Advances in direct NOx decomposition catalysts

Direct decomposition of nitrogen oxides (NOx), which are the main air pollutants responsible for photochemical smog and acid rain, into N2 and O2 (2NO → N2 + O2) offers the most ideal route for NOx removal by catalysis. Direct decomposition of NOx is versatile and economic because no reductants are required. However, the catalytic activities of conventional catalysts are insufficient, particularly in the presence of other gases such as O2 and CO2. In recent years, however, investigation of different catalyst structures and compositions has led to enhanced catalytic activity. In particular, significant advances have been made in improving the tolerance of the catalyst to coexisting gases. These direct NO decomposition catalysts have been designed with a view to maximizing the cavity space and number of oxide anion vacancies in the crystal lattice. In this review article, recent advances in the direct NO decomposition catalysts are summarized.

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► Direct decomposition of NOx offers an ideal and reasonable route for NO removal.
► Catalysts for direct NO decomposition into nitrogen and oxygen.
► Cu ion-exchange zeolites, perovskite-type oxides, and rare earth oxides show high NOx decomposition activities.
► C-type cubic rare earth oxides and their related materials exhibit excellent resistance to O2 and CO2.