Since the late 1980s, the scientific community has been attracted to microwave energy as an alternative method of heating, due to the advantages that this technology offers over conventional heating technologies. In fact, differently from these, the microwave heating mechanism is a volumetric process in which heat is generated within the material itself, and, consequently, it can be very rapid and selective. In this way, the microwave-susceptible material can absorb the energy embodied in the microwaves. Application of the microwave heating technique to a chemical process can lead to both a reduction in processing time as well as an increase in the production rate, which is obtained by enhancing the chemical reactions and results in energy saving. The synthesis and sintering of materials by means of microwave radiation has been used for more than 20 years, while, future challenges will be, among others, the development of processes that achieve lower greenhouse gas (e.g., CO 2 ) emissions and discover novel energy-saving catalyzed reactions. A natural choice in such efforts would be the combination of catalysis and microwave radiation. The main aim of this review is to give an overview of microwave applications in the heterogeneous catalysis, including the preparation of catalysts, as well as explore some selected microwave assisted catalytic reactions. The review is divided into three principal topics: (i) introduction to microwave chemistry and microwave materials processing; (ii) description of the loss mechanisms and microwave-specific effects in heterogeneous catalysis; and (iii) applications of microwaves in some selected chemical processes, including the preparation of heterogeneous catalysts.A chemical process is conventionally energized by means of conductive heating with a steam boiler as a typical heat source. Nevertheless, a large variety of other forms of energy can be applied for PI, including ultrasounds (for reactions or crystal nucleation), light (in photocatalytic processes), electric fields (in extraction or for orientation of molecules), or microwaves. The microwave (dielectric) heating of materials has been known for a long time, and microwave ovens have been developed from more than 60 years. The studies by Gedye et al. in 1986 and 1988 [3,4] opened a period of very intensive investigation of the microwave effects on chemical reactions in homogeneous systems. Since then, hundreds of research papers have been published, and research has also expanded toward heterogeneous catalysis and its related chemical processes. This review gives an overview of the application of microwave technology to heterogeneous catalysis, including various chemical processes, as well as to the preparation of catalysts.

An Al 2 O 3 -based catalyst was employed for the first time in the H 2 S oxidative decomposition in order to obtain simultaneous sulfur and hydrogen. The influence of the reaction temperature (in the range of 700−1100 °C) and the contact time (in the range of 17−33 ms) were investigated in terms of H 2 S conversion, H 2 yield, and SO 2 selectivity. Good catalytic performances were obtained at 1000 and 1100 °C with experimental values very close to those ones expected from the thermodynamic equilibrium. At a temperature of 1000 °C, the H 2 S conversion and H 2 yield were, respectively, about 50% and 17%; in particular, the SO 2 selectivity decreased of a magnitude order ∼0.5% with respect to the value observed in the homogeneous case (4%). A predictive mathematical model of H 2 S oxidative decomposition in the presence of a catalyst was developed through the identification of the main reactions occurring in the system. The results obtained from the kinetic investigations evidenced that the catalyst, in addition to the H 2 S decomposition reaction and the partial oxidation reaction to sulfur, was able also to promote the SO 2 conversion by the Claus reaction allowing it to avoid the presence of SO 2 at the reactor outlet.

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