Influence of the Sol-Gel Processing Method on the Structure and the Porous Texture of Nondoped Aluminas

Elaloui, E.; Pierre, Alain C.; Pajonk, G.M.

doi:10.1006/jcat.1997.1540

Cited by 58 publications

(31 citation statements)

References 15 publications

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“…Conventionally, the preparation of cobalt catalysts is performed by incipient wetness impregnation using suitable cobalt precursors on commercial alumina at low pH. Weak interaction is normally observed between the positively charged alumina carrier and the cobalt cations resulting in relatively large crystallite sizes [1][2][3][4]. Continuous efforts have been made in the last few decades by several groups [5][6][7] to synthesize porous alumina with high surface area by high-temperature dehydration of bulk powders [8], modified sol-gel synthesis in the presence of organic moieties [9,10], different surfactants [3], block copolymers [11][12][13][14], or evaporation-induced self-assembly (EISA) with colloidal precursors and amine structural agents [15,16].…”

Section: Introductionmentioning

confidence: 99%

Catalytic Behaviour of Mesoporous Cobalt-Aluminum Oxides for CO Oxidation

Bordoloi

Sánchez

Noei

et al. 2014

Journal of Catalysts

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Ordered mesoporous materials are promising catalyst supports due to their uniform pore size distribution, high specific surface area and pore volume, tunable pore sizes, and long-range ordering of the pore packing. The evaporation-induced self-assembly (EISA) process was applied to synthesize mesoporous mixed oxides, which consist of cobalt ions highly dispersed in an alumina matrix. The characterization of the mesoporous mixed cobalt-aluminum oxides with cobalt loadings in the range from 5 to 15 wt% and calcination temperatures of 673, 973, and 1073 K indicates that Co2+ is homogeneously distributed in the mesoporous alumina matrix. As a function of the Co loading, different phases are present comprising poorly crystalline alumina and mixed cobalt aluminum oxides of the spinel type. The mixed cobalt-aluminum oxides were applied as catalysts in CO oxidation and turned out to be highly active.

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Section: Introductionmentioning

confidence: 99%

Catalytic Behaviour of Mesoporous Cobalt-Aluminum Oxides for CO Oxidation

Bordoloi

Sánchez

Noei

et al. 2014

Journal of Catalysts

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“…As has been mentioned above, the HZSM-5 catalyst with c-alumina was prepared through sol-gel method. Previous reports [36,37] have demonstrated that mesopores were prone to generate through sol-gel synthesis.…”

Section: Characterizationmentioning

confidence: 99%

Effect of γ-alumina as active matrix added to HZSM-5 catalyst on the aromatization of methanol

Chen

Zhang

et al. 2015

Appl Petrochem Res

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HZSM-5-based catalyst is a recognized catalyst which is particularly selective towards the formations of aromatics in the methanol reaction. However, studies on HZSM-5-based catalyst were mainly focused on the addition of metallic or/and nonmetallic element. Quite few studies have reported the effect of active matrix such as calumina on the aromatization of methanol. In this study, calumina was introduced into HZSM-5-based catalyst for the purpose of investigating the effect of c-alumina in methanol to aromatics reaction. The catalysts were characterized by X-ray diffraction, Temperature-programmed Desorption of NH 3 (NH 3 -TPD), Pyridine adsorption FT-IR diffuse reflection spectroscopy and adsorption-desorption measurements of nitrogen, respectively. Characterizations showed that the introduction of c-alumina increased the amount of mesopores and acid sites in the catalyst. The experimental mainly includes two parts. Firstly, separate reaction performances over the catalyst with/without calumina and c-alumina showed that c-alumina could significantly promote the formations of aromatics. However, c-alumina alone could merely convert methanol to dimethyl ether with a minor quantity of gaseous hydrocarbons. Acid properties showed that the introduction of c-alumina increased the percentage of Lewis acid on catalyst surface and enhanced acid strength, as a result, promoted the production of active intermediates which was essential for aromatic formation. The rise of aromatics selectivity might be caused by the combined effect of acid site density and acid strength. Follow-up work was mainly focused on the effect of the loading amount and loading order of the catalyst with c-alumina. Results indicated that the total aromatic yield increased gradually with the increasing amount of catalyst with c-alumina regardless of the loading order of the catalyst with c-alumina. Gasoline compositions showed that the increased aromatics were at the expense of paraffins, olefins, and naphthenes. Besides, all single aromatic hydrocarbons increased gradually with the increasing amount of catalyst with c-alumina. And the aromatics had a larger variation change when methanol first passed through the catalyst with c-alumina.

