Highly selective hydrodehydroxylation of 2-hydroxyadipamide to bio-based adipamide over N-doped Mo2C catalysts

Abstract

Adipamide (ADM) is an important intermediate for various polyamides and nitrogen-containing fine chemicals. However, the selective dehydroxylation of α-hydroxyamides remains a significant challenge in catalytic deoxygenation, due to the high bond dissociation energy of aliphatic C–OH bonds and the pronounced electron-withdrawing and intramolecular hydrogen-bonding effects of the amide groups. These structural features greatly stabilize the molecular framework, making C–OH activation difficult under conventional hydrodeoxygenation (HDO) conditions and often leading to undesired C–N or C–C cleavage. In this work, a series of N-modified β-Mo₂C catalysts were designed to promote the hydrodehydroxylation (HDH) of 2-hydroxyadipamide (2-HADM) to bio-based ADM. Structural characterizations reveal that nitrogen incorporation forms interstitial Mo–N–Mo environments within the Mo₂C lattice, thereby tuning the electronic structure and acid–base properties of Mo sites. The optimized β-Mo₂C-N-650 catalyst achieves a 33.2 % conversion and 92.0 % selectivity to ADM at 150 °C and 4 MPa H₂. Density functional theory (DFT) calculations further suggest that nitrogen doping may lower the transition-state barrier for C–OH bond scission and stabilize the key intermediates, thus enhancing dehydroxylation selectivity. This study demonstrates that tailoring the local electronic structure of Mo₂C provides mechanistic insights and a potential design principle for achieving mild and selective deoxygenation of multifunctional α-hydroxyamide substrates.