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A series of V2O5/WO3-TiO2 and V2O5/SiO2-WO3-TiO2 catalysts containing 2 wt%, 3.5 wt% and 5 wt% V2O5, respectively, were prepared by impregnation method. The NH3-SCR activity and thermal stability of the catalysts were investigated. It is noted that both V2O5 loading and SiO2 modification could affect the thermal stability of the V2O5/WO3-TiO2 catalysts. Increasing V2O5 loading improved the low temperature SCR activity of the catalysts in fresh state, but high V2O5 loading aggravated the deactivation of the catalysts upon aging. With relatively high V2O5 loading (3.5 wt% and 5 wt% V2O5), V2O5/SiO2-WO3-TiO2 showed remarkably improved thermal stability than V2O5/WO3-TiO2 NH3-SCR catalysts. The catalysts were characterized by BET, XRD, SEM, Raman, XPS, H2-TPR and NH3-TPD. The results indicated that high V2O5 loading on V2O5/WO3-TiO2 catalyst can accelerate the phase transition of anatase TiO2 to rutile TiO2 upon thermal aging, which resulted in the loss of surface area and consequently led to the deactivation, while introduction of silica prevented the phase transition of TiO2, therefore enhancing the thermal stability of the catalysts.

Pd-based small-pore zeolites with different framework structures (AEI, CHA and RTH) were synthesized by a facile incipient wetness impregnation method. The zeolites were utilized as low-temperature passive NOx adsorbers (PNA) for NOx storage before and after hydrothermal aging. It was found that 1 wt% Pd/AEI showed better PNA behavior than the 1 wt% Pd/CHA and Pd/RTH samples, regardless of hydrothermal aging at 750 and 800 ℃. The AEI zeolite has a three-dimensional but tortuous pore channel structure, which accelerated Pd dispersion at 750 ℃ but inhibited Pd aggregation at 800 ℃ when subjected to hydrothermal aging. Pd/CHA showed a slight increase in Pd dispersion at 750 ℃, but extensive Pd aggregation at 800 ℃ due to its straight and unhindered three-dimensional pore structure. The Pd species in Pd/RTH zeolite were prone to accumulation during hydrothermal aging due to the two-dimensional pore structure. Therefore, Pd/AEI can be utilized as an efficient and stable PNA after activation by mild hydrothermal aging treatment.

The surface species formed in the reaction of NO and NO2 with pre-adsorbed NH3 over a Fe-ZSM-5 catalyst (1.27 wt.% Fe, SiO2/Al2O3 = 25) at low temperature (140°C) were studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Through using a background spectrum of NH3-saturated Fe-ZSM-5, we clearly observed the formation of common intermediates resulting from the reaction of NO2 or NO + O2 with pre-adsorbed NH3. This presents strong evidence that the oxidation of NO to form surface nitrates and nitrites is the key step for standard SCR at low temperature. In addition, the results suggest that in the SCR reaction at low temperature, the NH4+ ions absorbed on Bronsted acid sites are less active than NH3 adsorbed on Lewis acid sites related to Fe species.

The control of NOx emission from diesel vehicles is of great importance to the environment, and Cu-SAPO-34 is considered to be an effective catalyst for the abatement of NOx from diesel vehicles. Along with catalytic activity, hydrothermal stability is a key property for NOx abatement catalysts. The attack of Cu species and framework atoms by H2O may result in activity loss under both low/high temperature humid conditions, which are inevitable in practical application. Therefore, apart from good catalytic activity, hydrothermal stability under both low/high temperatures for Cu-SAPO-34 is also critical for NOx control in diesel vehicles. Three Cu-SAPO-34 samples were prepared by a one-pot hydrothermal method using propylamine, triethylamine, and morpholine, with Cu-TEPA (tetraethylenepentamine) as the cotemplate. The NH3-SCR activity and the effects of hydrothermal aging at 70 and 800 °C on these Cu-SAPO-34 samples were investigated. The type of cotemplate can affect the Si and Cu species in one-pot-synthesized Cu-SAPO-34 catalysts, so that the catalytic activity as well as the low/high temperature hydrothermal stability is affected by the choice of template. Generally speaking, Cu-SAPO-34 prepared using PA as cotemplate showed superior catalytic activity and hydrothermal stability under low/high temperatures compared with the other two catalysts, which makes PA a more suitable template for one-pot-synthesized Cu-SAPO-34 for use in NOx abatement from diesel vehicle exhaust.

