TiO2 Selective Catalytic Reduction Research Articles

Effect of Mn or Fe on CrMoOx /TiO2 selective catalytic reduction catalyst

Developing a high-efficiency catalyst with both superior low-temperature activity and good sulfur and water resistance is still challenging for the NH3 selective catalytic reduction (SCR). Herein, a series of Mn- and Fe-doped CrMoOx/TiO2 catalysts were elaborately designed and the Cr3Mo6Mn2/TiO2 catalyst exhibits the best NOx conversion rate, reaching 81. 8% at 90 ℃ and closing to 100% at 150 ℃, and the NOx conversion reach ∼71% at 150 ℃ for 30 h in presence of H2O+SO2. A series of characterization studies revealed that the abundance of Lewis acidic sites on the catalysts and the protective effect of Mo are conducive to the enhancement of SO2+H2O resistance. cr3Mo6Mn2/TiO2 dominates the SCR reaction through the Eley-Rideal (E-R) pathway between adsorbed NH4+/NH3 and gaseous NOx, generating N2 and H2O. This work provides a new strategy for improving the tolerance of chromium-based oxide catalysts to sulfur dioxide and water at low temperatures.

Synthesis and Characterization of V2O5 Supported on TiO2 Selective Catalytic Reduction (SCR) Catalyst for De-NOX Application

Synthesis and Characterization of V2O5 Supported on TiO2 Selective Catalytic Reduction (SCR) Catalyst for De-NOX Application

Experimental and numerical investigation of dual-fuel CI ammonia engine emissions and after-treatment with V2O5/SiO2–TiO2 SCR

Ammonia (NH3) is one of the most promising fuels regaining interest in recent years, as an alternative to fossil fuels. It is often suggested as a more favorable solution than supplying pure hydrogen due to its higher volumetric energy density. In this study a dual fuel CI engine running on ammonia and diesel mixture was tested, as a means to utilize ammonias potential in diesel engines. The injection strategy was port injection for ammonia, where it was mixed with air, and direct injection of diesel oil. A set of different NH3-diesel mixtures were tested. Due to partial substitution of diesel fuel by NH3 the elementary composition of fuel has changed. It increased nitrogen’s and reduced carbon’s mass in the combustion chamber. Consequently, the exhaust species have also changed. The Fourier Transform Infrared Spectroscopy was used to analyze the composition of flue gas. On top of investigating changes in CO2, CO, HC, NOX, residual ammonia molar fraction was observed. Possibility of using residual ammonia to activate selective catalytic reduction (SCR) system and its effectiveness in different operating points of engine were investigated. As part of the research, a numerical model of operation of the used SCR system was also developed. Results from the experiments have served to validate numerical model. Created model was then used to analyze wider spectrum of operating conditions of the engine and SCR.

Synergistic poisoning of KCl and PbCl2 on commercial V2O5-MoO3/TiO2 catalysts for MSW incineration flue gas denitrification

Alkali and heavy metal chlorides cause the deactivation of selective catalytic reduction (SCR) catalysts during municipal solid waste incineration. In this study, the synergistic poisoning of KCl and PbCl2 on commercial V2O5-MoO3/TiO2 SCR catalysts was investigated. Compared with KCl, PbCl2 could combine with Mo components and protect V sites from poisoning. Besides, the chemical bonds between PbCl2 and V sites were weaker. Hence, the single poisoning of PbCl2 was weak to the denitrification of SCR catalyst. Whereas, under the co-poisoning of KCl and PbCl2, V-O-Cl structures were formed, which suppressed NH3 activation, thereby causing the deactivation of SCR catalyst.

Low-Temperature SCR Catalyst Development and Industrial Applications in China

In recent years, low-temperature SCR (Selective Catalytic Reduction) denitrification technology has been popularized in non-power industries and has played an important role in the control of industrial flue gas NOx emissions in China. Currently, the most commonly used catalysts in industry are V2O5-WO3(MoO3)/TiO2, MnO2-based catalysts, CeO2-based catalysts, MnO2-CeO2 catalysts and zeolite SCR catalysts. The flue gas emitted during industrial combustion usually contains SO2, moisture and alkali metals, which can affect the service life of SCR catalysts. This paper summarizes the mechanism of catalyst poisoning and aims to reduce the negative effect of NH4HSO4 on the activity of the SCR catalyst at low temperatures in industrial applications. It also presents the outstanding achievements of domestic companies in denitrification in the non-power industry in recent years. Much progress has been made in the research and application of low-temperature NH3-SCR, and with the renewed demand for deeper NOx treatments, new technologies with lower energy consumption and more functions need to be developed.

