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A series of ceria modified CuO/γ-Al 2 O 3 (CuO-CeO 2 /γ-Al 2 O 3 ) catalysts were prepared via stepwise impregnation (CuCeAl-SI) and co-impregnation (CuCeAl-CI) method and tested in the model reaction of NO reduction by CO. It was found that the influence of impregnation modes on the catalytic properties of CuCeAl samples mainly lies on the control of ceria particle sizes and modulation of the distribution of various copper species. In both impregnation modes, ceria was mainly spread on γ-Al 2 O 3 as small particles while copper species were highly dispersed. A quantitative estimation of copper species was tentatively provided via a combined surface acid leaching experiment and H 2 -TPR characterization for the first time. The results showed that for CuCeAl-CI catalyst, about 55% and 25% copper species were dispersed on γ-Al 2 O 3 and nanosized ceria, respectively, while about 20% was migrated into ceria lattice during the calcination process. In contrast, in CuCeAl-SI sample, the corresponding values changed to about 25%, 70% and 5%, respectively. The synergistic effect between copper species and ceria can promote the improvement of catalytic performance, which results in higher activity of CuCeAl-SI than that of CuCeAl-CI catalyst. [ABSTRACT FROM AUTHOR]

Monolithic Mn-Fe-Ce-Al-O catalyst with honeycomb cordierite ceramic as a carrier was reported for the first time for low temperature deNOx application. In the reaction of selective catalytic reduction (SCR) of NO with NH3, a NO conversion of above 80% at 100 °C was obtained. Notably, the catalyst also showed excellent resistance against SO2 and H2O. About 60% NO conversion was maintained after successive operation in the mixed stream of SO2 and H2O for 168 h. The Brunner−Emmet−Teller (BET) measurement, SEM, EDS, thermogravimetric analysis (TG), FT-IR, and XPS results of the used catalysts indicated that certain amounts of ammonium sulfate was formed on the surface of the catalyst. XPS results revealed that partial of Fe2+ was oxidized to Fe3+ during the reaction process, and Fe2+ species have strong redox ability, which can explain the decrease in activity after reaction. In addition, SO2 and H2O induced a transformation of Ce from Ce4+ to Ce3+ on the surface of the catalyst, which increased the amount of chemisorbed oxygen. Owing to these factors, the addition of Ce and Fe species contributes to excellent resistance of the catalyst to SO2 and H2O. [ABSTRACT FROM AUTHOR]

Modifying CeO 2 with acid sites is a common strategy for designing efficient catalysts for the selective catalytic reduction of NO x by NH 3 (NH 3 -SCR of NO x). However, the effect of acid metal oxide modification on the SO 2 resistance of CeO 2 has not been well revealed. In this work, it was found that the SO 2 resistance of CeO 2 modified with several acid metal oxides (i.e. , MoO 3 , WO 3 and Nb 2 O 5), followed an order of Mo/CeO 2 ≥ W/CeO 2 > Nb/CeO 2. Further systematic characterizations revealed that Mo-OH and W-OH on CeO 2 as Brønsted acid sites could better inhibit the SO 2 adsorption and the sulfation of active sites than highly dispersed NbO x mainly as Lewis acid sites because NH 4 + coordinated to Brønsted acid sites could help trap SO 2 to form ammonium sulfates rather than metal sulfates. The findings in this work provided important guidance for the design of efficient catalysts with superior SO 2 resistance performance. [Display omitted] • CeO 2 modified with varying acid metal oxides showed different resistance to SO 2. • Highly dispersed MoO 3 or WO 3 could better shield CeO 2 from SO 2 poisoning than Nb 2 O 5. • Mo and W sites as Brønsted acid sites could better inhibit the SO 2 adsorption on CeO 2. • SO 2 could interact with both highly dispersed Nb 2 O 5 and CeO 2 on Nb/CeO 2. • A strategy for designing efficient catalysts with superior resistance to SO 2 was provided. [ABSTRACT FROM AUTHOR]

