Selective Catalytic Reduction of NO by NH₃ over Photocatalysts (Photo‐SCR): Mechanistic Investigations and Developments

Abstract

This account describes the work of our group in the selective catalytic reduction of nitrogen oxides (NO ) with ammonia over heterogeneous photocatalysts (photo-SCR) in the past 16 years. We have found that the photo-SCR proceeds over heterogeneous photocatalysts using a gas flow reactor, elucidated the reaction mechanism under UV- and visible-light irradiation by spectroscopic and kinetic studies, and developed a highly active photo-SCR system by improving the photocatalyst material itself and the reaction system with several approaches based on the reaction mechanism.

Construction of LaFe1−xMnxO3/attapulgite nanocomposite for photo-SCR of NOx at low temperature

“…Wavelength/nm that with the increase of irradiation time, the conversion of NO increases slightly. This phenomenon is different with the previous report whereas the conversion of NO rate decreases slightly with the increase of irradiation time, which may be due to the instability of sensitized porphyrin derivative under photoirradiation [22,23]. In other words, the perovskite oxides constructed on the ATP support may benefit the photostability.…”

“…Fe 3+ and become weaker in Fig.11b which indicates that Fe 3+ decreases [55,56]. New signals are observed at g=2.007, 2.009 and 2.021 in Fig.11b which may be ascribed to the generation of NH 2 radical under photoirradiation [22]. This phenomenon has also been identified by S.Yamazoe et al who proves that NH 2 radical is formed on TiO 2…”

“…Interestingly they found that photo-SCR of NO took place over TiO 2 even under visible light due to the formation of donor band from N 2p level by NH 3 adsorption to Lewis acid sites and direct excitation [20,21]. However, higher activity under high-GHSV conditions is largely required in terms of practical application when such in situ doping approach is adopted [22]. In order to improve the activity of the photocatalysts driven by visible light, a series of dye sensitized TiO 2 have been developed, however stability of the dye is not enough due to the photo-induced decolorization effect [23,24].…”

Palygorskite Immobilized Direct Z-Scheme Nitrogen-Doped Carbon Quantum dots/PrFeO3 for Photo-SCR Removal of NOx

“…The effect of the redox property plays an important role in the NO conversion, as revealed in H 2 -TPR; in addition, the excessive N-CQDs deposited on the surface of PrFeO 3 /Pal may shield the visible light and obstruct the light absorption of PrFeO 3 . The NO conversion of N-CQDs/PrFeO 3 /Pal is more than that of the TiO 2 counterpart or N 3 -dye-modified TiO 2 under visible light in the previous report . The stability of N-CQDs/PrFeO 3 /Pal at 150 °C was carried out, and the data are demonstrated in Figure S1.…”

“…Photodecomposition is rather difficult to realize since the conversion rate of nitrogen oxides is rather low. In contrast, photo-SCR has considerable merits, including high conversion and high selectivity of N 2 at low temperature. , Tanaka reported several photocatalysts, such as TiO 2 or dye-modified TiO 2 , for NO x removal at ambient conditions, but the reactions were realized at the low gas hourly space velocity (GHSV), which did not meet the requirements of practical use. , Moreover, the dyes are generally unstable, making it a challenge in the photo-SCR process, not to mention that the existence of SO 2 and H 2 O may easily cause the poisoning of the catalysts. , To overcome these problems, there is an imperative need to develop new stable photocatalysts for the photo-SCR of NO x .…”