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1.
Studies on Nickel Oxide Mixed Catalysts. XI. Surface Chemical Properties of NiO/SiO2 Catalysts NiO/SiO2 catalysts with different composition prepared by precipitation have been investigated which are characterized by a nickel layersilicate-like structure. The determination of the surface chemical properties was carried out by infrared spectroscopy (before and after pyridine adsorption), 1H-NMR-measurements, chemisorption of ammonia, and titration with n-butylamine. It has been found three kinds of hydroxid groups which are assigned to Ni? OH and Si? OH groups with respect to investigations on definite nickel layersilicates. Furthermore, coordinatively unsaturated NiII surface sites were indicated. The number of the OH groups as well as the centers determined by chemisorption of bases increase with increasing NiO content. The obtained results allow the conclusion that the OH groups and the coordinatively unsaturated NiII surface sites are weakly acid. 相似文献
2.
Studies on Nickel Oxide Mixed Catalysts. XV. Surface Chemical Properties of NiO/Al2O3-SiO2 Catalysts Surface chemical properties of precipitated NiO/Al2O3? SiO2 catalysts different compositions and the corresponding Al2O3? SiO2 carriers have been investigated. Infrared spectroscopic measurements (before and after adsorption of pyridine and ammonia), 1H-n.m.r. and ammonia adsorption measurements showed that the number of the Lewis-acidic sites are increased mainly by incorporation of the nickel component on the X-ray amorphous Al2O3? SiO2 carriers, whereas the number of the hydroxide groups do not change significantly. With growing alumina content the number and the strength of the Lewis-acidic sites are increased where the part of the NiII surface sites decreases and those of the AlIII surface sites increases. Brönsted-acidic sites are detectable at high alumina contents. 相似文献
3.
Studies on Nickel Oxide Mixed Catalysts. XVI. Reduction Behaviour of Amorphous NiO? Al2O3/SiO2 Catalysts The reduction behaviour of NiO? Al2O3/SiO2 catalysts prepared by precipitationdeposition is influenced by the phase composition (amorphous nickel layersilicates and nickel alumino layersilicates, nickel spinels, nickel oxide) and the differences of the composition between surface and bulk. TPR measurements, determinations of the reduction degree, and the nickel particle sizes by static magnetic measurements showed that the reducibility of the NiO? Al2O3/SiO2 catalysts is enhanced and the nickel dispersity is decreased at low Al2O3 contents. The decrease of the reducibility at Al2O3 contents >5 mole% is caused by the formation of nickel spinels and the decrease of the NiII ion surface concentration. 相似文献
4.
Studies on Catalytically Active Surface Compounds. XIII. Structure and Catalytic Properties of Molybdenum Oxide/SiO2 Catalysts The catalytic properties of Mo oxide/SiO2 catalysts in the selective oxidation of methanol to formaldehyde are described. It is shown that, independently on the preparation conditions, all catalysts showed relative high activity and selectivity values which were however, not constant during the reaction time. The high initial activity could be stabilized to a limited extent both by prereduction with methanol (but not with hydrogen) and by decreasing the oxygen concentration of the reaction gas. ESR measurements showed that in dependence on the means of reduction (methanol or hydrogen) two different coordinated Mo5+ ions were formed. Evidence was given by IR spectroscopy that prereduction in methanol caused the formation of methoxy groups stabilizing catalytically active Mo5+ ions. UV-Vis, ESCA, and electron microscopic measurements showed however, that further aggregation and formation of microcrystallites of MoO3 took place during the catalytic reaction which caused the observed decrease of the activity. 相似文献
5.
Effect of Alkali Contamination on the Catalytic Properties of Al2O3? Si2 Catalytic properties of amorphous Al2O3? SiO2 catalysts containing different amounts of Al2O3 in dehydration of isopropanol and cracking of cumene were examined after a defined contamination of the acid centers by sodium ethylate from alcoholic solution. In both reactions, the catalytic activity is decreased by treatment with sodium ethylate, the cracking of cumene being suppressed at a lower alkali concentration than the dehydration of isopropanol. In dehydration of isopropanol, the dependence of the catalytic activity on the alkali content is influenced strongly by the Al2O3 content of the catalysts. In the cracking of cumene, strongly acid Brönsted centers are active, whereas the dehydration of isopropanol proceeds by joint action of acid Lewis or Brönsted centers, respectively, with basic centers at the surface of the catalyst (hydroxide groups or oxygen anions). 相似文献
6.
