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1.
Studies on Oxide Catalysts. XXXIV. Redoxbehaviour of Nickel in Zeolite NiNaY. 1. Reducibility and Reoxidizability of Nickel in Zeolites NiNaY The properties of metallic nickel in reduced (470–870 K) and reoxidized (470, 670 K) samples were studied by chemical analysis (reaction with K2Cr2O7) and spectroscopic methods (FMR, IR after CO adsorption, UV/VIS). The reduction of Ni2+ cations from oxidic clusters proceeds in an onestep reaction. Contrary to this, isolated Ni2+ cations are reduced stepwise to Ni+ cations and subsequently to metallic nickel. The reduction degree depends in characteristic manner on the reduction temperature. Metallic nickel which was reduced at temperatures < 620 K, can be completely reoxidized at 470 K. Higher temperatures result in metallic aggregations which are not completely reoxidized even at 670 K.  相似文献   

2.
Studies on Oxide Catalysts. XXVIII. Influence of Pretreatment on Catalytic Properties of Zeolites NiNaY and NiCoNaY The influence of the pretreatment conditions on the acidic properties, the reduction degree of nickel, and the catalytic activity and selectivity of zeolites NiNaY and NiCoNaY in the alkylation of benzene with ethylene has been investigated. From the experimental results can be concluded that sec. buthylbenzene from benzene and ethylene is only formed on zeolite samples which contain both together BRÖNSTED acidic centres and Ni2+ cations or NiO. Catalysts which contain only metallic nickel are inactive for this reaction. Catalysts with nickel in different forms are active in the formation of ethylbenzene, diethylbenzene, butane and sec. buthylbenzene, the yields depending on the relation of Ni°, Ni2+, and NiO. Changing this relation makes possible to regulate the selectivity in the alkylation of benzene with ethylene.  相似文献   

3.
Studies on Oxide Catalysts. XXX. Characterization of the Me2+ Localization in Zeolites CaNaY, MgNaY, and CaMgNaY Data for exchange of the cations Ca2+, Mg2+, as well as Ca2+ and Mg2+ into the zeolite NaY have been determined. From this it was concluded on the localization of Me2+ cations in hydrated samples. The adsorption of ammonia in the temperature region of 420 to 670 K, the determination of the heats of immersion in water and nitromethane and the Me2+ ? CO-interaction indicated by IR spectroscopy yielded informations on the localization of cations in dehydrated samples. The results show that cations Ca2+ more selectively than cations Mg2+ occupy positions in the small cages. In the case of the competitive cation exchange this fact causes a site directed distribution of cations in zeolite cages.  相似文献   

4.
采用了BET、XRD、TG-DSC、TPR、FTIR、微量量热吸附和异丙醇催化反应等测试方法,对以共沉淀法合成的水滑石(HT)和类水滑石(HTLcs)为前体制备的4Mg/Al、3Ni/Mg/Al、3.5Ni/0.5Mg/Al和4Ni/Al混合氧化物和前体进行了研究。测定表明:制备的混合氧化物的比表面积较大、随着镍含量的增大而降低。由于Ni2+离子的氧化还原属性,Ni2+离子进入后,削弱了HT层对阴离子的键合能力,从而使得样品的热分解温度及热稳定性降低,导致焙烧后  相似文献   

5.
FT-FIR spectra of xeolites A containing Mn2+, Co2+, Ni2+, Cu+ and Zn2+ ions were recorded after heat treatment at 573 K in vacuo. The bands were assigned to the vibrations of the cations with respect to the zeolite framework. From obeying the Butler expression it can be inferred that transition metal ions preferably occupy SI sites in zeolite A. Upon adsorption of rare gas and diatomics the bands of the cation vibration diminish and are unspecifically shifted up- and downscale.  相似文献   

6.
Studies on Oxide Catalysts. XLii. Redox Behaviour of Nickel in Zeolites NiNa? Y. 4. Influence of Composition on the Reducibility of Nickel in Zeolites NiNa? Y By chemical analysis (reaction with K2Cr2O7) and ESCA investigations we determined the degree of reduction in reduced samples NiNa-Y as function of the mole ratio SiO2/Al2O3 (module), of the Ni2+ degree of exchange and the kind of the second cations. (NH4+, Ca2+, Co2+, and Nd3+) in the temperature region of 620–770 K. The degree of nickel reduction increases with increasing module, decreasing degree of exchange and decreasing number of Brönsted acidic centres. This behaviour is caused by the influence of the interaction between cations Ni2+ and zeolite lattice on the reduction equilibrium.  相似文献   

