Investigation of the reaction kinetics of isolated Lewis acid sites in Beta zeolites for the Meerwein–Ponndorf–Verley reduction of methyl levulinate to γ-valerolactone

Abstract

We investigate the reaction kinetics of the Meerwein–Ponndorf–Verley (MPV) reduction of methyl levulinate (ML) to 4-hydroxypentanoates and subsequent lactonization to γ-valerolactone (GVL) catalyzed by Lewis acid zeolites. Reaction kinetics studies show a first-order dependence on ML and 2-butanol, confirm that the hydride shift is the rate-limiting step, and support a dual-binding mechanism on a single Lewis acid site. All catalysts generate GVL with selectivities >97%, with Hf-Beta exhibiting the highest activity in the temperature range of 393–453K. Sn-, Zr-, and Hf-Beta show apparent activation energies of ca. 52kJmol−1, which is significantly lower than that of Ti-Beta (69kJmol−1). Secondary alcohols consistently exhibit higher reaction rates than primary alcohols with lower apparent activation energies. Increasing polarity of the hydrogen donor leads to a decrease in reaction rates. The experimental data are used to build a kinetic model for the MPV reaction in a tubular packed-bed reactor.