7.
Structural Investigations on Cs2[B12H12] The crystal structure of Cs2[B12H12] has been determined from X‐ray single‐crystal data collected at room temperature. Dicesium dodecahydro‐closo‐dodecaborate crystallizes as colourless, face‐rich crystals (cubic, Fm 3; a = 1128.12(7) pm; Z = 4). Its synthesis is based on the reaction of Na[BH4] with BF3(O(C2H5)2) via the decomposition of Na[B3H8] in boiling diglyme, followed by subsequent separations, precipitations (with aqueous CsOH solution) and recrystallizations. The crystal structure is best described as anti‐CaF2‐type arrangement with the Cs+ cations in all tetrahedral interstices of the cubic closest‐packed host lattice of the icosahedral [B12H12]2–‐cluster dianions. The intramolecular bond lengths are in the range usually found in closo‐hydroborates: 178 pm for the B–B and 112 pm for the B–H distance. Twelve hydrogen atoms belonging to four [B12H12]2– icosahedra provide an almost perfect cuboctahedral coordination sphere to the Cs+ cations, and their distance of 313 pm (12 ×) attests for the salt‐like character of Cs2[B12H12] according to {(Cs+)2([B12H12]2–)}. The 11B{1H}‐NMR data in aqueous (D2O) solution are δ = –12,70 ppm (1JB–H = 125 Hz), and δ = –15,7 ppm (linewidth: δν1/2 = 295 Hz) for the solid state 11B‐MAS‐NMR. 相似文献
8.
Investigations on Metal Catalysts. XI. Investigations on Pt? η-Al2O3 Catalysts Modifieded by Iron, Cobalt, and Nickel Pt? Me? η-Al2O3 catalysts (M: Fe, Co, Ni) were characterized by magnetic investigations, reflectance spectra and determination of dispersity (chemisorption of CO, oxygen-hydrogen titration), respectively. The phase structure of platinum-rich catalysts is composed of a high degree by Pt3Fe super-structure. All the Pt? Fe? η-Al2O3 catalysts contained FeIII ions in octahedral symmetry. The dispersity of the metallic components is determined essentially by their phase structure. 相似文献
9.
Yu. P. Sayzev K. M. Kholyavenko V. A. Zazhigalov V. M. Belousov B. Parlitz K. Wencke R. Fricke G.
hlmann 《无机化学与普通化学杂志》1981,479(8):199-211
Studies on Catalytically Active Surface Compounds. VII. Catalytic Properties of Oxidic Vanadium-Chromium Catalysts The catalytic properties of silica supported vanadium-chromium catalysts for the oxidation of ethanol, butane, propene, and butene are described and completed by ESR measurements. Differences in catalytic activity of chromium-free vanadium catalysts which are caused by different values of the silanol group concentration of the support are shown to become levelled by the addition of chromium. V? O? Cr species of medium catalytic activity are considered to be the catalytic active center. ESR spectra taken after the reaction show the existence of Cr3+ and VO+2 species. A correlation between the intensity of the VO2+ signal and the catalytic activity of the samples is observed. 相似文献
10.
B. Unger K.-P. Wendlandt H. Bremer W. Reschetilowski D. Freude P. Kraak 《无机化学与普通化学杂志》1988,566(1):39-48
Studies on Oxide Catalysts. XLVI. Synthetic Boroaluminosilicates with Pentasil Structure (SABO): Structural, Surface Chemical, and Catalytical Properties A remarkable modification of ZSM-5 type zeolites is possible by isomorphous substitution of silicon and/or aluminium by boron. In the H-forms of these SABO zeolites the boron atoms mainly exist in a trigonal lattice oxygen environment and hence they are not envolved in the formation of Broensted acid sites. Consequences of incorporated boron for catalytic reactions result from a decrease in the strength of existing Broensted sites as well as from a partial lattice contraction. 相似文献
11.
