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

• Bimetallic Pd–Cu/Al2O3 and Pd–Zn/Al2O3 exhibited enhanced selectivity to styrene.
• The Cu/Pd and Zn/Pd molar ratios affected the activity and selectivity of catalyst.
• The geometric effect resulted in increased selectivity to styrene of Pd–Cu/Al2O3.
• Both geometric and electronic effects led to increased selectivity of Pd–Zn/Al2O3.
• Pd–Zn/Al2O3 with a Zn/Pd molar ratio of 6 showed the best selectivity to styrene.

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.

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