Impact of Pd single-site coordination structure on catalytic performance for semihydrogenation of acetylene
Yu Zeng, Minqi Xia, Fujie Gao, Changkai Zhou, Xueyi Cheng, Liwei Liu, Jiao Liu, Qiang Wu, Xizhang Wang, Lijun Yang, Yining Fan, Zheng Hu
Abstract
Semihydrogenation of trace acetylene in an ethylene gas stream is a vital step for the industrial production of polyethylene, in which Pd single-site catalysts (SSCs) have great potential. Herein, two Pd SSCs with different coordination structures are prepared on hierarchical nitrogen-doped carbon nanocages (hNCNC) by regulating the nitrogen species with or without using dicyandiamide. With using dicyandiamide, the obtained Pd1-Ndicy/hNCNC SSC features the coordinated Pd by two pyridinic N and two pyrrolic N (PdN 2 py N 2 pr ). Without using dicyandiamide, the obtained Pd1/hNCNC SSC features the coordinated Pd by pyridinic N and C (PdN py C4−x, x = 1–4). The former exhibits an 18-fold increase in catalytic activity compared to the latter. Theoretical results reveal the abundant unoccupied orbital states above the Fermi level of PdN 2 py N 2 pr moiety, which can facilitate the activation of substrate molecules and dynamics of acetylene hydrogenation as supported by the combined theoretical and experimental results. In addition, the PdN 2 py N 2 pr moiety presents a favorable desorption of ethylene. Consequently, the Pd1-Ndicy/hNCNC SSC exhibits high C2H2 conversion (99%) and C2H4 selectivity (87%) at 160 °C. This study demonstrates the impact of Pd single-site coordination structure on catalytic performance, which is significant for the rational design of advanced Pd SSCs on carbon-based supports.