Commercial SCR Catalyst Research Articles

Transformation of Arsenic from Poison into Active Site by Construction of Unique AsOx/CeO2 Interface for Stable NOx Removal.

Arsenic in the flue gas has been widely reported as a common poison for SCR catalysts; however, an appropriate coping strategy is still lacking to improve the arsenic resistance performance. Herein, a unique AsOx/CeO2 interface is constructed to transform arsenic from poison into active site with balanced acid-redox property, successfully achieving efficient NOx removal. The optimized AsOx/CeO2 exhibits high NOx removal efficiency, four times that of the As-poisoned V2O5/TiO2 catalyst, and even comparable to the state-of-the-art SCR catalysts. It was found that the As-O-Ce interfacial sites in oxygen-bridged As dimers on CeO2 can provide both Lewis acid sites and active lattice oxygen species, enhancing the adsorption and activation of NH3 to form key -NH2 intermediates, thereby facilitating the NH3-SCR reaction. More surprisingly, a thin CeO2 layer on the top of V2O5/TiO2 can capture arsenic to protect catalysts from arsenic attacking, which improves the catalytic activity to 2.8 × 10-7 mol g-1 s-1, even higher than that of fresh V2O5/TiO2 (2.0 × 10-7 mol g-1 s-1). Therefore, this strategy provides new ideas not only for designing antipoisoning SCR catalysts but also a feasible solution for the stable operation of commercial SCR catalysts in arsenic-containing flue gas.

Against catalyst deactivation during toluene oxidation on CuCeOx in flue gas: High oxidation efficiency and rapid oxidation pathway

The removal of volatile organic compounds (VOCs) from flue gas by a tightly coupled catalytic oxidation process in the NH3-SCR unit is a cost-effective approach. A CuCeOx bimetallic mixed oxide catalyst prepared by the co-precipitation method has demonstrated the ability to completely convert toluene at 350 ℃ under simulated flue gas conditions. Cu oxide is considered as the main active site for toluene oxidation, and the introduction of Ce induced a synergistic effect which enhanced the surface adsorbed oxygen and oxidation performance. The CuCeOx catalyst was found to outperform commercial VOC catalysts (Pt/Al2O3) and SCR catalysts (V2O5-WO3/TiO2) under the influence of different flue gas components. The negative effect of the flue gas on CuCeOx almost diminished at 350 ℃. The mechanism study showed that toluene on CuCeOx underwent a rapid oxidation pathway, thereby avoiding the potential interaction between intermediates and flue gas components. The superior catalytic performance of CuCeOx in the simulated flue gas conditions were attributed to the higher toluene adsorption efficiency and weaker adsorption towards the flue gas components.

The modification of commercial SCR catalyst with low V loading for benzene degradation: Improvement of the COx selectivity and inhibition of transformation to PAHs

V2O5-WO3/TiO2 (VWT) was modified by Fe and Mo to degrade benzene at selective catalytic reduction with NH3 (NH3-SCR) reaction temperature (350 °C). Mo modified catalyst (Mo-VWT) was found greatly increased COx selectivity from 74.80 % (VWT) to 94.00 %. Meanwhile, the transformation of benzene into polycyclic aromatic hydrocarbons (PAHs) was effectively inhibited, with the PAHs selectivity decreased from 3.04 % (VWT) to 0.34 %. According to X-ray photoelectron spectroscopy (XPS), Mo could play as the carrier to efficiently transform electron from V to W, increasing the amount of V5+ and oxygen vacancies (Ov). Temperature programmed reduction (TPR) experiments proved that Mo could also play as the carrier for surface lattice oxygen (W-Olat-s) migrating from W to V, replenishing adsorbed oxygen species (Oads) and keeping a higher amount of V5+-Oads for benzene degradation. Based on temperature programmed desorption of benzene (benzene-TPD) and in situ diffuse-reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) results, it was found that surface Mo-OH could provide new benzene activation sites to form strongly adsorbed phenol, which was easily oxidized by V5+-Oads. For VWT, benzene would be weakly activated to form the weakly adsorbed phenol, which would desorb as phenyl to transform into PAHs. When the degradation of benzene was carried out under NO + NH3, catalyst surface Oads and Olat-s tended to be occupied by NH3, which hindered the migration of W-Olat-s and weakened the oxidation of phenol. Therefore, more phenol would desorb and transform to PAHs.

