Dimerization of n-butenes on nickel mordenite catalysts

The catalytic activity of synthetic and natural nickel exchanged mordenites of different compositions has been investigated in dimerization of n-butenes at high pressure in the liquid phase. High selectivities to n-octenes and methylheptenes were found. It is suggested that the mordenite channel structure influences the product distribution.

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- . - . .

     

Diffusion of hydrocarbons in mordenite and molecular-sieve selectivity of mordenite catalysts

The diffusion of n-octane and n-propylbenzene in mordenite and the molecularsieve selectivity in hydrocracking of octane-propylbenzene binary mixtures over a mordenite catalyst have been studied. The hydrocarbon diffusivities and molecular-sieve selectivity change are accounted for by diffusion through mordenite channel mouths poisoned with an easily adsorbable hydrocarbon.

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- , () -. , , .

     

Magic angle spinning29Si and27Al NMR study of mordenite dealumination

Magic angle spinning²⁹Si NMR presents a rapid qualitative method of assessing the degree of dealumination of sodium mordenite modified by acid leaching and heat treatment. A quantitative determination of the²⁹Si coordination sphere is hampered by the overlap of chemical shift ranges for Si?O?Al and Si?O?H species. MAS²⁷Al NMR indicates the presence of octahedrally coordinated Al in interstitial sites in all treated samples. On treating mordenite samples at high temperatures (～700°C) much of the Al becomes invisible to the NMR experiment because of its location in sites of low symmetry and large quadrupole coupling constant.     

Characterization of nickel loaded mordenite catalysts by temperature programmed reduction

Temperature programmed reduction (TPR) has been used to study the redox behavior of Ni(II) ions in nickel sodium mordenite (NiNaM) and decationated nickel mordenite (NiHM). The TPR profiles suggest that Ni(II) ions occupy nonequivalent sites with different cooridination states in the mordenite. The reducibility of Ni(II) depends strongly on the zeolite acidity.

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() Ni^II NiNaM NiHM. . .

     

制备条件对磷化钼加氢脱硫催化活性的影响

采用程序升温还原方法制得磷化钼(MoP)催化剂,在常压连续微型化反应装置中,以噻吩为模型化合物,对催化剂的加氢脱硫活性进行评价。考察了还原温度、磷钼摩尔比、不同磷源等制备条件对MoP催化活性的影响。实验结果表明,在MoP生成温度区间内,随着还原温度的升高,催化剂活性降低;磷钼摩尔比为1∶1时,噻吩转化率最高,而磷钼摩尔比为1∶2和2∶1时制备催化剂的催化活性相当;采用磷酸二氢铵、磷酸铵以及磷酸为磷源,均可制得磷化钼,而以磷酸二氢铵为磷源时制备磷化钼催化剂的活性最佳。在噻吩加氢脱硫反应条件下反应后,不同磷源制备的磷化钼整体物相均没有发生变化。     

Effect of the electronic structure on hydrogenation of 4-tert-butylphenol on metallic catalysts

A quantum chemical analysis of the hypothetical mechanisms of hydrogenation of 4-tert-butylphenol was conducted with the reactivity index method using the INDO approximation. The effect of the form of adsorption of 4-tert-butylphenol on perturbations of ring aromaticity was examined.D. V. Sokol'skii Institute of Organic Catalysis and Electrochemistry, Kazakh Academy of Sciences, 480100 Alma-Ata. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1033–1037, May, 1992.     

Thermal characterisation of molybdenum and platinum-molybdenum catalysts

Alumina supported Mo and Pt-Mo catalysts was subject to temperature programmed reduction (TPR) using H₂ and CO. After earlier oxidation step TPR–H₂ profiles shows different surface species, which depends on the composition of the catalysts and reduction temperature. Change in reducing gas from H₂ into CO results in significant changes in catalyst system. Hydrogen causes a decrease in oxidation number of metals, while carbon monoxide reacts with chemisorbed chemicals.     

State of molybdenum in silica-molybdenum oxide catalysts

In the synthesis of silica-molybdenum oxide catalysts by spray drying of an aerosol suspension in an aqueous ammonium paramolybdate a silicamolybdenum heteropolyacid (SMA) is formed which is not decomposed up to 500–600°C due to stabilization of the heteropolyanion by the support surface.

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, 500–600°C .

     

Effect of structural defects on the electronic structure and stability of cubic molybdenum carbide

Institute of Chemistry, Ural Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 2, pp. 19–24, March–April, 1989.     

Para-selectivity of SAPO-5 and mordenite catalysts in the alkylation of cumene with 2-propanol

Alkylation of cumene with 2-propanol was studied on SAPO-5 and mordenite catalysts. The primary products of the alkylation on every catalyst examined here were p- and m-diisopropylbenzene (DIPB) in a ratio of 75:25. The p-DIPB fraction in DIPB isomers (para-selectivity) decreased with increasing yield of DIPB, due to the secondary reaction of p-DIPB to m-DIPB. On SAPO-5, mordenite and silica-alumina, this secondary reaction proceeds through dealkylation of p-DIPB to cumene, followed by re-alkylation of the resultant cumene to m-DIPB. The dealkylation of p-DIPB would occur preferentially over that of m-DIPB. This was due to the higher reactivity of p-DIPB and probably to the reactant molecular shape selectivity of SAPO-5 and mordenite. The para-selectivity was improved by supporting boron oxide on SAPO-5 and mordenite; this improvement was caused by suppression of the secondary dealkylation of p-DIPB.     

