Surface Peroxide Species Research Articles

Environment-Driven Variability in Absolute Band Edge Positions and Work Functions of Reduced Ceria.

The absolute band edge positions and work function (Φ) are the key electronic properties of metal oxides that determine their performance in electronic devices and photocatalysis. However, experimental measurements of these properties often show notable variations, and the mechanisms underlying these discrepancies remain inadequately understood. In this work, we focus on ceria (CeO2), a material renowned for its outstanding oxygen storage capacity, and combine theoretical and experimental techniques to demonstrate environmental modifications of its ionization potential (IP) and Φ. Under O-deficient conditions, reduced ceria exhibits a decreased IP and Φ with significant sensitivity to defect distributions. In contrast, the IP and Φ are elevated in O-rich conditions due to the formation of surface peroxide species. Surface adsorbates and impurities can further augment these variabilities under realistic conditions. We rationalize the shifts in energy levels by separating the individual contributions from bulk and surface factors, using hybrid quantum mechanical/molecular mechanical (QM/MM) embedded-cluster and periodic density functional theory (DFT) calculations supported by interatomic-potential-based electrostatic analyses. Our results highlight the critical role of on-site electrostatic potentials in determining the absolute energy levels in metal oxides, implying a dynamic evolution of band edges under catalytic conditions.

Cerium Oxide Catalyzed Disproportionation of Hydrogen Peroxide: A Closer Look at the Reaction Intermediate.

Cerium oxide nanoparticles (CNPs) have recently gained increasing interest as redox enzyme-mimetics to scavenge the intracellular excess of reactive oxygen species, including hydrogen peroxide (H2 O2 ). Despite the extensive exploration, there remains a notable discrepancy regarding the interpretation of observed redshift of UV-Visible spectroscopy due to H2 O2 addition and the catalase-mimicking mechanism of CNPs. To address this question, we investigated the reaction mechanism by taking a closer look at the reaction intermediate during the catalase mimicking reaction. In this study, we present evidence demonstrating that in aqueous solutions, H2 O2 adsorption at CNP surface triggers the formation of stable intermediates known as cerium-peroxo (Ce-O2 2- ) and/or cerium-hydroperoxo (Ce-OOH- ) complexes as resolved by Raman scattering and UV-Visible spectroscopy. Polymer coating presents steric hinderance for H2 O2 accessibility to the solid-liquid interface limiting further intermediate formation. We demonstrate in depth that the catalytic reactivity of CNPs in the H2 O2 disproportionation reaction increases with the Ce(III)-fraction and decreases in the presence of polymer coatings. The developed approach using UV-Visible spectroscopy for the characterization of the surface peroxide species can potentially serve as a foundation for determining the catalytic reactivity of CNPs in the disproportionation of H2 O2 .

Catalytic ozonation mechanism over M1-N3C1 active sites

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M1-N3C1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M1-N3C1 units induce locally polarized M − C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan.

Direct electron transfer double-defect core–shell LaVCuOδ@CeOx nanoreactors boosting hydrogen peroxide activation for enhanced quinoline removal

Double oxygen vacancies (VO) tuned core–shell LaVCuOδ@CeOx (VO-LCO@CeOx) nanoreactors with direct electron transfer (DET) structure was synthesized as an effective heterogeneous Fenton-like catalyst for the quinoline removal. The DET structure was constructed by electron-rich ≡Cu center of VO-LCO core and electron-capture center of CeOx shell for electrons supplying and consuming. This structure elevated total VO levels of catalyst through the removal of oxygen atoms in CeO2 from attice to interface sites. Meanwhile, the ≡Ce(III) acted as reactive sites for the adsorption of hydrogen peroxide (H2O2) to form surface peroxide species, and then the electron-rich ≡Cu center was further provided electrons to surface peroxide species by DET to produce hydroxyl radical. Moreover, the newly formed surface VO would also be further promote hydroxyl radical production through self-activation of H2O2. This catalyst displayed excellent catalytic activity and stability. The density functional theory (DFT) results further pointed out that this structure had excellent adsorption energy, and generable electron transfer from VO-LCO to CeOx. This work provided a novel approach for the development of heterogeneous Fenton-like catalysts to degrade quinoline wastewater.