Study on impregnation process optimization for regenerating the spent V2O5-WO3/TiO2 catalysts

It is of great economic value and environmental significance to extend the service life of commercial SCR catalysts. Water and acid wash as well as thermal regeneration were often used to remove toxic substances (such as dust, metal sulfates and metal chlorides) residual on catalyst surface so as to reduce the replacement frequency of catalyst, but easily lead to the loss of active components. In this paper, impregnation method was used to supplement the lost active components of the spent honeycombed V2O5-WO3/TiO2 (labeled as VW/Ti) catalyst, and the effects of drying duration and impregnation solution concentration on NH3-SCR performance of catalyst were studied. The results showed that the catalyst dried for 6 h at 110 °C exhibited the best deNOx activity and sulfur/water resistance. Further prolonging or shortening drying duration reduced the catalytic activity instead. It can be attributed that proper drying duration constructs abundant pore channels inside catalyst, optimizes active components dispersion, reduces diffusion resistance of reactants into the inner surface and provides more effective active sites on catalyst surface for adsorption and oxidation of reactants. With rise of V content in impregnation solution from 1.06 wt.% to 3.61 wt.%, deNOx activity as well as SO2/H2O resistance of catalyst improves at 150–300 °C. Besides, key influence factors are also discussed based on reaction kinetics analysis.

Experimental investigation on the decomposition of NH4HSO4 over V2O5-WO3/TiO2 catalyst by NH4NO3 at low temperature

Deactivation by NH4HSO4 deposition is one of the major problems faced by commercial SCR catalysts at low temperatures. In this study, NH4NO3 was added to the SCR reaction atmosphere in the presence of H2O and SO2 at 250 °C, which is lower than the typical temperatures suitable for the V2O5-WO3/TiO2 catalyst. After a long test, the catalyst activity decreased from 82 % to 75 %, which is much smaller than the activity drop in the atmosphere without NH4NO3. The characterization results indicate that the addition of NH4NO3 effectively reduced the deposition of NH4HSO4 on the catalyst surface, thus weakening the degree of catalyst poisoning deactivation. In addition, we examined the effect of NH4NO3 addition on the regeneration of catalysts deactivated by NH4HSO4. The activity of the catalyst deactivated by 5 wt% NH4HSO4 recovered efficiently after the deactivated catalyst was treated by NH4NO3, NO and O2 for 1 h at 250 °C. The SEM, FTIR, and BET characterization results reveal the positive effect of NH4NO3 in promoting the decomposition of NH4HSO4.

DeNOx Characteristics of Commercial SCR Catalyst Regenerated On-Line by Dry Ice Blasting in a Coal-Fired Power Plant

DeNO<i>x</i> Characteristics of Commercial SCR Catalyst Regenerated On-Line by Dry Ice Blasting in a Coal-Fired Power Plant

Commercial SCR catalyst modified with different noble metals (Ag, Pt, Pd) to efficiently remove slip ammonia and NOx in the flue gas

