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Eliminating vehicle emission is of importance due to the severe limit value. The work reports a convenient strategy of improving dispersion of platinum-based catalyst with the assistance of polyvinyl alcohol in a varied addition amount. Following the "two-step" annealing techniques, the catalytic performance of the polymer-assisted catalysts in diesel was obviously enhanced because of the improved dispersion of the platinum. Based on experimental results, the long chains of polymer resulting in the steric effect are presumed to isolate platinum ion, inhibiting the aggregation of platinum particles and then improving its dispersion. And the hydroxyl bonding between the polymers could convey electron to platinum species, leading to the lower platinum valence state. Both effects are positive resulting in an excellent NO maximum conversion of around 65% at the optimal introduction of 5 mass% of polymer, as the diesel oxidation catalyst (DOC), which could be inclined to a good purification in the diesel aftertreatment. Hopefully, the convenient research method could initiate the exploration and application of polymer-assisted catalysts for well-dispersed noble metal nanoparticles in eliminating exhaust emission. [ABSTRACT FROM AUTHOR]

The Pd catalyst supported on the Zr0.5Al0.5O1.75 composite material was prepared by the conventional impregnation and double solvent impregnation method. The effects of preparation method on the catalytic properties of the Pd/Zr0.5Al0.5O1.75 catalyst for methane combustion have been investigated systematically. The measurement was evaluated in a multiple fixed-bed continuous flow micro-reactor by passing a gas mixture simulating the exhaust emissions from lean-burn natural gas vehicles. The as-prepared catalysts were characterized by CO chemical adsorption, transmission electron microscopy (TEM), hydrogen-temperature programmed reduction (H2-TPR),and X-ray photoelectron spectroscopy (XPS) measurements. The results of TEM and CO chemisorption showed that the introduction of double solvent during the preparation of Pd/Zr0.5Al0.5O1.75 was beneficial for the dispersion of Pd nanoparticles and obtained superior resistance to the sintering of Pd on the surface of Zr0.5Al0.5O1.75. The H2-TPR measurements demonstrated that the double solvent method increased the reducibility of the Pd catalyst. The XPS results further indicated that more active surface oxygen species also can be formed on the catalyst prepared via double solvent process. Thus, this catalyst exhibited better catalytic performance and hydrothermal aging resistance in the methane oxidation compared to its analogues with the same Pd content prepared by the conventional impregnation method. [ABSTRACT FROM AUTHOR]

To preferably catalyze the oxidation of NO to NO in diesel after-treatment system, a series of CeO-MnO composite oxides was supported on silica-alumina material by the co-impregnation method. The maximum conversion of NO of the catalyst with a Ce/Mn weight ratio of 5:5 was improved by around 40%, compared to the supported manganese-only or cerium-only sample. And its maximum reaction rate was 0.056 μmol g s at 250 °C at the gas hourly space velocity of 30,000 h. The experimental results suggested that Ce-Mn solid solution was formed, which could modulate the valence state of cerium and manganese and exhibit great redox properties. Moreover, the strong interaction between ceria and manganese resulted in the largest desorption amount of strong chemical oxygen and oxygen vacancies, leading to the maximum O area ratio of 62.26% from the O 1s result. These effective oxygen species could be continually transferred to the surface, leading to the best NO catalytic activity of 5Ce5Mn/SA catalyst. [ABSTRACT FROM AUTHOR]

Pt/SiO 2 -Al 2 O 3 (Pt/SA) is commonly used as diesel oxidation catalysts (DOC) in industry, but it could be seriously deactivated caused by H 2 O at long-term high temperature. In this paper, the inhibition mechanism of water on Pt/SA for NO oxidation was studied. The fresh Pt/SA (Pt/SA-F) was treated in an air flow with/without 10% H 2 O at 700 °C for 10 h to obtain the hydrothermally/thermally aged catalysts named as Pt/SA-HA and -A, respectively. NO oxidation tests showed that Pt/SA-HA had lower activity than Pt/SA-A. A series of characterizations proved H 2 O didn't affected Pt states and support structure as they were similar over two aged catalyst. 1H NMR and In-situ DRIFTS testified that water deactivation was a result of the acidity loss of catalysts, which inhibited the decomposition and desorption of reaction intermediate, finally resulting in bad NO oxidation activity. [Display omitted] • H 2 O inhibition mechanism at hydrothermal aging on Pt/SiO 2 -Al 2 O 3 for NO oxidation was investigated. • H 2 O leaded to the loss of Brönsted acid sites (like-bridge Al-OH-Si). • The loss of acid sites induced by H 2 O suppressed decomposition of nitrate species resulting in low NO activity. [ABSTRACT FROM AUTHOR]

