Metal Oxides in Heterogeneous Oxidation Catalysis: State of the Art and Challenges for a More Sustainable World

International audienceThis Review presents current knowledge, recent results, and challenges for the future in heterogeneous oxidation catalysis in liquid and gaseous phases on solid metal oxide catalysts. Metal oxides that are used as catalysts and their main structures and properties are summarized, as well as their catalytic properties in selective and total oxidation reactions, which were studied intensively, experimentally and theoretically, by Professor Jerzy Haber during his scientific life. Some emphasis is placed on the classical and unusual catalyst activation procedures for improving catalytic properties for better efficiency. For a more sustainable world, several examples are given of the oxidation of biomass derivatives to synthesize valuable chemicals and of other applications of metal oxides, such as depollution, photocatalysis, hydrogen production and fuel‐cell components. The importance of metal oxide catalysis in environmental and green chemistry and sustainability is discussed, and challenges for the future are considered

Heterogeneous Partial (amm) Oxidation and Oxidative Dehydrogenation Catalysis on Mixed Metal Oxides

International audienceThis paper presents an overview of heterogeneous partial (amm)oxidation and oxidative dehydrogenation (ODH) of hydrocarbons. The review has been voluntarily restricted to metal oxide-type catalysts, as the partial oxidation field is very broad and the number of catalysts is quite high. The main factors of solid catalysts for such reactions, designated by Grasselli as the " seven pillars " , and playing a determining role in catalytic properties, are considered to be, namely: isolation of active sites (known to be composed of ensembles of atoms), Me–O bond strength, crystalline structure, redox features, phase cooperation, multi-functionality and the nature of the surface oxygen species. Other important features and physical and chemical properties of solid catalysts, more or less related to the seven pillars, are also emphasized, including reaction sensitivity to metal oxide structure, epitaxial contact between an active phase and a second phase or its support, synergy effect between several phases, acid-base aspects, electron transfer ability, catalyst preparation and activation and reaction atmospheres, etc. Some examples are presented to illustrate the importance of these key factors. They include light alkanes (C 1 –C 4) oxidation, ethane oxidation to ethylene and acetic acid on MoVTe(Sb)Nb-O and Nb doped NiO, propene oxidation to acrolein on BiMoCoFe-O systems, propane (amm)oxidation to (acrylonitrile) acrylic acid on MoVTe(Sb)Nb-O mixed oxides, butane oxidation to maleic anhydride on VPO: (VO) 2 P 2 O 7-based catalyst, and isobutyric acid ODH to methacrylic acid on Fe hydroxyl phosphates. It is shown that active sites are composed of ensembles of atoms whose size and chemical composition depend on the reactants to be transformed (their chemical and size features) and the reaction mechanism, often of Mars and van Krevelen type. An important aspect is the fact that surface composition and surface crystalline structure vary with reaction on stream until reaching steady state, which makes characterisation of active and selective surface sites quite difficult. The use of oxidants other than O 2 , such as H 2 O 2 , N 2 O or CO 2 , is also briefly discussed. Based on such analysis and recent discoveries and process developments, our perspective is given

Acid–base characterization of heterogeneous catalysts: an up-to-date overview

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Heterogeneous Catalysis on Metal Oxides

This review article contains a reminder of the fundamentals of heterogeneous catalysis and a description of the main domains of heterogeneous catalysis and main families of metal oxide catalysts, which cover acid-base reactions, selective partial oxidation reactions, total oxidation reactions, depollution, biomass conversion, green chemistry and photocatalysis. Metal oxide catalysts are essential components in most refining and petrochemical processes. These catalysts are also critical to improving environmental quality. This paper attempts to review the major current industrial applications of supported and unsupported metal oxide catalysts. Viewpoints for understanding the catalysts’ action are given, while applications and several case studies from academia and industry are given. Emphases are on catalyst description from synthesis to reaction conditions, on main industrial applications in the different domains and on views for the future, mainly regulated by environmental issues. Following a review of the major types of metal oxide catalysts and the processes that use these catalysts, this paper considers current and prospective major applications, where recent advances in the science of metal oxide catalysts have major economic and environmental impacts

Characterization of Solid Materials and Heterogeneous Catalysts: From Structure to Surface Reactivity, Volume 1&2

International audienceThis two-volume book provides an overview of physical techniques used to characterize the structure of solid materials, on the one hand,and to investigate the reactivity of their surface, on the other. Therefore this book is a must-have for anyone working in fields related to surfacereactivity. Among the latter, and because of its most important industrial impact, catalysis has been used as the directing thread of the book.After the preface and a general introduction to physical techniques by M. Che and J.C. Védrine, two overviews on physical techniques arepresented by G. Ertl and Sir J.M. Thomas for investigating model catalysts and porous catalysts, respectively.The book is organized into four parts: Molecular/Local Spectroscopies, Macroscopic Techniques, Characterization of the Fluid Phase (Gas and/or Liquid), and Advanced Characterization. Each chapter focuses upon the following important themes: overview of the technique, most important parameters to interpret the experimental data, practical details, applications of the technique, particularly during chemical processes,with its advantages and disadvantages, conclusions

Recent development of heterogeneous catalysis in ring-opening, biocatalysis, and selective partial oxidation reactions on metal oxides

International audienceIn this review article, we analyze the state of the art and future developments in three important domains of heterogeneous catalysis, namely ring opening, biocatalysis, and partial oxidation on metal oxides. After recollecting the scientific bases of each domain, we consider several examples, some recent improvements/developments, and some prospective views

Effect of Brønsted acidity in propane oxidation over Cs2.5H1.5PV1Mo11-xWxO40 polyoxometallate compounds

