Enhanced catalytic activity of MgO-grafted aluminium isopropoxide in heterogeneous H-transfer reduction reactions through surface support modification

Abstract

The heterogenization of aluminium isopropoxide [Al(OⁱPr)₃] on modified magnesium oxide (MgO) supports was investigated to develop efficient catalysts for hydrogen-transfer (H-transfer) reduction reactions. MgO surfaces were functionalized with octadecyltrichlorosilane (OTES) or dibromobutane (DBB) to optimize the surface chemistry of commercial MgO. The OTES-modified MgO exhibited a porous “nest-like” structure with a markedly increased surface area of 84.3 m² g⁻¹, compared to 2.9 m² g⁻¹ for the unmodified MgO. In contrast, DBB-modified MgO displayed a “brush-like” morphology attributed to the flexibility of the immobilized carbon chains. The modified heterogenized catalysts demonstrated substantial improvements in activity compared to the unmodified MgO-based systems. Among the heterogenized catalysts, Al–DBB–MgO achieved the highest turnover frequency (TOF), which is attributed to enhanced substrate adsorption and reduced steric hindrance, facilitating efficient reactant access to active sites. The activity of the two modified catalysts after 5 reduction cycles shows no obvious change in terms of the TOF of Al–DBB–MgO, while the TOF of Al–OTES–MgO dropped by around 14%. These findings highlight the critical role of MgO surface modification in enabling effective Al(OⁱPr)₃ immobilization and enhancing catalytic performance for H-transfer reactions, offering a promising strategy for designing advanced heterogenized catalysts for reduction of carbonyl compounds.