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1.
A series of MoO3 doped Fe2O3 catalysts prepared by the co-precipitation method were investigated in the selective catalytic reduction of NO by NH3 (NH3-SCR). The catalysts displayed excellent catalytic activity from 225 to 400°C and high tolerance to SO2/H2O poisoning at 300°C. To characterize the catalysts the N2-BET, XRD, Raman, NO-TPD, NH3-TPD and in situ DRIFTS were carried out. It was found that the main reason explaining a high NH3-SCR performance might be the synergistic effect between Fe and Mo species in the catalyst that could enhance the dispersion of Fe2O3 and increase NH3 adsorption on the catalyst surface. 相似文献
2.
Nitric oxide (NOx), as one of the main pollutants, can contribute to a series of environmental problems, and to date the selective catalytic reduction (SCR) of NOx with NH3 in the presence of excess of O2 over the catalysts has served as one of the most effective methods, in which Mn-based catalysts have been widely studied owing to their excellent low-temperature activity toward NH3-SCR. However, the related structure-activity relation was not satisfactorily explored at the atomic level. By virtue of DFT+U calculations together with microkinetic analysis, we systemically investigate the selective catalytic reduction process of NO with NH3 over Mn3O4(110), and identify the crucial thermodynamic and kinetic factors that limit the catalytic activity and selectivity. It is found that NH3 prefers to adsorb on the Lewis acid site and then dehydrogenates into NH2* assisted by either the two- or three-fold lattice oxygen; NH2* would then react with the gaseous NO to form an important intermediate NH2NO that prefers to convert into N2O rather than N2 after the sequential dehydrogenation, while the residual H atoms interact with O2 and left the surface in the form of H2O. The rate-determining step is proposed to be the coupling reaction between NH2* and gaseous NO. Regarding the complex surface structure of Mn3O4(110), the main active sites are quantitatively revealed to be O3c and Mn4c. 相似文献
3.
Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NOX. Novel Fe-doped V2O5/TiO2 catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NOX conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H2-TPR, NH3-TPD) techniques showed that the iron existed in the form of Fe3+ and Fe2+ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO2 and H2O. 相似文献
4.
Fengxiang Li Junlin Xie De Fang Feng He Kai Qi Pijun Gong 《Research on Chemical Intermediates》2017,43(10):5413-5432
A series of Ce–MnO x /TiO2 catalysts were prepared using a novel sol–gel template method and investigated for low-temperature selective catalytic reduction (SCR) of NO with NH3 at temperatures ranging from 353 to 473 K. The 0.07Ce–MnO x /TiO2 catalyst showed the highest activity and best resistance to SO2 poisoning. The structure and properties of the catalysts were characterized using X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), thermogravimetry (TG)–differential scanning calorimetry (DSC)–mass spectroscopy (MS), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) measurements, H2-temperature-programmed reduction (TPR), and NH3-temperature-programmed desorption (TPD). The superior catalytic activity of the 0.07Ce–MnO x /TiO2 catalyst was probably due to a change in the active components, an increase in surface active oxygen and surface acid sites, and lower crystallinity and larger surface area with Ce doping. Furthermore, the reduction ability also became stronger. The SO2 poisoning resistance of the 0.07Ce–MnO x /TiO2 catalyst improved because doping with Ce can effectively decrease the formation of ammonium salt on the catalyst surface and the sulfation of MnO x . In situ diffuse-reflectance infrared Fourier-transform (DRIFT) spectroscopy experiments indicated that addition of Ce could promote adsorption of NH3 and inhibit generation of some nitryl species. The SCR reactions over the catalysts mainly followed the Eley–Rideal mechanism accompanied with a partial Langmuir–Hinshelwood mechanism. 相似文献
5.
Hao Li Guang-Fei Qu Yan-Kang Duan Ping Ning Qiu-Lin Zhang Xin Liu Zhong-Xian Song 《Chemical Papers》2015,69(6):817-826
Ce-Ti-W-O x catalysts were prepared and applied to the NH3-selective catalytic reduction (SCR) reaction. The experimental results showed that the Ce-Ti-W-O x catalyst prepared by the hydrothermal method exhibited higher NO conversion than those synthesised via the sol-gel and impregnating methods, while the optimal content of WO3 and molar ratio of Ce/Ti were 20 mass % and 4: 6, respectively. Under these conditions, the catalyst exhibited the highest level of catalytic activity (the NO conversion reached values higher than 90 %) across a wide temperature range of 225–450°C, with a range of gas hourly space velocity (GHSV) of 40000–140000 h?1. The catalyst also exhibited good resistance to H2O and SO2. The influences of morphology, phase structure, and surface properties on the catalytic performance were investigated by N2 adsorption-desorption measurement, XRD, XPS, H2-TPR, and SEM. It was found that the high efficiency of NO removal was due to the large BET surface area, the amorphous surface species, the change to element valence states, and the strong interaction between Ce, Ti, and W. 相似文献
6.
