Insight into the role of varied acid-base sites on fast pyrolysis kinetics and mechanism of cellulose

Abstract

In the present research, a series of metal oxides were employed to investigate the role of varied acid-base site on kinetics and mechanism for catalytic fast pyrolysis of cellulose using TG-MS and Py-GC/MS. The results showed that the modulation of acidity-to-basicity value via altering metal oxides constituents significantly affected the transformation pathway for cellulose pyrolysis. Higher acidity-to-basicity ratios accelerated the proceeding of deoxygenation process, wherein 39.4% aromatics and 34.7% aliphatic hydrocarbons were achieved using Al₂O₃ (acidity-to-basicity value of 1.38) at 750 °C with a catalyst/cellulose mass ratio of 15:1. In comparison, lowering acidity-to-basicity ratios mainly facilitated the ketonization and aldol condensation, therefore over 70% ketones was attained in the case of CaO catalysis. The kinetic studies further verified the promotional role of acid-base sites on cellulose pyrolysis with apparent activation energy as low as 33.72 kJ/mol, in comparison with that of cellulose pyrolysis without adding catalysts. From another aspect, the composite metal oxides with better porous structures contributed to deoxygenation conversion for the production of aromatics and aliphatic hydrocarbons. Moreover, plausible reaction pathway for cellulose pyrolysis over metal oxides was proposed. This work would provide a good reference for the realization of product regulation from cellulose pyrolysis via adjusting acid-base sites in metal oxides.

Keywords: Acid-base site; Catalytic pyrolysis; Kinetics; Pyrolysis mechanism.