Selective hydrogenation of phenylacetylene over bimetallic Pd-Cu/Al2O3 and Pd-Zn/Al2O3 catalysts

Bimetallic Pd-Cu/Al2O3 and Pd-Zn/Al2O3 catalysts with various Cu/Pd and Zn/Pd molar ratios were prepared and applied to the selective hydrogenation of phenylacetylene to styrene. The structure properties of the bimetallic catalysts were characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), CO chemisorption, high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Different from Pd-Cu/Al2O3 where the interaction between Pd and Cu only generated the geometric effect, both geometric and electronic effects were observed for Pd-Zn/Al2O3. The activity and selectivity of the bimetallic catalysts can be tuned by varying the Cu/Pd and Zn/Pd molar ratios, which were essentially determined by the geometric and electronic effects of the catalysts. Although both Pd-Cu/Al2O3 and Pd-Zn/Al2O3 exhibited improved selectivity to styrene compared to monometallic Pd/Al2O3, there is a difference in the activity and selectivity between the two types of bimetallic catalysts at the same Cu/Pd and Zn/Pd molar ratio, which is mainly caused by the different modification degrees of Cu and Zn on Pd. Among all the catalysts prepared in this work, the Pd-Zn/Al2O3 with a Zn/Pd molar ratio of 6 displayed the best selectivity to styrene, being 86.3% at 99.5% phenylacetylene conversion. (C) 2015 Elsevier B.V. All rights reserved.