P. Schwendt D. Dudášová J. Chrappová M. Drábik J. Marek 《Journal of Thermal Analysis and Calorimetry》2008,91(1):293-297
The compound [Ni(NH3)6][VO(O2)2(NH3)]2 was prepared and characterized by elemental analysis and vibrational spectra. The single crystal X-ray study revealed that
the structure consists of [Ni(NH3)6]2+ and [VO(O2)2(NH3)]− ions. As a result of weak interionic interactions V′···Op (Op-peroxo oxygen), ([VO(O2)2(NH3)]−)2 dimers are formed in the solid-state. The thermal decomposition of [Ni(NH3)6][VO(O2)2(NH3)]2 is a multi-step process with overlapped individual steps; no defined intermediates were obtained. The final solid products
of thermal decomposition up to 600°C were Ni2V2O7 and V2O5. 相似文献
7.
M. D. Smolikov K. V. Kazantsev E. V. Zatolokina D. I. Kir’yanov E. A. Paukshtis A. S. Belyi 《Kinetics and Catalysis》2010,51(4):584-594
The state of surface Pt atoms in the Pt/SO4/ZrO2/Al2O3 catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al2O3 alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO4/ZrO2/Al2O3 superacid catalyst were used in this study. With the use of IR spectroscopy (COads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced
form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties
of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic
activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation
of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization. 相似文献
8.
Ye Liu Ping Ning Kai Li Lihong Tang Jiming Hao Xin Song Guijian Zhang Chi Wang 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2017,91(3):490-499
A series of modified porous activated carbon (AC) catalysts prepared by impregnation were investigated for the low-temperature (≤250°C) selective catalytic reduction (SCR) of NO x with NH3 with simultaneous removal of SO2. The effects of various preparation conditions and reaction conditions on NO and SO2 conversions were observed, such as support type, active components, copper loading, calcination temperature and presence of H2O and O2. The modified AC catalysts were characterized by BET, XRD, TG and TPX methods. The activity test results showed that the optimal catalyst is 15% Cu/WCSAC which can provide 52% NO conversion and 68% SO2 conversion simultaneously at 175°C with a space velocity of 30000 h?1, and the optimal calcination temperature was 500°C. The presence of H2O could inhibit NO conversion and promote the SO2 conversion. The effect of O2 (0–5%) was evaluated, and the NO and SO2 conversions were best when the concentration of O2 was 3%. Research demonstrated that Cu/WCSAC catalyst was a kind of potential catalysts due to the amorphous phase, high specific areas and high active ability. 相似文献
9.
10.
Magdalena Jabłońska 《Chemical Papers》2015,69(9):1141-1155
Copper or iron supported on commercially available oxides, such as γ-Al2O3, TiO2 (anatase) and monoclinic tetragonal ZrO2 (mt-ZrO2) were tested as catalysts for selective catalytic oxidation of ammonia into nitrogen and water vapour (NH3-SCO) in the low temperature range. Different commercial oxides were used in this study to determine the influence of the specific surface area, acidic nature of the support and crystalline phases as well as of the type of species and aggregation state of transition metals on the catalytic performance in selective ammonia oxidation. Copper modified oxide supports were found to be more active and selective to nitrogen than catalysts impregnated with iron. Activities of both transition metal modified samples decreased in the following order: mt-ZrO2, TiO2 (anatase), γ-Al2O3. Quantitative total ammonia conversion was achieved with the Cu/ZrO2 catalytic system at 400°C. Characterisation techniques, e.g. H2-temperature programmed reduction, UV-VIS-diffuse reflectance spectroscopy, suggest that easily reducible copper oxide species are important in achieving high catalytic performances at low temperatures. 相似文献
11.
