Influences of Mesoporosity Generation in ZSM-5 and Zeolite Beta on Catalytic Performance During n-Hexane Isomerization

Modhera, Bharat; Chakraborty, Mousumi; Bajaj, Hari C.; Parikh, Parimal A.

doi:10.1007/s10562-011-0610-6

Cited by 20 publications

(19 citation statements)

References 34 publications

(47 reference statements)

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“…Song et al [21] studied the effect of the desilication treatment on ZSM-5, and observed an enhancement in the yield of dibranched isomers due to the formation of mesopores. Modhera et al [22] also studied the catalytic performance of Pt impregnated desilicated ZSM-5 and Beta zeolites for n-hexane hydroisomerization, reporting modifications in Pt location that were correlated to a reduced catalyst deactivation by sintering.…”

Section: Introductionmentioning

confidence: 99%

Catalytic behavior of alkali-treated Pt/HMOR in n-hexane hydroisomerization

Monteiro

Ania

Rocha

et al. 2014

Applied Catalysis A: General

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Bifunctional Pt-HMOR catalysts were prepared by incipient wetness impregnation of various desilicated MOR obtained by alkaline treatment using NaOH concentrations ranging from 0.1 to 0.5 M. The zeolite structural changes upon modification were investigated by several techniques including powder X-ray diffraction, 27 Al and 29 Si MAS-NMR spectroscopy, N 2 adsorption, pyridine adsorption followed by infrared spectroscopy and the catalytic model reaction of m-2 xylene transformation. For low alkaline concentration the zeolite acidity is preserved, along with a slight increase of the volume correspondent to the larger micropores due to the removal of extra-framework debris already existent at the parent zeolite At higher NaOH concentrations there is a significant loss of crystalinity and acidity as well as the formation of mesoporosity. The characterization of the metal function show similar patterns for Pt-HMOR and Pt-M/0.1 samples, with Pt particles located mainly inside the inner porosity. In contrast, large Pt particles become visible at the intercrystalline mesoporosity of MOR crystals developed during the desilication treatments at severe alkaline conditions. The catalytic results obtained for n-hexane hydroisomerization showed an improved selectivity for dibranched over monobranched isomers for Pt-M/0.1 sample, likely due to the preservation of the support acidity and the slight enlargement of the micropores. This work is a new example in which the mesoporous development does not improve the catalytic efficiency of the zeolites, whereas mild alkaline desilication might be considered as an effective solution to produce customized catalysts with enhanced performance for a given application.

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Section: Introductionmentioning

confidence: 99%

Catalytic behavior of alkali-treated Pt/HMOR in n-hexane hydroisomerization

Monteiro

Ania

Rocha

et al. 2014

Applied Catalysis A: General

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“…From our earlier experiences with hierarchical zeolite Beta for isomerization of n-hexane, we deduced the following operating conditions to afford the highest isomer yields: catalyst mass 1 g, n-hexane flow rate 6 mL/h, H 2 /hydrocarbon 2 mol/mol, pressure 1 atm, temperature 350 °C, and reaction in continuous down flow reactor [2]. The present work is an extension of our previous efforts to increase the catalyst life and enhance the isomer selectivity.…”

Section: Resultsmentioning

confidence: 99%

“…Among the probable candidates, keeping hydrothermal stability of the catalyst in mind, zeolites Beta has remained the catalyst of choice. Readers are referred to relatively recent works [1,2] for introduction to paraffin isomerization and review articles by Valavarasu and Sairam [3], and Akhmedov et al [4] for details and comprehensive intricacies of various commercial processes. Now, when the molecular size of product increases as a result of the reaction, it is worth expecting that (a) smaller crystal size, preferably in nanometer size affording smaller diffusion length and enhanced external surface area and (b) generation of mesoporosity in zeolites crystals would be beneficial for the reaction.…”

Section: Introductionmentioning

confidence: 99%

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Combined influence of alkaline earth metals and CO2 on performance of hierarchical zeolite Beta in n-hexane isomerization

2018

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The present work deals with isomerization of straight chain paraffin, n-hexane with an aim to make up loss in gasoline quantity as well as octane. This is due to its reduced benzene content warranted by its carcinogenic nature. Performance of impregnation of alkaline earth metals (Mg, Ca, Sr, and Ba) on Pt/desilicated (and dealuminated) zeolites Beta was studied and found that isomer selectivity as high as 99% with stable catalytic performance is achievable. Furthermore, replacing part of hydrogen (15%) with carbon dioxide in hydrogen as carrier gas improves hexane conversion. Hexane conversion increased as Mg-< Ba-< Ca-< Sr-Pt/deSi Beta. Observed performance parameters have been explained on the basis of reported variation in acidity due to both alkaline earth metals and CO 2 .

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“…The latter catalysts are particularly advantageous as they are less corrosive and less prone to deactivation by the contaminants (i.e. water, sulfur) present in the feed [20,21]. Nevertheless, Pt-zeolites catalysts present some disadvantages such as high operating temperatures, high hydrogen pressure and lower acidity which, in the end, leads to lower selectivity to branched molecules [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Pinto

Szeto

Oueslati

et al. 2016

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-Heteropolyacids (HPA) immobilized onto SBA-15 silica were prepared by two different ways using either impregnation or encapsulation methodologies. Two Keggin-type HPA, H 3 PW 12 O 40 and H 4 SiW 12 O 40 were considered in this study. The resulting hybrid materials were fully characterized by N 2 adsorption-desorption isotherms, XRD, FT-IR, Raman, diffuse reflectance UV-Vis spectroscopies and 31 P MAS NMR. All characterization methods showed that at room temperature the catalysts contained well-dispersed and intact Keggin units throughout the solid. The catalytic activity of these solids was investigated in the isomerization of n-hexane. The impregnated and encapsulated phosphotungstic catalysts performed similarly in catalysis showing that the amount of active sites was nearly the same in both catalysts. On the contrary, the tungstosilicic encapsulated material was completely inactive while its impregnated counterpart was even more active than the phosphotungstic derived catalysts. The acidity of the solids was measured by various methods: microcalorimetry of ammonia adsorption, ammonia desorption followed by Temperature Programmed Desorption (TPD) and DRIFT/GC-MS and pyridine adsorption followed by infrared spectroscopy. Only pyridine adsorption and ammonia desorption followed by DRIFT/GC-MS agreed with the catalytic data. Ammonia adsorption followed by microcalorimetry was not able to differentiate between the four catalysts while the TPD experiments led to unreliable results, as not only the evolved ammonia but also other molecules such as water were taken into account in the measurements. The behavior difference between the encapsulated silico-and phosphotungstic acids was explained by a more pronounced encapsulation in the case of silicon. de préparation. L'activité catalytique de ces matériaux a ensuite été étudiée dans l'isomérisation du n-hexane.

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Influences of Mesoporosity Generation in ZSM-5 and Zeolite Beta on Catalytic Performance During n-Hexane Isomerization

Cited by 20 publications

References 34 publications

Catalytic behavior of alkali-treated Pt/HMOR in n-hexane hydroisomerization

Catalytic behavior of alkali-treated Pt/HMOR in n-hexane hydroisomerization

Combined influence of alkaline earth metals and CO2 on performance of hierarchical zeolite Beta in n-hexane isomerization

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

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