Plasma-assisted catalysis has been employed for the degradation of benzene by hybrid surface/packed-bed discharge (HSPBD) plasmas over a series of Ag-x Ce1-x/gamma-Al2O3 catalysts in in-plasma catalysis (IPC) and post-plasma catalysis (PPC) configurations. In order to study the influence of catalysts placement on discharge characteristics and the consequent synergetic effect in plasma-catalysis process, the catalysts were introduced inside and downstream the surface discharge region (region I) and packed-bed discharge region (region II), respectively, and the benzene degradation performance was investigated in these systems. The effects of the Ag/Ce molar ratio and water vapor have also been investigated in terms of benzene degradation efficiency and CO2 selectivity. Compared with the plasma-only process, the combination of plasma with Ag-x Ce1-x/gamma-Al2O3 catalyst significantly improved the reaction performance, and the combined degradation efficiency is a synergistic effect rather than simply an additive effect. Besides, the emission of discharge products (O-3 and NOx) and hazardous intermediates (formic acid and CO) was markedly suppressed with the introduction of catalyst. The highest benzene degradation efficiency of 96.2% and CO2 selectivity of 77.3% can be achieved with Ag0.9Ce0.1/gamma-Al2O3 catalyst at the SIE of 400J/L. This result suggests that the interaction between a certain proportion of Ag and Ce species over the catalyst is capable of activating the surface lattice and generating more surface adsorbed oxygen (O-ads), which favors the plasma-catalytic oxidation reaction. PPC processes can decompose O-3 and destroy benzene more effectively than IPC processes, especially when the catalyst was introduced downstream the region II. Adding a small amount of water vapor into plasma-catalysis system enhanced the catalyst activity, however, further increased the water vapor caused an obvious negative impact on the catalyst activity. (C) 2015 Elsevier B.V. All rights reserved.