Transport properties of alkanes through ceramic thin zeolite MFI membranes

Polycrystalline randomly oriented defect free zeolite layers on porous α-Al₂O₃ supports are prepared with a thickness of less than 5 μm by in situ crystallisation of silicalite-1. The flux of alkanes is a function of the sorption and intracrystalline diffusion. In mixtures of strongly and weakly adsorbing gases and a high loadings of the strongly adsorbing molecule in the zeolite poze, the flux of the weakly adsorbing molecule is suppressed by the sorption and the mobility of the strongly adsorbing molecule resulting in pore-blocking effects. The separation of these mixtures is mainly based on the sorption and completely different from the permselectivity. At low loadings of the strongly adsorbing molecules the separation is based on the sorption and the diffusion and is the same as the permselectivity. Separation factors for the isomers of butane (n-butane/isobutane) and hexane (hexane/2,2-dimethylbutane) are respectively high (10) and very high (> 2000) at 200°C. These high separation factors are a strong evidence that the membrane shows selectivity by size-exclusion and that transport in pores larger than the zeolite MFI pores (possible defects, etc) can be neglected.     

Cu-loaded dealuminated Y zeolites active in selective catalytic reduction of nitric oxide with ammonia

The selective catalytic reduction of NO with ammonia in the presence of oxygen has been carried out on Cu-loaded dealuminated Y zeolite catalysts. Copper was introduced by the usual ion-exchange procedure with an aqueous solution of cupric acetate. On deeply dealuminated USY zeolites, Cu²⁺ was supported in the amount larger than 2Cu/Al = 2, resulting in the formation of CuO fine particles in addition to the isolated and dimer Cu²⁺ species. The specific catalytic activity per surface copper on the CuO particles was very high compared with these Cu²⁺ species. NO adsorption measurement revealed the higher dispersion of CuO on the deeply dealuminated USY than on SiO₂, which made Cu/USY a better catalyst for the reduction of NO. The reaction intermediates were investigated through the IR spectra of adsorbed species.     

Cu-loaded dealuminated Y zeolites active in selective catalytic reduction of nitric oxide with ammonia

The selective catalytic reduction of NO with ammonia in the presence of oxygen has been carried out on Cu-loaded dealuminated Y zeolite catalysts. Copper was introduced by the usual ion-exchange procedure with an aqueous solution of cupric acetate. On deeply dealuminated USY zeolites, Cu²⁺ was supported in the amount larger than 2Cu/Al=2, resulting in the formation of CuO fine particles in addition to the isolated and dimer Cu²⁺ species. The specific catalytic activity per surface copper on the CuO particles was very high compared with these Cu²⁺ species. NO adsorption measurement revealed the higher dispersion of CuO on the deeply dealuminated USY than on SiO₂, which made Cu/USY a better catalyst for the reduction of NO. The reaction intermediates were investigated through the IR spectra of adsorbed species.     

Pt-KL zeolite catalysts of different preparation: Part I. Catalyst characterization

0.8% Pt on KL zeolite was prepared by reduction with H₂ and NaBH₄. Transmission electron microscopy and X-ray diffraction were used for characterization of morphology of the metal particles; acidity of the zeolite framework was measured with IR spectra of adsorbed pyridine. Reduction by NaBHP₄ produced rather large, needle-like Pt crystallites on the outer surface of zeolite grains which contained very little acidity. Subsequent hydrogen treatment brought about their severe sintering; at the same time, small crystallites appeared. A bimodal distribution was seen when the catalyst was reduced with hydrogen; this sample exhibited appreciable acidity. X-ray diffraction data showed the presence of Pt particles above noise level in the case of borohydride-reduced catalyst only, in agreement with EM data.     

Ni-Ti-O混合氧化物的制备、表征及其富氧选择性催化还原NO

采用均匀共沉淀法制备了不同Ni/Ti摩尔比的Ni-Ti-O混合氧化物,考察了它们在富氧条件下丙烯选择性催化还原NO反应中的催化性能,并运用X射线衍射,N₂吸附-脱附、吡啶吸附、程序升温脱附和原位红外光谱对催化剂进行了表征.结果表明,Ni/Ti摩尔比为1的催化剂表现出最佳催化活性,430℃时NO_x转化率达68%.该催化剂具有锐钛矿结构,比表面积较高(149m²/g),有利于提高催化活性;其表面Lewis酸性位有利于硝酸盐物种的吸附,而硝酸盐物种是该反应的重要中间体.     

