Phenylacetylene hydrogenation coupled with benzyl alcohol dehydrogenation over Cu/CeO2: A consideration of Cu oxidation state

We have examined the effect of copper oxidation state in the continuous gas phase coupled phenylacetylene hydrogenation (to styrene) with benzyl alcohol dehydrogenation (to benzaldehyde) over Cu/CeO2. Analysis by H-2-TPR, XPS, XRD and STEM-EDX analyses demonstrates the generation of a range of Cu oxidation states (Cu-0 (13-77%), Cu+ (13-74%), Cu2+ (0-55%)). The stepwise formation of styrene and ethylbenzene was promoted in the stand-alone phenylacetylene hydrogenation. An increase in Cu-0/Cu+ (from H-2-TPR and XPS) enhanced H-2 chemisorption and styrene TOF, but with low hydrogen utilisation efficiency. The formation of benzaldehyde and toluene was promoted in the stand-alone dehydrogenation of benzyl alcohol, where benzaldehyde selectivity and TOF correlate with the concentration of Cu-0. Full hydrogen utilisation, exclusive benzaldehyde/styrene formation and a (3-fold) greater styrene TOF (to attain 100% yield) was achieved in the coupled process, where hydrogenation/dehydrogenation activity correlates with Cu+/Cu-0. This opens new directions for sustainable hydrogen free hydrogenations over non-noble Cu catalysts. (c) 2020 Elsevier Inc. All rights reserved.

Automated summary

The study examined the impact of copper oxidation state on the products formed in the continuous gas phase reactions of phenylacetylene hydrogenation and benzyl alcohol dehydrogenation over Cu/CeO₂ catalyst. It was found that the concentration of Cu-0 and Cu+ influenced the selectivity and turnover frequency of the products significantly. In the coupled process, full hydrogen utilization, exclusive benzaldehyde/styrene formation, and a greater styrene turnover frequency were achieved, showing the potential of sustainable hydrogen free hydrogenations using non-noble Cu catalysts.