Thermogravimetric analysis of coking during dry reforming of methane

Nickel-based catalysts used for dry reforming of methane (DRM) suffer from coking and sintering, which hinders the broad application of the process in the industry. Thermogravimetric analysis was employed to investigate coking on a commercial nickel catalyst with an anti-coking additive (CaO). It was found that the catalyst sintered at temperatures between 850 and 900 °C, which resulted in permanent catalyst deactivation. For the tested Ni/CaO–Al₂O₃ catalyst, the coking and carbon gasification rates are equal at the temperatures of 796–860 °C, depending on the heating rate (5–20 K/min). Significant differences in the temperatures related to the maxima on TG curves for various heating rates follow from DRM kinetics. This work reveals that the coking rate is lower at higher temperatures. After 50 min, the weight gains amount to about 20% and 40% at 800 °C and 600 °C, respectively. Lower sample weight gains were observed at higher temperatures for a methane decomposition reaction over the Ni/CaO catalyst, unlike for the second tested catalyst – activated carbon. For the nickel catalyst, the reaction order for methane decomposition is 0.6 in the temperature range 640–800 °C, while the sign of the activation energy changes at 700 °C. The elaborated kinetic equation predicts the initial CH₄ decomposition rate with 15% accuracy.