Catalytic conversion of volatiles over homologous char: Distinct interaction patterns at different temperatures

Char produced at specific pyrolysis temperatures has specific surface properties, which is also expected to have specific interaction patterns with volatiles produced at the same temperature. In this study, the char produced at varied temperatures was used for catalyzing conversion of homogenous volatiles generated at the same temperature. The aim was to explore the change of properties of char catalyst via volatiles-char interaction, which was almost equivalent to the evolution of property of char in pyrolysis. The results suggested that the char-300 (the number refers to temperature (degrees C) for production of char) and char-450 retained abundant oxygen-containing functionalities, rendering them superior activity for cracking of aliphatics and aromatics, producing less bio-oil with a lower abundance of pi-conjugated structures but more gases (especially over char-450, increased by 57.8%). Char-600 and char-750, with a lower abundance of oxygen-containing functionalities, were not that active for cracking or interaction with volatiles, and their properties were also not changed that much. In comparison, the spent char-300 and char-450 experienced remarkable dehydrogenation and deoxygenation via interaction with volatiles, resulting in overall net weight loss, increased carbon content as well as enhanced thermal stability, aromatic degree, and carbon crystallinity. The biggest change of char-600 and char-750 could be the filling of pores with volatiles-derived deposits. The characterization of catalytic pyrolysis with in-situ IR technique also confirmed that the char-300 showed higher capability than char-750 for catalyzing conversion -OH and CO via varied reaction routes.