Recently, our team of researchers Li Weizhen, Qiao Botao, and Academician Zhang Tao from the Catalysis and New Materials Research Laboratory collaborated with Professor Martin from Peking University to make new progress in the preparation of highly stable Pd based methane combustion catalysts. Using magnesium aluminum spinel (MgAl2O4) as a carrier, the excessive oxidation of Pd was suppressed by adding non reducing oxides (Al2O3, ZrO2, SiO2), achieving high hydrothermal stability of Pd nanoparticles.
Methane catalytic combustion has received widespread attention due to its important applications in clean energy conversion and utilization, as well as environmental protection. The loaded Pd catalyst exhibits excellent catalytic activity in this reaction, but in practical use, the catalyst often faces high humidity reaction gases and high-temperature reaction conditions, resulting in the sintering and growth of Pd nanoparticles, which reduces the performance of the catalyst. Therefore, developing methane catalytic combustion materials with high activity and high hydrothermal stability is extremely challenging. The team has long been committed to the preparation of high-temperature stable noble metal nanoparticle catalysts. In previous research, it was found that Pt and Au nanoparticles can form epitaxial structures with spinel that matches the interface, allowing the loaded Pt and Au nanoparticles to withstand high temperatures of 800-1200 ° C without significant growth (Nat. Commun., 2013; Nano Lett., 2018). Pd and Pt have similar lattice constants, and theoretically, the same strategy can be used to improve the thermal stability of Pd supported catalysts. However, due to the easy oxidation of Pd nanoparticles in air, the mismatch at the metal carrier interface increases, resulting in the loss of sintering resistance.



To address this issue, the team effectively suppressed the excessive oxidation of Pd through inert oxide modification, which not only improved the stability of Pd nanoparticles but also enhanced their catalytic activity. High resolution electron microscopy revealed that Pd nanoparticles can form epitaxial growth structures on the MgAl2O4 {111} crystal plane. However, when Pd undergoes excessive oxidation, the lattice spacing expands, disrupting the stable structure between the metal and the support. The modification of non reducing oxides can suppress the excessive oxidation of Pd and maintain the epitaxial structure. Mechanism studies have shown that methane catalytic combustion follows the MvK mechanism, and the modification of Al2O3 can promote the oxidation-reduction cycle of Pd between 2+and 0 valence, thereby enhancing the low-temperature activity of the catalyst. Due to its strong interaction with Pd and strong oxygen overflow ability, reducible oxides make it more difficult for Pd2+to be reduced to Pd0, and even cause some Pd to be further oxidized to Pd4+in an oxygen atmosphere. This strategy has good universality and is expected to be applied in many chemical and environmental protection fields involving high-temperature reaction processes.
The research results were published in Angew. Chem. Int. Ed. The above research work has been supported by projects such as the National Natural Science Foundation of China, the National Key Research and Development Program, and the Strategic Leading Science and Technology Project B of the Chinese Academy of Sciences, entitled "The Essence and Regulation of Energy Chemical Conversion".