Amount Of Active Oxygen Species Research Articles

Perovskite catalysts for oxidative coupling of methane improved by Y‐doping

AbstractOxidative coupling of methane (OCM) is an effective route for methane direct conversion to ethylene. Perovskite oxides (ABO3) with variable properties are potential catalysts for OCM by adjusting the compositions. In this study, four perovskite catalysts, BaMO3‐δ and BaM1‐xYxO3‐δ (M = Zr, Ce; x = 0.2), were prepared by the sol–gel method to explore their catalytic performance of OCM. All catalysts are active toward OCM and reach the highest catalytic performance at 800°C. The OCM performance of Ce‐based catalysts is higher than that of Zr‐based catalysts. The selectivity of C2 compounds is significantly improved by Y‐doping. At CH4/O2 mol ratio of 8, a C2 selectivity of 67% was achieved on BaCe0.8Y0.2O3‐δ. Compared with Zr‐based catalysts, more amounts of active oxygen species, which are beneficial to OCM, were observed on BaCeO3‐δ and BaCe0.8Y0.2O3‐δ. Meanwhile, higher contents of moderate and strong basic sites, which are beneficial to OCM, were found on the Y‐doped catalysts. This is attributed to the generation of oxygen vacancies caused by Y‐doping in the B‐site. Therefore, BaCe0.8Y0.2O3‐δ with more active oxygen species and stronger basicity exhibits the highest performance among the four catalysts.

Porous Ni−Al−O Fabricated by a Facile Hydrothermal Method: Improved Catalytic Performance for the Oxidative Dehydrogenation of Ethane to Produce Ethylene

AbstractThe oxidative dehydrogenation of ethane (ODHE) to ethylene is a process with many advantages (such as energy conservation and coke resistance). Herein, flower‐like Ni−Al−O catalysts with hierarchical structure and high surface areas were fabricated through a hydrothermal route and were applied to ODHE using O2 as oxidant. Compared with NiO alone, the Al3+ insertion into NiO matrix not only increases the C2H4 selectivity by 3–4 times, but also prevents the generation of CO2 and CH4 above 500 °C. At 550 °C, all Ni−Al−O catalysts maintain approximately 50 % ethylene selectivity regardless of Al content. The ethylene yield of 29.5 % with C2H4 selectivity 55.7 % over Ni−Al0.8‐O sample can be reached at 500 °C. Moreover, the Ni−Al0.8‐O catalyst presents a good stability and has no loss of activity after 100 h continuous evaluation. The various characterizations were carried out for investigating the nature of as‐prepared Ni−Al−O catalysts with different Al loadings. Experimental results demonstrate that the addition of Al not only affects the structure and texture properties of NiO, but also impacts the reducibility of Ni species and the amount of active oxygen species. It is found that the Al3+ substitution results in: (1) smaller NiO size; (2) larger specific surface area; (3) weaker reducibility and (4) fewer non‐stoichiometric oxygen species. Therefore, the significant improvement of ethylene selectivity is observed in Ni−Alx‐O catalysts.

A dual-site doping strategy for developing efficient perovskite oxide electrocatalysts towards oxygen evolution reaction

Perovskite-type ABO3 transition metal oxides are promising electrocatalysts for oxygen evolution reaction (OER), but still suffer from insufficient activities. Traditional efforts are mainly based on a single-site doping of heteroatom ions into either B-sites or O-sites of the ABO3 structures. Here we propose a dual-site doping strategy by simultaneous incorporation of iodine cations and anions into the B-sites and O-sites of ABO3 perovskite oxides, respectively. Consequently, both activated B-site transition metals with optimal eg orbital occupancy and large amount of active oxygen species were achieved for remarkably improved OER activities. Using this approach, significantly improved OER activities are achieved in some representative perovskite oxides, including Ba0.5Sr0.5(Co0.8Fe0.2)0.9O3–δ (BSCF), SrCo0.9O3−δ (SCO) and SrNi0.9O3−δ (SNO). Specifically, the iodine dual-site doped BSCF boosts a small overpotential of 290 mV at 10 mA cm−2 and a small Tafel slope of 53 mV dec−1, which is about 130 mV and almost half times lower than that of pristine BSCF, respectively. Besides, this general dual-site doping strategy can also realize scale-up synthesis and achieve a gram-scale production. Our findings show a unique doping strategy to design efficient perovskite oxide electrocatalysts beyond the conventional approaches.

