Role of cobalt chloride indicator in the methane dry reforming over inexpensive allochroic silica gel supported nickel catalysts

Reducing the catalyst cost by using inexpensive support material is essential to its scale-up application in methane dry reforming (MDR) process. Herein, we report an allochroic silica gel (ASG) supported nickel catalyst for MDR reaction, considering abundant SiO2 resources and its direct granular shape. A series of catalysts were prepared by a facile impregnation method and the role of the contained cobalt chloride indicator was particularly studied. Characterization results implied that the cobalt chloride indicator was transformed into a mixture of cobalt oxides (CoOx) after calcination. The activity tests showed that ASG supported catalyst (Ni/ASG) had lower CH4 and CO2 conversion than the Co-free catalyst supported on ordinary silica gel (Ni/OSG), which is caused by the decreased Ni dispersion after Co addition. Adding Co into Ni/OSG can cause surface aggregation of CoOx species, which is less uniform than Ni/ASG. On the contrary, the 30-h stability test showed that the absence of CoOx species is detrimental to the catalyst durability due to the heavy carbon deposition of Ni/OSG. The origin of coke formation is elucidated from reaction mechanism perspective via in-situ DRIFTS analysis, where both Co-containing and Co-free catalysts are similar in CH4 stepwise dissociation and CO2 breakage forming bridged carbonyls but diverge in the carbonate intermediates. The special existence of carbonate intermediates interfere the desorption process of bridged carbonyls meanwhile enhance the interaction between C radicals and Ni actives, which further accumulate into the substantial deposited carbon.