Cation Substitution Induced d‐Band Center Modulation on Cobalt‐Based Spinel Oxides for Catalytic Ozonation

AbstractCo3O4 spinel is a promising transition metal oxide (TMO) catalyst for the catalytic ozonation of volatile organic compounds (VOCs). Herein, metal–organic frameworks (MOFs)‐derived Ni‐ and Mg‐ substituted Co3O4 catalysts retain similar spinel structures, but display improved and reduced ozonation performance of methyl mercaptan (CH3SH), respectively. Remarkably, the NiCo2O4 catalyst can still ≈90% removal of CH3SH after running for 20 h at room temperature under an initial concentration of 50 ppm CH3SH and 40 ppm O3, relative humidity of 60%, and space velocity of 300 000 mL h−1 g−1, exceeding the reported values. Experimental characterizations have unveiled that the substitution of Ni and Mg into the Co3O4 spinel altered surface acidity, oxygen species mobility, and Co2+/Co3+ ratio. The in situ Raman spectra reveal the dynamic formation Co(III)‐Oad* via the transformation of O3 into surface atomic oxygen (Oad*) and peroxide species (O2*). Theoretical calculations verify that Ni‐substitution increases nonuniform charges and Fermi density, leading to a moderate increase in d‐band center energy levels, thereby promoting O3 specific adsorption/activation to convert Oad*/O2* and •OH/1O2/•O2−, which contributes to eliminate CH3SH and prevent poisoning. The concept of tuning the d‐band center can provide valuable insights for the design of other catalysts for catalytic ozonation.

Electronic structure and oxygen vacancy tuning of Co & Ni co-doped W18O49 nanourchins for efficient TEA gas sensing

Inducing oxygen vacancies in metal oxides by dual doping metal ions is the key to modulating their electronic structure and designing highly sensitive noble metal-free materials for detecting hazardous toxic gases. This study reports nickel (Ni) and cobalt (Co) co-doping in W18O49 crystal lattices leads to electronic structure modulation and generates oxygen vacancies to highly activate the redox capability and catalytic efficacy of the urchin-like W18O49 sensor toward triethylamine (TEA) gas species. The electronic structure modulations and physisorption interactions between TEA molecules and W18O49 and/or Co&Ni co-doped W18O49 nanourchins were calculated by density functional theory (DFT). The experimental results and DFT calculations confirmed more significant charge transfers due to bandgap excitation and reactivity of TEA with Co&Ni co-doped W18O49 verifying their strong binding interactions. Electrons move from lattice oxygen to surface O2 molecules through co-doped cations-induced oxygen vacancies, which provide active sites and form surface superoxide and peroxide species incorporated into the sensing materials surface. Benefiting from the high specific surface area, abundant active sites, and faster electron/charge transport capability, the optimized 2 %Ni-doped W18O49, and 1 %Co&2%Ni co-doped W18O49 nanourchins exhibited excellent sensitivity towards TEA gas molecules. The sensing response of Co&Ni-W18O49 (Ra/Rg = 156) is higher than Ni-W18O49 (Ra/Rg = 114) and W18O49 (Ra/Rg = 76) at 250 °C, fast response/recovery (16/13), and superior selectivity. The XRD and XPS results combining the DFT calculations verify the improved sensitivity due to the synergistic modulation of electronic structure, which paws a friendly strategy for enriching the free electronics to design cost-effective gas sensors.

Operando Investigation of Toluene Oxidation over 1D Pt@CeO2 Derived from Pt Cluster-Containing MOF.

A unique 1D nanostructure of Pt@CeO2-BDC was prepared from Pt@CeBDC MOF. The Pt@CeO2-BDC was rich in oxygen vacancies (i.e., XPS Oβ/(Oα + Oβ) = 39.4%), and on the catalyst, the 2 nm Pt clusters were uniformly deposited on the 1D mesoporous polycrystalline CeO2. Toluene oxidation was conducted in a spectroscopic operando Raman-online FTIR reactor to elucidate the reaction mechanism and establish the structure-activity relationship. The reaction proceeds as follows: (I) adsorption of toluene as benzoate intermediates on Pt@CeO2-BDC at low temperature by reaction with surface peroxide species; (II) reaction activation and ring-opening involving lattice oxygen with a concomitant change in defect densities indicative of surface rearrangement; (III) complete oxidation to CO2 and H2O by lattice oxygen and reoxidation of the reduced ceria with consumption of adsorbed oxygen species. The Pt clusters, which mainly exist as Pt2+ with minor amounts of Pt0 and Pt4+ on the surface, facilitated the adsorption and reaction activation. The Pt-CeO2 interface generates reduced ceria sites forming nearby adsorbed peroxide at low temperature that oxidize toluene into benzoate species by a Langmuir-Hinshelwood mechanism. As the reaction temperature increases, the role of lattice oxygen becomes important, producing CO2 and H2O mainly by the Mars-van Krevelen mechanism.

