Catalytic activity evaluation and deactivation progress of red mud/carbonaceous catalyst for efficient biomass gasification tar cracking

Abstract

Developing an efficient and inexpensive catalyst to remove tar is critical to biomass gasification technology. Herein, a red mud/carbonaceous catalyst was prepared by in-situ carbothermal reduction of sawdust and red mud and used in tar catalytic cracking with a two-stage fixed-bed reactor. Through the carbothermal reduction process, the catalyst was not only endowed with a porous carbon structure, but also reduced Fe2O3 in red mud to Fe0, which was beneficial to improve the catalytic activity and stability of the catalyst. The tar conversion efficiency of RM/SD catalyst reached 88.70% at the catalytic cracking temperature of 700 °C, which remained at 80.15% after nine cycles compared with RM (61.79%). The catalytic activity and deactivation progress of RM/SD catalyst were investigated by a variety of characterizations for the chemical states, crystallite sizes and pore structure of RM/SD catalyst after different cycles. Coke deposition and metal oxidation were the main reasons causing catalyst deactivation. During the tar catalytic cracking process, alkaline metals in red mud migrated to the surface of catalyst and cooperated with Fe active phase, which promoted the gasification of coke and alleviated the rapid deactivation of catalyst derived from coke deposition. Meanwhile, the presence of carbon support delayed the oxidation of metal active phase and made the catalyst keep a good tar catalytic cracking performance. Therefore, a potential scheme is proposed for the development and utilization of bauxite residue and forestry wastes for tar cracking.