tetrahedron Letters 47, n. 20 (maggio 2006): 3475–78. http://dx.doi.org/10.1016/j.tetlet.2006.03.014.

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24

Prakash, Dhan, Ravi Kumar, R. K. Jain e B. N. Tiwary. "Novel Pathway for the Degradation of 2-Chloro-4-Nitrobenzoic Acid by Acinetobacter sp. Strain RKJ12". Applied and Environmental Microbiology 77, n. 18 (29 luglio 2011): 6606–13. http://dx.doi.org/10.1128/aem.00685-11.

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ABSTRACTThe organismAcinetobactersp. RKJ12 is capable of utilizing 2-chloro-4-nitrobenzoic acid (2C4NBA) as a sole source of carbon, nitrogen, and energy. In the degradation of 2C4NBA by strain RKJ12, various metabolites were isolated and identified by a combination of chromatographic, spectroscopic, and enzymatic activities, revealing a novel assimilation pathway involving both oxidative and reductive catabolic mechanisms. The metabolism of 2C4NBA was initiated by oxidativeorthodehalogenation, leading to the formation of 2-hydroxy-4-nitrobenzoic acid (2H4NBA), which subsequently was metabolized into 2,4-dihydroxybenzoic acid (2,4-DHBA) by a mono-oxygenase with the concomitant release of chloride and nitrite ions. Stoichiometric analysis indicated the consumption of 1 mol O2per conversion of 2C4NBA to 2,4-DHBA, ruling out the possibility of two oxidative reactions. Experiments with labeled H218O and18O2indicated the involvement of mono-oxygenase-catalyzed initial hydrolytic dechlorination and oxidative denitration mechanisms. The further degradation of 2,4-DHBA then proceeds via reductive dehydroxylation involving the formation of salicylic acid. In the lower pathway, the organism transformed salicylic acid into catechol, which was mineralized by theorthoring cleavage catechol-1,2-dioxygenase tocis, cis-muconic acid, ultimately forming tricarboxylic acid cycle intermediates. Furthermore, the studies carried out on a 2C4NBA−derivative and a 2C4NBA+transconjugant demonstrated that the catabolic genes for the 2C4NBA degradation pathway possibly reside on the ∼55-kb transmissible plasmid present in RKJ12.

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Shin, Bok-Kyu, Joong-Hoon Ahn e Jaehong Han. "N-Terminal Region of GbIspH1,Ginkgo bilobaIspH Type 1, May Be Involved in the pH-Dependent Regulation of Enzyme Activity". Bioinorganic Chemistry and Applications 2015 (2015): 1–8. http://dx.doi.org/10.1155/2015/241479.

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GbIspH1, IspH type 1 inGinkgo bilobachloroplast, is the Fe/S enzyme catalyzing the reductive dehydroxylation of HMBPP to isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) at the final step of methylerythritol phosphate pathway in chloroplast. Compared to the bacterial IspH, plant IspH, including GbIspH1, has an additional polypeptide chain at theN-terminus. Here, biochemical function of theN-terminal region of GbIspH1 was investigated with theN-terminal truncated GbIspH1 (GbIspH1-truncated). Both wild type GbIspH1 (GbIspH1-full) and GbIspH1-truncated were catalytically active and produced IPP and DMAPP in a ratio of 15 : 1. Kinetic parameters ofKM(17.3 ± 1.9 and 14.9 ± 2.3 µM) andkcat(369 ± 10 and 347 ± 12 min−1) at pH 8.0 were obtained for GbIspH1-full and GbIspH1-truncated, respectively. Interestingly, GbIspH1-full and GbIspH1-truncated showed significantly different pH-dependent activities, and the maximum enzyme activities were obtained at pH 8.0 and 7.5, respectively. However, catalytic activation energies (Ea) of GbIspH1-full and GbIspH1-truncated were almost the same with 36.5 ± 1.6 and 35.0 ± 1.9 kJ/mol, respectively. It was suggested that theN-terminal region of GbIspH1 is involved in the pH-dependent regulation of enzyme activity during photosynthesis.

