In-situ catalytic upgrading of coal pyrolysis tar coupled with CO2 reforming of methane over Ni-based catalysts

Tar was upgraded by integrating in-situ catalytic cracking of coal pyrolysis tar with CO2 reforming of methane (CRM) over Ni-based catalysts to improve light tar yield. The results showed that Ni-based catalysts can catalyze coal tar cracking and CRM simultaneously, and some radicals, like H and CHx, produced in CRM over Ni-based catalysts could combine with the radicals from catalytic cracking of tar to avoid excessive cracking of tar. The catalyst 5Ni/Al2O3 (Ni/Al2O3 with 5 wt% Ni) showed the best performance for tar upgrading owing to its appropriate activity of both tar cracking and CRM. Compared with non-upgrading tar, the average molecular weight of upgrading tar over 5Ni/Al2O3 decreases from 279 to 193 amu, and the content and yield of light tar (boiling point < 360 °C) over 5Ni/Al2O3 increase by 53% and 32% at 650 °C. The contents of light fractions increase and that of pitch decreases apparently. The light components, such as benzenes, phenols and naphthalenes, are all improved, and long aliphatic chains and aromatics with 3 or 4 rings have an obvious decrease. Active components in upgrading catalysts obviously affect the upgrading effect of coal tar. 5Ni/Al2O3 exhibits higher content and yield of light tar compared with 5Co/Al2O3 and 5Fe/Al2O3.