Dissertations / Theses on the topic 'Topological selection'

In this work we analyze some selection principles over some classes of hyperspaces. In the first part we consider selective variations of tightness over a class of function spaces whose topologies are determined by bornologies on the space. As results, we extend several well known translations between covering properties and closure properties of the topology of pointwise convergence. In the second part we consider artificial hyperspaces that assist the analysis of productive topological properties. We emphasize the results characterizing productively ccc preorders and the characterization of the Lindelöf property via closed projections.
Neste trabalho analisamos alguns princípios seletivos quando considerados sobre alguns tipos de hiperespaços. Na primeira parte consideramos variações seletivas do tightness sobre diversos tipos de espaços de funções, cujas topologias são determinadas por bornologias no espaço. Como resultados, estendemos diversas traduções conhecidas entre propriedades de recobrimento e propriedades de convergência na topologia da convergência pontual. Na segunda parte consideramos hiperespaços artificiais que auxiliam na análise de propriedades topológicas produtivas. Destacamos os resultados que caracterizam as pré-ordens produtivamente ccc e a caracterização da propriedade de Lindelöf em termos de projeções fechadas.

This thesis consists of two chapters. In the first one, we investigate some selective and monotone versions of covering properties; in particular we study two selective properties: the selective absolute star-Lindelöfness, defined by S. Bhowmik, and the selective strong star- Menger property. Furthermore, we define and study several properties related to monotone normality. In the second chapter, we give some bounds to the cardinality of particular classes of topological spaces.

This thesis is in the intersection of two proliferating research fields, namely data mining and bioinformatics. With the emergence of graph data in the last few years, many efforts have been devoted to mining frequent subgraphs from graph databases. Yet, the number of discovered frequentsubgraphs is usually exponential, mainly because of the combinatorial nature of graphs. Many frequent subgraphs are irrelevant because they are redundant or just useless for the user. Besides, their high number may hinder and even makes further explorations unfeasible. Redundancy in frequent subgraphs is mainly caused by structural and/or semantic similarities, since most discovered subgraphs differ slightly in structure and may infer similar or even identical meanings. In this thesis, we propose two approaches for selecting representative subgraphs among frequent ones in order to remove redundancy. Each of the proposed approaches addresses a specific type of redundancy. The first approach focuses on semantic redundancy where similarity between subgraphs is measured based on the similarity between their nodes' labels, using prior domain knowledge. The second approach focuses on structural redundancy where subgraphs are represented by a set of user-defined topological descriptors, and similarity between subgraphs is measured based on the distance between their corresponding topological descriptions. The main application data of this thesis are protein 3D-structures. This choice is based on biological and computational reasons. From a biological perspective, proteins play crucial roles in almost every biological process. They are responsible of a variety of physiological functions. From a computational perspective, we are interested in mining complex data. Proteins are a perfect example of such data as they are made of complex structures composed of interconnected amino acids which themselves are composed of interconnected atoms. Large amounts of protein structures are currently available in online databases, in computer analyzable formats. Protein 3D-structures can be transformed into graphs where amino acids are the graph nodes and their connections are the graph edges. This enables using graph mining techniques to study them. The biological importance of proteins, their complexity, and their availability in computer analyzable formats made them a perfect application data for this thesis.

Cette thèse présente la recherche d'oscillations d'antineutrinos actifs vers des antineutrinos stériles avec le détecteur SoLi∂. Ce détecteur promeut un concept innovant basé sur un sandwich de plastiques scintillant formé de polyvinyle-toluène composite et de scintillateurs 6LiF:ZnS(Ag). Trois contributions principales à cette recherche sont rapportées dans ce document. La première concerne une nouvelle méthode de reconstruction basée sur l'algorithme ML-EM. Elle vise à transformer la réponse brute du détecteur en une liste de positions (avec des énergies dédiées) où l'interaction physique réelle dans le détecteur a eu lieu. La seconde concerne l'étalonnage en énergie du détecteur. Elle comprend à la fois l'étalonnage relatif au moyen de muons cosmiques horizontaux et l'exploration de plusieurs options pour la détermination de l'échelle d'énergie absolue. Enfin, la thèse présente une nouvelle méthode de sélection des candidats antineutrinos basée sur l'analyse de la partie électromagnétique du signal de désintégration bêta inverse et leur classement en fonction de la géométrie des événements dans le détecteur (topologies). L'analyse a été développée en aveugle et la méthode a été validée avec une petite fraction de l'échantillon de données
This thesis presents the search for active-to-sterile antineutrino oscillations with the SoLi∂ detector, which has an innovative concept based on a sandwich of composite polyvinyl-toluene and 6LiF:ZnS(Ag) scintillators. Three main contributions to this search are reported. The first one describes the new reconstruction method based on the ML-EM algorithm. It is aimed at transformation of the raw detector response to the list of positions (with dedicated energies) where actual physics interaction in the detector took place. The second one describes the energy calibration of the detector. It includes both relative calibration with the cosmic horizontal muons and exploration of several options for the absolute energy scale derivation. Finally, the thesis presents a novel method for selecting antineutrino candidates based on the analysis of the electromagnetic part of the inverse beta decay signal and categorising them according to the geometry of the events in the detector (topologies). The analysis was developed blindly and the method was validated with a small fraction of the data sample

