Hydrogen production via propane dry reforming: Carbon deposition and reaction-deactivation study

Carbon deposition during carbon dioxide reforming reaction of C₃H₈ has been studied over alumina-supported bimetallic Mo/Co–Ni catalysts. To better understand the carbon-induced deactivation during the reforming reaction, changes in catalyst morphology and carbon deposition kinetics were examined. Different characterization techniques were used for both fresh and rejuvenated catalysts including liquid nitrogen adsorption/desorption, chemisorption via hydrogen, ammonia and CO₂ desorption, and thermogravimetric measurement of the coked catalysts. The time dependant reaction rate profiles indicated that Mo–Ni catalyst has higher syngas (H₂/CO) formation rates with lower CO₂ rate of consumption compared to Co–Ni catalyst. However, the H₂:CO ratio values were almost the same for both catalysts suggesting similarity in the product formation pathway. Conversion-time analysis showed that Mo–Ni catalyst was more stable and active during a 72-h run while Co–Ni suffered noticeable deactivation after 30 h on-stream. Reaction-deactivation models implicated a higher deactivation coefficient (k_d) with activation energy of E_d = 78.1 kJ mol⁻¹ for the cobalt-containing Ni catalyst, while the Ni catalyst with molybdenum had a lower deactivation coefficient with smaller activation energy of just under 70 kJ mol⁻¹. Post-mortem analysis (TPR-TPO dual cycle and TOC) of spent catalysts confirmed that the surface of Co–Ni catalyst has more carbon residue than the Mo–Ni sample which was consistent with the higher deactivation of Co–Ni.