Search

Ceria catalysts have attracted considerable interest in the NH3-SCR reaction. The modification of SO42− into CeO2 promotes the NH3-SCR reaction. NH3 adsorption property and four possible reaction paths are further design over CeO2 (111) and SO42−–CeO2 (111) surface. The results reveal that NH3 adsorption of the Lewis acid site is stronger than the Brønsted acid site, and the adsorption energies of the Lewis acid site range from − 0.397 to − 0.963 eV with the modification of SO42−. Thus, the introduction of SO42− into CeO2 increases the adsorption site stability of NH3. NH3 adsorption is the first step in NH3-SCR reaction, and then, the key intermediates such as NH2, NH2NO, NNOH, NH3NO2 species are found. Standard SCR reaction and fast SCR reaction constitute a catalytic cycle in CeO2 catalyst. The different paths of NH3NO2 and NH2NO formation are different, and it led to NNOH only emerge in the fast SCR reaction. Lewis acid site is main reaction site for the standard SCR reaction. Energy barriers of Lewis acid site range from 15.82 to 15.68 kcal/mol by the introduction of SO42−, which makes the NH3-SCR reaction easily occur. [ABSTRACT FROM AUTHOR]

A series of CeO2-modified TiO2–ZrO2–SO42− catalysts were employed to the selective catalytic reduction (SCR) of NOx by NH3. The obtained results indicated that the interaction between CeO2 and TiO2–ZrO2–SO42− contributed to the increased reducibility and decreased surface acidity with the augment of CeO2. The in situ DRIFTS results suggested that suitable surface acidity and reducibility could be offered by increasing the ceria loadings from 24 to 40 wt%. The amount of adsorbed NH3 species, amide species (–NH2) and activated nitrate was increased with the augment of ceria. Excessive addition of CeO2 (80 wt%) resulted in the lacking of surface acid sites and induced the inert nitrate species generation on the catalysts surface. [ABSTRACT FROM AUTHOR]

The promoting effects of SO42− on N2 selectivity for selective catalytic oxidation (SCO) of ammonia to nitrogen over RuO2/ZrO2 catalyst were systematically investigated. The catalysts were measured by different characterization methods (BET, XRD, TEM, NH3–TPD and in situ DRIFTS). The results showed that the introduction of SO42− into RuO2/ZrO2 presented obvious effects on the structure, surface acidity and N2 selectivity of RuO2/ZrO2. The introduction of SO42− obviously increased the amount of surface acid sites, which could promote the adsorption of ammonia species and prevent the excessive oxidation of ammonia to NOx, improving the N2 selectivity dramatically. The DRIFTS results confirmed that the SCO of ammonia over RuO2/ZrO2–SO42− followed the in situ selective catalytic reduction of NOx (i-SCR) mechanism, involving NH3 oxidation to NO species and –NH2 reacted with NO to form the main product N2. The presence of SO42− not only increased the surface acid sites of the catalyst, but also inhibited the production of nitrate species, which was beneficial to improve the N2 selectivity. [ABSTRACT FROM AUTHOR]

CuO-Fe 2 O 3 catalysts categorized by the thermal treatment were systematically investigated for ammonia oxidation to nitrogen. The activity results exhibited that the calcination temperature had a significant contribution to the difference of the catalytic performance. Lower calcination temperature (≤500 °C) resulted in the excellent catalytic activity owing to the formation of large surface area, superior redox behavior and abundant surface oxygen species. On the contrary, the catalytic activity of catalysts declined with further raising the calcination temperature (≥600 °C) due to the destroyed structure and acid sites. In addition to this, DRIFTS study revealed that the reaction of ammonia oxidation largely depended on the presence of surface active oxygen on the catalysts. In particular, fast ammonia activation was observed on CuO-Fe 2 O 3 –500 °C, which was reflected by the rapid formation of –NH 2 and nitrate species on DRIFTS combining the XPS results. The intermediates –NH 2 and NO of internal selective catalytic reduction (iSCR) predominantly accounted for the excellent catalytic activities. The significant difference of the activation of surface species and catalytic activity impacted by the calcination temperature was observed, and the complete conversion temperature of NH 3 on CF-500 is 25 °C lower than that of CF-400. The NH 3 -SCO reaction over CuO-Fe 2 O 3 catalysts followed the same "internal" selective catalytic reduction (iSCR) mechanism. The key intermediate (-NH 2) could rapidly react with the in situ-generated NO ad-species to form N 2 and H 2 O. Unlabelled Image • The calcination temperature displayed a significant effect on CuO-Fe 2 O 3 for ammonia oxidation. • The CuO-Fe 2 O 3 –500 °C reached 100% conversion of NH 3 at 225 °C. • Calcination temperature influenced the physicochemical property and acidity of catalysts. • CuO-Fe 2 O 3 calcined at different temperatures showed similar reaction mechanism following iSCR path. [ABSTRACT FROM AUTHOR]