• The catalyst activity is affected by surface composition and oxygen vacancies. • For catalysts without κ-Ce 2 Zr 2 O 8 structure, the activity is positively related with the content of CeO 2. • For catalysts with κ-Ce 2 Zr 2 O 8 structure, there exists a balance between the oxygen vacancies and surface Ce-O x species. CeO 2 -based catalysts have attracted widespread attention in gasoline vehicle exhaust purification, and their catalytic performance is often intimately associated with the supports used. In this work, a series CeO 2 -ZrO 2 (CZ) supports with varying composition and phase structure (with or without partial κ-Ce 2 Zr 2 O 8 structure) have been employed for Pd-only three-way catalysts (TWCs), and the corresponding activities were evaluated. It was found that for catalysts without κ-Ce 2 Zr 2 O 8 structure, the activity is positively related with the content of CeO 2 in CZ due to the increased Pd-O-Ce interfaces. However, as the formation of κ-Ce 2 Zr 2 O 8 structure is accompanied by the increased surface oxygen vacancies but decreased surface Ce-O x species, for catalysts with κ-Ce 2 Zr 2 O 8 structure, there exists a balance between the reasonable concentration of oxygen vacancies and surface Ce-O x species in determining the corresponding activities. Among these catalysts, only the Pd-only TWC with medium content of CeO 2 and partial κ-Ce 2 Zr 2 O 8 structure (Pd/κMC) exhibits superior activity than that in the same composition but without κ-Ce 2 Zr 2 O 8 structure (Pd/MC). This may be associated with the obviously increased surface oxygen vacancies introduced in κMC, which could compensate the slight decrease of its surface Ce-O x species to stabilize the supported Pd species in smaller size and higher oxidation states. This finding enhances the understanding of support effects to rationally design efficient heterogeneous catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

To improve the fuel economy, it is crucial to promote the low-temperature performance in eliminating diesel emissions. The work investigates the impact of different MnO 2 /Mn 2 O 3 phase ratio on the low-temperature performance of Pt-based monolithic diesel oxidation catalyst. Near equal ratio of MnO x phase could form the three-phase (platinum, MnO 2 , Mn 2 O 3) interfacial structure, leading to the smaller platinum particle size and exhibiting the higher interface rate (1.6–11.1 times) than other mono-manganese oxide with platinum. Besides, the higher oxygen mobility and more active oxygen species could be contributed to the positive effect of Pt/MnO x interface, which are prevalent to activate the reactant and greatly enhance the TOF value (1.4–20.8 times). The results imply that the modification of multi-phase metal/oxide interface is potential in dispersing platinum for greatly enhancing the catalytic efficiency. Catalyst with near equal ratio of MnO x phase could promote the formation of three phases interface structure, which has a relative higher interface rate and TOF value for the oxidation reaction, indicating the excellent low-temperature performance. [Display omitted] • Equal ratio of MnO x phase on catalysts form the three phases interface structure. • Catalyst with multi-interfacial structure has a relative higher interface rate. • Multi-interfacial structure improves the platinum dispersion and TOF value. • The low temperature oxidation performance was improved via controlling MnO x phase. [ABSTRACT FROM AUTHOR]

Abstract: TiO2/BaAl2O4: Eu2+, Dy3+ photocatalysts were prepared by loading TiO2 sol on the surface of BaAl2O4: Eu2+, Dy3+ via sol–gel method. The photocatalytic activity was evaluated by the decomposition of gaseous benzene under UV light illumination. The as-prepared photocatalysts were characterized by nitrogen adsorption–desorption, powder X-ray diffraction and X-ray photoelectron spectroscopy. Results reveal that the optimum loading amount of TiO2 on BaAl2O4: Eu2+, Dy3+ can enhance the photocatalytic activities. The BaAl2O4: Eu2+, Dy3+ samples are all hexagonal phase, the deposited Titania is highly dispersed on the surface of carrier, and a certain interaction exists between TiO2 and BaAl2O4: Eu2+, Dy3+. [Copyright &y& Elsevier]