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Aprilliza AM, Mozart Nuzul, Yenny Nur Anggraeny e Elizabeth Wina. "The Role of Catechin Compounds and Its Derivates to Mitigate Methane Gas Production in the Rumen Fermentation". Indonesian Bulletin of Animal and Veterinary Sciences 31, n. 1 (30 marzo 2021): 13. http://dx.doi.org/10.14334/wartazoa.v31i1.2548.

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Enteric fermentation and its corresponding to methane emissions take place in many wild and domestic ruminant species, such as deer, buffalo, cattle, goats, sheep. Ruminant animals are different from other animals in that they have a rumen, a large fore-stomach with a complex microbial environment. A resulting of this process is methane (CH4), which has a global warming potential (25 times that of carbon dioxide (CO2)). Because the digestion process is not 100% efficient, some of the energy intake is lost in the form of methane. Recently, natural plant products, such as tea leaves which are often inexpensive and environmentally safe have been introduced in methane mitigation strategies. Tea leaves have potential for use as an additives in ruminant diets. The adding of catechin 10-40 g/Kg DM were able to declined methane emission 7.4–13.5%. Furthermore, catechin could decrease the methane production. Catechin decreased CH4 production both in vitro and in vivo. Catechin causes direct inhibition of methanogens as well as may act as hydrogen sinks during degradation by rumen microbes via cleavage of ring structures and reductive dehydroxylation reactions. The objective of this paper is to review existing knowledge related to discuss how catechins can act as methane-lowering agents from rumen fermentation on ruminants.

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Murdiati, TB, CS McSweeney e JB Lowry. "Metabolism in sheep of gallic acid, tannic acid and hydrolysable tannin from Terminalia oblongata". Australian Journal of Agricultural Research 43, n. 6 (1992): 1307. http://dx.doi.org/10.1071/ar9921307.

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Hydrolysable tannin (HT) is present in a variety of tropical browse plants, some of which poison ruminants. In an attempt to clarify the toxic action, we investigated the major urinary metabolites resulting from dosing of sheep with the HT, tannic acid; its simplest and major phenolic component, gallic acid; and the HT-containing and toxic Terminalia oblongata. Phenolic metabolites were separated by HPLC and their structures investigated by proton and 13C NMR. Gallic acid was less toxic (w/w) than tannic acid. Comparison of urinary metabolites from rumen and abomasal administration indicated that decarboxylation and reductive dehydroxylation of phenolics occurred principally in the rumen and a significant proportion was totally degraded. Rumen metabolism appeared to prevent toxicity from gallic and tannic acid at dose rates of <0.4 g/kg liveweight per day. Resorcinol glucuronide and the glucuronide of 2-carboxy-2'4'4,6,-tetrahydroxy diphenyl 2, 2'-lactone were the major urinary metabolites derived from tamic acid and probably from yellow-wood HT while resorcinol glucuronide was the major product of gallic acid metabolism. Minor urinary metabolites included unconjugated pyrogallol, resorcinol and phloroglucinol. Toxicity appeared to correlate with the passage of the diphenyl lactone metabolite, presumably arising from the degradation of the hexahydroxydiphenic acid moiety in HT. The current studies indicate that yellow-wood toxicity probably occurs under circumstances when animals ingest leaf containing high levels of HT without prior conditioning. A diagnosis of yellow-wood toxicity could be confirmed by the detection of resorcinol and diphenyl lactone metabolites in urine of affected ruminants.

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Gallert, C., e J. Winter. "Anaerobic degradation of 4-hydroxybenzoate: reductive dehydroxylation of 4-hydroxybenzoyl-CoA and ATP formation during 4-hydroxybenzoate decarboxylation by the phenol-metabolizing bacteria of a stable, strictly anaerobic consortium". Applied Microbiology and Biotechnology 42, n. 2-3 (1 dicembre 1994): 408–14. http://dx.doi.org/10.1007/s002530050271.

