Search

Selective catalytic reduction (SCR) of NO x with NH 3 has been widely used for the removal of NO x. Because of the inevitable disadvantages of conventional V 2 O 5 -WO 3 (MoO 3)/TiO 2 catalysts such as poor low-temperature SCR activity and toxicity of vanadium, as well as the high-cost and over-strong NH 3 adsorption of zeolite catalysts, the development of efficient and non-toxic metal oxide SCR catalysts is highly demanded. Previously, we have developed an environmentally-benign CeO 2 -SiO 2 mixed-oxide SCR catalyst (CeSi 2), which exhibited superior SO 2 resistance ability. However, the low-temperature SCR activity on CeSi 2 was not that satisfactory. In this work, we proposed a new strategy of Mo doping to improve the low-temperature SCR activity on CeSi 2 , which was very crucial for its practical application. By a simple co-precipitation method, a homogenous Mo-Ce-Si mixed-oxide catalyst was prepared. The Mo doping could significantly enhance the NH 3 -SCR activity on CeSi 2 below 250 °C, and the optimal catalyst was Mo 0.1 CeSi 2 , which could achieve 80% NO x conversion at 200 °C. Mo 0.1 CeSi 2 also exhibited superior N 2 selectivity and resistance to SO 2 /H 2 O poisoning. Via a series of characterizations, it was found that the redox properties and surface acidity on CeSi 2 by Mo doping, which accounted for the enhanced low-temperature NH 3 -SCR activity on Mo 0.1 CeSi 2. The reaction mechanism on Mo 0.1 CeSi 2 was also fully revealed by in situ DRIFTS experiments. This work provided a new insight for the development of efficient low-temperature SCR catalysts with superior SO 2 resistance ability. [Display omitted] • A homogeneous Mo-Ce-Si mixed-oxide catalyst was prepared. • Enhanced low-temperature NH 3 -SCR activity was achieved on Mo doped CeO 2 -SiO 2. • Mo-Ce-Si catalyst exhibited excellent resistance to SO 2 poisoning. • Surface acidity and redox properties of CeO 2 -SiO 2 were promoted by Mo doping. • NH 3 -SCR reaction on Mo-Ce-Si catalyst proceeds through E-R mechanism. [ABSTRACT FROM AUTHOR]

Due to the capacity to offer abundant catalytic sites within porous solids featuring high surface areas, metal-organic frameworks (MOFs) and their derivatives have garnered considerable attention as prospective catalysts in environmental catalysis. To promote the industrial application of MOFs, there is an urgent need for an effective and environmental-friendly preparation approach. Breaking through the limitation of the traditional two-step preparation method that Pd was introduced to the already prepared Ce-BTC (Pd/Ce-BTC, BTC = 1, 3, 5 benzenetricarboxylate), in this work, we present a novel one-pot solvothermal method for synthesizing the Pd material supported by Ce-BTC (Pd@Ce-BTC). After pyrolysis in N 2 flow or air flow, Pd-CeO 2 catalysts derived from Pd@Ce-BTC exhibited much higher CO oxidation activity than those from Pd/Ce-BTC. Moreover, Pd/Ce-BTC and Pd@Ce-BTC pyrolyzed in N 2 flow (Pd/Ce-BTC-N and Pd@Ce-BTC-N) could better catalyze the oxidation of CO than Pd/Ce-BTC and Pd@Ce-BTC pyrolyzed in air flow (Pd/Ce-BTC-A and Pd@Ce-BTC-A). Further characterizations revealed that the abundant surface Ce3+ species, rich surface adsorbed oxygen species and superior redox properties were the main reasons for the superior CO oxidation activity of Pd@Ce-BTC-N. [Display omitted] • A one-pot solvothermal method was developed for the preparation of Pd incorporated in Ce-BTC • The Pd-CeO 2 catalyst derived from one-pot generated Pd@Ce-BTC exhibited superior CO oxidation activity • The activity of the Pd-CeO 2 catalyst obtained through pyrolysis in nitrogen flow surpassed that obtained in air flow • High Pd dispersion and rich surface Ce3+ species contributed to the improved CO oxidation activity on Pd-CeO 2 [ABSTRACT FROM AUTHOR]

[Display omitted] • Small and uniform CeO 2 nanoparticles were prepared on Al 2 O 3 (CA-T) using a two-step incipient wetness impregnation method. • Pt single sites anchored to step sites of small CeO 2 entities within CA-T were more stable than those anchored to crystal surface of large CeO 2 particles on regular ceria-alumina. • The reactivity of CO adsorbed on Pt sites decreased by Pt cluster step sites ≈ Pt cluster terrace sites > Pt cluster corner sites ≫ Pt single sites on CeO 2. • Abundant Pt cluster step and terrace sites as well as rich Pt-CeO 2 interfaces facilitated the activated Pt/CA-T catalyst for efficient CO oxidation at low temperatures. In heterogeneous catalysis, the promotion of low temperature activity and enhancement of thermal stability simultaneously especially for precious metal catalysts is always highly demanded but very challenging. Herein we report a novel Pt catalyst on ceria-alumina (CeO 2 /Al 2 O 3) support (Pt/CA-T) engineered by a two-step ceria deposition strategy, exhibiting superior thermal stability and low-temperature carbon monoxide (CO) oxidation activity after activation. Pt single sites anchored to engineered CeO 2 edge sites are much more stable than that to CeO 2 (111) surface, and such stable single sites can be transformed into highly active Pt clusters for efficient low-temperature CO oxidation. Active site identification indicates that the CO oxidation activity of different Pt sites follows such sequence: Pt cluster step sites ≈ Pt cluster terrace sites > Pt cluster corner sites ≫ Pt single sites on CeO 2. The excellent low temperature activity of activated Pt/CA-T catalyst for CO oxidation is associated with its abundant Pt cluster step and terrace sites as well as rich Pt-CeO 2 interfaces, which facilitate the adsorption of active CO species and superior oxygen activation/transfer ability. The present study provides new insights into the structure–activity relationship of Pt-CeO 2 -Al 2 O 3 catalyst, which can also guide the preparation of other highly robust supported catalysts for important industrial applications. [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]

