Transfer hydrogenation of cinnamaldehyde to cinnamyl alcohol over SnO-MgO composite catalysts

A concerted function of SnO and MgO leads to enhanced catalytic performance in transfer hydrogenation of cinnamaldehyde . • SnO-MgO composite catalyst was prepared by coprecipitation-reduction method. • SnO-MgO sample exhibits good performance toward transfer hydrogenation reaction. • Synergy of acid sites on SnO and basic sites on MgO plays a vital role. • The performance of SnO-MgO catalyst was comparable to noble metal catalyst at 70 °C. • SnO-MgO showed excellent catalytic activity, stability, universality. Catalytic transfer hydrogenation, known for its high selectivity in converting α,β-unsaturated aldehydes, necessitates the presence of Lewis acid sites in conjunction with basic sites. In the study, SnO-MgO composite catalysts were synthesized by partial reduction of SnO 2 -MgO precursor at 400 °C with 37.5 % hydrogen in nitrogen. The catalytic performance of the prepared catalysts was tested in transfer hydrogenation of cinnamaldehyde (CAL) to produce cinnamyl alcohol (COL) using isopropanol (IPA) as the hydrogen donor and solvent. SnO gave a CAL conversion of 17.4 %, whereas the SnO-MgO composite presented considerably higher conversion (100 %) with 100 % selectivity to COL at 70 °C and atmospheric pressure (N 2 ), which was comparable to noble metal catalysts. The characterizations by means of EPR, NH 3 -TPD, pyridine-adsorbed FT-IR, and poisoning experiments demonstrated that, when SnO 2 was converted to SnO, a large number of oxygen vacancies were generated, leading to the formation of Lewis acid sites. It was indicated that SnO was the catalytically active phase for the transfer hydrogenation whereas MgO was an efficient promoter to help deprotonate the hydroxyl group in IPA. Notably, after five consecutive catalytic cycles, the SnO-MgO composite retained its activity, with no detectable changes in the crystal structures of SnO and MgO. Furthermore, the SnO-MgO composite catalyst demonstrated exceptional performance in the transfer hydrogenation of other α,β-unsaturated aldehydes, including furfural, benzaldehyde, geranialdehyde, and syringaldehyde. A catalytic reaction mechanism involving a six-membered ring intermediate is tentatively proposed.