Liquid-phase selective hydrogenation of phenylacetylene on palladium nanoparticles supported on mesoporous silica

Abstract

A series of palladium catalysts with ca. 1 wt% palladium supported on mesoporous silica with different pore sizes (MCM-41, SBA-15, and MCF) were prepared by deposition of colloidal Pd nanoparticles (Pd/X_col) and Pd(II)acetate solution (Pd/X_imp). MCM-41 and SBA-15 showed the XRD characteristic peaks indicating highly ordered hexagonal pore structure while MCF consisted of spherical cell and frame structure with average pore size of 2.7, 3.9, and 7.8 nm, respectively. Sizes of the colloidal Pd nanoparticles were about 2.3 nm. The supports pore structure did not affect the Pd particle size of Pd/X_col catalysts. For the Pd/X_imp, the Pd particle size was increased with increasing pore diameter of the supports. However, the largest Pd particle size was obtained on Pd/SBA-15_imp since the Pd particles were formed in a long cylindrical shape similar to SBA-15. The Pd/SBA-15_col exhibited the best catalyst performance in the liquid-phase selective hydrogenation of phenylacetylene under mild conditions (40 degress celsius, H2 pressure = 1-5 bar, 30 min). The appropriated pore structure and pore size of SBA-15 could provide a better encapsulation of Pd particles so that high styrene selectivity was attained at complete conversion of phenylacetylene. All the Pd/X_col catalysts exhibited no change in the catalyst activities/selectivity during the recyclability test for four cycles while the Pd/X_imp showed an increase of catalyst activity and lower styrene selectivity in some cases.