Designing Local Microwave Heating of Metal Nanoparticles/Metal Oxide Substrate Composites

Microwave (MW) heating promotes various reactions catalyzed by supported metal nanoparticles (NPs); the mechanism is based on selectively heating the NPs, thereby inducing hot spots at the active reaction sites. Here, we demonstrate the effects of the sizes and loadings of platinum (Pt) NPs supported on single-crystal metal oxide (MOx) substrates (Al2O3, MgAl2O4, TiO2, SrTiO3) having different relative permittivities and conductivities. Considerable heating occurred when Pt NPs were deposited on MOx substrates having low relative permittivities and conductivities, indicating that the MW transparency of the substrate is the most critical parameter. Magnetic field heating was preferred when the loading amount of Pt NPs was large. Electromagnetic field simulations suggested that the electric field concentration between Pt NPs formed local hot spots. Moreover, the MW absorption behavior of the NP/MOx composite depended on the conductivity of the supported metal, and the frequency of the MWs. We conclude that the relative permittivity and conductivity of the MOx support are the most important parameters for ensuring efficacious MW heating by Pt NPs, followed by size and loading of the supported metal NPs. The synergistic effect of the metal NPs and MOx support results in targeted MW heating of the supported metal catalyst.

Automated summary

Microwave heating promoted by supported platinum nanoparticles on metal oxide substrates is influenced by the transparency of the substrate, with low relative permittivities and conductivities leading to considerable heating. The size and loading of the platinum nanoparticles, as well as the conductivity of the supported metal and the frequency of the microwaves, all play significant roles in the effectiveness of microwave heating. The synergy between metal nanoparticles and metal oxide support results in targeted microwave heating of the supported metal catalyst.