Surface science approach to modeling supported catalysts (original) (raw)
Catalysis Letters, 2013
Surface science studies allow processes impor tant for heterogeneous catalysis to be investigated in greatest detail. Starting from the simplest model of a catalytic surface, a metal single-crystal surface under ultrahigh vacuum conditions, enormous progress has been made in the last decades towards extending the surface science of catalysis to technically more relevant dimensions. In this perspective, we highlight recent work, including our own, dealing with the influence of water on metal-support interactions in surface science studies of oxide-supported metal nanoparticle model catalysts. In particular, the effect of hydroxyl groups on nucleation and sintering of metal nanoparticles, and surface science investigations into catalyst preparation using wet-chemical procedures are addressed. Keywords Heterogeneous catalysis \ catalysis Á Oxide supports \ preparation and materials Á Metal-support interaction \ preparation and materials Á Characterization \ methodology and phenomena Á Thin films \ methodology and phenomena Á Spectroscopy and general characterisation
Importance of surface science and fundamental studies in heterogeneous catalysis
Catalysis letters, 1999
At Union Carbide Corporation, surface science and fundamental studies have played extremely important roles in the discovery, development, and diagnosis of several valuable commercial and developmental catalyst systems. Prior to the late '60s, it was very common among scientists and engineers to refer to catalysis, particularly heterogeneous catalysis, as either an "art" or "magic". Primary reasons behind these labels were our inability to understand the performance of "poor" and "good" catalysts nominally having the same bulk composition. With the development of surface science in the early '70s, heterogeneous catalysis field was relatively easy picking for diagnosis and improved understanding of many of these poorly understood catalyst systems. In fact, there were many "sad" stories across the chemical industry of catalysts that prematurely deactivated or essentially died and there was no known cause or relationship of performance with observable physical-chemical properties. In all such instances, the bulk characterization techniques failed to identify or uncover the cause or causes of such activity decline. However, through the use of surface science and fundamental characterizations, three such "sad stories" turned into "success stories" at Union Carbide. In addition, it will also be shown that the early use of surface science and fundamental studies led to the discovery, development and enhanced understanding of several catalyst systems. Many of the early surface science techniques along with the newly developed techniques continue to and will play a very important role in the future development of next generation catalysts and catalytic processes for the industrial use and environmental protection.
Norskov Nature Chemistry Catalyst Design 2010
D uring the past century chemists have developed efficient chemical reactions for converting fossil resources into a broad range of fuels and chemicals, and this can be considered one of the most important and far-reaching scientific developments up to now. Today, essentially all transportation fuels are refined in a number of catalytic processes and most chemicals are also produced using technologies based on catalysis 1. A few well-known examples illustrate the impact: about half of all petrol in the world is now produced by fluid catalytic cracking using specially designed zeolite catalysts, and the Haber–Bosch process — featuring an iron catalyst — continues to have a key role in the production of fertilizers. The list of important small-and large-scale processes by which fossil resources are converted into fuels and chemicals is almost endless. Such catalytic technologies have also resulted in various environmental issues — even the best processes do not allow a complete elimination of undesirable byproducts. Many innovative, catalytic technologies have subsequently been implemented to remedy these new problems; one famous example is the precious-metal-based three-way catalyst installed in most petrol-fuelled passenger cars. Moreover, these developments have contributed to an increased use of fossil resources and thus to the increasing carbon dioxide levels in the atmosphere. Currently, there is a significant drive to relinquish our dependence on fossil fuels and to minimize the emission of carbon dioxide. Clearly, this calls for many new and improved catalytic processes, and for catalytic technologies that focus on prevention rather than on remediation. Reducing environmental impact will require entirely new catalysts: catalysts for new processes, more active and more selective catalysts and preferably catalysts that are made from earth-abundant elements. This represents a formidable challenge and it will demand an ability to design new catalytic materials well beyond our present capabilities. The ultimate goal is to have enough knowledge of the factors determining catalytic activity to be able to tailor catalysts atom-by-atom. The catalytic properties of a material are in principle determined completely by its electronic structure, so the objective is the engineering of electronic structure by changing composition and physical structure. The approach is illustrated in Fig. 1. Over the past few decades our understanding of why particular materials are good catalysts for given reactions has improved. The challenge Over the past decade the theoretical description of surface reactions has undergone a radical development. Advances in density functional theory mean it is now possible to describe catalytic reactions at surfaces with the detail and accuracy required for computational results to compare favourably with experiments. Theoretical methods can be used to describe surface chemical reactions in detail and to understand variations in catalytic activity from one