Dry reforming of methane at elevated pressures

The dry reforming of methane (CO₂ + CH₄ → 2 H₂ + 2 CO) can be an alternative to steam (CH₄ + H₂O → 3 H₂ + CO) or autothermal reforming for the production of CO rich syngas. However, its high tendency to coking has prevented the process from been applied in chemical industry. Due to pricing and availability base metals are preferred as active metals in dry reforming, even though they are more prone to coke deposition. To overcome this drawback and create suitable base metal catalysts, a detailed understanding of the carbon deposition mechanism is mandatory.

In the work presented we compare the reactions leading to coke buildup on Nickel and Platinum at reaction conditions close to technical application (850°C, 10bar). We analyzed the deposited coke by reactant isotope labeling (¹³CO₂), SEM, TEM and TPO and revealed that the main deposits after 2 hours of reaction are carbon-nano-tubes. The coke formation on the Ni catalyst was about ten times higher compared to the Pt catalysts. The isotope composition of the coke indicated that on the Nickel both reactants (¹²CH₄ and ¹³CO₂) contributed to the carbon formation, whereas on Platinum coke was formed predominately from ¹²CH₄. Numerical simulations of the reaction rates of the individual pathways support the experimentally derived kinetic results and give insights in the main reaction routes on the catalytic surfaces. Based on the findings we propose a carbon deposition mechanism that explains the stronger resistance of Pt based catalysts against coking.