In this study, the CeO2 nanorods as the supports of Pt/BaO/CeO2 catalysts were synthesis by the alkali-assisted hydrothermal method in a solution containing different content of NaOH. Pt/BaO/CeO2 catalyst with 7.5M NaOH pre-added in the support preparation process showed higher NOx storage capacity and NOx removal efficiency than samples derived from other concentration NaOH. Moreover, even under shorter rich time (3s) and more lean-rich cycles (60), Pt/BaO/CeO2-7.5M still maintained above 80% NOx conversion from 250 to 450 °C, exhibiting good fuel economy and durability. A series of characterization techniques including XRD, N2-adsorption, TEM, XPS, Raman, H2-TPR, and NO2-TPD were conducted to investigate the physical, chemical properties. Combining the activity with the structure of catalysts, a linear relationship between the NOx storage capacity (NSC) of NSR catalysts and the amount of oxygen vacancies was drawn. Meanwhile, the strong synergetic effect among Pt and CeO2 attributed to the role of oxygen vacancies in anchoring the active component Pt, promoting the mobility of surface oxygen species, was also related to the NSC value of NSR catalysts. These results indicated that the oxygen vacancies were responsible for the excellent catalytic activity.

In this work, the Cu-SSZ-39 catalyst was sulfated at different temperatures (200 °C, 400 °C or 600 °C) in the presence of water to investigate the effects of sulfation on its catalytic performance in NH3-SCR. Sulfation at 200 °C and 400 °C resulted in a significant decrease in NOx conversion at low temperatures, while sulfation at 600 °C showed only slight effect on the SCR activity of Cu-SSZ-39. The coverage of active sites by H2SO4 was the main reason for the deactivation of the catalyst sulfated at 200 °C and 400 °C, while the formation of stable CuSO4 species should also be responsible for the catalytic activity loss of the catalysts sulfated at 200 °C, 400 °C and 600 °C. After regeneration at 600 °C, the activities of the sulfated catalysts could be recovered partially but were still lower than those of the fresh catalysts, due to the formation of stable sulfated Cu species.

Two Cu-SAPO-34 samples with similar chemical compositions but different crystallite sizes of 10 μm and 2 μm, respectively, were obtained by modifying crystallization conditions. The effect of crystallite size on the low-temperature hydrothermal stability of Cu-SAPO-34 was comparatively investigated. The results showed that Cu-SAPO-34 with smaller particle size possessed better resistance to treatment at 70 °C in humid conditions. During low-temperature hydrothermal aging, isolated Cu2+ species in Cu-SAPO-34 tended to be attacked by water vapor to form Cu(OH)2 species, which can combine with extra-framework Al to form inactive CuAl2O4 species. The superior stability of Cu-SAPO-34 with smaller crystallite size is primarily attributed to the lower Cu concentration on the crystal surface compared with the sample with larger particle size. Thus, more active Cu sites were maintained on small-size Cu-SAPO-34 after low-temperature hydrothermal aging.

Three types of Cu–Ti interfacial structures have been fabricated by using different preparation methods. The mechanism regarding the interfacial effect on oxidation of CO and resistance to SO2 has been elaborated. It is proposed that an O vacancy-steered catalytic oxidation of CO prevails over an in situ Cu-doped TiO2 (DT) catalyst while a lattice O-initiated one proceeds on the other two catalysts that are obtained via solvent free and mechanical mixing methods. The former catalyst exhibits a strong Cu–Ti interface due to the high dispersion of copper species on TiO2 and partial incorporation of Cu2+ into the TiO2 matrix. This not only creates rich O vacancies, enhances O mobility and thus leads to superior redox ability of DT, hence promoting CO oxidation, but also restricts the interaction of SO2 with strongly-anchored Cu2+ species and thus increases the SO2 tolerance of DT. Meanwhile, the latter two catalysts have aggregated CuO either above or inside TiO2, which leads to rapid sulfation of CuO and deactivation of the catalysts.

A series of cerium-doped iron–titanium composite oxide catalysts (FeCeaTi, a = 0.1–1.0) prepared by a urea homogeneous precipitation method were investigated for selective catalytic reduction of NOx with NH3 (NH3-SCR). Over all the FeCeaTi samples, a promotion effect for NOx reduction was induced by the introduction of cerium, with the FeCe0.3Ti catalyst exhibiting the best catalytic performance, even at a high GHSV of 250 000 h−1. As indicated by kinetic studies, interestingly, the FeCe0.3Ti catalyst exhibited a higher activation energy for the NH3-SCR process while possessing a pre-exponential factor three orders of magnitude higher than that of FeTi. Going deeper, extensive characterization including N2-physisorption, XRD, Raman, NH3/NOx-TPD, XPS, EPR, and H2-TPR was carried out. XRD and Raman results showed that the introduction of suitable amounts of Ce into the FeTi samples promoted the dispersion of Fe and Ti. Such higher dispersion of these two components increased the capacities for NOx adsorption and activation and weakly bonded ammonia over FeCe0.3Ti, thus promoting the occurrence of the L–H pathway of NH3-SCR at low temperatures. H2-TPR results indicated that the reduction of FeCe0.3Ti occurred at a higher temperature than that of FeTi, which may be a reason for its higher activation energy for NH3-SCR.

