NiK catalysts supported on CeyZr1-yO2-Al2O3 (NiK/xCeZr-Al) (x = 0, 5, 10, 20, 30, and 40) systems were prepared as novel catalysts for cracking of vacuum residue with steam and their catalytic performances were tested using a fixed bed reactor at 500 degrees C and under atmospheric pressure. The addition of Ce and Zr was found to greatly improve the catalytic performance, increasing the total yield of liquid plus gaseous products as well as the H/C ratio of the liquid products. Active oxygen species were generated from steam over zirconia particles and then spilled over the CeyZr1-yO2 surface, where oxidative cracking of heavy oil occurred to produce CO2 and lighter molecules. Active hydrogen species obtained from steam decomposition were then added to these lighter molecules on nickel active phases, resulting in the increased H/C ratio of the liquid products. Oxidative cracking with steam over NiK/CeZr-Al catalysts has great potential as industrial processes of vacuum residue cracking. (C) 2016 Elsevier Ltd. All rights reserved.