Depositing Pd on the outmost surface of Pd1Ni/SiO2 single-atom alloy via atomic layer deposition for selective hydrogenation of acetylene

Supported Pd single-atom alloy (SAA) catalysts are selective in acetylene semi-hydrogenation. However, it is a challenge to prepare Pd SAA where Pd single atoms dispersed on the outmost surface of the catalysts because the Pd atoms on Pd SAA prepared by conventional impregnation distribute inside the alloyed particle or on the support surface after activation. In this work, we firstly synthesized Ni/SiO2 nanocatalysts by impregnation, followed by H2 reduction to generate metal Ni particles on SiO2. Subsequently, Pd single atoms are selectively deposited on the Ni particle surface by atomic layer deposition (ALD). The Pd species on the Pd1Ni/SiO2 prepared by ALD dispersed on the outmost surface of catalyst, presenting the improved catalytic performances in acetylene hydrogenation, as compared to a reference Pd1Ni/SiO2 catalyst prepared by impregnation. The Pd1Ni/SiO2 catalyst prepared by ALD with 5 cycles (0.04 wt. %Pd, 5c-Pd1Ni/SiO2) shows both superior hydrogenation activity (92 %) and selectivity (88 %) under mild temperature (80 °C) in the selective semi-hydrogenation of acetylene. Moreover, the specific activity of the 5c-Pd1Ni/SiO2 catalyst is the highest, as compared to the catalysts reported in literature. Therefore, we conclude that the metal single atoms on metal SAA catalyst prepared by ALD locate on the outmost surface of the catalyst, presenting the unusual catalytic performances in catalysis.