Supported transition metal oxides

This process has many similarities to the Phillips process and is based on the use of a supported transition metal oxide in combination with a promoter. Reaction temperatures are of the order of 230-270°C and pressures are 40-80 atm. Molybdenum oxide is a catalyst that figures in the literature and promoters include sodium and calcium as either metals or as hydrides. The reaction is carried out in a hydrocarbon solvent. 

The use of supported transition metal oxide and Ziegler-Natta-type catalysts for polymerising aliphatic olefins (alkenes) was extended in the 1960s and 1970s to the ring-opening polymerisation of cyclo-olefins. 

The effect of chemisorption temperature on the ammonia uptake capacity of 6.5 wt% V20c/Ti02 is shown in Fig. 1. Ammonia chemisorption capacities increase with temperature upto 150°C and then decrease with further Increase up to 400°C. It is worth noting that there is considerable NH uptake even at 400°C. These results are in accordance with the reported literature. A number of studies have been reported on the acidic character of supported transition-metal oxides (22,34-38). Ammonia on V20g can be either adsorbed in the form of NH species on Bronsted acid sites or coordlnatively bonded to vanadium ions on Lewis acid sites (39,40). The latter species were observed up to 250°C,... 

The excitation spectra coincides with the position of the charge-transfer spectra as measured by diffuse reflectance spectroscopy. In the case of supported transition-metal oxides, quenching of phosphorescence occurs on adsorption indicating that the luminescence centers are located at the surface, in contrast to mixed transition-metal oxides where these centers are in the bulk (160b). In many cases (71b,e, 160b,c,d), the quenching is reversible at room temperature and probably occurs via the formation of a weak complex. 

This dynamic behavior of the catalyst, depending on the degree of hydration, is typical of many supported transition metal oxides, as evidenced by the changes in their Raman modes (Brown et al., 1977, Brown et al., 1977), as discussed below. The transformations are usually reversible. 

The first Raman spectra of bulk metal oxide catalysts were reported in 1971 by Leroy et al. (1971), who characterized the mixed metal oxide Fe2(MoC>4)3. In subsequent years, the Raman spectra of numerous pure and mixed bulk metal oxides were reported a summary in chronological order can be found in the 2002 review by Wachs (Wachs, 2002). Bulk metal oxide phases are readily observed by Raman spectroscopy, in both the unsupported and supported forms. Investigations of the effects of moisture on the molecular structures of supported transition metal oxides have provided insights into the structural dynamics of these catalysts. It is important to know the molecular states of a catalyst as they depend on the conditions, such as the reactive environment. 

The group 5-7 supported transition metal oxides (of vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and rhenium) are characterized by terminal oxo bonds (M =0) and bridging oxygen atoms binding the supported oxide to the cation of the support (M -0-MSUpport). The TOF values for ODH of butane or ethane on supported vanadia were found to depend strongly on the specific oxide support, varying by a factor of ca. 50 (titania > ceria > zirconia > niobia > alumina > silica). 

Although this chapter focuses on oxidation reactions involving redox supported vanadium oxide catalysts, similar trends with surface coverage and specific oxide support also apply for other redox supported transition metal oxide catalysts, such as supported M0O3 [51], CrOs [52] and Re207 [53], The redox supported vanadium oxide catalytic system was chosen for this review because of the extensive studies that these catalysts have received in recent years as well as their widespread industrial appHcations. 

Baltes, M., O. Collar , P. Van Der Voort, and E. F. Vansant, Synthesis of Supported Transition Metal Oxide Catalysts by the Designed Deposition of Acetylacetonate Complexes , Langmuir (1999), 15, 5841-5. 

Transition Metal Salts and Oxides on Alumina. Transition metal salts, particularly chlorides and nitrates, are frequently used as starting materials for the preparation of supported transition metal oxides or supported precursors for supported metal catalysts. Also, many catalytic materials, particularly supported molybdenum and tungsten oxide and sulfide catalysts, contain transition metal ions, namely Co, Ni , and Fe " as promoters. Thus, it is interesting to study the spreading and wetting behavior of salts of these transition metals and of their oxides. This is of particular importance for promoted catalyst materials, since in practice the incorporation of the active phase and the promoter should be possible in one step for economic reasons. 

Catalytic total oxidation of volatile organic compounds (VOC) is widely used to reduce emissions of air pollutants. Besides supported noble metals supported transition metal oxides (V, W, Cr, Mn, Cu, Fe) and oxidic compounds (perovskites) have been reported as suitable catalysts [1,2]. However, chlorinated hydrocarbons (CHC) in industrial exhaust gases lead to poisoning and deactivation of the catalysts [3]. Otherwise, catalysts for the catalytic combustion of VOCs and methane in natural gas burning turbines to avoid NO emissions should be stable at higher reaction temperatures and resists to thermal shocks [3]. Therefore, the development of chemically and thermally stable, low cost materials is of potential interest for the application as total oxidation catalysts. 

Klimisch, R. L. "Oxidation of CO and Hydrocarbons over Supported Transition Metal Oxide Catalysts", Proceedings of the 1st National Symposium on Heterogeneous Catalysis for Control of Air Pollution, Philadelphia, Franklin Institute, November, 1963. 

Whereas the Mobil process starts with syn gas based methyl alcohol, Olah s studies were an extension of the previously discussed electrophilic functionalization of methane and does not involve any zeolite-type catalysts. It was found that bifunctional acidic-basic catalysts such as tungsten oxide on alumina or related supported transition metal oxides or oxyfluorides such as alumina or related supported transition metal oxides or oxyfluorides such as tantalum or zirconium oxyfluoride are capable of condensing methyl chloride, methyl alcohol (dimethyl ether), methyl mercaptan (dimethyl sulfide), primarily to ethylene (and propylene) (equation 65) . 

Bertinchamps F, Gregoire C, Gaigneaux EM. Systematic Investigation of Supported Transition Metal Oxide Based Formulations for the Catalytic Oxidative Elimination of (Chloro)-Aromatics. Part II Influence of the Nature and Addition Protocol of Secondary Phases to VOx/Ti02. Appl Catal B Environ 2006 66 10-22. 

Lee, E. and Wachs I. (2008). In situ raman spectroscopy of Si02-supported transition metal oxide catalysts An isotopic 180-160 exchange study, J. Phys. Chem. C, 112, pp. 6487-6498. 

Weckhuysen, B.M., Jehng, J.M., and Wachs, I.E. In situ Raman spectroscopy of supported transition metal oxide catalysts 02- 02 isotopic labeling studies. J. Phys. Chem. B 2000,104, 7382-7387. 

Preparation of Zeolite-Supported Transition Metal Oxides. 346... 

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