Machine learning methods for theoretical heterogeneous catalysis: current status and challenges

The semihydrogenation of phenylacetylene to styrene is a critical process for styrene purification, and the rational design of catalysts with high activity and selectivity remains a key challenge. Transition metal containing zeolite catalysts offer unique advantages in semihydrogenation, while the reaction mechanism remains unclear, thereby hindering the performance optimization of catalysts. Using density functional theory calculations, a representative Ni@FAU catalyst, with Lewis pairs comprising a FAU six-membered ring-confined Ni(II) ions and adjacent framework oxygen atoms as the active sites, are investigated for phenylacetylene semihydrogenation. At 0 K, H2 fails to dissociate directly at clean Lewis pairs, but phenylacetylene preadsorption (PhC≡CH_Ni*) at Ni sites promotes H2 dissociation at the classical Lewis pairs, forming [H_Oz+H_Ni]* intermediates. These intermediates can convert to [H_Oz+H_Oz]* via hydride/proton transfer, with PhC≡CH_Ni* stabilizing both [H_Oz+H_Ni]* and [H_Oz+H_Oz]* intermediates and facilitating hydrogen transfer. Analysis of four phenylacetylene hydrogenation pathways shows that ethylbenzene formation is suppressed by a high barrier (2.46–2.71 eV) for the second H2 dissociation (rate-determining step) due to steric hindrance. In contrast, styrene formation is kinetically favorable, with Pathway 3 (α-carbon first, then β-carbon) being optimal, featuring a low rate-determining step barrier (0.67 eV) for proton transfer. This work clarifies how the Ni@FAU catalyst achieves high styrene selectivity by inhibiting overhydrogenation to ethylbenzene, aligning well with experimental observations, and further deepens mechanistic understandings of phenylacetylene semihydrogenation over the Ni@FAU catalyst for the rational design of selective hydrogenation catalysts.

Metal oxides are highly important as components in heterogeneous catalysts. It is also well established that as the building blocks of nanoscaled materials get smaller, surfaces become increasingly important in determining their properties. Very early on, researchers found that catalytic activity is only indirectly related to the surface area; in fact it depends on the density of active sites. Although solid-state defects have been proposed to be the active sites in heterogeneous catalysis, active centers have rarely been conclusively identified and the rational design of catalysts is still out of reach. Processes in heterogeneous catalysis associated with the production of energy-storage molecules, for example, methanol as a storage molecule for hydrogen, is presently of great interest. Low-pressure production of methanol is conducted industrially with catalysts containing Cu and ZnO as the active phases and alumina as the support. Composites (Cu + ZnO), however, exhibit higher activities than that expected based on the performance of the single components. This was attributed to a strong metal–support interaction (SMSI) effect. Nevertheless, the active sites in Cu/ZnO and even in the pure ZnO have not yet been identified experimentally. Some important information concerning pure ZnO catalysts is already available: Generally, the catalytic activity of ZnO does not increase linearly with the increasing BET surface area. It was concluded that the catalytic formation of methanol over ZnO is a structure-sensitive reaction requiring the presence of polar ZnO facets. According to the most recent models of the methanol-synthesis reaction on the polar ZnO(0001) surface, oxygen vacancies formed on this surface of ZnO crystals serve as the active sites (Scheme 1). However, there has been no definite experimental proof for this assumption.

To understand technologically complex catalytic systems and to tailor both activity and selectivity in heterogeneous catalysis and photocatalysis, there is the challenge of bridging the materials gap that exists between two- and three-dimensional model catalytic systems and real catalysts, which are comprised of highly dispersed, oxide-supported metal nanoparticles. While colloid nanoparticles synthesized using wet chemistry have the potential for tuning size, shape, and composition, there are complexities related to the organic capping layers. Therefore, the development of new model catalysts without a capping layer is crucial. Coaxial vacuum arc plasma deposition (APD) is a method to fabricate non-colloidal nanocatalysts that has the potential for large-scale synthesis of nanocatalysts and, at the same time, allows for systematic investigation of intrinsic factors that affect catalytic activity. In this article, we describe the fabrication of catalytic nanoparticles using APD, and their application in heterogeneous catalysis and photocatalysis research. Direct vaporization of metallic materials to deposit active materials on two-dimensional or three-dimensional oxide supports has drawn considerable interest due to its simplicity, high reproducibility, and the possibility for large-scale production. We highlight recent studies on metal–support interactions, the effect of doping on the oxide, and hot electron-driven chemical reactions. In the case of photocatalysis, APD was used to fabricate metal nanoparticles on a hierarchically porous oxide; enhanced hydrogen evolution by doping and porosity was also demonstrated. Therefore, the materials gap in catalysis can be bridged by the potential for large-scale synthesis of a variety of catalysts using APD.

Activation of surface lattice oxygen and chemisorbed oxygen on catalyst surfaces constitutes a pivotal step in heterogeneous oxidative catalysis. Herein, we report a strategy for enhancing oxygen activation by rational design of catalysts with single-atom promoters. Single-site Zr species in CeO2 (Zr1-CeO2) are synthesized using the atom-trapping method. The Zr1-CeO2-supported Pt catalyst exhibits enhanced catalytic performance over the CeO2-supported Pt catalyst in the oxidation of CO, C3H8, and C3H6, achieving significantly lower T50 values (temperature required to reach 50% conversion). This enhanced catalytic activity is attributed to the formation of an asymmetric Zr1-O-Pt1 structure, which favors the activation of the adjacent surface lattice oxygen and chemisorbed molecular oxygen. This work exemplifies that incorporating single-site atoms into oxide support facilitates oxygen activation, providing new insights into the role of atomically dispersed promoters in heterogeneous catalysis.

