A DFT Study on the Catalytic CO Oxidative Coupling to Dimethyl Oxalate on Al-Doped Core–Shell Pd Clusters

A series of core–shell catalysts aiming at CO oxidative coupling to dimethyl oxalate (DMO) were constructed, and effects of the second metal doping and surface structures on the reaction activity and favorable reaction path were investigated by using the density functional theory (DFT) method. Pd₁₃, Al@Pd₁₂, and Ag@Pd₁₂ were first studied to find the proper doping metal. Our results showed that the activity of CO oxidative coupling to DMO follows the order of Al@Pd₁₂ > Pd₁₃ > Ag@Pd₁₂, and the same result was also obtained via the electronic analysis. In addition, Al₆@Pd₃₂ and Al₁₃@Pd₄₂ catalysts with higher doping ratio and lower cost than that of Al@Pd₁₂ were selected to examine the influence of surface structure on the reaction activity. It showed that CO + CH₃O → COOCH₃ + CO → OCCOOCH₃ + CH₃O → DMO is the favorable pathway on the (100) surface of Al₆@Pd₃₂ catalyst, while CO + CH₃O → CO + CH₃O (COOCH₃) → COOCH₃ + COOCH₃ → DMO is the optimal pathway on the (111) surface of Al@Pd₁₂ and Al₁₃@Pd₄₂, which indicated that the surface structure of catalysts affected the preferable pathway of DMO formation. Moreover, activities of CO oxidative coupling to DMO on AlPd core–shell catalysts followed the order of Al@Pd₁₂ > Al₁₃@Pd₄₂ > Al₆@Pd₃₂. In addition, Al₁₃@Pd₄₂ also exhibited a good selectivity between DMO and DMC. Thus, Al₁₃@Pd₄₂ is a proper catalyst with high activity, high selectivity, and low cost because of high Al:Pd ratio.