First, we show that the Rothberger and 2-Rothberger games are equivalent. Then we adjust the former proof and introduce another game, the restricted Menger game, in order to obtain a broader result. This provides an answer in the context of Hausdorff spaces for an open question posed by Aurichi, Bella, and Dias.

Este trabalho se dedica ao estudo da interação entre princípios de seleção e jogos topológicos. Isto inclui uma abordagem não-topológica destes tópicos, com aplicações à indestrutibilidade de espaços de Lindelöf e a uma versão seletiva de d-separabilidade, dentre outros. Provamos ainda a não-equivalência consistente entre indestrutibilidade e o princípio de seleção naturalmente associado a esta propriedade, o que conduz à investigação da indestrutibilidade de espaços compactos. Finalmente, mostramos que algumas afirmações que limitam a cardinalidade de espaços de Lindelöf indestrutíveis são equiconsistentes com a existência de certos tipos de grandes cardinais.
In the present work we focus on the interplay between selection principles and topological games. This includes a nontopological approach to these topics, with applications to indestructibility of Lindelöf spaces and a selective version of d-separability, among others. We also show the consistent nonequivalence between indestructibility and the selection principle naturally associated to it, which leads to an investigation of indestructibility of compact spaces. We conclude by showing that some constraints on the cardinality of Lindelöf indestructible spaces are equiconsistent with the existence of some kinds of large cardinals.

The evolution of the genome is driven, among other factors, by the composition of the genome, the functional output of the gene products, and by environmental pressures. Among the environmental factors, pathogens are one of the strongest selective pressures. In this thesis we describe two examples of this: i) the convergent evolution in immune-related genes in East Africa populations despite having different ethnical and genetic backgrounds, ii) the rapid adaptation in variants associated with differential cytokine production in the Roma people since their migration from the Indian subcontinent. We also propose that positive selection acted in the cytochrome P450 system after the out of Africa, whereas genetic drift is the main force behind the genetic variability present in taste receptors genes. Gene evolution is also affected by the location and connectivity of their products within the metabolic network. Positive selection detected at interspecific and intraspecific levels show opposite but complementary patterns: the first is detected in peripheric genes, whereas the second is detected mainly in central genes.
L'evolució del genoma depèn, entre altres factors, de la composició del genoma, del paper funcional que realitzen els productes del gen, i de les pressions mediambientals. Dins dels factors mediambientals, els patògens són una de les pressions selectives més fortes. En aquesta tesi descrivim dos exemples d’aquest fet: i) l'evolució convergent en gens amb funcions immunològiques a poblacions de l’est d'Àfrica, malgrat pertànyer a diferent grups ètnics i fons genètics, ii) la ràpida adaptació als Roma en variants associades amb la producció diferencial de citocines des de la seva migració des del subcontinent Indi. També proposem que la selecció positiva va actuar a la súper família dels citocroms després de la expansió des del continent Africà, mentre que la deriva gènica és la principal força darrere de la variabilitat genètica observada als receptors del gust. L’evolució dels gens també és veu influïda per la ubicació i connectivitat dels seus productes dins de la xarxa metabòlica. La detecció de la selecció positiva a nivell interespecífic i intraespecífic mostra un patró oposat però complementari: la primera és detectada a la perifèria de la xarxa, mentre que la segona és detectada principalment en gens centrals.

