Comprehensive understanding of base catalysis derived from nitrogen species incorporated into the frameworks of silica and carbon porous materials

Abstract

A base-catalytic nitrogen site in a specific and confined nanospace on the surfaces of silica and carbon was developed using mesoporous silica SBA-15 and its replicated porous carbon nitride PCN. Knoevenagel condensation reactions using differentially active methylene compounds and diffusion studies using CO2 as the probe molecule for the basic site revealed that the primary amine-based N component showed high activity for the base-catalyzed reaction. Among the samples investigated, primary amine-grafted SBA-15 showed the highest performance owing to the activity and location density of primary amines, as well as its surrounding hydrophobic nature. Although NSBA-15 showed moderate catalytic performance owing to an isolated active N species located on its mesopore surface, methylation of the N species led to enhanced catalytic performance because of its isolation effect. Carbonaceous PCN showed high hydrophobicity and durability during reaction and storage. A general design for N-based basic catalytic materials was also proposed.