Acid-base properties of modified γ-alumina

Kania, W.; Jurczyk, Krzysztof

doi:10.1016/s0166-9834(00)82441-0

Cited by 25 publications

(9 citation statements)

References 15 publications

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“…Because the total amount adsorbed is the same before and after modification, the amount of weak base centres must have decreased to balance the increased strong base centres. This is in accordance with recent literature studies [27], which indicate that introduction of magnesia leads to an increase in the number of strongest base centres and to a decrease in base sites of moderate strength .…”

Section: Interaction : Adsorptionsupporting

confidence: 94%

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Gas and surface diffusion in modified γ-alumina systems

Uhlhorn

Keizer

Burggraaf

1989

Journal of Membrane Science

171

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SummaryThe transport of pure gases through a microporous membrane is described. The alumina-based membrane (pores 2 .5-4 nm) is suitable for Knudsen diffusion separation . To improve the separation factor, interaction with and mobility on the pore wall of one of the gases of a mixture is necessary . To introduce surface diffusion of oxygen and hydrogen, a y-alumina membrane was impregnated with silver . If temperature and atmosphere are controlled carefully, finely dispersed silver up to 17% by weight can be introduced . At higher loads and under oxidizing conditions, particle growth occurs. In adsorption experiments, little oxygen adsorption on the silver-modified y-alumina could be detected . This is due to a decrease in accessible surface area of the silver because of particle growth of silver under oxygen . The mobility of hydrogen on the surface was tested by counterdiffusion experiments, of which the theory is given. Hydrogen shows a considerable mobility on the surface at 293 K . At low pressures the flux ratio of hydrogen to nitrogen improved from 3 .8 to 8.8. Magnesia was introduced into the y-alumina membrane to enhance the adsorption and mobility of CO2. It is known that 30% of the CO 2 transport on non-modified yalumina is surface diffusion . The highest achievable magnesia load was 2 .2% by weight . Introduction of magnesia into the y-alumina surface gives more strong base sites and fewer weak base sites . This results in stronger bonding of C0 2 on the surface, but the amount adsorbed is comparable with the amount of C02 adsorbed on non-modified y-alumina . The contribution of surface diffusion to the total transport decreases with the introduction of magnesia, as is shown by counterdiffusion. The more strongly bonded CO 2 is less mobile, resulting in a smaller surface flux .

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Section: Interaction : Adsorptionsupporting

confidence: 94%

“…y-Alumina shows strong acid-base properties . In- TABLE 2 Loads after impregnation with a 1 M magnesium salt/2 M urea solution troduction of magnesia causes a change in these properties [25][26][27], which will also change the adsorption and surface diffusion behaviour of CO 2.…”

Section: Synthesis : Loadmentioning

confidence: 99%

Gas and surface diffusion in modified γ-alumina systems

Uhlhorn

Keizer

Burggraaf

1989

Journal of Membrane Science

171

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“…The reduced xNi-yCo/Al 2 O 3 catalysts and g-Al 2 O 3 were tested by NH 3 -TPD. It was reported that the aluminates, NiAl 2 O 4 and CoAl 2 O 4 , which were 38,41 In other studies, more complicated effects were reported. S2 †).…”

Section: Resultsmentioning

confidence: 89%

“…0.346 (0.029) 2.4 (2.1) 96.5 (65.7) 20 b 0.160 (0.023) 2.8 (2.2) 99.9 (99.9) 20(SI) b 0.264 (0.045) 2.2 (1.9) 90.3 (88.7) a Reaction conditions: 80 C, 6.0 MPa, catalyst in 200-400 mm containing 0.25 g Ni and 0.0625 g Co, 80 mL toluene and 20 mL methanol as solvent, 2.9 g IPN feed, 0.086 g NaOH, 180 mL min À1 hydrogen gas ow, 800 rpm stirring. However, the literatures38,[40][41][42] had no consensus about the effects of the metal on the acidity. In NiAl 2 O 4 and CoAl 2 O 4 spinel, the positive charge of the surface is higher than on g-Al 2 O 3 , and is present in the form of Al 3+ surface cations, which act as Lewis acid sites.…”

mentioning

confidence: 99%

Role of acid sites and surface hydroxyl groups in isophthalonitrile hydrogenation catalyzed by supported Ni–Co catalysts