The mechanism of H2-assisted NH3-selective catalytic reduction (SCR) over Ag/Al2O3 was systematically investigated by kinetic measurements and in situ diffuse reflectance infrared Fourier transform...

A mesoporous LaCoO

Commercial Cu-exchanged small-pore SSZ-13 (Cu-SSZ-13) zeolite catalysts are highly active for the standard selective catalytic reduction (SCR) of NO with NH

Small and medium-sized enterprises (SEMs) are the important part of economic society whose innovation activities are of have great significance for building innovative country. In order to investigate how technological innovation (TI) and business model design (BMD) affect the business performance (BP) of SMEs, samples of 268 SMEs in the artificial intelligence industry and hierarchical regression models are used in the analysis. The results indicate that TI, BMD, and the matching of them have different effects on the innovation of SMEs of different sizes. These findings are helpful for enriching the theory of the fit between TI and BMD and providing theoretical guidance for the innovation activities in SEMs.

Adsorption is an efficient method for atmospheric NOx abatement under ambient conditions; however, traditional adsorbents suffer from limited adsorption capacity and byproduct formation. Developing a low-cost material with high capacity for atmospheric NO2 elimination remains a challenge. Here, we synthesized a nanodispersed Mn3O4/γ-Al2O3 (Mn/Al) material that exhibits excellent ability to remove NO2. The 10 wt % Mn/Al sample showed the highest removal capacity, with 247.6 mgNO2/gMn/Al, which is superior to that of activated carbon (42.6 mgNO2/g). There were no byproducts produced when Mn/Al was tested with ppb-level NO2. The NO2 abatement mechanism with Mn/Al is different from physisorption or chemisorption. NO2 removal is mainly a catalytic process in air, during which surface hydroxyls and lattice oxygen are involved in the oxidation of NO2 to nitrate. In contrast, a chemical reaction between Mn3+ and NO2 is dominant in N2, where Mn3+ is converted into Mn4+ and NO2 is reduced to nitrite. Washing with deionized water is an effective and convenient method for the regeneration of saturated Mn/Al, and an 86% adsorption capacity was recovered after one washing. The results suggest that this low-cost Mn/Al material with easy preparation and regeneration is a promising candidate material for atmospheric NO2 elimination.

The sulfur tolerance of Ag/Al2O3 catalysts in H2-assisted C3H6-SCR was investigated by UV–vis, TPR, TPSR, DRIFTS-MS, and DFT calculations. Ag/Al2O3 with higher silver loadings exhibited better deNOx performance and sulfur tolerance, especially the 4% Ag/Al2O3 catalyst. UV–vis and H2-TPR revealed that highly dispersed Ag+ cations were predominant on 2% Ag/Al2O3, while more metallic Ag clusters with large sizes were present on the 4% Ag/Al2O3. After exposure to SO2, large amounts of sulfates were adsorbed on the Ag sites and Al sites of the Ag/Al2O3 surface. The sulfates were reduced to H2S and SO2 in a reducing atmosphere, while they showed little decomposition under real SCR reaction conditions. DRIFTS-MS experiments showed that sulfate species transferred rapidly between Ag sites and Al sites on the Ag/Al2O3 catalysts with higher amounts of Ag clusters. DFT calculations revealed that Ag1 cations show stronger affinity for sulfate species than Ag clusters, thus resulting in blockage by sulfates at the Ag-O-Al interface. Such blocking by sulfates suppressed the activation of C3H6 as well as the formation of -NCO species, and thus severely inhibited the deNOx performance of 2% Ag/Al2O3. In contrast, the rapid mobility of sulfate species on 4% Ag/Al2O3 made more active sites available for the formation of key intermediates of HC-SCR, finally contributing to its excellent sulfur tolerance.

Seeds were utilized to synthesize high crystallinity and an economical SSZ-13 substrate zeolite with relatively high Si/Al ratio (∼11) via a solvent-free method. NH3-SCR tests, hydrothermal stability, and many characterizations such as XRD, 27Al-NMR, EPR, H2-TPR, and XAFS were conducted over the fresh and hydrothermally aged Cu2+ ion-exchanged zeolite catalysts (Cu-SSZ-13). The fresh catalysts showed high deNOx activity and tolerance to high space velocity in the temperature range from 150 to 550 °C. The active Cu2+ ions were hydrothermally stable, resulting in only slight decrease after hydrothermal aging at 800 °C for 16 h. The results showed that the Cu ion-exchanged SSZ-13 catalyst synthesized by the solvent-free method is a promising alternative candidate for actual implementation in diesel engines.

