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•Negative impact of the desilication of ZSM-5 on the propane aromatization.•Negative impact of the desilication of ZSM-5 on the cyclohexane dehydrogenation.•No impact of the ...desilication of ZSM-5 on the n-hexane cracking.•At higher gallium content, a steric retention of coke precursors in the mesopores.
Gallium containing ZSM-5 zeolites were prepared by ion exchange and mechanical mixture from the parent ZSM-5 and two desilicated zeolites to be tested in propane aromatization. The alkaline treatment was made by sodium hydroxide, with or without tetrabutylammonium hydroxide. The catalysts prepared from desilicated zeolites are less active in propane aromatization and cyclohexane transformation and less selective into aromatics than those prepared from the parent zeolite. The desilication did not affect the acid properties, especially the strength of acid sites as seen by CO adsorption at 77 K and n-hexane cracking.
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•Propane aromatization and cyclohexane transformation were carried at 803 K.•Gallosilicates are less active than ion exchange and mechanical mixture samples.•Activation of propane is ...by an alkyl mechanism.•Higher coke content is formed on gallosilicates.•The coke is toxic and localized in the micropores.
Three series of gallium-containing MFI zeolite were prepared with different gallium content by weight, by hydrothermal synthesis Ga-MFI (0.2–4.7 wt% Ga), ion exchange Ga/P (0.5–6.8 wt% Ga) and mechanical mixture Ga+P (0.5–10 wt% Ga). Under hydrogen at 600 °C on the aluminosilicate doped with gallium, a reducing solid ionic exchange occurs between a mobile species (Ga2O) and the protonic sites of the zeolite. The proportion of Ga implied in this exchange depends on both the proximity between Ga2O3 and the zeolite and the initial gallium content. The solid reductive exchange remains limited, ranging from 25% to only a few percent; therefore the gallium species content located in the zeolite micropores is only 0.2–0.4 wt%. The aluminosilicates doped with Ga are more active in both cyclohexane dehydrogenation and propane aromatization than the gallosilicates: the gallium in the framework is much less active than gallium in the exchange position.
The catalytic fast pyrolysis of oak over two zeolites (microporous and hierarchical) was investigated in a microfluidized bed reactor (MFBR) at 500 °C and as a function of the biomass-to-catalyst ...ratio. A hierarchical zeolite was produced by desilication with a NaOH solution of a conventional HZSM-5 zeolite. The outlet of the MFBR was connected to a single photoionization mass spectrometer (SPI-MS) for the on-line analysis of volatiles. This on-line analysis method allows studying the dynamics of volatile formation (in real time) and the deactivation of 2 zeolites upon stepwise injections of wood particles. Strikingly, the selectivity of targeted mono-aromatic compounds (quantified by gas chromatography) is doubled after desilication of the zeolite. The coked zeolites were characterized by TEM-EDX, digestion in fluoric acid, MALDI-TOF MS, etc . Three different types of coke are evidenced: (1) coke trapped inside micropores, (2) external coke formed on the outer surface of the crystals and (3) coke precursors deposited in the mesopores. The latter two cokes are much less toxic than the microporous coke. The open mesopores produced after desilication can be seen as “highways” where big molecules (such as levoglucosan) can diffuse to more accessible pore mouths. Brønsted acid sites present on microporous mouths can be active for the conversion of bigger molecules to small fragments. These fragments diffuse and form aromatics in the micropores (shape selectivity). The mesopores also promote the evacuation of catalytic products, thus enhancing the selectivity of mono-aromatic hydrocarbons. Desilicated zeolites present higher selectivity to mono-aromatics and stability upon coke deposition than microporous zeolites.
Location and distance between coke molecules inside the HBEA zeolite at 30bar and 623K obtained by molecular simulation and pulsed EPR DEER experiment. Display omitted
► HBEA (11) deactivates by ...coking during ethanol transformation. ► Coke molecules were characterized by several spectroscopic techniques. ► The coke was classified into 17 families following their unsaturation numbers. ► Coke molecules inside the pore are mainly hexamethylbenzene or alkyl-pyrenes.
