当前位置：
X-MOL 学术
›
Chem. Mater.
›
论文详情
Our official English website, www.x-mol.net, welcomes your
feedback! (Note: you will need to create a separate account there.)
Effect of Defect Site Preorganization on Fe(III) Grafting and Stability: A Comparative Study of Delaminated Zeolite vs Amorphous Silica Supports
Chemistry of Materials ( IF 7.2 ) Pub Date : 2017-07-25 00:00:00 , DOI: 10.1021/acs.chemmater.7b02062
Nicolás A. Grosso-Giordano , Alexander J. Yeh , Alexander Okrut , Dianne J. Xiao , Fernande Grandjean 1 , Gary J. Long 1 , Stacey I. Zones 2 , Alexander Katz
Chemistry of Materials ( IF 7.2 ) Pub Date : 2017-07-25 00:00:00 , DOI: 10.1021/acs.chemmater.7b02062
Nicolás A. Grosso-Giordano , Alexander J. Yeh , Alexander Okrut , Dianne J. Xiao , Fernande Grandjean 1 , Gary J. Long 1 , Stacey I. Zones 2 , Alexander Katz
Affiliation
|
The stabilization of isolated grafted Fe3+ sites on siliceous supports is investigated by a comparative study of crystalline versus amorphous materials. Our synthetic approach treats crystalline delaminated zeolite DZ-1 and amorphous silica (SiO2) with an aqueous NaFeEDTA cation precursor complex, to result in grafting of isolated Fe3+ sites via covalent attachment to support hydroxyl groups. Thermogravimetric analysis and UV–visible spectroscopy demonstrate the complete detachment of chelating EDTA ligand upon Fe3+ grafting on both supports. Before calcination treatment, both Fe/DZ-1 and Fe/SiO2 have similar UV–visible spectral features, with absorption bands at 208–225 and 257 nm, characteristic of framework Fe3+ sites in zeolites. Calcination does not affect the UV–visible spectroscopic characteristics of Fe/DZ-1 but changes the spectrum of Fe/SiO2 to a single absorption band at 260 nm, indicating better thermal stability of Fe3+ sites in Fe/DZ-1 as compared to Fe/SiO2. This stability persists for Fe/DZ-1 even during alkane oxidation catalysis in the presence of hydrogen peroxide, which causes aggregation of Fe3+ into oxide oligomers for Fe/SiO2. 57Fe Mössbauer spectroscopy of calcined materials indicates a more uniform distribution of sites in Fe/DZ-1 relative to Fe/SiO2. We thus attribute the greater robustness and site uniformity of Fe/DZ-1 to the chelation of Fe3+ by the rigid crystalline silicate DZ-1 framework, engendered by the spatial preorganization of grafting hydroxyls groups within its uniform defect sites, which are templated by framework B3+ removal during delamination. Such preorganization enables cooperativity between neighboring hydroxyl groups. This contrasts with more randomly distributed hydroxyl groups on SiO2, which lack such preorganization, leading to decreased hydrothermal stability and an Fe3+ grafting density that is ∼7-fold lower for Fe/SiO2 relative to Fe/DZ-1. These observations reveal how the silicate surface onto which a cation is grafted can act as a relevant ligand, capable of controlling material synthesis and functionality akin to ligands in homogeneous metal complexes, and demonstrate the advantages of support crystallinity in having this ligand be hydrothermally stable and tunable via templating.
