Regioselectivity and confinement effects for catalytic conversion of carbohydrates within zeolite H-BEA

Abstract

Zeolites have established the importance during biomass conversion, and H-form zeolites, although extensively used, produce hydroxymethylfurfural (HMF) with low yields. Herein, dispersion-corrected density functional calculations are employed with aim to comprehensively understand glucose conversion to HMF within zeolite H-BEA and unravel the role of confinement effects. The low HMF yields originate from regioselectivity: The preferentially activated O3 and O6 sites are significantly driven to humin precursors, while less reactive O1 and O2 sites lead favorably to HMF. Glucose-to-fructose isomerization occurs only at O5 site, while seems unnecessary for HMF production. Owing to the peculiar confinement effects, HMF precursors are prone to emerge within H-BEA, both upon dehydration and during catalysis, while may turn to be acyclic within aqueous solutions. Direct conversion to levulinic acid without HMF as intermediate thus becomes difficult within acidic zeolites. Results facilitate catalyst design for biomass conversion, and further understanding of regioselective catalysis and confinement effects.