BackgroundWith the increasingly strict emission standard of flue gas, ammonia escape has been one of the urgent problems to be solved in the SCR process of coal-fired power plants. Slip ammonia is regarded as the secondary pollution in SCR process. Moreover, slip ammonia cannot only result in the deactivation of SCR catalyst, thus reducing NO removal efficiency, but also form NH4HSO4 and then corrode the equipment, which can do serious harm to the operation safety. Therefore, it is important to find ways to efficiently remove slip ammonia from the coal-fired plants with the complex gas composition. MethodsCommercial SCR (V2O5-WO3-TiO2) catalysts were modified with various noble metals (Ag, Pd, Pt) by improved impregnation methods. The NH3 oxidation performance of them was tested to select the most significant catalyst in selective catalytic oxidation of ammonia (NH3-SCO) and the effect of NO, SO2 and H2O were also investigated. Significant findingsThe experimental results showed that noble metals modification could all markedly improve the oxidation ability to remove slip ammonia from coal-fired plants and Ag/SCR catalyst obtained the best application prospect due to its low price. The NH3 conversion of Ag/SCR catalyst reached 92% at 350 °C. Moreover, 95% NOx could be removed when NO was introduced in the gas. Based on the characterization results, the introduction of noble metals had no visible influence on the structure and specific surface area of commercial SCR catalyst but it could increase the redox properties and the number and intensity of surface acidic sites. In addition, the redox cycles between noble metals and vanadium species on SCR catalyst surface were conducive to generate more active oxygen and promote the oxidation capacity of the catalysts.

Improvement in the Resistance to Kcl and Pbcl2 Synergistic Poisoning of the Commercial Scr Catalyst by Ce(So4)2 Modification: A Combined Experimental and Spin-Polarized Dft Study

Improvement in the Resistance to Kcl and Pbcl2 Synergistic Poisoning of the Commercial Scr Catalyst by Ce(So4)2 Modification: A Combined Experimental and Spin-Polarized Dft Study

Transition metals modified commercial SCR catalysts as efficient catalysts in NH3-SCO and NH3-SCR reactions

Different transition metals were used to modify commercial V2O5-WO3-TiO2 catalysts to remove slip ammonia and residual NOx from the tail of SCR system. The performance of selective catalytic oxidation of NH3 (NH3-SCO) and selective catalytic reduction of NO by NH3 (NH3-SCR) of different catalysts at 150-400 ℃ was studied. The results showed that the loading of transition metals could significantly improve the NH3 oxidation ability of the catalysts, and the presence of NO furtherly promoted it. Cu-SCR catalyst obtained the best activity of both NH3 oxidation and NOx reduction at 350 ℃, and had excellent SO2 and H2O resistance in the presence of NO. The characterization results indicated that the transition metals enhanced the amounts of acid sites and redox ability of the catalysts. Moreover, the transition metals could increase the active oxygen and improve the catalytic performance of the catalysts by the redox reaction with V4+/V5+.

Enhancement of Hg0 oxidation removal in chloride-free flue gas over FeOCl-modified commercial selective catalytic reduction catalyst

SCR denitration catalysts have been considered for the synergistic catalytic oxidation of gaseous elemental mercury (Hg0) depending on HCl in flue gas. In this study, FeOCl was used for the enhancement of Hg0 removal in chloride-free flue gas over a commercial SCR catalyst. The results indicated that loading 10% FeOCl can significantly improve the Hg0 removal efficiency of SCR catalyst to 97% at 250 °C in chloride-free flue gas. O2 exerted an important positive effect on the conversion of Hg0 to HgO. The FeOCl/SCR catalyst exhibited satisfactory SO2 and H2O resistance. The examination of the mechanism of action indicated that Hg0 reacts with •Cl released from FeOCl/SCR to form HgCl2. A spot of Hg0 can directly react with adsorbed surface oxygen to generate HgO fixed on the active site of FeO on the FeOCl/SCR catalyst via chemisorption.

