Oxydation catalyseur heterogene de composes organiques sur des oxydes metalliques et des oxydes mixtes de metaux

Principles of Oxidative Catalysis on Solid Oxides

V-Sb-oxide catalysts are claimed in several patents as the active components for a new process of direct acrylonitrile synthesis from propane. In this review the main catalytic, kinetic and mechanistic features of these catalysts are discussed with reference to the role of vanadium as the key component. Specific topics discussed include: (i) nature of the phases present in V-Sb-oxide catalysts, their modification during the catalytic reaction and nature of the non-stoichiometry of vanadium antimonate, (ii) catalytic and kinetic behavior as well as some specific aspects which characterize their reactivity, (iii) structure-activity and selectivity relationships, and (iv) reaction mechanism, influence on the surface reactivity of chemisorbed species (ammonia, in particular) and presence of competitive pathways of transformation.

VSb-oxide catalysts for the ammoxidation of propane

Introduction Selective ammoxidation of paraffins into corresponding nitriles is of a prime practical significance as it could add to the sources for synthesis of a number of valuable organic products currently produced from oil. On the whole these processes seem to be more promising for commercial synthesis than partial oxidation of paraffins, as nitriles are more stable than corresponding oxy products and a higher yield of the desirable product may potentially be achieved.

Mechanism of Selective Paraffin Ammoxidation

The influence of ammonia on propane oxidation over a Ga−Sb oxide catalyst has been studied. Acrylonitrile is formed upon the interaction of acrolein with partially dehydrogenated ammonia. Ammonia increases the rates of overall and selective oxidation of propane. This is assumed to be due to the formation of electron-donor sites promoting proton separation from the propane molecule.

Influence of ammonia on propane oxidation over a gallium-antimony oxide catalyst

Publisher Summary Many substances can be partially oxidized by oxygen if selective catalysts are used. In such a way, oxygen can be introduced in hydrocarbons, such as olefins and aromatics, to synthesize aldehydes (e.g, acrolein and benzaldehyde) and acids (e.g, acrylic acid and phthalic acid anhydride). A selective oxidation can also result in a dehydrogenation (butene → butadiene) or a dealkylation (toluene → benzene). Other molecules can also be selectively attacked by oxygen. Methanol is oxidized to formaldehyde and ammonia to nitrogen oxides. Olefins and aromatics can be oxidized with oxygen together with ammonia to nitriles (ammoxidation). The Gibbs free energy change for the total combustion of such molecules always has a larger negative value than partial oxidation. Hence, a catalyst to control kinetically the oxidation process is an absolute necessity. By choosing the right conditions and the proper type of catalyst, the oxidation process can be directed toward intermediates that do not react further.

Chapter 2 Heterogeneous Oxidation Processes

The influence of ammonia on the direction of the oxidative transformations of propylene has been studied. Ammonia has been shown to block the surface oxygen of antimony catalysts. As a result, an increase in the selectivity with respect to the products of partial oxidation is observed.

G. B. Barannik

Papers

Influence of ammonia on propylene oxidation on tin-antimony and bismuth-antimony catalysts