Cu2+-exchanged zeolite catalysts with the chabazite (CHA) structure have been thought to be optimal candidates for selective catalytic reduction of NOx with NH3. In real applications, however, SCR catalysts readily undergo hydrothermal aging and sulfur poisoning. In this work, the co-effect of SO2 and hydrothermal aging at high temperature was investigated. Different from the reversible inhibition of SO2 poisoning that occurs at low temperatures, the sulfur poisoning at high temperature is permanent due to the destruction of the zeolite structure, and no deposit of sulfate is observed. Cu-SSZ-13 catalysts were characterized through solid state 27Al nuclear magnetic resonance (27Al-NMR), X-ray diffraction (XRD), temperature-programmed desorption of NH3 and NO (NH3/NO-TPD), electron paramagnetic resonance (EPR), temperature-programmed reduction by H2(H2-TPR), in situ DRIFTS, and thermogravimetric analysis with mass spectrometric detection (TG-Mass) to develop an understanding of the degradation mechanisms during hydrothermal aging and sulfurization at high temperature. The results indicated that SO2 dislodged the extra-framework Al atoms that resulted from the dealumination process that occurs during hydrothermal aging. More Cu2+ species were accumulated as CuOx for Cu-SSZ-13 after sulfurization at high temperature compared to that treated by hydrothermal aging only. The dealumination and accumulation of Cu2+ species caused a loss of acid and active sites for the Cu-SSZ-13 catalyst, and resulted in degradation of NH3-SCR performance.

Pt/BaO/Al2O3 catalysts with different BaO loadings prepared from Al2O3 nanorods (Pt/BaO/Al2O3-nr) and irregular Al2O3 nanoparticles (Pt/BaO/Al2O3-np) were investigated for NOx storage and reduction (NSR). The Pt/BaO/Al2O3 materials derived from Al2O3 nanorods always exhibited much higher NOx storage capacity (NSC) over the whole temperature range of 100–400°C than the corresponding Pt/BaO/Al2O3-np samples containing the same BaO loading, giving the maximum NSC value of 966.9 μmol/gcat at 400°C, 1.4 times higher than that of Pt/BaO/Al2O3-np. Higher catalytic performance of nanorod-supported NSR samples was also observed during lean-rich cyclic conditions (90 sec vs. 5 sec), giving more than 98% NOx conversion at 300–450°C over the Pt/BaO/Al2O3-nr sample with 15% BaO loading. To reveal this dependence on the shape of the support during the NSR process, a series of characterization techniques including the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were also conducted. It was found that intimate contact of Ba–Al and Ba–Pt sites was achieved over the Pt/BaO/Al2O3 surface when using Al2O3-nr as a support. This strong interaction among the multi-components of Pt/BaO/Al2O3-nr thus triggered the formation of surface nitrite and nitrate during the lean period, and also accelerated the reverse spillover of ad-NOx species onto the Pt surface, enhancing their reduction and leading to high NSR performance.

The Cu-exchanged RTH-type zeolites (Cu-RTH) were applied in ammonia-selective catalytic reduction (NH3-SCR) of NOx. The effects of Cu loading and distribution on the NOx reduction efficiency were investigated. The hydrothermal stabilities of a series of Cu-RTH catalysts were also presented. Excellent NOx conversion activity was observed for Cu-RTH catalysts with high Cu loadings (2.5–4.4 wt%) in the temperature range from 150 °C to 550 °C. Two possible sites (α and β species) for Cu2+ species were proposed based on the analysis of H2-TPR and DRIFTS results. The α species next to the 8-membered rings showed significantly higher TOF (turnover frequency) of NO conversion than the β species present next to the rth cage. The Cu-RTH catalysts showed lower activation energies (30–40 kJ mol−1) compared with that of the Cu-SSZ-13 catalyst (∼54 kJ mol−1) due to the different zeolite framework structures. After undergoing hydrothermal aging, although the zeolite framework structure stayed stable, the active Cu2+ species migrated to inactive sites, which resulted in the loss of NOx conversion for the NH3-SCR reaction. The saturated Cu2+-exchanged Cu4.4-RTH catalyst showed the best hydrothermal stability due to the limited Cu2+ mobility, which stabilized the active Cu2+ species.

