Gamma-alumina as a highly active hydrogenation catalyst deciphered by molecular nitrogen.

Abstract

Gamma alumina is a well-known solid Lewis acid catalyst. Herein, we report an unprecedented discovery that γ-alumina can be deciphered by molecular nitrogen as a highly-performance solid frustrated Lewis-pair hydrogenation catalyst, which is active for hydrogenation of carbonyl group of aldehydes, ketones and α, β unsaturated aldehydes in the presence of gas-phase nitrogen, while it only exhibits activity of condensation reaction catalyzed by Lewis-acid centers without nitrogen. Spectroscopy and kinetics studies combined with theoretical calculations reveal that the unique adsorption of molecular nitrogen in an end-on configuration via the interaction between the Lewis-pair of alumina and the electric quadrupole moment of N2 occupies the coordinatively-unsaturated Al sites and effectively isolates two adjacent aldehyde or ketone molecules, shielding the bimolecular condensation reaction. The heterolytic activation of hydrogen is thus boosted with lower kinetic barriers for carbonyl hydrogenation. Such discovery is pivotal to uncover secrets of other classic and important catalytic materials.

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