Vanadia-molybdena

Additional information about the reactivity was obtained by determining the kinetic parameters during methanol oxidation for vanadia, molybdena, rhenia, and chromia on different oxide supports. For all these systems the activation energy is approximately the same, 18-22 kcal/mol. The activation energy corresponds to that expected for the breaking of the C-H bond of a surface methoxide intermediate, and should be... 

Vanadia-molybdena V205-Mo03 solid solution Benzene/butene to maleic anhydride... 

For most of the oxide-supported monolayer oxides (e.g. vanadia, molybdena and tungsta supported on alumina), titania, zirconia and silica surface species are... 

Both titania and titania/silica supported vanadia, molybdena, tungsta and chromia have been applied as SCR catalysts. Low-temperature and high temperature catalysts have been developed. The vanadia on titania catalysts have received most attention. 

According to ESCA measurements carried out with vanadium oxide, consistent with the data presented in [12], the Ols characteristic of On oxygen species is very close to the V=0 doubly bonded oxygen atoms exposed at the surface of (010) planes of V2O5 crystals. The oxygen species with Ols characteristic of Oi do not exist at the surface of individual main components of catalysts A,B - vanadia, molybdena, or exist in small concentration at the surface of magnesia or TM. They... 

The large-scale production of sulfuric acid, overall one of the most important products in the chemical industry, exploits the redox activity of vanadium(V) oxide. Vanadia-, molybdena-, and tin oxide-based catalysts are used further for a host of selective hydrocarbon oxidation processes including dehydrogenation, oxidative coupling, and oxygenation (3,41. Much recent activity in this area has been aimed at the development of more active and more selective catalysts by dispersing oxides in the form of monolayers on bulk oxide supports. This approach has proven extremely successful for tailoring catalyst properties to... 

Standard Oil A process for polymerizing ethylene and other linear olefins and di-olefins to make linear polymers. This is a liquid-phase process, operated in a hydrocarbon solvent at an intermediate pressure, using a heterogeneous catalyst such as nickel oxide on carbon, or vanadia or molybdena on alumina. Licensed to Furukawa Chemical Industry Company at Kawasaki, Japan. 

Commercial SCR catalysts are made of homogeneous mixtures of titania, tungsta and vanadia (or molybdena). Titania in the anatase form is used as a high surface and sulfur-resistant carrier to disperse the active components. Tungsta or molybdena is employed in large amounts (10 and 6% w/w, respectively) to increase the surface acidity and the thermal stability of the catalyst and to limit the oxidation of SO2. Vanadia is responsible for the activity in the reduction of NO, but it is also active in the oxidation of SO2. Accordingly, its content is kept low, usually below 1-2% w/w. 

Fully oxidized vanadia is a poor, nonselective catalyst for benzene oxidation. Reduction to lower oxides brings about a large increase in catalytic activity and some improvement in selectivity. Substantial enhancement of selectivity can be achieved by the addition of molybdena,1009 reaching a maximum at a M0O3 content of about 30%. Promoters (Ag, Ti, Ni, Co) lead to further improvements.1006... 

Payen et al. (1986) investigated the reduction of alumina-supported molybdena and ascribed a Raman band at 760 cm-1 to reduced supported molybdenum oxide. The transformations could be reversed by reoxidization (Payen et al., 1986). Mestl and Srinivasan (1998) described some reduced phases formed from bulk molybdena, whereas reduced dispersed vanadia and chromia catalysts do not show Raman bands (Airaksinen et al., 2005 Banares et al., 2000a Gasior et al., 1988 Weckhuysen and Wachs, 1996). 

Xie et al. (2001) measured UV-vis spectra of the bulk oxides niobia, molybdena, tungsten trioxide, and vanadia and determined the position of the band edge as a function of temperature. In a separate experiment, they investigated the samples by Raman spectroscopy. To understand the changes in the Raman intensities, they analyzed the intensity in the UV-vis spectra at the wavelength of the incident laser irradiation and at the... 

Bulk niobia, molybdena, tungsten trioxide, and vanadia Aluminophosphates (CoAPO) Temperatures up to 748 K Formation under hydrothermal conditions at temperatures up to 448 K... 

Early studies on titania powders showed that methanol generated methyl formate as the principle photooxidation product. Molybdena- and vanadia-modified Ti02 catalysts demonstrated at least an eighty percent drop in activity relative to pure titania, although selectivity to dimethoxymethane (and thus suppression of further oxidation products) was almost total [87]. 

In recent years there has been much interest in the conversion of methane to value added products, such as ethane/ethylene [1], methanol [2], formaldehyde [3-5] and synthesis gas [6]. Many studies have been carried out on the partial oxidation of methane to formaldehyde over silica [7], and over molybdena [8,9], vanadia [5,10] supported on silica, or FeNbB-0 [11] with nitrous oxide [7-9] or oxygen [7,10] as the oxidant. 

It has also been proposed that methanol adsorption and its oxidation to formaldehyde occurs at coordinatively unsaturated sites, possessing four-fold coordination, rather than coordinatively saturated sites, possessing six-fold coordination [19]. Unfortunately, the surface vanadia species predominantly possess four-fold coordination which prevents this issue from being address with the current data. However, supported molybdena catalysts possesses both four-fold and six-fold coordination and their TOFs for methanol oxidation have been measured [27]. It was found that, contrary to above hypothesis, the coordinatively saturated surface molybdena species is approximately four times more active than the coordinatively unsaturated molybdena species for titania supported molybdena catalysts. Thus, methanol oxidation proceeds on both coordinatively saturated and coordinatively unsaturated sites at relatively comparable reaction rates (TOFs). 

Results consistent with those of ammonia adsorption were obtained in the analysis of supported vanadia and molybdena. The development of protonic acidity with the increase of the vanadia loading on dealuminated BEA zeolite can be easily traced by adsorption of pyridine (Figure 2.39). 

Banares, M. and Khatib, S. (2004). Structure-activity Relationships in Alumina-supported Molybdena-vanadia Catalysts for Propane Oxidative Dehydrogenation, Catal. Today, 96, pp. 251-257. 

In addition, Raman spectroscopy also provides structural information about the presence of small metal oxide crystallites and surface reaction intermediates. Several extensive reviews of supported metal oxide catalysts have recently appeared in the literature, which have emphasized Raman spectroscopy vanadia [7,83-85], chromia [7,85,86], molybdena [7,87], niobia [7,88], rhenia [7,85], tungsten oxide [7], titania [85], and nickel oxide [89]. 

Heracleous, E., Machli, M., Lemonidou, A. A., and Vasalos, I. A. Oxidative dehydrogenation of ethane and propane over vanadia and molybdena supported catalysts. J. Mol. Catal. A Chem. 232,29-39 (2005). 

Banares, M. A., and Khatib, S. J. Structure-activity relationships in alumina-supported molybdena-vanadia catalysts for propane oxidative dehydrogenation. Catal. Today 96,251-257(2004). 

---