Abstract Hydroprocessing of de-ashed coal liquid bottoms (DAO) derived from Victorian brown coal liquefaction was carried out in a fixed-bed reactor loaded with molybdenum catalyst. The conventional hydroprocessing catalyst is deactivated by the preasphaltene contained in the coal liquid bottoms. This deactivation is believed to be due to the fact that nitrogen compounds are strongly adsorbed on the acid sites, and converted into coke-like products by poly-condensation and dehydrogenation. They then cover the hydrogenation sites, which are active sites for DAO conversion to oil. The catalyst CaONiOMoO 3/ Al 2O 3, investigated on the basis of this hypothesis, showed stable activity for a long time and was active for DAO with a high concentration of preasphaltene. Coke analysis of the used catalyst showed that Ca modified catalyst had a lower deposition of coke-like products and a lower nitrogen concentration in the deposit, supporting the hypothesis.