Low-Temperature Methane Oxidation Triggered by Peroxide Radicals over Noble-Metal-Free MgO Catalyst.

Methane is a greenhouse gas that contributes to global warming. Hence, effectively removing the low concentration (<1000 ppm) of methane in the environment is an issue that deserves research in the field of catalysis. In this study, oxygen-magnesium bivacancies are simultaneously imbedded into MgO by designing an in situ reduction combustion atmosphere for oxygen release and substituting magnesium with carbon to induce the formation of magnesium vacancies. The DFT calculations reveal that the surface electron density of MgO is improved by the oxygen vacancy structure and the substitution of Mg by C in bulk; this accelerates migration of the charge from the material surface to the adsorbed oxygen species, which leads to abundant surface peroxide species that enable activation and oxidation of methane at a low temperature (below 200 °C). This work could provide a concept for developing non-noble or transition metal oxides for low-temperature activation and conversion of alkanes in the thermocatalytic field through reactive oxygen species.

Direct evidence of the key role of UV-formed peroxide species in photocatalytic gas-solid oxidation in air on anatase TiO2 particles.

IR spectroscopy was applied for the in situ investigations of surface intermediates formed on the surface of TiO2 (anatase) and ZnO under UV light illumination in air and their reactivity in the elimination of simple pollutant molecules. UV-irradiation of TiO2 (anatase) in air leads to the generation of peroxo-species with the peaks at 852 and 912 cm-1, but the bands of O2˙-ads were not detected. This is, to our knowledge, the first direct in situ IR spectroscopic detection of O2 photosorption intermediates in moist air. The formation of peroxo-species in these conditions is specific for TiO2 (anatase), whereas on ZnO the predominant species under UV light illumination in air are O2˙-ads and H2O2, desorbing into gas phase. Adsorbed water and surface hydroxyl groups contribute to the formation and stabilization of peroxo-species on TiO2 anatase during UV illumination in an oxygen atmosphere. If UV-irradiation is carried out in the environment of moist argon instead of moist air, the peroxo-species on TiO2 anatase are formed from water in a negligible quantity. Peroxo-species formed after O2 photoadsorption on TiO2 anatase in moist air have band positions similar to peroxo-species formed after photodecomposition of H2O2 (with accompanying color change of this sample from yellow to white). Direct experimental IR-spectroscopic evidence of peroxo-species reactivity as oxidative intermediates on TiO2 (anatase) in CO and ethanol vapor photooxidative processes is firstly obtained. These results confirm our early conclusion that peroxo-species formed under UV-irradiation in O2 on the hydrated surface of TiO2 (anatase) can be responsible for the surprising extreme dependence of the CO photooxidation rate on the adsorbed water coverage with the maximum at ∼0.5 ML. The ZnO sample was not active in the photooxidation of these molecules in air. It is concluded that UV formed peroxo-species are important diamagnetic oxidative intermediates in heterogeneous photochemical gas-solid oxidation processes on TiO2 (anatase).

CeO2–Nb2O5 photocatalysts for degradation of organic pollutants in water

The photocatalytic properties of CeO2–Nb2O5 photocatalysts in heterogeneous photocatalysis (under ultraviolet and visible radiation) and in Fenton-like process were reported. Methylene blue dye (MB) and phenol (Ph) were used as models of pollutant molecules for these reactions, and the photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and thermally stimulated luminescence (TL). The results indicated that the addition of CeO2 (0.3 wt%, 1.0 wt% and 2.0 wt%) to Nb2O5 sensitized the resultant materials, increasing light absorption in the visible region. However, there is a suitable formulation of CeO2–Nb2O5 photocatalysts to improve each photocatalytic process. In heterogeneous photocatalysis, the addition of small CeO2 quantities to Nb2O5 was enough to improve the photocatalytic activity of CeO2–Nb2O5 photocatalysts (The best composition reported was CeO2 0.3 wt%.). The effectiveness of the catalyst was explained by the decrease in the number of trapping and luminescence centers in the conduction band of the material after the addition of CeO2 to Nb2O5, but a large amount of CeO2 decreased the number of trapping, luminescent and active centers to a large extent. Contrarily, in a Fenton-like process, the addition of CeO2 to Nb2O5 was favorable in all the proportions studied. (The best composition was 2.0 wt% CeO2.) In this case, the effectiveness was explained by the influence of the adsorption process (adsorption-triggered process), and the interactions between H2O2 and Ce3+ of the CeO2 in each photocatalyst thus formed surface peroxide species O22−, which induced the removal of the organic molecules under visible light.

