Tungsten, silica-supported

Thomas, R., Moulijn, J.A., Debeer, V.H.J. and Medema, J. (1980) Structure-metathesis-activity relations of silica supported molybdenum and tungsten-oxide. J. Mol. Catal., 8, 161. 

SMPO [styrene monomer propylene oxide] A process for making propylene oxide by the catalytic epoxidation of propylene. The catalyst contains a compound of vanadium, tungsten, molybdenum, or titanium on a silica support. Developed by Shell and operated in The Netherlands since 1978. 

Other important measurements on the chemisorption of hydrogen include those of Rideal and Trapnell (90-92) on tungsten films and those of Schuit and his coworkers (93, 94a, b) on silica-supported metal catalysts. In each case the heat of adsorption was observed to decrease to very low values as complete coverage was approached. 

A new catalyst formulation containing alkali metals and W on a silica support gives more promising results.549 Alkali metals are able to lower the phase transition temperature from amorphous silica to a-crystoballite, shown to be critically important for an effective catalyst, while incorporation of W enhances catalytic activity to ensure high methane conversion and excellent ethylene selectivity. An alkali-stabilized tungsten oxo species is thought to be the active site. 

The measurements are performed in a non-interacting hydrocarbon solvent (e.g. cyclohexane) whose molecular mass is close to that of the donor (e.g. pyridine) in order to cancel out contributions from a dispersion component to the measured enthalpy [25]. As an example, the acid strength of tungsten oxide supported on a silica gel has been determined by this method [26]. 

A mixture of formalin and ethanol was passed at 240—320 C over various metal oxides supported on silica gel and metal phosphates. The main products were acrolein, acetaldehyde, methanol, and carbon dioxide. Acidic catalysts such as V-P oxides promoted the dehydration of ethanol to ethene. The best catalytic performances for acrolein formation are obtained with nickel phosphate and silica-supported tungsten, zinc, nickel, and magnesium oxides. With a catalyst with a P/Ni atomic ratio of 2/3, the yields of acrolein reach 52 and 65 mol% on ethanol basis with HCHO/ethanol molar ratios of 2 and 3, respectively. Acetaldehyde and methanol are formed by a hydrogen transfer reaction from ethanol to formaldehyde. Then acrolein is formed by an aldol condensation of formaldehyde with the produced acetaldehyde [40],... 

R. Gauvin, O. Coutelier, E. Berner, A. Mortreux, L. Delevoye, J.F. Paul, A.S. Matnede, E. Payen, A well-defined silica-supported dinuclear tungsten(III) amido species synthesis, characterization and reactivity, Dalton Trans. 2007 (2007) 3127-3130. 

N. Merle, G. Girard, N. Popoff, A. De MaUmann, J. Trebosc, E. Bertier, J.F. Paul, I. Del Rosal, L. Maron, R.M. Gauvin, L. Delevoye, M. Taoufik, On the track to silica-supported tungsten oxo metathesis catalysts input firom 0 solid-state NMR, Inorg. Chem. 52 (2013) 10119-10130. 

It was developed in order to valorize the C3 fraction of a local naphtha cracker. Shawinigan Chemicals Inc. Used this process in thewir plant near Montreal (at Varennes) in Canada from 1966 to 1972. The plant had a capacity of 50000 tons of feedstock per year. The catalyst used was tungsten oxide supported on silica and doped with sodium to prevent the double bond shift reaction of but-2-ene (which should decrease the selectivity). The operating temperature was between 370 and 450°C and the. conversion (40 - 43%) corresponded to near equilibrium conditions. The selectivity towards ethylene and but-2-ene was very high (> 95%). In addition, instead of pure propene, it was possible to use directly the C3 fraction (propane + propene) of the naphtha cracker. 

Synthesis and characterization of several catalyst precursors of [Ta] and [W] on different supports like silica [44], alumina [45], or silica-alumina [70] have been discussed in the previous section. These catalyst precursors were tested mainly in propane metathesis under similar condition in batch reactor at 150°C for 120 h. Catalytic performances revealed that the [Si02-Al203.5oo-W-H] and [AI2O3.500-W-H] have similar and better activity (TON) than the corresponding silica-supported tantalum-based catalyst precursors (Table 2). It was also observed that the product selectivity for tungsten hydrides is narrower than for tantalum hydrides [71]. 

The chemistry of various Group 6 carbonyl species on surfaces or in zeolites continues to be prominent in the literature Ozin and co-workers have continued to explore the chemistry of Mo(CO>5 in NaY zeolites " the carbonyl species formed by UV photoreduction of silica-supported Mo(VI) in a carbon monoxide atmosphere have been characterized by their infrared spectra and the kinetics of the thermolysis of Mo(CO)g on a tungsten surface have been released . 

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