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Gallert, C., e J. Winter. "Anaerobic degradation of 4-hydroxybenzoate: Reductive dehydroxylation of 4-hydroxybenzoyl-CoA and ATP formation during 4-hydroxybenzoate decarboxylation by the phenol-metabolizing bacteria of a stable, strictly anaerobic consortium". Applied Microbiology and Biotechnology 42, n. 2-3 (novembre 1994): 408–14. http://dx.doi.org/10.1007/bf00902750.

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O'Connor, F., W. H. Cheung e M. Valix. "Reduction roasting of limonite ores: effect of dehydroxylation". International Journal of Mineral Processing 80, n. 2-4 (settembre 2006): 88–99. http://dx.doi.org/10.1016/j.minpro.2004.05.003.

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Xie, Hao, Sheng Wang, Yuquan Wang, Peng Guo e Xing-Zhong Shu. "Ti-Catalyzed Reductive Dehydroxylative Vinylation of Tertiary Alcohols". ACS Catalysis 12, n. 2 (3 gennaio 2022): 1018–23. http://dx.doi.org/10.1021/acscatal.1c05530.

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Zhang, Hongen, Lang Li, Tao Long, Prabir Sarker, Xiaoshuang Shi, Gaochuang Cai e Qingyuan Wang. "The Effect of Ordinary Portland Cement Substitution on the Thermal Stability of Geopolymer Concrete". Materials 12, n. 16 (7 agosto 2019): 2501. http://dx.doi.org/10.3390/ma12162501.

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The influence of using cement on the residual properties of fly ash geopolymer concrete (FAGC) after exposure to high temperature of up to 800 °C was studied in terms of mass loss, residual compressive strength and microstructure. The mass loss was found to increase with the increase of exposure temperature, which is attributed to vaporization of water and dehydroxylation of sodium aluminosilicate hydrate (N-A-S-H) gels. The dehydroxylation of calcium silicate hydrate (C-S-H) gels and the disintegration of portlandite were responsible for higher mass loss ratio of FAGCs containing cement. The results showed that cement could increase compressive strength of FAGCs up to 200 °C, after which a significant reduction in residual strength was observed. It was found that FAGCs without cement yielded higher residual strength than the original strength after heating up to 600 °C. The observed increase of compressive strength up to 200 °C was attributed to the secondary geopolymerization which was evidenced in the scanning electronic microscopy (SEM) images.

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Mouttaki, Housna, Mark A. Nanny e Michael J. McInerney. "Metabolism of Hydroxylated and Fluorinated Benzoates by Syntrophus aciditrophicus and Detection of a Fluorodiene Metabolite". Applied and Environmental Microbiology 75, n. 4 (29 dicembre 2008): 998–1004. http://dx.doi.org/10.1128/aem.01870-08.

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ABSTRACT Transformations of 2-hydroxybenzoate and fluorobenzoate isomers were investigated in the strictly anaerobic Syntrophus aciditrophicus to gain insight into the initial steps of the metabolism of aromatic acids. 2-Hydroxybenzoate was metabolized to methane and acetate by S. aciditrophicus and Methanospirillum hungatei cocultures and reduced to cyclohexane carboxylate by pure cultures of S. aciditrophicus when grown in the presence of crotonate. Under both conditions, transient accumulation of benzoate but not phenol was observed, indicating that dehydroxylation occurred prior to ring reduction. Pure cultures of S. aciditrophicus reductively dehalogenated 3-fluorobenzoate with the stoichiometric accumulation of benzoate and fluorine. 3-Fluorobenzoate-degrading cultures produced a metabolite that had a fragmentation pattern almost identical to that of the trimethylsilyl (TMS) derivative of 3-fluorobenzoate but with a mass increase of 2 units. When cells were incubated with deuterated water, this metabolite had a mass increase of 3 or 4 units relative to the TMS derivative of 3-fluorobenzoate. 19F nuclear magnetic resonance spectroscopy (19F NMR) detected a metabolite in fluorobenzoate-degrading cultures with two double bonds, either 1-carboxyl-3-fluoro-2,6-cyclohexadiene or 1-carboxyl-3-fluoro-3,6-cyclohexadiene. The mass spectral and NMR data are consistent with the addition of two hydrogen or deuterium atoms to 3-fluorobenzoate, forming a 3-fluorocyclohexadiene metabolite. The production of a diene metabolite provides evidence that S. aciditrophicus contains dearomatizing reductase that uses two electrons to dearomatize the aromatic ring.

