Syngas production from CH4 dry reforming over Co–Ni/Al2O3 catalyst: Coupled reaction-deactivation kinetic analysis and the effect of O2 co-feeding on H2:CO ratio

The dry and oxidative dry reforming of CH4 over alumina-supported Co–Ni catalysts were investigated over 72-h longevity experiments. The deactivation behaviour at low CO2:CH4 ratio (≤2) suggests that carbon deposition proceeds via a rapid dehydropolymerisation step resulting in the blockage of active sites and loss in CO2 consumption. In particular, at high temperatures of 923 K and 973 K, a ‘breakthrough’ point was observed in which deactivation that was previously slow suddenly accelerated, indicating rapid polymerisation of deposited carbon. Only with feed CO2:CH4 > 2 or with O2 co-feeding was coke-induced deactivation eliminated. In particular, O2 co-feeding gave improved carbon removal, product H2:CO ratios more suitable for downstream GTL processing and stable catalytic performance. Conversion-time data were adequately fitted to the generalised Levenspiel reaction-deactivation model. Activation energy estimate (66–129 kJ mol−1) was dependent on the CO2:CH4 ratio but representative of other hydrocarbon reforming reactions on Ni-based catalysts.

Graphical abstractBeneficial effect of O2 co-feeding on H2:CO ratio at 923 K.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Carbon deposition from rapid dehydropolymerisation resulted in loss in CO2 activity. ► Excess CO2 or O2 co-feeding eliminated carbon-induced deactivation. ► O2 co-feeding gave H2:CO product ratios more suitable for downstream processing. ► Deactivation was adequately fitted to a generalised reaction–deactivation model.