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.

Oxygen defects and surface chemistry of ceria: quantum chemical studies compared to experiment.

Perovskite oxides with formula ABO3 or A2BO4 are a very important class of functional materials that exhibit a range of stoichiometries and crystal structures. Because of the structural features, they could accommodate around 90% of the metallic natural elements of the Periodic Table that stand solely or partially at the A and/or B positions without destroying the matrix structure, offering a way of correlating solid state chemistry to catalytic properties. Moreover, their high thermal and hydrothermal stability enable them suitable catalytic materials either for gas or solid reactions carried out at high temperatures, or liquid reactions carried out at low temperatures. In this review, we addressed the preparation, characterization, and application of perovskite oxides in heterogeneous catalysis. Preparation is an important issue in catalysis by which materials with desired textural structure and physicochemical property could be achieved; characterization is the way to explore and understand the textura...

Perovskite Oxides: Preparation, Characterizations, and Applications in Heterogeneous Catalysis

Perovskites as substitutes of noble metals for heterogeneous catalysis: dream or reality.

The catalytic removal of nitrogen oxide (NOx) under lean‐burn conditions is one of the most important targets in catalysis research. Some lean‐NOx control technologies such as the direct decomposition of NOx, NOx storage‐reduction (NSR), and selective catalytic reduction (SCR) using different reducing agents (diesel soot, NH3, or hydrocarbon) are described. The reaction mechanism of NSR, which is the most promising technology, together with some novel NSR catalysts is discussed. Some mechanisms of SCR of NOx by hydrocarbon (HC‐SCR) were classified into two categories: one is the adsorption/dissociation mechanism, and the other is the oxidation‐reduction mechanism. Based on the discussion of the reaction mechanism, the influence of some factors (catalyst support, metal loading, calcination temperature, catalyst preparation method, oxygen, reducing agents, water, and sulfur) on the activity of HC‐SCR catalyst is discussed. It seems that Ag/Al2O3 catalyst offers the most promising for SCR of NOx by hydrocarb...

Recent Advances in Catalytic DeNOX Science and Technology

A series of MoO3-doped CeO2/TiO2 catalysts prepared by the impregnation method were investigated for the selective catalytic reduction of NO,c by NH3(NH3-SCR). It was found that CeO2-MoO3/TiO2 catalyst is much more active than CeO2/TiO2 for NH3-SCR and the optimum MoO3 loading is 5%. The mechanistic cause of the promoting effect of MoO3 on the activity of CeO2/TiO2 catalyst for NH3-SCR was studied using in situ diffuse reflectance infrared transform spectroscopy (DRIFTS). The results revealed that the highly dispersed molybdenum on CeO2-MoO3/TiO2 catalyst not only resulted in more Brensted acid sites formed on the catalyst surface, but also reduced the thermal stability of the inactive nitrate specie, leaving more active sites available for the adsorption of NH3, both of which are favorable for the promotion of SCR activity. (C) 2013 Elsevier B.V. All rights reserved.

Promoting effect of MoO3 on the NOx reduction by NH3 over CeO2/TiO2 catalyst studied with in situ DRIFTS

Mn-Ce-Ti mixed-oxide catalyst prepared by the hydrothermal method was investigated for the selective catalytic reduction (SCR) of NOx with NH3 in the presence of oxygen. It was found that the environmentally benign Mn-Ce-Ti catalyst exhibited excellent NH3-SCR activity and strong resistance against H2O and SO2 with a broad operation temperature window, which is very competitive for the practical application in controlling the NOx emission from diesel engines. On the basis of the catalyst characterization, the dual redox cycles (Mn4+ + Ce3+ Mn3+ + Ce4+, Mn4+ + Ti3+ Mn3+ + Ti4+) and the amorphous structure play key roles for the high catalytic deNO(x) performance. Diffuse reflectance infrared Fourier transform spectroscopy studies showed that the synergetic effect between Mn and Ce contributes to the formation of reactive intermediate species, thus promoting the NH3-SCR to proceed.

Novel Mn–Ce–Ti Mixed-Oxide Catalyst for the Selective Catalytic Reduction of NOx with NH3

Selective catalytic reduction of NOx with NH3 over Mn-Ce mixed oxide catalyst at low temperatures

The effect of Ce on the activity and alkali resistance of V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NOx by NH3 has been investigated It was found that the addition of Ce not only reduced the vanadium loading of V2O5/TiO2 but also enhanced its activity and alkali resistance The NOx conversion over 05%V2O5-5%CeO2/TiO2 was much higher than that over 1%V2O5/TiO2 catalyst Based on the catalyst characterization, the redox cycle (V4+ + Ce4+ V5+ + Ce3+) can account for the excellent NH3-SCR catalytic performance of 05%V2O5-5%CeO2/TiO2 catalyst In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) measurements revealed that the role of Ce on the V2O5-CeO2/TiO2 catalyst was to contribute to the formation of NO2 and monodentate nitrate species, both of which were reactive intermediates for the NH3-SCR of NOx (C) 2014 Elsevier BV All rights reserved

Novel V2O5–CeO2/TiO2 catalyst with low vanadium loading for the selective catalytic reduction of NOx by NH3

https://www.rsc.org/suppdata/cc/c3/c3cc43041c/c3cc43041c.pdf

Zhiming Liu

Papers

Promoting effect of MoO3 on the NOx reduction by NH3 over CeO2/TiO2 catalyst studied with in situ DRIFTS

Novel Mn–Ce–Ti Mixed-Oxide Catalyst for the Selective Catalytic Reduction of NOx with NH3

Selective catalytic reduction of NOx with NH3 over Mn-Ce mixed oxide catalyst at low temperatures

Novel V2O5–CeO2/TiO2 catalyst with low vanadium loading for the selective catalytic reduction of NOx by NH3

A superior catalyst with dual redox cycles for the selective reduction of NOx by ammonia