Meervein-Ponndorf-Vereley reduction of carbonyl compounds in monolithic siliceous microreactors doped with Lewis acid centres

Meerwein-Ponndorf-Vereley chemoselective reduction of cyclohexanone and benzaldehyde was studied in monolithic continuous-flow microreactors, with various Lewis acid centres derived from different metal precursors, i.e. metal alkoxides, chelated metal alkoxides and salts. The productivities achieved in the microreactors, doped with metal centres terminated by propoxy ligands, were significantly higher, ca. 30%, than those obtained for oxides modified monoliths. The highest efficiency of Zr-doped microreactors was proved and their superiority over aluminium and titanium functionalized ones was demonstrated. Higher efficiency of microreactors compared to batch reactors with powdered catalysts has been shown. Stability of proposed materials has been demonstrated. The catalytic outcomes were correlated with structural and physicochemical properties of materials, obtained using low-temperature nitrogen adsorption, mercury porosimetry, SEM microscopy, ICP-MS, FTIR study and pyridine adsorption.