(544cv) Pore Size Effect on the Hydrogenation of Diesters over Ordered Hierarchical Cu/HPS Catalyst

An ordered hierarchical porous silica (HPS) having both mesopores and
micropores was fabricated and used for the preparation of Cu/HPS catalysts. High dispersion of both Cu⁰ and Cu⁺
species together with ordered porous structure were achieved on the as-prepared
Cu/HPS catalysts. The anchoring effect of micropores hindered the agglomeration
of copper species, while the formation of Cu-O-Si species, derived from the
strong interaction between surface silica and copper precursor, was prompted by
the ammonia evaporation approach. Because
of these outstanding properties, a
remarkable 1,6-hexanediol (HDO) yield of about 89% was achieved in dimethyl adipate (DMA)
hydrogenation at a nearly total conversion
of DMA
under the WHSV of 1.2 h^-1. This excellent
catalytic performance of Cu/HPS could result from the high surface areas of copper
species, appropriate Cu⁰/Cu⁺
ratio and high sintering resistance. Additionally, the pore size of
the catalysts
plays a determining
role in the hydrogenation of DMA. By tuning the pore size of the
ordered mesoporous HPS, the catalytic activity and
selectivity can be significantly improved. More interestingly, it is also revealed that the control step for various diester hydrogenation is different: dimethyl oxalate (DMO) hydrogenation is controlled by the
surface reaction, while DMA hydrogenation will be easily influenced by the pore diffusion, due to the porous structure of HPS. These investigations give an
important instruction to rationally design copper-based catalysts for the
hydrogenation of various esters.