On the coke deposition in dry reforming of methane at elevated pressures

The reaction pathways leading to coke formation in dry reforming on Ni and Pt-based catalysts were investigated. Using isotope-labeled reactants (i.e., CH4 + (CO2)-C-13 reversible arrow 2CO + 2H(2)) showed that initially (CO2)-C-13 is converted faster than CH4 and that this higher activity leads to a higher concentration of (CO)-C-13 compared with (CO)-C-12 in the product stream, suggesting little isotope scrambling among products at this stage. Gasification of carbon deposits was found to be an important pathway enhancing the catalyst stability. Analysis of the pathways leading to carbon deposits suggests that coke is formed predominantly via reverse Boudouard reaction on Ni, while both metals contribute to CH4 dissociation. The pronounced reversibility of the C-H and C-O bond formation and cleavage was also shown by the presence of (CH4)-C-13 formed from (CO2)-C-13 and (CO)-C-12 formed from (CH4)-C-12. Numeric calculations complementing the experimental results led to the proposal of a reaction pathway for the surface reactions, accounting for the differences between Ni and Pt. (C) 2015 Elsevier B.V. All rights reserved.