Gold, still a surprising catalyst: Selective hydrogenation of acetylene to ethylene over Au nanoparticles

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.