Catalytic Upgrading of in Situ Coal Pyrolysis Tar over Ni-Char Catalyst with Different Additives

Ni-char catalyst doped with different additives was used to catalytically upgrade coal pyrolysis tar in situ generated in a laboratory-scale dual-stage reactor. The additives including Fe, Mg, Ce, Zr were all beneficial to the catalytic activity for tar cracking. The best result of tar upgrading was achieved with Ce-Ni-char at a Ce-to-Ni molar ratio of 0.4. The upgrading test at 500 degrees C over a layer of such a catalyst (20% of the tested coal mass) increased the light tar (boiling point <360 degrees C) yield by 10.1%, and the light tar fraction in the tar product to 75 wt % from 52 wt %. The corresponding increase in the molar ratio of H to C of the tar was 61.796. About 60% of the pitch in the original tar from coal pyrolysis was cracked in the catalytic upgrading. The contents of element N and S in the tar after catalytic cracking decreased by 50.5% and 45.8%, respectively. NH3 temperature-programmed desorption results revealed that there were weak Lewis and strong Bronsted acidic sites on the Ni-char catalyst, but many more Lewis acidic sites existed on the Ce-Ni-char catalyst. The addition of Ce into Ni-char facilitated the dispersion of nickel and increased the ability of the catalyst for inhibiting coke deposition.