Exploring kaolinite as dry methane reforming catalyst support: Influences of chemical activation, organic ligand functionalization and calcination temperature

Kaolinite, the main mineral in raw kaolin clay (RK) was explored as catalyst support for dry methane reforming (DMR) to produce syngas. Due to the inactiveness of the RK, it was activated by 5 M HCl and 5 M NaOH to produce acid treated kaolinite (ATK) and base treated kaolinite (BTK) catalyst supports, respectively. Two types of Ni active metal was incorporated into the modified supports, the first was the conventional nickel nitrate salt, and the second, organometallic nickel precursor synthesized via oxalate ligand functionalization (OxLF) of nickel particles. All the synthesized catalysts were calcined at 700 or 800 degrees C to study the effect of thermal treatment. The characterization results showed that OxLF was able to restrict the loss of Ni during washing and filtering at the synthesis stage according to the XRF result. The BTK support summarily transformed into SOD zeolite. Furthermore, the BTK supported catalyst showed comparable higher basicity than the ATK supported, however, as calcination temperature increases, there is loss of basic sites in both ATK and BTK supported catalysts, increase in the Ni mean particle sizes, and decrease in the Ni dispersion which cumulatively reduced the reaction rates leading to lower syngas yield. Irrespective of the catalyst support type and the calcination temperature, the oxalate ligand functionalized catalyst showed the lowest Ni mean particle sizes, highest metal dispersion and their Ni2p(3/2) peaks were observed to shift towards lower binding energy according to the XPS results signifying higher reducibility which was verified by H-2-TPR. The most efficient catalysts was NiOx/BTK-700 with 21.85% and 28.49% yield of H-2 and CO, respectively. It also has the highest activity stability after 20 h TOS. The results showed that kaolinite is a possible future catalyst support for DMR.