Synthesis of methanol by hydrogenolysis of biobased methyl formate using highly stable and active Cu-spinel catalysts in slurry and gas phase reactions

Abstract

This contribution deals with a new atom efficient two-stage production route for green methanol (MeOH) from biomass that includes biomass conversion to methyl formate (MF)/formic acid (FA) mixtures followed by hydrogenolysis to MeOH. Herein, we focus on the hydrogenolysis step and propose a materials solution to the problem of catalyst corrosion by the acidic MF/FA mixture formed in the previous biomass oxidation step. We show that Cu_0.9Al₂O₄ spinel materials are very effective hydrogenolysis catalysts for the conversion of MA/FA mixtures to MeOH. Compared to commercial catalysts such as CuO/Cr₂O₃, the spinel material does not contain hazardous chromium compounds or require them during synthesis. Furthermore, this spinel catalyst shows much lower corrosion than known commercial hydrogenolysis catalysts. By using reactive frontal chromatography, nitrogen sorption, IR-ATR and XRD measurements, we show that CuO/MgO/ZnO/Al₂O₃ and CuO/Cr₂O₃ suffer from leaching of copper and chromium in the presence of FA due to the formation of mobile metal formate species. In contrast, the strongly fixed nature of copper in the highly ordered crystal structure of our Cu_0.9Al₂O₄ spinel type catalyst leads to exceptional stability in the presence of FA and in continuous hydrogenolysis experiments for more than 110 h time-on-stream.