富氧条件下乙炔选择催化还原NOx

Acetylene as a reducing agent of metal exchanged HY catalysts, for selective catalytic reduction of NO in the reaction system of 0.16% NO, 0 （C2H2-SCR） was investigated over a series 08% C2H2, and 9.95% O2 （volume percent） in He. 75% of NO conversion to N2 with hydrocarbon efficiency about 1.5 was achieved over a Ce-HY catalyst around 300 ℃. The NO removal level was comparable with that of selective catalytic reduction of NOx by C3H6 reported in literatures, although only one third of the reducing agent in carbon moles was used in the C2H2-SCR of NO. The protons in zeolite were crucial to the C2H2-SCR of NO, and the performance of HY in the reaction was significantly promoted by cerium incorporation into the zeolite. NO2 was proposed to be the intermediate of NO reduction to N2, and the oxidation of NO to NO2 was rate-determining step of the C2H2-SCR of NO over Ce-HY. The suggestion was well supported by the results of the NO oxidation with O2, and the C2H2 consumption under the conditions in the presence or absence of NO.     

Palladium species in Pd/H-ZSM-5 zeolite catalysts for CH4-SCR

The active state of palladium for NO reduction with methane (CH₄-SCR) was investigated by comparing the catalytic activity of Pd/H-ZSM-5 with that of PdO/SiO₂. High catalytic activity for CH₄-SCR was given by Pd/H-ZSM-5 in the temperature range of 300–500 °C. PdO/SiO₂ catalyzed the reaction between NO₂ and CH₄ in the absence of oxygen, which retarded the reaction by consuming CH₄ in combustion. CH₄ combustion occurred on either zeolite-supported or silica-supported catalyst, while NO preferentially retarded the combustion on Pd/H-ZSM-5. NO was found to be chemisorbed on the palladium sites in zeolite, while it was hardly chemisorbed on PdO/SiO₂. NaCl titration showed that the palladium species in zeolite are Pd²⁺ cations content, on which NO is strongly chemisorbed resulting in high selectivity for CH₄-SCR.     

Determination of Free Oxygen in the Catalytic Reduction of Nitrogen Oxides on Palladium-Containing Catalysts

A procedure is proposed for the in situdetermination of free oxygen in the high-temperature solid-phase catalytic reduction of NO based on an EPR study of the behavior of a reference addition of BaO. An approximating function for the dependence of the relative intensity of EPR spectra on the concentration of resulting BaO₂was found. Concentrations of surface oxygen produced on the catalytic decomposition of NO and NO₂on palladium in the system 0.4% Pd + BaO were determined.     

Conversion of Nitric Oxide into Nitrous Oxide as Triggered by the Polarization of Coordinated NO by Hydrogen Bonding

Reduction of the {Co(NO)}⁸ cobalt–nitrosyl N‐confused porphyrin (NCP) [Co(CTPPMe)(NO)] ( 1 ) produced electron‐rich {Co(NO)}⁹ [Co(CTPPMe)(NO)][Co(Cp*)₂] ( 2 ), which was necessary for NO‐to‐N₂O conversion. Complex 2 was NO‐reduction‐silent in neat THF, but was partially activated to a hydrogen‐bonded species 2 ??? MeOH in THF/MeOH (1:1, v/v). This species coupling with 2 transformed NO into N₂O, which was fragmented from an [N₂O₂]‐bridging intermediate. An intense IR peak at 1622 cm^?1 was ascribed to ν(NO) in an [N₂O₂]‐containing intermediate. Time–course ESI(?) mass spectra supported the presence of the dimeric [Co(NCP)]₂(N₂O₂) intermediate. Five complete NO‐to‐N₂O conversion cycles were possible without significant decay in the amount of N₂O produced.     

Effect of Fe-zeolite on formation of N<Subscript>2</Subscript>O in selective reduction of NO by NH<Subscript>3</Subscript> over V<Subscript>2</Subscript>O<Subscript>5</Subscript>–WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> catalyst

An approach for significantly suppressing N₂O formation in reduction of NO by NH₃ over V₂O₅–WO₃/TiO₂ (VWT) catalyst has been studied by coating different amounts of a Fe-exchanged zeolite (FeZ) onto the catalyst. FeZ-promoted VWT samples were characterized using N₂ sorption, X-ray diffraction (XRD) analysis, and NH₃ adsorption/desorption techniques to understand the primary role of FeZ in lowering N₂O production levels. At high temperatures (≥450 °C), VWT gave N₂O production with high concentrations, while N₂O formation was noticeably reduced when using FeZ-promoted catalysts, which also showed somewhat lower NO removal activities (<5 %) at all temperatures. N₂ sorption and XRD measurements revealed no perceptible physical or chemical alterations of each constituent, even in VWT catalysts after FeZ coating following high-temperature calcination. Adsorption of NH₃ on unpromoted and FeZ-promoted catalysts and subsequent desorption yielded very complicated spectra for N₂O that might primarily come from NH₃ oxidation, and the interaction between V–NO species at temperatures >580 °C. NO on neighboring sites seems to be produced via decomposition of N₂O generated at lower temperatures. The FeZ in the promoted VWT catalysts could be responsible for N₂O decomposition and N₂O reduction with unreacted NH₃ at temperatures >400 °C, thereby significantly lowering N₂O emission levels. This promotional effect bodes well for use in many industrial deNO _x applications.     

