Dry reforming activity due to ionic Ru in La1.99Ru0.01O3: The role of specific carbonates

Dry reforming of methane was carried out over La<inf>2-2x</inf>Ru<inf>2x</inf>O<inf>3</inf> (x = 0.005, 0.01). Substitution of just 0.5 atom% of Ru in La<inf>2</inf>O<inf>3</inf> enhanced the activity by 20 times in terms of conversion when compared to the activity exhibited by La<inf>2</inf>O<inf>3</inf>. The oxygen storage capacity of the Ru doped sample was considerably higher than undoped La<inf>2</inf>O<inf>3</inf>, which resulted in higher conversions of CH<inf>4</inf> and CO<inf>2</inf>. The measured conversion of CH<inf>4</inf> and CO<inf>2</inf> was 72 and 80%, respectively, at 850 °C. The same was merely 4% with La<inf>2</inf>O<inf>3</inf> 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-La<inf>2</inf>O<inf>3</inf> 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 La<inf>2-2x</inf>Ru<inf>2x</inf>O<inf>3</inf> to be a novel and efficient dry reforming catalyst.