L. S. Ivashkevich A. F. Selevich A. S. Lyakhov A. I. Lesnikovich 《Russian Journal of Inorganic Chemistry》2007,52(8):1274-1279
The characteristics of crystal structures of the titanium(IV) diammonium (Ti(NH4)2P4O13) and tin(IV) diammonium (Sn(NH4)2P4O13) tetraphosphates, which are isostructural with similar silicon(IV) and germanium(IV) salts, have been obtained by the Rietveld method using X-ray powder diffraction data. The compounds crystallize in the triclinic system, space group P \(\overline 1 \), Z = 2, a = 15.0291(7) Å, b = 7.9236(4) Å, c = 5.0754(3) Å, α = 99.168(3)°, β = 97.059(3)°, γ = 83.459(3)° for Ti(NH4)2P4O13 and a = 15.1454(7) Å, b = 8.0103(5) Å, c = 5.1053(3) Å, α = 99.898(6)°, β = 96.806(3)°, γ = 83.881(4)° for Sn(NH4)2P4O13. The structure is refined in the isotropic approximation using the pseudo-Voigt function: R p = 0.077, R Bragg = 0.045, R F = 0.057 for Ti(NH4)2P4O13; R p = 0.082, R Bragg = 0.044, R F = 0.046 for Sn(NH4)2P4O13. The hydrogen atoms of the ammonium cations are placed in the calculated positions. A comparative analysis of the structures of the compounds of the MIV(NH4)2P4O13 (MIV = Si, Ge, Ti, Sn) series has been carried out. 相似文献
12.
Junseo Choi Ji-Young Ban Suk-Jin Choung Jinsoo Kim Haznan Abimanyu Kye Sang Yoo 《Journal of Sol-Gel Science and Technology》2007,44(1):21-28
Mesoporous TiO2/γ-Al2O3 composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules
can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of
the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH3 decomposition, TiO2/γ-Al2O3 granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO2/γ-Al2O3 granules using titania made by hydrothermal method had comparable performance in NH3 decomposition. 相似文献
13.
V. A. Matyshak A. N. Il’ichev O. N. Sil’chenkova V. A. Sadykov V. N. Korchaka 《Kinetics and Catalysis》2016,57(5):677-685
The adsorption of reactant mixtures is quantitatively and qualitatively different from the adsorption of the individual reactants. Thus, O2 is almost not adsorbed on ZrO2; however, a considerable concentration of molecular oxygen was detected among the products of desorption after the adsorption of a mixture of NO + O2 and the total amount of desorbed molecules was greater by a factor of 10 than their total amount after the individual adsorption of NO and O2. Among the qualitative differences is the formation of the O2- radical anion on the surface only upon the adsorption of the mixture of NO + O2. Similarly, the number of desorbed molecules upon the simultaneous adsorption of C3H6, NO, and O2 was much greater than that upon their individual adsorption; this is related to the formation of paramagnetic and nonparamagnetic NO2–hydrocarbon complexes on the surface, which contained the NO2 group and a hydrocarbon fragment. 相似文献
14.
Zakaria Benzekri Sara Sibous Houda Serrar Ali Ouasri Said Boukhris Ali Rhandour Abdelaziz Souizi 《Journal of the Iranian Chemical Society》2018,15(12):2781-2787
In this work, the condensation of aromatic aldehydes with different two-substituted aniline catalyzed by NH3(CH2)5NH3BiCl5 as heterogeneous and recyclable catalyst was reported. It was demonstrated that NH3(CH2)5NH3BiCl5 can act as an efficient and active catalyst and is reusable for six runs without a significant loss of their catalytic activity. Simple preparation of the catalyst, high catalytic activity and good reusability are noteworthy advantages of this catalytic system in the synthesis of benzoxazole, benzimidazole and benzothiazole heterocycles at room temperature under solvent-free conditions. 相似文献
15.
A. N. Kholodovich P. A. Simonov R. I. Kvon A. V. Bukhtiyarov V. I. Zaikovskii Yu. A. Chesalov A. V. Romanenko 《Kinetics and Catalysis》2008,49(6):886-892
In the synthesis of Pt/C catalysts via H2PtCl6 adsorption onto a carbon support, NH4Cl can be formed catalytically during the reduction of the precursor with H2 at 250°C. This compound favors the sintering of metal particles. This effect is likely due to the weakening of metal-support bonding because of NH4Cl adsorption on the Pt surface. The sources of nitrogen and chlorine atoms are basic surface sites of the support, which contain nitrogen atoms in their structure and adsorb Cl? ions from the precursor solution. This effect is typical of active carbons, whose surface contains chemically bound nitrogen as amino groups, and weakens as the Pt/N atomic ratio in the supported catalyst precursors is increased. 相似文献
16.