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34

Puhakka, Jaakko A., Päivi M. Mäkinen, Margareta Lundin e John F. Ferguson. "Aerobic and Anaerobic Biotransformations and Treatment of Chlorinated Pulp Bleach Waste Constituents". Water Science and Technology 29, n. 5-6 (1 marzo 1994): 73–80. http://dx.doi.org/10.2166/wst.1994.0703.

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Biotransformations and treatment of several chlorinated, hydroxylated and methoxylated monoaromatic compounds were studied in batch bottle bioassays and continuous-flow fluidized-bed reactors. With the aerobic enrichment, polychlorinated phenols were biodegraded with simultaneous release of inorganic chloride in amounts equal to mineralization stoichiometrics. Aerobic removal of 4,5-dichlorocatechol and 4,5- dichlorovanillin were associated with the release of inorganic chlorine. The aerobic enrichment showed no activity against mono- or di-O-methylated phenols. With the anaerobic enrichment, reductive transformations of these compounds were observed. These transformations included reductive dechlorinations, de-O-methylations and dehydroxylations. High-rate operation of an aerobic fluidized-bed reactor resulted in over 99.7% biodégradation of polychlorophenols. In the anaerobic fluidized-bed reactor, over 95% removal of chlorophenols with no apparent accumulation of lower chlorinated phenols indicated complete dechlorination.

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35

Grbic-Galic, D. "O-Demethylation, dehydroxylation, ring-reduction and cleavage of aromatic substrates by Enterobacteriaceae under anaerobic conditions". Journal of Applied Bacteriology 61, n. 6 (dicembre 1986): 491–97. http://dx.doi.org/10.1111/j.1365-2672.1986.tb01721.x.

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36

Franco, F., L. A. Pérez-Maqueda e J. L. Pérez-Rodríguez. "Influence of the particle-size reduction by ultrasound treatment on the dehydroxylation process of kaolinites". Journal of Thermal Analysis and Calorimetry 78, n. 3 (gennaio 2004): 1043–55. http://dx.doi.org/10.1007/s10973-005-0469-0.

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37

Soedarsono, Johny Wahyuadi, Adji Kawigraha, Rianti Dewi Sulamet-Ariobimo, M. Amryl Asy'ari, Andre Yosi e Eko Mulia Putra. "The Influence of Coal and Reduction Process Parameters in Producing Iron Nugget". Advanced Materials Research 789 (settembre 2013): 517–21. http://dx.doi.org/10.4028/www.scientific.net/amr.789.517.

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Abstract (sommario):

Limitation of iron ore reserve having high quality ore and of energy has enhanced development in iron and steel producing technology and method. The ITmk3 process is one of iron making technology that can cope with the problems. It uses composite pellet as feeding material. In this process the ratio between iron and carbon are very important. Carbon holds an important role in the reduction process of iron. The transformation from iron oxides to iron metal will complete if composite pellet contains enough carbon. This paper discusses the influence of carbon ratio in iron reduction process. Nickel saprolite and coal are used as iron and carbon source. They are grinded, crushed, sieved, mixed and formed in cylinders. The weight ratios of ores to coal are 1:1 and 2:1. The reduction held in a furnace at 1100OC for 60 minutes and 1250OC for 120 minutes. The results show that the reduction could not complete. Weak peak of FeNi is due to reduction process do not immediately follow the dehydroxylation process.

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38

Jang, Kyoung-oh, Venkata R. M. Nunna, Sarath Hapugoda, Anh V. Nguyen e Warren J. Bruckard. "Chemical and mineral transformation of a low grade goethite ore by dehydroxylation, reduction roasting and magnetic separation". Minerals Engineering 60 (giugno 2014): 14–22. http://dx.doi.org/10.1016/j.mineng.2014.01.021.

