Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ZrO2

Coke deposition is one of the main challenges in the commercialisation of dry reforming of methane oversupported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for thecatalyst lifetime. Accordingly, in this study, we analysed the effect of Na, K, and Cs promoters on boththese variables over Ni/ZrO2catalysts. Besides blocking the most active coke-forming sites already at lowloading, the promoting effect of the alkali metals is also contributed to by their coke gasification activity.To evaluate the additional impact of the latter, the behaviour of alkali-doped catalysts was compared tothat for Mn-doped catalysts, exclusively featuring the site-blocking promotion mechanism. While theconversion is barely affected by the type of promoter, it has a profound effect on the amount and thecomposition of carbon deposits formed during the reaction. Promoting with K or Mn reduces the cokecontent to a similar degree but with less carbon fibres observed in the case of K. The promotion by Cs andNa results in the lowest coke content. The superior performance of Cs and Na-doped Ni/ZrO2catalysts isattributed to the enhanced coke gasificationviacarbonate species on top of the site blocking effects.