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New insight into the phase transformation of sepiolite upon alkali activation: Impact on composition, structure, texture, and catalytic/sorptive properties
Applied Clay Science ( IF 5.3 ) Pub Date : 2020-09-01 , DOI: 10.1016/j.clay.2020.105740
A. Walczyk , A. Michalik , B.D. Napruszewska , J. Kryściak-Czerwenka , R. Karcz , D. Duraczyńska , R.P. Socha , Z. Olejniczak , A. Gaweł , A. Klimek , M. Wójcik-Bania , K. Bahranowski , E.M. Serwicka

Abstract Wet NaOH activation of natural sepiolite was studied for the purpose of endowing the material with enhanced basicity for potential catalytic/sorptive applications. A series of synthesized solids were characterized with X-ray powder diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), X-ray fluorescence (XRF), atomic absorption spectroscopy (AAS), N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and 29Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). Surface basicity was determined by titration with benzoic acid. The study led to the major reinterpretation of the existing knowledge on the sepiolite phase transformation to its sodium form (loughlinite). Activation with NaOH involved significant desilication of sepiolite, while the loss of Mg from the solid was prevented due to the intracrystalline preciptation of amorphous Mg(OH)2. Formation of Mg(OH)2 affected the material composition, hindered the access of nitrogen molecules to the micropore system, and enhanced the product basicity. For the first time the Si sites at the centre of structural ribbons were identified as part of the silicate framework most susceptible to leaching upon alkaline treatment. Although the NaOH treated product had the structure of loughlinite, it was in fact a composite of desilicated loughlinite and amorphous Mg(OH)2. The materials were tested as catalysts in aldol self condensation of acetone and oxidation of cyclohexanone to e-caprolactone, and as CO2 sorbents.

中文翻译:

对碱活化后海泡石相变的新见解:对组成、结构、质地和催化/吸附性能的影响

摘要 研究了天然海泡石的湿 NaOH 活化,目的是赋予材料增强的碱度,用于潜在的催化/吸附应用。通过 X 射线粉末衍射 (XRD)、扫描和透射电子显微镜 (SEM/TEM)、X 射线荧光 (XRF)、原子吸收光谱 (AAS)、N2 吸附/解吸、X-射线光电子能谱 (XPS)、傅里叶变换红外光谱 (FTIR) 和 29Si 魔角自旋核磁共振光谱 (MAS NMR)。通过用苯甲酸滴定确定表面碱度。该研究导致对海泡石相转变为其钠形式(loughlinite)的现有知识进行了重大重新解释。用 NaOH 活化涉及海泡石的显着脱硅,而由于无定形 Mg(OH)2 的晶内沉淀,防止了 Mg 从固体中流失。Mg(OH)2 的形成影响了材料组成,阻碍了氮分子进入微孔系统,并提高了产品的碱度。首次将结构带中心的 Si 位点确定为硅酸盐骨架的一部分,在碱处理时最容易浸出。虽然 NaOH 处理过的产品具有菱镁矿结构,但它实际上是脱硅菱镁矿和无定形 Mg(OH)2 的复合物。测试这些材料作为丙酮羟醛自缩合和环己酮氧化为ε-己内酯的催化剂,以及作为CO 2 吸附剂。Mg(OH)2 的形成影响了材料组成,阻碍了氮分子进入微孔系统,并提高了产品的碱度。首次将结构带中心的 Si 位点确定为硅酸盐骨架的一部分,在碱处理时最容易浸出。虽然 NaOH 处理过的产品具有菱镁矿结构,但它实际上是脱硅菱镁矿和无定形 Mg(OH)2 的复合物。将这些材料作为丙酮羟醛自缩合和环己酮氧化成ε-己内酯的催化剂以及作为CO 2 吸附剂进行测试。Mg(OH)2 的形成影响了材料组成,阻碍了氮分子进入微孔系统,并提高了产品的碱度。首次将结构带中心的 Si 位点确定为硅酸盐骨架的一部分,在碱处理时最容易浸出。虽然 NaOH 处理过的产品具有菱镁矿结构,但它实际上是脱硅菱镁矿和无定形 Mg(OH)2 的复合物。将这些材料作为丙酮羟醛自缩合和环己酮氧化成ε-己内酯的催化剂以及作为CO 2 吸附剂进行测试。首次将结构带中心的 Si 位点确定为硅酸盐骨架的一部分,在碱处理时最容易浸出。虽然 NaOH 处理过的产品具有菱镁矿结构,但它实际上是脱硅菱镁矿和无定形 Mg(OH)2 的复合物。测试这些材料作为丙酮羟醛自缩合和环己酮氧化为ε-己内酯的催化剂,以及作为CO 2 吸附剂。首次将结构带中心的 Si 位点确定为硅酸盐骨架的一部分,在碱处理时最容易浸出。虽然 NaOH 处理过的产品具有菱镁矿结构,但它实际上是脱硅菱镁矿和无定形 Mg(OH)2 的复合物。将这些材料作为丙酮羟醛自缩合和环己酮氧化成ε-己内酯的催化剂以及作为CO 2 吸附剂进行测试。
更新日期:2020-09-01
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