Nitrogen-doped hierarchical porous carbon-supported copper catalysts for methanol oxidative carbonylation: effect of nitrogen species

Abstract

High-specific-surface-area nitrogen-doped hierarchical porous carbon materials (NHPC) were synthesized using cellulose as the carbon precursor, with ammonium oxalate, melamine, and ammonium bicarbonate as nitrogen sources and sodium bicarbonate as a pore-forming agent. These materials served as supports for copper-based catalysts, which were evaluated for the liquid-phase oxidative carbonylation of methanol to dimethyl carbonate (DMC). The Cu/NHPC154-40010 catalyst, prepared with ammonium oxalate and a cellulose:ammonium oxalate:NaHCO3 mass ratio of 1:5:4, exhibited optimal performance, achieving a DMC selectivity of 97.1%, a methanol conversion of 13.33%, and a space-time yield of 19.16 g/(g·h). The catalyst with 5 wt% copper loading demonstrated superior stability, retaining 45% of its initial activity after 10 cycles while maintaining a DMC selectivity of 96.89%. Characterization via BET, XRD, TEM, and XPS revealed that catalytic activity correlates strongly with Cu nanoparticle dispersion and the surface content of Cu⁺ species. The hierarchical porous structure, featuring interconnected micropores and mesopores, enhances copper anchoring and facilitates efficient mass transport. Nitrogen doping increases the specific surface area, improves metal dispersion, and stabilizes Cu⁺ species, thereby enhancing catalytic performance and stability. This work provides a practical strategy for optimizing copper-based catalysts in methanol oxidative carbonylation using nitrogen-doped hierarchical carbon supports.