Multiple synergistic effects exerted by coexisting sodium and iron on catalytic steam gasification of coal char

Abstract

Numerous studies have been concerned with inexpensive sodium- and iron-based catalysts for coal gasification. This work aims to investigate the steam gasification of coal char using a Na/Fe bimetallic catalyst. The bimetallic catalyst with an appropriate loading exhibited a higher activity for accelerating the gasification rate than the Na or Fe monometallic catalyst at 700–800 °C. Compared to the sodium catalyst, the bimetallic catalyst was favorable to a higher production of H2 by the reactions with steam. Mechanism study revealed that the coexistence of iron and sodium significantly suppressed the growth of a crystalline Na2CO3 phase and the evaporation of sodium during the gasification leading to the preserve of more sodium as an effective form. Meanwhile, the sodium compounds promoted the reduction of hematite to form α-Fe during the heat-up and the dispersion of iron on the char during the gasification. These interactions were responsible for the transformation of graphitic carbon to amorphous carbon. The bimetallic catalyst could alleviate some shortcomings of the single sodium or iron catalyst.