Miroslaw Derewinski

A new Mo/HZSM-5 catalyst (3 wt% Mo, Si/Al = 26) comprising a carbon-templated zeolite having intracrys-talline mesopores sizing ca. 10–20 nm (HZSM-5-BP) has been prepared. For comparison purposes, an equivalent catalyst has also been prepared from a commercial zeolite (HZSM-5-ref). The materials have been extensively characterized by XRD, ICP-OES, N 2 physisorption, SEM-TEM, 27 Al MAS NMR, FTIR-pyridine, NH 3-TPD, H 2-TPR, TG-DTG analyses and TPO, and their catalytic activity evaluated for methane dehydroaromatization (MDA) at 700 • C, 1 bar, and 1500 ml/g cat h. The hierarchical Mo/HZSM-5-BP catalyst displayed a lower deactivation rate during MDA than the reference one, leading to a higher and stable aromatics yield at T.O.S. above 3 h, despite a higher amount of less reactive coke (associated to the zeolite acid sites) was produced in the former. We hypothesize that the enhanced tolerance to carbon deposits of the carbon-templated zeolite could be related to the intracrystalline mesopores acting as a trap for coke molecules and leaving a higher fraction of acid sites within the channels active for aromatization.

ABSTRACT Immobilization of ethylene in the channel system of HZSM-5 was evaluated from the breakthrough curves of ethylene and desorption curves of ethylene transformation products measured on a zeolite bed between 308K and 523K. The kinetics of the overall immobilization/mobilization reaction was measured on a series of HZSM-5 samples in an integral flow reactor with a fixed bed of zeolite at 623K. The aluminum content of the samples ranged from 3.2 to 6.4 Al atoms per unit cell. The zeolites were characterized by XRD, SEM, chemical analysis, 27Al MAS NMR, water sorption, TPD of NH3 and FTIR spectroscopy. The results of kinetic measurements are represented by a family of S-shaped curves plotted as ethylene conversion versus contact time. The form of the curves suggests a contribution of an autocatalytic rate step to the kinetics. The length of the induction period increases with increasing crystal size and decreasing aluminum content in the catalyst. The kinetic curves obtained for crystals of the same aluminum content are strongly influenced by the crystal size. The ethylene breakthrough curves exhibit at the beginning a sharp breakthrough peak which decreases with accelerating oligomerization. The temperature threshold of zeolite bed production was estimated to lie at 418K. At this temperature C2–C5 hydrocarbons were found in the gas phase in the gas leaving the reactor. The curve plotted as the amount of immobilized species against the temperature of the zeolite bed exhibits a steep increase to a flat maximum occurring between 353K and 433K, followed by a steep decrease. Adsorption of water on samples loaded with the immobilized species provides information about the space accessible from the gas phase and indicates differences in the nature of immobilized species formed at different temperatures.

The interaction of bases (pyridine, 2,6-dimethylpyridine) is studied on SAPO-37, pretreated at nonusual high temperatures from 873 to 1173 K. XRD, infrared, and P-31, Al-27, and Si-29 MAS NMR spectroscopies are used, the spectra being recorded in the presence of the bases. Several types of interactions are shown by infrared and NMR, depending on the pretreatment temperatures. The Al-27 and Si-29 MAS NMR spectra are modified in the presence of bases. The protonic acidity, studied with the two probes, decreases when the temperature rises, as usual in zeolites for the bridging Si-OH-Al hydroxyls, but very strong acid sites are created after the 1173 K heating. At least three kinds of Lewis sites are seen by infrared. Besides the 1455-cm(-1) Lewis band of pyridine in oxides, new species vibrating also at 1430 and 1455 cm(-1) are observed. The 1430-cm(-1) band decreases with the pretreatment temperature while the new 1455-cm(-1) one increases. Both could be assigned to pentacoordinated A...

ABSTRACT The long-term sorption kinetics of p-ethyltoluene on HZSM-5 zeolite was investigated using a McBain balance. The kinetic data suggested that the transport is coupled with immobilization. In situ isomerization of p-ethyltoluene as well as temperature-programmed desorption (TPD) of the samples containing a preloaded mixture of ethyltoluenes were followed by Fourier transform infrared spectroscopy (FTIR). TPD results indicate that no significant release of immobilized m-ethyltoluene was observed at temperatures below 543K. TPD patterns of p-ethyltoluene were found to depend strongly on the temperature of the zeolite preloading. The removal and/or isomerization of p-ethyltoluene molecules trapped by the m-ethyltoluene species immobilized on the strong acid sites can occur only when the meta-isomer leaves the zeolite channels at temperatures above 543K.

