Hydrogenation activity of Tungsten Carbides Preopared by CVD Method

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The preparations of tungsten carbide by CVD method and the application of the carbides to hydrogenation catalyst have been studied in the present project. The tungsten hexafluoride reacted with cyclo-hydrocarbon on an activated carbon surface resulted in tungsten carbides with high surface area. Main substances in the carbides were WC and W_2C.The former was effective for hydrocracking of n-butane. The turnover frequency of the carbides for the hydrocracking was almost the same as that of a platinum catalyst supported on alumina. However, the reaction rate calculated from unit catalyst mass of the carbide catalyst was smaller than that of the platinum catalyst due to the low concentration of effective species on the carbides.The catalytic activity of the tungsten carbide for hydrogenation of ethylene was almost the same as those of platinum catalyst and nickel catalyst. The reaction rate of the hydrogenation over platinum and nickel catalysts decreased with reaction temperature higher than 220"*"C, but the catalytic activity of the carbides increased up to 350"*"C.This is very unique property of the tungsten carbides. The reaction of cyclohexene was carried out over the carbides to elucidate the effect of preparation conditions on the conversion of cyclohexene and the selectivity of the products. The main product for the reaction was 1-methyl-cyclopentene produced by isomerization of cyclohexene. The isomerization indicated that the carbide was solid acid catalyst. When the carbides was treated in hydrogen atmosphere at 700"*"C, it was found that the hydrogenation activity was gradually recovered with treating period. This result suggested that a tungsten oxide simultaneously produced with tungsten carbide showed the solid acid property.