Structure evolution of mesoporous silica supported copper catalyst for dimethyl oxalate hydrogenation

A modified ammonia evaporation method with an ordered mesoporous silica as the precursor of the support was applied to prepare the well dispersed copper-based catalysts. Appropriate amount of ammonia was used during the aging stage to prevent the destruction of the ordered mesoporous structure, which can ensure the homogeneous pre-distribution of the copper precursor ([Cu(NH3)(4)](2+)) in the mesopores. Then the formation of copper phyllosilicate or surface Cu-O-Si species can be prompted during the ammonia evaporation stage, resulting in large surface areas of both Cu and Cu+ species in the final catalysts. It was also revealed that the formation of copper phyllosilicate led to the destruction of mesoporous silica structure in the ammonia evaporation stage especially at the higher copper loading. The catalysts with various copper loading were systematically characterized and applied in the hydrogenation of dimethyl oxalate to ethylene glycol (EG). An excellent low-temperature catalytic performance and stability were achieved on 20Cu/OMS with EG selectivity of 98.2% at 453 K, due to the superior surface areas of both Cu and Cu+, as well as the highest ratio of Cu+/(Cu-0 + Cu+).