Effect of N₃^- species on selective acetylene hydrogenation over Pd/SAC catalysts

Selective hydrogenation of acetylene to ethylene is very important for removing a trace amount of acetylene from ethylene. Tuning catalyst acidity is critical for hydrogenation reaction to prevent oligomerization. In this work, NaN₃ was introduced to Pd catalyst serving as Lewis base sites. NaN₃-Pd/SAC catalysts with different N₃^- loadings (0-15 wt.%) were prepared by impregnation method and analyzed with BET, temperature-programmed reduction (TPR), Fourier-transferred Infrared (FTIR) spectroscopy, CO pulse chemisorption, temperature-programmed desorption (TPD) of hydrogen and acetylene. The results showed NaN₃ covered some Pd species and increased the reduction temperatures of catalysts. Also NaN₃ addition decreased the catalyst surface areas due to blocking some pores on the support. N₃^- on the catalysts lowered hydrogen adsorption capacity but showed superior adsorption capability for acetylene, the selectivity and conversion of the acetylene hydrogenation was negatively affected by N₃^- species under the current operation conditions. The amount of the adsorbed hydrogen and the types of acetylene adsorption played important roles for the hydrogenation reaction. This work provides insights on how to prepare an effective catalyst for removing acetylene impurity from ethylene.