The hydrogenation of C(2)H(2) in the presence and the absence of C(2)H(4) has been studied over un-promoted and promoted Au/Al(2)O(3). A number of parameters have been varied: the Au particle size, the pre-treatment conditions (hydrogen versus oxygen) and the nature of the promoters. Promoters include ceria, lithium and barium oxides. Our results show that hydrogenation of C(2)H(2) proceeds with 100% selectivity towards C(2)H(4), both in the presence and the absence of C(2)H(4). Moreover, there is a strong dependence of the catalytic performance on the size of the Au particles: Au particles below 3 nm enhance the C(2)H(2) conversion both in the absence and the presence of C(2)H(4), without decreasing the selectivity to C(2)H(4). Furthermore, metallic Au and Ce(4+) appear to be more effective than Au(3+) and Ce(3+). Our findings also indicate that Li(2)O has a beneficial effect on C(2)H(2) conversion, while BaO has a slight detrimental effect, both having no influence on the selectivity to C(2)H(4). The key to 100% selectivity to C(2)H(4) resides in non-competitive adsorption of C(2)H(2) and C(2)H(4) on the Au surface when both hydrocarbons are present in the feed. The deactivation during C(2)H(2) hydrogenation is a reversible process and is due to accumulation of C deposits on the catalyst surface, as result of C(2)H(2) adsorption on different active Au sites. These deposits can be easily burned off by a thermal treatment in oxygen. (C) 2010 Elsevier B.V. All rights reserved.