Impact of Small Promoter Amounts on Coke Structure in Dry Reforming over Ni/ ZrO2

Abstract

Coke deposition is one of the main challenges in the commercialization of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of different metal promoters on both these variables over Ni/ ZrO$_{2}$ catalysts. Alkali metals are known to block the most active coke forming sites already at low loading, leading to an investigation of Na, K and Cs. To analyse the possible contributions of coke gasification activity of the alkali metals, Mn was additionally used as a comparison. While the conversion is barely affected by the type of promoter, it has profound effect on the amount and the composition of carbon deposits formed during reaction: Addition of K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. Promotion by Cs and Na results in the lowest coke content, which is attributed to enhanced coke gasification via carbonate species