The reaction and adsorption amounts of NO, NO2, and NH3 and the reaction pathway of the selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures in the absence and presence of H2O on CeWOx were quantitatively determined by a transient response method (TRM). The distribution of the active sites was quantitatively determined based on the results of TRM, X-ray photoelectron spectroscopy and temperature programmed desorption. NOx adsorbed on O vacancies and oxidized Ce sites, with surface concentrations of 40–63 and 20 μmol g−1 respectively, while NH3 adsorbed on [Ce4+]-OH and W species, at 61–70 and 90–99 μmol g−1 respectively. Both the reaction between NO and NH4NO3 to form N2, H2O and NO2, and reaction between nitrite and NH3 to form N2 and H2O were present. H2O weakened NH3 adsorption, decreased the adsorption amount at 150 °C, and inhibited the reaction between NO and NH4NO3/adsorbed NH3, impeding NH3-SCR on CeWOx.

The effect of K deactivation on V2O5/WO3-TiO2 and Ce-doped V2O5/WO3-TiO2 catalysts in the selective catalytic reduction (SCR) of NOx by NH3 was studied. Ce-doped V2O5/WO3-TiO2 showed significantly higher resistance to K deactivation than V2O5/WO3-TiO2. Ce-doped V2O5/WO3-TiO2 with K/V=4 (molar ratio) showed 90% NOx conversion at 350°C, whereas in this case V2O5/WO3-TiO2 showed no activity. The fresh and K-poisoned V2O5/WO3-TiO2 and Ce-doped V2O5/WO3-TiO2 catalysts were investigated by means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), NH3-temperature progress decomposition (NH3-TPD), X-ray photoelectron spectroscopy (XPS) and H2-temperature program reduction (H2-TPR). The effect of Ce doping on the improving resistance to K of V2O5/WO3-TiO2were discussed.

Small-pore Cu–SSZ-13 zeolites with varying Cu loadings were applied in the standard and the fast selective catalytic reductions (SCR) of NO with NH3. It was found that increased Cu loadings contrib...

Mn-based oxides exhibit outstanding low-temperature activity for the selective catalytic reduction of NO

Alumina supported Pd catalyst (Pd/Al

Zeolites, as efficient and stable catalysts, are widely used in the environmental catalysis field. Typically, Cu-SSZ-13 with small-pore structure shows excellent catalytic activity for selective catalytic reduction of NOx with ammonia (NH3-SCR) as well as high hydrothermal stability. This review summarizes major advances in Cu-SSZ-13 applied to the NH3-SCR reaction, including the state of copper species, standard and fast SCR reaction mechanism, hydrothermal deactivation mechanism, poisoning resistance and synthetic methodology. The review gives a valuable summary of new insights into the matching between SCR catalyst design principles and the characteristics of Cu2+-exchanged zeolitic catalysts, highlighting the significant opportunity presented by zeolite-based catalysts. Principles for designing zeolites with excellent NH3-SCR performance and hydrothermal stability are proposed. On the basis of these principles, more hydrothermally stable Cu-AEI and Cu-LTA zeolites are elaborated as well as other alternative zeolites applied to NH3-SCR. Finally, we call attention to the challenges facing Cu-based small-pore zeolites that still need to be addressed., This review article summarizes the major advances, opportunities and challenges of Cu-based small-pore zeolites applied to environmental catalysis, which provides guidance for the design of highly efficient and stable zeolite-based catalysts.

The control of NO

In order to reduce black carbon (BC) emissions from diesel vehicles, a regional atmospheric chemistry model (WRF-Chem) was used to investigate the effects of installing a high-efficiency device for vehicle exhaust control, a diesel particulate filter (DPF), on diesel vehicles in China. To reduce the uncertainty of estimation, three sensitivity experiments were designed and conducted for different emission scenarios. The first experiment uses the standard black carbon emissions of diesel vehicles without engaging in any emission control actions (referred to as CTRL), and the other two experiments were conducted using different DPF devices to reduce BC emissions by 65% (CASE1) and 39% (CASE2), respectively. The results show that the model simulation reasonably represents the measured BC concentrations. The highest BC concentrations occurred in large cities of the North China Plain (NCP) and present important seasonal variations. The results suggest that the reduction in diesel vehicle emissions has great benefits for reducing BC pollution not only in winter but also in other seasons. Sensitivity studies show that in CASE1, the average BC concentrations decreased about ~6% in January and by more than 10% in the other seasons. The greatest reduction exceeded 50%. In CASE2, the average BC concentrations decreased by about ~3.5% in January and by more than 7% in the other seasons. This study suggests that adding DPF to a diesel vehicle can have a significant influence on reducing BC concentrations in China. Thus, this study provides a practical basis by which diesel vehicle emissions can be reduced.

