(560gg) Improved Catalytic Performance of (RE, TM) Co-Doped Ceria for CO Oxidation

Environmental pollution is becoming a critical issue all over the world, and accordingly, automobile exhaust gas regulations to remove the pollutants such as CO, NO_X, and HC have also been continuously strengthened. Among them, CO is an environmental pollutant that can cause fatal poisoning to humans. The exhaust catalysts working at low temperature to remove it are critical to the automotive industry because they can reduce energy costs and meet regulations. The precious metal catalysts currently used in many applications have high activity, but since they are expensive and limited, it is necessary to design the catalysts using inexpensive metals. As a condition to replace the precious metals, the catalysts using inexpensive metals should have the catalytic activity at least similar to the precious metal catalysts. Furthermore, if those catalysts are proved to have good stability beyond simply having high activity, they would bring great economic advantages. It has been reported from previous studies that a different type of dopant metals have a different effect on metal-doped CeO₂ catalyst systems. Rare earth (RE)-doped CeO₂ catalysts have increased both specific surface area and catalyst stability. Overall, however, they have relatively low CO oxidation activity. On the other hand, transition metal (TM)-doped CeO₂ has the high catalytic activity even at low temperature, but there is a problem of the reduction of active sites due to particle growth.

In this study, we synthesized (RE, TM) co-doped CeO₂ catalysts to take both advantages of TM and RE dopants. (RE, TM) co-doped CeO₂ was characterized by XRD, BET and HR-STEM measurements. XPS, Raman and H₂-TPR were used to confirm the defect (e.g. oxygen vacancies) of the catalyst surfaces, and the catalytic activity test was performed by GC. In addition, CO-TPD, TPR and DRIFTS analysis further confirmed the cause of active site and catalyst stability. Lastly, theoretical analysis including DFT calculations was performed to elucidate the experimental results. It was found that (RE, TM) co-doped CeO₂ catalysts had improved specific surface area and catalytic activity, and furthermore showed good stability to prevent the reduction of active sites by inhibiting the particle aggregation. Therefore, we believe that our approach to combine RE and TM doping into CeO₂ provide the considerable possibility of replacing precious metal catalysts for CO oxidation reaction.