Effect of the Al2O3 Crystal Phase on the Supported Pd Performance of Semihydrogenation Alkynes

The development of alkyne semihydrogenation catalysts with high conversion and selectivity under mild conditions is extremely challenging. Here, the modulation of Pd by different crystalline aluminas was investigated to improve the reaction performance. XPS confirmed that different crystalline aluminas modified the electronic structure of palladium. The Pd0.5/γ-Al2O3 catalyst with a Pd loading of 0.48 wt % attained 98% conversion and 91% selectivity. Stronger interaction of the γ-Al2O3 support with the loaded Pd nanoparticles resulted in electron deflection toward the support. The electronic structure of Pd was altered by modulating the crystallographic shape of the support, resulting in metal nanoparticles containing more Pd2+. Electron-deficient Pd2+ adsorbs more strongly on an electron-rich C≡C, which in turn modulates the competitive adsorption of alkenes and alkynes. Finally, the effective semihydrogenation of phenylacetylene was realized at low temperature and pressure.