7.
Electrochemical properties of lanthanum nickel oxide, LaNiO284, were studied in alkaline solutions. It was concluded that redox reactions of Ni4+/Ni3+ and Ni3+/Ni2+ in a solid surface layer took place at 0.4 V and ?0.4 V (vs. Hg/HgO), respectively. As the conductivity of the oxide is a function of the oxygen concentration due to σ* bond formation, the resistivity of the electrode was changed depending on polarization potentials. The catalytic activity for oxygen reduction of a preoxidized electrode seemed to be higher than that of an electrode not intentionally oxidized, and the activity depended on the concentration of the alkaline solution. It was presumed that Ni3+ cations which form the σ* bond with oxygen have an important role in the electrocatalysis of oxygen reduction on lanthanum nickel oxide.  相似文献   

8.
The reaction of ferrocene with the acidic hydroxy groups in the supercages of zeolite HY dehydrated at 673 K and the reactivity of the resultant surface species towards CO and O(2) were investigated by temperature-programmed decomposition (TPD) and reduction (TPR) and IR, X-ray absorption fine structure analysis (XAFS), and X-ray photoelectron (XP) spectroscopy. In situ FTIR, TPD, TPR, and chemical analysis reveal that the Cp(2)Fe molecule adsorbed on the zeolite surface loses one cyclopentadienyl group under vacuum at 423 K, which leads to the formation of a well-defined mononuclear surface Fe-C(5)H(6) complex grafted to two acidic sites and one ([triple bond]Si-O-Si[triple bond]) unit, as confirmed by the lack of Fe-Fe contributions in the EXAFS spectra. Each iron atom is coordinated, on average, to three oxygen atoms of the zeolite surface with a Fe--O distance of 2.00 A and to five carbon atoms with a Fe--C distance of 2.09 A. IR spectra indicate that the cyclopentadiene-iron species grafted on the surface of the zeolite is quite stable in vacuo or under an inert or hydrogen atmosphere below 423 K, and is also relatively stable under oxygen at room temperature. However, the cyclopentadiene ligand readily reacts with CO to form a compound containing carbonyl at 323 K, and even at room temperature. The single carbonyl band in the IR spectra provides evidence for the nearly uniform formation of a cyclopentadiene-iron species on the surface of the zeolite.  相似文献   

9.
Reaction of nickel(II) thiocyanate and pyridazine (pdz) as organic spacer ligand leads to the formation of the ligand‐rich 1:2 (1:2 = metal to ligand ratio) trinuclear nickel(II) complex of composition [Ni3(NCS)6(pdz)6]. Depending on the reaction solvent, different polymorphic modifications are obtained: Reaction in acetonitrile leads to the formation of the new modification 1I and reaction in ethanol leads to the formation of modification 1II reported recently. In their crystal structures discrete [Ni3(NCS)6(pdz)6] units are found, in which each of the Ni2+ cations exhibits a NiN6 distorted octahedral arrangement. The central Ni2+ cation is coordinated by four bridging pdz ligands and two thiocyanato anions in trans positions. Both thiocyanato anions exhibit the end‐on bridging mode. The peripheral Ni2+ cations are bridged by one thiocyanato anion and by two pdz ligands with the central Ni2+ cation. Further they are coordinated by two terminal N‐bonded thiocyanato anions and one terminal N‐bonded pdz ligand. The structure of 1I was determined by X‐ray single crystal structure investigation and emphasized by infrared spectroscopy. Magnetic measurements revealed a quasi Curie behavior with net ferromagnetic interactions for 1I and net antiferromagnetic interactions for 1II . Solvent‐mediated conversion experiments clearly show that modification 1I represents the thermodynamic most stable form at room temperature and that modification 1II is metastable. On thermal decomposition, both modification transform quantitatively in a new ligand‐deficient intermediate. Elemental analysis revealed a 3:4 compound of composition [Ni3(NCS)6(pdz)4]. A structure model supported by IR spectroscopic investigations was assumed, in which three coordination modes of the thiocyanato anion exist, resulting in a 2D polymeric network.  相似文献   

