Understanding the role of Al/Zr ratio in Zr-Al-Beta zeolite: Towards the one-pot production of GVL from glucose

Abstract

The direct one-pot transformation of glucose into γ-valerolactone (GVL) can be accomplished by means of a cascade of reactions in which Brønsted acid-catalyzed transformations are combined with catalytic transfer hydrogenation (CTH) by using 2-propanol as sacrificial alcohol, avoiding the use of high-pressure hydrogen. Catalysts containing Zr Lewis acid sites have been successfully applied in CTH reactions while the acid-driven transformations can be preferentially promoted by Brønsted Al-related acidity. Here, we present the combination of Zr and Al as active sites within a BEA zeolite structure as catalyst, with the possibility of adjusting the Al/Zr ratio from ∞ (commercial H-Beta) to 0 (aluminium-free Zr-Beta), which show a scale of Brønsted/Lewis acid sites ratios. The Al/Zr ratio has a strong impact on the products distribution. As the Zr content increases, higher amount of GVL is obtained, leading to a maximum over the catalyst with high amount of Zr and low content of Al acid sites (Al/Zr = 0.2). An increase of reaction temperature, as well as reaction time, allows an enhancement of yields towards the desired products, leading to a maximum yield towards GVL of 24 mol% over Zr-Al-Beta (2.0), and a maximum yield towards isopropyl lactate of 26 mol% over Zr-Beta at 190 °C.