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The production of high-value-added chemicals and their raw materials by partial oxidation of methane (POM) is advantageous. The screening of 31 simple oxide catalysts for direct POM showed that ZrO2had the highest syngas yield (CO and H2) and was thus a promising catalyst. Kinetic analysis indicated that POM over the ZrO2catalyst proceeded in a Langmuir–Hinshelwood mechanism and that CH4activation was the rate-limiting step. Density functional theory calculations showed that CH4was activated on coordinatively unsaturated Zr4+cations formed by the dehydration of the hydroxyl groups on the ZrO2surface. In situdiffuse reflectance infrared Fourier transform spectroscopy revealed that CH4was converted into CO and H2through CH4-oxygenated intermediates, such as methoxy and formate species. The CH4-oxygenated intermediates on the ZrO2catalyst were closely related to the catalytic performance of the oxide catalysts in POM. A comprehensive investigation of the POM reaction over ZrO2-based catalysts was then conducted. ZrO2modification with tungsten oxide (WOx) or lanthanum oxide (LaOx) was examined to determine their ability to improve the catalytic properties of ZrO2for POM. ZrO2modification with WOxand LaOxenhanced its acidity and basicity, respectively. CO selectivity was increased by modifying ZrO2with a small amount of WOx. Moreover, modification with LaOxincreased CH4conversion and H2yield at low temperatures.

Metal nanoparticles (MNPs) supported on oxides are used in various catalytic reactions, such as petrochemical processes and exhaust gas purification. Metal–support interactions (MSIs) between MNPs and oxides affect the morphology and thermal stability of the MNPs, which are known to be related to the catalytic activity of the MNPs. However, the effect of MSIs is still a matter of debate. We conducted density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) to investigate the geometric structure and migration behavior of Pd clusters on various Al2O3surfaces. The MSIs of the Pd clusters with different Al2O3surfaces resulted in different morphologies of the clusters. The shape of Pd clusters on α-Al2O3(0001) were deformed to oblate and on γ-Al2O3(110) to prolate. On the other hand, the shape of Pd clusters on γ-Al2O3(100) did not change from that in a vacuum. The migration rate of Pd clusters was also affected by the MSI, which was higher on γ-Al2O3(110) than on α-Al2O3(0001) and γ-Al2O3(100). To evaluate the interactions between Pd clusters and Al2O3surfaces, we calculated the interaction energies for Pd clusters with various sizes on Al2O3surfaces. The interaction energy of Pd/Al2O3systems depended on the coordination number (CN, number of bonds per Pd atom) of Pd–Al and Pd–O. Despite the smaller atomic density of Al and O of the γ-Al2O3(110) surface than that of α-Al2O3(0001) and γ-Al2O3(100) surfaces, the number of bonds formed between Pd clusters and γ-Al2O3(110) was greater than that of α-Al2O3(0001) and γ-Al2O3(100). According to AIMD simulations and perpendicular displacements of Al and O atoms bound to the Pd cluster on the Al2O3surface from the bare Al2O3surface, coordinatively unsaturated Al3+sites on γ-Al2O3(110) were more flexible than those on α-Al2O3(0001) and γ-Al2O3(100). The flexibility of γ-Al2O3(110) facilitated the formation of bonds with the Pd cluster, resulting in stronger MSIs. When the coordinatively unsaturated Al3+sites were hydrated, the MSIs were found to be weakened.