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39

Zhou, S. W., C. Lu, B. Zhang, B. Li e Y. G. Wei. "Investigation on the garnierite and limonite mixed laterite ore for nickel recovery". Journal of Mining and Metallurgy, Section B: Metallurgy 57, n. 2 (2021): 245–52. http://dx.doi.org/10.2298/jmmb201129020z.

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Laterite, as an important resource of nickel, has become the focus of development and utilization. This study adopted the method of mixing ore (garnierite and limonite) to increase the recovery rate of nickel in garnierite ore. The phase transformation of the two ores was investigated during the heating process; dehydroxylation and recrystallization were observed and the iron oxides phase was finally transformed into the iron-containing spinel. By changing the proportion of the two ores, increasing the iron content in the sample was beneficial to the reduction of nickel. Then, Fe2O3, Fe3O4, and Fe were used as the iron source to study the mechanism of the iron-bearing minerals in promoting the reduction of nickel. The results indicated that hematite and/or magnetite would react with amorphous silicate minerals to generate magnesioferrite and enstatite, thereby avoiding additional forsterite generation; moreover, the trevorite phase would be formed, which strengthens the aggregation of nickel and iron.

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40

Guo, Wei, Libin Yang, Jinghao Lu, Peng Gao, Wenjing Li e Zhiying Feng. "An Accurate Growth Mechanism and Photocatalytic Degradation Rhodamine B of Crystalline Nb2O5 Nanotube Arrays". Catalysts 10, n. 12 (17 dicembre 2020): 1480. http://dx.doi.org/10.3390/catal10121480.

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Abstract (sommario):

To effectively improve photocatalytic activity, the morphology and crystallinity of semiconductor photocatalysts must be precisely controlled during the formation process. Self-aligned Nb2O5 nanotube arrays have been successfully fabricated using the electrochemical anodization method. A novel growth mechanism of Nb2O5 nanotubes has been proposed. Starting from the initial oxidation process, the “multi-point” corrosion of fluoride ions is a key factor in the formation of nanotube arrays. The inner diameter and wall thickness of the nanotubes present a gradually increasing trend with increased dissociative fluorine ion concentration and water content in the electrolyte. With dehydroxylation and lattice recombination, the increased crystallinity of Nb2O5 represents a reduction of lattice defects, which effectively facilitates the separation and suppresses the recombination of photo-generated carriers to enhance their catalytic degradation activity.

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41

Kawigraha, Adji, Johny Wahyuadi Soedarsono, Sri Harjanto e Pramusanto. "Thermogravimetric Analysis of the Reduction of Iron Ore with Hydroxyl Content". Advanced Materials Research 774-776 (settembre 2013): 682–86. http://dx.doi.org/10.4028/www.scientific.net/amr.774-776.682.

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Iron ore with high hydroxyl content such as goethit is widely spread in Indonesia. Such iron ore is not used as feed in ironmaking industry. However due to limitation of primary iron ore reserve such material is an option to substitute the conventional iron ore. Unfortunately the characteristic of iron ore with high hydroxyl content is totally different to conventional iron ore. Such iron ore contains hydroxyl part that can be released at high temperature. This research uses composite pellet which is mixture of iron ore and coal. The iron ore contains goethite which is one of iron phase. The composition of two materials is fixed 1 to 3 molar for iron total to fixed carbon. The mixture is formed a pelet before dried. The small part of dry pellet is analysed using STA with 0.6667 °K/s. The reduction is characterised based on thermogravimetry graphs. The research found that the reduction of iron ore occurs in some stages. First stage correspond to dehydroxylation at around 300 °C and second stage corresponds to reduction of iron ore at around 625 °C and 825 °C or 880 °C. The composite lost of 4.64 % and 2.85 % of weight. The hydroxylation is followed by reduction. Hydroxylation transforms goethite to hematite with lost of water. While the reduction transforms hematite to magnetite and magnetite to Fe.