Construction of a Nanorod Structure-Confined Pt@CeO2 Catalyst by an In-Situ Encapsulation Strategy for Low-Temperature Catalytic Oxidation of Toluene.

In this work, Pt@CeO2 catalysts with a nanorod structure (Pt@CeO2 -R) and a bunch structure (Pt@CeO2 -B) were synthesized through an in-situ encapsulation strategy of Pt species in Ce-MOFs, respectively. It was discovered that the Pt@CeO2 -R catalyst possessed the best catalytic performance for toluene catalytic combustion, and this result was mainly caused by the confinement of Pt nanoparticles in Ce-MOFs, which was related to the chemical state of Pt species, redox ability, and the amount of active oxygen species. The Pt@CeO2 -R catalyst contained more Ce3+ species, rich Pt4+ species, and abundant active oxygen species due to the existence of the confined effect, which was conducive to promote catalytic oxidation of toluene. In addition, the Pt@CeO2 -R catalyst also exhibited more redox ability, which may speed up the catalytic reaction rates. On the contrary, the Pt/CeO2 -R catalyst was synthesized through a simple impregnation method and exhibited the poor activity for toluene catalytic combustion due to poor Pt4+ species and active oxygen species. Therefore, this work provides a feasible experimental basis for the study of different morphologies and encapsulated metal nanoparticles.

Construction of urchin-structured Fe2O3 microspheres supported potassium for diesel soot catalytic elimination

The catalytic combustion was considered as a promising approach to eliminate diesel soot particulates. However, the development of this technology was limited by the lack of high efficient catalysts due to the poor contact efficiency between catalysts and soot particulates, and insufficient active oxygen species. Herein, urchin-structured Fe2O3 microspheres supported potassium (K/Fe2O3 US) was designed and successfully prepared through a facile hydrothermal and impregnation route. The as-obtained K/Fe2O3 US showed superior catalytic combustion activities for soot elimination. The ignition temperature at the soot conversion rates of 10% (T10) and 50% (T50) for K/Fe2O3 US are 300 °C and 351 °C, respectively. The results of multiple characterizations revealed the origin of the activity enhancement over K/Fe2O3 US catalysts. The urchin structure could improve the contact efficiency between catalyst and soot particulates. The loading of potassium on Fe2O3 increased the amounts of active oxygen species, promoting the oxidation property of the catalysts.

Catalytic diesel soot elimination over potassium promoted transition metal oxide (Co/Mn/Fe) nanosheets monolithic catalysts

A series of potassium promoted transition metal oxide crossed nanosheets (KTMO-NS: KCo-NS, KMn-NS and KFe-NS) on the monolithic three-dimensional macroporous (3-DM) nickel foam substrate was prepared through the facile hydrothermal and wet impregnation methods, and utilized to evaluate for catalytic soot oxidation. The KTMO-NS catalysts display higher activity than that potassium-free catalysts (TMO-NS) for soot elimination. The results of XPS O1s, Soot-TPR and the amount of active oxygen species indicate that the interaction between potassium and transition metal oxides can generate more oxygen vacancies, so that the catalysts have more active oxygen species, especially for KCo-NS and KFe-NS. Under O2/N2 atmosphere, the KCo-NS and KFe-NS display the higher catalytic activity because of the more surface oxygen species and the stronger interaction between potassium and cobalt/ferric oxide. After introducing NO in the O2/N2 ambient, the KMn-NS possesses the similar catalytic activity with the KFe-NS owing to the higher oxidation ability of NO. Among these catalysts, the KCo-NS shows the highest catalytic soot performance with the lowest T10 (229 °C) and T50 (333 °C), which is higher than the Pt promoted transition metal oxide catalysts.

Insight into the activity and SO2 tolerance of hierarchically ordered MnFe1-δCoδOx ternary oxides for low-temperature selective catalytic reduction of NOx with NH3

