Catalytic upgrading of ex-situ heavy coal tar over modified activated carbon

•KOH and steam are excellent activators for preparing a high-efficiency AC catalyst.•Light tar content shows good linear relationship with mesoporous surface area of AC.•Removal of the minerals in AC is unbeneficial to tar upgrading.•Modified AC is conductive to the formation of benzenes and naphthalenes. Commercial activated carbon (AC) was modified by steam activation (ST) and chemical activation (AT), and their catalytic upgrading of ex-situ heavy coal tar was investigated. The results show that both AT and ST methods could significantly increase the total surface area, promote the formation of mesopores, and further improve the catalytic upgrading performances. The light tar content was increased to 90.5% over AC-0.25ST and 85.0% over AC-2AT, respectively. The specific textural properties of AC exerted an obvious effect on the resultant tar quality, and a good linear relationship between light tar content and mesoporous surface area of AC was first revealed. The removal of minerals in AC is unbeneficial to the tar upgrading, suggesting that the minerals play a catalytic role. The modified ACs could obviously increase the contents of light oil and naphthalene oil, and the pitch content was declined to 9.5% over AC-0.25ST. H2 and CH4 yields were also remarkably increased during tar upgrading. The resultant ACs exhibited good selectivity to benzenes and naphthalenes during tar upgrading, along with a decrease in aliphatic compounds and more than 3-ring polycyclic aromatic hydrocarbons (PAHs), and 50.3% and 47.2% naphthalenes were acquired over the AC-0.25ST and AC-2AT, respectively. This study is expected to guide the preparation of upgrading catalysts and the products regulation during the catalytic upgrading of heavy coal tar.