To remove H2S and NH3 simultaneously from coal-based synthesis gas, Zn-Al-based sorbents promoted with transition metals such as cobalt, nickel and iron additives were prepared by the co-precipitation method. The decomposition of NH3 and the absorption capacities of H2S of the sorbents were studied in a micro-reactor at 1 atm and 650 degrees C. The additives, cobalt, nickel and iron, were found to be active components in the NH3 decomposition reaction as well as in the absorption of H2S, while the major components, ZnO and Al2O3, did not show any activity in the NH3 decomposition reaction. Especially, cobalt oxide showed excellent NH3 decomposition ability, regardless of the H-2 concentration, while the ability of iron and nickel oxides depended on the H-2 concentration. After the oxides were converted to the sulfide form, the NH3 decomposition rates over the cobalt and nickel sulfides were dramatically decreased in the presence of excess H-2. Optimized Zn-Al-based sorbent promoted with cobalt oxide was prepared and showed excellent NH3 decomposition ability under a gas composition of 11% H-2, 1% H2S and 0.5% NH3, which was due to the improvement of its physical properties such as its surface area, pore size and pore volume, and nano-particle size. (C) 2008 Elsevier B.V. All rights reserved.