10.
The influence of synthesis conditions on the phase composition and texture of porous nickel supports as plates with a magnesium oxide underlayer were investigated by X-ray diffraction, low-temperature nitrogen absorption, and electron microscopy combined with X-ray microanalysis. Nickel catalysts supported on these plates were studied. Thermal treatment of Mg(NO3)2 in nitrogen yields a magnesium oxide underlayer with a small specific surface area (support I). The replacement of nitrogen with hydrogen leads to a larger surface area (support II). The formation of MgO is accompanied by the incorporation of Ni2+ cations from the oxide film into the underlayer. Upon subsequent reduction with hydrogen or under the action of the reaction medium, these cations form fine crystallites of nickel. The supports having an oxide underlayer show a higher activity in methane steam reforming than the initial metallic nickel. Nickel catalysts on supports I and II show similar activities. The activity of the catalysts was stable throughout 50-h-long tests; no carbon deposits were detected by TEM.  相似文献   

11.
The possibility of the ion-exchange of Na+ and K+ cations contained in OFF-type zeolite for H+, Ni2+, Cu2+, Co2+, and La3+ cations is investigated. Chemical and phase compositions, the morphology of crystals, and the adsorption properties of synthesized samples are studied via X-ray fluorescence and X-ray diffraction analysis, IR spectroscopy, scanning electron microscopy, and adsorption measurements.  相似文献   

12.
Irradiations of Ni/TiO2 catalyst by UV in hydrogen at 77 K produced not only Ni+ ions on the catalyst surface, but also Ni3+ and Ti3+ species in bulk or near the interface between nickel and titania. These photo-generated species were detected and characterized by low temperature electron paramagnetic resonance (EPR) spectroscopy. Relative spin concentrations of the photogenerated paramagnetic species (Nin+ and Ti3+) varied with the nickel content in titania. A high nickel content in the sample resulted in a high peak intensity ratio of Nin+ to Ti3+. It was found that the photoinduced self-redox reaction of Ni2+ ions to form Ni+ and Ni3+ ions has a priority over the photoreduction of Ti4+ to Ti3+ ions. The characteristic EPR spectrum of the Ni3+ (3d7) ions with g1 = 2.268, g2 = 2.237, and g3 = 2.045 indicates that the Ni3+ ions are most likely located in the substitutional sites of TiO2, possibly near the surface rutile phase. The Ni+ species (3d9) with g4 = 2.130 and g1 = 2.063 are on the surface of TiO2. Both Ni+ and Ni3+ ions are quite stable in hydrogen. The Ni3+ ions seem to be responsible for anchoring the nickel ions onto titania and stablizing the Ni+ species on the surface. The Ni+ ions are thus free from oxygen poisoning and still show a high activity toward olefin oligomerization.  相似文献   

13.
The reduction of Ni-Mg aluminosilicates with the amesite structure was studied using thermogravimetry, high-resolution electron microscopy, XPS, and XRD. It was found that the reduction with hydrogen at 920 K resulted in the formation of nickel particles coated with a difficult-to-reduce amorphous oxide shell. The reduced samples were incapable of chemisorbing oxygen; however, they exhibited a high adsorption capacity for hydrogen. The Ni0 core-oxide shell decorated particles were highly active in steam methane reforming and CO hydrogenation reactions. At the same time, they were inactive in the formation of graphite-like carbon in both methane decomposition and CO disproportionation.  相似文献   

14.
The effect of the metal cations, Na+, K+, Ca2+, Mg2+, Zn2+, and Ni2+, on the oxide film structure and morphology changes during long-term immersion corrosion tests of aluminum alloy (A3003) in model tap waters was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. The effect of the metal cations on the corrosion behavior was also investigated with mass change and electrochemical tests. The hardness of the metal cations, X, based on the hard and soft acids and bases (HSAB) concept was applied to explain the effect of metal cations on the passive oxide film structure and corrosion resistance. The mass change rate and corrosion current density decreased with increasing metal cation hardness. The XPS results showed that hard metal cations like Zn2+ and Ni2+ were incorporated in the oxide films, while the four soft metal cations were not incorporated in the oxide films. The results are in good agreement with those which could be expected from the HSAB hardness of the metal cations.  相似文献   

