Selective catalytic reduction with NH3 (NH3-SCR) is the most efficient technology to reduce the emission of nitrogen oxides (NOx) from coal-fired industries, diesel engines, etc. Although V2O5-WO3(MoO3)/TiO2 and CHA structured zeolite catalysts have been utilized in commercial applications, the increasing requirements for broad working temperature window, strong SO2/alkali/heavy metal-resistance, and high hydrothermal stability have stimulated the development of new-type NH3-SCR catalysts. This review summarizes the latest SCR reaction mechanisms and emerging poison-resistant mechanisms in the beginning and subsequently gives a comprehensive overview of newly developed SCR catalysts, including metal oxide catalysts ranging from VOx, MnOx, CeO2, and Fe2O3 to CuO based catalysts; acidic compound catalysts containing vanadate, phosphate and sulfate catalysts; ion exchanged zeolite catalysts such as Fe, Cu, Mn, etc. exchanged zeolite catalysts; monolith catalysts including extruded, washcoated, and metal-mesh/foam-based monolith catalysts. The challenges and opportunities for each type of catalysts are proposed while the effective strategies are summarized for enhancing the acidity/redox circle and poison-resistance through modification, creating novel nanostructures, exposing specific crystalline planes, constructing protective/sacrificial sites, etc. Some suggestions are given about future research directions that efforts should be made in. Hopefully, this review can bridge the gap between newly developed catalysts and practical requirements to realize their commercial applications in the near future.

Selective Catalytic Reduction of NOx with NH3 by Using Novel Catalysts: State of the Art and Future Prospects.

Low-temperature selective catalytic reduction of NOx with NH3 over metal oxide and zeolite catalysts—A review

Surfactants And Interfacial Phenomena

(Fe3−xMnx)1−δO4 was synthesized using a co-precipitation method and then developed as a catalyst for the low temperature selective catalytic reduction (SCR) of NO with NH3. The SCR activity of (Fe3−xMnx)1−δO4 was clearly enhanced with the increase of Mn content. The results of in situ DRIFTS study demonstrated that both the Eley–Rideal mechanism (i.e. reaction of activated ammonia with gaseous NO) and the Langmuir–Hinshelwood mechanism (i.e. reaction of adsorbed ammonia species with adsorbed NOx species) might happen during the SCR reaction over (Fe3−xMnx)1−δO4. According to the kinetic analysis, the respective contribution of the Langmuir–Hinshelwood mechanism and the Eley–Rideal mechanism on the SCR reaction was studied. Only the adsorption of NO + O2 on (Fe2.8Mn0.2)1−δO4 was promoted, so the Langmuir–Hinshelwood mechanism predominated over NO conversion on (Fe2.8Mn0.2)1−δO4 especially at lower temperatures. Both the adsorption of NO + O2 and the adsorption of NH3 on (Fe2.5Mn0.5)1−δO4 were obviously promoted, so NO conversion on (Fe2.5Mn0.5)1−δO4 mainly followed the Eley–Rideal mechanism especially at higher temperatures. Both the nitrate route and the over-oxidization of adsorbed ammonia species contributed to the formation of N2O on (Fe2.8Mn0.2)1−δO4 above 140 °C. However, the formation of N2O on (Fe2.5Mn0.5)1−δO4 mainly resulted from the over-oxidization of adsorbed ammonia species. Although the activity of (Fe2.5Mn0.5)1−δO4 was suppressed in the presence of H2O and SO2, the deactivated catalyst can be regenerated after the water washing.

Low temperature selective catalytic reduction of NO with NH3 over Mn–Fe spinel: Performance, mechanism and kinetic study