Cs2.5H1.5PV1Mo11-xWxO40 Keggin-type polyoxometallate (POM) compounds have been synthesised and studied for selective propane oxidation in the 300-400 °C temperature range. Prior to reaction the samples were pre-treated at either 300 °C or 400 °C in order to change the concentration in Brønsted acid sites by decreasing the amount of constitutional water. Acid strength was enhanced by substituting increasing amounts of W6+ in the Keggin anion for Mo6+, between 0 and 6 per Keggin Unit (KU) as shown by NH3-TPD of the H+ form and IR of the lattice vibrational modes (Mdouble bond, longO and Msingle bondOsingle bondM with M = Mo6+ or W6+). As a matter of fact vibrational mode frequencies and thus the corresponding bond energies were observed to increase with W6+ substitution. This results in more covalent Msingle bondO bonds and thus to freer protons. Chemical analysis, IR and DTA/TG data allowed us to determine the extent of W6+ substitution for Mo6+, the amount of constitutional water and any structural change in the samples. It was observed that under catalytic conditions, (C3/O2/He = 2/1/2, flow rate 15 cm3 min-1, 12 h on stream, reaction temperature in the 300-400 °C range) the catalyst structure was maintained, with only a very small part of the substituted elements (V5+, W6+ and Mo6+ atoms) being extracted from the Keggin anion. Catalytic data have shown that introduction of W6+ to replace Mo6+ led to lower propane activation, which may be due to a decrease of lattice oxygen anion mobility, related to the stronger Msingle bondO bond (see supra and as shown by the higher reaction temperature necessary for the same conversion level). Compared to pre-treatment temperature at 300 °C, pre-treatment at 400 °C was observed to result in a higher extent of constitutional water removal i.e. a loss of Brønsted acid sites by a factor of 2-4.5 when W6+ amount varies from 0 to 6 per KU without destroying the primary Keggin structure, and to favour the formation of propene at the expense of acetic and acrylic acids and COx. This also shows that substituting W6+ for Mo6+, which enhances Brønsted acid strength is detrimental to propene formation and leads to higher selectivity to acetic acid and COx, i.e. the propane oxidation pathway via the isopropanol route and acetone rather at the expense of the usual main pathway forming acrylic acid via propylene. © 2006 Elsevier B.V. All rights reserved

Heterogeneous partial oxidation catalysis on metal oxides

International audienceThis review paper presents an overview of heterogeneous selective ammoxidation and oxidative dehydrogenation (ODH) of light alkanes, particularly of ethane. The conversion of ethane to ethene is in great demand in the domestic and worldwide chemical industry. The review has been voluntarily restricted to metal oxide-type catalysts, as it is devoted to the special issue honouring Edmond Payen and is based on 30 years of experience and discussions with pioneering scientists in the field. The main key factors, designated by Grasselli as the “7 pillars”, have been emphasised: isolation of active sites, M–O bond strength, crystalline structure, redox features, phase cooperation, multifunctionality and the nature of the surface oxygen species. The main features and physical and chemical properties of solid catalysts for selective oxidation compared to total oxidation have also been emphasised. Several case studies have been presented to illustrate the concept and importance of the key factors of catalyst preparation and activation and of the catalytic atmosphere. Based on such analysis and recent discoveries and process developments perspective views are also given

Molybdenum oxide model catalysts and vanadium phosphates as actual catalysts for understanding heterogeneous catalytic partial oxidation reactions: A contribution by Jean-Claude Volta

International audienceThis review summarises and expands part of the work that Jean Claude Volta carried out during his scientific career at the Institut de Recherches sur la Catalyse (IRC), CNRS, University of Lyon in France. The first part deals with the structure sensitivity of molybdenum oxide (MoO3) for oxidation reactions. The second part concerns the development of vanadium phosphate catalysts for butane oxidation which encompasses intensive studies of catalyst preparation, activation, and characterisation, including some of the first real in situ studies of a complex oxide catalytic system. J.-C. Volta was one the first scientists to develop real in situ studies with on-line GC analysis of the reactants and products under working conditions and their simultaneous characterisation by Raman spectroscopy. He also developed the spin-echo mapping technique for determining the oxidation state of V through the chemical shift of 31P NMR peak and used this to help unravel the complexity of transformations in VPO materials during preparation, activation and reaction allowing him to make meaningful structure–activity relationships. He contributed extensively to our understanding of how selective oxidation heterogeneous catalysts function

Total Oxidation of Methane on Oxide and Mixed Oxide Ceria-Containing Catalysts

Methane, discovered in 1766 by Alessandro Volta, is an attractive energy source because of its high heat of combustion per mole of carbon dioxide. However, methane is the most abundant hydrocarbon in the atmosphere and is an important greenhouse gas, with a 21-fold greater relative radiative effectiveness than CO2 on a per-molecule basis. To avoid or limit the formation of pollutants that are dangerous for both human health and the atmospheric environment, the catalytic combustion of methane appears to be one of the most promising alternatives to thermal combustion. Total oxidation of methane, which is environmentally friendly at much lower temperatures, is believed to be an efficient and economically feasible way to eliminate pollutants. This work presents a literature review, a statu quo, on catalytic methane oxidation on transition metal oxide-modified ceria catalysts (MOx/CeO2). Methane was used for this study since it is of great interest as a model compound for understanding the mechanisms of oxidation and catalytic combustion on metal oxides. The objective was to evaluate the conceptual ideas of oxygen vacancy formation through doping to increase the catalytic activity for methane oxidation over CeO2. Oxygen vacancies were created through the formation of solid solutions, and their catalytic activities were compared to the catalytic activity of an undoped CeO2 sample. The reaction conditions, the type of catalysts, the morphology and crystallographic facets exposing the role of oxygen vacancies, the deactivation mechanism, the stability of the catalysts, the reaction mechanism and kinetic characteristics are summarized