Effects of Precursors on Preparation of Pd/α-alumina Catalyst for Synthesis of Dimethyl Oxalate

The influence of two palladium precursors, PdCl 2 and Pd(NO 3 ) 2, on the preparation of catalyst applied in the CO coupling reaction to synthesize dimethyl oxalate was studied. It is revealed that PdCl 2 is much more difficult to decompose than Pd(NO 3 ) 2 during calcination, and for catalyst prepared from PdCl 2, temperatures as high as 773 K are necessary to obtain surface Pd 0, while for catalyst prepared from Pd(NO 3 ) 2, the corresponding temperature is 473 K. Furthermore, two palladium distributions across the pellet supports are illustrated. The eggshell palladium distribution resulting from using Pd(NO 3 ) 2 as precursor was proven more suitable for the present coupling reaction than the uniform palladium distribution obtained by using PdCl 2 . The results suggest that Pd(NO 3 ) 2 is superior to PdCl 2 in preparing catalysts for the CO coupling reaction, and the active components on the support outer face have a more efficient utilization than that on the support inner face, which makes moderate reduction of Pd loading feasible.