Covalent Organic Framework-Derived B/N Co-Doped Carbon FLPs Metal-Free Catalysts for the Selective Hydrogenation of α,β-Unsaturated Aldehydes to Unsaturated Alcohols

An ongoing challenge is to precisely tailor the frustrated Lewis pairs (FLPs) sites to construct all-solid-state FLPs metal-free catalysts that are as effective as or even more effective than homogeneous/metal catalysts in H₂ activation. In this study, B/N codoped carbon (SNW-BCN) catalysts were prepared by precisely tailoring FLPs sites by targeted doping of B atoms in the nitrogen-rich covalent organic framework (SNW-1) using the ligand-exchange strategy and self-templated carbonization. The catalysts were then applied in the selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols. It was found that a significant amount of pyridinic-N sites could be obtained from nitrogen-rich SNW-1. Moreover, targeted doping of B atoms can be accomplished by introducing organic ligands (4-formylphenylboronic acid) with Lewis acid heteroatoms to pre-empt the ligand site of SNW-1. Additionally, the B–N covalent bond, which preferentially forms between B and neighboring N at high temperature, can function as a Lewis acid site. DFT calculations and in situ characterizations show that the neighboring electron-rich pyridinic-N and the electron-deficient B–N site can form B–N/pyridinic-N FLPs sites, which can effectively activate H₂ and the C═O of α,β-unsaturated aldehydes, with only 0.36 eV of H–H bond dissociation energy. This work encourages the environmentally friendly synthesis of unsaturated alcohols and offers fresh concepts for the development and synthesis of all-solid-state FLPs metal-free catalysts. Additionally, experiments on catalyst scale-up were also investigated because they might shed light on catalyst production on a large scale.