Regeneration study on active components supplement of waste V2O5-WO3/TiO2 SCR catalyst

The waste selective catalytic reduction (SCR) catalysts were regenerated by active components supplement on the basis of alkali/acid washing treatment. Through orthogonal design, the regenerated SCR catalyst restored the denitration activity of 98.36% at optimal regeneration parameters of 6% WO3 loaded after 1.2% V2O5 loaded and then calcined at 500 oC. The catalysts were characterized by XRD and H2-TPR techniques. The XRD patterns and the FT-IR spectrogram showed that the supplemented V2O5 and WO3 were dispersed uniformly in amorphous state on the surface of TiO2 support which remained as anatase phase. The H2-TPR characterization reported that V2O5 significantly affected on the low-temperature activity while WO3 mainly affected the high-temperature activity, the loading sequence of V2O5 before WO3 not only enhanced the interaction between V2O5 and TiO2 but also facilitated the enrichment of WO3 on TiO2 surface.

Cement solidification/stabilization of the toxicants from spent commercial SCR catalyst

AbstractBACKGROUNDThe present work focuses on a harmless treatment of hazardous substances in spent commercial selective catalytic reduction (SCR) catalyst by using cement as a binder. The spent V2O5‐WO3/TiO2 SCR catalysts were ground and mixed with the cement to prepare the solidified products, according to a simple method in this study. The solidified products were subsequently submitted to a characterization process based on inductively coupled plasma mass spectrometry (ICP‐MS), X‐ray diffraction (XRD), X‐ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and N2 adsorption–desorption analysis. The leaching characteristics of hazardous substances, such as V, As, Cr and Pb, in solidified products were studied and the effects of mixed ratio between deactivated SCR catalyst and cement on leaching characteristics of hazardous substances were investigated.RESULTSThe experimental results showed that the cement was effective in immobilizing hazardous substances (V, As, Cr and Pb) present in the spent catalyst. When the cement hardened with 50% spent catalyst addition, the solidified products exhibited extremely low leaching concentrations of V, As, Cr and Pb, which are 0.6, 1.3, 2.3 mg L−1 and 16.5 μg L−1, respectively.CONCLUSIONThe leaching toxicity of hazardous substances is far lower than that of the National Standard of China and European regulations. The characterization analysis revealed that the active silicate sand hydroxyl compounds play an important role in immobilizing hazardous substances in spent SCR catalyst. The cement solidification method was expected to achieve the harmless treatment on spent SCR catalyst for the first time. © 2020 Society of Chemical Industry (SCI)

Interaction mechanism between Se species in flue gas and V2O5-MoO3/TiO2 catalyst: An in-depth experimental and theoretical study

The deactivation of denitrification catalysts has attracted widespread attention, whereas little is known about the poisoning effect of selenium (Se) species to date. In this study, the influence of element Se (Se0), SeO2 and CaSeO3 on the activity of V2O5-MoO3/TiO2 selective catalytic reduction (SCR) catalyst were evaluated under different temperatures. It was found that under 200 °C Se species had no significant effects on the denitrification efficiency. However, the performances of the catalysts were notably suppressed over 250 °C. The interaction mechanism between Se species and V2O5-MoO3/TiO2 catalyst was unveiled via combined comprehensive characterizations and density functional theory (DFT) calculations. The results indicated that the role of CaSeO3 was mainly physical poisoning and little interaction was observed, while Se0 and SeO2 could cause chemical deactivation because of the strong electron transfer. On the catalyst surface, Se0 could react with V2O5 and MoO3 to form Se4+ species (SeO2, VxSeyOz and MoxSeyOz). The formation of VxSeyOz reduced the acid sites on the catalyst, causing irreversible denaturation of the active component V2O5. The formed MoxSeyOz could protect the V2O5 to a certain extent and decompose at higher temperatures to restore the chemical properties of MoO3. SeO2 could be reduced to Se0 by NH3, forming a SeO2 → Se0 → SeO2 cycle beside the SCR process, which continuously hindered the removal of NOx. As the temperature gradually increased, SeO2 sublimated away from the catalyst, partially restored the catalytic activity.

