Aluminum chloride grafted mesoporous molecular sieves as alkylation catalysts (original) (raw)
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Microporous and Mesoporous Materials, 2003
A series of mesoporous molecular sieves (AlMCM-41) were synthesized with varying silicon-to-aluminium ratios and using three different aluminium sources, viz., sodium aluminate, aluminium isopropoxide and aluminium sulphate. The samples were characterized systematically using XRD, TG-DTA, BET surface area, and ICP-AES. In addition, the extent of framework substitution as well as the nature of acid sites was deduced employing 27 Al MAS-NMR, pyridine FT-IR, and NH 3 -TPD methods. These studies indicate that in case of samples prepared with sodium aluminate, most of the aluminium existed in tetrahedral positions even after calcination. Also, such samples posses moderate-to-strong (Br€ o onsted) acid sites along with small amounts of structural as well as non-framework Lewis acid sites. The density of non-framework acid sites depended upon the source of aluminium following a trend in the order of sodium aluminate < aluminium sulphate < aluminium isopropoxide. Among the various catalysts investigated, those having a silicon-toaluminium ratio of around 60 irrespective of aluminum sources exhibited highest conversion and good selectivity for vapour phase tertiary-butylation of phenol. This characteristic is attributed to the presence of larger number of moderate-to-strong acid sites and a smaller number of Lewis acid sites.
Catalysis today, 2000
Mesoporous AlMCM-41 molecular sieves were synthesized using various aluminium sources, viz., sodium aluminate, aluminium sulphate, aluminium isopropoxide and pseudoboehmite. The influence of different aluminium sources on the framework substitution of aluminium as well as on the catalytic properties of t-butylation of phenol was studied. Among the aluminium sources, the use of sodium aluminate for the AlMCM-41 synthesis showed maximum incorporation of aluminium in the framework. Further, the catalyst also showed good catalytic activity for the chosen reaction.
Mesoporous molecular sieves: alkylation of anisole usingtert-butylalcohol
Catalysis Letters, 2006
Mesoporous aluninosilicate Al-MCM-41 molecular sieves with Si/Al ratios 25, 50, 75 and 100 have been synthesized under hydrothermal condition and these materials were characterized by XRD, FTIR, BET and pyridine adsorption techniques. The catalytic performance was examined in the vapor phase tert-butylation of anisole with tert-butanol at the temperatures between 150 and 250 °C under atmospheric pressure. The results indicate that Al-MCM-41 (25) was found to be more active than its relatives. The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4-DTBA). Maximum conversion of anisole is observed at 175 °C and decreased thereafter with increasing temperature. The influence of molar feed ratio, influence of temperature, WHSV and time on stream on the selectivity of products was investigated and the results are discussed.
Alkylation and disproportionation of aromatic hydrocarbons over mesoporous molecular sieves
Microporous and Mesoporous Materials, 2001
Toluene alkylation with propylene and trimethylbenzene (TMB) disproportionation were investigated over mesoporous molecular sieves of MCM-41 type of dierent pore dimensions, possessing various Si/Al ratios or modi®ed with heteropoly acids (HPA) of Keggin type. It was shown that the acid strength of (Al)MCM-41 was sucient to activate propylene in the alkylation of toluene providing cymene selectivity over 96% while the rate of consecutive reactions was negligible. In contrast, TMB disproportionation proceeded at a signi®cantly lower extent than over zeolites. Siliceous MCM-41 modi®ed by HPA (HPA-MCM-41) exhibited a lower rate of cymene isomerization compared to (Al)MCM-41. Moreover, m-cymene was mainly formed at the expense of o-cymene. In TMB disproportionation over HPA-MCM-41 HPA H 6 PV 3 Mo 9 O 12 signi®cantly higher concentrations of xylenes were reached in comparison with (Al)MCM-41. m-and o-xylenes as primary products of TMBs disproportionation were preferentially formed. Ó
Mesoporous silica-aluminas as catalysts for the alkylation of aromatic hydrocarbons with olefins
Microporous and Mesoporous Materials, 1999
Two amorphous mesoporous silica-aluminas are compared with the amorphous microporous silica-alumina (ERS-8) and the zeolite beta in the liquid-phase alkylation of toluene with propylene. The catalytic activity, the selectivity to o-, m-and p-cymenes and the formation of polyalkylates are discussed as a function of acidity and porosity. The catalytic behaviour of MSA, MCM-41, ERS-8 and zeolite beta is also compared with data reported in the literature for traditional alkylation catalysts (AlCl 3 -HCl and supported phosphoric acid, SPA) and for other acidic zeolites. MSA and MCM-41 show alkylation activities comparable with zeolite beta, while their isomerization and transalkylation activities are lower than those of zeolite beta and AlCl 3 -HCl, but similar to SPA. Such behaviour is in agreement with the Brønsted acidity of the materials studied.