中文翻译：
缺陷部位预组织对Fe（III）接枝和稳定性的影响：层状沸石与无定形二氧化硅载体的比较研究
通过对晶体材料与无定形材料进行比较研究，研究了硅质载体上分离的接枝Fe 3+位点的稳定性。我们的合成方法使用含水的NaFeEDTA阳离子前体复合物处理结晶的脱层沸石DZ-1和无定形二氧化硅（SiO 2），从而通过共价键接支撑羟基来接枝分离出的Fe 3+位点。热重分析和紫外可见光谱法表明，在两种载体上接枝Fe 3+后，螯合的EDTA配体完全脱离。煅烧处理前，Fe / DZ-1和Fe / SiO 2都具有相似的紫外可见光谱特征，在208-225和257 nm处有吸收带，这是沸石中骨架Fe 3+位点的特征。煅烧不会影响Fe / DZ-1的紫外可见光谱特性，但会改变Fe / SiO 2的光谱到260 nm处的单个吸收带，表明Fe / DZ-1中Fe 3+位点的热稳定性更好，因为与Fe / SiO 2相比。即使在过氧化氢存在的烷烃氧化催化过程中，Fe / DZ-1的稳定性仍然存在，这会导致Fe 3+聚集成Fe / SiO 2的氧化物低聚物。57煅烧材料的FeMössbauer光谱表明，相对于Fe / SiO 2，Fe / DZ-1中的位点分布更均匀。因此，我们将Fe / DZ-1的更大的稳固性和位点均匀性归因于刚性结晶硅酸盐DZ-1骨架对Fe 3+的螯合，这是由于在其均匀缺陷位点内接枝羟基的空间预组织而产生的，这些位置被模板化在分层过程中通过框架B 3+去除。这样的预组织使得相邻的羟基之间具有协同作用。与此相反，SiO 2上的羟基更随机分布，而羟基缺乏这种预组织，导致水热稳定性下降，Fe 3+Fe / SiO 2的接枝密度比Fe / DZ-1低约7倍。这些观察结果揭示了将阳离子接枝到其上的硅酸盐表面如何充当相关的配体，能够控制材料的合成和功能，类似于均质金属络合物中的配体，并证明了使该配体具有水热稳定性和可结晶性的优点。可通过模板进行调整。
更新日期：2017-07-26
中文翻译：
缺陷部位预组织对Fe（III）接枝和稳定性的影响：层状沸石与无定形二氧化硅载体的比较研究
通过对晶体材料与无定形材料进行比较研究，研究了硅质载体上分离的接枝Fe 3+位点的稳定性。我们的合成方法使用含水的NaFeEDTA阳离子前体复合物处理结晶的脱层沸石DZ-1和无定形二氧化硅（SiO 2），从而通过共价键接支撑羟基来接枝分离出的Fe 3+位点。热重分析和紫外可见光谱法表明，在两种载体上接枝Fe 3+后，螯合的EDTA配体完全脱离。煅烧处理前，Fe / DZ-1和Fe / SiO 2都具有相似的紫外可见光谱特征，在208-225和257 nm处有吸收带，这是沸石中骨架Fe 3+位点的特征。煅烧不会影响Fe / DZ-1的紫外可见光谱特性，但会改变Fe / SiO 2的光谱到260 nm处的单个吸收带，表明Fe / DZ-1中Fe 3+位点的热稳定性更好，因为与Fe / SiO 2相比。即使在过氧化氢存在的烷烃氧化催化过程中，Fe / DZ-1的稳定性仍然存在，这会导致Fe 3+聚集成Fe / SiO 2的氧化物低聚物。57煅烧材料的FeMössbauer光谱表明，相对于Fe / SiO 2，Fe / DZ-1中的位点分布更均匀。因此，我们将Fe / DZ-1的更大的稳固性和位点均匀性归因于刚性结晶硅酸盐DZ-1骨架对Fe 3+的螯合，这是由于在其均匀缺陷位点内接枝羟基的空间预组织而产生的，这些位置被模板化在分层过程中通过框架B 3+去除。这样的预组织使得相邻的羟基之间具有协同作用。与此相反，SiO 2上的羟基更随机分布，而羟基缺乏这种预组织，导致水热稳定性下降，Fe 3+Fe / SiO 2的接枝密度比Fe / DZ-1低约7倍。这些观察结果揭示了将阳离子接枝到其上的硅酸盐表面如何充当相关的配体，能够控制材料的合成和功能，类似于均质金属络合物中的配体，并证明了使该配体具有水热稳定性和可结晶性的优点。可通过模板进行调整。
京公网安备 11010802027423号