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., CO₂) 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.

Ceria-supported vanadium catalysts were studied for H₂S removal via partial and selective oxidation reactions at low temperature. The catalysts were characterized by N₂ adsorption at 77 K, Raman spectroscopy, X-ray diffraction techniques, and X-ray fluorescence analysis. X-ray diffraction and Raman analysis showed a good dispersion of the V-species on the support. A preliminary screening of these samples was performed at fixed temperature (T = 327 °C) and H₂S inlet concentration (10 vol%) in order to study the catalytic performance in terms of H₂S conversion and SO₂ selectivity. For the catalyst that exhibited the higher removal efficiency of H₂S (92%) together with a lower SO₂ selectivity (4%), the influence of temperature (307–370 °C), contact time (0.6–1 s), and H₂S inlet concentration (6–15 vol%) was investigated.

Cordierite honeycomb structured catalysts were studied for the reaction of H₂S decomposition in the presence of oxygen to obtain H₂ and sulphur. An Al₂O₃-based washcoat was deposited on the honeycomb monolith by a dip-coating procedure. In particular, three different washcoat percentages (15, 20 and 30 wt%) were deposited on the structured carrier and the obtained samples were characterized by N₂ adsorption and SEM analysis. The evaluation of the catalytic performance of the three samples was carried out at two different temperatures (1000 °C and 1100 °C). The sample with 30 wt% washcoat content showed the lowest SO₂ selectivity at 1000 °C (<0.4%), whereas the H₂S conversion and H₂ yield values were very similar to those achieved for the samples at 15 and 20 wt% washcoat loading. Based on these results, additional tests were carried out on the catalyst with 30 wt% Al₂O₃-based washcoat loading, varying the contact time and the H₂S inlet concentration to identify the operating conditions that minimize the SO₂ formation, obtaining good H₂S conversion and H₂ yield. The comparison of the structured catalyst with the powder alumina sample has shown the same catalytic performance, exhibiting lower SO₂ selectivity.

Hydrogen sulfide is one of the main waste products of the petrochemical industry; it is produced by the catalytic hydrodesulfurization processes (HDS) of the hydrocarbon feedstocks, and it is a byproduct from the sweetening of sour natural gas and from the upgrading of heavy oils, bitumen, and coals