Emission of secondary ions from osmium under oxygen and the nitrogen oxides N2O, NO and NO2

Summary Small briquettes compressed of high-purity Os powder were bombarded by primary Ar⁺ ions for moderate dynamic SIMS conditions. Secondary ion mass spectra were observed for positive ions which were produced under residual gas and under O₂, N₂O, NO, NO₂. For the different reactant gases these spectra were found rather similar, indicating that the nitrogen oxides mainly act as sources of reactive oxygen. But also some individual secondary ions containing nitrogen or NO are emitted from the target surface which, at least in the case of N₂O and NO₂, give some evidence of partial adsorptive fragmentation of the respective reactant gas molecules.     

15N NMR studies of the No?NH3?O2 reaction over ZSM-5 type zeolites and vanadia supported catalysts

¹⁵N nuclear magnetic resonance spectra produced by adsorption of NO together with O₂ and NH₃ on H-ZSM-5 and V₂O₅/Al₂O₃ catalysts have been examined. Several surface species and reaction intermediates have been identified by their characteristic¹⁵N NMR spectra. The intermediate complexes between the products of disproportionation and partial oxidation of NO, on one hand, and ammonia, on the other hand, were found to be formed in the reaction. On V₂O₅/Al₂O₃ catalyst the reaction proceeds more rapidly compared with ZSM-5 but some details of the mechanism are similar for both catalysts.     

Multifunctional NO-delivery vessel derived from aminopropyl-modified mesoporous zeolites

A new strategy, releasing nitric oxide (NO) and adsorbing nitrosamines simultaneously by zeolitic materials in the digestive system, is validated in this paper. Three types of moisture-saturated molecular sieves, HZSM-5 zeolite, mesoporous zeolite, and mesoporous silica MCM-41, are used as NO-delivery vessels in mimic gastric juice after modification of γ-aminopropyltriethoxysilane (APTES). APTES modification dramatically increased the capability of zeolite and mesoporous silica in NO release in acidic solution, because more NO can be adsorbed in the composite and stored in the form of nitrite. Some composites released the NO 10 times more than their parent materials, and synchronously captured the carcinogen nitrosamines in mimic gastric juice. The influences of APTES modification on the porous structure and surface state of zeolite and mesoporous silica were investigated by XRD, N(2) adsorption, and FTIR tests, through which the mesoporous zeolite is proven to be the optimal support. With this hierarchical material a controllable APTES modification is realized in which a lot of aminopropyl groups are grafted in mesopores while the zeolitic structure is maintained, so the resulting sample exhibits a high capability in releasing NO and adsorbing nitrosamines. This investigation provides a clue for elevating the efficiency of zeolites in the application of life science.     

Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

In this study, IR studies of the coadsorption of ethanol and CO on Cu⁺ cations evidenced the transfer of electrons from ethanol to Cu⁺, which caused the lowering of the frequency of the band attributed to CO bonded to the same Cu⁺ cation due to the more effective π back donation of d electrons of Cu to antibonding π* orbitals of CO. The reaction of ethanol with acid sites in zeolite HFAU above 370 K produced water and ethane, polymerizing to polyethylene. Ethanol adsorbed on zeolite Cu(2)HFAU containing acid sites and Cu⁺_exch also produced ethene, but in this case, the ethene was bonded to Cu⁺ and did not polymerize. C=C stretching, which is IR non-active in the free ethene molecule, became IR active, and a weak IR band at 1538 cm⁻¹ was present. The reaction of ethanol above 370 K in Cu(5)NaFAU zeolite (containing small amounts of Cu⁺_exch and bigger amounts of Cu⁺_ox, Cu²⁺_exch and CuO) produced acetaldehyde, which was further oxidized to the acetate species (CH₃COO⁻). As oxygen was not supplied, the donors of oxygen were the Cu species present in our zeolite. The CO and NO adsorption experiments performed in Cu-zeolite before and after ethanol reaction evidenced that both Cu⁺_ox and Cu²⁺ (Cu²⁺_exch and CuO) were consumed by the ethanol oxidation reaction. The studies of the considered reaction of bulk CuO and Cu₂O as well as zeolites, in which the contribution of Cu⁺_ox species was reduced by various treatments, suggest that ethanol was oxidized to acetaldehyde by Cu²⁺_ox (the role of Cu⁺_ox could not be elucidated), but Cu⁺_ox was the oxygen donor in the acetate formation.     