[Display omitted] • The de-toluene ability after metal-doping was significantly improved. • Metal modification can promote the generation of structural defect and O-vacancy. • Cu-doping significantly inhibits by-product accumulation on the catalyst surface. • In situ DRIFTS analysis provided further evidence for the reaction mechanism. Achievement of catalytic oxidation of volatile organic compounds (VOCs) at low temperature is still a challenge to be addressed. Promoting catalytic activity via constructing oxygen vacancy defect is an attractive strategy in heterogeneous catalysis. Herein, a series of Ce 2 Co 1 M 1 (M = Cu, Mn, Zr) catalysts were prepared by modified co-precipitation method and their catalytic oxidation performance of toluene was measured. Activity results suggested that the introduction of doping-metals significantly enhanced the catalytic performance of Ce 2 Co 1 O x , with Ce 2 Co 1 Cu 1 possessed the optimal catalytic activity (T 90 = 210 ℃), robust stability, water resistance, GHSV tolerance and anti-aging ability. It has been demonstrated that Cu-doping resulted in the formation of Cu-Ce solid solution and constructed a Cu2+-O-Ce4+ complex active site. Benefiting from this, the redox and gaseous oxygen molecule capture & activation capabilities of the catalyst are tremendously improved via constructing abundant oxygen vacancies. The in-situ DRIFTS results revealed that Ce 2 Co 1 Cu 1 exhibited a better C=C breaking of aromatic rings ability, a faster consumption rate of benzoate and maleic anhydride, and is less prone to accumulation of by-products, the above account for its enhanced low-temperature catalytic performance for toluene. This work may provide a new strategy to design the high-efficiency toluene oxidation catalysts. [ABSTRACT FROM AUTHOR]