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42

Krajči, Ľudovít, Ivan Janotka, Marta Kuliffayova e Peter Uhlik. "Effect of Metakaolin Sand on Properties of Cement Composites". Advanced Materials Research 897 (febbraio 2014): 176–79. http://dx.doi.org/10.4028/www.scientific.net/amr.897.176.

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The Slovak natural raw material kaolin sand containing 36 wt.% of kaolinite from Vyšný Petrovec deposit was thermally transformed at 650 °C for 1 hour to the metakaolin sand with relevant content of metakaolinite. Behaviour of cement composites having replacement of Portland cement with metakaolin sand including 0; 5; 10 and 15 wt.% of metakaolinite and water to solids ratio of 0.5 cured in water for 28 days and 90 days was studied by thermal analysis, X-ray diffraction analysis and mercury intrusion porosimetry analysis. The study concerned calciumsilica hydrate and calcium aluminate hydrate formation, portlandite dehydroxylation and calcite decarbonation. The influence of curing time and metakaolinite content were estimated. The replacement of Portland cement by metakaolin sand led to positive effect on relevant compressive strengths. The changes in microstructure involved especially reduction in portlandite content and pore structure refinement.

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43

Maziarz, Paulina, e Jakub Matusik. "The effect of acid activation and calcination of halloysite on the efficiency and selectivity of Pb(II), Cd(II), Zn(II) and As(V) uptake". Clay Minerals 51, n. 3 (giugno 2016): 385–94. http://dx.doi.org/10.1180/claymin.2016.051.3.06.

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AbstractThe present study investigated the efficiency and mechanisms of aqueous Pb(II), Cd(II), Zn(II) and As(V) adsorption on natural (H), calcined (HC), and acid-activated halloysite (HA). The XRD and FTIR measurements indicated that the aluminosilicate framework was not affected by high-temperature treatment, in contrast to acid activation, which led to structural changes mainly in the tetrahedral sheet. The sorption of cations on H sample was low, though it was most effective for As(V). The X-ray photoelectron spectroscopy results suggested that removal of As(V) might be related to its reduction to As(III) involving oxidation of Fe(II) present in the mineral structure and/or iron minerals. The calcination enhanced halloysite sorption capacity for cations, while the As(V) sorption decreased. This was due to partial dehydroxylation and the subsequent formation of additional active sites. The acid treatment induced selective adsorption of Pb(II).

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44

Sharma, Renu. "Design and Applications of Environmental Cell Transmission Electron Microscope for In Situ Observations of Gas–Solid Reactions". Microscopy and Microanalysis 7, n. 6 (novembre 2001): 494–506. http://dx.doi.org/10.1007/s10005-001-0015-1.

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Abstract (sommario):

AbstractThe environmental transmission electron microscopy (E-TEM) is a budding technique for in situ study of gas–solid chemical reactions with numerous applications. Recent improvements in the design have made it possible not only to obtain atomic level information but also the chemical information during the reaction by incorporating an imaging filter or electron energy-loss spectrometer to an E-TEM. We have been involved in modifying a couple of microscopes to incorporate environmental cells in order to convert them into E-TEMs. These microscopes have been used to obtain atomic level information of the structural and chemical changes during dynamic processes by in situ electron diffraction, high-resolution imaging, and electron energyloss spectroscopy. The applications include, but are not limited to, oxidation, reduction, polymerization, nitridation, dehydroxylation, hydroxylation, chemical vapor deposition, etc. We report recent developments in the design and application along with the limitations of an E-TEM.

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45

Mikhailova, Olesia, e Pavel Rovnaník. "Effect of Polymer Admixtures on Metakaolin-Based Geopolymer". Materials Science Forum 865 (agosto 2016): 67–71. http://dx.doi.org/10.4028/www.scientific.net/msf.865.67.