Selective catalytic reduction (SCR) technology has been widely used for the removal of NOx from flue gas. However, it is still a challenge to develop novel low-temperature catalysts for SCR of NOx, especially at temperatures below 200 °C. This paper reviewed the recent progress on the Mn-based catalysts for low-temperature SCR de-NOx with NH3. Catalysts were divided into four categories, single MnOx, Mn-based multi-metal oxide, Mn-based multi-metal oxide with support, and Mn-based monolith catalyst. In the section of single MnOx, the effects of several factors, such as Mn oxidation state, crystallization state, specific surface area and morphology on catalytic activity were systematically reviewed. In the section of multi-metal oxide catalysts, the various roles played by the components of catalysts were intentionally summarized from four aspects, improving de-NOx efficiency, enhancing N2 selectivity, improving resistance to SO2 and H2O, extending operation temperature window, respectively. Moreover, the newly emerging morphology-dependent nanocatalysts were highlighted at the end of this section. In the introduction of supported metal oxide catalysts, the effects of supports were systematically analyzed according to their types, such as Al2O3, TiO2, carbon materials, etc. Considering the actual operation, Mn-based monolith catalysts were also introduced with regard to monolith supports, such as ceramics, metal wire mesh, etc. Subsequently, NH3-SCR mechanisms at low temperature, including E-R and L-H mechanisms, were discussed. At last, the perspective and the future direction of low-temperature SCR of NOx were proposed.

Manganese oxide-based catalysts for low-temperature selective catalytic reduction of NOx with NH3: A review

A review on selective catalytic reduction of NOx by supported catalysts at 100–300 °C—catalysts, mechanism, kinetics

Activated coke impregnated with cerium chloride used for elemental mercury removal from simulated flue gas

Due to the contribution to air pollution, the controlling of NO discharge needs further studies. In this paper, loaded catalysts of 10–40% (w/w) CeO2/ACF were prepared by impregnation method and used for the selective catalytic reduction of NO with ammonia in the presence of O2. Such catalysts were characterized by surface area measurement (BET), thermo gravimetric (TG) analysis and Fourier transform infrared (FTIR) spectroscopy. The catalytic activity of 10–40% CeO2/ACF at different temperatures, and the catalytic stability at 200 °C were studied. Moreover, the experimental results were compared with those of previous studied catalysts. The results show that the 10% CeO2/ACF and 20% La2O3/ACF can yield higher NO conversion and maintain higher catalytic activity at higher temperature than others. 10% CeO2/ACF yields about 70% NO conversion in the SCR of NO at 150 °C, and meanwhile 20% La2O3/ACF and 10% CeO2/ACF yield over 90% NO conversion when the temperatures are higher than 350 °C. The catalytic activity and the catalyst stability of 10% CeO2/ACF and 20% La2O3/ACF are both higher than those of many reported catalysts. Based on the catalytic and characterizing results, such as BET, TG and FTIR, it can be found that the SCR of NO mechanism of loaded catalysts is different from those of ACF and HNO3/ACF. ACF-C is the catalyst and reducing agent in the SCR of NO of ACF and HNO3/ACF, while the metal oxides loaded by ACF are the catalytic centers, NH3 is the main reducing agent in the SCR of loaded catalysts.

Low temperature selective catalytic reduction of NO by activated carbon fiber loading lanthanum oxide and ceria

The effects of zeolite (HZSM-5 was chosen for use) modified by CeO2 (CeO2/HZSM-5) on the gas-phase elemental mercury (Hg0) removal were investigated under simulated flue gas. The Brunauer–Emmett–Teller surface area analyses, powder X-ray diffraction measurements, and thermogravimetric analyses were employed to characterize the samples. The experimental results showed that there was a synergetic effect between CeO2 and HZSM-5 on Hg0 removal. The acidic sites of HZSM-5 could effectively adsorb Hg0 from the flue gas, and CeO2 could significantly enhance the oxidation of adsorbed Hg0. However, the surface area of CeO2/HZSM-5 decreased because of excess CeO2, which was detrimental to its Hg0 removal efficiency. Moreover, the temperature tests manifested that 6% CeO2/HZSM-5 achieved high Hg0 removal efficiency at low reaction temperatures (<300 °C). Additionally, the Hg0 removal efficiencies of CeO2/HZSM-5 were found to be significantly affected by the flue gas components. In the presence of O2, promotional eff...

Pei Lu

Papers

A review on selective catalytic reduction of NOx by supported catalysts at 100–300 °C—catalysts, mechanism, kinetics

Activated coke impregnated with cerium chloride used for elemental mercury removal from simulated flue gas

Low temperature selective catalytic reduction of NO by activated carbon fiber loading lanthanum oxide and ceria

Hg0 Removal from Simulated Flue Gas over CeO2/HZSM-5

The effects of Cu/HZSM-5 on combined removal of Hg0 and NO from flue gas