catalyst to another. Here, we review the first steps towards using computational methods to design new catalysts. Examples include screening for catalysts with increased activity and catalysts with improved selectivity. We discuss how, in the future, such methods may be used to engineer the electronic structure of the active surface by changing its composition and structure. is to invert this problem; given that we need to catalyse a certain reaction under a set of specified conditions, which material should we choose? The aim of controlling matter at the molecular scale by engineering the electronic structure is not restricted to catalytic materials; it is a general challenge in chemistry, physics and materials science, and there is considerable progress in several areas such as materials for batteries 2 , hydrogen storage 3 , optical absorption 4 and molecules for homogeneous catalysis 5,6. Catalysis at surfaces is particularly well suited for electronic structure engineering, primarily because the link between the atomic-scale properties and the macroscopic functionality — the kinetics — is well developed. In addition, the theoretical description of surface reactions has been enhanced considerably by the availability of a large number of quantitative experimental surface-science studies of adsorption and reaction phenomena 7–12. Here, we review some of the first examples of the computer-based design of solid catalysts. We introduce a number of concepts linking catalytic performance to the properties of the catalyst's surface, and in turn discuss how the surface electronic structure determines the catalytic properties. Finally, we discuss some of the challenges ahead. trends and descriptors of catalytic activity The extraordinary progress in density functional theory (DFT) calculations for surface processes is the key development that has created the possibility of computer-based catalyst design 13. Current methods are fast enough to allow the treatment of complex, extended systems 14,15. They can also now provide the interaction energies of molecules and atoms with metal surfaces with sufficient accuracy to describe trends in reactivity for transition metals and alloys 16. There are now several cases where the complete kinetics of a catalytic reaction has been evaluated solely on the basis of DFT calculations of reaction barriers, reaction energies and the associated entropies 17–20. Figure 2 shows the comparison between calculated and measured rates for three different reactions and catalytic surfaces. Overall, the agreement between DFT-based kinetic models and experiment is surprisingly good, and they serve to illustrate the accuracy and value of current density functional theory. The agreement between theory and experiment is particularly noteworthy in two cases for supported metal catalysts (ruthenium
Concluding remarks: progress toward the design of solid catalysts
Faraday Discussions, 2016
The 2016 Faraday Discussion on the topic "Designing new Heterogeneous Catalysts" brought together a group of scientists and engineers to address forefront topics in catalysis and the challenge of catalyst design-which is daunting because of the intrinsic nonuniformity of the surfaces of catalytic materials. "Catalyst design" has taken on a pragmatic meaning which implies the discovery of new and better catalysts on the basis of fundamental understanding of catalyst structure and performance. The presentations and discussion at the meeting illustrate rapid progress in this understanding linked with improvements in spectroscopy, microscopy, theory, and catalyst performance testing. The following essay includes a statement of recurrent themes in the discussion and examples of forefront science that evidences progress toward catalyst design. Catalysis and catalyst design Catalysis is the key to control of chemical change, in processes ranging from the biological to the technological. It is used to make products including chemicals, fuels, materials, food, beverages, and personal care products, and together these have a value of roughly 5-10 trillion dollars (US) per year worldwide. Catalysis is also essential for the removal of environmental pollutants such as those generated in motor vehicles and fossil fuel-fired power plants. Thus, the science underlying catalytic technology is essential. Catalysis science is also challenging, because almost all large-scale industrial catalysts are solids. These work at their surfaces-and these surfaces are notoriously nonuniform in both composition and structure, often being substantially different from simple terminations of the bulk material-and they undergo changes when exposed reactants.
Fundamental issues on practical Fischer–Tropsch catalysts: How surface science can help
Catalysis Today, 2014
The present article highlights the contribution of surface science and molecular modeling to the understanding of Fischer-Tropsch catalysis, in particular related to carbon-induced Co Fischer-Tropsch catalyst deactivation. The role of atomic and graphitic carbon in surface restructuring is discussed. Both forms of surface carbon stabilize surface roughness, while molecular CO promotes mobility of Co surface atoms. In a proposed chain growth mechanism on Co(0 0 0 1) chain elongation proceeds via alkylidyne + CH. The resulting acetylenic species is hydrogenated to alkylidyne, the route to further growth. (Cyclo-)polymerization of acetylenic species produces (aromatic) forms of polymeric surface carbon, a slow side reaction.
The molecular approach to supported catalysts synthesis: state of the art and future challenges
Journal of Molecular Catalysis A: Chemical, 2000
This contribution addresses some of the molecular-level aspects of classical supported metal catalysts preparation procedures. While the problems selected here have been chosen for their fundamental and practical relevance, important studies due to Knozinger and coworkers will be quoted in each case, and this short review may thus be regarded as a homagë to their early activity in the field.
