Insights into Higher Alcohols Selectivity Modulation of CuLa/Al2O3 Catalyst for Ethanol Upgrading

The higher alcohols selectivity and yield of CuLa/Al₂O₃ catalysts were largely ascribed to the cooperation of the large quantity of the medium acidity and the highly dispersed Cu species with suitable Cu⁺/Cu⁰ ratio. The highly dispersed and stable Cu-based catalyst was achieved mainly by the strong interaction between the coordinatively unsaturated Al³⁺Penta sites on the γ-Al₂O₃ support and the Cu species.

Abstract

The structure-performance relationship of the CuLa/Al₂O₃ catalyst for ethanol upgrading to higher alcohols was established with a focus on the Cu⁺/Cu⁰ ratios and acidity. Due to the strong metal-oxide interaction and the La promotion, the Cu species were highly dispersed and existed in the forms of Cu⁺ and Cu⁰ with the former as main phase. The Cu⁺/Cu⁰ ratios increased with the decrease of reduction temperatures and the high Cu⁺ contents led to the increase of ethyl acetate selectivity dramatically. The high reduction temperature also enhanced the acidity of CuLa/Al₂O₃ catalysts. The strong Lewis acid sites of the sample reduced at 823 K worked as an efficient catalyst for the intermolecular dehydration of ethanol and promoted the formation of diethyl ether. For other samples, the higher alcohols selectivity and yield increased linearly with the medium acidity, indicating that the medium acidity was the critical influence factor of the higher alcohols formation for the CuLa/Al₂O₃ catalysts in the present study and the determining step should be the aldol condensation catalyzed by the medium acid sites.

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