15.
The Norrish Type I and Type II reactions in the photolysis of 2-pentanone included within the alkali metal cation-exchanged ZSM-5 zeolite have been investigated by experimental and theoretical approaches. Changes in the molecular environment of the zeolite cavities by exchanging the cations had significant effects not only on the adsorption state but also on the photochemical reactions of the ketones included within the zeolite cavities. The yields of the photolysis decreased and the ratio of the Type I/Type II reactions increased, respectively, by changing the ion-exchanged cations from Cs+ to Li+. The observed IR and phosphorescence spectra of the adsorbed ketones and the ab initio molecular orbital calculations of this host-guest system indicate that the ketones interact with two different adsorption sites, i.e. the surface OH groups and alkali metal cations, while the interaction between the ketones and cations increased by changing the cations from Cs+ to Li+. Molecular orbital calculations were also carried out and indicated that the zeolite framework promotes the delocalization of the charge density of the alkali metal cations which can modify the interaction between the adsorbed ketones and cations, resulting in significant changes in the photolysis of these ketones.  相似文献   

16.
Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N2O decomposition. The amount of Cu2+ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu2+ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO x properties of Cu-ZSM-5 depend considerably on the NH4OH/Cu2+ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH4OH/Cu2+ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu2+ ions bonded with extraframework oxygen, which are more active in DeNO x than isolated Cu2+ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH4OH/Cu2+ = 3).  相似文献   

17.
Improved synthetic approaches for preparing small‐sized Ni nanoparticles (d=3 nm) supported on HBEA zeolite have been explored and compared with the traditional impregnation method. The formation of surface nickel silicate/aluminate involved in the two precipitation processes are inferred to lead to the stronger interaction between the metal and the support. The lower Brønsted acid concentrations of these two Ni/HBEA catalysts compared with the parent zeolite caused by the partial exchange of Brønsted acid sites by Ni2+ cations do not influence the hydrodeoxygenation rates, but alter the product selectivity. Higher initial rates and higher stability have been achieved with these optimized catalysts for the hydrodeoxygenation of stearic acid and microalgae oil. Small metal particles facilitate high initial catalytic activity in the fresh sample and size uniformity ensures high catalyst stability.  相似文献   

18.
The ionic exchange of the NaX zeolite by Ni2+ and Cr3+ cations was progressively driven and studied by adsorption of nitrogen and carbon dioxide. For each cation-exchanged X zeolite sample, the development of characteristics such as profile of isotherms, RI criterion, isosteric adsorption heat and microporous volume using both the Dubinin–Radushkevich (DR) equation and the t-plot, was followed through the nitrogen adsorption. Results show that the cationic exchange process, in the case of Cr3+ introduced at middle degree, is accompanied by a textural damage for Cr(x)X, in contrast to Ni2+-exchanged X zeolites. This degradation occurs without significant presence of mesopores, because the RI criterion values were found to be much lower than 2.2. The CO2 adsorption isotherms were measured at intervals of 30 K from 273 K and the equilibrium pressures ranged from 0.5 to 600 Torr. The experimental data were correlated by the Toth model. The associated three adjustable parameters were estimated by nonlinear least-squares analysis. The effect of temperature on the model parameters and the Henry’s law slope, K H , represented by the product of Toth parameters, are discussed.  相似文献   

19.
Studies on Oxide Catalysts. XXXV. Redoxbehaviour of Nickel in Zeolite NiNaY. 2. Investigation on the Dispersion of Ni- und Ni/NiO-Species in Reduced and Reoxidized NiNaY Samples Oxygen chemisorption and electronmicroscopic measurements (ultramicrotome technique) correspondingly show a decrease of the metal dispersion with increasing reduction temperature (470–870 K) and exchange degree (10, 29, 54 equ.-% resp.). Contrary to this results electronmicroscopic measurements with replica technique don't reflect such a dependence. Increase of particle size after reoxidation (470 K) and reduction at 470 to 870 K (regeneration) of the NiNaY samples are attributed on the one hand to the aggregation of oxidic particles and on the other hand to metal sintering by the subsequent reduction step. A decrease of dispersion after a reoxidation process at 670 K is caused by formation and relocalisation of isolated nickel ions.  相似文献   

20.
A new approach has been developed to simultaneously analyse the evolution of metallic cation and inorganic anion solution concentrations within a crevice micro-environment using capillary electrophoresis. The chemical conditions within a Cortest crevice assembly have been studied when the bold surface of nickel–aluminium bronze was exposed to a bulk 3.5% (0.6 M) NaCl solution. The crevice solution chemistry was assessed intermittently over a period of 6 months. Capillary electrophoresis was used since it is capable of analysing nanolitre solution volumes with widely disparate concentrations of species. A methodology has been optimised for the first time to simultaneously evaluate inorganic anion and metal cation crevice solution composition, without the need for extensive sample pre-treatment. Analyses for chloride and a range of metal cations, including Cu2+, Ni2+ and Fe3+ are presented.  相似文献   

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