Microchimica Acta, 2006
Heterogeneous catalysis is one of the fields of modern technology, in which a characterization of structural and chemical properties of solid surfaces at the microscopic level is of enormous importance. For a long time, such insights have been precluded by the complexity of most catalytically active materials. Recently, substantial progress has been made, however, toward a microscopic-level understanding of complex catalyst surfaces. We discuss the driving factors for these advancements, which are based on the development of new well-defined model systems as well as on advances in experimental technology and theory. Scrutinizing the example of planar model catalysts, we identify the process of linking structural and chemical information to microscopic reaction kinetics as a particular challenging aspect of today's work. We review the kinetic effects which may have an influence on the reaction kinetics on complex surfaces. As an example how structural and kinetic information can be correlated at the microscopic level we discuss the case of surface oxidation and oxygen induced restructuring of Pd nanoparticles as studied by molecular beam methods.
Density functional theory in surface chemistry and catalysis
Proceedings of the National Academy of Sciences, 2011
Recent advances in the understanding of reactivity trends for chemistry at transition-metal surfaces have enabled in silico design of heterogeneous catalysts in a few cases. The current status of the field is discussed with an emphasis on the role of coupling theory and experiment and future challenges.
2003
This review substantiates the molecular approach to the study of the catalytic action of various systems, which consists in the comparative study of the nature and reactivity of adsorbed species and considering the problems of pressure and material gaps. The pressure gap problem can be solved by a continuous increase in the pressure of the reaction mixture, including carrying out in situ studies. The solution to the problem of material gap is possible when one passes from bulk to dispersed samples, which model real supported catalysts. As the last step that can build a bridge between surface science and catalysis, the study of nanoparticle reactivity toward the reactants of a catalytic reaction with varying sizes of nanoparticles is proposed. The scope of such an approach is demonstrated by the study of silver catalysts of ethylene epoxidation. It was found that the catalytic action of silver in the process of ethylene oxide synthesis is determined by the possibility of formation of electrophilic adsorbed atomic oxygen. Its formation is more efficient under the action of reaction mixtures at high pressures and on the surfaces of silver species with sizes smaller than 50 nm. It is shown that the reaction center should also contain the nucleophilic form of O ads , which itself is only active in the complete oxidation of ethylene but creates the Ag 1+ sites for ethylene adsorption. The disappearance of O nucl with a decrease in the size of silver particles below 50 nm leads to a drastic decrease in the rate of ethylene epoxidation. The reaction mechanism made it possible to propose systems with an abnormally high value of selectivity to ethylene oxide (>90%).
A prospective: Surface science and catalysis at the nanoscale
Surface Science, 2009
Surface science has progressed from its beginnings, which focused on simple materials and adsorbates, to the study of much more complex materials. In this article I focus on the developments in the field of nanoparticle surface science, especially those relating to advances in our understanding of heterogeneous catalysis. Methods to make such materials and to characterise oxidic supports have advanced enormously in the last few years, but efforts in the field are still rather limited and patchy. Such work will expand significantly in the next few years and many new, exciting discoveries await us. Important areas for development include the fabrication of ordered arrays of monodisperse nanoparticles, imaging small metal particles at atomic resolution and carrying such investigations out under high pressure/temperature conditions in order to identify active sites on nanoparticles under realistic conditions.
Chapter model systems in heterogeneous catalysis at the atomic level: a personal view
Science China Chemistry, 2020
The review presents an overview of studies in the surface science of oxide and related surfaces with an emphasis of the studies performed in the authors’ group. Novel instruments and technique developments, as well as their applications are reported, in an attempt to cover studies on model systems of increasing complexity, including some of the key ingredients of an industrially applied heterogeneous catalyst and its fabrication. The review is intended to demonstrate the power of model studies in understanding heterogeneous catalysis at the atomic level. The studies include those on supported nano-particles, both, prepared in vacuum and from solution, interaction of surfaces and the underlying bulk with molecules from the gas phase, strong metal support interaction, as well as the first attempt to include studies on reactions in confined spaces.
The Catalytic Mechanics of Dynamic Surfaces: Stimulating Methods for Promoting Catalytic Resonance
Transformational catalytic performance in rate and selectivity is obtainable through catalysts that change on the time scale of catalytic turnover frequency. In this work, dynamic catalysts are defined in the context and history of forced and passive dynamic chemical systems, with classification of unique catalyst behaviors based on temporally-relevant linear scaling parameters. The conditions leading to catalytic rate and selectivity enhancement are described as modifying the local electronic or steric environment of the active site to independently accelerate sequential elementary steps of an overall catalytic cycle. These concepts are related to physical systems and devices that stimulate a catalyst using light, vibrations, strain, and electronic manipulations including electrocatalysis, back-gating of catalyst surfaces, and introduction of surface electric fields via solid electrolytes and ferroelectrics. These catalytic stimuli are then compared for capability to improve catalysis across some of the most important chemical challenges for energy, materials, and sustainability. File list (2) download file view on ChemRxiv Perspective_Manuscript_ChemRxiv.pdf (3.88 MiB) download file view on ChemRxiv Perspective_Supporting_Information_ChemRxiv.pdf (149.75 KiB)