Low cost fumed silica modified by amine addition with the ability to remove both carbon dioxide (CO2) and hydrogen sulfide (H2S) was developed. The effect of amine type (polyethyleneimine with a molecular weight of 800 (PEI800), aminoethylethanolamine, N-(3-trimethoxysilypropyl) diethylenetriamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine), loading level and sorption temperature were investigated. The selected sorbent was then evaluated in a single-and double-stage systems. The polymeric amine PEI800 gave the best compromise between the highest CO2 and H2S sorption capacities with minimal amine leaching, and was optimal at a 40% loading level onto fumed silica, in terms of giving the highest breakthrough and saturation capacity. The amount of available amine groups in the sorbent and the interaction between amine groups and CO2 or H2S were the two major factors that affected the sorption capacity and amine efficiency. The sorption of H2S was predominately determined by thermodynamics, while a high temperature helped the diffusion of CO2 molecules from the surface into the bulk of PEI800. The sorbent favored CO2 sorption and the sorbed CO2 hindered the sorption of H2S. However, the sequential sorption of CO2 followed by H2S in a double-stage system was found to solve this problem. (C) 2015 Elsevier Ltd. All rights reserved.