Pyridinic Nitrogen Sites Dominated Coordinative Engineering of Subnanometric Pd Clusters for Efficient Alkynes Semi-hydrogenation.

Supported metal catalysts have played an important role in optimizing selective semi-hydrogenation of alkynes for fine chemicals. Thereinto, nitrogen-doped carbons, as a type of promising support materials, have attracted extensive attentions. However, due to the general phenomenon of random doping for nitrogen species in the support, it is still a tremendous challenge to finely identify which nitrogen configuration dominates the catalytic property of alkynes semi-hydrogenation. Herein, we report that uniform mesoporous N-doped carbon spheres derived from mesoporous polypyrrole spheres are used as supports to immobilized subnanometric Pd clusters, which provides a particular platform to research the influence of nitrogen configurations on the alkynes semi-hydrogenation. Comprehensive experimental results and DFT calculation indicate that pyridinic nitrogen configuration dominates the catalytic behavior of Pd clusters. The high contents of pyridinic nitrogen sites offer abundant coordination sites to them, which greatly reduces the energy barrier of the rate-determining reaction step and makes Pd clusters own high catalytic activity. The electronic effect between pyridinic nitrogen sites and Pd clusters enables Pd to possess a high catalytic selectivity. Additionally, the good mesostructures also promote the fast transport of substrate. Based on the above, catalyst Pd@PPy-600 exhibits high catalytic activity (99%) and selectivity (96%) for phenylacetylene semi-hydrogenation. This article is protected by copyright. All rights reserved.