Kinetics and mechanistic insights into the acidic-basic active sites for water-containing catalytic hydrogenation of hydroxymethylfurfural over ceria-doped Ni/Al2O3

This work presents a novel, systematic experimental and in silico study for hydroxymethylfurfural hydrogenation using ceria-doped Ni/Al2O3 catalysts with and without water-containing media. Despite improvements to reducibility, ceria-doped Ni/Al2O3 catalyst slowed reaction rates and TOFs relative to unpromoted Ni/Al2O3. Nonetheless, the NiCe/Al2O3 catalyst demonstrated enhanced ring opening and ring-saturation capability compared to unpromoted Ni/Al2O3 due to modifications of acidic-basic sites on the catalyst surface. Incorporating water as a co-solvent caused deoxygenation reactions to be essentially eliminated, resulting in 1,2,6-hexanetriol and 2,5-bishydroxmethyltetrahydrofuran as the only main products. Adsorbed water was determined to nullify oxygen vacancies and block strong acidic sites. Pretreating ceria under higher temperatures and in an oxygen-free atmosphere facilitated oxygen vacancy formation, leading to elevated dehydration in the absence of water. However, adding water into the system enhanced 1,2,6-hexanetriol formation and is anticipated to be dependent on the prevalence of basic sites that are associated with surface hydroxyls.