HBEA (11) zeolite was deactivated rapidly by coking during the ethanol transformation into hydrocarbons, at 623K and 30bar. The nature of carbonaceous deposit was studied, after zeolite dissolution by hydrofluoric acid both by gas chromatography coupled with mass spectrometry and by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The coke on the external zeolite surface was characterized directly on the spent catalyst by laser desorption/ionization time of flight mass spectrometry (LDI-TOF MS). The coke species were identified and classified into 17 families following their unsaturation number (4–23). The coke was polyaromatic, and it was very alkylated (methyl, ethyl, and propyl groups). It is compounded of alkylbenzenes, mainly hexamethylbenzene (HMB), and alkyl-pyrenes, located within the zeolite pore, which could migrate to the external zeolite surface and grow into polyaromatic compounds constituted up to eight aromatic rings and up to 40 carbon atoms. Pulsed electron paramagnetic resonance spectroscopy measurements and molecular simulation by using Cerius2 software have shown that HMBs are distant of 0.6nm inside the zeolite pores.
Compact model of single-walled semiconducting carbon nanotube field-effect transistors (CNTFETs) implementing the calculation of energy conduction subband minima under VHDLAMS simulator is used to ...explore the high-frequency performance potential of CNTFET. The cutoff frequency expected for a MOSFET-like CNTFET is well below the performance limit, due to the large parasitic capacitance between electrodes. We show that using an array of parallel nanotubes as the transistor channel combined in a finger geometry to produce a single transistor significantly reduces the parasitic capacitance per tube and, thereby, improves high-frequency performance.
The electron–ion scattering experiment ELISe is part of the installations envisaged at the new experimental storage ring at the International Facility for Antiproton and Ion Research (FAIR) in ...Darmstadt, Germany. It offers an unique opportunity to use electrons as probe in investigations of the structure of exotic nuclei. The conceptual design and the scientific challenges of ELISe are presented.
Scheme of the EtOH transformation in the presence of radical coke species.
•EtOH was transformed into hydrocarbons at 623K and 30bar on HZSM-5.•Coke molecules composed of alkylbenzenes and ...alkylnaphtalenes poisoned Brønsted acid sites.•“Coke” can transform into radical molecules by spontaneous ionization.•Radical “coke” participates in the ethanol transformation into hydrocarbons.•Hydroquinone enhances the coke growth into inactive species.
During ethanol-to-hydrocarbons (ETH) process at 623K and 30bar on HZSM-5(40), side reactions occur leading to the formation of carbonaceous materials, defined as “coke” which is composed mainly of alkylbenzenes and alkylnaphthalenes. The “coke” molecules, trapped inside the channels have first a direct effect on the Brønsted acid sites by poisoning them; however, they can also have an indirect effect. Indeed, some “coke” molecules lead to radicals formation by spontaneous ionization which could potentially act as active species in ethene oligomerization. Nevertheless, the radicals could also condensate into bulkier molecules leading to inactive species and consequently undergoing to catalyst deactivation. The participation of radical “coke” in EtOH transformation into higher hydrocarbons was demonstrated by adding in the feed gas a radical inhibitor such as hydroquinone (HQ). Indeed, the consumption of radical species by HQ, enhanced the catalyst deactivation.
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•Direct liquefaction reaction of waste organic matter using Raney Nickel and tetralin.•Biological pretreatment enhances Humin content and the liquefaction process.•Humin fraction as ...promoter and Humic acids as refractory to liquefaction reaction.•Bio oil heating value close to biopetroleum.
The bio-oil synthesis from a mixture of wastes (7wt.% straw, 38wt.% wood, and 45wt.% grass) was carried out by direct liquefaction reaction using Raney Nickel as catalyst and tetralin as solvent. The green wastes were biologically degraded during 3months. Longer the destructuration time; higher the yield into oil is. Biological pretreatment of green wastes promotes the liquefaction process. Among the components of degraded biomass, Humin, the major fraction (60–80wt.%) that was favored by the biological treatment, yields to a bio oil extremely energetic with a HHV close to biopetroleum (40MJkg−1), contrariwise, Fulvic acids (2–12wt.%), the minor fraction is refractory to liquefaction reaction.
The entanglement between two electrons in a degenerate electron gas is studied as a function of their separation and of temperature. It is found that interaction leads to a suppression of the ...entanglement distance.
The entanglement between two electrons in a degenerate electron gas is studied as a function of their separation. We have taken into account the screened Coulomb interaction between electrons. It is ...found that interaction leads to a suppression of the entanglement distance. The interaction leads also to a direct dependence of entanglement distance on density.
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