The deposition of VWOx on the CuCeOy microflower for the selective catalytic reduction of NOx with NH3 at low temperatures

Fabrication of wide temperature FexCe1-xVO4 modified TiO2-graphene catalyst with excellent NH3-SCR performance and strong SO2/H2O tolerance

Selective catalytic reduction of NO with NH₃ (NH₃-SCR) is one of the most common technique for elimination of NO_x. The promotional effect of Fe additive on the NH₃-SCR activity of the CeVO₄/TiO₂-graphene (GE) is systematically studied. The results exhibited that the low-temperature NO_x conversion could be enhanced dramatically via the addition of Fe and Fe_0.5Ce_0.5VO₄/TiO₂-GE displayed the highest conversion of NO_x in the wide temperature window (200-400 °C). It is because that Fe³⁺ + Ce³⁺ ↔ Fe²⁺ + Ce⁴⁺ facilitated the oxidization of NO to NO₂ at low temperature and led to the "Fast SCR," thereby raising the SCR performance. What is more, the introduction of Fe enhanced redox ability, the surface relative percentage of Ce³⁺, V⁵⁺ and the chemical adsorbed oxygen. Furthermore, the high surface concentration of Ce³⁺ species can produce more active oxygen and leads to the "Fast SCR" reaction. In addition, the Fe_0.5Ce_0.5VO₄/TiO₂-GE catalyst showed excellent H₂O/SO₂ tolerance, which may be due to the decomposition of ammonium bisulphite under high temperature and the hydrophobicity of graphene. What is more, it displayed outstanding the stability. This work would provide theoretical reference for the practical application of NO_x abatement via NH₃-SCR.

Simultaneous catalytic removal of NO, mercury and chlorobenzene over WCeMnOx/TiO2-ZrO2: Performance study of microscopic morphology and phase composition

Nitrogen oxides, mercury and chlorobenzene are important air pollutants emitted by waste incineration and other industries. Coordinated control of multiple pollutants has become an important technology for air pollution control. Through solid-phase structure control, the catalytic performance of the WCeMnO_x/TiO₂-ZrO₂ catalyst for simultaneous catalytic removal of NO, mercury and simultaneous removal of NO and chlorobenzene were improved. MnWO₄ improved the solid acidity of the catalyst and improved the catalytic activity at high temperature. The formation of Ce_0·75Zr_0·25O₂, Ce₂WO₆, Ce₂Zr₂O₇ and Ce₂Ti₂O₇ improved the catalytic activity at low temperature. The presence of TiOSO₄ would affect the valence of metal ions and the reduction of chemisorbed oxygen, thereby reducing the catalytic activity at low temperature. Within the same size range of nanoparticles, cyclic nanoparticles exposed more active sites due to their hollow structure, and their catalytic performance was better than spherical nanoparticles. The thickness of the circular nanoparticles of WCM/TZ-14 catalyst was about 14 nm, and the diameter was about 40 nm Ce_0.75Zr_0.25O₂ and MnWO₄ were also present in the phase composition. Therefore, it exhibited the best performance for simultaneous catalytic removal of NO, mercury and simultaneous removal of NO and chlorobenzene. The coincidence temperature window was 347-516 °C. Finally, WCM/TZ-14 catalyst followed both E-R and L-H mechanisms in the NH₃-SCR reaction.

An efficient strategy to screen an effective catalyst for NOx-SCR by deducing surface species using DRIFTS

HYPOTHESIS

Transition metal supported TiO₂ is one of the hottest catalysts in the field of selective catalytic reduction (SCR) of nitrogen oxides. Various formulas have been put forward for an enhanced activity. However, seldom work emphasizes on easy and fast screening of an effective catalyst.

EXPERIMENTS

In this work, Diffuse Reflection Fourier Transform Infrared (DRIFTS) screened catalyst by analyzing intermediates during SCR.

FINDINGS

TiO₂ provided main adsorption sites for NH₃ and the "Eley-Rideal" mechanism dominated the catalysis. The transition metals served as the bridge of electron transport. Moreover, the area reduction rate of adsorbed NH₃ and NH₄⁺ species in DRIFTS represented the electron-transfer rate as well as catalytic activity. In other words, a faster area reduction indicated a better SCR activity. Therefore, this work supplied a fast strategy to screen the most effective catalyst among different materials even without using a nitrogen oxides detector. At the same time, less ammonia and nitrogen oxides were used or discharged.

CuCeOx/VMT powder and monolithic catalyst for CO-selective catalytic reduction of NO with CO

The reaction path of a CuCe/VMT(M) catalyst in the CO-SCR reaction at N2O low temperature was found.

FeVO4-supported Mn–Ce oxides for the low-temperature selective catalytic reduction of NOx by NH3

Iron vanadate (FeVO4) nanorods are used as a carrier to support manganese (Mn) and cerium (Ce) oxides for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3 for the first time.

Recent Progress on Improving Low-Temperature Activity of Vanadia-Based Catalysts for the Selective Catalytic Reduction of NOx with Ammonia

Selective catalytic reduction of NOx with NH3 (NH3-SCR) has been successfully applied to abate NOx from diesel engines and coal-fired industries on a large scale. Although V2O5-WO3(MoO3)/TiO2 catalysts have been utilized in commercial applications, novel vanadia-based catalysts have been recently developed to meet the increasing requirements for low-temperature catalytic activity. In this article, recent progress on the improvement of the low-temperature activity of vanadia-based catalysts is reviewed, including modification with metal oxides and nonmetal elements and the use of novel supports, different synthesis methods, metal vanadates and specific structures. Investigation of the NH3-SCR reaction mechanism, especially at low temperatures, is also emphasized. Finally, for low-temperature NH3-SCR, some suggestions are given regarding the opportunities and challenges of vanadia-based catalysts in future research.

Modification of composite catalytic material CumVnOx@CeO2 core-shell nanorods with tungsten for NH3-SCR

Novel composite material CumVnOx-NF@Ce-MOF nanorods with a core-shell structure were successfully fabricated by the in situ growth of Ce-MOF on electrospun copper vanadate precursor nanofibers. Following calcination at 500, 600 and 700 °C, Cu2V2O7@CeO2, Cu3(VO4)2@CeO2 and Cu11O2(VO4)6@CeO2, respectively, were obtained. The CeO2 shell not only protected the copper vanadate nanofibers from breaking apart during the calcination process, but also induced an interaction between Ce, Cu and V species, which resulted in an excellent redox capacity. This revealed its potential as a catalyst for the selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR). Further surface modulation was accomplished by WOx anchoring on the shell of CumVnOx@CeO2. According to a series of characterizations, the crystallinity of surface ceria on CumVnOy@CeO2-WOx was apparently reduced and the amount of acid on its surface was also significantly increased. In addition, different calcination temperatures also had nonnegligible effects on the amount of surface acid as well as the redox capacity of the composite catalytic material CumVnOy@CeO2-WOx. With the largest total quantity of acid sites as well as a suitable balance between acidity and reducing ability, the Cu3(VO4)2@CeO2-WOx calcined at 600 °C exhibited satisfactory catalytic performance in the NH3-SCR process, and the NO conversion could remain above 90% at 230-380 °C.