Amirali Abbasi Jaber Jahanbin Sardroodi 《Journal of the Iranian Chemical Society》2017,14(12):2615-2626
Density functional theory calculations were carried out to investigate the adsorption behaviors of O3 molecules on the undoped and N-doped TiO2/MoS2 nanocomposites. With the inclusion of vdW interactions, which correctly account the long-range dispersion energy, the adsorption energies and final geometries of O3 molecules on the nanocomposite surfaces were improved. For O3 molecules on the considered nanocomposites, the binding sites were located on the fivefold coordinated titanium atoms of the TiO2 anatase. The structural properties of the adsorption systems were examined in view of the bond lengths and bond angles. The variation of electronic structures was also discussed in view of the density of states, molecular orbitals and distribution of spin densities. The results suggest that the adsorption of the O3 molecule on the N-doped TiO2/MoS2 nanocomposite is more favorable in energy than that on the pristine one, indicating that the N-doped nanocomposite has higher sensing capability than the pristine one. This implies that the N-doped TiO2/MoS2 nanocomposite would be an ideal O3 gas sensor. However, our calculations thus provide a theoretical basis for the potential applications of TiO2/MoS2 nanocomposites as efficient O3 sensors, leading to very interesting results in the context of air quality measurement. 相似文献
17.
Modeling of the interaction of an H2 molecule with the surface of the Pd21 cluster in different spin states was performed using the DFT/PBE scalar relativistic approximation. The spin multiplicity of the system significantly affects the mechanism of adsorption, its parameters, and migration of hydrogen atoms. The H atoms can migrate over the cluster surface with low barriers (1.6 kcal mol–1). The complex with C 2v symmetry, wherein the H atoms occupy adjacent fcc sites, is the most energetically stable. 相似文献
18.
Zhe-Shan Zhang Xin-Pu Fu Wei-Wei Wang Zhao Jin Qi-Sheng Song Chun-Jiang Jia 《中国科学:化学(英文版)》2018,61(11):1389-1398
Transition metal catalysts have been considerably used for NH3 decomposition because of the potential application in COx-free H2 generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co3O4-Al2O3) catalysts. The Co3O4-Al2O3 catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm3 gcat?1 h?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H2-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H2-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts. 相似文献
19.
T. V. Belysheva G. N. Gerasimov V. F. Gromov E. Yu. Spiridonova L. I. Trakhtenberg 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(9):1554-1559
The conductivity of films consisting of a mixture of SnO2 and In2O3 nanocrystals at 200–500°C was studied. Based on the experimental data, it was assumed that in films containing less than
20 wt % In2O3, the current flows along SnO2 nanocrystals. A model of conductivity in these films is presented; it includes an electron transfer from In2O3 to SnO2, which forms positively charged In2O3 nanocrystals that contact the negatively charged SnO2 nanocrystals. In the presence of In2O3 nanocrystals, the activation energy of the electron transfer between SnO2 nanocrystals decreased substantially because of a decrease in the barrier of electron transfer between SnO2 crystals under the action of the negative charge. As a result, a percolation cluster of charged SnO2 crystals formed. At high contents of In2O3 (over 20 wt %), the conductivity increased dramatically. The curve of the temperature dependence of conductivity changed
because of the appearance of a percolation cluster of In2O3 nanocrystals, in which the current passed. The conductivity of a mixed film of this kind differed from that of the nanocrystalline
film of pure In2O3. 相似文献
20.
Summary The adsorption of 99Tc on the adsorbers Fe, Fe2O3 and Fe3O4 was studied by batch experiments under aerobic and anoxic conditions. The effects of pH and CO32- concentration of the simulated ground water on the adsorption ratios were also investigated, and the valences of Tc in solution after the adsorption equilibrium were studied by solvent extraction. The adsorption isotherms of TcO4- on the adsorbers Fe, Fe2O3 and Fe3O4 were determined. Experimental results have shown that the adsorption ratio of Tc on Fe decreases with the increase of pH in the range of 5-12 and increases with the decrease of the CO32- concentration in the range of 10-8M-10-2M. Under aerobic conditions, the adsorption ratios of 99Tc on Fe2O3 and Fe3O4 were not influenced by pH and CO32-concentration. When Fe was used as adsorbent, Tc existed mainly in the form of Tc(IV) after equilibrium and in the form of Tc(VII) when the adsorbent was Fe2O3 or Fe3O4 under aerobic conditions. The adsorption ratios of Tc on Fe, Fe2O3 and Fe3O4 decreased with the increase of pH in the range of 5-12 and increased with the decrease of the CO32- concentration in the range of 10-8M-10-2M under anoxic conditions. Tc existed mainly in the form of Tc(IV) after equilibrium when Fe, Fe2O3 and Fe3O4 was the adsorbent under anoxic conditions. The adsorption isotherms of TcO4- on the adsorbers Fe, Fe2O3 and Fe3O4 are fairly in agreement with the Freundlich’s equation under both aerobic and anoxic conditions. 相似文献