Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

Abstract

Supported vanadium oxide catalysts are active in a wide range of applications. In this review, an overview is given of the current knowledge available about vanadium oxide-based catalysts. The review starts with the importance of vanadium in heterogeneous catalysis, a discussion of the molecular structure of vanadium in water and in the solid state and an overview of the spectroscopic techniques enabling to study the chemistry of supported vanadium oxides. In the second part, it will be shown that advanced spectroscopic tools can be used to obtain detailed information about the coordination environment and oxidation state of vanadium oxides during each stage of the life-span of a heterogeneous catalyst. Three topics will be discussed: (1) the molecular structure of supported vanadium oxide catalysts under hydrated, dehydrated and reduced conditions, including the parameters, which influence the molecular structures formed at the surface of the support oxide; (2) elucidation of the active surface vanadium oxide during the oxidation of methanol to formaldehyde, the reaction mechanism and the vanadium oxide-support effect; and (3) deactivation of fluid catalytic cracking (FCC) catalysts by migration of vanadium oxides and the development of a method preventing the structural breakdown of zeolites by trapping the mobile vanadium oxides in an aluminum oxide coating.

Covalent immobilization of the Jacobsen catalyst on mesoporous phenolic polymer: A highly enantioselective and stable asymmetric epoxidation catalyst

“…Unfortunately, also XPS measurements have proven to be largely unreliable, probably due to a combination of the highly insulating character of the support, creating heavy surface charging and the fact that transition metals tend to reduce in high vacuum in the presence of carbon or phenolic resins [38] . In any case, our XPS measurements resulted in a irreproducible mix of several oxidation types of Mn on the surface, even when the same batch of samples was measured several times.…”

Application of AXAFS Spectroscopy to Transition‐Metal Oxides: Influence of the Nearest and Next Nearest Neighbour Shells in Vanadium Oxides

“…[1][2][3][4][5][6][7] Various researchers have investigated the activities and selectivities of metal oxide catalysts. However, little is known about the parameters that are truly responsible for the catalytic action of transition-metal oxides.…”

“…[42] The g-Al 2 O 3 crystal was built up from X-ray diffraction data obtained and interpreted by Zhou et al [43] Subsequently, this crystal was cut along the (110) plane to expose the preferentially exposed surface; that is, the D layer according to the LEIS measurements performed by Stobbe-Kreemers et al [44] To create a structural model for supported monomeric vanadium oxide, a VO 4 moiety was attached to the Al 2 O 3 surface. The distances of the V= O (1) and VÀO (2) coordinations of the VO 4 unit, as found in the EXAFS analysis, were used as input parameters for the Cerius 2 molecular modelling program. The coordination numbers and distances of the VÀO (3) and VÀAl (4) higher coordination shells, as found in the EXAFS analysis, were taken as structural constraints.…”

Effect of CaF2/CaO Composite Additive on Roasting of Vanadium-Bearing Stone Coal and Acid Leaching Kinetics

“…Vanadium is a significant strategic resource which plays an important role in many fields, such as ferrous and nonferrous alloy production, thermistors, redox flow batteries, catalysts, the chemical industry, and medicine [1][2][3][4][5]. China has very large reserves of stone coal, which is a special vanadium-containing resource for the country.…”