The effect of different pH values (8, 9, 10 and 11) on the catalytic activity over CeSiW catalysts was investigated for the selective catalytic reduction of NO by NH3. CeSiW-9 showed a remarkable higher NOx conversion. The strongest interaction was observed between silicotungstic acid and CeO2 over CeSiW-9, resulting in the improvement of redox ability and surface acidity, which could increase the catalytic activity. The superior catalytic performance of the CeSiW-9 catalyst was attributed to the favored pore structures, excellent redox ability and the abundance of surface acid sites, which depended on pH values in the preparation process of CeSiW catalysts. [ABSTRACT FROM AUTHOR]

Abstract: A series of CeO2 prepared with H2SO4 (C-S), H3PO4 (C-P) and H2SO4 + H3PO4 (C-P-S) were investigated in selective catalytic reduction of NOx with NH3. The sulfates contributed to the improvement of Brønsted (B) acid sites, while phosphates were prone to the enhancement of Lewis (L) acid sites, which could improve the catalytic activity. Furthermore, sulfates existed in the surface of C-P-S and C-S; phosphates occurred on the subsurface region or were highly dispersed on the surface of C-P-S and C-P. Besides, the nitrates adsorbed on the CeO2 and NH3 contacted with the sulfates, which followed the L-H mechanism at 200 °C on C-P-S and C-S. The adsorption and activation of NO and NH3 over C-P occurred at the same active sites, which obeyed the E-R mechanism at 200 °C. C-P-S possessed the best catalytic activity because of the appropriate surface acidity and redox property, and more than 80% conversion of NOx was obtained at 220-450 °C.Graphical abstract: CeO2 modified by H2SO4 (C-S), H3PO4 (C-P) and H2SO4 + H3PO4 (C-P-S) was prepared and used for selective catalytic reduction of NOx by NH3. The presence of sulfate species over C-S and C-P-S contributed to the formation of surface acidity. CeO2 modified by phosphoric acid favored excellent oxidation ability. [ABSTRACT FROM AUTHOR]

Highlights • The interaction between CeO 2 and silicotungstic acid occurred. • Formation of Ce3+ O W6+ contributed to NO oxidation ability and surface acidity. • Monodentate nitrate and bridging nitrate reacted with NH 4 + to generate NH 4 NO 3. • The production of NH 4 NO 3 was reduced by NO to form NO 2. • Both Langmuir–Hinshelwood mechanism and Eley–Rideal mechanism existed. Abstract A series of silicotungstic acid modified CeO 2 (SC- x, x represents the pH value of solution that is used for the preparation of catalysts) were prepared for the selective catalytic reduction (SCR) of NO x with NH 3. SC-9 showed the best catalytic activity among the samples. The monodentate nitrate, bidentate nitrate, bridging nitrate and NO 2 were detected over SC-9 and SC-10. Monodentate nitrate and bridging nitrate disappeared over SC-8. Furthermore, the monodentate nitrate and bridging nitrate could react with NH 4 + on Brønsted acid sites to generate NH 4 NO 3 , and then was reduced by NO to form NO 2 , accompanied with the fast reaction between NO 2 and coordinated NH 3 on Lewis acid sites in the presence of gaseous NO. Besides, the SCR reaction pathway of SC catalysts followed by the Langmuir–Hinshelwood mechanism and the Eley–Rideal mechanism. Graphical abstract Image, graphical abstract Silicotungstic acid modified CeO 2 catalysts (SC) were prepared by a facile one pot method and used for the selective catalytic reduction (SCR) of NO with NH 3. Monodentate nitrate and bridging nitrate could react with NH 4 + to produce NH 4 NO 3 , and then reduced by NO to form NO 2. Bidentate nitrate and NO 2 reacted with coordinated NH 3 to generate N 2 and H 2 O. [ABSTRACT FROM AUTHOR]

Abstract: FeOx, MnOx and Fe-Mn-Ox catalysts were prepared by the co-precipitation method and used for the selective catalytic reduction (SCR) of NOx by NH3 at low temperature. Fe-Mn-Ox catalyst showed the best catalytic activity and above 80% NOx conversion was obtained at 50-150 °C. Nearly 80% N2 selectivity of Fe-Mn-Ox catalyst was acquired at the whole temperature range. The excellent low-temperature SCR activity and N2 selectivity were ascribed to the abundant surface acid sites, the formation of Fe-O-Mn species, co-existence of multiple valence states (Mn4+, Mn3+ and Mn2+) and the proper redox ability. In addition, the interaction between Fe and Mn species over the Fe-Mn-Ox catalyst was responsible for the improvement of SCR performance and N2 selectivity.Graphical Abstract: Fe-Mn-Ox catalysts were prepared by the co-precipitation method and used for the selective catalytic reduction (SCR) of NOx by NH3 at low temperature. The formation of Fe-O-Mn species contributed to the co-existence of multiple valence states (Mn4+, Mn3+, Mn2+, Fe3+ and Fe2+), resulting in an increase in catalytic activity and N2 selectivity. Besides, the abundance of acid sites was responsible for the superior N2 selectivity. [ABSTRACT FROM AUTHOR]