A negative temperature dependence was found for the selective catalytic reduction of NOx by ethanol (ethanol-SCR) over Ag/Al2O3 in the absence of water vapor. Activation energy measurements for this process confirmed that two reaction routes occurred in different temperature ranges. In situ DRIFTS experiments revealed that these temperature-dependent reactions were closely related to the process of the partial oxidation of ethanol. During the partial oxidation of ethanol at low temperatures below 400 °C, enolic species and acetates were produced, the former of which exhibited much higher activity for NOx reduction than the latter. Therefore, the formation of enolic species and their further transformation to produce N2 governs the low-temperature route for ethanol-SCR. At temperatures above 400 °C, only acetate appeared during the partial oxidation of ethanol, and its further reaction with NOx accounts for the high-temperature route. More importantly, introduction of water vapor significantly enhanced the...

Microbial mediated iron cycling drives the biogeochemical cycling of carbon, nitrogen, sulfur, and phosphorus. However, the fate of the microbial community and the relative metabolic pathways in paddy soil after the addition of biogas slurry are poorly understood. In this study, the response of functional genes was investigated by growing one-season rice in paddy soils in a pot experiment. Seven treatments were prepared: 1) control (CK); 2) organic carbon (OC); 3) fertilizer (F); 4) 5% of biogas slurry (B05); 5) 10% of biogas slurry (B10); 6) 15% of biogas slurry (B15); 7) 20% of biogas slurry (B20). In the biogas slurry treatments, Geobacter increased more than in the other treatments during rice growth, which were structured by TOC. Particularly, in the B10 treatment, the relative abundance of Geobacter was 1.6 and 14.8 times higher than that of CK at the heading and mature stages, respectively. At the heading stage, the addition of biogas slurry and OC shifted the microbial phosphorus-transformation communities differently. There were no significant differences in the carbon, nitrogen, and sulfur metabolic pathways between the two treatments. At the mature stage, the carbon: nitrogen: phosphorus balance was significantly influenced by the regulation of functional gene expression and metabolic activities. These findings provide insight into the key factors affecting carbon, nitrogen, sulfur, phosphorus, and iron during rice growth after carbon inputs.

The control of nitrogen oxides (NOx) from heavy-duty diesel vehicles is becoming increasingly urgent due to its detrimental effects on the environment. Cu-SSZ-39, with its exceptional NH3-SCR activity and hydrothermal stability, has attracted more and more attention in the field of diesel vehicle emission control. In this work, an unexpected phenomenon was observed for Cu-SSZ-39 after hydrothermal aging. Generally, the hydrothermal aging process causes deterioration of the catalytic performance of catalysts. However, a remarkable increase in low-temperature NH3-SCR catalytic activity was observed in Cu-SSZ-39 after it was exposed to 850 ℃ hydrothermal aging conditions for 16 h. EPR, DRIFTS, H2-TPR, UV–vis and XANES were utilized to detect the changes in Cu species. It was determined that a portion of the Cu2+ ions near double six-membered rings (d6r) transformed into CuxOy species after hydrothermal treatment. These CuxOy species facilitated the production of nitrate species which were critical intermediates in the NH3-SCR process, resulting in an increase in low-temperature catalytic activity.

The influence of the silver valence state on Ag/Al2O3 on the water tolerance of H2-C3H6-SCR of NOx was investigated. The valence state of silver species on Ag/Al2O3, which was carefully characterized by XPS, UV-vis, and XANES measurements, was adjusted by varying the calcination temperature from 500 oC to 900 oC. Oxidized silver species were predominant on Ag/Al2O3 calcined at temperatures below 600 oC (LT-catalysts), while further increasing the calcination (temperatures above 600 oC, HT-catalysts) promoted the transformation of oxidized silver species into metallic silver clusters. The samples with higher amounts of oxidized silver species exhibited better water tolerance in the H2-C3H6-SCR. Activation energy measurements confirmed that the mechanism of NOx reduction on these catalysts was the same. In situ DRIFTS studies demonstrated that metallic silver species promoted the formation of active enolic species and the complete oxidation of formate, thus improving the low-temperature activity of HT-catal...

The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies on the (110) surface of CeO2 have been studied combining aberration-corrected transmission electron microscopy and first-principles calculations. The oxygen adatoms were estimated to be located on top of Ce atoms with 50% coverage, forming a c(2×2) reconstruction. The oxygen vacancies can form stable configuration, with the Ce atoms partly reduced.

The water-soluble and oil-soluble amidoamine-structured hyperbranched polymers (PAMAM & PPAMAM) were synthesized as initiators for steam cracking of naphtha to promote the production of light olefins. Within 740–840 °C, both PPAMAM and PAMAM significantly improved the gas yield and yields of light olefins, and the PPAMAM showed better performance. The effect of PPAMAM increased with the molecular weight. At 800 °C, when adding 570 ppm PPAMAM with the molecular weight of 12,500 , yields of ethylene and propylene increased from 29.81 wt% and 17.47 wt% to 33.06 wt% and 17.70 wt% respectively, which were even higher than those obtained by cracking pure naphtha at 840 °C (32.72 wt% and 16.08 wt%). Combined with the simulated pyrolysis reaction network and measured thermal decomposition products of PAMAM and PPAMAM, it was found that three active free radicals (•H, •NH2, •CH3) generated by the additives played important roles in the initial cracking stage of hydrocarbons.