Effects of Se and SeO2 on the denitrification performance of V2O5-WO3/TiO2 SCR catalyst

Various trace elements in flue gas emitted from coal combustion can cause the deactivation of selective catalytic reduction (SCR) catalysts, yet rare studies have been reported on selenium species. Herein, the effects of Se and SeO2 on the denitrification performance of commercial V2O5-WO3/TiO2 SCR catalyst were investigated. Results indicated that the activities of Se and SeO2-doped catalysts were significantly inhibited at temperatures above 250 °C. During the NH3-SCR process, metallic Se was oxidized by V2O5 to generate Se4+ (SeO2 and binary oxides VxSeyOz), while part of Se4+ was reduced to Se by NH3. Se and SeO2 deactivated the catalyst by consuming V2O5 and NH3 during the NH3-SCR process, covering the active sites and relieved the redox performance of catalysts. With the sublimation of Se and SeO2, the deactivation effect on the catalyst was greatly relieved, while the presence of residual VxSeyOz resulted in the incomplete recovery of the catalyst activity.

Durability of V2O5-WO3/TiO2 selective catalytic reduction catalysts for heavy-duty diesel engines using B20 blend fuel

The durability of V2O5-WO3/TiO2 selective catalytic reduction (SCR) catalysts for heavy-duty diesel engines was evaluated based on 500 h SCR durability tests conducted using B20 fuel (20% v/v biodiesel + 80% v/v petroleum diesel). The fresh and deteriorated SCR catalysts were characterized by X-ray fluorescence, X-ray diffraction, and Brunauer-Emmett-Teller surface area measurements to investigate the deterioration mechanism of the catalysts. The results show that the SCR de-NOx performance is degraded after SCR durability testing, particularly at high engine speeds. The NOx conversion efficiency of the deteriorated SCR catalysts decreases at temperatures above 400 °C but remains high at temperatures between 250 and 400 °C. The catalyst characterization results reveal that the deterioration in the de-NOx performance is not owing to anatase-to-rutile transformation of TiO2, but because of a decrease in the specific surface area and the loss of the catalyst components, which are greater in the front cross section of the SCR than in the rear cross section. For a given catalyst cross section, the decrease in the specific surface area exhibits a positive correlation with the flow rate of the exhaust gas.

Adsorption / Desorption Performance and NOx Removal Efficiency of BaO Loaded V2O5-WO3/TiO2 Selective Catalytic Reduction Catalyst

Adsorption / Desorption Performance and NOx Removal Efficiency of BaO Loaded V2O5-WO3/TiO2 Selective Catalytic Reduction Catalyst

The combined promotive effect of SO2 and HCl on Pb-poisoned commercial NH3-SCR V2O5-WO3/TiO2 catalysts

In this study, the deactivation of commercial V2O5-WO3/TiO2 selective catalytic reduction catalysts by Pb was discussed primarily, and the combined promotive effects of SO2 and HCl on Pb-poisoned V2O5-WO3/TiO2 catalysts were studied. The results show that the treatment with SO2 and HCl markedly improves the NOx conversion of Pb-poisoned catalysts. SO2 and HCl react with Pb chemisorbed on V2O5, which increases effectively the ratio of V5+ and active oxygen species and the amount of acid sites.

The synthesis of titanium dioxide nanoparticles from titanium slag and its use for low temperature SCR catalyst

The titanium dioxide nanoparticles with high purity and specific surface area were synthesized through an alkali-solution and acid-isolation method with titanium slag as raw material. As a catalyst support of V2O5-WO3-MoO3/TiO2 selective catalytic reduction catalyst, the high specific surface area TiO2 nanoparticles can improve the low temperature activity of the catalyst and enhance its resistance to sulfur poisoning.

