The importance of cobalt disulfide morphology for cellulose depolymerization: Hydrogenolysis versus acid catalysis

Acid-catalyzed hydrolysis and metal-catalyzed hydrogenolysis are two important methods for conversion of cellulose into high value-added chemicals, which preferentially use homogeneous acids and precious metals as catalysts, respectively. This paper reports that cobalt disulfide (CoS 2 ) can be competent in both acid hydrolysis and hydrogenolysis reactions as an inexpensive heterogeneous catalyst by controlling its morphology. Two kinds of CoS 2 with imperfect spherical (A-CoS 2 ) and regular octahedral (Syn-CoS 2 ) morphologies were tested in the conversion of 5-hydroxymethylfurfural (HMF) under a hydrogen atmosphere. Interestingly, A-CoS 2 showed high activity in the hydrogenolysis of HMF to 2,5-hexanedione (2,5-HD) with a yield of 81.5 wt%, while Syn-CoS 2 was responsible for the acid hydrolysis of HMF to methyl levulinate (ML) in high yield of 90.8 wt%. Characterization of the two catalysts suggested that Syn-CoS 2 had higher Co 2+ /Co 3+ ratio in comparison to A-CoS 2 , leading to a proportional difference in their acid site numbers. The unique activity of these two catalysts was also reflected in the conversion of cellulose. In particular, Syn-CoS 2 exhibited high selectivity to ML formation from cellulose and good recyclability.