Improving the Coke Resistance of Ni-Ceria Catalysts for Partial Oxidation of Methane to Syngas: Experimental and Computational Study

The synthesis of syngas (H₂  : CO=2) via catalytic partial oxidation of methane (CPOM) is studied over noble metal doped Ni-CeO₂ bimetallic catalysts for CPOM reaction. The catalysts were synthesized via a controlled deposition approach and were characterized using XRD, BET-surface area analysis, H₂ -TPR, TEM, Raman and TGA analysis. The catalysts were experimentally and computationally studied for their activity, selectivity, and long-term stability. Although the pure 5Ni/CeO2 catalyst showed high initial activity (∼90%) of CH₄ conversion, it rapidly deactivates around 20% of its initial activity within 140 hours of TOS. Doping of Ni/CeO₂ catalyst with noble metal was found to be coke resistant with the best-performing Ni-Pt/CeO₂ catalyst showed ∼95% methane conversion with >90% selectivity at a temperature of 800 °C, having exceptional stability for about 300 hours of time-on-stream (TOS). DFT studies were performed to calculate the activation barrier for the C-H activation of methane over the Ni, Ni₃ Pt, Ni₃ Pd, and Ni₃ Ru (111) surfaces showed nearly equal activation energy over all the studied surfaces. DFT studies showed high coke formation tendency of the pure Ni (111) having a very small C-C coupling activation barrier (14.2 kJ/mol). In contrast, the Ni₃ Pt, Ni₃ Pd, and Ni₃ Ru (111) surfaces show appreciably higher C-C coupling activation barrier (∼70 kJ/mol) and hence are more resistant against coke formation as observed in the experiments. The combined experimental and DFT study showed Ni-Pt/CeO₂ as a promising CPOM catalyst for producing syngas with high conversion, selectivity and long-term stability suited for future industrial applications.

Mechanistic and multiscale aspects of thermo-catalytic CO2 conversion to C1 products

The increasing environmental concerns due to anthropogenic CO2 emissions have called for an alternate sustainable source to fulfill rising chemical and energy demands and reduce environmental problems. The thermo-catalytic activation and conversion of abundantly available CO2, a thermodynamically stable and kinetically inert molecule, can significantly pave the way to sustainably produce chemicals and fuels and mitigate the additional CO2 load. This can be done through comprehensive knowledge and understanding of catalyst behavior, reaction kinetics, and reactor design. This review aims to catalog and summarize the advances in the experimental and theoretical approaches for CO2 activation and conversion to C1 products via heterogeneous catalytic routes. To this aim, we analyze the current literature works describing experimental analyses (e.g., catalyst characterization and kinetics measurement) as well as computational studies (e.g., microkinetic modeling and first-principles calculations). The catalytic reactions of CO2 activation and conversion reviewed in detail are: (i) reverse water-gas shift (RWGS), (ii) CO2 methanation, (iii) CO2 hydrogenation to methanol, and (iv) dry reforming of methane (DRM). This review is divided into six sections. The first section provides an overview of the energy and environmental problems of our society, in which promising strategies and possible pathways to utilize anthropogenic CO2 are highlighted. In the second section, the discussion follows with the description of materials and mechanisms of the available thermo-catalytic processes for CO2 utilization. In the third section, the process of catalyst deactivation by coking is presented, and possible solutions to the problem are recommended based on experimental and theoretical literature works. In the fourth section, kinetic models are reviewed. In the fifth section, reaction technologies associated with the conversion of CO2 are described, and, finally, in the sixth section, concluding remarks and future directions are provided.

Understanding the origin of structure sensitivity in hydrodechlorination of trichloroethylene on a palladium catalyst

Mechanistic understanding on the origin of structure sensitivity in the hydrodechlorination of trichloroethylene.