Characterization Method for Gas Flow Reactor Experiments—NH3 Adsorption on Vanadium-Based SCR Catalysts

In this study, NH3 adsorption isotherms for a commercial vanadium-based SCR catalyst coated on a monolith substrate were obtained using a gas flow reactor over a wide range of parameters which have not been performed before in a single study. The isotherms were obtained under different conditions, where adsorption temperature, NH3 concentration, water concentration, washcoat loading, and catalyst oxidation state were varied. For this purpose, a systematic data processing method was developed, which characterizes the dispersion and delay effects in the experimental setup using a residence time distribution model, and artifacts such as NH3 adsorbed in the experimental setup and uncertainties in the washcoat loading were removed. As a result, data from different catalyst samples were integrated, and adsorption isotherms with low data spread and well-defined regions were obtained. This allows the identification of the complex nature of the catalyst and dynamics, where multiple types of adsorption sites are present. For instance, the oxidized catalyst has 50% higher NH3 storage capacity compared to the reduced state of the sample. Moreover, water reduces the NH3 storage capacity at high concentrations (5.0%), whereas at low concentration (0.5%), water increases the NH3 adsorption capacity for an oxidized catalyst. The proposed data processing method can be extended for the analysis of further phenomena in catalysts studied using gas flow reactors, complementing current methods and providing information for models with extended validity and lower parameter correlations.

질소산화물 저감을 위한 Cu-SCR 촉매의 TiO2 첨가가 내구성에 미치는 영향

This study is to investigate the effect on TiO₂ loading amounts to improve the durability of thermal aging and coking of commercial chabasite SCR catalysts. The 4. Cu-SCR+7wt%TiO₂ catalyst showed the highest NOx conversion rate of 61% on average in the entire temperature range of 200~50 0℃. The Cu-SCR catalysts containing on 2, 5, and 7wt%TiO₂ compared to fresh Cu-SCR catalyst decreased NOx conversion rate to -19%, -19% and -20% under thermal aging conditions at 850℃ for 24 hours. The de-NOx performance of the Cu-SCR+2wt%TiO₂ catalyst was improved. The promoter TiO₂ is acidic and has improved durability against carbon poisoning caused by oxidation of C₃HSUB6/SUB. 2. Cu-SCR+2wt%TiO₂ was improved the de-NOx performance than other catalysts under the coking condition of 16.5 g/L C. When considering the evaluation of the thermal aging and durability against coking of the Cu-SCR commercial catalysts, the proper amounts of TiO₂ was 2wt%.

상용 차바사이트 SCR 촉매의 열적 열화와 코킹의 내구성 향상을 위한 조촉매 연구

This study is to investigate the promoter to improve the durability of thermal aging and coking of commercial chabasite SCR catalysts. Cu-SCR+WO₃ SCR catalyst has improved NOx conversion at low and medium temperature, and WO₃ increased the strength of acid point to speed up the reaction rate. When C₃HSUB6/SUB coexisted (C/N = 9), the de-NOx/CO performance of the Cu-SCR+TiO₂ SCR catalyst was improved by adding TiO₂ to poisoning. An appropriate amount of TiO₂ strengthened the acidity of the SCR catalyst, which improved durability against carbon poisoning. The Cu-SCR+TiO₂ SCR catalyst had a 4.7% higher NOx conversion under C₃HSUB6/SUB coexistence conditions in de-NOx performance according to 54 g/L coking and C3H6 coexistence (C/N = 9) poisoning. This deteriorated de-NOx performance by clogging the active site of the SCR catalyst when coking excessively at 54 g/L. Cu-SCR+TiO₂ SCR catalyst on which TiO₂ was loaded has improved durability against catalyst coking when C₃HSUB6/SUB coexists. It is necessary to derive an optimal loading amount in the future.

Simultaneous improvement of ammonia mediated NOx SCR and soot oxidation for enhanced SCR-on-Filter application

The integration of NOx reduction and catalytic soot oxidation was investigated for the SCRoF (Selective Catalytic Reduction on Filter) applications. By physically mixing a commercial SCR catalyst (either Fe-ZSM-5 and Cu-ZSM-5) with a soot oxidation catalyst (K/CeO2-PrO2), it was possible to lower the soot oxidation temperature by more than 150 degrees and, by optimizing the catalysts mass ratio in the mixture, NOx conversion simultaneously increased, because NO oxidation induced a fast SCR reaction pathway, unlike during standard SCR. Such an improvement in NOx conversion was more pronounced with the Fe-ZSM-5 than with the Cu-ZSM-5 zeolite, as the latter was more sensitive to the NO2/NOx ratio. In order to make the soot oxidation catalyst inactive towards ammonia oxidation, poisoning of the surface acid sites with 3.0 wt.% K2CO3 (corresponding to only 1.0 wt.% K) was performed. In the soot oxidation and SCR catalysts physical mixture, the soot was oxidized mainly by O2 and the contribution of NO2 to oxidation was negligible, as NO2 itself was a key reactant in the (kinetically much faster) SCR reaction.

