Selective hydrogenation of phenylacetylene over a nano-Pd/α-Al2O3 catalyst

Selective hydrogenation of phenylacetylene is an important reaction for increasing the purity of the styrene monomer. In this study a series of supported nano-Pd/α-Al2O3 catalysts were prepared and applied to the selective hydrogenation of phenylacetylene. The preparation procedure consisted of two steps: synthesis of colloidal Pd nanoparticles by a reduction-by-solvent method, followed by impregnation onto α-Al2O3. In the first step, NaBH4 was used as a reducing agent to reduce Pd2+ ions in the C2H5OH/H2O solvent system, and polyvinylpyrrolidone (PVP) was used as a protecting agent to stabilize Pd nanoparticles. The prepared colloids and catalysts were characterized by N2 physisorption, CO chemisorption, XRD, UV–vis, FT-IR, ICP and HRTEM techniques. It was found that the amounts of NaBH4, C2H5OH and PVP had effects on the Pd particle size, which in turn influenced the catalyst performance. The selective hydrogenation of phenylacetylene was sensitive to the structure of the nano-Pd/α-Al2O3 catalysts. In the case where the Pd particle size varied from 3.8 to 6.6 nm, the specific activity and the selectivity to styrene increased with increasing particle size, but when the particle size increased in the range of 6.6–12.1 nm, the specific activity increased slowly and the selectivity to styrene decreased gradually. Nano-Pd/α-Al2O3 can be reused several times without loss of activity and selectivity and no distinct variation in the Pd particle size was observed, indicating its good stability in the selective hydrogenation of phenylacetylene.