Probing the temperature of supported platinum nanoparticles under microwave irradiation by in situ and operando XAFS

Abstract

Microwave irradiation can cause high local temperatures at supported metal nanoparticles, which can enhance reaction rates. Here we discuss the temperature of platinum nanoparticles on γ-Al2O3 and SiO2 supports under microwave irradiation using the Debye–Waller factor obtained from in situ extended X-ray absorption fine structure (EXAFS) measurements. Microwave irradiation exhibits considerably smaller Deby–Waller factors than conventional heating, indicating the high local temperature at the nanoparticles. The difference in the average temperatures between the platinum nanoparticles and the bulk under microwaves reaches 26 K and 132 K for Pt/Al2O3 and Pt/SiO2, respectively. As a result, Pt/SiO2 exhibits considerably more reaction acceleration for the catalytic dehydrogenation of 2-propanol under microwave irradiation than Pt/Al2O3. We also find microwaves enhance the reduction of PtOx nanoparticles by using operando X-ray absorption near edge structure (XANES) spectroscopy. The present results indicate that significant local heating of platinum nanoparticles by microwaves is effective for the acceleration of catalytic reactions.

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

“…Metal nanoparticles (NPs) are selectively heated by MWs when supported on metal oxide (MO x ) catalyst supports such as Al 2 O 3 or SiO 2 , which are generally transparent to MWs. , The reaction is accelerated by the rapid formation of high-temperature “hotspots” at the catalyst active sites, enabled by the direct MW irradiation of the supported metal NPs. Jie et al reported that the use of MWs accelerates the dehydrogenation of fossil fuels using Fe@SiC catalyst by selectively heating the Fe NPs and enables a very high selectivity for hydrogen production. , Deng et al reported that the selective heating of Fe supported on a zeolite catalyst with a low Si/Al ratio by MWs promoted the dehydroaromatization of methane .…”

“…We have recently experimentally demonstrated the formation of local high-temperature “hotspots” at Pt NPs supported on Al 2 O 3 and SiO 2 under MW irradiation. Extended X-ray absorption fine structure (EXAFS) of the Pt-L III edge was measured under MW heating, and the average temperature of the supported Pt nanoparticles was estimated using the temperature dependence of the Debye–Waller factor obtained by curve fitting . The degree of the local temperature at the supported metal nanoparticles depended on the catalyst support; the difference between the temperatures of supported Pt NPs and the bulk catalyst was 26 K for Pt/Al 2 O 3 , whereas that for Pt/SiO 2 reached 132 K. However, the mechanism whereby the support influences the formation of local high temperatures at the site of the metal NPs is not well-understood.…”

“…Extended X-ray absorption fine structure (EXAFS) of the Pt-L III edge was measured under MW heating, and the average temperature of the supported Pt nanoparticles was estimated using the temperature dependence of the Debye−Waller factor obtained by curve fitting. 8 The degree of the local temperature at the supported metal nanoparticles depended on the catalyst support; the difference between the temperatures of supported Pt NPs and the bulk catalyst was 26 K for Pt/Al 2 O 3 , whereas that for Pt/SiO 2 reached 132 K. However, the mechanism whereby the support influences the formation of local high temperatures at the site of the metal NPs is not wellunderstood. A mechanistic understanding of the interactions between metal NPs and MOx catalyst support will lead to the rational design of catalysts for maximizing local temperatures and, thereby, the reaction rates.…”

Decrease in the Crystallite Diameter of Solid Crystalline Magnetite around the Curie Temperature by Microwave Magnetic Fields Irradiation

“…Microwave processing exhibits some unique features, such as rapid heating, rapid cooling, and selective heating, which are different from conventional processing using an electric furnace. Thus, microwave heating provides many benefits for material processing, such as decreasing the sintering time, synthesizing functionalized nanomaterials, and promoting catalytic reactions [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. Additionally, “non-thermal effects”, phenomena of which cannot be explained by thermal effects, have also been reported [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”

Microwave Heating of Nanocrystals for Rapid, Low-Aggregation Intermetallic Phase Transformations

“…At the bulk scale, the use of microwaves to trigger phase transformations has been well studied. − At the nanoscale, microwaves have been used as a method of NC synthesis, ,,, or catalytic excitation, ,, but they have not yet been used to induce intermetallic phase transformations. Microwave irradiation at the nanoscale allows localized heat generation from the NCs rather than their environment. − Localized heating allows for a temperature difference between the NCs and their local support environment of nearly 100 °C. , …”