The introduction of WO 3 species on to FeTiO x catalysts led to the formation of Fe(3+n)+-O-W(6−n)+ and Ti(4+n)+-O-W(6−n)+ structures, increasing the ratio of chemical adsorbed oxygen, surface W-OH species, which were beneficial to the NH 3 -SCR reaction. [Display omitted] • The catalytic activity of FeTiO x was improved after the loading of WO 3 species. • The amount and strength of Brønsted acid sites was enhanced. • Fe(3+n)+-O-W(6−n)+ raised the count of chemical adsorbed oxygen, surface W-OH species. A series of WO 3 modified iron-titanate mixed metal oxides catalysts (the molar ratio of Fe/Ti = 4:1) were synthesized by conventional impregnation method and tested for selective catalytic reduction of NO x by NH 3. The addition of WO 3 species could enhance the catalytic performance of FeTiO x and 6 W/FeTiO x showed optimal activity with above 80 % NO conversion under a wide operating temperature window of 200–400 °C. It also exhibited excellent stability in the presence of H 2 O and SO 2 at 250 °C, even as low as 225 °C, which provided a suitable deNO x candidate for stationary sources. The characterization methods including XRD, BET, XPS, H 2 -TPR, NH 3 -TPD, NO-TPD and in situ DRIFTs were used to investigate the structure and surface properties of catalysts and their influence on the catalytic activity. The results demonstrated that the impregnation of WO 3 species led to the strong electronic inductive effects between Fe3+and W6+, Ti4+ and W6+ in the forms of Fe(3+n)+-O-W(6−n)+ and Ti(4+n)+-O-W(6−n)+ structures, increasing the ratio of chemical adsorbed oxygen species, surface OH-, which were stimulative to low-temperature NH 3 -SCR reaction. The increased amount of surface Brønsted acid sites mainly came from W-OH species. Besides, the reaction pathway over 6 W/FeTiO x mainly followed Eley-Rideal mechanism at 225 °C through the reaction between gaseous NO and adsorbed NH 3 species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel effect of strong acid-redox interface hinders NH 3 -SCR activity is reported. • Three Ce 2 (SO 4) 3 -CeO 2 catalysts with distinct interfaces are constructed. • NO adsorption and oxygen vacancy formation are limited after Ce 2 (SO 4) 3 addition. • Weak interface promotes NO activation and the formation of active nitrites. The occurrence of NH 3 -SCR (selective catalytic reduction of NO with NH 3) reaction on catalyst surface typically requires acid and redox sites. However, the role of acid-redox interaction on NH 3 -SCR performance is still obscure due to complex acidities and entangled acid-redox sites. Herein, three types of model Ce 2 (SO 4) 3 -CeO 2 catalysts with distinct interfaces are constructed to reveal the effect of acid-redox interaction on NH 3 -SCR performance. That is, SO 4 2-/CeO 2 -VS (vapor sulfation of ceria) with strong acid-redox interfacial contact, SO 4 2-/CeO 2 -WI (wet impregnation), and SO 4 2-/CeO 2 -SG (solid grinding) with limited interfaces. It is found the redox property is significantly disturbed as a result of the electron-withdrawing effect from the sulfate. Theoretical result unravels that the introduction of Ce 2 (SO 4) 3 retards the oxygen vacancy formation over CeO 2. Due to restricted interfaces in SO 4 2-/CeO 2 -SG, the negative influence from acid sites is greatly alleviated. Further mechanism study discloses the weakened acid-redox interaction actually changes the nature of surface NO x species, resulting in the generation of reactive species (*O-N-O* and cis -N 2 O 2 2-) and the promotion of surface reaction via Langmuir-Hinshelwood (L-H) mechanism. [ABSTRACT FROM AUTHOR]