Enhancement of CeO2 modified commercial SCR catalyst for synergistic mercury removal from coal combustion flue gas.

CeO2 modified commercial SCR (selective catalytic reduction) catalysts with different CeO2 content were prepared and researched for synergistic mercury removal from coal combustion flue gas in this study. The characterization analyses on the catalysts indicated that the introduction of CeO2 increased the surface area, the dispersity of the metal oxides on the TiO2 support and the redox behavior of the catalyst, which was beneficial to the catalytic activity. The experimental results confirmed that the CeO2 loading improved the catalytic efficiencies over the commercial SCR catalyst. The catalyst with a CeO2 content of 4% displayed the optimal performance for NO and synergistic Hg0 removal, of which the NO conversion and Hg0 removal efficiency reached 90.5% and 78.2%, respectively, at 300 °C in simulated coal-fired flue gas. The Hg0 removal activity, the independence of Hg0 removal from HCl concentration and the effects of SO2, NO and NH3 on Hg0 removal efficiency all became positive over the modified catalyst compared to over the raw one, which was mainly due to the sufficient chemisorbed oxygen derived from the synergy of V2O5 and CeO2 and the redox transformation between Ce3+ and Ce4+ on the catalyst surface. The CeO2 modification generated a significant enhancement on the catalytic performance and made the commercial SCR catalyst more suitable to be employed for NO and synergistic mercury removal in a coal combustion power plant.

Correction to: Regeneration of commercial SCR catalyst deactivated by arsenic poisoning in coal-fired power plants

The article Regeneration of commercial SCR catalyst deactivated by arsenic poisoning in coal-fired power plants, written by Qiang Lu*,†, Zulfiqar Ali*, Hao Tang*, Tahir Iqbal*, Zulqarnain Arain**, Min-shu Cui*, Ding-jia Liu*, Wen-yan Li*, and Yong-ping Yang*, was originally published on the publisher’s internet portal (currently SPringerLink) on 08 February 2019 with misprinted DOI number, 10.1007/s11814-018-0227-9, due to the technical error from converting manuscript file from Microsoft Word to PDF. The correct DOI number for the article is 10.1007/s11814-019-0314-y.

Influence mechanism of the compositions in coal-fired flue gas on Hg0 oxidation over commercial SCR catalyst

Optimizing the performance of commercial SCR catalyst (i.e., V2O5–WO3/TiO2) for Hg0 oxidation remained stagnant as the influence mechanism of the compositions of flue gas on Hg0 oxidation was unclear. In this work, the mechanism of Hg0 oxidation and the influence mechanism of the compositions of flue gas on Hg0 oxidation over V2O5–WO3/TiO2 were investigated. The reaction orders of Hg0 oxidation over V2O5–WO3/TiO2 in regard to both the concentrations of Hg0 and HCl in gas phase were approximately 0. Hence, Hg0 oxidation over V2O5–WO3/TiO2 primarily followed the Langmuir–Hinshelwood mechanism, and the elementary reactions of Hg0 oxidation primarily involved the physical adsorption of Hg0, the formation of Cl* radial, and the reaction of physically adsorbed Hg0 and Cl* radial. SO2, NO, H2O, and NH3 not only restrained the Cl* radial formation but also disturbed the reaction of physically adsorbed Hg0 and Cl* radial. Meanwhile, the physical adsorption of Hg0 was restrained by both H2O and NH3. Hence, Hg0 oxidation over V2O5–WO3/TiO2 was obviously restrained when SO2, NO, H2O, and NH3 were present in flue gas.