Assumindo a existência de $\\mathfrak c$ ultrafiltros seletivos dois a dois incomparáveis (segundo a ordem de Rudin-Keisler) provamos que o grupo abeliano livre de cardinalidade $\\mathfrak c$ admite uma topologia de grupo enumeravelmente compacta com uma seqüência não trivial convergente. Sob as mesmas hipóteses, mostramos que um grupo topológico abeliano quase livre de torção $(G, +, \\tau)$ com $|G| = |\\tau| = \\mathfrak c$ admite uma topologia independente de $\\tau$ que o torna um grupo topológico e caracterizamos algebricamente os grupos abelianos de não torção que têm cardinalidade $\\mathfrak c$ e que admitem uma topologia de grupo enumeravelmente compacta (sem seqüências não triviais convergentes). Provamos, ainda, que o grupo abeliano livre de cardinalidade $\\mathfrak c$ admite uma topologia de grupo que torna seu quadrado enumeravelmente compacto e construímos um semigrupo de Wallace cujo quadrado é, também, enumeravelmente compacto. Por fim, assumindo a existência de $2^{\\mathfrak c}$ ultrafiltros seletivos, garantimos que se um grupo abeliano de não torção e cardinalidade $\\mathfrak c$ admite uma topologia de grupo enumeravelmente compacta, então o mesmo admite $2^{\\mathfrak c}$ topologias de grupo enumeravelmente compactas (duas a duas não homeomorfas).
Assuming the existence of $\\mathfrak c$ pairwise incomparable selective ultrafilters (according to the Rudin-Keisler ordering) we prove that the free abelian group of cardinality $\\mathfrak c$ admits a countably compact group topology that contains a non-trivial convergent sequence. Under the same hypothesis, we show that an abelian almost torsion-free topological group $(G, +, \\tau)$ with $|G| = |\\tau| = \\mathfrak c$ admits a group topology independent of $\\tau$ and we algebraically characterize the non-torsion abelian groups of cardinality $\\mathfrak c$ which admit a countably compact group topology (without non-trivial convergent sequences). We also prove that the free abelian group of cardinality $\\mathfrak c$ admits a group topology that makes its square countably compact and we construct a Wallace\'s semigroup whose square is countably compact. Finally, assuming the existence of $2^$ selective ultrafilters, we ensure that if a non-torsion abelian group of cardinality $\\mathfrak c$ admits a countably compact group topology, then it admits $2^$ (pairwise non-homeomorphic) countably compact group topologies.

Les avancées technologiques ont permis le stockage de grandes masses de données en termes de taille (nombre d’observations) et de dimensions (nombre de variables).Ces données nécessitent de nouvelles méthodes, notamment en modélisation prédictive (data science ou science des données), de traitement statistique adaptées à leurs caractéristiques. Dans le cadre de cette thèse, nous nous intéressons plus particulièrement aux données dont le nombre de variables est élevé comparé au nombre d’observations.Pour ces données, une réduction du nombre de variables initiales, donc de dimensions, par la sélection d’un sous-ensemble optimal, s’avère nécessaire, voire indispensable.Elle permet de réduire la complexité, de comprendre la structure des données et d’améliorer l’interprétation des résultats et les performances du modèle de prédiction ou de classement en éliminant les variables bruit et/ou redondantes.Nous nous intéressons plus précisément à la sélection de variables dans le cadre de l’apprentissage supervisé et plus spécifiquement de la discrimination à catégories multiples dite multi-classes. L’objectif est de proposer de nouvelles méthodes de sélection de variables pour les modèles de discrimination multi-classes appelés Machines à Vecteurs Support Multiclasses (MSVM).Deux approches sont proposées dans ce travail. La première, présentée dans un contexte classique, consiste à sélectionner le sous-ensemble optimal de variables en utilisant le critère de "la borne rayon marge" majorante du risque de généralisation des MSVM. Quant à la deuxième approche, elle s’inscrit dans un contexte topologique et utilise la notion de graphes de voisinage et le critère de degré d’équivalence topologique en discrimination pour identifier les variables pertinentes qui constituent le sous-ensemble optimal du modèle MSVM.L’évaluation de ces deux approches sur des données simulées et d’autres réelles montre qu’elles permettent de sélectionner, à partir d’un grand nombre de variables initiales, un nombre réduit de variables explicatives avec des performances similaires ou encore meilleures que celles obtenues par des méthodes concurrentes
The technological progress has allowed the storage of large amounts of data in terms of size (number of observations) and dimensions (number of variables). These data require new methods, especially for predictive modeling (data science), of statistical processing adapted to their characteristics. In this thesis, we are particularly interested in the data with large numberof variables compared to the number of observations.For these data, reducing the number of initial variables, hence dimensions, by selecting an optimal subset is necessary, even imperative. It reduces the complexity, helps to understand the data structure, improves the interpretation of the results and especially enhances the performance of the forecasting model by eliminating redundant and / or noise variables.More precisely, we are interested in the selection of variables in the context of supervised learning, specifically of multiclass discrimination. The objective is to propose some new methods of variable selection for multiclass discriminant models called Multiclass Support Vector Machines (MSVM).Two approaches are proposed in this work. The first one, presented in a classical context, consist in selecting the optimal subset of variables using the radius margin upper bound of the generalization error of MSVM. The second one, proposed in a topological context, uses the concepts of neighborhood graphs and the degree of topological equivalence in discriminationto identify the relevant variables and to select the optimal subset for an MSVM model.The evaluation of these two approaches on simulated and real data shows that they can select from a large number of initial variables, a reduced number providing equal or better performance than those obtained by competing methods

