n-Butane hydroisomerization over Pd/HZSM-5 catalysts. Palladium loaded by ion exchange

Cañizares, Pablo; Lucas, Antonio de; Dorado, Fernando; Sepúlveda-Aguirre, Jovany

doi:10.1016/s1387-1811(00)00327-9

Cited by 14 publications

(9 citation statements)

References 29 publications

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“…The above analysis of the possible processes provides an alternative and rational explanation for the origin of the two high-temperature H 2 -TPR maxima often found for Pt/zeolites and interpreted as reduction of Pt species having different reducibilities. 44,52,65 If the H 2 pressure above the catalyst in the fully reduced state is decreased (Scheme 1, right), for example, by purging the catalyst with inert gas at elevated temperature, such as 723 K, the Pt 0 and Pt 0…”

Section: Pt Oxidation Statementioning

confidence: 99%

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Activation of Hydrogen and Hexane over Pt,H-Mordenite Hydroisomerization Catalysts

et al. 2009

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Various Pt species were shown to be present in Pt/H-mordenite catalyst preparations containing 1.5 and 2.6 wt % Pt. Air calcination of the catalyst precursor generated large Pt 0x metal particles (average size of >10 nm) by autoreduction, whereas a fraction of the platinum was converted to cations and oxycations, such as Pt 2+ and Pt 2 O 2+ , balancing negative charges on the zeolite framework. The results of temperature-programmed H 2 reduction (H 2 sTPR) suggested that Pt 2 O 2+ was reduced to Pt + below 550 K. The Pt n+ cations (n ) 1 or 2) became reduced to Pt 0 and Pt 0x above 550 K. Reduction was introduced by heterolytic H 2 dissociation, generating neutral platinum hydride and zeolite Brønsted acid sites, [PtsnH] 0 and H + . A similar platinum species, x[Pt 0 snH], was obtained from homolytic H 2 dissociation on Pt 0x . When H 2 was removed from the system, electrons were transferred from Pt 0 atoms or Pt 0x nanoparticles to the zeolite protons. When H 2 was released, acid sites were annihilated, and the highly dispersed metal again became the zeolite cation Pt n+ . The oxidation state and the chemical environment of the platinum were characterized by the vibrational spectra of chemisorbed CO. The spectral feature in the 2090-2100 cm -1 range, present in the spectrum of each H 2 -reduced catalyst, was shown to stem from two overlapping component bands. These bands were assigned to CO bound to Pt + and Pt 0 . The results confirm that the active surface intermediates of alkane hydroisomerization are platinum hydride/carbenium ion and platinum hydride/zeolite proton pair sites, such as [Pt 0 sH]/ZO -C n H 2n+1 + (species 1) and [Pt 0 sH]/ZO -H + (species 2) sites, in dynamic equilibrium with gas-phase alkane and H 2 . Hydrogen promotes release of the alkane from species 1 by generating species 2 (hydride transfer). If the rate of isomer formation is governed by the transformation rate of the carbenium ion, this suggested mechanism corresponds to kinetics that is first-order in hexane and negative-order in hydrogen. The large Pt 0x clusters were shown to catalyze the saturation of the eventually formed alkenes and, thereby, to suppress coke formation and catalyst deactivation.

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Section: Pt Oxidation Statementioning

confidence: 99%

“…It was argued that (i) isolated Pt 0 atoms cannot chemisorb H 2 , because H 2 homolysis requires at least two metal atoms, and (ii) the highly dispersed metal loses its metallic property in strong interaction with the acidic support and, therefore, it cannot chemisorb hydrogen. 10,20,23,57,65,71,72 4.2. Carbonyls of Pt/H-Mordenites.…”

Section: Pt Oxidation Statementioning

confidence: 99%

Activation of Hydrogen and Hexane over Pt,H-Mordenite Hydroisomerization Catalysts

et al. 2009

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“…Increasing the WHSV over Pt-MCM-41 shows a significant decline in the rate of conversion and higher hydrogen pressures favoring hydrogenolysis [9]. Cañizares et al reported that reduction temperatures are influential on the dispersion of Pt atoms loaded by ion exchange whereby higher reduction temperatures reduce the activity of the catalyst also due to sintering [188,190]. [190].…”

Section: The Influence Of Dopant Loadingmentioning

confidence: 99%

Butane Isomerization as a Diagnostic Tool in the Rational Design of Solid Acid Catalysts

et al. 2020

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The growing demand for isobutane as a vital petrochemical feedstock and chemical intermediate has for many decades surpassed industrial outputs that can be supplied through liquified petroleum gases. Alternative methods to resource the isobutane market have been explored, primarily the isomerization of linear n-butane to the substituted isobutane. To date the isobutane market is valued at over 20 billion US dollars, enticing researchers to seek unique and novel catalytic materials to improve on current commercial practices. Two main classes of catalysts have dominated the butane isomerization literature in the last few decades; namely microporous zeolites and sulfated zirconia. Both have been widely researched for butane isomerization, to the point where key catalytic descriptors such as acidity, framework topology and metal doping are becoming well understood. While this provides new researchers with a roadmap for developing new materials, it is has also begun developing into an invaluable tool for diagnosing and understanding the effect of these individual descriptors on catalytic properties. In this review we explore the different factors that influence the active site behavior of particularly zeolites and sulfated zirconia catalysts towards understanding the use of butane isomerization as a diagnostic tool for solid-acid catalysts.

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“…A known volume of an aqueous metal precursor solution was then poured over the zeolite. As metal precursor, H 2 PtCl 6 or Pd(NO 3 ) 2 were used because they are commonly used in bibliography [13,14] and in the case of the palladium precursor, the use of amminated ion precursors could show more calcination difficulties [2,15]. Next, the solvent was removed by evaporation under vacuum.…”

Section: Catalyst Preparationmentioning

confidence: 99%

Effect of the metal loading in the hydroisomerization of n-octane over beta agglomerated zeolite based catalysts

Lucas

Sánchez

Dorado

et al. 2005

Applied Catalysis A: General

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n-Butane hydroisomerization over Pd/HZSM-5 catalysts. Palladium loaded by ion exchange

Cited by 14 publications

References 29 publications

Activation of Hydrogen and Hexane over Pt,H-Mordenite Hydroisomerization Catalysts

Activation of Hydrogen and Hexane over Pt,H-Mordenite Hydroisomerization Catalysts

Butane Isomerization as a Diagnostic Tool in the Rational Design of Solid Acid Catalysts

Effect of the metal loading in the hydroisomerization of n-octane over beta agglomerated zeolite based catalysts

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