Manganese (Mn)-based mixed oxides are considered the most efficient catalysts for low-temperature ammonia selective catalytic reduction of nitrogen oxides (NOx) (NH3-SCR of NOx). Water resistance and sulfur tolerance, especially the SO2 tolerance of Mn-based catalysts, are the main obstacles preventing their practical application. Therefore, in this study, a series of cobalt (Co)-doped MnFeOx ternary mixed oxides catalysts with a hierarchically ordered structure (Hierc-MnFe1-δCoδOx, δ = 0.2, 0.4 and 0.6) were developed and applied for NH3-SCR of NOx at low temperature. Compared with Hierc-MnFeOx, Hierc-MnFe1-δCoδOx catalyst exhibited enhanced low-temperature activity and a broadened temperature window (NOx conversion above 80% was between 90 and 343 °C over Hierc-MnFe0.6Co0.4Ox), as well as better H2O resistance and SO2 tolerance. The enhanced low-temperature activity was attributed to a larger amount of active oxygen species, a higher proportion of Mn4+, Fe3+ and Co3+ content, and the improvement of surface acidity, which can facilitate the adsorption and activation of NO and NH3. Additionally, the Hierc-MnFe0.6Co0.4Ox catalyst exhibited superior soot tolerance due to its special hierarchically ordered architecture. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that the Co-modified Hierc-MnFe1-δCoδOx ternary oxide catalyst could efficiently protect nitrate species on Hierc-MnFe0.6Co0.4Ox from the poisoning effect of SO2, thereby boosting its SO2 tolerance. This study provides a good candidate for low-temperature deNOx application with enhanced SO2 and soot tolerance.

Hydrothermal-treatment-based facile one-step preparation of K-promoted NOx adsorbents derived from hydrotalcite-like compounds

K-promoted mixed metal oxides were prepared from K2CO3-promoted Co-Mg-Al hydrotalcite-like compounds using a simple hydrothermal synthesis method. The introduced K2CO3 largely increased the NOx uptake by generating active oxygen species; however, the presence of an excessive amount of K2CO3 in the aggregated bulk phase suppressed the formation of active oxygen species. The developed NOx adsorbents presented excellent NOx uptake at low temperatures (0.566 and 2.63 mmol g−1 at 150 and 250 °C, respectively). In addition, the effects of active oxygen species on the NO oxidation and NOx adsorption ability were investigated. The amount of active oxygen species and the NOx adsorption performance at 150 °C were highly correlated. However, the NOx uptake at 250 °C gradually increased with the amount of K2CO3, although the K2CO3 species in the aggregated bulk phase inhibited the formation of active oxygen species. It was revealed that the K2CO3 in the bulk phase promoted the adsorption of NOx at 250 °C by directly trapping it. Overall, the introduced K2CO3 enhanced the NOx adsorption performance in two ways: (1) as a surface modifier to generate active oxygen species and (2) via the direct adsorption of NOx at high temperature.

Boosting Toluene Combustion by Engineering Co–O Strength in Cobalt Oxide Catalysts

Exploring active and low-cost transition metal oxides (TMOs) based catalysts for volatile organic compounds (VOCs) abatement is vital for air pollution control technologies. Since 18 oxygen atoms are required for the complete mineralization of a toluene molecule, the participation of a large amount of active oxygen is a key requirement for the catalytic oxidation of toluene. Here, toluene degradation was improved by weakening the Co-O bond strength on the surface of cobalt oxide, so as to increase the amount of active oxygen species, while maintaining the high stability of the catalyst for toluene combustion. The bond strength of Co-O and the amount of surface active O2 was regulated by tuning the pyrolysis temperature. The catalyst's redox ability and surface oxygen species activity are improved due to the weakening of the Co-O bond strength. It has been demonstrated that active oxygen plays a crucial role in boosting toluene combustion by engineering Co-O strength in cobalt oxide catalysts. This work provides a new understanding of the exploration and development of high-performance TMO catalysts for VOCs abatement.

Hydroxyapatite-Supported Low-Content Pt Catalysts for Efficient Removal of Formaldehyde at Room Temperature.

Indoor environmental quality directly affects the life quality and health of human beings, and therefore, it is highly vital to eliminate the volatile organic compounds especially formaldehyde (HCHO), which is regarded as one of the most common harmful pollutants in indoor air. Hydroxyapatite (HAP)-supported Pt (Pt/HAP) catalysts with a low content of Pt (0.2 wt %) obtained via hydrothermal and chemical reduction processes could effectively remove gaseous HCHO from the indoor environment at room temperature. The influence of modifier in the preparation on the catalyst activity was investigated. The HAP and HAP modified by sodium citrate and hexamethylenetetramine-supported 0.2 wt % Pt could completely decompose HCHO into CO2 and water, while HAP modified by sodium dodecyl-sulfate-supported Pt removed HCHO primarily via adsorption. The HAP modified by the sodium citrate catalyst exhibited superior catalytic performance of HCHO compared to the HAP and HAP modified by hexamethylenetetramine and sodium dodecyl-sulfate-supported Pt catalysts, which was mainly because of its higher surface Ca/P ratio providing more Lewis acidic sites (Ca2+) for co-operational capture of HCHO molecules and a larger amount of active oxygen species. Our results indicate that an optimized combination of functional supports and low-content noble metal nanoparticles could be a route to fabricate effective room-temperature catalysts for potential application in indoor air purification.