A series of ceria modified zirconium phosphate catalysts were synthesized for selective catalytic reduction of NO with ammonia (NH 3 -SCR). Over 98% NO x conversion and 98% N 2 selectivity were obtained by the CeO 2 /ZrP catalyst with 20 wt.% CeO 2 loading at 250–425 °C. The interaction between CeO 2 and zirconium phosphate enhanced the redox abilities and surface acidities of the catalysts, resulting in the improvement of NH 3 -SCR activity. The in situ DRIFTS results indicated that the NH 3 -SCR reaction over the catalysts followed both Eley-Rideal and Langmuir-Hinshelwood mechanisms. The amide ( NH 2 ) groups and the NH 4 + bonded to Brønsted acid sites were the important intermediates of Eley-Rideal mechanism. [ABSTRACT FROM AUTHOR]

For the selective catalytic reduction (SCR) of NO x by NH 3 , a variety of SO 4 2−/α-Fe 2 O 3 catalysts were created and utilized. The consequences manifest that the sulfation treatment signally boosted the NO x conversion of α-Fe 2 O 3. With varying SO 4 2− loadings, the T 90 of SO 4 2−/α-Fe 2 O 3 catalysts ranges from 10% SO 4 2−/α-Fe 2 O 3 (301 °C) > 15% SO 4 2−/α-Fe 2 O 3 (306 °C) > 5% SO 4 2−/α-Fe 2 O 3 (314 °C) > 20% SO 4 2−/α-Fe 2 O 3 (321 °C). The optimum concentration of sulfate treatment samples was 10% wt., producing approximately 100% NO x conversion at 325–400 °C. Although the introduction of SO 4 2− weaken the redox capacity of α-Fe 2 O 3 , the quantity and strength of acidic sites on SO 4 2−/α-Fe 2 O 3 was dramatically enhanced. Meanwhile, introducing SO 4 2− to α-Fe 2 O 3 hindered the ammonia oxidation process and increased the pore volume of the catalyst, enhancing SCR activity. In situ DRIFTS investigations demonstrated that NH 3 adsorbed on Brønsted acid sites displayed better stability over SO 4 2−/α-Fe 2 O 3 catalysts. Due to the decreased capacity of the catalyst surface to adsorb NO x , the E-R route prevails on 10% SO 4 2−/α-Fe 2 O 3 catalyst. [Display omitted] • SO 4 2− could effectively improve the SCR activity of SO 4 2−/Fe 2 O 3 catalyst. • The 10% SO 4 2−/α-Fe 2 O 3 catalyst showed >95% conversion of NO x at 325–400 °C. • SO 4 2− treatment can obviously enhanced the surface acidity of the catalyst. • The 10% SO 4 2−/α-Fe 2 O 3 catalyst mainly follows the E-R mechanism. [ABSTRACT FROM AUTHOR]

A series of CeO 2 supports over phosphotungstic acid doped CeO 2 (P-W/CeO 2 ) prepared by hydrothermal (Cat-A), sol–gel (Cat-B) and precipitation (Cat-C) methods were investigated in selective catalytic reduction of NO x by NH 3 . The catalytic activity of P-W/CeO 2 was dramatically affected by the preparation methods of CeO 2 supports. Results implied that the incorporation of W species could cause the decease of cell parameter and lattice contraction, resulting in inducing the formation of more Ce 3+ and oxygen vacancies over the Cat-A catalyst, leading to the excellent oxidation ability and SCR activity. Furthermore, the Cat-A catalyst possessed the most amount of Lewis acid sites, resulting in the superior catalytic activity. Besides, the larger specific area and the excellent redox ability were responsible for the outstanding SCR performance. In brief, the favorable activity in NH 3 oxidation, as well as NO oxidation, contributed to the excellent catalytic activity. Therefore, the Cat-A catalyst exhibited the best SCR activity and over 90% NO x conversion was obtained at 190–450 °C. [ABSTRACT FROM AUTHOR]

A series of CuO-CeO 2 -ZrO 2 catalysts were prepared by different methods and applied to the selective catalytic reduction of NO with NH 3 reaction at low temperature. The results showed that the SCR activities, morphology, particles dimension, and the surface chemical state of CuO-CeO 2 -ZrO 2 catalysts were obviously influenced by the preparation method. The SCR performance results showed that the CuO-CeO 2 -ZrO 2 catalyst prepared by co-precipitation method presented the best activity in the temperature range of 125–180 °C. The characterization results showed that the Ce 4+ , Ce 3+ , Cu 2+ and Cu + species were coexistence in the CuO-CeO 2 -ZrO 2 catalysts, and the Cu species mainly existed as Cu 2+ . It was also found that the high surface area, the synergistic effect between copper and ceria, enhanced acidity and the highly dispersed copper species were responsible for the high SCR activity of the CuO-CeO 2 -ZrO 2 catalyst. [ABSTRACT FROM AUTHOR]