Heterogeneous catalysts, which often consist of metal nanoparticles loaded on supports such as metal oxides, can undergo several types of restructuring under reaction and catalytic conditions. Advanced characterizations now allow the surface structure of a catalyst in a gas phase to be determined to some extent. Metal nanoparticles may experience changes in shape, surface structure and composition, and atomic packing in response to the pressure of a reactant or product gas, temperature, and reaction between the catalyst surface and gas. Metal oxide supports can partially or fully encapsulate metal nanoparticles, altering their electronic structure and reactivity. Restructuring is a main approach to creating active catalytic sites. The rational design of catalysts must anticipate that such restructurings can occur under reaction or catalytic conditions and gain knowledge of how they occur. It is expected that computational studies can predict such restructurings and that advanced synthesis may be used to prepare pristine catalysts with enhanced resistance to restructurings.

The coordination geometry of silver complexes of the green fluorescence protein chromophore is highly diverse and dependent on the size and shape of the counteranion in the complexes. Only complexes that have vacancies at the silver atom prove to be heterogeneous catalysts in the “green” synthesis of 1,4‐benzodioxines. The results reveal an interesting strategy of exploiting crystal packing forces to enhance catalytic efficiency by just changing the counteranion.

Review: [130 refs.

Catalysis is a ubiquitous element of the modern economy, representing a cornerstone of many sectors including energy, materials, and pharmaceuticals. Within this realm, 80% of reactions are carried out by heterogeneous catalysts due to their advantageous physical and chemical characteristics. In some heterogeneous systems, the reaction rate can be optimized through rational catalyst design, in which support materials can be tailored structurally and stereoelectronically for targeted purposes to better facilitate the catalytic reaction. To this end, metal–organic frameworks (MOFs) have garnered recent attention due to their high porosity, crystallinity, and chemical tunability, which can be used to derive structure–activity relationships in the design of catalysts. In this Perspective, we survey examples of catalytically active guest metals on the inorganic nodes of MOFs. This is done with the intention of providing design guidelines for tailoring chemical reactivity and insights into the opportunities for future growth in this field. Strategies for rational design in MOF catalysis include electronic tuning of the metal node in the MOF support, installing promoter ions onto the node to effect the reactivity of grafted metals, modulation of the spatial environment around the transition metal using the metal node structure, and achieving site uniformity in supported catalysts. By highlighting these efforts, we seek to underscore the role of MOF nodes as nonspectator supports for catalytic metal complexes and provide future directions for rational catalyst design by tuning reactivity on these anchoring platforms.

15 - Nanoalloys and catalytic applications

High-throughput experimentation (HTE) in catalysis and materials science has become a mature technology since the late 1990s. The reasons for the success of HTE are the potential of increased R&D efficiency, which allow shortening of experimental periods, quick systematic insights, and finally faster time-to-market. Key elements of HTE technology are parallelization, fast sequential execution of experimental operations, and implementation of highly automated hardware and software components into HTE. This article contains sections titled: 1. Introduction 1.1. Origin of High-Throughput Experimentation in Catalysis and Materials Science 1.2. Definition and Scope of HTE 1.3. Workflow Development 1.4. Classification of Screening Approaches into Experimental Stages 1.5. Experimental Planning and Use of Complex Advanced Algorithms in HTE 2. Approaches for High-Throughput Synthesis of Heterogeneous Catalysts and Advanced Materials 3. HTE in Catalysis 3.1. HTE in Heterogeneous Catalysis 3.2. Environmental Catalysis 3.3. Petrochemical Applications 3.4. Homogeneous Catalysis 3.4.1. Homogeneous Catalyst Libraries 4. HTE in Materials Science 4.1. Materials for Optical Applications 4.2. Materials for Electronic Applications 4.3. Materials for Magnetic Applications 5. Conclusions and Perspectives

Chemical kinetics is a key subdiscipline of physical chemistry that studies the reaction rate in every elemental step and corresponding catalytic mechanism. It mainly concludes molecular reaction dynamics, catalytic dynamics, elemental reaction dynamics, macrodynamics, and microdynamics. Such a research field has wide applications in heterogeneous catalysis. Based on the Arrhenius plot fitted by the catalytic conversions below 15% without the mass transfer effect and heat transfer effect, the apparent activation energy echoing with the intrinsically catalytic sites and the pre-exponential factor echoing with the relative number of active sites can be, respectively, derived from the slope and intercept of the Arrhenius plots, which can be used to compare the intrinsically catalytic activity of different catalysts and the relative amount of active sites. Reaction orders of both reactants and products are derived from the reaction rate equation and also fitted by the catalytic conversions below 15% without the mass transfer effect and heat transfer effect. According to the acquired reaction orders, the reaction mechanism can be proposed and even defined in some simple reactions. Therefore, investigations of chemical kinetics are of extreme importance and meaning in heterogeneous catalysis.

In situ MAS NMR at the service of catalysis by zeolites: From the unraveling catalytic mechanisms towards the elucidation of the mechanisms of synthesis and rational design of zeolite catalysts

Designing of highly selective and high-temperature endurable RWGS heterogeneous catalysts: recent advances and the future directions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRational design of a heterogeneous palladium catalyst for the selective hydrogenation of alkynesJudith G. Ulan, Wilhelm F. Maier, and David A. SmithCite this: J. Org. Chem. 1987, 52, 14, 3132–3142Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://doi.org/10.1021/jo00390a032RIGHTS & PERMISSIONSArticle Views1044Altmetric-Citations75LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts Get e-Alerts

Accurate interatomic force field for molecular dynamics simulation by hybridizing classical and machine learning potentials