Effects of various pyrolysis temperatures on the physicochemical characteristics of crop straw-derived biochars and their application in tar reforming

As a by-product of the rapid pyrolysis of biomass, biochar not only plays an important role in the biomass conversion process but also holds significant potential value in the catalytic conversion field. This study aimed to evaluate the physicochemical properties changes of biochars at different pyrolysis temperatures and their potential application in tar reforming. Biochars derived from three feedstocks of maize straw (MS), rice husk (RH), and cotton straw (CS) were achieved by fast pyrolysis within a broad temperature range of 300~900 °C, respectively. The results showed that the pyrolysis temperature exerted a pronounced influence on the structural characteristics of biochar. With increasing temperature, the H/C and O/C ratios progressively decreased, accompanied by a significant reduction in oxygen-containing structures. In addition, elevated pyrolysis temperatures contributed favorably to the formation of the crystalline structure of biochar. Raman analysis unveiled a correlation between the fused aromatic ring system and H/C ratios, validating the aromatization progress of biochar. In the tar catalytic reforming process, the three representative biochars, under the effect of MS-600 (standing for MS biochar derived at 600 °C), RH-600, and CS-600 catalysts, exhibited outstanding catalytic performance with tar conversion efficiencies of 73.26%, 68.51%, and 71.43%, respectively. This study provided systematic support for the high-value use of biochar from crop straw.