Constructing a high-performance magnesium single-atom catalyst for the transfer hydrogenation of biomass-derived carbonyl compounds in ethanol

Endogenous hydrogen systems, consisting of metal–organic coordination catalysts and alcohols, have been widely applied for the transfer hydrogenation (TH) of biomass-derived carbonyl compounds in recent years. Metal-organic coordination catalysts showed satisfactory ability of TH in the secondary alcohols, but most of them could not effectively employ the cheaper primary alcohols as hydrogen donors. Furthermore, they commonly contained high metal contents, which also led to low catalytic efficiency in significant measure. In this work, we constructed a novel magnesium single-atom catalyst (Mg-NC) with merely 0.37 wt% Mg by means of a combined self-assembly and pyrolysis strategy. The characterization results indicated that Mg was atomically dispersed and it was coordinated with four pyridinic-N in Mg-NC. Due to the obvious electron transfer from Mg to its coordinated pyridinic-N, Mg–N₄ active centers displayed high Lewis acid-base strength with abundant content, which brought remarkable catalytic activity. When Mg-NC was used for the TH of 5-hydroxymethylfurfural (HMF) in ethanol (EtOH), 2,5-bis(hydroxymethyl)furan (BHMF) yield was up to 96.3 % with high productivity of 19.85 mol_BHMF mol_Mg⁻¹ h⁻¹ at 150 °C for 5 h. More interestingly, the process of TH over Mg-NC in EtOH was proved to proceed via the hydrogen radical mechanism. Additionally, Mg-NC exhibited powerful catalytic universality; it could not only utilize other primary alcohols (such as n-propanol and n-butanol) as hydrogen donors, but also catalyze the TH of other carbonyl compounds (such as furfural, 5-methylfurfural, benzaldehyde, cyclohexanone, and levulinic acid). Overall, this work offered some important clues and references to reinforce the hydrogen-supplying ability of primary alcohols in the TH of various biomass-derived carbonyl compounds to high-value fine chemicals.