Abstract: A series of WO3–ZrO2 carriers were prepared by co-precipitation method with different mass fractions (0wt%, 5wt%, 10wt%, 15wt% and 20wt%) of WO3, and MnO x –CeO2/WO3–ZrO2 monolith catalysts were prepared for selective catalytic reduction of NO x with ammonia (NH3-SCR) in the presence of excessive O2. The catalysts were characterized by N2 adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and NH3/NO temperature-programmed desorption (NH3/NO-TPD). The experimental results showed that, the tungsten modified monolith catalyst MnO x –CeO2/WO3–ZrO2 with the WO3 content 10wt% had the best catalytic activity and the widest reaction window; it possessed a better thermal stability than V2O5/WO3/TiO2 catalyst, and showed a better H2O and SO2 tolerance than MnO x –CeO2/ZrO2. The characterization results indicated that MnO x –CeO2/10% WO3–ZrO2 had the best textural properties, a well-dispersed state of WO3, the lowest binding energy of Ce3+ 3d5/2, the maximum value of Ce3+:Ce=20.7%, the suitable molar ratio of Mn:Ce≈1, and a co-existence state of MnO2–Mn2O3. In addition, it had the most adsorbed sites of NH3 or NO species. The NO x conversion was more than 80% in the temperature range of 150°C to 380°C at the space velocity of 10,000h−1. It possessed better potential for practical application. [Copyright &y& Elsevier]

A series of Ce/Fe-Zr-SO 4 2 - catalysts have been prepared and developed for selective catalytic reduction of NO with ammonia (NH 3 -SCR). The catalysts were characterized by XRD, H 2 -TPR, N 2 adsorption-desorption, NH 3 -TPD and DRIFTS. The characterization results demonstrated that the coexistence of cerium and sulfuric acid on Fe-Zr catalyst could contribute to excellent SCR performance. Among all samples, Ce/Fe-Zr-0.3 S catalyst showed the optimal NO X conversion, reaching more than 80% at 250 °C at a GHSV of 60,000 h−1. Moreover, the optimum concentration of SO 4 2- to modify Ce/Fe-Zr catalyst was 0.3 mol/L. The low sulfuric acid concentration contributed to improving low-temperature activity, while high concentration leaded to outstanding high-temperature activity. According to H 2 -TPR and NH 3 -TPD, the presence of SO 4 2- increased the total amount of acid sites and more stable sulfate species were formed with higher concentration of sulfuric acid. In situ DRIFTS revealed the NH 3 molecule was mainly activated at the Lewis acid site and reacted with the adsorbed NO X species (such as bidentate nitrates) to produce N 2 and H 2 O, which conformed to the L-H reaction mechanism. [Display omitted] • The optimal sulfuric acid concentration for the acid-treated Ce/Fe-Zr support was 0.3 mol/L. • The superior catalytic activity was greatly due to proper surface acid sites and redox ability. • The introduction of both CeO 2 and SO 4 2- improved low-temperature catalytic activity of Fe-Zr catalysts. • Different concentrations of sulfuric acid had different effects on catalytic activity. [ABSTRACT FROM AUTHOR]

Iron-tungsten composite oxides catalyst prepared by grinding methods (FW-GR) exhibits excellent catalytic activity for SCR NO by NH 3. The FW-GR catalyst possessed higher surface acidic sites and acidic strength, the main reaction mechanisms follows the "L-H" at low temperature and "E-R" at high temperature. • The iron-tungsten catalysts prepared by grinding and sol–gel methods exhibited high activity for the NH 3 -SCR of NO x. • The NO conversion was strongly related to the FeWO 4 species. • The iron-tungsten catalysts prepared by grinding leads to increased Lewis and Brønsted acid sites and proper redox property. • Grinding method was simple and environmentally friendly. A series of iron-tungsten composite oxides catalysts prepared by grinding methods (FW-GR), incipient impregnation (FW-IM), sol–gel (FW-SG) and microemulsion (FW-ME) methods were used for selective catalytic reduction of NO by NH 3 (NH 3 -SCR). The SCR activity was significantly depended on the preparation method, the NO conversions over different catalysts were following the order of FW-GR > FW-SG > FW-ME > FW-IM. The results indicated that the NO conversion was strongly related to the FeWO 4 species. It also discovered that the catalyst with higher specific surface area, surface Fe2+ content, surface adsorbed oxygen species, redox potential, surface acidic sites and acidic strength showed better NO reduction activity among all catalysts. In situ DRIFTS results revealed that the main reaction mechanisms of iron-tungsten catalysts were "L-H" at low temperature and "E-R" at high temperature. The SCR reaction over FW-GR sample involved the formation of NH 2 intermediate and subsequent reduction by NO, while the formation of NH 4 NO 3 species over FW-IM was easily transformed into N 2 O species. [ABSTRACT FROM AUTHOR]

The HSiW(x)/Ce‐Fe catalysts were used to research the effect of silicotungstic acid contents on the catalytic activity in the selective catalytic reduction of NOx with NH3. Doping different contents of silicotungstic acid affected surface species and redox property as well as the catalytic activity. With the increasing amount of HSiW (x = 5%, 10% and 20%), the redox reaction between Fe3+/Fe2+ and Ce4+/Ce3+ enhanced, which could improve the ratio of Ce3+ and Fe3+. And then, more Ce3+ increased the ratio of chemisorbed oxygen (Oα). Besides, the type and strength of acid sites over HSiW(x)/Ce‐Fe was affected by the HSiW contents. These factors facilitated the catalytic performance. Thus, the NOx conversion of HSiW(x)/Ce‐Fe(x = 20%) was higher than 90%, which maintained in a wide temperature range between 200 and 400 °C. [ABSTRACT FROM AUTHOR]

