Phosphor-doped hexagonal boron nitride nanosheets as effective acid–base bifunctional catalysts for one-pot deacetalization–Knoevenagel cascade reactions

Abstract

One-pot cascade reactions over metal-free heterogeneous bifunctional catalysts have been attracting increased attention in green chemistry owing to the advantage of process intensification, as well as the elimination of wastes and metal contamination. In this paper, phosphor-doped hexagonal boron nitride nanosheets (BNP) can act as excellent metal-free acid–base bifunctional catalysts for one-pot deacetalization–Knoevenagel cascade reactions. XRD, FT-IR, XPS, and solid NMR characterizations indicate that phosphor was doped into the framework of h-BN mainly at the corner (N₂PO) and bayer (N₃P–OH) sites. The CO₂-TPD and NH₃-TPD characterizations showed that the BNP sample with optimal phosphor-doping amounts simultaneously possessed the highest amount of acid and base sites. When correlated with the catalytic performance, it can be concluded that mainly N₃P–OH acts as the Brønsted acid sites and –BNH₂ and N₂PO as the Lewis and Brønsted base sites, respectively. In addition, the good recycling stability and immobilization feasibility on a monolith support confirm its potential in practical applications.