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Abstract (sommario):

Geopolymers are presented in many studies as binders alternative to ordinary Portland cement. Several inorganic materials have been used as raw materials for the production of geopolymers. One of them is metakaolin which is produced by dehydroxylation of kaolin. Metakaolin has a much larger surface area than cement, resulting in an increase in water demand to maintain workability. Polymer admixtures may contribute to reduction of this demand. However, another problem should be considered: plasticizers which improve rheological properties in cement technology are not effective for geopolymers. The aim of this study was to analyze the effect of different polymer admixtures on the compressive and flexural strength, pore size distribution and microstructure of alkali-activated metakaolin material. The results revealed that a maximum compressive strength of 18.6 MPa was achieved by adding 1.5% of VINNAPAS 7016 F, and a maximum flexural strength of 2.2 MPa when adding 0.5 or 1% of the same polymer admixture.

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46

BRACKMANN, Ruth, e Georg FUCHS. "Enzymes of anaerobic metabolism of phenolic compounds. 4-Hydroxybenzoyl-CoA reductase (dehydroxylating) from a denitrifying Pseudomonas species". European Journal of Biochemistry 213, n. 1 (aprile 1993): 563–71. http://dx.doi.org/10.1111/j.1432-1033.1993.tb17795.x.

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47

Peters, Franziska, Dimitri Heintz, Jörg Johannes, Alain van Dorsselaer e Matthias Boll. "Genes, Enzymes, and Regulation of para-Cresol Metabolism in Geobacter metallireducens". Journal of Bacteriology 189, n. 13 (20 aprile 2007): 4729–38. http://dx.doi.org/10.1128/jb.00260-07.

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ABSTRACT In aerobic and facultatively anaerobic bacteria, the degradation of para-cresol (p-cresol) involves the initial hydroxylation to p-hydroxybenzyl alcohol by water catalyzed by the soluble, periplasmatic flavocytochrome p-cresol methylhydroxylase (PCMH; α2β2 composition). In denitrifying bacteria the further metabolism proceeds via oxidation to p-hydroxybenzoate, the formation of p-hydroxybenzoyl-coenzyme A (CoA), and the subsequent dehydroxylation of the latter to benzoyl-CoA by reduction. In contrast, the strictly anaerobic Desulfobacterium cetonicum degrades p-cresol by addition to fumarate, yielding p-hydroxybenzylsuccinate. In this work, in vitro enzyme activity measurements revealed that the obligately anaerobic Geobacter metallireducens uses the p-cresol degradation pathway of denitrifying bacteria. Surprisingly, PCMH, which is supposed to catalyze both p-cresol hydroxylation and p-hydroxybenzyl alcohol oxidation to the corresponding aldehyde, was located in the membrane fraction. The α subunit of the enzyme was present in two isoforms, suggesting an αα′β2 composition. We propose that the unusual asymmetric architecture and the membrane association of PCMH might be important for alternative electron transfer routes to either cytochrome c (in the case of p-cresol oxidation) or to menaquinone (in the case of p-hydroxybenzyl alcohol oxidation). Unusual properties of further enzymes of p-cresol metabolism, p-hydroxybenzoate-CoA ligase, and p-hydroxybenzoyl-CoA reductase were identified and are discussed. A proteomic approach identified a gene cluster comprising most of the putative structural genes for enzymes involved in p-cresol metabolism (pcm genes). Reverse transcription-PCR studies revealed a different regulation of transcription of pcm genes and the corresponding enzyme activities, suggesting the presence of posttranscriptional regulatory elements.

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48

Wang, Yang, Wubiao Duan, Bo Liu, Xidong Chen, Feihua Yang e Jianping Guo. "The Effects of Doping Copper and Mesoporous Structure on Photocatalytic Properties of TiO2". Journal of Nanomaterials 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/178152.

