Alkylation and disproportionation of aromatic hydrocarbons over mesoporous molecular sieves (original) (raw)
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Journal of Molecular Catalysis A: Chemical, 2002
Mesoporous aluminosilicate Al-MCM-41 with Si/Al = 93 and 104 were synthesized using cetyltrimethylammonium bromide as the structuring agent and the materials were characterized using several techniques. The mesoporous structure was confirmed by X-ray diffraction (XRD) technique. The surface area, pore size and wall thickness was calculated by BET equation and BJH method using nitrogen sorption technique. Fourier transform-infrared (FT-IR) spectroscopy was used in order to obtain information on incorporated aluminum atoms in the mesoporous structure of Al-MCM-41. Thermogravimetric-differential thermal analyzer (TG-DTA) was used to determine the thermal stability of the materials. The effect of reaction temperature, WHSV and isopropanol:toluene ratios on the selectivity of p-cymene were studied. The Al-MCM-41 (93) catalyst exhibited excellent selectivity in the production of p-cymene by the isopropylation of toluene using isopropanol as the propylating agent.
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.
Aluminum chloride grafted mesoporous molecular sieves as alkylation catalysts
Microporous and Mesoporous Materials, 2005
The aim of this work is to study the influence of different mesoporous molecular sieves (MMSs) type and the effect of pore diameter on MMSs silica grafted aluminum chloride catalysts and their activity in benzene alkylation by 1-dodecene. Four samples (two hexagonal and two wormhole like structures with different pore diameters) were prepared by post-synthesis grafting reaction in moisture free conditions (Schlenk technique). The physico-chemical properties were monitored by N 2 adsorption, XRD, atomic adsorption, 29 Si and 27 Al MAS NMR. Acidity data were obtained by TPD of ammonia, and FTIR of adsorbed pyridine. The alkylation of benzene is carried out in a Schlenk tube under dry conditions at room temperature. The products were analyzed by GC-MS. Grafting aluminum chloride on MMSs increases the yield of monoalkylated products.
Oxidative dehydrogenation of isobutane on MCM-41 mesoporous molecular sieves
Applied Catalysis A-general, 2002
MCM-41 mesoporous molecular sieves containing silicon and vanadium have been prepared by a direct hydrothermal route. Aluminium-containing [Si,Al]-MCM-41 and purely siliceous [Si]-MCM-41 solids were synthesised for comparison purposes. 51 V static and magic-angle-spinning NMR studies of [Si,V]-MCM-41 showed one type of VO 4 in the as-prepared samples (site I) and two types of monodispersed and distorted to various extent VO 4 tetrahedra, chemically bound to the walls of MCM-41 (sites IVa and IVb), in the calcined and rehydrated samples. NMR parameters of vanadium units are given. The catalytic performance of MCM-41 materials was probed in the oxidative dehydrogenation (ODH) of isobutane. The highest selectivities to isobutene (48-59%) were observed for the [Si,V]-MCM-41 materials with Si/V = 85 and 30, respectively.
Activity and selectivity of zeolites MCM-22 and MCM-58 in the alkylation of toluene with propylene
Microporous and Mesoporous Materials, 2002
The influence of the pore architecture of zeolites MCM-22 and MCM-58 on their catalytic activity and selectivity in the gas-phase alkylation of toluene with propylene has been investigated. The results obtained with MCM-22 as catalyst revealed that, despite the expectations due to the presence of 10-membered-ring pores in the structure of this zeolite, no enhanced selectivity to p-cymene is observed. Moreover, also n-propyltoluenes, which are usually formed over threedimensional 10-membered-ring zeolites (e.g., ZSM-5 and ZSM-11) via bimolecular transalkylation/isomerization reactions of cymenes with toluene, are only formed to a negligible extent. This has been rationalized by the assumption that most of the reactions occurring in this system take place on acid sites at or close to the external surface. This is supported by the FTIR-spectroscopic observation that p-cymene can reach only about one half of the bridging OH groups, while the smaller d 3 -acetonitrile reaches/covers virtually all remaining Brønsted and Lewis acid sites. Over zeolite MCM-58, relatively high selectivities to n-propyltoluenes were observed, which has been ascribed to the peculiar undulating 12-membered-ring channel system of this zeolite. It is proposed that the 1,2-p-ditolylpropane-type transition state required for the formation of n-propyltoluenes is preferentially located in positions similar to those which are occupied by the N-benzyl-1,4-diazabicyclo[2.2.2]octane cations used as templates for the synthesis of zeolite MCM-58. Ó
Journal of Catalysis, 2010
Ordered mesoporous molecular sieves of the M41S family, containing their organic template, were evaluated as-synthesized in a basic catalyzed reaction, the transesterification of rapeseed oil with ethanol. These materials [CTA]Si-MCM-48, [CTA]Si-MCM-50, [CTA]Si-MCM-41 (CTA stands for cetyltrimethylammonium cation), which still possess their organic template occluded in the silica pores, were characterized by calorimetry of CO 2 adsorption. These hybrid catalysts present weak basic sites, with low differential heat of CO 2 adsorption between 70 and 90 kJ mol À1 ; however, the adsorption phenomena were disclosed to be totally reversible at 30°C. Surprisingly, these hybrid catalysts were shown to be remarkable catalysts for the transesterification of rapeseed oil with ethanol in mild temperature conditions, 79°C: a total oil conversion was achieved in 1 h with the [CTA]Si-MCM-48, while in equivalent conditions, one of the most efficient mineral solid base, ZrOCs, gave only a conversion of 65%. ZrOCs is considered as a solid base of higher strength, characterized by the heat of CO 2 adsorption of 130 kJ mol À1 ; interestingly, the CO 2 adsorption is totally irreversible at 30°C. The most active material in the hybrid molecular sieves series, [CTA]Si-MCM-48, possesses active sites in intermediate position between physisorption and chemisorption in regard to CO 2 adsorption. This solid is characterized by the presence of the most energetic centers within the hybrid catalysts series with the heat of CO 2 adsorption of 90 kJ mol À1 combined with a complete reversibility of the CO 2 adsorption.
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.
2017
The catalytic activity, selectivity to xylenes and time-on-stream stability were investigated in the transalkylation of toluene with 1, 2, 4-trimethylbenzene. The catalytic tests were carried out in a fixed bed reactor over zeolite Beta (Si/Al = 12.5, 75 and 150) and Y (Si/Al = 2.6, 6, 15 and 30). The operating parameters used were 400 °C, 1.0 Mpa, H2/HC = 4 and WHSV of 5 h-1. The length of each catalytic testing experiment was 50 hours, and for zeolite beta samples, the highest stability and selectivity to xylenes were achieved using the lowest Si/Al ratio with conversion of 41 wt. % and selectivity of 61 wt. %. In contrast, zeolites Y with Si/Al ratio of 2.6 showed the highest deactivation rate, whereas Y zeolites with Si/Al = 6 – 30 exhibited similar conversion (~ 27 wt. %) and selectivity to xylenes (~ 43 wt. %). The effects of Bronsted and Lewis acid sites on catalytic results are discussed.