Graphical Mesoporous TiO 2 spheres with large specific surface area were synthesized by a simple two-step method for the electrocatalytic reduction of oxalic acid. The maximum Faradaic efficiency for glycolic acid reached 73.9 % at −0.5 V at ambient temperature, exceeding most recently reported results. Reducing oxalic acid to glycolic acid electrochemically remains a significant challenge due to the high overpotential and low selectivity and stability. This study uses mesoporous TiO 2 spheres of anatase phase as catalysts to reduce oxalic acid to glycolic acid with low overpotential. The maximum Faradaic efficiency of glycolic acid reaches 73.9 % at −0.5 V vs RHE. The mesoporous structure not only increases the specific surface area, but also limits the escape of intermediate glyoxalic acid from the catalyst surface due to the space-limiting effect of the mesoporous channel, such that oxalic acid can be deeply reduced to glycolic acid. Moreover, a mechanism for oxalic acid reduction is proposed, and the Ti 3+ /Ti 4+ redox pair plays an important role in the reduction of oxalic acid.
Ethyl glycolate (EGly) is a platform molecule in various fields, which has been widely applied for the production of various valuable chemicals. Despite being a traditional catalyst for the conversion of diethyl oxalate (DEO) to EGly, Ag/SiO 2 catalyst exhibits insufficient activity. The present study introduces a novel preparation method that couples H 2 O 2 reduction with deposition precipitation to augment the performance of the catalyst. Performance results show that Ag/SiO 2 catalyst prepared by the new method attains a DEO conversion of 95.6% and an EGly selectivity of 78.0%, showing respective improvements of 10.0 and 15.2% over excess impregnation-evaporating solvent method. Characterization results show that the average silver particles size of Ag/SiO 2 catalyst prepared by the new method is 6 nm, which is 1/2 of the excess impregnation-evaporation solvent method. Simultaneously, it contains a greater quantity of Ag 0 . The smaller and more uniform particles offer greater active site density, leading to enhanced DEO conversion. An increased presence of Ag 0 diminishes DEO overactivation and inhibits the dissociative adsorption of H 2 . Moreover, the amplified quantity of Ag 0 could be attributed to the reduced interfacial charge transport triggered by metal-support interactions (MSIs).
Fengling Zheng,Jiang Gong,Hanqing Zhang,Weihan Shu,Xue Wang,Siqian Qin,Chuancai Zhang,Bin Dai
The Co-Ag x /TiO 2 catalysts with low mass content of Co and Ag were synthesized through the impregnation method and investigated for dimethyl oxalate (DMO) hydrogenation to methyl glycolate (MG). Remarkably, the Co-Ag 0.7 /TiO 2 catalyst with an Ag concentration of 0.7 wt%, exhibited an impressive yield of MG of ∼94.4 %, surpassing the yields of MG obtained with Co/TiO 2 (∼54 %) and Ag 0.7 /TiO 2 (∼69 %) catalysts. Various characterizations elucidated that the exceptional catalytic performance of Co-Ag 0.7 /TiO 2 can be ascribed to the synergy between Co and Ag, resulting in the formation of AgCoO 2 as high active site can improve the adsorption and activation of DMO and H 2 on catalyst surface. Additionally, the doping of a small amount of Ag regulated the contents of Lewis acidic and Brønsted acidic sites, leading to a high conversion of DMO and selectivity of MG. Furthermore, the excellent MG yield and long-term stability (at least 200 h) facilely obtained over our catalyst under mild reaction conditions guarantee a feasible prospect in the industrial application. This study not only unraveled the superior performance of the Co-Ag synergistic catalyst, but also carried significant implications for developing catalysts with low-content in DMO hydrogenation to MG.
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