2015

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Xylylenediamine (m-XDA) is industrially produced by the hydrogenation of isophthalonitrile (IPN) using Raney® Ni/Co and basic additives. Compared with Raney® Ni/Co, the supported Ni/Co catalysts are safer and have better mechanical strength. This work aimed at studying the catalytic performance of the supported Ni-Co catalysts in hydrogenation of IPN to m-XDA. The active sites for the condensation side reactions were studied using Ni-Co catalysts supported on different oxides and with different loadings. It was found that the acid sites catalyzed the condensation reactions between intermediate imines and amines. Two types of acid sites existed on the supported Ni-Co catalysts, namely, the original acid sites of the support and new acid sites formed by Ni/Co aluminates. In addition to acid sites, the surface hydroxyl groups on the oxide supports also catalyzed the condensation reactions, but were not active for the hydrogenation reaction. By increasing the Ni-Co loading, the selectivity to m-XDA was significantly enhanced, which was attributed to the suppression of both acid sites and hydroxyl groups.Compared to the low-loading catalysts (5Ni-1.25Co/Al 2 O 3 and 5Ni-1.25Co/SiO 2 ), the high-loading catalysts (20Ni-5Co/Al 2 O 3 and 20Ni-5Co/SiO 2 ) increased the m-XDA selectivity from $45.5 to 99.9%.

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“…The slightly high intensity peaks of (PtSnZn)/A correspond to comparatively weak acidic sites. The extent of either weak and/or strong acid sites [63,64] reflected to the unequal dispersion of the active metal Pt in each catalyst. Based on the results, the dispersion of Pt in (PtSn)/A was better as to that in (PtSnZn)/A catalyst.…”

Section: Nh 3 -Tpd Studymentioning

confidence: 99%

Sequential and/or Simultaneous Wet‐Impregnation Impact on the Mesoporous Pt/Sn/Zn/γ‐Al₂O₃ Catalysts for the Direct Ethane Dehydrogenation

Ali

Zahrani

Daous

et al. 2022

Journal of Nanomaterials

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This study is aimed at investigating the impact of catalyst preparation’s approach (either sequential and/or simultaneous wet impregnation) to a mesoporous series of Pt/A, Sn/A, PtSn/A, SnPt/A, (PtSn)/A, (PtSn)Zn/A, and (PtSnZn)/A catalysts for direct ethane dehydrogenation. The (PtSn)/A and (PtSnZn)/A had shown both higher initial specific activity (s-1) and reaction rate constant K d (h-1) (13063.86 (s-1) and 12489.69 (s-1) and 0.09 (h-1) and 0.06 (h-1)), respectively. The catalyst preparation approach had direct impact to the availability and dispersion of mesoporous particles of either active metal and/or promoter that influences either to hinder the C-C cleavage and/or to promote C-H bond cleavage in the dehydrogenation of ethane to ethene. The active metal component was present in the form of Pt, Pt+2, Al+3, Sn+4, and Zn+2 states. The enhanced catalytic activity is attributed to the Pt4Sn and PtZn formed phases in addition to highly dispersed mesoporous Pt particles. Based on the obtained results, the catalysts prepared by using simultaneous wet impregnation had shown higher catalytic activity and catalyst stability as to that of sequential wet impregnation.

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Acid-base properties of modified γ-alumina

Cited by 25 publications

References 15 publications

Gas and surface diffusion in modified γ-alumina systems

Gas and surface diffusion in modified γ-alumina systems

Role of acid sites and surface hydroxyl groups in isophthalonitrile hydrogenation catalyzed by supported Ni–Co catalysts

Sequential and/or Simultaneous Wet‐Impregnation Impact on the Mesoporous Pt/Sn/Zn/γ‐Al₂O₃ Catalysts for the Direct Ethane Dehydrogenation

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Acid-base properties of modified γ-alumina

Cited by 25 publications

References 15 publications

Gas and surface diffusion in modified γ-alumina systems

Gas and surface diffusion in modified γ-alumina systems

Role of acid sites and surface hydroxyl groups in isophthalonitrile hydrogenation catalyzed by supported Ni–Co catalysts

Sequential and/or Simultaneous Wet‐Impregnation Impact on the Mesoporous Pt/Sn/Zn/γ‐Al2O3 Catalysts for the Direct Ethane Dehydrogenation

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Product

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Sequential and/or Simultaneous Wet‐Impregnation Impact on the Mesoporous Pt/Sn/Zn/γ‐Al₂O₃ Catalysts for the Direct Ethane Dehydrogenation