KINETICS OF THE WATER-GAS SHIFT REACTION OVER SEVERAL ALKANE ACTIVATION AND WATER-GAS SHIFT CATALYSTS

The water-gas shift reaction (WGS) over three commercial WGS catalysts and four oxide catalysts used for alkane activation has been studied at atmospheric pressure and in the temperature range of 160 to 600-deg rees-C. The oxide catalysts used were two ethane oxydehydrogenation ca talysts, namely Mo19V5Nb1Ox and V5Nb1Ox, and two methane coupling cata lysts, namely Ca3NiK0.05Ox and LiMgO(x). The commercial water-ps shift catalysts used were two Fe3O4-Cr2O3 catalysts and one CuZnO/Al2O3 cat alyst. All catalysts except the ethane oxidehydrogenation catalysts an d LiMgO(x) showed high activity for the water-gas shift reaction below 400-degrees-C. It is evident that Fe, Cr, Zn, Cu and Ni oxides or met als enhance the water-ps shift reaction. The commercial CuZnO/Al2O3 ca talyst was the most active WGS catalyst per gram of the catalyst at 16 0-250-degrees-C, whereas the Fe3O4-Cr2O3 catalysts showed high activit y above 300-degrees-C. The specific rates of CaNiK0.05Ox and LiMgO(x) were, however, higher than the specific rates of the commercial cataly sts. The apparent activation energies for the conversion of carbon mon oxide to carbon dioxide were 53 kJ/mol for CuZnO/Al2O3, 68 kJ/mol for LiMgO(x), 86 kJ/mol for Ca3NiK0.05Ox, 95 kJ/mol and 110 kJ/mol for the Fe3O4-Cr2O3 catalysts, 101 kJ/mol for Mo19V5Nb1Ox and 132 kJ/mol for V5Nb1Ox. For the commercial catalysts, the power-law rate model with c oncentration exponents of carbon monoxide and water close to one and z ero, respectively, gave the best results. For V5Nb1Ox and Ca3NiK0.05Ox the concentration exponents of carbon monoxide and water close to 0.5 fit the results best. For Mo19V5Nb1Ox the reaction was first order in carbon monoxide concentration whereas for LiMgO(x) it was zero order in carbon monoxide concentration and 0.5 order in water concentration. Ca3NiK0.05Ox and LiMgO(x) were active for the water-gas shift reactio n in the temperature range of oxidative methane coupling. Thus, it is probable that the water-gas shift reaction can occur during methane co upling when these catalysts are used. The water-gas shift reaction is, however, unlikely to occur during the oxidative dehydrogenation of et hane since the conversions of carbon monoxide to carbon dioxide were v ery low at 350-500-degrees-C.