Effects of Si and Al elements in coal on Fe-catalyzed brown coal pyrolysis

•Si and Al (content 1.0 wt%;•The Fe-O-Si and FeO.Al2O3 attenuated catalytic activity of Fe-loaded coal pyrolysis. In our previous work, the experiments mainly investigated the effects of inherent minerals (K, Na, Ca and Mg) on Fe catalyst (5 wt%), respectively. Currently, the effects of Si and Al on Fe catalyst were further explored, and the aim is to improve the catalytic activity of Fe-catalyzed coal pyrolysis. The results indicate that the activity of Fe catalyst is improved with the increase of Si or Al content (0.1–1.0 wt%), and the promotion is affected by the ash content of coals. Simultaneously, Si or Al inhibits the activity of Fe catalyst with the increase of content (>1.0 wt%). The reasons were that Si surface substituted the hydroxyl of FeOOH in Fe catalyst to form Fe-O-Si which hindered the reduction of FeO to Fe, and Al2O3 inhibited the FeO reduction through the generation of FeO•Al2O3. The activity of promoters (K, Na, Ca and Mg) on Fe catalyst was investigated. The results reveal that Ca-Fe compounds in raw coal facilitate the formation of H2, and Mg-Fe compounds promote the generation of liquid. The work was beneficial to further understand the promotion/inhibition of Si and Al for Fe-catalyzed coal pyrolysis.