EPR study of the mechanism of interaction of NO and NO2 molecules with zeolite surfaces

The adsorption of the paramagnetic molecules of NO and NO₂ by zeolites in the alkali and alkaline earth cationic forms has been studied by EPR and reflectance spectroscopic methods. The change in the EPR spectra of adsorbed nitric oxide with increase in the degree of covering of the surface of the alkali cationic form of the zeolites, and also the nature of the change in the spectra when oxygen is adsorbed on zeolites on which NO has previously been adsorbed, indicate the existence of two types of adsorption center. At low degrees of covering of the surface, on the order of 10¹⁸ g^–1, as can be judged from the EPR spectra, the adsorbed NO molecule is strongly polarized and the unpaired electron is almost completely localized on the oxygen atom. At high degrees of covering, for an appreciable proportion of the NO molecules, the bond with the surface is weaker. In this case, the EPR spectra show a hyperfine structure (HFS) with a constant which changes with change in the cation in the order Li⁺ Na⁺ K⁺. The replacement of the singly charged Na⁺ by the doubly charged Ca²⁺ produces a marked change in the adsorption properties of the zeolite. The adsorption of NO on CaA leads not only to polarization of the adsorbed molecule but also to transfer of the electron from the nitrogen atom to the atoms of the adsorbent; this is recorded in the EPR spectrum in the form of an F-center. On further adsorption, the NO molecules are adsorbed both on the nitrogen atom and on the oxygen atom of the first molecule; thus, NO₂ and N₂O are formed.     

Gas phase nitration of benzene by nitric acid on ZSM-5 zeolite

Gas phase nitration of benzene on ZSM-5 zeolite has been studied at 140–170°C. Increase in the HNO₃/C₆H₆ ratio of the starting mixture was shown to increase the nitrobenzene yield. Process parameters worsened with time since reagents and products were strongly adsorbed and left the zeolite surface only at 220–250°C as CO, CO₂ and NO.     

Local structure of highly dispersed lead species incorporated within zeolite: experimental and theoretical studies

XAFS (both XANES and FT-EXAFS) measurements revealed that the Pb²⁺ /ZSM-5 catalyst prepared from precursor H-ZSM-5 by a conventional ion-exchange method includes a highly dispersed 3-fold coordinated Pb²⁺ ion species within the zeolite framework. UV-irradiation of Pb²⁺ /ZSM-5 led to effective decomposition of NO and N₂O producing N₂. The photocatalytic decomposition of NO is found to be slightly preferable than that of N₂O. The isolated Pb²⁺ ions play a significant role in the decomposition of pollutant NO _x . Ab initio and DFT quantum chemical studies at the HF/Lanl2dz and B3PW91/Lanl2dz levels further shed light on local structures of the Pb²⁺ active site of lead-containing zeolites, as well as on their interactions with pollutant NO and N₂O molecules. In agreement with experiments, 3-fold coordination was found to be the most favorable state for the Pb²⁺ site within the zeolite framework.     

Preparation of Silicates Using HSi(OC2H5)3 and Their NO x -Adsorption Behavior

The preparation and NO-adsorption/desorption behavior of Li, Ca and Ba silicates were investigated aiming at the application to a NO_x-absorbent. Li silicate was prepared by reaction of HSi(OC₂H₅)₃ with aqueous lithium silicate solution (LSS). Ca and Ba silicates were prepared from gels obtained using CH₃Si(OC₂H₅)₃, Si(OC₂H₅)₄, HSi(OC₂H₅)₃ and alkaline-earth alkoxides. The surface of these silicates indicated the solid basicity of H₀ = 9 and adsorbed the acidic gas of NO. FT-IR spectra of the silicates adsorbing NO showed the absorption peaks in the range of 1300–1600 cm^{– 1} corresponding to ionic and covalent nitrate NO₃^–. The complete desorption of adsorbed NO species occurred above 500°C in the Li silicate, above 500°C in the Ca and Ba silicates prepared using CH₃Si(OC₂H₅)₃, and above 700°C in the Ba and Ca silicates prepared using Si(OC₂H₅)₄. Regarding the Ca and Ba silicates, the difference in siloxane structure is thought to cause the difference in adsorption state and desorption behavior of NO.     

Oxide Nanoparticles within a host microporous matrix: Polynuclear copper species in Cu-ZM5 and their role in the reduction of NO

The role of copper-oxide nanoparticles inside a host ZSM5 zeolite, identified by UV-Visible-NIR diffuse reflectance spectroscopy on the reactivity in NO reduction to N₂ in the presence of propane/O₂ or ammonia/O₂ is discussed. These species lead to an enhancement in the rate of alkane depletion in the reduction of NO in the presence of propane/O₂, whereas they cooperate with isolated ions at exchangeable sites in determining the overall catalytic behaviour in NO reduction in the presence of ammonia/O₂. Also the stability of these species depends on the type of reductant.