We demonstrate a facile method to prepare atom-dispersed palladium catalysts with excellent catalytic activity and stability for lean methane combustion.

Palladium nanoparticles (NPs) were successfully deposited on surface-modified metal oxides (mod-MO x , M = Hf, Ti, Zr, Ce, and Al) and applied as catalyst materials for lean methane combustion. It was found that the surface modification of support materials improved the light-off performance of 1.0Pd/mod-HfO2 (palladium catalyst supported on surface-modified HfO2 with a content of 1.0 wt %), 1.0Pd/mod-ZrO2, and 1.0Pd/mod-CeO2, but lowered the purification efficiency of 1.0Pd/mod-TiO2 and 1.0Pd/mod-Al2O3 when compared with their 1.0Pd/MOx counterparts. Over the best-performing 1.0Pd/mod-HfO2 material, 90% of methane was removed at 317 °C and a space velocity of 60 000 mL g–1 h–1, which was 120 °C lower than that required for the untreated 1.0Pd/HfO2 sample. Detailed characterization of representative HfO2-related materials showed that the introduced silicon modifier materials, which existed as an amorphous phase covering the HfO2 surface, could improve the dispersion of palladium nanoparticles due to their steric confinement and strengthen the generation of surface-adsorbed oxygen species via electron transfer. We believe that this surface modification strategy, which could promote the catalytic performance of palladium nanoparticles supported on other cost-effective host materials as well, provides a feasible method for the design of methane combustion catalysts with excellent low-temperature performance.

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Mesoporous silica-supported palladium nanoparticles represent promising catalyst materials for lean methane oxidation. However, as only secondary palladium–silica interactions could be generally established in such compounds, active phases would inevitably agglomerate during the long-term reaction and finally result in performance deterioration and poor recyclability. Via the ammonia evaporation (AE) method, we successfully prepared highly active, stable, and recyclable Pd/Santa Barbara amorphous-15 (SBA-15) catalysts for lean methane oxidation. Our Pd/SBA-15-AE catalyst, which not only exhibited excellent catalytic performance for lean methane oxidation (T 90 = 335 °C in the first reaction cycle) but also achieved complete methane oxidation at 400 °C in the fifth reaction cycle of the designed test, presented more application potential than its impregnated and ion-exchanged counterparts. Combined with systematic characterizations, the enhanced palladium–silica interaction in AE-prepared catalysts was confirmed and proved to be critical for their excellent catalytic properties. DFT calculations revealed that the binding strength of palladium atoms on the surface-defected silica surface was enhanced when comparing with that on the perfect ones, finally rationalizing the obtained conclusion at the molecular level. The approach proposed in this work to create enhanced metal–support interactions may provide some inspiration for the design of application-oriented palladium catalysts.

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