Catalytic Decomposition of N<sub>2</sub>O in the Presence of O<sub>2</sub> through Redox of Rh Oxide in a RhO<sub><i>x</i></sub>/ZrO<sub>2</sub> Catalyst
Yuan Jing, Koichiro Taketoshi, Ningqiang Zhang, Chenxi He, Takashi Toyao, Zen Maeno, Teppei Ohori, Naoya Ishikawa, Ken‐ichi Shimizu
Abstract
The removal of N2O from the atmosphere by its catalytic decomposition to N2 and O2 is an important process for curbing global warming. In this study, we investigated a variety of catalysts, and a ZrO2-supported RhOx (RhOx/ZrO2) catalyst was identified as the optimum catalyst for N2O decomposition at a relatively low temperature (∼350 °C) in the presence of O2. RhOx supported on ZrO2 performs better than RhOx loaded on other supports, as well as other metal oxides supported on ZrO2 and Cu- and Fe-based zeolite catalysts. The average particle sizes of RhOx in RhOx/ZrO2 at Rh loadings of 1, 5, 10, and 15 wt % were 1.5, 1.9, 2.0, and 2.5 nm, respectively. According to the catalytic decomposition rate per Rh used, the loading amount of Rh species has a significant impact on the efficiency of N2O decomposition, with the optimal Rh loading being 10 wt % (Rh metal basis). The apparent activation energy (Ea) for the catalytic decomposition of N2O over RhOx/ZrO2 with 10 wt % Rh was 111 kJ mol–1, which is almost the same as that for bulk Rh2O3 (110 kJ mol–1). These results suggest that the RhOx species in relatively large particles serve more effectively as catalytically active sites compared to those in particles smaller than 1.5 nm. Moreover, kinetic studies and in situ/operando X-ray absorption spectroscopy studies revealed that the reaction is mediated by the redox cycles of the RhOx species, during which N2O acts as an oxidizing agent to fill the oxygen vacancies that are created upon heating with concomitant formation of molecular O2.