The formation of local high temperature regions, or so-called “hot spots”, in heterogeneous reaction systems has been suggested as a critical factor in the enhancement of chemical reactions using microwave heating. In this paper, we report the generation of local high temperature regions between catalyst particles under microwave heating. First, we demonstrated that reaction rate of the dehydrogenation of 2-propanol over a magnetite catalyst was enhanced 17- (250 °C) to 38- (200 °C) fold when heated with microwave irradiation rather than an electrical furnace. Subsequently, the existence of microwave-generated specific local heating was demonstrated using a coupled simulation of the electromagnetic fields and heat transfer as well as in situ emission spectroscopy. Specific high-temperature regions were generated at the vicinal contact points of the catalyst particles due to the concentrated microwave electric field. We also directly observed local high temperature regions at the contact points of the particles during microwave heating of a model silicon carbide spherical material using in situ emission spectroscopy. We conclude that the generation of local heating at the contact points between the catalyst particles is a key factor for enhancing fixed-bed flow reactions under microwave irradiation.

We successfully prepared face-centered cubic (fcc) Cu–Ni (core–shell) nanoparticles by intramolecular reduction of formate complexes of Cu²⁺ and Ni²⁺ with long-chain amine ligands in a one-pot reaction within an extremely short time realized only under microwave irradiation. Observation by an HAADF-STEM technique showed that the nanostructure in one particle consisted of a Ni-rich shell and a Cu-rich core. Cu₄Ni₆ nanoparticles with an average size of 11.7 nm were comprised of a Cu core with a diameter of ca. 6.0 nm, a Ni shell ca. 1.6 nm thick and a 0.9 nm thick interlayer of mixed Cu–Ni alloy between the Cu core and the Ni shell. Both the oxidation characteristics and the magnetic properties were dramatically affected by the molar ratios of Cu : Ni in the Cu–Ni nanoparticles. The magnetization of Cu₃Ni₇ and Cu₄Ni₆ comprised of a diamagnetic Cu-rich core, ferromagnetic Ni-rich shell and antiferromagnetic NiO-rich layer on the particle surface showed an exchange bias (209 and 143 Oe, respectively).

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-Al₂O₃and SiO₂supports 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/Al₂O₃and Pt/SiO₂, respectively. As a result, Pt/SiO₂exhibits 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 PtO_xnanoparticles 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.

Magnesium (Mg) is a lightweight metal with applications in transportation and sustainable battery technologies, but its current production through ore reduction using the conventional Pidgeon process emits large amounts of CO₂ and particulate matter (PM2.5). In this work, a novel Pidgeon process driven by microwaves has been developed to produce Mg metal with less energy consumption and no direct CO₂ emission. An antenna structure consisting of dolomite as the Mg source and a ferrosilicon antenna as the reducing material was used to confine microwave energy emitted from a magnetron installed in a microwave oven to produce a practical amount of pure Mg metal. This microwave Pidgeon process with an antenna configuration made it possible to produce Mg with an energy consumption of 58.6 GJ/t, corresponding to a 68.6% reduction when compared to the conventional method.