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This paper describes a system for the synthesis of Cu-doped mesoporous TiO2nanoparticles by a hydrothermal method at relatively low temperatures. The technique used is to dope the as-prepared mesoporous TiO2system with copper. In this method, the copper species with the form of Cu1+, which was attributed to the reduction effect of dehydroxylation and evidenced by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), was well dispersed in the optimal concentration 1 wt.% Cu-doped mesoporous TiO2. In this as-prepared mesoporous TiO2system, original particles with a size of approximately 20 nm are aggregated together to shapes of approximately 1100 nm, which resulted in the porous aggregate structure. More importantly, the enhancement of the photocatalytic activity was discussed as effects due to the formation of stable Cu(I) and the mesoporous structure in the Cu-doped mesoporous TiO2. Among them, Cu-doped mesoporous TiO2shows the highest degradation rate of methyl orange (MO). In addition, the effects of initial solution pH on degradation of MO had also been investigated. As a result, the optimum values of initial solution pH were found to be 3.

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49

Bobrowski, Artur, Karolina Kaczmarska, Maciej Sitarz, Dariusz Drożyński, Magdalena Leśniak, Beata Grabowska e Daniel Nowak. "Dehydroxylation of Perlite and Vermiculite: Impact on Improving the Knock-Out Properties of Moulding and Core Sand with an Inorganic Binder". Materials 14, n. 11 (29 maggio 2021): 2946. http://dx.doi.org/10.3390/ma14112946.

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Abstract (sommario):

The article presents the results of research aimed at examining the type of swelling material introduced into moulding or core sand to improve their knock-out properties. Tests on Slovak perlite ore (three grain sizes), Hungarian perlite ore and ground vermiculite (South Africa) were carried out. For this purpose, thermal and structural analyses (FTIR—Fourier Transform Infrared Spectroscopy), a chemical composition test (XRF-X-Ray Fluorescence), phase analysis (XRD—X-Ray Diffraction), and scanning electron microscopy (SEM—Scanning Electron Microscope) as well as final strength tests of moulding sands with the addition of perlite ore and vermiculite were carried out. The results of thermal studies were related to IR (Infrared Spectroscopy) spectra and XRD diffractograms. It has been shown that the water content in the pearlite ore is almost three times lower than in vermiculite, but the process of its removal is different. Moreover, the chemical composition of the perlite ore, in particular the alkali content and its grain size, may influence its structure. The phenomena of expansion (perlite) and peeling (vermiculite) have a positive effect on the reduction of the final sand strength and eliminate technological inconveniences (poor knocking out) that significantly limit the wide use of moulding sands with inorganic binders.

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50

Zhao, Feng, Shuangde Li, Xiaofeng Wu, Renliang Yue, Weiman Li, Xicuo Zha, Yuzhou Deng e Yunfa Chen. "Catalytic Behaviour of Flame-Made CuO-CeO2 Nanocatalysts in Efficient CO Oxidation". Catalysts 9, n. 3 (13 marzo 2019): 256. http://dx.doi.org/10.3390/catal9030256.

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Abstract (sommario):

CuO-CeO2 nanocatalysts with varying CuO contents (1, 5, 9, 14 and 17 wt %) were prepared by one-step flame spray pyrolysis (FSP) and applied to CO oxidation. The inﬂuences of CuO content on the as-prepared catalysts were systematically characterized by X-ray diﬀraction (XRD), N2 adsorption-desorption at −196 °C, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen-temperature programmed reduction (H2-TPR). A superior CO oxidation activity was observed for the 14 wt % CuO-CeO2 catalyst, with 90% CO conversion at 98 °C at space velocity (60,000 mL × g−1 × h−1), which was attributed to abundant surface defects (lattice distortion, Ce3+, and oxygen vacancies) and high reducibility supported by strong synergistic interaction. In addition, the catalyst also displayed excellent stability and resistance to water vapor. Significantly, in situ diﬀuse reﬂectance infrared Fourier transform spectroscopy (in situ DRIFTS) showed that in the CO catalytic oxidation process, the strong synergistic interaction led readily to dehydroxylation and CO adsorption on Cu+ at low temperature. Furthermore, in the feed of water vapor, although there was an adverse effect on the access of CO adsorption, there was also a positive effect on the formation of fewer carbon intermediates. All these results showed the potential of highly active and water vapor-resistive CuO-CeO2 catalysts prepared by FSP.

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