• The influence of surface configuration over FeCe/Al catalysts was studied. • The existence states and content for each coordinated FeO x species was determined. • Clustered FeO x was identified as the main active species for CO oxidation. The surface configuration of a catalyst, including the present state, coordination environment and related content of the active and additive species, has dominant effect on its physicochemical properties and catalytic performance. Herein, two types of FeCe/Al catalysts with different surface configurations, FeCe/Al-CI (co-impregnation) and FeCe/Al-SI (stepwise impregnation) were synthesized by adjusting the preparation conditions. Both catalysts together with the reference sample Fe/Al and Ce/Al were characterized by means of XRD, BET, TEM, EPR, UV–vis, Mössbauer spectra, H 2 -TPR and XPS. The results showed that (1) in both impregnation modes, ceria presented as small particles, while the iron species existed in two forms: the isolate state (tetrahedral coordination), cluster state (octahedral coordination); (2) iron species in different existence state can be characterized qualitatively or quantitatively via EPR, UV–vis and Mössbauer spectra, and the contents of FeO x clusters follows: FeCe/Al-SI < FeCe/Al-CI < Fe/Al. (3) With the help of HNO 3 leaching operation, FeO x clusters were identified as the main active species for CO oxidation. Although Fe/Al sample contained the highest concentration of active cluster FeO x species, the deficiency of Fe-O-Ce structures led to the lowest number of surface oxygen, Ce3+ and Fe2+ species, which resulted in poor CO oxidation activity for Fe/Al catalyst. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The addition of TiO 2 improves the physicochemical property of Mn/CZ-NR catalyst. • Catalytic activity of Mn/CZ-NR catalyst is obviously enhanced by TiO 2 modification. • TiO 2 modification can inhibit the generation of N 2 O over Mn/CZ-NR catalyst. • Mn-Ti/CZ-NR catalyst exhibits excellent H 2 O + SO 2 tolerance in NH 3 -SCR reaction. Abstract In the present work, we chose MnO x /CeO 2 -ZrO 2 nanorod (i.e. , Mn/CZ-NR) as a benchmark catalyst, and used TiO 2 as a modifier with the purpose of inhibiting the formation of N 2 O (by-product) as well as further enhancing the catalytic activity and H 2 O + SO 2 tolerance of Mn/CZ-NR catalyst. These samples were characterized by TEM, HRTEM, XRD, Raman, H 2 -TPR, XPS, NH 3 -TPD, and in situ DRIFTS. De NO x performance and H 2 O + SO 2 tolerance of these samples were evaluated by low-temperature NH 3 -SCR reaction. The obtained results show that the TiO 2 modified catalyst (i.e. , Mn-Ti/CZ-NR) exhibits higher catalytic activity than Mn/CZ-NR catalyst due to larger amount of oxygen vacancy accompanied with more Ce3+, higher ratios of Mn4+ and surface adsorbed oxygen species, as well as the improvement of surface acidity. Furthermore, TiO 2 modification effectively inhibits the non-selective oxidation of NH 3 to N 2 O through appropriately weakening the redox property of Mn/CZ-NR catalyst, which is beneficial to the enhancement of N 2 selectivity. Finally, Mn-Ti/CZ-NR catalyst exhibits excellent H 2 O + SO 2 tolerance, which indicates that it has the potential to be used for practical low-temperature de NO x application. [ABSTRACT FROM AUTHOR]

Understanding how H 2 O affects SO 2 tolerance of SCR catalysts at different working temperatures is of great importance. Herein, we reported that H 2 O addition at ultra-low temperature of 100 °C induced a significant promotion on SO 2 tolerance of MnO x -CeO 2 catalysts. Sole SO 2 led to serious activity loss from 100% to 20%, while H 2 O coexistence alleviated the deactivation and an admirable activity of 60% was reserved. Combining experimental characterizations with DFT calculation, we demonstrated that H 2 O promoted hydroxyl formed on defect sites, which promoted more sulfite formation and retarded sulfates with strong electron-withdrawing capacity disturbing active Mn sites. In comparison with sulfates, sulfites exhibited less interference in adsorbed species, ensuring the occurrence of Eley-Rideal and Langmuir-Hinshelwood mechanisms. The present study discloses the unique temperature-dependent effect of H 2 O on SO 2 tolerance, which is expected to deepen our understanding on the role of H 2 O in modulating surface species and catalytic behaviors of SCR