• P modified Cu-SAPO-34 were prepared using bulk CuO particles as Cu2+ precursor. • The high-temperature hydrothermal aging significantly enhanced de-NO x performance. • The amount of active sites-isolated Cu2+ and Brønsted acid sites was greatly enhanced. • Phosphate ions also contributed to the catalysis performance of the aged samples. Phosphate ions promoted Cu-SAPO-34 (P-Cu-SAPO-34) were prepared using bulk CuO particles as Cu2+ precursor by a solid-state ion exchange technique for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). The effects of high temperature (H-T) hydrothermal aging on the NO x removal (de-NO x) performance of Cu-SAPO-34 with and without phosphate ions were systematically investigated at atomic level. The results displayed that both Cu-SAPO-34 and P-Cu-SAPO-34 presented relatively poor NO x removal activity with a low conversion (< 30%) at 250-500°C. However, after H-T hydrothermal treatment (800°C for 10 hr at 10% H 2 O), these two samples showed significantly satisfied NO x elimination performance with a quite high conversion (70%-90%) at 250-500°C. Additionally, phosphate ions decoration can further enhance the catalytic performance of Cu-SAPO-34 after hydrothermal treatment (Cu-SAPO-34H). The textural properties, morphologies, structural feature, acidity, redox characteristic, and surface-active species of the fresh and hydrothermally aged samples were analyzed using various characterization methods. The systematical characterization results revealed that increases of 28% of the isolated Cu2+ active species (Cu2+-2Z, Cu (OH)+-Z) mainly from bulk CuO and 50% of the Brønsted acid sites, the high dispersion of isolated Cu2+ active component as well as the Brønsted acid sites were mainly responsible for the accepted catalytic activity of these two hydrothermally aged samples, especially for P-Cu-SAPO-34H. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The amorphous WO 3 state and Ce 2 (WO 4) 3 compounds were formed over CeO 2 -ZrO 2 -WO 3. • WO 3 amorphous contributed to the generation of monodentate nitrate and acid sites. • Reaction between monodentate nitrate and NH 3 -adsorbed facilitated SCR activity. • The reaction pathway followed Langmuir-Hinshelwood mechanism. The CeO 2 -ZrO 2 -WO 3 catalysts were investigated for the selective catalytic reduction of NO x by NH 3 (NH 3 -SCR). The results indicated that monodentate nitrate species generated from amorphous WO 3 , and these species could not be observed over CeO 2 -ZrO 2 -WO 3 with the presence of Ce 2 (WO 4) 3 compounds. The formation of amorphous W species resulted in the abundant of Ce3+ and oxygen vacancies. Besides, the amorphous W species could enhance the surface acidity and NO oxidation ability. Nitrate species (bridging nitrate and monodentate nitrate), coordinated NH 3 and NH 4 + all participated in the NH 3 -SCR process. The NH 3 -SCR reaction pathway of CeO 2 -ZrO 2 -WO 3 mainly followed Langmuir-Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

A series of CeO 2 –ZrO 2 –WO 3 (CZW) catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction (SCR) of NO with NH 3 over a wide temperature of 150–550°C. The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H 2 O. The fresh catalyst showed above 90% NO x conversion at 201–459°C, which is applicable to diesel exhaust NO x purification (200–440°C). The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures (below 300°C), while the activity was notably enhanced at high temperature (above 450°C). The aged CZW catalyst (hydrothermal aging at 700°C for 8 hr) showed almost 80% NO x conversion at 229–550°C, while the V 2 O 5 –WO 3 /TiO 2 catalyst presented above 80% NO x conversion at 308–370°C. The effect of structural changes, acidity, and redox properties of CZW on the SCR activity was investigated. The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO 2 –ZrO 2 solid solution, amorphous WO 3 phase and optimal acidity. In addition, the formation of WO 3 clusters increased in size as the hydrothermal aging temperature increased, resulting in the collapse of structure, which could further affect the acidity and redox properties. [ABSTRACT FROM AUTHOR]

