A review on dry-based and wet-based catalytic sulphur dioxide (SO2) reduction technologies.

While sulphur dioxide (SO2) is known for its toxicity, numerous effective countermeasures were innovated to alleviate its hazards towards the environment. In particular, catalytic reduction is favoured for its potential in converting SO2 into harmless, yet marketable product, such as elemental sulphur. Therefore, current review summarises the critical findings in catalytic SO2 reduction, emphasising on both dry- and wet-based technology. As for the dry-based technology, knowledge related to SO2 reduction over metal-, rare earth- and carbon-based catalysts are summarised. Significantly, both the reduction mechanisms and important criteria for efficient SO2 reduction are elucidated too. Meanwhile, the wet-based SO2 reduction are typically conducted in reactive liquid medium, such as metal complexes, ionic liquids and organic solvents. Therefore, the applications of the aforesaid liquid mediums are discussed thoroughly in the similar manner to dry-technology. Additionally, the pros and cons of each type of catalyst are also presented to provide valuable insights to the pertinent researchers. Finally, some overlooked aspects in both dry- and wet-based SO2 reduction are identified, with potential solutions given too. With these insights, current review is anticipated to contribute towards practicality improvement of catalytic SO2 reduction, which in turn, protects the environment from SO2 pollution.