Fabrication of chemical composition controlled YbFe2O4 epitaxial thin films

The crystal growth of YbFe2O4 requires oxidant-poor conditions, thus YbFe2O4 usually contains a large number of iron deficiencies even in the bulk single crystal. The use of an ArF laser for laser ablation is effective to reduce the amount of active oxygen species and a wide process window to form the YbFe2O4 epitaxial films becomes available. By using the widened process window and an iron-rich target, the chemical composition of the YbFe2O4 epitaxial thin films is successfully controlled. The effect of the iron composition on the charge ordering transition can be discussed using the nonlinear I–V behavior. The threshold electric field changes depending on the iron composition owing to the broadening of the 3-dimensional (3D) charge order region, which affects the robustness of the 3D charge order against an electric field in YbFe2O4 thin films.

Key role of NO + C3H8 reaction for the elimination of NO in automobile exhaust by three-way catalyst.

Pd-only three-way catalysts with improved catalytic activity for NO elimination were prepared. In order to explore the catalytic reaction rules of NO reduction under a three-way catalytic system, a series of single reactions related to NO reduction were evaluated. It was found that the reaction temperatures of NO + H2 or NO + CO or NO + C3H6 reactions were below 250°C, while that of NO + C3H8 was up to 350°C. Thus, the reaction NO + C3H8 served as the key reaction in determining the purification efficiency of NO at the high-temperature stage. By in situ FTIR, we proposed that three possible steps were involved in NO + C3H8 reaction. The first step was the oxidation of C3H8 and NO to acetone and nitrate species by active oxygen species, respectively (C3H8 + O* → C3H6O, NO + O* → NO3-). XPS results revealed that the amount of active oxygen species in Pd/CeO2-ZrO2-Al2O3 (Pd/CZA, 73.7%) was much higher than that in Pd/CexZr1-xO2+Al2O3 (Pd/CZ+A, 64.1%). This was in line with the higher reaction efficiency of the first step over Pd/CZA. Then the NO + C3H8 reaction was accelerated by the first step, which consequently contributed to the higher NO elimination efficiency of Pd/CZA.

Promotional effect of Ce and Fe addition on Cu-based extruded catalyst for catalytic elimination of co-fed acrylonitrile and HCN

The promotional effect of Ce and Fe modified Cu-based extruded catalysts on their performance for the catalytic elimination of co-fed acrylonitrile and HCN was investigated. The CuCeFe-ZTA catalyst exhibited great catalytic performance and stability. The introduction of Ce led to an increase in the amount of active oxygen species and better reducibility of the catalyst, while more strong acid sites were formed upon further modification of the catalyst upon addition of Fe. These features are critical in promoting catalyst performance for nitrile and HCN oxidation reactions, and the results of this work may facilitate the research in developing industrial catalysts for the purification of nitrile and HCN-containing exhaust gas streams.

Aerobic Baeyer-Villiger oxidation of ketones over mesoporous Mn-Ce and Mn-Co composite oxides in the presence of benzaldehyde: The effect of valence state

Aerobic Baeyer-Villiger oxidation of ketones into corresponding esters were performed over mesoporous Mn-Ce and Mn-Co composite oxides prepared by co-impregnation method and benzaldehyde was used as the sacrificing agent. It was found that the best conversion and selectivity were obtained when the Mn/Ce mole ratio was 1:2 (denoted as Mn0.33Ce0.67Os) through investigating the effect of Mn/Ce mole ratio on the catalytic activity. Interestingly, Mn0.33Co0.67Os (Mn/Co mole ratio was 1:2) catalyst had no catalytic activity for this reaction. X-ray diffraction (XRD) results showed that MnOx was completely dissolved into the CeO2 lattice, and Mn0.33Co0.67Os sample was existed in the form of spinel structure (Co, Mn) (Mn, Co)2O4 and obvious peaks of Co3O4. Nitrogen adsorption-desorption measurements revealed that Mn0.67Ce0.33Os, Mn0.5Ce0.5Os, Mn0.33Ce0.67Os and Mn0.33Co0.67Os materials possessed mesoporous structure. X-ray photoelectron spectroscopy (XPS) analysis showed that the highest concentration of Ce3+ on the surface of Mn0.33Ce0.67Os catalyst, which could create unsaturated chemical bonds, charge imbalance, and oxygen vacancies on the surface of samples, it is beneficial to the oxidation reaction. Additionally, XPS data revealed that Mn0.33Ce0.67Os catalyst has great potential in catalytic oxidation due to the large amount of active oxygen species on the surface. In addition, manganese and cobalt species on the surface of Mn0.33Co0.67Os are almost present in the form of Mn2+ and Co3+, it is known that Mn2+ can serve as a potent antioxidant and scavenge the activity of active oxygen species, while Co3+ ions can prevent the formation of oxygen vacancies and inhibit the release of reactive oxygen species, thus the presence of Mn2+ and Co3+ inhibited the catalytic activity of Mn0.33Co0.67Os catalyst. The diffuse reflectance ultraviolet-visible spectroscopy (DR-UV-vis) and hydrogen temperature-programmed reduction (H2-TPR) results are in accordance XPS data.