É bem conhecido o fato de que todo grupo compacto tem sequências não triviais convergentes. A existência de grupos enumeravelmente compactos sem sequências não triviais convergentes, foi provada usando axiomas adicionais à axiomática usual ZFC: A. Hajnal e I. Juhász sob CH, E. K. van Douwen sob MA, A. H. Tomita sob MA(sigma-centrada) e R.E. Madariaga-Garcia e A. H. Tomita usando ultrafiltros seletivos. Neste trabalho, estudaremos algumas construções recentes relacionadas com as citadas acima, usando o Axioma de Martin, ultrafiltros seletivos e forcing. Essas construções estão relacionadas com algumas questões indicadas por A.D. Wallace, E. van Douwen, M. Tkachenko, D. Dikranjan e D. Shakhmatov
It is well known that every compact group has non-trivial convergent sequences. The existence of countably compact groups without non-trivial convergent sequences was proved using extra set-theoretical assumptions: A. Hajnal and I. Juhasz under CH, E. K. van Douwen under MA, A.H.Tomita under MA(centered) and R.E.Madariaga-Garcia and A.H. Tomita using a selective ultrafilter. I n this work, we study some recent constructions related to the ones given above using Martin Axiom, selective ultrafilters and forcing, related to questions raised by A.D. Wallace, E. van Douwen, M. Tkacenko, D. Dikranjan and D. Shakhmatov.

As redes atuais de telecomunicações utilizam tecnologias de comutação de pacotes para integração de voz, dados, imagens e outros serviços. O tráfego nessas redes costuma ser feito por meio de tecnologias como o MPLS-TP e com regras heurísticas para a determinação dos melhores caminhos. O uso de boas regras afeta diretamente o desempenho e a segurança da operação. Este trabalho propõe o uso de simulação de baixo custo para prever o comportamento e avaliar regras de escolha de caminhos. Para isso, este trabalho avalia três métodos de seleção de caminhos de LSPs, combinados com duas heurísticas de recuperação, usados em redes MPLS-TP em malha com mecanismos de proteção em malha compartilhada. Os resultados das simulações medem o impacto dos métodos e heurísticas utilizados, demonstrando o quanto uma melhor seleção de caminhos pode contribuir para a redução do uso dos recursos da rede e do número máximo de LSPs afetados em caso de falhas na rede. Os resultados deste trabalho, bem como a técnica de análise proposta, almejam ser uma contribuição para a padronização de regras de seleção de LSPs em redes heterogêneas.
The telecommunications networks nowadays use packet-switching technologies for integration of voice, data, images and other services. The traffic on these networks is usually done through technologies such as MPLS-TP and with heuristic rules to determine the best paths. The use of good rules directly affect the performance and security of operation. This paper proposes the inexpensive use of simulation to predict the behavior and evaluate rules for choosing paths. For this, this study evaluates three methods of selection of LSPs paths, combined with two recovery heuristics, used in MPLS-TP mesh networks with shared mesh protection mechanisms. The results of the simulations measure the impact of the methods and heuristics used, demonstrating how much better path selection can contribute to reducing the use of network resources and the maximum number of LSPs affected in the event of network failures. These results and the proposed analysis technique yearn to be a contribution to the standardization of LSPs selection rules in heterogeneous networks.

This diploma thesis deals with design of axle carrier for Formula Student. The axle carrier is topologically optimized and additively manufactured with Selective Laser Melting technology. Material for its production is aluminium alloy AlSi10Mg, which has worse mechanical properties than commonly used high-strength alloys. Therefore the aim was, by using topology optimization, to design a component, which would have comparable properties with milled component. The stress strain analysis was carried out by the finite element method and maximum deformation and safety coef-ficients were acquired. The prototype was made and its dimensions were controlled by optical digitization, which proved accuracy of manufacturing. The strength calcu-lations were verified by special testing device and photogrammetry measurement. The load during the tests was 20 % higher than in the analysis and no limit state was observed. This verified its safety and functionality.