Thermal stability is crucial for the practical application of heterogeneous catalysts. In particular, the development of catalysts with excellent hydrothermal stability remains a big challenge for diesel exhaust after-treatment technologies. Here, we synthesized a Ce1W0.24Sn2Ox catalyst with high hydrothermal stability for the NOx removal from diesel engines. The catalyst shows >90 % NOx conversion at 300−550 °C even after an extreme aging treatment at 1000 °C, with much better hydrothermal stability than the Ce1W0.24Ox catalyst and the commercial catalysts such as Cu-SSZ-13 and V2O5-WO3/TiO2. The experimental and theoretical results reveal that the SnO2-related particles modified by W and Ce species show outstanding sintering resistance at high temperature, which provides sufficient Ce-W active phase for the catalytic reaction. This study may provide new opportunities for the application of metal oxide catalysts for diesel engine NOx emission control and a new idea for the development of catalysts with high thermal stability.

In this study, a 10 %Cs/3 %Co/Ce0.5Sn0.5O2 catalyst with outstanding soot oxidation performance was developed, by doping Cs to 3 %Co/Ce0.5Sn0.5O2. Remarkably, doping Cs lowered the T50 of the catalyst by 163 °C under a H2O/O2/N2 atmosphere and loose contact. It was also noteworthy that the 10 %Cs/3 %Co/Ce0.5Sn0.5O2 catalyst exhibited excellent water and sulfur dioxide resistances. Characterizations indicated that the doping of Cs had dual functional effects on soot catalytic oxidation. On one hand, the introduction of Cs induced the formation of more oxygen defects, which was beneficial to the activation of surface chemisorbed oxygen. On the other hand, it also benefited the catalytic performance by increasing the mobility of the surface-active oxygen species, which favored the contact between soot and catalyst. Therefore, the alkali metal cesium was found to be an excellent promoter for soot catalytic oxidation, and the developed 10 %Cs/3 %Co/Ce0.5Sn0.5O2 catalyst is very promising for practical applications in diesel soot oxidation.

Applications of ceria (CeO2) in catalysis are closely related to the behavior of oxygen at the surface and subsurface. In this study, we show that the steps at the (1 1 1) surface of CeO2 are highly reducible. Using aberration-corrected transmission electron microscopy, we observed simultaneous loss of surface and subsurface oxygen close to a step. Despite their large changes in atomic coordination, the outermost Ce atoms in the Ce-terminated surface has a negligible relaxation compared with the O-terminated surface. The outermost and subsurface Ce atoms of the Ce-terminated surface are reduced to valences of +1 and +3, and electronic configuration of 5s25p64f16s2 and 5s25p64f1, respectively. Both of them have a local magnetic moment and they couple antiferromagnetically. The existence of the Ce-termination is important for a complete understanding of the surface structure and properties of CeO2.

The structure and properties of CeO2 surfaces have been intensively studied due to their importance in a lot of surface-related applications. Since most of surface techniques probe the structure information inside the outermost surface plane, the subsurface structure information has been elusive in many studies. Using the profile imaging with aberration-corrected transmission electron microscopy, the structure information in both the outermost layer and the sublayers of the CeO2 (100) surface has been obtained. In addition to the normal structures that have been reported before, where the surface is Ce- or O-terminated, a metastable surface has been discovered. In the new structure, there is an atomic layer reversal between the outermost layer and the sublayer, giving a structure with O as the outermost layer for the stoichiometry of normal Ce-terminated surface. The charge redistribution for the polarity compensation has also been changed relative to the normal surface.

Water vapor is typically present in diesel engine exhausts, and thus the design of catalysts with high water-tolerance is highly desired. The addition of water vapor was shown to have quite different influences on the activity of Ag/Al2O3 catalysts with different Ag loadings during the H2-assisted C3H6-SCR of NOx (H2-C3H6-SCR). The 2 wt% Ag/Al2O3 catalyst showed the best activity for H2-C3H6-SCR, with excellent water resistance over the whole temperature range. An enhancement in NOx conversion was observed after water vapor was introduced, particularly at low temperatures. Over this catalyst, kinetic studies confirmed that H2O addition did not change the apparent activation energy for NOx reduction, while it increased the reaction order of C3H6 from −0.62 to 0.73. This result indicated that the reaction pathway for NOx reduction was hardly changed by the introduction of water vapor, while a poisoning effect related to C3H6 oxidation was decreased. In situ DRIFTS studies and DFT calculations revealed that water vapor significantly inhibits the formation of inert formate during the H2-C3H6-SCR process, and thus more sites are available for the formation of active enolic species and acetates, finally leading to increased activity for 2 wt% Ag/Al2O3 in NOx reduction.