• Strong Pd–ZrO 2 interaction intensified the phase transformation from monoclinic ZrO 2 to tetragonal ZrO 2. • The transformation was accompanied by increasing surface oxygen vacancies. • Increasing oxygen vacancies obviously promoted Pd/ZrO 2 activity for methane oxidation under dry conditions. • The promoting effect was weakened by water poisoning under wet reaction conditions. A series of ZrO 2 materials were prepared by calcining ZrO 2 · x H 2 O at temperatures from 600 to 900 °C. The oxide materials were used to prepare Pd/ZrO 2 catalysts coated on the monolith. Under lean conditions, the monolithic catalysts were tested for complete oxidation of CH 4 in the presence and absence of water. In process of the preparation of supports, the ratio of monoclinic ZrO 2 (m-ZrO 2) to tetragonal ZrO 2 (t-ZrO 2) increased with calcination temperature. Strong interaction between palladium and ZrO 2 further induced the transformation of t-ZrO 2 to m-ZrO 2 when supporting Pd on ZrO 2. Phase transformation in samples including ZrO 2 supports and Pd/ZrO 2 catalysts was accompanied by an increase in the concentration of surface oxygen vacancies, improving the mobility of oxygen species over the samples. It was found that the Pd catalyst using ZrO 2 calcined at 900 °C as the support had the highest oxygen vacancy concentration among the four catalysts as synthesized. Under dry reaction conditions, this catalyst showed considerably higher activity in methane oxidation promoted by oxygen vacancies. However, under wet reaction conditions (10 vol% H 2 O), water poisoned the surface-active sites for all the catalysts. The promoting effect of increasing oxygen vacancies on the activity of CH 4 oxidation was thus weakened significantly by the water poisoning, resulting in slight differences in activity among the catalysts. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Doping ceria was favorable for NO oxidation due to more active oxygen. • Oxygen diffusion promoted the formation and transformation of nitrates. • Ce could anchor Pt, resulting in a better thermal-stability in NO oxidation. Abstract Catalytic NO oxidation is crucial in oxidizing soot and promoting NH 3 reduction during the emission eliminations of diesel vehicles by the modern after-treatment systems. To create more active oxygen species in favor of NO oxidation, ceria-modified monolithic Pt-based diesel oxidation catalyst was prepared by the step-impregnation method to improve its NO catalytic performance. Its NO maximum conversion was up to around 60% in the gas hourly space velocity of 60 kh−1. Experimental results suggested that the ceria addition could have a better dispersion due to the inhibition effect of platinum aggregation. Especially, it is found that more active oxygen and oxygen vacancies over the catalyst played a significant role in strengthening the interaction of NO molecule with catalyst surface, resulting in the formation and transformation of more bridging/chelating nitrates confirmed by in situ FTIR studies. After thermal ageing, the catalyst with ceria addition still enabled a excellent NO catalytic performance, up to 50% NO maximum conversion. It would be proposed that active oxygen from the interaction bewteen ceria and Pt improved its NO catalytic activity and thermal-stability. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Soot oxidation reactivity can be correlated with the structure and morphology. • Real soot has larger promotion on non-catalytic reactivity in NO 2 + O 2. • Soot catalytic oxidation in NO + O 2 has higher reactivity than that in NO 2 + O 2. • The reactivity under different contacts follows the order: tight > pressure > loose. Abstract The aim of the present work is to investigate and compare the non-catalytic and catalytic reactivities of real and model soot samples through temperature-programmed oxidation (TPO). Such reactivity was furthermore correlated with soot structural properties, determined by laser granulometry, XRD, Raman and HRTEM. Biodiesel soot samples were obtained through the combustion of different fuels in a real engine, whereas model soot samples were produced in a laminar burner. TPO evidenced that the soot generated with 100% Biodiesel (methyl ester) was more reactive than real soot generated with 7% Biodiesel (7% methyl ester). The model soot from the diesel surrogate (Aref) containing 7% oxygenate additive (C 11 H 22 O 2) exhibited higher reactivity than the model soot containing 30% additive, whereas a carbon black (Degussa Printex U) showed the poorest reactivity of this series. The presence of NO 2 promoted the non-catalytic oxidation of real soot. In the presence of the MnO x -CeO 2 catalyst, soot reactivity depended both on reactant gas composition and on soot-catalyst contact. [ABSTRACT FROM AUTHOR]

Graphical abstract NO adsorption/desorption on MnO x -CeO 2 catalyst promotes the generation of active oxygen and thereby improves soot oxidation activity. Highlights • NO adsorption changes chemical states of surface Ce and Mn ions in MnO x -CeO 2 mixed oxides. • The formation of surface NO-adsorbed species increases the oxygen vacancies. • The main products during nitrates decomposition are NO and O 2 rather than NO 2. • NO adsorption/desorption improves the soot oxidation rate. Abstract The role of NO adsorption/desorption on soot oxidation activity of MnO x -CeO 2 mixed oxides was investigated in this work. NO adsorption/desorption on MnO x -CeO 2 results in a visible promotion of the low-temperature reactivity. Physico-chemical characterization reveals that the formation of NO adsorbed species, mainly nitrates, leads to changes in the surface Ce/Mn states and in an increase of oxygen vacancies. Moreover, TPD-MS indicates that the decomposition of surface nitrates accelerates the desorption of oxygen in the catalyst. Soot-TPR-MS confirms that the oxygen species desorbed from nitrates decomposition play an important role during soot oxidation. The isothermal experiments evidence that NO adsorption/desorption enhances soot oxidation rate, with active oxygen playing a key role in a cooperative C + NO 2 + O 2 reaction with the catalyst. [ABSTRACT FROM AUTHOR]

To stabilize Pt, Magnesium-modified SiO 2 -Al 2 O 3 materials was used to impregnate with Pt, which could strengthen the bonding effect between Pt and Mg. Before and after aging, both showed a higher dispersion. High valence state of Pt in fresh modified catalyst was unfavorable of NO oxidation, indicating that the valence state of Pt was the leader factor in fresh catalytic performance. While for the aged Mg-modified sample, its reaction temperature of 30% NO conversion lowered by around 30 °C. The Pt stabilization via interacting with Mg derives a relation that the variation of Pt valence state and its exposed sites played a significant role in fresh and aged catalytic NO activity, respectively. [ABSTRACT FROM AUTHOR]

