Reconstruction of Cu-ZnO catalyst by organic acid and deactivation mechanism in liquid-phase hydrogenation of dimethyl succinate to 1,4-butanediol

A reconstructed Cu-ZnO catalyst with improved stability was fabricated by organic acid treatment method for the liquid-phase hydrogenation of dimethyl succinate to 1,4-butanediol.According to the characterization results of the fresh Cu-ZnO and reconstructed Cu-ZnO,three different forms of ZnO were suggested to be presented on the catalysts:ZnO having strong interaction with Cu species,ZnO that weakly interacted with Cu species and isolated ZnO.The first form of ZnO was believed to be beneficial to the formation of efficient active site Cu^(+),while the latter two forms of ZnO took the main responsibility for the deactivation of Cu-ZnO catalysts in the liquid-phase hydrogenation of diesters.The reconstruction of the Cu-ZnO catalyst by the organic acid treatment method resulted in a new Cu-ZnO catalyst with more Cu^(+)and less ZnO species that leads to deactivation.Furthermore,the deactivation mechanism of Cu-ZnO catalysts in liquid-phase diester hydrogenation in continuous flow system was proposed:the deposition of the polyesters on the catalysts via transesterification catalyzed by weakly interacted ZnO and isolated ZnO leads to the deactivation.These results provided meaningful instructions for designing highly efficient Cu-Zn catalysts for similar ester hydrogenation systems.

Reductive amination of n-hexanol to n-hexylamine over Ni-Ce/γ-Al_(2)O_(3) catalysts

The amination of alkyl alcohols is one of the most promising paths in synthesis of aliphatic amines.Herein,cerium doped nickel-based catalysts were synthesized and tested in a gas-phase amination of n-hexanol to n-hexylamine.It was found that the activity of the Ni/γ-Al_(2)O_(3)catalyst is significantly improved by doping an appropriate amount of cerium.The presence of cerium effectively inhibits the agglomeration of nickel particle,resulting in better Ni dispersion.As Ni particle size plays critical role on the catalytic activity,higher turnover frequency of n-hexanol amination was achieved.Cerium doping also improves the reduction ability of nickel and enhances the interactions between Ni and the catalyst support.More weak acid sites were also found in those cerium doped catalysts,which promote another key step—ammonia dissociative adsorption in this reaction system.The overall synergy of Ni nanoparticles and acid sites of this Ni-Ce/γ-Al_(2)O_(3)catalyst boosts its superior catalytic performance in the amination of n-hexanol.

Enhanced synergy between Cu^(0) and Cu^(+) on nickel doped copper catalyst for gaseous acetic acid hydrogenation

As the substitution of common noble catalysts in the hydrogenation of carboxylic acid,a highly effective Cu-Ni/SiO_(2) catalyst was prepared by a novel stepwise ammonia evaporation method.Its performance in the gasphase hydrogenation of acetic acid was further examined.With the introduction of Ni dopant,more stable Cu^(δ+) sites,which can adsorb more acetic acid,were formed due to the electron transfer from Cu to Ni.This makes more Cu^(0) sites available for hydrogen adsorption,which was suggested as the rate-determining step in acetic acid hydrogenation.A conversion of 99.6% was successfully achieved on this new Cu/SiO_(2)-0.5Ni catalyst,accompanied by the ethanol selectivity of 90%.The incorporation of nickel between copper nanoparticles enhances the synergistic effect between Cu^(0) and Cu^(+).It also helps mitigate the aggregation of copper nanoparticles due to the Ostwald ripening effect induced by acetic acid and enhance the stability of copper catalyst in the conversion of carboxylic acid.