Selective reduction of acetic acid to ethanol over novel Cu2In/Al2O3 catalyst

• Indium doped catalysts are highly efficient for acetic acid reduction to ethanol.
• Promoting effect of indium on Cu catalysts comes from alloy (Cu2In) formation.
• Novel CuIn/Al2O3 composite is more active than conventionally used Adkins catalyst.

Volatile fatty acids (VFAs) can be produced efficiently by simple thermochemical or biological biomass degradation. For the processing of these organic acids in hydrogen atmosphere, the consecutive reactions of acetic acid (AA) hydroconversion were studied in details looking for conditions of selective ethanol production over a novel and advantageous bimetallic composite applying indium as co-catalyst. The reactions were investigated in vapor phase at 240–380 °C, 7–21 bar hydrogen and 0.5–3.5 bar acetic acid partial pressures in a fixed bed flow-through reactor using supported copper catalysts. In2O3 admission can significantly increase AA hydroconversion activity of copper catalysts supported on various oxides and the yield of the produced ethanol. Efficient hydrogenating catalysts, containing finely dispersed metal particles were obtained by in situ reduction with H2 at 450 °C. In the catalysts modified with In2O3 additive, formation of an intermetallic compound (Cu2In) was strikingly observed resulting in a different, more advantageous catalytic behavior as of pure copper particles supported on different oxide supports. On comparing a commercial, conventionally used catalysts (Adkins: 72 wt% CuCr2O4 + 28 wt% CuO) with the bimetallic alumina supported composite (Cu2In/Al2O3) the new catalyst proved to be much more active and selective for producing ethanol. A schematic representation of reactions involved in the hydroconversion of acetic acid was explored and verified. The activity dependence on the reactant partial pressures denotes rate-controlling surface reaction according to Langmuir–Hinshelwood mechanism.

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