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... By Jerzy Haber*, Tadeusz Machej, Mirostaw Derewinski, Robert Janik, Joanna Krysciak and Halina Sadowska ... GHSV was 10,000 h '. Some experiments were done using air saturated with water vapour (24 Tr) at 25 °C. Methyl chloride (CH3C1), C02, and HC1 were the only ...

ABSTRACT A new Mo/HZSM-5 catalyst (3wt% Mo, Si/Al=26) comprising a carbon-templated zeolite having intracrystalline mesopores sizing ca. 10–20nm (HZSM-5-BP) has been prepared. For comparison purposes, an equivalent catalyst has also been prepared from a commercial zeolite (HZSM-5-ref). The materials have been extensively characterized by XRD, ICP-OES, N2 physisorption, SEM-TEM, 27Al MAS NMR, FTIR-pyridine, NH3-TPD, H2-TPR, TG-DTG analyses and TPO, and their catalytic activity evaluated for methane dehydroaromatization (MDA) at 700°C, 1bar, and 1500ml/gcath. The hierarchical Mo/HZSM-5-BP catalyst displayed a lower deactivation rate during MDA than the reference one, leading to a higher and stable aromatics yield at T.O.S. above 3h, despite a higher amount of less reactive coke (associated to the zeolite acid sites) was produced in the former. We hypothesize that the enhanced tolerance to carbon deposits of the carbon-templated zeolite could be related to the intracrystalline mesopores acting as a trap for coke molecules and leaving a higher fraction of acid sites within the channels active for aromatization.

ABSTRACT A drastic change in the environment of Si atoms in SAPO-37 after heating at 1173 K is seen in the29Si MAS NMR spectrum. This suggests a modification of the location of Si, Al and P atoms. Three main phases would coexist in large amounts in the faujasite structure, the SAPO-37 originating phase, pure SiO4 islands and an aluminosilicate phase comparable to Si-Al faujasite.

ABSTRACT SBA-15 type mesoporous molecular sieve was prepared and used as a parent material for synthesis of a SBA-15/zeolite composite. Thus, after addition of an aluminum source into the pristine sample, it was subjected to recrystallization in the water-vapor phase to give the SBA-15/MFI composites. The samples obtained were characterized by XRD, nitrogen sorption, scanning and transmission electron microscopies, 27Al MAS NMR and FT IR. The materials after recrystallization retained their mesoporous character. Characteristics of the material revealed that all the aluminum added was inserted into the final hybrid. As shown by FT IR and NMR, at least some of aluminum was introduced into the nanoparticles of MFI and adopted four-fold coordination, typical for zeolites. Formation of Brønsted acid centres was directly confirmed by IR studies. The catalytic activity was screened in the liquid-phase isomerization of α-pinene. The main products of α-pinene transformations were camphene, limonene and γ-terpinene. The overall selectivity toward camphene+limonene was ca. 90%. Taking into account the low amount of the MFI phase present in a composite sample, calculated initial reaction rate was comparable with other catalytic systems explored in the isomerization of α-pinene.

ABSTRACT A bifunctional hierarchical micro-mesoporous Pd/HZSM-5-BP catalyst (2wt% Pd) has been prepared by impregnating an HZSM-5 sample hydrothermally synthesized in the presence of nearly uniform carbon nanoparticles (Black Pearls 2000) of ca. 12nm in size in order to generate intracrystalline mesovoids (mostly in the 10–20nm range, as ascertained by TEM). An equivalent catalyst (Pd/HZSM-5-ref) comprising an HZSM-5 zeolite having roughly the same Si/Al ratio (26, from ICP-OES), crystallite size and morphology (SEM), and acidity (FTIR-pyridine and NH3-TPD) but synthesized in the absence of carbon has also been prepared for comparison purposes. TEM, CO chemisorption and XPS results on reduced catalysts (400°C in H2 flow) revealed that Pd0 is better dispersed in the catalyst involving the hierarchical carbon-templated zeolite, for which a large fraction of metal nanoparticles was found to be confined within the intracrystalline mesocavities (TEM). Despite the differences in dispersion, both bifunctional catalysts were found to be well balanced in terms of metal/acid ratio and consequently equally active and selective for the hydroconversion of n-octane (which is able to easily access all the acid sites in the 10-ring channels of ZSM-5) in the absence of sulfur. However, after addition of 100ppm sulfur to the n-octane feed, the hierarchical Pd/HZSM-5-BP catalyst displayed a superior thioresistance leading to a notably higher steady conversion (48% as compared to 21% attained on Pd/HZSM-5-ref). The higher sulfur resistance of the hierarchical catalyst is ascribed to the inhibition of the sulfur-induced migration and sintering of Pd0 nanoparticles on the external zeolite surface when confined within the mesovoids, as revealed by TEM after catalysis.