The promoting effect of CeO2@Ce-O-P multi-core@shell structure on SO2 tolerance for selective catalytic reduction of NO with NH3 at low temperature

A series of CeO2@Ce-O-P “multi-core@shell” catalysts were synthesized in this paper for selective catalytic reduction (SCR) of NO with NH3. The experimental results had showed that CeO2@Ce-O-P-30:3 yielded best SO2 tolerance of an over 70% deNOx efficiency at 250 °C in the presence of 100 ppm SO2 for 20 h, which was much higher compared to pure Ce-O-P and CeO2 samples. Further characterization results indicated that Ce-O-P coating layer could somewhat inhibit sulfur depositing on the catalysts during SCR reaction in the presence of SO2, thereby protecting the active sites from SO2 poisoning. Especially, O2-TPD results illustrated that a great amount of active oxygen species were retained on used CeO2@Ce-O-P catalyst after a long term reaction. The synergetic effect of “multi-core@shell” structure could be attributed to such enhanced performances. The “core” CeO2 devoted abundant active oxygen sites to fulfill the SCR reaction. And the “shell” Ce-O-P could not only provide acid sites, but also protect the active oxygen species by avoiding the over-adsorption of SO2 on the catalyst. This work could provide a new way to increase the sulfur resistance for low temperature SCR catalysts.

Three-dimensionally ordered macroporous CeO2/Al2O3-supported Au nanoparticle catalysts: Effects of CeO2 nanolayers on catalytic activity in soot oxidation

A series of catalysts consisting of three-dimensionally ordered macroporous (3DOM) x-CeO2/Al2O3-supported Au nanoparticles (x = 2, 10, 20, and 40 wt%) were successfully synthesized using a reduction-deposition method. These catalysts were characterized using scanning electron microscopy, the Brunauer-Emmett-Teller method, X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, and temperature-programmed reduction by H2. Au nanoparticles of mean particle size 5 nm were well dispersed and supported on the inner walls of uniform macropores. The 3DOM structure improved the contact efficiency between soot and the catalyst. An Al-Ce-O solid solution was formed in the multilayer support, i.e., x-CeO2/Al2O3, by the incorporation of Al3+ ions into the CeO2 lattice, which resulted in the creation of extrinsic oxygen vacancies. Strong interactions between the metal (Au) and the support (Ce) increased the amount of active oxygen species, and this promoted soot oxidation. The catalytic performance in soot combustion was evaluated using a temperature-programmed oxidation technique. The presence of CeO2 nanolayers in the 3DOM Au/x-CeO2/Al2O3 catalysts clearly improved the catalytic activities in soot oxidation. Among the prepared catalysts, 3DOM Au/20%CeO2/Al2O3 showed high catalytic activity and stability in diesel soot oxidation.

Synthesis of a Highly Active and Stable Nickel‐Embedded Alumina Catalyst for Methane Dry Reforming: On the Confinement Effects of Alumina Shells for Nickel Nanoparticles

AbstractA 12 % Ni@Al2O3 catalyst was synthesized by using an inverse microemulsion technique and evaluated for the dry reforming of methane (DRM). We used TEM to reveal that the core–shell structure was formed successfully in the 12 % Ni@Al2O3 catalyst, in which the Ni nanoparticle cores with an average grain size around 10 nm are encapsulated by mesoporous Al2O3 shells. In comparison with a 12 % Ni/Al2O3 catalyst prepared by an impregnation method, much smaller Ni grain sizes and higher metallic Ni active surface areas can be achieved in the core–shell catalyst, which was evidenced by using TEM and H2 adsorption–desorption analysis. In addition, a larger amount of active oxygen species was formed on the surface of 12 % Ni@Al2O3 than on 12 % Ni/Al2O3. Importantly, the formation of the core–shell structure in 12 % Ni@Al2O3 can effectively impede the migration of the Ni active species at elevated temperatures, which prevents agglomeration. Consequently, the 12 % Ni@Al2O3 core–shell catalyst shows a remarkable activity and stability and a potent coke resistance during a 50 h durability evaluation at 800 °C for DRM. It is believed that the core–shell structure is the major factor that accounts for the superior DRM performance over that of the 12 % Ni@Al2O3 catalyst, which might open a new way for the design and development of improved catalysts for DRM for hydrogen production.