catalysts. [Display omitted] • Unusual temperature-dependent H 2 O promotion effect on SO 2 tolerance of SCR catalysts was reported. • The addition of H 2 O greatly alleviated the SO 2 poisoning of MnO x -CeO 2 catalysts at ultra-low temperature of 100 °C. • Hydroxyl group derived from H 2 O disassociation restricted the electron interaction between sulfur species and Mn sites, protecting active Mn via more sulfites forming. • Sulfites showed less interference on surface active adsorbed species and ensured the occurrence of both L-H and E-R mechanism over MnCe-SO 2 +H 2 O catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel hybrid strategy is employed to design catalysts with superior K resistance. • The main reason for CeMn deactivation is cut-off of L-H mechanism resulting from the formation of stable nitrates. • The addition of ZSM-5 can re-activate the inert nitrates. • Alkali metals poisoned catalysts can be regenerated by ZSM-5 hybridization. The application of cerium-manganese oxides (CeMn) in controlling exhaust gas from biomass combustion is greatly inhibited due to poor resistance to alkali metals. Herein, we report a smart strategy to circumvent the K poisoning problem of CeMn by physically coupling with ZSM-5, which exhibited almost no activity loss even under a high loading of 2 wt % K 2 O. Results showed that in contrast to the conventionally believed disturbance of redox property and reduction of acid sites, the dominant effect from K loading on the deactivation of CeMn catalysts lies on the formation of chemically inert nitrates, which significantly restrains the reaction cycle via Langmuir-Hinshelwood route. With ZSM-5 hybridization, the stable nitrates over CeMn can be facilely activated and consumed by NH 4 + species introduced by ZSM-5, thus transforming poisoning sites into active sites and ensuring superior catalytic performance. The study presenting here not only provides an efficient strategy for fabricating NH 3 -SCR catalysts with superior K resistance but also sheds new light on the deactivation mechanism of K over CeMn catalysts. [ABSTRACT FROM AUTHOR]

Schematic illustration of RhB photocatalytic reaction mechanism over the rutile-TiO 2 /g-C 3 N 4 photocatalyst. [Display omitted] • The rutile-TiO 2 /g-C 3 N 4 photocatalyst is constructed by a simple solid grinding method. • The optimized rutile-TiO 2 /g-C 3 N 4 photocatalyst has more excellent photocatalytic performance than the pure rutile-TiO 2 and g-C 3 N 4. • The direct Z-scheme heterojunction mechanism is proposed over the rutile-TiO 2 /g-C 3 N 4 photocatalyst. Constructing a direct Z-scheme heterojunction is an effective method to improve the catalytic performance of photocatalyst. Here, the direct Z-scheme heterojunction rutile-TiO 2 /g-C 3 N 4 photocatalyst was constructed by a simple solid grinding method. This method can not only avoid the weak activity of rutile-TiO 2 in high synthesized temperature condition, but also precisely control the amount of g-C 3 N 4. The evaluation of photodegradation reaction suggests that the rutile-TiO 2 /g-C 3 N 4 photocatalyst exhibits higher photodegradation efficiency than the pure rutile-TiO 2 and the pure g-C 3 N 4 under simulated sunlight irradiation, and the optimal photocatalytic performance is achieved when the mass ratio of rutile-TiO 2 to g-C 3 N 4 is 2:5. The experimental results prove that a direct Z-scheme heterojunction is formed over the rutile-TiO 2 /g-C 3 N 4 photocatalyst, which promotes the effective electron-hole separation and the higher redox potential over the rutile-TiO 2 /g-C 3 N 4 photocatalyst. This work provides an attractive strategy to construct the direct Z-scheme photocatalyst consisted of rutile-TiO 2 and g-C 3 N 4. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Pt x Ir alloy nanoparticles were fabricated via ethylene glycol reduction method. • The Pt 2.5 Ir/CeO 2 catalysts shows an excellent activity for toluene combustion. • The Pt 2.5 Ir/CeO 2 has abundant oxygen vacancies and the best reducibility. • The interaction between Pt and Ir is helpful for the best activity of Pt 2.5 Ir/CeO 2. • The possible reaction pathway over Pt 2.5 Ir/CeO 2 is studied by the in-situ DRIFTS. Herein, bimetallic Pt-Ir alloy nanoparticles (NPs) were successfully fabricated by ethylene glycol reduction of H 2 PtCl 6 ·6H 2 O and IrCl 3 through a microwave-assisted method. The Pt-Ir alloy NPs were deposited on CeO 2 catalysts for toluene combustion. The Pt 2.5 Ir/CeO 2 sample exhibited better catalytic activity at low reaction temperature, compared with monometallic catalysts. The excellent low-temperature catalytic activity was resulted from the interaction between Pt and Ir, richer adsorbed oxygen species and low-temperature reducibility. Furthermore, the in-situ DRIFTS was used to investigate the possible reaction pathway of Pt 2.5 Ir/CeO 2. It showed that the broken of benzene ring on Pt 2.5 Ir/CeO 2 can be accomplished at lower temperature, resulting in enhancing the deep oxidation of toluene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Research progress on ABS poisoning NH 3 -SCR catalysts are comprehensively reviewed for the first time. • General characterization methods for ABS on catalysts are collected. • Reported strategies for controlling ABS formation and decomposition are presented. • Future effort on addressing the problem of ABS poisoning is prospected. The urgent need for the treatment of flue gas from non-electric industries has stimulated great interest in developing NH 3 -SCR (selective catalytic reduction of NO with NH 3) catalysts that can work stably at low temperatures (< 300 °C). However, the performance of low-temperature NH 3 -SCR catalysts is expected to be largely hindered by surface accumulation of ammonium bisulfate (ABS), which inclines to induce significant deactivation of NH 3 -SCR catalysts due to active sites blocking. As such, how to solve the problem of ABS poisoning becomes a timely research topic. Herein, we focus on the recent progress on controlling ABS deposition/decomposition during the NH 3 -SCR process for sustainable denitration. The review starts with a brief introduction on physicochemical properties of ABS, then the common methods used for qualitative and quantitative analysis of ABS on catalyst surface are introduced. Afterwards, recent developed strategies on restraining ABS formation and accelerating ABS decomposition are reviewed. Lastly, some suggestions for the future study of ABS poisoning are prospected. We hope that this review can provide helpful guidance for designing NH 3 -SCR catalysts with great tolerance to ABS poisoning. [ABSTRACT FROM AUTHOR]

• Thin-layered titania confined in SBA-15 was successfully synthesized by grafting strategy. • The amorphous thin-layered titania exhibited much enhanced surface acidity and regulated electronic state. • Activity of Fe supported titania catalyst were greatly improved, and H 2 O surprisingly promoted the catalyst activity. • The catalyst revealed promising SO 2 resistance, SO 2 was confirmed to have negligible influence on reactants adsorption. TiO 2 is a famous support for selective catalytic reduction of NO with NH 3 (NH 3 -SCR). Engineering the morphology and structure of TiO 2 is effective to modulate the interaction with surface dispersed component, providing further opportunity to improve catalytic performance. In this study, we rationally construct thin-layered titania confined in mesoporous silica via a surface grafting strategy. It exhibits high specific surface area with amorphous structure along mesopore channel, and much more Brønsted acid sites are generated than bulk TiO 2 due to defect induced oxygen-related species. After iron oxide loading, both the denitration activity and H 2 O/SO 2 tolerance are greatly promoted as compared to conventional Fe/TiO 2. Further characterizations reveal the obtained catalyst displays uniform iron oxide dispersion and intense Fe-Ti interaction, resulting in superior redox behavior and increased acidity. Notably, it is found the introduction of H 2 O exhibits a promotional effect on NO conversion efficiency, which can be ascribed to enhancement of NH 3 adsorption capability. Besides, SO 2 has negligible disturbance on NO/NH 3 adsorption, leading to superior sulfur tolerance. The result of present study demonstrates vital role of surface structure engineering of TiO 2 for sustainable denitration, which opens up a new avenue for designing well-performed and stable NH 3 -SCR catalysts. [ABSTRACT FROM AUTHOR]