The present work elucidated the precipitants effect of pure CeO 2 on the activity of silicotungstic acid supported on CeO 2 catalysts toward NO x reduction. The results implied that the silicotungstic acid doped CeO 2 prepared by the NH 3 ·H 2 O precipitant showed the best SCR performance and nearly 100% NO x conversion was obtained at 225–450 °C. Silicotungstic acid doped CeO 2 prepared by NH 3 ·H 2 O (Cat-A) was enclosed by (1 1 1) and (2 2 0) planes; the catalyst with (NH 4 ) 2 CO 3 (Cat-B) predominantly exposed (2 2 0) and (2 0 0) surfaces, and the catalyst with the mixture of NH 3 ·H 2 O and (NH 4 ) 2 CO 3 (Cat-C) merely exhibited the (2 0 0) planes. Moreover, the aggregated WO 3 was observed over the Cat-B and Cat-C, the BET surface areas and total pore volume of the two samples significantly decreased compared with Cat-A. Besides, the Brönsted (B) acid sites only appeared on the Cat-A catalyst and the intensity of Lewis acid was visibly stronger than that of Cat-B and Cat-C. Importantly, the Cat-A possessed its higher concentration of Ce 3+ and surface chemisorbed oxygen Oα. As a result, the structure geometry and surface acidity were different on the (1 1 1) and (2 0 0) surfaces of CeO 2 , which were dependence on the different precipitants. [ABSTRACT FROM AUTHOR]

[Display omitted] • An alkali-resistant vanadium-based catalyst has been developed for NH 3 -SCR reaction. • The optimal 3.5 W-V conversion was 90 % at 160° C (193 °C for 3.5 W-V-1 %K). • The V-O-W structure acts as an acid site and redox site. • The V species plays a key role in protecting the active V-O-W species. The poisoning effect of alkali metals over Vanadium-based catalysts still faced a significant challenge in the selective catalytic reduction of NOx with NH 3 (NH 3 -SCR). In order to improve the alkali (mainly potassium resistance) resistance of the Vanadium-based catalysts, WO 3 was introduced into the vanadium oxide catalysts. The obtained 3.5WO 3 -V 2 O 5 (3.5 W-V) catalyst exhibited the excellent low-temperature NH 3 -SCR performance owing to the formation of V-O-W structures. Noteworthily, when 1 wt% K was introduced into the 3.5 W-V catalyst, vanadium oxide (V-O, V=O) species preferentially bonded to alkali metal K as an acidic sacrifice site, prompting more active V-O-W species to remain. Thus, the 3.5 W-V catalyst also possessed excellent alkali resistance. The NH 3 -TPD results showed that the 3.5 W-V-1 %K catalyst had a considerable acid site to ensure the adsorption capacity of NH 3 , while the XPS results showed that the 3.5 W-V-1 %K catalyst had excellent redox performance to ensure the activation capacity of the reactant NH 3. Moreover, in-situ DRIFTS transient experiments revealed that the 3.5 W-V and 3.5 W-V-1 %K catalysts were more capable of adsorbing and activating NH 3 species to rapidly react with gaseous NO, obeying the Eley-Rideal (E-R) pathway in NH 3 -SCR reaction. This work provides new insights into poisoning resistant of vanadium-based catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • (NH 4) 2 SO 4 was used instead of liquid H 2 SO 4 to introduce SO 4 2− into V 2 O 5 /CeO 2 ; • NO x conversion is over 95 % at 225–400 °C on 2 %SO 4 2−- V 2 O 5 /CeO 2 ; • The introduction of SO 4 2− enhanced Brønsted acid sites and the formation of polymeric vanadyl species; • The NH 3 -SCR reaction over 2 %SO 4 2−-V 2 O 5 /CeO 2 followed the Langmuir-Hinshelwood and Eley-Rideal routes concurrently. Ceria-supported vanadia (VO x /CeO 2) catalyst has been extensively investigated in the field of NO x selective catalytic reduction with NH 3 (NH 3 -SCR) but is limited in practical application owing to its poor sulfur resistance and high-temperature activity. Herein, a series of SO 4 2− modified V 2 O 5 /CeO 2 catalysts were fabricated to improve the overall catalytic performance. The 2 %SO 4 2−-V 2 O 5 /CeO 2 catalyst exhibited above 95 % NO x conversion, 90 % N 2 selectivity in the temperature range of 225–400 °C and excellent SO 2 + H 2 O tolerance, which was much better than V 2 O 5 /CeO 2 catalyst. Characterization results showed that the introduction of SO 4 2− over V 2 O 5 /CeO 2 increased the Ce3+/(Ce3++ Ce4+) ratio to promote the formation of oxygen vacancies and promoted the generation of more conducive polymeric vanadyl species. The synergistic effect of the redox sites and acid centers provided moderate redox property and enhanced surface acidity, thus improving the adsorption of NH 3 and inhibiting the over-oxidation of NH 3 that occurs on V 2 O 5 /CeO 2. In-situ DRIFTS indicated that the NO x reduction over V 2 O 5 /CeO 2 and 2 %SO 4 2−-V 2 O 5 /CeO 2 followed the Langmuir-Hinshelwood and Eley-Rideal routes concurrently. This study can expound the reasonable design of vanadium-based catalysts for efficient NO x reduction in industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • SO 4 2--FeO x -Nb 2 O 5 catalyst exhibits the best activity over the whole temperature range. • Niobium modifies the electronic structure and alleviates the reducibility of catalyst. • Sulfation provides more Brønsted acid sites for surface ammonia adsorption. • Niobium promotes the binding of iron to sulfate to form redox acid sites. A series of iron-based composite oxide catalysts, modified with acid and niobium, were produced for the purpose of selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) via co-precipitation. The obtained SO 4 2--FeO x -Nb 2 O 5 (S-FeNbO x) catalyst exhibited significantly better SCR performance than the unmodified FeO x catalyst, with a NO x conversion above 90% and N 2 selectivity higher than 95% in the temperature range of 275–450 °C. The characterization results suggest that the addition of Nb not only modifies the electronic structure and alleviates the reducibility but also enhances the surface acidity of the catalysts. The sulfuric acid modification of FeO x -Nb 2 O 5 catalyst promotes the formation of redox-acid sites. The in situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) results revealed that the combining sulfuric acid and niobium modifications resulted in a significant increase in the amount of Brønsted acid sites, and also led to a blue shift of the band related to the Lewis acid sites, implying the existence of a synergistic effect of the two modification methods. The creation of redox-acid sites significantly enhances the adsorption and activation capacity of NH 3 on the catalyst surface. These results suggest that the NH 3 -SCR reaction to primarily follow the Eley-Rideal (E-R) mechanism on the catalyst. [ABSTRACT FROM AUTHOR]

