Sulfur dioxide catalytic reduction for environmental sustainability and circular economy: A review

Air pollution sourced from untreated sulfur dioxide-rich flue gas is one of the major environmental and human health issues. Throughout the years, many sulfur dioxide removal technologies have been invented and imple-mented on a wide scale. Despite the high sulfur dioxide removal efficiency of conventional treatment methods, such as limestone-gypsum desulfurization and spray dry absorption, they generate a large number of secondary sulfur-containing by-products. Thus, sulfur dioxide catalytic reduction, with the help of suitable reducing agents, is sustainable with acceptable desulfurizing efficiency while recovering valuable solid sulfur. Herein, we review advances in sulfur dioxide catalytic reduction with critical insights contributed by internal and external factors. Sulfur dioxide catalytic reduction is a regenerative desulfurization treatment with lower space requirement and water consumption, simultaneously transforming waste sulfur dioxide to elemental sulfur. Catalytic sulfur di-oxide reduction to sulfur via transition metal-based catalysts (copper-alumina and nickel-alumina) and sulfided metal-based catalysts (cobalt-molybdenum/& gamma;-alumina) appeared to be highly promising for complete sulfur di-oxide conversion (100%) while maintaining high sulfur selectivity (more than 99.5%). High industrial and market demands for solid sulfur have also imposed great opportunities to advance this technology. However, the critical weaknesses of sulfur dioxide catalytic reduction are low process maturity and relatively energy-intensive, which is threatened by the high performance of conventional flue gas desulfurization and energy-efficient emerging desulfurization methods. Hence, several strategic directions through threat, opportunity, weakness, and strength analysis (TOWS) are discussed in-depth based on the strength, weakness, opportunity, and threats (SWOT) findings. In realizing environmental sustainability and a circular economy, sulfur dioxide catalytic reduction is a promising method to mitigate sulfur dioxide pollution while transforming waste-to-product, and this study serves as a guide to making sulfur dioxide catalytic reduction a mainstream desulfurization technology.