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“…[54] However, whatever the starting materials used in the synthesis, the nanofibrous boehmite intermediate will have to be formed [22] for the formation of the nanofibers as mentioned above. The starting Al precursor is first hydrolyzed with water to form the hydroxide [17,22,32,37,38], aged to the viscous gel fibers of hydrated AlOOH, which can be calcined directly or electrospun or drawn from the viscous gel and converted to ceramic fibers after firing [16,27,[31][32][33][34][35][36][37]. The metallic aluminum powder used for the process is prepared by exploding the metal wire by a high density current pulse normally produced by discharging a capacitor bank.…”

Section: Hydrothermal and Sol Gel Processesmentioning

confidence: 99%

Synthesis of Alumina Nanofibers and Composites

Noordin¹,

Liew²

2010

Nanofibers

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IntroductionAlumina, Al 2 O 3 , is a ceramic metal oxide of great importance as building material, refractory material, electrical and heat insulator, attributed to its high strength, corrosion resistance, chemical stability, low thermal conductivity, and good electrical insulation. One phase of alumina, the -phase is widely used as catalyst, catalyst support and adsorbent because its high porosity and surface area. It is conventionally prepared by heating the hydrated trihydroxides, gibbsite and bayerite, to temperature of > 1000 o C to obtain the -alumina, corundum, a material with great hardness and low surface area. The trihydroxides, gibbsite, bayerite, both are Al(OH) 3. nH 2 O and the monohydroxyl oxide, boehmite, AlO(OH)·αH 2 O, have the monoclinic crystal structure with similar lattice parameters (a=0.866 nm, b=0.506 nm, c=0.983 nm, =94°34′ in boehmite, a=0.868 nm, b=0.507 nm, c=0.972 nm, =94°34′ in gibbsite, and a=0.867 nm, b=0.506 nm, c=0.942 nm, =90°26′ in bayerite [1,2]. In the process of heat treatment, the trihydroxide undergoes a series of transformations. It loses the water of hydration, then dehydroxalate at < 300 o C to form the monohydroxyl oxide boehmite, AlO(OH), which on further heating to increasingly higher temperatures, changes to the transition aluminas, including the -, -, -, and -phases, which then transform finally to the -form. These transition aluminas are crystalline solids with high porosity and surface areas as well as acidic and basic properties, which make them suitable as adsorbents, catalyst, catalyst support and fabricated into filtration membranes as well as used as fillers or components in polymer/ inorganic composite materials with enhanced mechanical properties. The conventional alumina as obtained are usually powder of particulates. These could be fabricated into alumina fibers by various method, through melt growth techniques including the internal crystallization method and extrusion, electrospraying [3] and electrospinning [4][5][6][7][8] have been developed for producing Al 2 O 3 fibers. The high surface areas of transition aluminas are due to the presence of pores. These pores are irregular in sizes and size distributions, and are mainly micropores of diameter less than 2 nm. Since the synthesis of mesoporous materials was first reported in the late 1980s , a number of methods for the synthesis of mesoporous alumina have been reported [8,9]. More recently, interest in nano-materials and nanotechnology has spurred a fury of investigations

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Influence of the Sol-Gel Processing Method on the Structure and the Porous Texture of Nondoped Aluminas

Cited by 58 publications

References 15 publications

Catalytic Behaviour of Mesoporous Cobalt-Aluminum Oxides for CO Oxidation

Catalytic Behaviour of Mesoporous Cobalt-Aluminum Oxides for CO Oxidation

Effect of γ-alumina as active matrix added to HZSM-5 catalyst on the aromatization of methanol

Synthesis of Alumina Nanofibers and Composites

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