La conception sur-mesure de matériaux architecturés à l'échelle du milli/centimètre est une stratégie pour développer des matériaux de structure plus performants vis-à-vis de cahiers des charges multifonctionels. Ce travail de thèse s'intéresse en particulier à la conception optimale de panneaux architecturés périodiques, dans le but de combiner des exigences mécaniques de flexion et de cisaillement, ainsi que de conductivité thermique. Le comportement élastique peut être prédit grâce à l'identification sur la cellule périodique des coefficients de la matrice des souplesses équivalente. Ces calculs d'homogénéisation ont été mis en oeuvre par éléments finis pour estimer en particulier les souplesses en flexion et en cisaillement transverse. Après validation expérimentale, cette méthode de calcul constitue un outil d'évaluation des performances mécaniques pour chaque géométrie de cellule périodique (2D ou 3D). À titre d'exemple, et dans un contexte de développement de solutions matériaux architecturés pour l'automobile, la conception de tôles "texturées" est proposée en menant une étude paramétrique à l'aide de cet outil. L'implémentation d'un algorithme d'optimisation topologique couplé à la procédure d'homogénéisation permet d'enrichir les méthodes de conception sur-mesure en élargissant l'espace de recherche des "architectures". Après l'étude modèle du compromis entre flexion et cisaillement, le cas industriel d'un panneau sandwich isolant est traité. Dans ce cas, l'optimisation fournit plusieurs compromis prometteurs entre rigidité en cisaillement et isolation thermique. Ces géométries ont été réalisées et testées, et une nouvelle version améliorée du panneau sandwich a été sélectionnée.

博士
國立交通大學
資訊科學與工程研究所
106
The selection of influential network spreaders can be used to assist information diffusion on an online social website, to make a strategy for viral marketing, to monitor and control epidemic disease outbreak in a population, to analyze cascading failures in electrical power grids and the Internet, among many others. In this dissertation, we proposed solutions of an influence measure, a community detection algorithm and a community-centroid measure for selecting the maximal or multiple influential network spreaders. The computer simulation was used to verify the network-spreading ability of selected network spreaders. In our first research work, we proposed a two-step framework as a robust and reliable influence measure, which combines global diversity and local feature for selecting the maximal influential network spreader. The experiment results indicate that our proposed influence measure performs well and insensitively in network-spreading simulation for various network datasets. In our second research work, we proposed a rule-based hierarchical arc-merging (HAM) algorithm, which has good performance efficiency for community detection tasks of large-scale real-world networks; we also proposed a community-centroid measure to select the central nodes of community structures as multiple influential network spreaders. The experiment results indicate that our measure could result in the maximal 40% (or an average 30%) benefit in network-spreading simulations. In final, according to our results, we provided a decision diagram for determining an appropriate selection strategy of influential network spreaders for a network.