Investigations on Metal Catalysts. XIV. Physico-chemical and Catalytical Properties of Palladium-Rhenium Catalysts Characterization of carrier-free Pd? Re catalysts with regard to their phase structure, dispersity and catalytical activity were performed by X-ray measurements, sorption methods (adsorption of N2, chemisorption of CO, sorption of H2), and catalytical investigations (dehydrogenation of cyclohexane, hydrogenation of benzene). The dispersity of the catalysts is influenced by thenium to a remarkable extent. There are references, that the composition of the bulk phase and the surface layer of the crystallites differs from each other. Also a synergistic effect in catalytical activity is caused by rhenium. The similarities between Pd? Re and Pt? Re catalysts are discussed briefly. 相似文献
12.
Structural and Magnetic Investigations of Hexachlorotungstates(V) CsWCl6 crystallizes in the monoclinic space group C2/c with the lattice dimensions a = 12.097(8), b = 6.327(5), c = 15.30(1) Å, β = 128.4(1)° and 4 formula units. The compounds AWCl6 (A = Rb, K, NH4) are isotypic with CsWCl6 as shown by powder patterns. Single-crystal photographs of [N(C2H5)4]WCl6 show monoclinic symmetry, space group P21/n with a = 11.737(8), b = 10.239(7), c = 7.191(5), β = 101.46(8)° and Z = 2. Both structures are composed of scarcely deformed WCl6 octahedra. The trigonal compression of the octahedra results in a slightly negative deformation parameter according to the Figgis-model of the magnetic behaviour of d1-systems. Above 80 K the μ2 vs. T-curve is linear. This leads to a spin-orbit coupling constant of 1250 ± 200 cm?1 and a covalence parameter of 0.6–0.8. Comparing the spectra of WCl6, CsWCl6 and Cs2WCl6 the beginning of the charge-transfer region was determined. The crystal field strength for CsWCl6 was found as Δ = 16 000 cm?1. 相似文献
13.
Fred von Lampe 《无机化学与普通化学杂志》1985,524(5):168-176
Investigations on Belites and Dicalcium Silicates. I. Investigations of the Oxidation Number and the Crystallographic Position of Mn-Ions in the Crystal Lattice of Mn-doped Ca2SiO4 Light-blue Mn-doped monocrystals of Ca2SiO4 were grown from a CaCl2 flux using raw mixes (2 CaCO3 + 1 SiO2) with different contents of MnCO3. The MnO content in these crystals ranges up to ~0.50% and decreases with increasing duration of crystal growth thus generating a Mn profile in the crystals obtained. The oxidation number of Mn is predominantly 2+, but a little amount of Mn with a higher oxidation degree is also present. Some experiments suggest the existence of Mn5+ ions in the crystals. Mn2+ ions substitute Ca2+ ions in their irregular coordination polyhedra (coordination number 7 and 8), whereas Mn ions of higher valency substitute Si4+ ions in tetrahedra. 相似文献
14.
G. Recker 《无机化学与普通化学杂志》1976,423(3):242-254
Formation and Properties of Acylphosphines. I. Mono Substitution Reactions of Substituted Disilylphosphines with Pivalie Chloride Between ?30°C and ?10°C one trimethylsilyl group of substituted bis(trimethy1-sily1)phosphines is replaced by the acgl moiety in the reaction Rith pivalic chloride. The keto forms are thermally labile arid rearrange with migration of the silyl group from phosphorus to oxygai just below room temperature. The new compounds (enol forms) we stable in the absence of moisture and air and show an unusual structure with a P? C double bond. The spectroscopic properties are discussed. 相似文献
15.
K.-H. Steinberg H. Bremer F. Hofmann Ch. M. Minachev R. V. Dmitriev A. N. Detjuk 《无机化学与普通化学杂志》1974,404(2):129-141
Hydroxide Groups on Zeolites. I. Number and Properties of Hydroxide Groups on CaNaY and MgNaY Zeolites of Different Degree of Ion Exchange The number of hydroxide groups was studied on CaNaY and MgNaY zeolites by D2 exchange in dependence on the degree of exchange, and their properties were examined by infrared spectroscopy. At these zeolites there exist five types of hydroxide groups which differ by their concentration, their acidic strength, and their thermal stability. The OH-groups are produced mainly by dissociative chemisorption of water at the bivalent cations. The concentration of OH groups shows a characteristic dependence on the degree of ion exchange. There are OH groups which are strongly acid BRÖNSTED centers, capable of protonisation of pyridine, and others which are only capable of weak interactions with pyridine. The number of the acid BRÖNSTED centers increases with the degree of ion exchange analogous to the total number of the hydroxide groups and is highly dependent on the species of the cations exchanged and on the preheating temperature. Compared with CaNaY zeolites, MgNaY zeolites posess a greater number of hydroxide groups which are thermally more stable. 相似文献
16.
