A study of the surface acidity of acid-treated montmorillonite clay catalysts

Flessner, U; Jones, Deborah J.; Rozière, Jacqués; Zając, Jerzy; Storaro, Loretta; Lenarda, Maurizio; Pavan, Massimo; Jiménez‐López, Antonio; Rodríguez‐Castellón, Enrique; Trombetta, Marcella; Busca, Guido

doi:10.1016/s1381-1169(00)00540-9

Cited by 116 publications

(65 citation statements)

References 20 publications

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“…The initial exchange of H + for Na and Ca in the interlayer of the bentonite and other minerals and the relative resistance of the feldspar, cristabolite, and tridymite impurities to acid treatment (Table 1) are consistent with previously reported results for non-swelling phyllosilicate layers. [18][19][20] XRPD patterns of raw and acid-activated bentonites Figure 1 shows the XRPD patterns of the RB and AAB samples. (Figure 1a).…”

Section: Chemical Composition Of Raw and Acid-activated Bentonitesmentioning

confidence: 99%

“…However, only a part of the clay surface is effectively utilized, and most of the surface does not contribute to the catalytic capacity of the clay. [17][18][19] Furthermore, the composition of the smectite layers substantially affects their stability against acid treatment; trioctahedral clays dissolve much faster than their dioctahedral counterparts, and the extent of dissolution of the central atoms from the tetrahedral and octahedral sheets depends on both the clay mineral type and the reaction conditions, such as the acid concentration, time, and temperature of the treatment. 20,21 The uses of the bentonite deposits in Turkey vary depending on the types and amounts of constituents found, such as smectites, other clay minerals, and non-clay minerals, including quartz, calcite, dolomite, and feldspar.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Unye bentonite after treatment with sulfuric acid

Çağlar¹,

Afsin²,

Koksal³

et al. 2013

Quím. Nova

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Recebido em 4/9/12; aceito em 25/3/13; publicado na web em 13/6/13Unye bentonite was found to consist predominantly of a dioctahedral smectite along with quartz, tridymite, cristobalite, and minor fractions of feldspar and anatase. A considerable amount of Al was retained as a constituent in acid-resistant impurities following the decomposition of the montmorillonite via acid treatment at an acid/clay ratio of 0.4. These impurities were mesoporous with a maximum surface area of 303.9±0.4 m 2 g -1 . A sharp decrease in the d 001 lattice spacing of the montmorillonite to 15.33 Å reflected the reduction of the crystallinity in the activated products. In addition, the increase in the ease with which newly formed hydroxyl groups were lost paralleled the severity of the acid treatment.

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Section: Chemical Composition Of Raw and Acid-activated Bentonitesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterization of Unye bentonite after treatment with sulfuric acid

Çağlar¹,

Afsin²,

Koksal³

et al. 2013

Quím. Nova

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“…The purpose was to evaluate the versatility of the acid-activated clays as catalysts in the synthesis of esters from carboxylic acids and alcohols with different chemical structures. The montmorillonite K10, a commercial catalyst produced by the acid treatment of raw clay, 32 was also used. The reactions were performed at atmospheric pressure, and neither a Dean-Stark apparatus nor a co-solvent was used.…”

Section: Resultsmentioning

confidence: 99%

Preparation, characterisation and evaluation of brazilian clay-based catalysts for use in esterification reactions

Rezende

Pereira

Santos

et al. 2012

J. Braz. Chem. Soc.

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Catalisadores a base de argilas naturais brasileiras foram preparados, caracterizados, e sua atividade catalítica foi avaliada em reações de esterificação. As argilas naturais foram ativadas por tratamento ácido como recebidas, sem qualquer tratamento prévio. As argilas naturais e as argilas ácidas foram caracterizadas por DRX, TPD-NH 3 , termodessorção de n-butilamina, análise de adsorção de N 2 , FT-IR, TGA e DTA. O desempenho catalítico foi investigado em reações de esterificação de diversos ácidos carboxílicos com diferentes álcoois. As reações foram realizadas com razão molar ácido carboxílico/álcool 1:3, a 100 °C e pressão atmosférica, por 3 h. As argilas ácidas forneceram boas conversões e apresentaram desempenho melhor que a argila comercial K10. Natural Brazilian clay-based catalysts were prepared, characterised, and their catalytic activity was assessed in esterification reactions. The natural clays were acid activated as received, without any previous treatment. Both natural and acid-activated clays were characterised by XRD, NH 3 -TPD, thermodesorption of n-butylamine, N 2 adsorption analysis, FT-IR, TGA and DTA. The catalytic performance was investigated in the esterification of several carboxylic acids with different alcohols. The reactions were carried out in a 1:3 carboxylic acid/alcohol molar ratio at 100 °C and atmospheric pressure for 3 h. The acid-activated clays provided good yields and better performance than commercial clay K10. Keywords: acid activation, clay, smectite, esterification IntroductionEsterification reactions are widely employed in a variety of chemical industries. 1 The procedure generally uses either sulfuric, hydrochloric or sulfonic acid as catalyst. These catalysts generate large quantities of acidic waste, which require appropriate treatment before disposal. The most widely used catalyst is sulfuric acid. It is a low cost reagent and is very active. However, it is also corrosive and presents problems of storage and control. 2 To minimise the problems associated with the homogeneous process, intensive research has been recently devoted to the development of heterogeneous catalysts for esterification. Some examples include functionalised mesoporous materials, 3,4 ion-exchange resin, 1 oxides 5-7 and metal complexes. 8,9 There is considerable interest in developing catalysts based on clays. In terms of their environmental aspect, these materials are one of the most friendly solid catalysts. Additionally, clay-based catalysts are very promising because of the low cost of the raw material, ease of properties manipulation and ease of recovery and reuse. 10 Ion exchange capacity and the potential for increased interlayer spacing are important characteristics of clay minerals that strongly influence their physical-chemical and technological properties. These characteristics, as well as their high surface area, have lead clay minerals to be explored as catalysts. The acid activation method is usually employed to modify the textural characteristics of clays.Clays are being employe...

