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 (CoS2) can be competent in both acid hydrolysis and hydrogenolysis reactions as an inexpensive heterogeneous catalyst by controlling its morphology. Two kinds of CoS2 with imperfect spherical (A-CoS2) and regular octahedral (Syn-CoS2) morphologies were tested in the conversion of 5-hydroxymethylfurfural (HMF) under a hydrogen atmosphere. Interestingly, A-CoS2 showed high activity in the hydrogenolysis of HMF to 2,5-hexanedione (2,5-HD) with a yield of 81.5 wt%, while Syn-CoS2 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-CoS2 had higher Co2+/Co3+ ratio in comparison to A-CoS2, 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-CoS2 exhibited high selectivity to ML formation from cellulose and good recyclability.

Automated summary

This study reports that cobalt disulfide can act as an inexpensive heterogeneous catalyst in both acid hydrolysis and hydrogenolysis reactions by controlling its morphology. Two different morphologies of the catalyst exhibited different activities and selectivities in the conversion reactions.