TUngsten catalysts carbon monoxide hydrogenation

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

Some metal oxide catalysts are activated by thermal reduction with hydrogen or carbon monoxide. For example, the catalytic activity of molybdenum oxide and tungsten oxide for the metathesis reaction of olefins is very much enhanced by their slight reduction (1). The catalytic activity for butene isomerization and ethene oligomerization appears on niobium oxide by its... 

Several catalyst samples of tungsten carbide and W,Mo mixed carbides with different Mo/W atom ratios, have been prepared to test their ability to remove carbon monoxide, nitric oxide and propane from a synthetic exhaust gas simulating automobile emissions. Surface characterization of the catalysts has been performed by X-ray photoelectron spectroscopy (XPS) and selective chemisorption of hydrogen and carbon monoxide. Tungsten carbide exhibits good activity for CO and NO conversion, compared to a standard three-way catalyst based on Pt and Rh. However, this W carbide is ineffective in the oxidation of propane. The Mo,W mixed carbides are markedly different having only a very low activity. 

Transition metal carbides (mainly of W and Mo) have been shown to be effective catalysts in some chemical reactions that are usually catalyzed by noble metals such as Pt and Pd (ref.1). Their remarkable physical properties added to lower cost and better availability could make them good candidates for substitute materials to noble metals in automobile exhaust catalysis. Hence, for this purpose, we have prepared several catalysts of tungsten carbide and W,Mo mixed carbides supported on y alumina with different Mo/W atom ratios. The surface composition has been studied by XPS while the quantitative determination of catalytic sites has been obtained by selective chemisorption of hydrogen and of carbon monoxide. The catalytic performances of these catalysts have been evaluated in the simultaneous conversion of carbon monoxide, nitric oxide and propane from a synthetic exhaust gas. 

Catalysts prepared from metals of the iron and platinum group of the periodic system convert carbon monoxide and hydrogen at temperatures above 400°C. to methane, carbon, and other undesirable products. Similar negative results were obtained with molybdenum and tungsten. 

---