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“…The temperature-programmed desorption of basic gas molecules (Arena et al 1998;Breen et al 1987; Adams and McCabe 2006;Singh et al 2007) and Hammett indicators (Walling 1950;Benesi 1957;Liu et al 2011) have been used to evaluate the strength of acid sites. In addition, Brønsted and Lewis acid sites can be distinguished by differentiating vibrational bands of the adsorbed basic probe molecules using Fourier transform infrared spectroscopy (FTIR) (Akçay 2005;Billingham et al 1996;Brown and Rhodes 1997;Cseri et al 1995;Flessner et al 2001;Liu et al 2011;Reddy et al 2009;Reddy et al 2007;Singh et al 2007;Tyagi et al 2006). Based on these investigations, the number of acid sites in montmorillonite obtained from different sources has been found to range from 0.09 to 0.60 mmol/g (Flessner et al 2001;Hart and Brown 2004;Liu et al 2011;Walling 1950).…”

Section: Introductionmentioning

confidence: 99%

“…In addition, Brønsted and Lewis acid sites can be distinguished by differentiating vibrational bands of the adsorbed basic probe molecules using Fourier transform infrared spectroscopy (FTIR) (Akçay 2005;Billingham et al 1996;Brown and Rhodes 1997;Cseri et al 1995;Flessner et al 2001;Liu et al 2011;Reddy et al 2009;Reddy et al 2007;Singh et al 2007;Tyagi et al 2006). Based on these investigations, the number of acid sites in montmorillonite obtained from different sources has been found to range from 0.09 to 0.60 mmol/g (Flessner et al 2001;Hart and Brown 2004;Liu et al 2011;Walling 1950). However, the solid acidity of montmorillonite is difficult to compare directly between different studies because both the samples used and the applied measurement methods are not uniform.…”

Section: Introductionmentioning

confidence: 99%

Studies on the solid acidity of heated and cation-exchanged montmorillonite using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy

Liu

Yuan

et al. 2013

Phys Chem Minerals

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The effects of heating and cation exchange on the solid acidity of montmorillonite were investigated using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared spectroscopy. The number of total, Brønsted, and Lewis acid sites showed the same modulation tendency with increasing heating temperature, reaching a maximum at 120°C and subsequently decreasing until it reaches a minimum at 600°C. The Lewis acid sites result from unsaturated Al 3? cations, and their number increased with the heating temperature due to the dehydration and dehydroxylation of montmorillonite. The generation and evolution of Brønsted acidity were mainly related to interlayer-polarized water molecules. Water adsorbed on the unsaturated Al 3? ions also acted as a Brønsted acid. The acid strength of the Brønsted acid sites was dependent on the polarization ability of the exchangeable cation, the amount of interlayer water, and the degree of dissociation of the interlayer water coordinated to exchangeable cations. All cation-exchanged montmorillonites exhibited different numbers of acid sites and various distributions of acid strength. Brønsted acidity was predominant in Al 3? -exchanged montmorillonite, whereas the Na ? -and K ? -exchanged montmorillonites showed predominantly Lewis acidity. Moreover, Mg 2? -and Li ? -exchanged montmorillonites exhibited approximately equal numbers of Brønsted and Lewis acid sites. The Brønsted acidity of cation-exchanged montmorillonite was positively correlated with the charge-to-radius ratios of the cations, whereas the Lewis acidity was highly dependent on the electronegativity of the cations. The acid strengths of Al 3? -and Mg 2? -exchanged montmorillonites were remarkably higher than those of monovalent cationexchanged montmorillonites, showing the highest acid strength (H 0 B -3.0). Li ? -and Na ? -exchanged montmorillonites exhibited an acid strength distribution of -3.0 \ H 0 B 4.8, with the acid strength ranging primarily from 1.5 to 3.3 in Li ? -exchanged montmorillonite, whereas only weaker-strength acid sites (1.5 \ H 0 B 4.8) were present in K ? -exchanged montmorillonite. The results of the catalysis experiments indicated that montmorillonite promoted the thermal decomposition of the model organic. The catalytic activity showed a positive correlation with the solid acidity of montmorillonite and was affected by cation exchange, which occurs naturally in geological processes.

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A study of the surface acidity of acid-treated montmorillonite clay catalysts

Cited by 116 publications

References 20 publications

Characterization of Unye bentonite after treatment with sulfuric acid

Characterization of Unye bentonite after treatment with sulfuric acid

Preparation, characterisation and evaluation of brazilian clay-based catalysts for use in esterification reactions

Studies on the solid acidity of heated and cation-exchanged montmorillonite using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy

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