Study of the thermal decomposition of a sepiolite by mid- and near-infrared spectroscopies

Mora, Manuel; López, María Isabel; Carmona, Miguel Ángel Velázquez; Jiménez‐Sanchidrián, César; Ruíz, José Rafael

doi:10.1016/j.poly.2010.08.009

Cited by 37 publications

(18 citation statements)

References 21 publications

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“…The spectra of the dehydrated samples exhibit six peaks in the region of stretching O-H vibrations. In agreement with the literature [20,[35][36][37][38][39], the peaks at 3740 and 3724 cm −1 are assigned to Si-OH groups of the tetrahedral silicate layer and those at 3691 and 3673 cm −1 to Mg(3)-OH groups in the octahedral sheets of the sepiolite structure. The bands at 3597 and 3531 cm −1 have been attributed to water molecules coordinated to Mg cations.…”

Section: Resultssupporting

confidence: 91%

Catalytic performance of microporous materials for the production of renewable fuels

et al. 2018

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ETS-10, zeolite A and sepiolite based nano-structured materials were prepared and modified with potassium containing compounds using ion-exchange or impregnation and evaluated as basic catalysts for transesterification of vegetable oils using microwave heating. The structural features of these catalysts were characterised in detail by the variable temperature in situ X-ray diffraction, N 2 adsorption-desorption, scanning electron microscopy with energy dispersive X-ray analysis and in situ FTIR spectroscopy using adsorption-desorption of acetylene as a basic probe in order to evaluate their structure-catalytic performance relationship in the methanolysis of triglycerides. A wide range of parameters were utilised in order to optimise the reaction conditions. Although a high yield of fatty acid methyl esters with almost 100% selectivity can be achieved in transesterification reactions in the presence of K-containing sepiolite, this system shows significant deactivation due to its structural degradation and loss of the active component during the reaction and regeneration cycles. In contrast, zeolite KA and ETS-10, which are thermally stable crystalline materials, demonstrated no decrease in their activity for up to four reaction runs, and therefore can be used as effective solid basic catalysts in this reaction. Here we explore for the first time how the thermal and structural stability of the supported clay can affect its activity, an essential issue which has not been sufficiently studied in the recent research related to the biofuel production over solid catalysts.

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Section: Resultssupporting

confidence: 91%

Catalytic performance of microporous materials for the production of renewable fuels

et al. 2018

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“…Subsequent thorough mid-infrared studies by Serna et al (1975) and Prost (1975) confirm the observations of Hayashi et al (1969) regarding band splitting, but assign the appearance of the two OH stretching components to the rearrangement of H-bonding patterns in sepiolite induced by folding. The near-infrared (NIR) spectra of sepiolite subjected to folding by calcination have been recently reported by Mora et al (2010) but their analysis is contrary to the previous literature because it assumes the coexistence of trioctahedral and dioctahedral layers.…”

Section: Introductionmentioning

confidence: 96%

Near-infrared investigation of folding sepiolite

Tsampodimou

Bukas

Stathopoulou

et al. 2014

American Mineralogist

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Sepiolite is an industrially important clay mineral of the palygorskite-sepiolite group with alternating 2:1 ribbons and hydrated tunnels. Dry sepiolite, Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 4 , loses half of its OH 2 content upon further heating and undergoes a structural collapse known as folding. This treatment is considered essential for enhancing the absorptive properties of the clay. In this paper, the folding process is studied by near-infrared (NIR) spectroscopy, mid-infrared attenuated total reflectance (ATR), and thermogravimetric analysis (TGA). The folded state, Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 2 , reveals a new spectrum of fundamental and higher-order OH 2 vibrations, as well as systematically split doublets of structural and surface O-H vibrations. Detailed assignments for the stretching, combination, and overtone O-H modes are proposed on the basis of the two non-degenerate populations of Mg 3 OH (and SiOH) present in the folded state. It is demonstrated that NIR is of particular diagnostic value in monitoring conveniently and non-invasively the folding process, which appears as a simple transition between well-defined dry-and folded-structures. At the level of elementary sepiolite particles (laths), folding is described as a cooperative process requiring the integrity of the ribbons and the inter-ribbon linkages (moderately acid-leached sepiolite does not fold). This is opposed to the skewed and sometimes complex OH 2 desorption trace observed by high-resolution TGA, which appears to indicate a multimodal distribution of laths. It is proposed that the rate-determining step for a sepiolite (also, palygorskite) lath to fold is the creation of a critical zone at mid-particle length, which is OH 2 -deficient and contains unstable, fivefold-coordinated Mg 2+ .

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“…Figure (b) shows the FTIR data of a‐SEP, SPDPC‐SEP, and PSPHD‐SEP. In the spectrum of a‐SEP, the weak adsorption peak at 3674 cm −1 indicates the stretching vibrations of hydroxyl groups (ν OH ) (belongs to Mg 3 OH) attached to octahedral Mg ions located in the interior blocks of SEP . The broad band at 3442 cm −1 is due to stretch vibration of Si‐OH or Mg‐OH groups on the external surface of SEP, as well as that of coordinated and zeolitic water molecules, which abundantly exists in the tunnel or surface of SEP fiber.…”

Section: Resultsmentioning

confidence: 99%

“…Other coordinated water is lost in the third dehydration process between 550°C and 650°C with a 2.04% weight loss. When heating to 950°C, the last dehydroxylation of SEP anhydride occurs with a 1.24% weight loss, which leads to the destruction of SEP structure and formation of enstatite and silica …”

Section: Resultsmentioning

confidence: 99%

Structure, morphology, and properties of LDPE/sepiolite nanofiber nanocomposite

Zhang

et al. 2015

Polymers for Advanced Techs

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Sepiolite (SEP) nanofibers have been modified by grafting with poly(pentaerythritol diphosphonate dichloridehexamethylendiamine) (PSPHD) and compounded with low density polyethylene (LDPE) to form a nanocomposite. The various modified SEPs were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared, transmission electron microscopy (TEM), and thermogravimetric analysis. The Fourier transform infrared and X-ray photoelectron spectroscopy tests show that covalent bonding exists between SEP fiber and modifiers. The nanoscale size and morphologies of SEP fiber and modified SEP nanofibers can be observed clearly by TEM. The thermogravimetric analysis results reveal that the multi-step thermal degradation process of SEP fiber is changed by grafting modification. The various LDPE/SEP nanocomposites were characterized by scanning electron micrograph, TEM, dynamic mechanical analysis, and tensile test. The results suggest that a good interfacial modification effect has been obtained between PSPHD-SEP and LDPE matrix. A particular improvement in tensile strength is reflected in tensile tests. Dynamic mechanical analysis shows that the storage moduli (E') of PSPHD-SEP/LDPE nanocomposites are much higher than that of neat LDPE and a-SEP/LDPE systems.

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Study of the thermal decomposition of a sepiolite by mid- and near-infrared spectroscopies

Cited by 37 publications

References 21 publications

Catalytic performance of microporous materials for the production of renewable fuels

Catalytic performance of microporous materials for the production of renewable fuels

Near-infrared investigation of folding sepiolite

Structure, morphology, and properties of LDPE/sepiolite nanofiber nanocomposite

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