Graphical abstract The hydrothermal stability of Cu-SAPO-34 was significantly enhanced by the addition of Ce or La. The introduction of Ce or La effectively mitigated the dealumination and restrained the aggregation of copper species. The hydrothermal treatment cut off the "E-R" reaction route over the Cu-SAPO-34 and opened the new reaction pathway ("L-H" mechanism) over the Cu/La-SAPO-34. Highlights • Adding Ce or La into Cu-SAPO-34 effectively enhanced the hydrothermal stability. • Cu2+ increased over Cu/La-SAPO-34 after aging and affected low-temperature activity. • The addition of Ce or La restrained the aggregation of Cu species and dealumination. • The introduction of Ce or La stabilized the surface acid sites of Cu-SAPO-34. • Hydrothermal aging changed SCR reaction route of Cu-SAPO-34 and Cu/La-SAPO-34. Abstract The effect of Ce or La on the hydrothermal stability of Cu-SAPO-34 catalyst was evaluated by the selective catalytic reduction of NO x by ammonia (NH 3 -SCR) reaction after hydrothermal aging at 700 °C in 10 vol% H 2 O/air for 10 h. The hydrothermal stability of Cu-SAPO-34 was dramatically enhanced by introducing small amount Ce or La into Cu-SAPO-34. More than 93% NO x conversion was maintained over the aged Ce or La modified Cu-SAPO-34 at 175–350 °C, while extremely poor NH 3 -SCR activity was obtained over the aged Cu-SAPO-34. In situ diffuse reflection infrared Fourier transform spectrum (DRIFTS) results illustrated that the hydrothermal treatment cut off the intrinsic "E-R" reaction route over the Cu-SAPO-34 and opened the new reaction pathway ("L-H" mechanism) over the La modified Cu-SAPO-34 catalyst. Additionally, the introduction of Ce or La effectively mitigated the dealumination progress and restrained the aggregation of copper species over Cu-SAPO-34 during the hydrothermal aging, further maintaining the relatively large specific surface area and uniform pore size distribution. Meanwhile, the incorporation of Ce or La enhanced the redox property and stabilized the surface acid sites of Cu-SAPO-34, further facilitating the adsorption and activation of reactants. [ABSTRACT FROM AUTHOR]

The effect of different pH values (8, 9, 10 and 11) on the catalytic activity over CeSiW catalysts was investigated for the selective catalytic reduction of NO by NH3. CeSiW-9 showed a remarkable higher NOx conversion. The strongest interaction was observed between silicotungstic acid and CeO2 over CeSiW-9, resulting in the improvement of redox ability and surface acidity, which could increase the catalytic activity. The superior catalytic performance of the CeSiW-9 catalyst was attributed to the favored pore structures, excellent redox ability and the abundance of surface acid sites, which depended on pH values in the preparation process of CeSiW catalysts. [ABSTRACT FROM AUTHOR]