Recovery TiO 2 and sodium titanate nanowires as Cd(II) adsorbent from waste V 2 O 5 -WO 3 /TiO 2 selective catalytic reduction catalysts by Na 2 CO 3 -NaCl-KCl molten salt roasting method

In this study, Cd(II) adsorbent has been recovered from waste and toxic WO3-V2O5/TiO2 Selective Catalytic Reduction (SCR) catalysts via a creative Na2CO3-NaCl-KCl (NNK) molten salt roasting method (MSM) followed by a leaching process to remove the toxic and valuable W and V. Such facile process enables a faster roasting reaction at a lower temperature compared to conventional roasting methods, achieving an optimized W and V leaching rate of 99.3% and 98.4%. The produced Cd(II) adsorbent mainly consists of TiO2 and sodium titanate nanowires (TiO2/STNWs) with a maximum Cd(II) adsorption capacity is 146.5 mg/g when the pH value is 6. The Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analysis show that the adsorption of Cd(II) by our products can be ascribed to the Cd(II) ion exchange with Na ions and the hydroxyl groups. This study proposes a sustainable and economic approach for producing large scale and high-quality Cd(II) adsorbent via disposing waste SCR catalysts, which shows a great potential in the industrial applications.

CaSO4 deactivated V2O5-WO3/TiO2 SCR catalyst for a diesel power plant. Characterization and simulation of the kinetics of the SCR reactions

The deactivation of a diesel SCR (Selective Catalytic Reduction) catalyst by impregnation with CaSO4 was studied. The loss in activity after 2729 h of use on the engine was lower than when deactivated by impregnation. This was the case even if the amount of Ca in the catalyst was high after use on the engine. In the used catalyst a surface layer of CaSO4 was built up on the monolith during use. This causes lower deactivation than when CaSO4 was introduced in the pore system of the catalyst.The kinetics of the SCR reaction, the oxidation of NH3 to N2 and two side reactions leading to N2O was used in the simulation. A coverage dependent heat of adsorption of NH3 was used. The heat decreased with the coverage and with the introduction of CaSO4 into the pores. After fitting the amounts of NO and N2O at the exit of the reactor against the temperature at the exit of the bed excellent agreements were obtained for the products N2 and H2O as well for the reactant NH3.This is the first time that the effect of CaSO4 poisoning of SCR catalysts and its effect on the kinetics is published.

Mn-Ce-V-WOx/TiO2 SCR Catalysts: Catalytic Activity, Stability and Interaction among Catalytic Oxides

A series of Mn-Ce-V-WOx/TiO2 composite oxide catalysts with different molar ratios (active components/TiO2 = 0.1, 0.2, 0.3, 0.6) have been prepared by wet impregnation method and tested in selective catalytic reduction (SCR) of NO by NH3 in a wide temperature range. These catalysts were also characterized by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), in situ Fourier Transform infrared spectroscopy (in situ FTIR), H2-Temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The results show the catalyst with a molar ratio of active components/TiO2 = 0.2 exhibits highest NO conversion value between 150 °C to 400 °C and good resistance to H2O and SO2 at 250 °C with a gas hourly space velocity (GHSV) value of 40,000 h−1. Different oxides are well dispersed and interact with each other. NH3 and NO are strongly adsorbed on the catalyst surface and the adsorption of the reactant gas leads to a redox cycle with the valence state change among the surface oxides. The adsorption of SO2 on Mn4+ and Ce4+ results in good H2O and SO2 resistance of the catalyst, but the effect of Mn and Ce are more than superior water and sulfur resistance. The diversity of valence states of the four active components and their high oxidation-reduction performance are the main reasons for the high NO conversion in this system.

DRIFT Studies on the Selectivity Promotion Mechanism of Ca-Modified Ce-Mn/TiO2 Catalysts for Low-Temperature NO Reduction with NH3

Manganese-based catalysts have shown excellent low-temperature selective catalytic reduction (SCR) activity for NOx removal. However, they would always produce a high amount of more toxic byproduct, N2O. Ca modification has been reported to be able to promote N2 selectivity for SCR catalysts, but the mechanism is still not clear. In this study, a series of Ca-modified Ce0.02Mn0.4/TiO2 SCR catalysts were utilized for mechanism study. In terms of DRIFT analysis, the addition of Ca had significantly reduced the formation of NH on catalyst surface, which limited its reaction with NO to form N2O. Furthermore, Ca addition had also caused a deceased formation of NO2, reducing its reaction with NH3 to form N2O, further increasing the N2 selectivity of the catalysts. The results present herein could be beneficial to the development of efficient low-temperature SCR catalysts, particularly for Mn-based SCR catalysts.