Robust Ni_xSn/ZSM-12 Catalysts with Zeolite as the Support and Sn as the Promoter for Acetylene Semi-hydrogenation

The synthesis of ethylene from semi-hydrogenation of acetylene is significant for the upgrading of coal. Different kinds of materials (SiO2, γ-Al2O3, and ZSM-12)-supported Ni catalysts were prepared and evaluated for the acetylene hydrogenation. It demonstrated that the Ni/ZSM-12 catalyst with synergistic effect of B (Brönsted) acid and L (Lewis) acid sites can promote semi-hydrogenation of acetylene better than those over Ni/SiO2 and Ni/γ-Al2O3 catalysts, in which both only have L acid sites. However, the pure Ni/ZSM-12 still exhibited low selectivity of ethylene and poor stability; thus, the Sn promoter was introduced into the Ni/ZSM-12 catalyst. Due to the geometric and electronic effects, the Ni7Sn/ZSM-12 sample achieves higher yield of ethylene (92.51%) with ethylene selectivity of 92.51% and acetylene conversion of 100% at 250 °C, which is an increase of 19.38% over the samples without Sn addition. Moreover, the stability of the Ni7Sn/ZSM-12 catalyst (100 h) is much better than those catalysts without Sn (14 h). This is because the carbon deposition over the Sn-containing catalyst was light hydrocarbons that could be removed at high temperature while the pure Ni/ZSM-12 catalyst produced heavy hydrocarbons. The outstanding performance of Ni7Sn/ZSM-12 was further illustrated by DFT calculations, which originates from its facilely accessible hydrogen dissociation, lower ethylene adsorption energy, and higher energy barrier for the formation of C2H5* intermediate.