The inhibition effect of oxygen in the calcination atmosphere on the catalytic performance of MnOx–CeO2 catalysts for NO oxidation

In this study, the widely studied MnCe (MnOx–CeO2) catalyst prepared by the co-precipitation method was used for investigating the effects of oxygen in the calcination atmosphere (referred as Oca) on its catalytic performance for NO oxidation. The evaluation of catalytic performance showed that MnCe-O (calcined in O2/Ar) exhibited a much lower NO conversion in comparison with MnCe-A (calcined in Ar) catalyst. The characterization results revealed that Oca could cause the sintering of MnCe catalysts and then reduce the surface area, which decreased the active sites for catalytic reaction. Simultaneously, Oca inhibited the incorporation of Mn ions into CeO2 lattice, which could weaken the interaction between MnOx and CeO2 supports. This weak interaction decreased the amounts of active oxygen species and weakened the redox properties of MnCe catalyst. Furthermore, the nitrate species adsorbed on MnCe-O was more stable than that on MnCe-A. Therefore, the inferior catalytic performance of MnCe-O could be attributed to the collective effect of low concentration active sites and active oxygen species, poor redox properties and stable adsorbed nitrate species.

Synergistic effect between copper and cerium on the performance of Cux-Ce0.5-x-Zr0.5 (x = 0.1–0.5) oxides catalysts for selective catalytic reduction of NO with ammonia

A series of Cux-Ce0.5-x-Zr0.5 oxides catalysts with different Cu/Ce ratio were synthesized by citric acid method. The catalysts were characterized by XRD, BET surface area, H2-TPR, NH3-TPD, NO-TPD, XPS and in-situ DRIFTS. The synergistic effect between copper and cerium on the catalytic performance of Cux-Ce0.5-x-Zr0.5 for selective catalytic reduction of NO with ammonia was investigated. It was found that the Cu0.2-Ce0.3-Zr0.5 catalyst show the excellent SCR activity, N2 selectivity and H2O/SO2 durability in a low temperature range of 150–270°C even at high gas hourly space velocity of 84,000h−1. The strong interaction leads to the improvement of the acidity and the increase in the amount of active oxygen species (oxygen vacancy), which are responsible for the higher activity at low temperatures. The SCR reaction process over Cu0.2-Ce0.3-Zr0.5 was also examined using in-situ DRIFTS. The DRIFTS results indicate that abundant ionic NH4+ (Brønsted acid sites), coordinated NH3 on the Lewis acid sites, as well as highly active monodentate nitrate and bridging nitrate species were the key intermediates in the SCR reaction.

Sol–gel synthesis of CuO-TiO2 catalyst with high dispersion CuO species for selective catalytic oxidation of NO

In this study, CuO-TiO2 (Cux-Ti) mixed-oxide catalysts with different Cu content prepared by sol-gel method were firstly used to selective catalytic oxidation (SCO) of NO. The catalytic activity test revealed that catalysts, especially Cu0.07-Ti, exhibited much higher catalytic performance than CuO supported TiO2 (Cu0.07/Ti) catalyst. XRD, EDS, Raman, XPS, H2-TPR, O2-TOD, NO-TPD and DRIFT measurements were used for characterizing the catalysts. The results of characterizations reveled that Cu0.07-Ti catalysts possessed high dispersed CuO. This feature of Cu0.07-Ti resulted in a strong interaction of Cu species with TiO2 support in compared to Cu0.07/Ti. This strong interaction not only enhanced amounts of active oxygen species by promoting the formation of oxygen vacancies, but also activated adsorbed NO over Cu0.07-Ti catalysts. In addition, on the basis of NO2 formation, it also promoted the decomposition of nitrate species to NO2 over Cu0.07-Ti catalyst. Based on the above mentioned favorable properties, Cu0.07-Ti catalysts had an excellent NO-SCO performance.