Enhanced Lewis acidity on modified H-ZSM-5 catalysed 5-hydroxymethylfurfural oxidation in aqueous solvent.

• The RuZS 90 displays good catalytic activity in water as a solvent with no external base, giving 67 % FDCA. • The NH 3 -TPD analysis indicates that RuZS 90 has 2.6 and 2.3 times higher total acidity than H-Z and RuH-Z. • The metallic Ru (77.6 %) in RuZS 90 predominantly contributes to HMF oxidation to FDCA compared to Ru on unmodified HZ (45.5 % metallic Ru). • NH 3 -DRIFT spectra exhibit that RuZS 90 contains more Lewis acidic sites than parent H-Z. • The poisoning study with potassium thiocyanate (KSCN) confirms the crucial role of Lewis acidic sites. The primary focus of the present study is to develop a zeolite-based catalyst that enhances Lewis acidity for catalysing 5-hydroxymethylfurfural (HMF) oxidation. The study modifies the parent H-ZSM-5 (H-Z) via desilication followed by Ru impregnation. The results show that RuZS 90 (Ru impregnated on desilicated H-Z for 90 min) exhibits higher catalytic activity for the HMF oxidation than Ru impregnated on parent H-Z. NH 3 -temperature programmed desorption (TPD) results indicate that RuZS 90 possesses more than 2.6 and 2.3 times higher total acidity than H-Z and RuH-Z, contributing to the higher catalytic activity. A poisoning study with potassium thiocyanate (KSCN), which passivates Lewis acidic sites, suggests that RuZS 90 yields no considerable oxidised furanic products, confirming the crucial role of Lewis acidic sites. The NH 3 -DRIFT study further corroborates that RuZS 90 contains more enhanced Lewis acidic sites than the parent H-Z, playing a vital role in the oxidation of HMF. Ru impregnated on modified H-ZSM-5 (RuZS 90), possessing enhanced Lewis acidic sites, exhibits about 20 and 3 times higher catalytic activity in terms of furanic products than parent H-ZSM-5 (H-Z) and Ru on parent H-ZSM-5(RuH-Z) due to the critical role of Lewis acidic sites. [Display omitted] [ABSTRACT FROM AUTHOR]