Chemo- and regioselective Meerwein-Ponndorf-Verley and Oppenauer reactions catalyzed by Al-free Zr-zeolite beta

Abstract

Al-free Zr-beta zeolite with Si/Zr up to 75 was synthesized in a fluoride medium. The incorporation of zirconium into zeolite beta induced the formation of increased amounts of polymorph B. Lewis acid sites were predominant in the Al-free Zr-beta. Zr-zeolite beta was found to be an excellent catalyst in the Meerwein-Ponndorf-Verley (MPV) reduction of several alkyl- and aryl-substituted cyclohexanones, with high selectivity to the corresponding alcohols. The catalyst was reusable and no leaching was detected under the reaction conditions. A prominent feature of the Zr-zeolite beta catalyst is its ability to maintain activity even in the presence of rather significant amounts of water, up to 9 wt%. The activity was unaffected by the presence of pyridine but was decreased by added acids. However, the poisoning effect could be easily reversed by washing. The excellent performance of Zr-zeolite beta in the MPVO reaction is due to an appropriate Lewis acidity and the ease of ligand exchange at the Zr active sites within the zeolite beta pore channels. © 2004 Elsevier Inc. All rights reserved.