Unravelling carbon formation behaviour and long-term stability of dry reforming of methane over Ru-doped ceria-zirconia catalyst

Carbon formation has long posed a significant challenge in an application for dry reforming of methane (DRM). The focus of this study was to understand carbon formation over the surface of a hydrothermally synthesised ceria-zirconia catalyst with a small amount (0.10 wt%) of ruthenium dopant. The characterisation of textural properties for both fresh and post-reaction samples was conducted through nitrogen adsorption-desorption and X-ray diffraction analysis. Hydrogen temperature programmed reduction (H2-TPR) was performed to examine reducibility of the catalyst samples before and after the DRM reaction. Characteristics of carbon formed during the DRM reaction at 600 °C (low temperature) and 850 °C (high temperature) were investigated using temperature programmed oxidation (TPO) coupled with a mass spectrometer, transmission electron microscopy (TEM) and Raman spectroscopy. The results revealed that at 600 °C, both amorphous carbon and graphitic carbon were observed, accounting for 0.70 wt% in total of the sample mass. On the other hand, only amorphous carbon was formed at 850 °C with 2.33 wt%. The average carbon deposition rates were 0.07 mg-C/(g-cat·h) at 600 °C and 0.23 mg-C/(g-cat·h) at 850 °C. Despite the carbon formation, it did not deactivate the catalysts at either temperature and remained high and stable catalytic conversions of CH4 and CO2, i.e., 41.3 % and 56.3 % at 600 °C, 92.6 % and 97.4 % at 850 °C over the 100 h DRM reaction.