Selective photocatalytic semihydrogenation of alkynols to alkenols on Pd-C3N4 nanosheets under ambient conditions

Selective hydrogenation of alkynols to alkenols is an essential process for producing fine and intermediate chemicals. Currently, thermocatalytic alkynol hydrogenation faces several challenges, e.g., the safety of high-pressure hydrogen (H2) gas and the need for elevated temperature, and unavoidable side reactions, e.g., overhydrogenation. Here, a novel photocatalytic strategy is proposed for selectively reducing alkynols to alkenols with water as a hydrogen source under ambient temperature and pressure. Under the irradiation of simulated solar light, carbon nitride (C3N4) nanosheets with palladium (Pd) nanoparticles as cocatalysts (Pd-C3N4 NSs) exhibit a 2-methyl-3-butyn-2-ol (MBY) conversion of 98% and 2-methyl-3-buten-2-ol (MBE) selectivity of 95%, outperforming state-of-the-art thermocatalysts and electrocatalysts. After natural-sunlight irradiation (average light intensity of 25.13 mW cm-2) for 36 h, a MBY conversion of 98% and MBE selectivity of 92% was achieved in a large-scale photocatalytic system (2500 cm2). Experimental and theoretical investigations reveal that Pd cocatalysts on C3N4 facilitate the adsorption and hydrogenation of MBY as well as the formation of active hydrogen species, which promote the selective semihydrogenation of alkynols. Moreover, the proposed strategy is applicable to various water-soluble alkynols. This work paves the way for photocatalytic strategies to replace thermocatalytic hydrogenation processes using pressurized hydrogen.

Ambient-Temperature Reductive Amination of 5-Hydroxymethylfurfural Over Al2 O3 -Supported Carbon-Doped Nickel Catalyst

An efficient catalytic system for the conversion of 5-hydroxymethylfurfural (HMF) into N-containing compounds over low-cost non-noble-metal catalysts is preferable, but it is challenging to reach high conversion and selectivity under mild conditions. Herein, an Al₂ O₃ -supported carbon-doped Ni catalyst was obtained via the direct pyrolysis-reduction of a mixture of Ni₃ (BTC)₂  ⋅ 12H₂ O and Al₂ O₃ , generating stable Ni⁰ species due to the presence of carbon residue. A high yield of 96 % was observed in the reductive amination of HMF into 5-hydroxymethyl furfurylamine (HMFA) with ammonia and hydrogen at ambient temperature. The catalyst was recyclable and could be applied to the ambient-temperature synthesis of HMF-based secondary/tertiary amines and other biomass-derived amines from the carbonyl compounds. The significant performance was attributable to the synergistic effect of Ni⁰ species and acidic property of the support Al₂ O₃ , which promoted the selective ammonolysis of the imine intermediate while inhibiting the potential side reaction of over-hydrogenation.

The influence of nickel loading on the structure and performance of a Ni–Al2O3 catalyst for the hydrogenation of 1,4-butynediol to produce 1,4-butenediol

In combination with a planetary ball-milling machine, a Ni–Al₂O₃ catalyst was prepared by a mechanochemical method.