XPS study on the change of carbon-containing groups and sulfur transformation on coal surface

 Two Chinese coals, Liuzhi (LZ) and Zunyi (ZY), were pyrolyzed in a fixed bed reactor under N₂ and H₂ atmospheres from 400℃ to 700℃. X-ray Photoelectron Spectroscopy (XPS) was used to study the changes of carbon-containing groups and sulfur transformation on the surface of coals and their chars. Under N₂ atmosphere, on the ZY chars surface, the contents of O=C－O, C－H or C－C groups have a decreasing trend and the one of C=O or O－C－O, C－O is increasing compared with that of raw coal at all temperatures. For LZ coal, the changes of O=C－O, C=O or O－C－O, C－O contents are similar to ZY coal, however the one of C－H and C－C content is contrary to that of ZY coal. Under H₂ atmosphere, for ZY coal, not only O=C－O content, but also C=O and O－C－O, C－O contents have a decreasing trend, while C－H and C－C contents increase compared with raw coal; for LZ coal, except for C=O and O－C－O content has a decreasing trend, and other carbonyl groups have the same trend as that under N₂ atmosphere. And for these coals, with the temperature increasing, the S/C ratio on the char surface increases under N₂ atmosphere, however the one decreases at the temperatures from 400℃ to 600℃ and increases much at 700℃ under H₂ atmosphere. This indicates that under both atmospheres, sulfur can transfer from inner to the surface during pyrolysis, but hydrogen can react with sulfur-containing radicals, so the S/C is lower than that under nitrogen.