Citric acid (CA), as the chelating agent, was introduced to obtain the enhanced Pt dispersion and catalytic activities for the Pt-based catalysts supported on oxygen-storage material. The role and content of CA were investigated systematically. It was found that the citric acid-assisted catalysts showed better Pt dispersion and smaller nanoparticle size of Pt. Thus, the catalyst had lower reduction temperature, preferable thermostability and possessed more oxidation state of Pt species under the oxidation atmosphere. The citric acid-induced fresh catalysts were excellent to convert CO and the corresponding aged ones exhibited higher activities for the elimination of all the target pollutants. Among the aged catalysts, P2-a (the mole ratio of Pt/CA is 2:1) presented the best performance. Particularly, compared with the reference sample (Pc-a), the light-off temperatures (T 50 ) of NO, HC and CO for P2-a decreased by 39 °C, 42 °C and 72 °C, respectively, and the full-conversion temperatures (T 90 ) of NO, HC and CO for P2-a decreased by 44 °C, 44 °C and 48 °C, respectively. Therefore, this work provides a facile and valid method to manufacture advanced catalysts for purification of the vehicle exhaust in the future. [ABSTRACT FROM AUTHOR]

A Pd catalyst supported on La-modified Al 2 O 3 (La-Al) with and without doping CeO 2 -ZrO 2 (CZ) is prepared via incipient wetness impregnation method. The catalysts are used as model catalyst for natural gas vehicles (NGVs) to investigate the active sites of methane oxidation within the range of air/fuel ratios (λ values) close to stoichiometric value (λ = 1). Both the two catalysts show high activity for methane oxidation under rich conditions. Under lean conditions, the methane oxidation activity over the dopant-free catalyst depend on the direction of λ change, and this catalyst displays relatively lower activity when the λ changes from richer values to lean ones. By contrast, the catalyst with dopant under the same lean conditions can nearly maintain its high activity regardless of the change direction. The results of X-ray powder diffraction (XRD) and temperature programmed reduction under H 2 (H 2 -TPR) indicate the existence of the interactions between the dopant and Pd species, and these interactions are beneficial to retain Pd in oxidized state. Ex situ X-ray photoelectron spectra (XPS) experiments are explored to correlate the catalytic activity of the methane oxidation with the oxidized valent state of Pd. The results confirm that the dopant can preserve most of the Pd species in PdO even under the rich conditions. The results also suggest that both metallic Pd and PdO can act as the active sites for methane oxidation under much richer conditions, and that under lean conditions, PdO instead of metallic Pd plays a role in methane oxidation. [ABSTRACT FROM AUTHOR]

• NO reduction is the reaction of the formed nitrite/nitrate species with CH 4. • N 2 O is formed by the competitive reaction of -CN and NCO* species with O 2 and NO x. • The high O ads of Pt/Ce-Rh/LA x promote CH 4 oxidation and inhibit NCO* formation. The mechanism of the NO conversion to poisonous substrates, such as NH 3 and N 2 O on a model Pt/CeO 2 +Rh/LA three-way catalyst (TWC) during the treatment of exhaust emission from natural gas vehicles (NGVs) was investigated. The in situ DRIFTS results showed that the main pathway of NO reduction is the reaction of nitrite/nitrate species formed by NO adsorbed on CeO 2 with CH 4. It was further elucidated by O1s and DRIFTS that the formation of N 2 O at low temperature is ascribed to competitive reactions of cyanide (-CN) species with O 2 and NO x. Specifically, for Pt/Ce catalysts, N 2 and CO 2 are formed due to the preferential reaction of -CN species with the surface adsorbed oxygen (O ads) species on the catalyst. While for Pt/Ce-Rh/LA 550 and Pt/Ce-Rh/LA 600 catalysts, N 2 O is formed due to the easier reaction of -CN with NO x. At high temperature, the catalyst mechanically mixed with Rh/LA x increased the concentration of O ads , which promoted CH 4 oxidation and inhibited the reaction of NO with C-containing compounds to isocyanate (NCO*), thus reducing NH 3 formation. Our work may provide new ideas for developing advanced TWC for NGVs with lower emission of NH 3 and N 2 O. [Display omitted] [ABSTRACT FROM AUTHOR]

