Abstract

This study shows how CeO₂/ZnO nanocatalysts were prepared by combining homogeneous precipitation with micro emulsion using a conventional heating technique. The catalysts were then used in a conventional fixed bed reactor for the oxidative coupling of methane using carbon dioxide as an oxidant. Catalyst performance tests were carried out at atmospheric pressure, feed gas of 33 and 45 ml/min, and reaction temperatures was in the range of 700 to 900°C. The effect of adding promoters such as Lithium (Li), Bismuth (Bi), and Zirconium (Zr) in various loadings was studied. In this regard, it was found that proper calcination conditions can yield a nanocatalyst structure. However, the conditions for the occurrence of a nanostructure depend strongly on the type of the added promoter. The effects of the number of operating parameters were studied. Catalysts prepared with Zr were found to be more active and selective to ethylene at high calcination temperatures. Catalysts prepared with Bi, on the other hand, showed better activity at lower reaction temperatures. As with Li, the catalysts showed nearly the same activity at low calcination temperatures. As to the effect of feed ratio of methane to carbon dioxide, catalysts prepared with Li showed good activity and selectivity with the increase in the feed ratio. In opposite, catalysts prepared with Zr showed better activity and selectivity at low feed ratios. As to Bi, the increase in feed ratio has an effect on the catalyst activity but not on the selectivity. The study of the effect of different loading of Zr showed that optimal loadings have to be below 5% in weight.

Key words: Oxidative coupling of methane, carbon dioxide, CeO₂/ZnO catalyst, homogeneous precipitation, micro emulsion.