Improving Selectivity and Activity of CO2 Reduction Photocatalysts with Oxygen

Summary A highly porous photocatalyst (copper on TiO2 aerogel) was synthesized and applied in aqueous CO2 reduction without using external sacrificial electron donors. For the first time, complete selectivity toward CO and improved catalyst productivity are observed in the presence of oxygen. The optimal activity is achieved in a feed containing 0.5 vol% O2 in CO2. In situ XAS, EPR, and UV-vis measurements suggest, among different Cu oxidation states, Cu(I) to be the most active species in photocatalytic CO2 reduction. Oxygen sensing of the catalyst in the presence of O2/CO2 mixtures indicated an unexpected photoadsorption of oxygen on the titania surface. We propose photooxidation of surface hydroxyl groups to be the electron source for CO2 reduction, which is supported by hydroxyl group consumption, detection of hydroxyl radicals using in situ EPR, and detection of surface peroxide species after the reaction.

Different adsorption-degradation behavior of methylene blue and Congo red in nanoceria/H2O2 system under alkaline conditions

The Fenton-like activity of nanoceria has attracted intensive attention for wastewater treatment in recent years. During the Fenton-like reaction, the adsorption of organic pollutants on catalyst surface plays a key role in their degradation. In this work, the adsorption-degradation of methylene blue (MB) and Congo red (CR) in nanoceria/H2O2 system was investigated under alkaline conditions. The MB exhibited weak adsorption on nanoceria surface via electrostatic attraction, while strong Lewis acid–base interactions between CR and cerium ions was observed. Moreover, the adsorption of MB was enhanced in the presence of H2O2 by the formation of surface peroxide species, but an adsorption competition existed between H2O2 and CR. With more Ce3+, CeO2 nanorods could degrade CR efficiently as Fenton-like catalyst. But the degradation of MB catalyzed by ceria was much lower than that of CR in the presence of H2O2.

Dual-functional millisphere of anion-exchanger-supported nanoceria for synergistic As(III) removal with stoichiometric H2O2: Catalytic oxidation and sorption

Aiming at efficient As(III) removal, a millimetric nanocomposite Ce-201, with dual functionalities of catalytic H2O2 oxidation and sorption, was synthesized by confined growth of hydrous nanoceria in macroporous anion-exchanger host D201. The removal of As(III) by Ce-201 was significantly enhanced by H2O2 at stoichiometric dosage (H2O2/As(III) molar ratio = 1–2), during which the catalytic oxidation of As(III) into As(V) played a vital role. The surface peroxide species formed on the surface of the embedded hydrous nanoceria induced by H2O2 were proved the predominant reactive species for As(III) oxidation, and the resultant As(V) was mostly sequestered by the quaternary ammonium groups of the D201 host. The removal of As(III) by Ce-201/H2O2 was favorable over wide pH range of 5–9, whilst the presence of chloride, carbonate (up to 10 mM), sulfate, silicate, nitrate (up to 1 mM), and humic acid (up to 30 mg DOC/L) posed negligible adverse effect on As(III) removal. The As-laden Ce-201 could be well regenerated by NaOH−NaCl binary solution for sustainable utilization without significant capacity loss. In fixed-bed mode, the working capacity of Ce-201 with H2O2 spiked into the influent at trace level (2.67 μM) for continuous As(III) removal (∼6500 BV) was over twenty times that of the classic nanocomposite HFO-201 or twice of Ce-201 without H2O2. Therefore, the Ce-201/H2O2 technique showed great potential for full scale application of highly efficient decontamination of As(III) from water.