Novel Ni-W-Mg mixed oxide catalysts (NiWMgOx) were prepared by homogeneous precipitation and attempted for the methanation of CO2. Adding W remarkably promoted the activity with improved stability, anti-CO-poisoning ability and resistance against coke formation compared to the undoped NiMgOx catalyst. The superior reactivity of monodentate formate towards hydrogenation than that of bidentate formate species was identified by DRIFTS analysis and the formation of more active monodentate formate species was indisputably facilitated by W additives, leading to the greatly enhanced catalytic activity. H-2-TPR and CO2-TPD characterization showed that doping W increased the number of stable CO2 adsorption sites and helped in anchoring the Ni sites as a result of strengthened Ni-Mg interaction, both of which were responsible for the enhanced CO2 methanation activity and the improved resistance against sintering. (C) 2016 Elsevier B.V. All rights reserved.

Adsorption is an efficient method for atmospheric NO

The coupling effect of polymeric vanadyl species greatly promotes the NH3-SCR de-NOx process over vanadia-based catalysts., The structure of dispersed vanadyl species plays a crucial role in the selective catalytic reduction (SCR) of NO with NH3 over vanadia-based catalysts. Here, we demonstrate that the polymeric vanadyl species have a markedly higher NH3-SCR activity than the monomeric vanadyl species. The coupling effect of the polymeric structure not only shortens the reaction pathway for the regeneration of redox sites but also substantially reduces the overall reaction barrier of the catalytic cycle. Therefore, it is the polymeric vanadyl species, rather than the monomeric vanadyl species, that determine the NH3-SCR activity of vanadia-based catalysts, especially under low-temperature conditions. The polymeric vanadia-based SCR mechanism reported here advances the understanding of the working principle of vanadia-based catalysts and paves the way toward the development of low vanadium–loading SCR catalysts with excellent low-temperature activity.

CeO2–WO3–ZrO2 mixed oxides were prepared by the homogeneous precipitation method for the selective catalytic reduction of NOx with NH3 (NH3–SCR). The effects of hydrothermal aging on the catalytic performances of CeO2–WO3–ZrO2 were investigated. The results showed that CeO2–WO3–ZrO2 catalyst exhibited excellent NH3–SCR activity for removal of NOx and hydrothermal stability. After hydrothermal aging at 850 °C for 16 h, the optimum CeO2–WO3–ZrO2 catalyst could still realize 80% NOx conversion at 300–500 °C even under a high gas hourly space velocity of 250 000 h–1. The structural properties, redox ability, surface species, and acidity of fresh and hydrothermally aged CeO2–WO3–ZrO2 catalysts were characterized by N2-physisorption, XRD, Raman, H2-TPR, XPS, NH3-TPD, and in situ DRIFTS. The characterization results showed that decreases of 89% of the surface area and 71% of the NH3 storage capacity as well as new phase formation occurred for the CeO2–WO3–ZrO2 sample after hydrothermal aging at 850 °C for 16 h. ...

Iron-based oxide catalysts for the NH3–SCR (selective catalytic reduction of NOx by NH3) reaction have gained attention due to their high catalytic activity and structural adjustability. In this work, iron–niobium, iron–titanate and iron–molybdenum composite oxides were synthesized by a co-precipitation method with or without the assistance of hexadecyl trimethyl ammonium bromide (CTAB). The catalysts synthesized with the assistance of CTAB (FeM0.3Ox-C, M = Nb, Ti, Mo) showed superior SCR performance in an operating temperature range from 150 °C to 400 °C compared to those without CTAB addition (FeM0.3Ox, M = Nb, Ti, Mo). To reveal such enhancement, the catalysts were characterized by N2-physisorption, XRD (Powder X-ray diffraction), NH3-TPD (temperature-programmed desorption of ammonia), DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and H2-TPR (H2-Total Physical Response). It was found that the crystalline phase of Fe2O3 formed was influenced by the presence of CTAB in the preparation process, which favored the formation of crystalline γ-Fe2O3. Owing to the changed structure, the redox-acid properties of FeM0.3Ox-C catalysts were modified, with higher exposure of acid sites and improved ability of NO oxidation to NO2 at low-temperature, both of which also contributed to the improvement of NOx conversion. In addition, the weakened redox ability of Fe prevented the over-oxidation of NH3, thus accounting for the greatly improved high-temperature activity as well as N2 selectivity.