Review on the selective catalytic reduction of NO_x with H₂ by using novel catalysts

Selective catalytic reduction is a common technology to control nitrogen oxides (NO_x) in coal-fired industries, diesel engines, etc., among which, selective catalytic reduction of NO_x by NH₃ (NH₃-SCR) has been commercially applied. However, its drawbacks such as the ammonia slipping, air heater fouling, catalyst poisoning, high investment and cost of operating have stimulated the development of new-type DeNO_x technology. Nowadays, selective catalytic reduction with H₂ (H₂-SCR) has been regarded as a promising DeNO_x technology. This review begins with the reaction mechanism of H₂-SCR and then the noble metal SCR catalysts (Pt-based and Pd-based ones) and the non-noble metal catalysts for NO_x removal are reviewed. Then, the effects of different preparation methods and different supports for H₂-SCR performance are discussed. What follows is the homogeneous reactions of H₂-SCR catalysts with O₂, H₂, H₂O, SO₂, CO, CO₂, etc. And the recent progress of SCR mechanism by DFT calculations is summarized. Finally, the challenges and prospects for H₂-SCR catalysts with the corresponding effective strategies are proposed. Hopefully, this article may provide insights into the gap between the newly developed H₂-SCR catalysts and the practical demand in NO_x removal, thus promoting their future commercial application.