17.
F. Vogt H. Wolf H. Bremer A. M. Rubintejn A. L. Klja
ko T. R. Brueva I. V. Min 《无机化学与普通化学杂志》1978,439(1):153-160
Studies on Oxide Catalysts. XXIV. Adsorption and Catalytic Properties of CeNaY and CrNaY Zeolites The adsorption of benzene, n-butylamine and ammonia(isotherms and heats of adsorption) on CeNaY and CrNaY zeolites of different exchange degrees has been measured. The acidic properties were characterized by titration with n-butylamine. As function of exchange degree the adsorption and catalytic properties (cracking of cumene) both change in the same manner. Whereas the reaction rate constants up to exchange degrees of 40–50% change only insignificantly, they are exponentially increasing at higher exchange degrees. The energies of activation are nearly independent of the degree and run to 23–25 kcal mol?1. 相似文献
18.
Mingfang Zheng Tianbo Zhao Wenguo Xu Fengyan Li Yue Yang 《Journal of Sol-Gel Science and Technology》2006,39(2):151-157
CuO/SiO2 and NiO/SiO2 with bimodal pore structure were prepared by sol-gel reactions of Tetra-methoxysilane (TMOS) and the respective metal nitrate
in the presence of poly (ethylene oxide) (PEO) with an average molecular weight of 10 000 and the catalyst of acetic acid.
In this process, the interconnected macroporous morphology was formed when transitional structures of spinodal decomposition
were frozen by the sol-gel transition of silica. The addition of copper and nickel into the silica-PEO system had a negligible
effect on the morphology formation. In gel formation, it was found that NiO crystalline sizes in the samples increased with
decreasing Si/Ni molar ratio. It was considered that PEO interacted with both silica and nickel cations. In the CuO/SiO2 with the presence of PEO, CuO crystalline sizes were larger than those of NiO/SiO2. It was considered that there was no obvious interaction between the Cu cation and PEO, most of the copper ions in wet silica
gel were present in the outer solution. They easily aggregated as copper salts in the drying process of wet gel and decomposed
into CuO particles in heating. While in the CuO/SiO2 with the absence of PEO, the Cu was selectively entrapped as small particles in the gel skeleton due to the interaction between
Cu aqua complex and silica gel network. 相似文献
19.
Trimethylsilyl Derivatives of Vb-Elements. I. Syntheses and Properties of Trimethylsilylarsanes Chlorotrimethylsilane and ?Na3As/K3As”? prepared from a sodium potassium alloy and arsenic powder in dimethoxyethane form tris(trimethylsilyl)arsane 4 in 80 to 90percent; yield. 4 reacts with methyllithium in THF or dimethoxyethane to lithiumbis(trimethylsilyl)arsenide 5 , which crystallizes with two molecules THF – 5a – or one molecule dimethoxyethane – 5b – per formula unit. The latter adduct is dimeric in benzene. In the reaction of 5 with primary and secondary alkyl halides methyl- 1a , ethyl- 1b , isopropyl- 1c , benzyl- 1d , diphenylmethylbis(trimethylsilyl)arsane 1e and bis[bis(trimethylsilyl)arsano]methane 1f are formed. With tert. butyl chloride a β-elimination results in the formation of bis(trimethylsilyl)arsane; in the reaction with chlorodiphenylmethane and dibromoethane an alkali metal-halogen-exchange takes place yielding tetrakis(trimethylsilyl)-diarsane 6 . On heating bis[bis(trimethylsilyl)arsano]dimethylsilane 7 , synthesized from 5 and dichlorodimethylsilane, to 240°C for several days it decomposes to 4 and dodecamethyl-hexasila-tetra-arsa-adamantane 8 . Tert. butyl- 1g and phenylbis(trimethylsilyl)arsane 1h which cannot be obtained from 5 are prepared from primary arsanes via the corresponding dilithium derivatives. 相似文献
20.
Ja. I. Isakov Ch. M. Mina
ev V. P. Kalinin F. Vogt F. Hofmann H. Bremer 《无机化学与普通化学杂志》1978,445(1):73-78
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