• The designed overlayer deposition method significantly decreased by 20 °C. • Construction of Pt/MnO x interfaces improves the platinum dispersion. • Electronic-transferring presents a weaker CO adsorption, facilitating CO oxidation. • Overlayer deposition shows a higher hydrothermal stability than impregnation. It is a challenge to improve the catalytic activity and hydrothermal stability of platinum-based catalyst in concurrently oxidizing CO/C 3 H 6 /NO. The construction of Pt/MnO x interface over Pt-based diesel oxidation catalyst via overlayer deposition to form partial-embedded structure, inhibiting the aggregation of platinum nanoparticles in Ostwald Ripening process. Even after hydrothermal aging, the average platinum particle size is equal to that of the fresh catalyst via traditional impregnation method. The electronic-transferring from platinum to manganese results in a weaker CO adsorption ability on Pt species and an improved oxygen activation ability with the help of the redox cycle of Pt and MnO x , as well as the formation of more active nitrate species via in situ DRIFTs. Measurement on the activity shows the lower apparent activation energy, so that the light-off temperature of CO/C 3 H 6 /NO on the partial-embedded catalyst via overlayer deposition method decreases by around 20 °C and 40% NO maximum conversion still keeps after severely aging comparing with the traditional catalyst. The work enlightens us the importance of interface sites in stabilizing platinum atoms and creating oxidize active sites. In comparing to impregnation method (IM), overlayer deposition method (OD) creates more Pt/MnO x interface, arresting the aggregation of platinum nanoparticles and enhancing the oxidation catalytic performance. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, an advanced diffuse reflectance infrared fourier transform spectra (DRIFTS) technology is used to describe the formation of surface sulfates on Pt/MnO x -CeO 2 and study the possible deactivation mechanism for soot oxidation reactions in NO + O 2 . IR spectra of CO adsorption and H 2 -TPR results reveal the surface coverage of Pt by sulfates and the loss of partial active oxygen species after the sulfation, respectively. More importantly, in situ DRIRT spectra show sulfur poisoning apparently inhibits the formation of surface intermediates such as monodentate/bidentate nitrates and nitro species, which directly limits the production of NO 2 . Furthermore, the O 2 -TPD results indicate that the sulfation weakens the desorption of surface active oxygen resulting from the decomposition of surface nitrates. The sulfate formation would affect the production of oxygen vacant sites and thereby the mobility of surface oxygen species in both NO + O 2 and O 2. These factors above would play an important role on the deactivation mechanism for soot oxidation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soot oxidation activity was greatly improved by regulating contact efficiency and Pt chemical state. • Porous CeO 2 -ZrO 2 was obtained by microsphere template assisted method. • Liquid phase reduction method is an effective and controllable way to obtain metallic Pt species. • Metallic Pt species is conducive to soot oxidation in O 2 /N 2. • Soot oxidation mechanism under different soot-contact efficiency and noble metal states in different atmospheres was proposed. Decreasing the ignition temperature of soot combustion is a key of the improved catalyst performances, but a much lower concentration of oxygen from gasoline vehicle exhaust makes the research of the catalyst extremely challenging. Improving the adsorption and activation of oxygen molecules on the catalyst surface and the effective migration rate of active oxygen species are the key factors to enhance soot oxidation. In this work, Pt/CeO 2 -ZrO 2 -re catalyst was synthesized by synergistically adjusting CeO 2 -ZrO 2 pore structure and Pt chemical state, as a result, the conversion temperature (T 50 , 50% soot was oxidized) was reduced by 113 ℃ in 1% O 2 /N 2. The pore structure of CeO 2 -ZrO 2 was optimized by copolymerization microsphere template assisted method, and better soot-contact efficiency and intrinsic properties were obtained, resulting in a higher availability of reactive oxygen species. In addition, adjusting Pt chemical state by using the liquid phase reduction method is significant for the adsorption and activation of oxygen molecules and catalytic cycle of soot oxidation. Structure-activity relationship studies showed that soot oxidation performance is highly related to the initial oxidation state of Pt and pore structure in 1% O 2 /N 2. Better soot-contact efficiency, improved intrinsic properties and the existence of metallic Pt are responsible for the higher soot oxidation activity of Pt/CeO 2 -ZrO 2 -re catalyst. [ABSTRACT FROM AUTHOR]