• The competitive adsorption between SO 2 and NO x is the main reason for the decrease of activity in low temperature. • The formation and consumption of ABS reach a dynamic equilibrium, making the negative effect on the SCR activity limited. • The accumulation of ferric sulfate species enhances the surface acidity and promotes E-R pathway, further facilitating the activity. • The higher the temperature, the more SO 4 2− accumulated, and the rapider climbing rate of the catalytic activity. SO 2 poisoning of NH 3 -SCR catalysts at low temperature (< 300 °C) is still an austere challenge. In this work, γ-Fe 2 O 3 was taken as a model catalyst and the effect of reaction temperature on the catalytic activity in the presence of SO 2 were fully revealed. SO 2 introduction has no negative effect on the activity at 300 °C, which gradually improves with the extension of time. While for 225−275 °C, the activity decreases firstly and then increases slowly. The formatted sulfate species inhibits the adsorption of NO x , cuts off L-H reaction pathway and leads to the initial decline. While the deposited ammonium bisulfate (ABS) can be consumed continuously by NO + O 2 , implying the formation and consumption of ABS have reached a dynamic equilibrium. Moreover, the formation of ferric sulfate species results in the enhancement of surface acidity, which leads to the promotion of the E-R reaction pathway and further facilitates the increase of activity. [ABSTRACT FROM AUTHOR]

• The dual effects of ABS on NH 3 -SCR performance of Fe 2 O 3 -WO 3 /MCM-41 is observed and illustrated for the first time. • The formation of surface metal sulfates sustainably promotes the catalytic performance. • Nearly 90% of sulfates in ABS are immobilized after NH 4 + consumption. • Both the acidity and redox properties of catalyst are greatly improved after metal sulfates formation. Ammonium bisulfate (ABS) has long been considered as a main poisoning material in the selective catalytic reduction by NH 3 (NH 3 -SCR) due to the inevitable coverage of sticky ABS on catalytic active sites in sulfur-containing atmospheres, which severely hinders the achievement of stable and highly active NH 3 -SCR catalysts. In the present study, we report a novel observation of the dual effects of ABS on the NH 3 -SCR reaction. That is, ABS inhibits the NH 3 -SCR performance of Fe 2 O 3 -WO 3 /MCM-41 catalyst at low temperatures (50–200 °C) but shows apparent and sustainable reaction promotion when the temperature surpasses 250 °C. X-ray photoelectron spectroscopy (XPS) and NO probing adsorption confirmed that when ABS is deposited on the catalyst surface, a partial interaction between ABS and the Fe 2 O 3 -WO 3 component occurs, resulting in blocking of the active sites and an obvious loss of catalytic activity. With increasing reaction temperature, the ammonium in ABS can be facilely consumed by NO/O 2 , thus inducing the disintegration of poisoning species. The sulfate group transforms into metal sulfate and survives at high temperatures. Importantly, owing to the strong inductive effect of sulfate species, both the acidity and redox properties of the catalyst are greatly improved, which contributes to the enhanced activity. The results of the present study expand our knowledge of the role of ABS in the NH 3 -SCR reaction and will be useful for designing high-performing NH 3 -SCR catalysts. [ABSTRACT FROM AUTHOR]