Enhanced mineralization of pharmaceuticals by surface oxidation over mesoporous γ-Ti-Al2O3 suspension with ozone

Titanium-doped mesoporous γ-Al2O3 (γ-Ti-Al2O3) was prepared by an evaporation-induced self-assembly method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption, scanning electron microscope, and FTIR spectra of chemisorbed pyridine. γ-Ti-Al2O3 revealed excellent catalytic ozonation activity and stability for mineralization of six drugs in aqueous solution, including ibuprofen, sulfamethoxazole, phenytoin, diphenhydramine, diclofenac sodium and acyclovir. The characterization studies showed that titanium was incorporated into the framework of γ-Al2O3 by AlOTi linkage, locating at tetrahedrally coordinated sites, which increased the Lewis acid sites of γ-Al2O3, especially the medium acid sites. The surface atomic oxygen (Al3−*O) and peroxide species (Ti4+−*O2) were commonly generated rather than hydroxyl radical from catalytic decomposition of ozone in γ-Ti-Al2O3 suspension on the basis of the electron paramagnetic resonance (EPR) and in situ Raman measurements. Furthermore, it was verified that the high mineralization of the tested pharmaceuticals came from the surface oxidization of organic acid intermediates by the common role of the surface atomic oxygen and peroxide species.

Synthetic and Spectroscopic Study of the Mechanism of Atomic Layer Deposition of Tin Dioxide

This study details the surface reaction chemistry relevant to the vapor deposition mechanism of SnO2 thin films by atomic layer deposition. The mechanism was elucidated by combining different spectroscopic studies. Initial nucleation of cyclic N2,N3-di-tert-butylbutane-2,3-diamidotin(II) (1) consists of surface SiOH protonation of ligands as shown by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This SiO2-surface-bound stannylene was further characterized by X-ray absorption (XAS) and resonance Raman spectroscopy. XAS, DRIFTS, and Raman spectroscopy were then used to follow the further reaction of the surface-bound stannylene with different oxygen sources and a second equivalent of 1. It was observed that water does not oxidize the initial surface-bound tin site, and a well-defined, three-coordinate tin(II) species, with two surface oxygen bonds and one coordinated water molecule, was characterized. Treatment of the surface stannylene with protic oxidants such as H2O2 or tBuOOH fully oxidizes tin to 4+, and coordination of additional oxygen ligands is observed. When a second equivalent of 1 is added to surface-bound Sn4+, the resulting surface tin is also found to be in the 4+ oxidation state, contrary to the nonoxidative nucleation step. As such, surface peroxide species provide a probable growth mechanism of SnO2 through oxidation, while nucleation occurs through protic ligand exchange.

Performances of pretreated ceria-zirconia nanomaterials/H&lt;SUB align="right"&gt;2O&lt;SUB align="right"&gt;2 system for the degradation of Orange II dye

In this work, the parameters affecting the reactivity of non-sulfated and sulfated commercial ceria-zirconia (CexZr1−xO2) nanomaterials with varying Ce content (x = 1, 0.80, 0.50, 0.21, 0) towards the degradation of Orange II dye have been evaluated. Characterisation of the catalysts was performed using nitrogen adsorption, XRD, Raman, TGA thermogravimetry and DR-UV-Vis spectroscopy. Briefly, it can be deduced that the sulfation treatment mostly affects the Ce rich catalysts by increasing the crystallite size and lowering the specific surface area. It is shown that the H2O2 dissociates on Ce (III) surface sites to yield peroxide-like species. Such species played a key role in enhancing the discoloration of the dye under dark and UV-Vis conditions. By contrast, the sulfation treatment is unfavorable for the adsorption of H2O2. Sulfates interfere in the formation and the chemical stability of the surface peroxide species via pre-chelating the cerium surface centers, resulting in reducing the catalytic activity of catalysts, especially for CeO2.

Catalytic total oxidation of 1,2-dichloroethane over VOx/CeO2 catalysts: Further insights via isotopic tracer techniques

Catalytic total oxidation of 1,2-dichloroethane (DCE) on CeO2 and VOx/CeO2 catalysts is investigated via various isotopic tracer techniques, including kinetic isotope effect (KIEs) measurements, in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFT) of deuterated 1,2-dichloroethane oxidation, H/D exchange of surface hydroxyl groups, temperature-programmed isotopic exchange (TPIE) and 18O2 isotope labeling experiments. The activation and dissociation of CCl bonds is determined to be the first step of DCE oxidation, and oxygen vacancies are identified as the main active sites by KIEs and density functional theory (DFT) calculations. For VOx/CeO2 catalysts, surface lattice oxygen is found to directly involve in oxidation of DCE via the formation of intermediate species of partial oxidation such as aldehyde species or CO, which are then totally oxidized into CO2 by the surface peroxide species. The occurrence of HCl is attributed to the reaction of surface hydroxyl groups with the dissociated Cl adsorbed on oxygen vacancies, whereas the rapid replenishment of the consumed OH is crucial for maintaining a better stability.

