Continuous-flow chemoselective reduction of cyclohexanone in a monolithic silica-supported Zr(OPri)4 multichannel microreactor

摘要

Meerwein-Ponndorf-Vereley reduction of cyclohexanone using 2-butanol as hydrogen donor was studied in the multichannel monolithic silica microreactors modified with zirconium species to demonstrate their higher efficacy than of conventional batch systems with powdered catalysts. Zr(OPri)4 species were attached onto the monoliths siliceous surface to obtain a nominal Zr/Si mass ratio in the range of 0.01-0.28. The value of 0.14 gave the largest concentration of Lewis acid sites and hence also the highest conversion (88%) after 20 min reaction/residence time and productivity of 2.22 mmol/g h. The monoliths prepared by the sol-gel process combined with phase separation were characterized using nitrogen adsorption, mercury porosimetry, thermogravimetry, SEM, FTIR and UV-Vis spectroscopy, pyridine adsorption and XRD. They featured very open 3D co-continuous structure of 20 nm textural meso- and flow-through macropores 30-60 m in diameter (4 cm(3)/g total pore volume) which was not appreciably changed after their modification with zirconium species. Diffraction peaks characteristic for crystalline zirconia were not detected even in materials with the highest Zr content. (C) 2017 Elsevier Inc. All rights reserved.