RESUMO
Dry reforming of methane was carried out over La2-2xRu2xO3 (x = 0.005, 0.01). Substitution of just 0.5 atom% of Ru in La2O3 enhanced the activity by 20 times in terms of conversion when compared to the activity exhibited by La2O3. The oxygen storage capacity of the Ru doped sample was considerably higher than undoped La2O3, which resulted in higher conversions of CH4 and CO2. The measured conversion of CH4 and CO2 was 72 and 80%, respectively, at 850 °C. The same was merely 4% with La2O3 under the same experimental conditions. DRIFTS studies demonstrated the role of a specific type of carbonates in promoting the activity of the catalyst. DFT calculations provided the rationale behind the selection of the Ru-in-La2O3 methane dry reforming catalyst. The surface structures of the pure and Ru-substituted compounds were determined, corroborating the experimental observation of enhanced oxygen storage capacity on Ru substitution. Different active surface oxygen species were identified and their roles in improving reducibilities and improving reactivities were established. The experimentally observed surface carbonate species were also identified using calculations. The combined experiment + calculation approach proved ionic Ru in La2-2xRu2xO3 to be a novel and efficient dry reforming catalyst.
RESUMO
The synthesis of novel and efficient catalysts for acetylene hydrogenation exhibiting high selectivity towards ethylene is important due to the presence of selective acetylene hydrogenation reaction in petrochemical processing. Since adsorption of C2 gases constitutes the primary step in catalytic hydrogenation and governs the selectivity of the catalysts, we have explored the C2-adsorption potential of reducible CeO2-based systems. The adsorption of C2-gases over CeO2-based materials was assessed using experimental in situ spectroscopic techniques and in silico theoretical studies based on density functional theory. The effect of Pd2+ substitution on adsorption was studied. The addition of Pd2+-ions was found to enhance the adsorption of the gases. Theoretical calculations provided insights into the modes of adsorption, adsorption energetics and reactant-catalyst interactions. The role of the presence of cationic substitution and anionic vacancies in strengthening the adsorption of gases was established. Pd-substituted reduced CeO2 showed activity for the adsorption of all C2 gases. On the basis of the aforementioned experimental and theoretical observations, the catalysts were tested for acetylene hydrogenation, and Pd-substituted CeO2 was found to be a good catalyst for the reaction with complete acetylene conversion observed below 100 °C.
