110th anniversary: Recent progress and future challenges in selective catalytic reduction of NO by H₂ in the presence of O₂

Over the past several years, selective catalytic reduction of NO_x with hydrogen (H₂-SCR) has been regarded as a promising technology for NO_x abatement under lean-burn conditions. In this review, we discuss the recent progress in the development and understanding of H₂-SCR catalysts. The various mechanisms that have been proposed in the literature are reviewed first. The influence of the catalyst chemical components (noble metals, supports, promoters, and perovskites) and their roles in H₂-SCR are then analyzed. Non-noble metal catalysts and the new strategy of alloying Pt with transition metals (Ni, Fe, Co, and Cu) are of particular interest and discussed. From a practical viewpoint, the effects of exhaust gas composition on H₂-SCR is also addressed. Finally, we propose potential opportunities and challenges in the area of H₂-SCR.