Transfer hydrogenation of quinolines with glycerol over N-doped carbon encapsulated non-noble metal catalysts: Mott-Schottky effect on the catalytic activity

Abstract

Catalytic transfer hydrogenation using glycerol (GLY) as a hydrogen donor presents a sustainable and secure approach for hydrogenation of quinoline and its derivatives. Conventional non-noble metal catalysts can effectively catalyze the transfer hydrogenation reaction with GLY. However, it is inevitable that metal leaching occurs under alkaline hydrothermal conditions. In this work, N-doped carbon encapsulated non-noble metal catalysts, such as Co@NC, Ni@NC, and CoNi@NC, were prepared by one-pot method combined with an acid leaching for this reaction. According to Mott-Schottky effect, encapsulating of Co, Ni, and CoNi nanoparticles with relatively smaller work function in NC shells constructed a rectifying contact and increased the electron density on NC shells. Density Functional Theory (DFT) calculations confirm that electrons transfer from metal cores to NC shell, with CoNi transferring the most, followed by Co and Ni. As a result, the catalytic activity followed the order of CoNi@NC＞Co@NC＞Ni@NC, where CoNi@NC exhibited highest catalytic activity, 92.2% GLY conversion and full quinoline conversion can be obtained over CoNi@NC at 180 °C with 89.7% and 99.3% of the selectivity to lactic acid and 1, 2, 3, 4-tetrahydroquinoline, respectively. In addition, CoNi@NC possessed excellent stability because NC shells physically isolate metal cores from the reactive environment. Such Mott-Schottky catalyst tuning could be an efficient way to design new non-noble catalysts.