Effects of alkali and alkaline earth metals of inherent minerals on Fe-catalyzed coal pyrolysis

In this work, the effects of alkali and alkaline earth metals (AAEM (K, Na, Ca and Mg)) on Fe (5 wt%) loaded-coal pyrolysis were conducted using the fixed-bed reactor at 700 °C with 0.1 MPa N2. The coal was pretreated by HCl and HF aqueous solutions (De-2 coal). These effects were investigated with AAEM additive into Fe loaded De-2 coal. The results indicate that K, Na, Ca and Mg (0.1 wt%-1.5 wt%) enhanced the catalytic effect of Fe catalyst, leading to the high H2 selectivity (59.34 ml/g →85.94 ml/g), as well as the low yield toward CO2 (157.50 ml/g →148.62 ml/g), and the catalytic activity follows the order of Na ≈ K > Ca > Mg. Characterization results reveal that the inherent AAEM promote the reduction of Fe species and the dispersion of Fe particles. The reason for that was AAEM combined with oxygen-containing functional group generated C–O-AAEM and COO-AAEM, and released active oxygen sites to activate carbon sites, leading to Fe catalyst bound with active oxygen sites formed iron oxide and Fe-(O)–C on char surface. This study was helpful to understand the promotion mechanism of AAEM on Fe catalyzed coal pyrolysis.