Star-shaped 800-TiN and 850-TiN coatings were deposited on the surface of 310S stainless steel foils by CVD and their oxidation behavior was investigated in ambient air, from 300 °C to 800 °C for 1800 s by XRD, SEM, EDX and Raman spectroscopy. Initial oxidation of 850-TiN coating with a partial color change occurs at 350 °C, remarkable oxidation of 850-TiN coating occurring between 400 °C and 450 °C. The EDX results show that obvious oxidation of 850-TiN starts at 400 °C with about 9 at% oxygen detected; no N atoms could be detected while the O content reaching a maximum of ca. 70% at oxidation temperature above 700 °C. The XRD and Raman results show that only rutile-TiO 2 formed on the surface of oxidized TiN coating. The oxidation of star-shaped TiN coating can be divided into three stages. In the case of mild oxidation (below 500 °C), TiN coating can maintain the star-shaped microstructure although oxygen diffuses into the TiN lattice resulting in replacement of N by O atoms. For moderate oxidation (550–600 °C), the star-shaped microstructures start to crack along the (111) twin planes, and the boundary of particles remains clear with oxide and oxynitride layer coexisting on the surface of 850-TiN coating. For severe oxidation (650–750 °C), the cracks of the star-shaped microstructures start to expand and become apparent, meanwhile the boundary of particles become uncertain. After oxidizing at 800 °C, the 850-TiN coating will lose efficacy due to the bad spalling resistance. [ABSTRACT FROM AUTHOR]

For diesel oxidation catalyst (DOC), the sintering and oxidation of active Pt0 nanoparticles leads to severe deactivation during long-term operating condition. Here, we have synthesized SiO 2 -modified Pt/SiO 2 -Al 2 O 3 (Pt-SiAl@Si) catalysts, and this silica coating layer not only can inhibit the migration of precious metals through physical isolation, but also restrain Pt0 oxidation by interfacial electron interaction between Pt and acid sites (Si-OH-Al). Before and after hydrothermal aging, the maximum NO conversion of Pt-SiAl@Si decreased slightly by 5%, showing excellent durability. TEM and CO chemisorption unveiled that no obvious differences in Pt size between fresh and aged Pt-SiAl@Si. 1H NMR and NH 3 -DRIFTS confirmed that Pt-SiAl@Si possessed more Brönsted acid sites (Si-OH-Al). And the Pt−acid sites interface caused more active Pt0 by the electronic effect. This bifunctional overcoating allows a wide application in other catalytic materials for various reactions. [Display omitted] • The SiO 2 overlayer of Pt-SiAl@Si is bifunctional. • SiO 2 shell as a physical barrier has an ability to retard sintering of Pt nanoparticles. • Pt-acid sites interfaces arising from interaction between SiO 2 shell and support enhanced the oxidation-resistance of Pt0. • The increased acidity of catalyst promoted the fast desorption and decomposition of nitrate species, facilitating NO oxidation. [ABSTRACT FROM AUTHOR]

