In situ XAFS investigation of Ca and K catalytic species during pyrolysis and gasification of lignite chars

A newly developed X-ray absorption fine structure (XAFS) spectroscopy technique was used to examine, in situ, the catalytic behaviour and properties of highly dispersed carboxyl-bound Ca and K in lignites, chars and related materials during pyrolysis and gasification. With this technique, the spectral changes noted for Ca at temperatures up to 420 °C were relatively minor (peak broadening, enhancement of minor pre-edge features, and slight CaO bond distance contraction) and not fully reversible. Such changes are consistent with rearrangement of the Ca site due to loss of volatile species molecules from the immediate coordination sphere around Ca. For K, similar minor changes were found during pyrolysis to 420 °C, but upon exposure to O2 and an increase in temperature to 500 °C, significant nonreversible spectral changes were observed that appeared consistent with transformation of the K catalytic species into K2CO3.