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.

The structure and magnetic properties of FeAl2O4 synthesized by microwave magnetic field (H-field) irradiation were investigated to reveal the effect of the H-field on the crystal structure and the magnetic characteristics of an antiferromagnetic material. The role of the H-field was investigated using a single-mode cavity, which can spatially separate the maximum points of the alternating electric field (E-field) and H-field in the cavity. In H-field irradiation, the crystallite diameter decreased compared to that in conventional heating. In conventional heating, the crystallite diameter did not change with increasing quenching speed. Thus, it is suggested that a decrease in crystallite diameter occurs during H-field irradiation. Furthermore, magnetization after H-field irradiation was greater than that after conventional heating. It is considered that magnetic clusters appear when Fe3+ partially replaces Al3+ in the octahedral sites in the grain boundaries, which were formed as a result of decreasing crystallite diameter