Journal of Molecular Catalysis A: Chemical, 2007
Iron-containing aluminophosphate molecular sieves were synthesized in AEL and AFI structure types by static hydrothermal crystallization. These materials have been characterized by elemental analysis, X-ray diffraction, scanning electron microscopy, N 2 adsorption-desorption, temperature programmed desorption of ammonia (NH 3 -TPD), and 57 Fe Mössbauer spectroscopy. Alkylation of benzene and other aromatics by benzyl chloride has been investigated over these solids. Indeed, the iron containing microporous aluminophosphates showed both high activity and high selectivity for this reaction. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > pxylene > anisole. More interesting is the observation that this catalyst can be reused in the benzylation of benzene for several times. Kinetics of the benzene benzylation over these catalysts has also been investigated.
Benzylation of benzene by benzyl chloride over iron mesoporous molecular sieves materials
Journal of Catalysis, 2004
The alkylation of benzene with benzyl chloride has been investigated over a series of iron-containing mesoporous silicas with different Fe contents. These materials (Fe-HMS-n) have been prepared at room temperature using a route based on hydrogen bonding and self-assembly between neutral primary amine micelles (S 0 ) and neutral inorganic precursors (I 0 ). They have been characterized by chemical analysis, BET, XRD, and UV-vis spectroscopy. The mesoporous Fe-containing materials were very active benzylation catalysts with almost 100% selectivity to monoalkylated product and showed excellent stability. The kinetics of the benzene benzylation over this catalyst have been thoroughly investigated. A mechanism in which the reaction could be initiated by an oxidation of benzyl chloride with formation of a charge transfer complex is proposed. (J.M.M. Millet).
Benzylation of benzene and other aromatics by benzyl chloride over mesoporous AlSBA-15 catalysts
Microporous and Mesoporous Materials, 2005
Aluminum-containing mesoporous molecular sieves AlSBA-15 with different n Si /n Al ratios and AlMCM-41 have been synthesized hydrothermally and characterized in detail by physicochemical methods, viz. XRD, N 2 adsorption and 27 Al NMR spectroscopy. The low angle XRD and N 2 adsorption measurements reveal that the structural order of SBA-15 was retained after the incorporation of Al. The increase of the unit cell parameter with increasing aluminum content and 27 Al MAS NMR spectroscopy confirm the incorporation of aluminum in the framework. Benzylation of benzene and substituted benzenes reaction employing benzyl chloride as the alkylating agent over AlSBA-15 and AlMCM-41 have been investigated. The influence of various reaction parameters such as reaction temperature, reactant feed ratio and catalyst amount affecting the activity and selectivity of AlSBA-15, have been studied. Among the mesoporous catalysts studied, , where the number in parentheses indicates the molar n Si /n Al ratio, shows both high conversion and high selectivity for the benzylation of benzene. The activity of this catalyst for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > mesitylene > anisole. Kinetics of the benzene benzylation over different catalysts have also been investigated.
Microporous and Mesoporous Materials, 2012
Hierarchical molecular sieves possess the characters of both microporous molecular sieves and mesoand/or macro-porous materials, and have potential application in adsorption and separation of macromolecules and diffusion limited catalytic reactions. In this work, hierarchical MeAPO-5 (MeAPO-5-meso, Me = Co, Mn, Fe, Mg and Ti) molecular sieves were synthesized directly using glucose as mesopore template. The synthesized MeAPO-5-meso molecular sieves were characterized by X-ray diffraction, X-ray fluorescence, N 2 physisorption, thermogravimetric analysis and scanning electron microscopy. It was proved that mesopores with the pore size distribution of 5-30 nm were introduced to MeAPO-5-meso. The improvement effect of the introduced mesopores on the catalytic performance of MeAPO-5-meso (Me = Mn, Fe and Co) was investigated in the oxidation of various hydrocarbons with different molecular dimensions including cyclohexene, ethylbenzene, indan, tetralin, diphenylenemethane and fluorene. For comparison, these oxidation reactions were also performed over the ordinary MeAPO-5. The results indicated that mesopores benefited the diffusion of the reactants and the products, so the conversion of the reactants was improved while the selectivity of the products was slightly improved or maintained at higher conversion. In addition, the promotion effect is dependent on the dimension of the substrates with respect to the micropore size of molecular sieves.