Investigation of sulphated CuCl2/TiO2 catalyst for simultaneous removal of Hg0 and NO in SCR process

To achieve the oxidation of mercury in the presence of HCl with low concentration and mitigate the inhibition effect of NH3, sulphated CuCl2/TiO2 catalyst was investigated for simultaneous removal of Hg0 and NO in SCR process. The sulphation was conducted by exposing CuCl2/TiO2 catalyst to a gas stream containing SO2 and O2.Characterizations of catalysts (BET, XRD, XRF, XPS, TG-MS and NH3-TPD) were carried out to illuminate the structure-performance relationship. Results showed that the remained CuCl2 and generated CuSO4 over this catalyst were responsible for Hg0 oxidation and NH3-SCR reaction. The generated CuSO4 increased the amount of acid sites on catalyst surface thus promoting the SCR activity. CuCl2(S18)/TiO2 catalyst exhibited simultaneous catalytic oxidation of Hg0 (around 73.9%) and NO (around 87%) at the temperature of 325 °C. Hg0 oxidation over this catalyst was not handicapped by the low content of HCl in gas stream, different from commercial SCR catalyst. Individual NO and NH3 showed insignificant effect on Hg0 oxidation. While the co-presence of NO and NH3 somewhat inhibited it. Moreover, good resistance to the moderate concentration of SO2 and H2O for the catalyst was observed.

Insight into regeneration mechanism with sulfuric acid for arsenic poisoned commercial SCR catalyst

Washing method by sulfuric acid was investigated in the context of deactivation and regeneration mechanism of arsenic deactivated catalyst over V2O5-WO3/TiO2 catalyst. The physical and chemical properties changes for catalysts were characterized by XRD, SEM, BET, Raman, XPS, NH3-TPD and in situ DRIFT, therein including morphology, structure, chemical states, surface acidity and functional groups. The results indicated that arsenic species mainly consisted of As2O5 on the arsenic poisoned catalyst surface. It increased N2O formation due to high active oxygen ratio of poisoned catalyst. After regeneration, the N2O formation was reduced. Arsenic oxides covering on catalyst surface could be almost wipe off with sulfuric acid. As-OH group disappeared, and the Brønsted and Lewis acid sites were re-exposed. Moreover, a new Brønsted acid sites (S-OH) was formed by chelating bidentate sulfates (SO42−) since it introduced S=O into anatase TiO2 lattice. However, some vanadium species were lost and the remaining species tended to form V4+, the activity had an apparent decrease in the temperature range of 300–400 °C.

Sulfation effect of Ce/TiO2 catalyst for the selective catalytic reduction of NO x with NH3: mechanism and kinetic studies.

Ceria-based catalysts are competitive substitutes for the commercial SCR catalysts due to their high SCR activity and excellent redox performance. For a better understanding of the SO2 poisoning mechanism over ceria-based catalysts, the sulfation effect of the Ce/TiO2 catalyst on the SCR activity over a wide reaction temperature range was systematically studied via comprehensive characterizations, in situ DRIFT studies and kinetic studies. The results demonstrated that the NO conversion at 150 °C is significantly inhibited by the formation of cerium sulfites/sulfates due to the inhibited redox properties and excessive adsorption of NH3, which restrict the dissociation of NH3 to NH2, resulting in a much lower reaction rate of E–R reaction over the sulfated Ce/TiO2 catalyst. With the increase in the reaction temperature, the reaction rate of the E–R reaction significantly increased due to the improved redox properties and weakened adsorption of NH3. Moreover, the rate of the C–O reaction over the sulfated Ce/TiO2 catalysts is obviously lower than that of the fresh Ce/TiO2 catalyst. The promotion of NO conversion over the sulfated catalyst at 330 °C is attributed to both the increase in the reaction rate of E–R reaction and the inhibition of the C–O reaction.