Abstract: A series of Pd/α-Al2O3 catalysts for the CO coupling reaction were prepared with α-Al2O3 from five different sources. The influence of impurities, specific surface area, and pore structure of the support on the catalyst activity was studied. X-ray diffraction and energy dispersive X-ray analysis results confirm the existence of various impurities in three α-Al2O3 samples due to their different production methods. The sodium oxides and γ-Al2O3 in the support decrease the catalyst activity from 45%CO conversion to 10%. The N2 adsorption result shows that the specific surface area and pore volume of the support are not as much important as the pore distribution for the activity of Pd/α-Al2O3, and the double pore structure of the support is necessary for preparing high activity catalysts. Moreover, the results of CO chemical adsorption on the five catalysts show that the CO coupling reaction does not need many active sites to get a high CO conversion.

Key words: carbon monoxide, coupling, methyl nitrite, dimethyl oxalate, palladium, alumina, support, supported catalyst