With the introduction of potassium species, the catalytic oxidation performance over the Pt1/CeO2 catalyst was significantly enhanced, where potassium ions acted as structural and electronic promoters, and formed Pt–O–K interactions with Pt to directly regulate the coordination environment and electronic state of Pt and the metal-support interaction between Pt and CeO2. [ABSTRACT FROM AUTHOR]

Understanding the nature of active sites on metal oxide catalysts in the selective catalytic reduction (SCR) of NO by NH 3 (NH 3 -SCR) is a crucial prerequisite for the development of novel efficient NH 3 -SCR catalysts. In this work, two CeO 2 -based SCR catalyst systems with diverse acidic metal oxides-CeO 2 interfaces, i.e., Nb 2 O 5 -CeO 2 (Nb 2 O 5 /CeO 2 and CeO 2 /Nb 2 O 5) and WO 3 -CeO 2 (WO 3 /CeO 2 and CeO 2 /WO 3), were prepared and used to reveal the relationship between NH 3 -SCR activity and surface acidity/redox properties. In combination with the results of the NH 3 -SCR activity test and various characterizations, it was found that the NH 3 -SCR performance of Nb 2 O 5 -CeO 2 and WO 3 -CeO 2 catalysts was highly dependent on the strong interactions between the redox component (CeO 2) and acidic component (Nb 2 O 5 or WO 3), as well as the amount of paired redox-acid sites. From a quantitative perspective, an activity-surface acidity/redox property relationship was proposed. For both Nb 2 O 5 -CeO 2 and WO 3 -CeO 2 catalysts systems operated at the more concerned low-temperature range (200 °C), the NH 3 -SCR activity in low NO x conversion region (< 40%) was mainly dominated by the surface acidity of catalysts, while the NH 3 -SCR activity in high NO x conversion region (> 40%) was more determined by redox properties. [Display omitted] • Nb 2 O 5 -CeO 2 and WO 3 -CeO 2 catalysts with tuned redox-acid property were synthesized. • Paired redox-acid sites formed through strong interaction between Nb 2 O 5 /WO 3 and CeO 2. • NH 3 -SCR activity was well controlled by the paired redox-acid sites. • Surface acidity and redox property were investigated from a quantitative perspective. • A clear surface acidity/redox property-activity relationship was established. [ABSTRACT FROM AUTHOR]

A Ti3+-rich rutile TiO2 with a surface lattice expansion structure was constructed by H2 treatment, on which the supported Pt single atoms were stabilized in a highly oxidized state under a CO oxidation reaction atmosphere and had a weaker affinity for CO, thus exhibiting robust catalytic performance. [ABSTRACT FROM AUTHOR]

We report a noble-metal-free photocatalyst, ultrathin TiO2 with atomic layer thickness, which is a potential catalyst for CO2 photoreduction. An excellent liquid-product yield of 463.9 μmol gcat−1 in 8 h with 98% selectivity to alcohols was achieved, owing to sufficient surface defects favoring CO2 adsorption/activation. [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]

[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]

• Unique surface structures of Pd/TiO 2 catalysts for indoor toluene reduction. • Synergistic Pd0 and surface defects boost toluene photocatalytic oxidation. • Enhanced Ti3+/oxygen defects and Pd-TiO 2 interaction promote ROS generation. • Unique Pd/TiO 2 -N affects toluene partial oxidation and ring-opening process. Indoor volatile organic compounds (VOCs), represented by toluene, can pose a serious threat to human health. In this work, a series of Pd/TiO 2 catalysts with different surface structures (i.e. , dispersion/valence of Pd species, surface Ti3+/oxygen defect concentration and Pd-TiO 2 interactions, etc.) was constructed by various methods. It was found that the Pd/TiO 2 catalyst prepared by one-step reduction of NaBH 4 method (Pd/TiO 2 -N) with metallic Pd particles possessed more surface Ti3+/oxygen defects and stronger Pd-TiO 2 interaction than Pd/TiO 2 catalysts prepared by ethylene glycol reduction loading method (Pd/TiO 2 -E) and incipient wetness impregnation method (Pd/TiO 2 -I). Further photochemical characterizations and reaction mechanism study revealed that the relatively higher concentration of Pd0 species on Pd particles, stronger Pd-TiO 2 interaction, and more surface Ti3+/oxygen defects on Pd/TiO 2 -N could facilitate the generation of more reactive oxygen species (ROS) under light irradiation. The partial oxidation of toluene to benzyl alcohol/benzaldehyde/benzoic acid and the subsequent ring-opening process were found to be highly determined by the valence states of Pd particles and the concentration of surface Ti3+/oxygen defects. This work provides instructive insights into the construction of highly efficient Pd/TiO 2 catalysts for the removal of indoor VOCs. [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]