Highly dispersed CeO₂ on TiO₂ nanotube: a synergistic nanocomposite with superior peroxidase-like activity.

In this report, a novel nanocomposite of highly dispersed CeO2 on a TiO2 nanotube was designed and proposed as a peroxidase-like mimic. The best peroxidase-like activity was obtained for the CeO2/nanotube-TiO2 when the molar ratio of Ce/Ti was 0.1, which was much higher than that for CeO2/nanowire-TiO2, CeO2/nanorod-TiO2, or CeO2/nanoparticle-TiO2 with a similar molar ratio of Ce/Ti. Moreover, in comparison with other nanomaterial based peroxidase mimics, CeO2/nanotube-TiO2 nanocomposites exhibited higher affinity to H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB). Kinetic analysis indicated that the catalytic behavior was in accordance with typical Michaelis-Menten kinetics. Ce(3+) sites were confirmed as the catalytic active sites for the catalytic reaction. The first interaction of surface CeO2 with H2O2 chemically changed the surface state of CeO2 by transforming Ce(3+) sites into surface peroxide species causing adsorbed TMB oxidation. Compared with CeO2/nanowire-TiO2, CeO2/nanorod-TiO2, and CeO2/nanoparticle-TiO2, the combination of TiO2 nanotube with CeO2 presented the highest concentration of Ce(3+) thus leading to the best peroxidase-like activity. On the basis of the high activity of CeO2/nanotube-TiO2, the reaction provides a simple method for colorimetric detection of H2O2 and glucose with the detection limits of 3.2 and 6.1 μM, respectively.

Improving the catalytic activity of CeO2/H2O2 system by sulfation pretreatment of CeO2

Organic pollutants can be effectively degraded by CeO2/H2O2 system, the catalytic activity of which is restricted by over-complexation of H2O2 with CeO2. In this study, nano ceria was pretreated simply in different ways. Degradation of AO7 was employed to evaluate the catalytic activity of the pretreated ceria samples in the presence of H2O2 in pre-adsorbed mode (AO7 pre-adsorbed on CeO2 before the addition of H2O2) and pre-mixed mode (CeO2 pre-mixed with H2O2 before the addition of AO7). Two sulfated ceria samples (H2SO4–CeO2 and Na2SO4–CeO2) exhibit enhanced catalytic performance in both modes compared with un-pretreated bare CeO2. XRD, BET, FTIR and potentiometric titration methods were used to characterize the pretreated ceria samples. The sulfated samples display stronger surface acidity due to the sulfate ions anchored on their surface. Raman and XPS measurements were carried out to analyze the samples after reacting with H2O2. A mechanism to explain the improved catalytic activity of sulfated CeO2 is proposed that the active surface peroxide species (Ce(III)O2H−), which are excessive due to the over-complexation of H2O2 with surface Ce3+ sites, can be decomposed into high-active hydroxyl radicals under surface acidic environment.

Study on the selective catalytic reduction of NO with toluene over CuO/CeZrO2. A confirmation for the three-function model of HC-SCR using the temperature programmed methods and in situ DRIFTS

This paper deals with the selective catalytic reduction of NO with the use of toluene as a reducer and in the presence of excess oxygen. The three-function model of HC-SCR of NO has been studied over ceria-zirconia supported copper oxide (CuO/CeZrO2). The particular functions of CuO/CeZrO2 catalyst have been proved by the catalytic runs carried out in temperature-programmed conditions (TPSR) and in situ DRIFTS. On the basis of obtained results it was observed that NO is oxidized by O2 to NO2, which is subsequently used for toluene activation. Obtained oxygenates (CxHyOz) clean the active sites from oxygen, which was left during NO reduction to N2. The DRIFTS studies have shown that NO adsorbs on the surface of ceria-zirconia forming (i) the bridging nitrate when the adsorption of NO is carried out in the absence of gaseous O2 and (ii) both nitrite and nitrate species when the adsorption is carried out in the presence of O2. Formation of these surface species can be due to the presence of surface peroxide species (O22−) or superoxide species (O2−). The presence of the latter enhances NO adsorption and influences the evolution of surfaces species during temperature programmed reaction.