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

Abstract

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 H2-TPR, XPS, XRD and STEM-EDX analyses demonstrates the generation of a range of Cu oxidation states (Cu0 (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 Cu0/Cu+ (from H2-TPR and XPS) enhanced H2 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 Cu0. 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+/Cu0. This opens new directions for sustainable “hydrogen free” hydrogenations over non-noble Cu catalysts.