To improve the stability of Pt nanoparticles, the redox cycles with oxidation at 800 °C and reduction at 250 °C for three times were adopted on the Mn-mullite doped Pt-based catalysts (Pt-YMO/SA-Red) to rearrange the Pt atoms. The light-off temperature toward CO/C 3 H 6 /NO oxidation on Pt-YMO/SA-Red decreases by 20–60 °C, and the NO maximum conversion is improved by 27 % than the catalyst with only oxidation treatment at 800 °C (Pt-YMO/SA-Oxi). Characterization results verify that the interaction of Pt with YMn 2 O 5 on Pt-YMO/SA-Red is reinforced via redox cyclic treatment to inhibit the aggregation of platinum particles and promote the formation of active oxygen species, in comparison to Pt-YMO/SA-Oxi. The easier active oxygen regeneration and more active platinum sites contribute to the excellent catalytic performances and stability. In addition, the mechanism for the high CO/C 3 H 6 /NO oxidation performance are analyzed via the detected reaction intermediate species. [Display omitted] • Redox cyclic treatment could strengthen the interaction of Pt with YMn 2 O 5. • Oxygen vacancies anchor platinum sites for reduction at low temperature (250 °C). • The ability of oxygen regeneration is improved for the redox cyclic catalyst. • The formation of bridged/chelating nitrates contribute to NO catalytic performance. • Platinum sites and active oxygen species are favor of the low temperature activity. [ABSTRACT FROM AUTHOR]

Abstract: Sr2CeO4-promoted photo-oxidation of gaseous benzene by UV/O3 process was studied. The kinetic study reveals that the photo-degradation process is a pseudo first-order reaction; the relationship between the initial concentration and the reaction rate constants abides by exponent formula. The experimental results show that the addition of hydrogen peroxide can increase the conversion of benzene, while the process is still first-order reaction. GC/MS analysis of ether-extracted surface species confirms that the main intermediates are (3-methyl-oxiran-2-yl)-methanol, ethyl acetate and butylated hydroxytoluene. Finally, the photo-oxidation pathway was speculated consequently. [Copyright &y& Elsevier]

Abstract: Photocatalytic oxidation of benzene in air was carried out over TiO2/Sr2CeO4 catalysts. The prepared photocatalyst was characterized by S BET, UV–vis diffuse reflectance and XPS. TiO2/Sr2CeO4 absorbs much more visible light than TiO2 in the visible light region. The XPS spectrum shows that the binding energy value of Ti 2p3/2 transfers to a lower value. The main purpose was to investigate the kinetic model and degradation mechanisms. The kinetic data matched well with the Langmuir–Hinshelwood (L–H) kinetic model with the limiting rate constant and the adsorption constant in this case were 0.0064mgl−1 min−1 and 9.2078lmg−1, respectively. No gas-phase intermediates were detected by direct GC/FID analysis under the conditions despite the high benzene concentration. Ethyl acetate and (3-methyl-oxiran-2-yl)-methanol were two major identified intermediates which were accompanied by butylated hydroxytoluene, 2,6-bis(1,1-dimethylethyl)-4,4-dimethylycyclohe, 2,5-cyclohexadiene-1,4,dione,2,6-bis(1,1-dim). It is plausible that at least one of these less-reactive intermediates caused the deactivation of the photocatalyst. Finally, the photocatalytic oxidation mechanisms were speculated. [Copyright &y& Elsevier]

• CTAB-assisted impregnation method was used for Mn/La-Al catalyst preparation. • CTAB-assisted impregnation provided higher dispersion of MnO x species. • Higher reducibility and oxygen mobility were achieved. • The intermediates more easily formed over Mn/La-Al-CTAB catalyst. The monolithic MnO x /La-Al 2 O 3 catalyst (Mn/La-Al-CTAB) prepared by CTAB (cetyl trimethyl ammonium bromide)-assisted impregnation method was used for the oxidation of toluene, and an improved catalytic performance (TOF = 4.76, T 90% = 273 °C) was achieved in comparison with the reference (Mn/La-Al) (TOF = 2.34, T 90% = 295 °C). The physicochemical properties of the catalyst were investigated through XRD, Raman spectra, TEM, BET, H 2 -TPR, O 2 -TPD, XPS and DRIFT spectra. It is confirmed that Mn/La-Al-CTAB possesses higher dispersion and smaller crystalline size of MnO x species as well as higher concentrations of Mn3+ and lattice oxygen. Thus, it exhibits better reducibility and oxygen mobility, which is a key factor to result in an increased catalytic activity. Moreover, DRIFT spectra indicate that the intermediates such as alkoxide species, benzaldehyde, benzoate and maleic anhydride more easily form on the surface of Mn/La-Al-CTAB, this is an important reason for the enhanced toluene oxidation. [ABSTRACT FROM AUTHOR]