Comparison of hydrochar- and pyrochar-based solid acid catalysts from cornstalk: Physiochemical properties, catalytic activity and deactivation behavior.

Biochar made from biowaste provides renewable carbon precursors for catalysts preparation. Here, solid acid catalysts were prepared through functionalizing biochars produced via hydrothermal and pyrolytic carbonization of cornstalk with -SO3H groups. Hydrochar-based catalysts (HAC) and pyrochar-based catalysts (PAC) exhibited significantly different physiochemical properties, catalytic activities and deactivation behaviors. The test of catalytic effects on cellulose degradation uncovered that HAC had a higher density of -SO3H but lower surface special area than PAC. Specifically, PAC prepared at 400 °C resulted in the maximum increase of cellulose conversion by 16.00-50.50%. In comparison, the highest yields of glucose (11.14%) and 5-hydroxymethylfurfural (29.54%) were achieved catalyzed via HAC prepared at 240 °C. The results of catalyst deactivation behavior further revealed that used catalysts had an obvious reduction of -SO3H density. Interestingly, used HAC-240 catalysts showed similar patterns of weight loss to fresh ones due to its high stability.