Boosting Efficiency for the Synthesis of Dimethyl Oxalate over Pd/MgAl2O4: Effect of Different Preparation Methods for MgAl2O4 Supports

High active Pd-based catalyst with low loading capacity for CO oxidative coupling with methyl nitrite (MN) to dimethyl oxalate (DMO) has aroused great interest in the large-scale production of DMO for the next hydrogenation to bring forth ethylene glycol (EG). Here, spinel composite oxide support, namely MgAl2O4, had been prepared through three different methods: solid combustion method (MAO-SC), hydrothermal method (MAO-HT) and co-precipitation method (MAO-CP), and further Pd nanoparticles were anchored to the surface of MgAl2O4 through a simple wetness impregnation method. In the CO direct esterification to DMO reaction, the Pd/MAO-SC catalyst, which used MgAl2O4 support prepared by solid combustion method, exhibited the highest intrinsic activity with Turnover frequency (TOF) value of 2.39 s(-1) and DMO weight space-time yield (956.8 g.kg(cat)(-1).h(-1)) with 44.1 % CO conversion and 97.8 % DMO selectivity, and showed negligible attenuation of activity during the process of continuous reaction for 100 h. The characterization results confirmed that abundant oxygen defect sites occurred in MAO-SC synthesized by combustion method not only can help to anchor the Pd nanoparticles with appropriate size and dispersion, but also can promote the interfacial electron transfer from MgAl2O4 support to Pd nanoparticles, thus significantly enhancing the metal-support interaction (MSI) and providing more CO bridge-adsorption sites that is favorable for the CO oxidative coupling with MN to DMO reaction.