Hydrogenation of diethyl oxalate over Cu/SiO2 catalyst with enhanced activity and stability: Contribution of the spatial restriction by varied pores of support

• The different spatial restriction created by the varied pores of support.
• The spatial restriction greatly affected the Cu particle size distribution.
• The Cu particles with sub-3-nm size afforded the enhanced activity.
• The H2-associative adsorption over Cu/SiO2 greatly affected the selectivity to EG.
• The sintering of Cu nanoparticles inhibited by spatial restriction of pores.

The Cu/SiO2 catalyst for gas-phase hydrogenation of diethyl oxalate (DEO) to ethylene glycol (EG) was prepared through the incipient wetness impregnation with the aid of complex agents (such as citric acid and ammonia) or not. The relative activity enhancement lied within the preparation of the catalyst by employment carriers having specific ranges of physical parameters, e.g., average pore diameter. For the Cu/SiO2 catalyst employed SiO2 with an average pore diameter of 3.0 nm, the selectivity and space time yield to EG of 94.6% and 0.46, which corresponded to 99.1% conversion of DEO, was achieved. In addition, the one also had excellent performance with no deactivation through severe conditions during 200 h run time. It was believed that the Cu particles with sub-3-nm size induced by spatial restriction were in favor of its superior activity; furthermore, the spatial restriction strategy by filling the Cu nanoparticles on mesoporous silica (ca. 3.0 nm of pore diameter) to conquer the sintering problem and help the stability (>200 h at 220–270 °C) has latent values in exothermic reactions. More interestingly, we found a close relationship between the amount of H2-associative adsorption and the hydrogenation of DEO. Thus, the spatial restriction created by the small pores of the support was helpful to increase the proportion of the filled Cu particles (sub-3-nm) and the more metal-active sites, which afforded the enhanced H2 activation ability. Besides, the nature of the metallic precursor derived from metal complexes interacting with the support was also important for the dispersing of metal copper particles.

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