Selective Oxidation: From a Still Immature Technology to the Roots of Catalysis Science

Abstract

The design of heterogeneous selective oxidation catalysts based upon complex metal oxides is governed at present by a set of empirical rules known as “pillars of oxidation catalysis”. They serve as practical guidelines for catalyst development and guide the reasoning about the catalyst role in the process. These rules are, however, not based upon atomistic concepts and thus preclude their immediate application in for example computer-aided search strategies. The present work extends the ideas of the pillar rules and develops the concept of considering a selective oxidation catalyst as enabler for the execution of a reaction network. The enabling function is controlled by mutual interactions between catalyst and reactants. The electronic structure of the catalyst is defined as a bulk semiconductor with a surface state arising form a terminating over layer being different from the structure of the bulk. These components that can be identified by in situ analytical methods form a chemical system with feedback loops, which is responsible for generating selectivity during execution of the reaction network. This concept is based upon physical observables and could allow for a design strategy based upon a kinetic description that combines the processes between reactants with the processes between catalyst and reactants. Such kinetics is not available at present. Few of the constants required are known but many of them are accessible to experimental determination with in situ techniques

MoO3–TiO2 synergy in oxidative dehydrogenation of lactic acid to pyruvic acid

“…[44][45][46] It has also been demonstrated that oxidative dehydrogenation of ethanol could be used as a model reaction to investigate the redox properties of V 2 O 5 /TiO 2 catalysts. 47 Inspired by these studies, we also applied ethanol oxidation as a model reaction to investigate these properties of the catalysts used for LA conversion.…”

The Catalytic Reduction of Carboxylic Acid Derivatives and CO2 by Metal Nanoparticles on Lewis‐Acidic Supports

“…Achieving this objective would pave a new way to realize the environmentally friendly and sustainable production of value‐added chemicals, in which the use of catalysis and the reduction of toxic reagents, stoichiometric amounts of promoters, waste, energy, and number of operational steps are important factors ,. In the current petroleum‐based production system, chemical production processes are mainly based on the catalytic oxidation of raw materials such as hydrocarbons, which reside in low oxidation states . In order to diminish the use of fossil petroleum resources and carbon dioxide (CO 2 ) emissions, alternative synthetic routes starting from renewable carbon resources are required, even though renewable carbon resources such as CO 2 and biomass derivatives such as carboxylic acids, esters, and amides exhibit high oxidation states .…”

Characterization of MoVTeNbOx Catalysts during Oxidation Reactions Using In Situ/Operando Techniques: A Review

“…Based on the Mars-van-Krevelen mechanism prevalent in these oxidation reactions, the role of lattice oxygen must be analyzed further to quantify their transport between the bulk and surface regions, as well as understand their role in selectivity [81]. The site isolation concept for oxidation catalysts is based on the idea that this reactive oxygen must be readily available while the rest of the structure acts as a control system for the electronic and physical properties of the catalysts [82].…”

“…The low oxygen reaction order indicates that the generation of activated oxygen is not involved in the kinetically-difficult step [81]. However, the rates with respect to different intermediate steps, C-H activation, C-C breaking, C-O formation, etc., are not yet systemically studied or known.…”

“…Taylor proposed in 1925 that only a fraction of surface atoms are responsible for heterogeneous catalysis [84]. These transient methods are important in catalyst development in a sense that 'the catalytic function is a transient property of the catalyst structure on its way to thermodynamic equilibrium' [81]. These transient characterization experiments have not been greatly explored and may be able to derive the role of key promoters or unique compositions for mixed metal oxide catalysts with improved catalyst activity.…”