The solid superacid TiO 2 -ZrO 2 -SO 4 2− -supported 20 wt.% CeO 2 catalyst (20CeO 2 /Ti-Zr-S) was synthesized for selective catalytic reduction of NO with NH 3 (NH 3 -SCR). The NH 3 -SCR performance was significantly enhanced by the construction of strong acid sites on the surface of 20CeO 2 /Ti-Zr-S and over 96% NO conversion was obtained at 225–425 °C. Meanwhile, the strong interaction between solid superacid and CeO 2 resulted in excellent redox property and abundant surface oxygen species. Furthermore, the NH 3 -SCR reaction over 20CeO 2 /Ti-Zr-S catalyst mainly followed the Langmuir-Hinshelwood mechanism at low-temperature (250 °C). The M-NO 2 (M = Ce, Ti, Zr) nitrate compounds, monodentate and bridging nitrates were the crucial intermediates in Langmuir-Hinshelwood mechanism. In addition, amide (–NH 2 ) species were available at 350 °C over 20CeO 2 /Ti-Zr-S catalyst, which facilitated the high-temperature NH 3 -SCR activity via Eley-Rideal pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • VO x /Fe 2 O 3 -S catalyst with low V loading is fabricated via simple impregnation method. • SO 2 pretreatment induces the generation of Fe 2 (SO 4) 3 on Fe 2 O 3 -S and VO x /Fe 2 O 3 -S. • The high active polymeric vanadyl species are formed on VO x /Fe 2 O 3 -S rather than VO x /Fe 2 O 3. • The synergistic effect of Fe 2 (SO 4) and polymeric vanadyl boost the SCR reaction of VO x /Fe 2 O 3 -S. • The NH 3 -SCR reaction over Fe 2 O 3 -S and VO x /Fe 2 O 3 -S followed the L-H and E-R mechanism synchronously. The construction of plausible alternatives of V 2 O 5 -WO 3 /TiO 2 for effectual NO x purification is becoming a research hotspot. Herein, a robust VO x /Fe 2 O 3 -S catalyst with SO 2 tailored surface acid sites and active VO x sites was engineered for boosting the NO x reduction performance. The VO x /Fe 2 O 3 -S catalyst afforded above 90% NO x conversion and 90 % N 2 selectivity at 275–425 °C, coupled with the exceptional long-term SO 2 + H 2 O resistance. Py-IR and in situ DRIFTS disclosed that the formation of Fe 2 (SO 4) 3 endowed Fe 2 O 3 -S and VO x /Fe 2 O 3 -S with abundant medium-strong Lewis and Brønsted acid sites rather than covering the active sites, strengthening the NH 3 adsorption and suppressing the overoxidation of NH 3 on the reducible Fe 2 O 3 support. Raman analysis revealed the generation of new species of polymeric vanadyl species on VO x /Fe 2 O 3 -S induced by the SO 2. In-depth mechanistic understanding through DFT analyses indicated that the NO x reduction reaction over the Fe 2 O 3 -S and VO x /Fe 2 O 3 -S obeyed the Langmuir-Hinshelwood and Eley-Rideal mechanism simultaneously. Moreover, the presence of polymeric vanadyl species dramatically lower the overall energy barrier for NO x reduction, thus speeding up the SCR reaction of VO x /Fe 2 O 3 -S. This study can shed light on the more rational design of VO x -based catalysts for highly efficient NO x reduction in industry. [ABSTRACT FROM AUTHOR]

The selective catalytic reduction (SCR) of NO by NH 3 has been investigated over the CeO 2 –ZrO 2 –WO 3 (CZW) catalysts prepared by hydrothermal synthesis, incipient impregnation, co-precipitation and sol–gel methods. The results indicate that the CZW catalyst prepared by hydrothermal method shows the best SCR activity, and more than 90% NO conversion is obtained at 195–450 °C with a gas hourly space velocity of 50,000 h −1 . The samples are characterized by XRD, N 2 adsorption–desorption, SEM, EDS, XPS, H 2 -TPR, NH 3 -TPD and Pyridine-IR techniques. The results imply that the superior SCR activity of CZW catalyst is contributed to the excellent redox property, strong acidity and highest content of chemisorbed oxygen species. Furthermore, the larger surface area and greater total pore volume improve the redox ability and enhance NO conversion at low temperature, while the co-existence of Lewis and Brønsted acid sites enhance the SCR activity at high temperature. [ABSTRACT FROM AUTHOR]

• WO 3 -FeO x catalysts were synthesized using a novel and facile solvent-free method. • The NO x removal efficiency of 0.3W-Fe was nearly 100 % in a wide temperature range of 225−500 °C. • The strong interaction between WO 3 and Fe 2 O 3 induced the formation of Fe 3 O 4. • The interaction between WO 3 and Fe 2 O 3 promoted the adsorption of NH 3 and NO x. • The NH 3 -SCR reaction over WO 3 -FeO x followed the L-H and E-R mechanism synchronously. WO 3 -FeO x catalysts with various WO 3 contents were synthesized through a facile solvent-free method, satisfying the selective catalytic reduction of NO (NH 3 -SCR). Strikingly, the optimum 30 %WO 3 -FeO x catalyst with the largest surface area exhibited the most outstanding catalytic activity, achieving the nearly 100 % NO x removal efficiency in a wide temperature window between 225−500 °C, which was better than that of Fe-W series catalysts reported in other studies. In addition, Raman and XPS results proved that the introduction of WO 3 altered the electronic environment of Fe 2 O 3 , inducing the formation of Fe 3 O 4 (Fe2+) and surface adsorbed oxygen. In situ DRIFTS demonstrated that the interaction between WO 3 and Fe 2 O 3 not only promoted the adsorption capacity of NH 3 on the catalyst, but also contributed to the formation of adsorbed NO x species. NO x reduction reaction on WO 3 -FeO x catalyst proceeded via the Eley-Rideal and Langmuir-Hinshelwood mechanism synchronously. All of these factors, jointly, accounted for the superior catalytic activity and N 2 selectivity of WO 3 -FeO x catalysts. [ABSTRACT FROM AUTHOR]