The selective catalytic reduction (SCR) of NO_X (x = 1,2) using Cu-exchanged zeolites is used commercially for the abatement of NO_X from on-road lean-burn diesel engines. At the low exhaust temperatures during cold-start and idle operation (<523 K), the SCR reaction proceeds via a Cu²⁺/Cu⁺ redox cycle of NH₃-solvated and mobilized Cu ions. Reduction of Cu²⁺ species proceeds via NO-assisted reduction of isolated NH₃-solvated Cu²⁺ ions. To complete Cu⁺ to Cu²⁺ oxidation, two [Cu(NH₃)₂]⁺ species react together with O₂ to form a dimeric O₂-bridged Cu²⁺ species that is subsequently reduced by NO and NH₃ to complete the SCR catalytic turnover. NH₃-solvated Cu ion species are nominally isolated under ex-situ conditions, however, motivating the critical research question studied in this work regarding how Cu ion mobility and dynamic interconversion of mononuclear and binuclear active sites facilitate SCR chemistry. In particular, this work focuses on understanding how active site proximity, zeolite pore connectivity and dimensionality, and catalyst poisons impact the number and reactivity of active Cu sites.
Steady-state SCR kinetics (473 K) measured at fixed gas conditions (10 kPa O₂) on a series of Cu-chabazite (CHA) zeolites with varied density of isolated Cu ions (0.078-0.35 Cu per 10³ ų) exhibit non-single site behavior because of changes in the kinetic relevance of Cu⁺ oxidation and Cu²⁺ reduction half-cycles, and the non-mean field nature of the Cu⁺ oxidation process. Measurement of SCR rates at dioxygen pressures (1-60 kPa O₂) far removed from typical operating conditions (3-17 kPa O₂) allows isolating the kinetic behavior under primarily Cu⁺ oxidation-limited and Cu²⁺ reduction-limited conditions, and estimating rate parameters for these two regimes by regressing SCR rates as a function of O2 pressure to an empirical Langmuirian rate expression. Apparent rate constants that are first-order in O₂ (k_first) increase systematically with Cu density, consistent with the dual-site Cu⁺ oxidation mechanism. Apparent rate constants that are zero-order in O2 (k_zero) show a weak dependence on Cu density, similar to the fraction of Cu that can be oxidized by O₂ at 473 K in transient experiments, suggesting that changes in k_zero reflect changes in the fraction of active Cu given the single-site nature of Cu²⁺ reduction mechanisms. The measured apparent activation energy in the Cu⁺ oxidation limit (E_app,first) increases systematically with Cu density, highlighting the non-mean field nature of Cu⁺ oxidation over the range of Cu densities studied. The measured apparent activation energies in the Cu²⁺ reduction limit are constant above a threshold Cu density (0.17 Cu per 10³ ų), consistent with mean-field behavior, but begin to deviate at lower densities (0.084-0.10 Cu per 10³ ų).
A series of Cu-zeolites with 2D (LEV, FER) and 1D (MOR) pore connectivity were synthesized to quantify how the framework topology and pore structure influences the mobility and reactivity of Cu ions during SCR. When compared to Cu-CHA, a 3D pore structure, values of k_first and k_zero (per total Cu) were several factors lower on the 2D and 1D zeolites, indicating that decreasing the effective volumetric footprint of Cu ions during SCR decreases both the rate of dual-site Cu⁺ oxidation and the fraction of Cu⁺ that oxidizes. When compared to other 3D double-six membered ring (d6r) zeolites with different pore shape (AEI) and size (AFX), rates (per total Cu) were generally a factor of 1.5 to 2 times higher on Cu-CHA, indicating that the open pore structure of cylindrical cages in CHA are favorable for low-temperature SCR reactivity.
The arrangement and density of framework Al atoms in CHA influences low-temperature SCR, as the framework Al atoms mediate Cu ion mobility and the arrangement of Al in the framework determines the chemical identity of the Cu active site precursors as either [CuOH]⁺ exchanged at an isolated framework Al center or Cu²⁺ exchanged at paired framework Al in a six-membered ring (6-MR). Synthesis of CHA zeolites with mixtures of Na⁺ and TMAda⁺ provides a strategy to alter the amount of Al centers in 6-MR paired configurations, because Na+ co-occludes in 6-MR voids adjacent to TMAda⁺ occluded within the cha cage. In contrast, synthesis of CHA zeolites with mixtures of K⁺ and TMAda⁺ results in primarily 6-MR isolated Al configurations because K⁺ cations displace TMAda⁺ from residing in cha cages. Thus, the use of different mixtures of organic and inorganic structure directing agents (SDAs) provide routes to synthesize CHA zeolites that favor the formation of either [CuOH]⁺ or Cu²⁺ species. The Cu speciation influences both hydrothermal stability and resistance to sulfur poisoning. SO₂ is a catalyst poison ubiquitous in automotive exhaust and is found to bind to [CuOH]⁺ sites more strongly than Cu²⁺ sites, both before and after high-temperature de-sulfation treatments.
Together, these findings reveal several of the important structural and active site requirements for low-temperature NO_X SCR with NH₃ on Cu-zeolites. The non-mean field nature of the SCR redox cycle on Cu²⁺/Cu⁺ ion sites, and the requirement for Cu ions to be located in proximal and accessible locations of zeolite void spaces becomes more favorable in 3D highly connected pore structures, highlighting a primary reason why low-temperature SCR rates (per Cu) are higher on Cu-CHA than on other Cu-zeolites. The synthetic procedures presented here to influence the Al arrangement in CHA zeolites provide new strategies to alter the speciation and density of isolated Cu ion sites, even among Cu-CHA zeolites of nominally identical elemental composition, which have implications for the stability and resistance to poisons of the catalyst under realistic operating conditions. Together, synthetic strategies to manipulate the proximity of active sites, methods to quantify transient and steady-state kinetics, and in situ and operando characterization are invaluable tools to study and understand the non-mean field dynamic interconversion of isolated and multinuclear sites during low-temperature SCR catalysis.