Tar reforming using char as catalyst during pyrolysis and gasification of Shengli brown coal

• Chars derived from brown coal showed excellent catalytic activity for tar reforming.
• The formation of large aromatics in tar was enhanced by the catalytic reforming reactions.
• High activity of activated char was mainly due to more active sites and amorphous carbon structure.

Coal chars were employed to catalyze the in situ tar reforming reactions during the pyrolysis and gasification of Shengli brown coal in a two-stage quartz reactor at different temperatures. Two different chars as catalysts were prepared. One (inactivated char) was prepared from decomposing brown coal in inert atmosphere while the other one (activated char) was obtained with additional 10 min steam activation. It was found that the activated char as catalyst has shown a much better catalytic performance for tar reduction than the inactivated char, especially for the tars from the gasification conditions. The catalytic reforming reactions could also cause the increase in the proportion of large aromatic rings in tars, whereas the presence of steam in the reaction zone could see the decrease of large aromatic rings in tars. The catalysts were characterized by SEM, EDX, BET, XRD and Raman, indicating that the high activity of activated char should be mainly attributed to its amorphous carbon structure, large surface area and abundant metal species (e.g. Na, K, Ca and Mg) on its surface.