Surface species in the direct amination of methanol over Brønsted acidic mordenite catalysts

Quantitative in situ infrared spectroscopy in combination with kinetic analysis is utilized to derive mechanistic aspects for the reaction of methanol with ammonia on Brønsted acidic mordenite. Under non-reactive conditions, a coadsorption complex between methanol and ammonia is found, in which only ammonia is in direct interaction with the Brønsted acid sites of the zeolite. This complex is proposed to be the precursor for the formation of protonated methylamines in the zeolite pores which are formed in sequential order up to tetramethylammonium ions. These methylamines are unable to desorb under reaction conditions in the absence of ammonia. They leave the surface either by ammonia adsorption assisted desorption or by scavenging of methyl groups from protonated methylamines by ammonia. Both steps are concluded to be potentially rate determining.     

Effect of titania structure on the properties of its supported copper oxide catalysts

A facile and rapid microwave irradiation method was explored for the synthesis of bismuth phosphate (BiPO(4)) nanostructures with various morphologies and phases in different solvents. The BiPO(4) products were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflection spectroscopy (DRS). The effect of the solvents on the formation of the BiPO(4) nanostructures was discussed on the basis of experimental results. The different BiPO(4) nanostructures exhibited different optical properties, BET surface areas and photocatalytic activities on the degradation of methyl orange (MO) under UV and visible light irradiation. The experimental results suggested that the photocatalytic activity was closely relative with the crystalline phase and band gap of BiPO(4). Hexagonal BiPO(4) nanoparticles with narrow band gap showed the highest photocatalytic performance.     

Effect of molybdenum on the structure formation of resorcinol-formaldehyde hydrogel studied by coherent x-ray scattering

A detailed study on the effect of Mo on the gelation process of resorcinol-formaldehyde systems is presented. The evolution of the system was followed by x-ray photon correlation spectroscopy, which allows in situ investigation of the dynamics as well as of the structural evolution in non-equilibrium processes. The Mo was introduced into the system after a pre-polymerization period (PP), the effect of which was also examined. Our results show that the presence of Mo substantially modifies the gelation process by favoring the growth of large compact clusters with weak bonds between them. However, this effect can be reduced by increasing PP.     

Mechanisms of methane activation and transformation on molybdenum oxide based catalysts

We present a comprehensive survey of different C-H activation pathways over various kinds of active sites of terminal oxygens [=O] and bridge oxygens [-O-] by using Mo3O9 model systems. This allows us to provide some insights into fundamental issues concerning C-H activation by metal oxo species involved in many heterogeneous, homogeneous, and enzymatic processes. We show that H abstraction is the most feasible reaction pathway for the activation of a C-H bond on molybdenum oxides; and that [=O] is more active than [-O-]. Our calculations also suggest that (2+2) can be an alternative if M=O bond possesses a high polarity, while (5+2) can provide another effective pathway if two M=O bonds are in close proximity. Implications for the related heterogeneous, homogeneous, and enzymatic processes are discussed.     

Influence of chemical dealumination on the properties of USY zeolite

Three series of dealuminated Y zeolites have been prepared by chemical extraction ofhydrothermally dealuminated Y zeolite(USY)with H_2Na_2EDTA,HCl and H_4EDTA.The unitcell constant,mesopore distribution,acidity and extraframework aluminum(EFAL)of thezeolites were studied with XRD,chemical analyses,adsorption,IR and NH_3-TPD techniques.It was shown that H_2Na_2EDTA only removed EFAL species deposited in the pores of USY,by contrast,HCl and H_4EDTA extract both extraframework and framework aluminum,andmake the zeolite framework further dealuminated.Adsorption tests gave evidence that a second-ary pore system exists in these dealuminated zeolites.H_2Na_2EDTA extraction increased bothmicropore and mesopore volumes,but after HCl and H_4EDTA treatments,new mesopores formedand the micropore volume was decreased.The pyridine-IR and NH_3-TPD measurements demon-strated that EFAL had no evident contribution to the zeolite acidity.     

调控制备pH值对铁钼催化剂结构及性能的影响

通过调控共沉淀中钼酸铵溶液的酸度制备了系列铁钼催化剂,采用N_2吸附-脱附、Raman、XRD、SEM、H2-TPR等方法对催化剂的结构进行了表征,并考察了不同酸度条件下制备的铁钼催化剂的甲醇氧化制甲醛催化活性。结果表明,钼酸铵溶液酸度影响催化剂的粒径、形貌及表层铁、钼物种的分布与富集。恰当的钼酸铵溶液酸度范围,优化了催化剂表层MoO_3和Fe_2(MoO_4)_3物种的比例,改善了催化剂的催化氧化性能,有利于甲醇氧化制甲醛收率和选择性的提高。     

ESR studies of the state of molybdenum in silica-molybdenum oxide catalysts

In the synthesis of catalysts on SiO₂ a silica-molybdenum heteropolyacid stable up to 500°C is formed. Its dehydration due to a thermal treatment distorts the octahedral oxygen ligand environment of Mo ions in the heteropolyanion and localizes the unpaired electron captured in reduction.

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SiO₂ , 500°C. .

     

Studies of molybdenum in Mo?Ti oxide catalysts

ESR studies indicate that in Mo–Ti oxide catalysts prepared via the addition of ammonium paramolybdate to pasted titanium hydroxide, Mo⁵⁺ ions are observed in three states: in heteropoly blue, disperse MoO₃ and a solid substitutional solution in TiO₂.

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, , - , - Mo⁵⁺— , MoO₃ TiO₂.