Technological solutions for NO_x, SO_x, and VOC abatement: recent breakthroughs and future directions

NO_x, SO_x, and carbonaceous volatile organic compounds (VOCs) are extremely harmful to the environment, and their concentrations must be within the limits prescribed by the region-specific pollution control boards. Thus, NO_x, SO_x, and VOC abatement is essential to safeguard the environment. Considering the importance of NO_x, SO_x, and VOC abatement, the discussion on selective catalytic reduction, oxidation, redox methods, and adsorption using noble metal and non-noble metal-based catalytic approaches were elaborated. This article covers different thermal treatment techniques, category of materials as catalysts, and its structure-property insights along with the advanced oxidation processes and adsorption. The defect engineered catalysts with lattice oxygen vacancies, bi- and tri-metallic noble metal catalysts and non-noble metal catalysts, modified metal organic frameworks, mixed-metal oxide supports, and their mechanisms have been thoroughly reviewed. The main hurdles and potential achievements in developing novel simultaneous NO_x, SO_x, and VOC removal technologies are critically discussed to envisage the future directions. This review highlights the removal of NO_x, SO_x, and VOC through material selection, properties, and mechanisms to further improve the existing abatement methods in an efficient way.