Effect of reducibility of transition metal oxides on in-situ oxidative catalytic cracking of tar

To understand the effect of reducibility of transition metal oxides (TMOs) on tar conversion, four TMOs including Fe2O3, MnOx, CuO, and NiO were selected and in-situ oxidative catalytic cracking of coal pyrolysis tar on a two-stage fixed bed reactor at 550 degrees C was performed. The reducibility of TMOs was measured by H-2-temperature programmed reduction (H-2-TPR). The effect of reducibility of TMOs on the pyrolysis products distribution and conversion was investigated. The changes of TMOs before and after reaction were also analyzed by several characterizations. The addition of TMOs results in the decrease of tar yield and heavy tar content, and the increase of gas yield. The reduction temperature of TMOs affects the products distribution and heavy tar conversion. Among these four TMOs, Fe2O3 shows the highest reduction temperature (390-700 degrees C with peak centered on 570 degrees C) and the largest heavy tar conversion (75.3 wt%). CuO shows the lowest reduction temperature (190-470 degrees C with peak centered on 326 degrees C) and heavy tar conversion (45.8 wt%). The main reactions on CuO is complete oxidation with high water yield (12.8 wt%) and CO2 formation (110 mL/g.coal(daf)). The coke formed on the used Fe2O3 is amorphous or disordered carbon, and shows the largest yield being 5.5 wt%.