Over the last ten years, the concept of pillaring has frequently been applied on layered double hydroxides (LDHs). Due to the variety of possible anionic pillaring species and the adjustable layer charge density, LDHs offer good perspectives with regard to the creation of porous adsorbents and catalysts. But despite these possibilities, their porosity properties can still not compete with those of industrially applicable materials like zeolites. In this study, theoretical calculations based on geometrical models and performed on both Fe(CN)6-MgAl-LDHs (A) and [PV2W10 O40]-ZnAl-LDHs (B) were reported. Properties such as the micropore volume and the interpillar distance were calculated, and compared to experimental data. For a M(II)/M(III) ratio in the layers of 3, the theoretical maximum micropore volumes were 0.3843 cm3/g (A) and 0.1497 cm3/g (B), respectively. By implementing parameters like the stack size, pillars on the outside of the stacks and the possibility of collapse, the model was adjusted in order to create a realistic picture of the microstructure of pillared LDHs. This led to a better understanding of the limiting factors, and gave an explanation for the relatively low micropore volumes of pillared LDHs. For the Fe(CN)6-MgAl-LDHs, small interpillar distances were responsible for the partial inaccessibility of the interlayer regions by N2. This effect was the most pronounced for high charge density LDHs. The situation for the [PV2W10O40]-ZnAl-LDHs is more complex. Probably due to an incomplete pillaring process, the theoretical maximum values are not reached. 相似文献
The catalytic partial oxidation of CH4 to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH4 into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl2O4 spinel phase had a positive effect on the stability of the catalyst. 相似文献
The preparation of surface-modified layered double hydroxides/unsaturated polyester (LDH/UP) nanocomposites were performed. By in situ coprecipitation, LDHs, modified through grafting of vinyltriethoxysilane (VTS) carrying a double bond using the anionic surfactant sodium dodecyl sulfate (SDS), were used as nanofillers for unsaturated polyester (UP). The morphology of LDH and nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Moreover, the thermal properties were determined by thermogravimetric analysis (TGA) and thermal degradation mechanism was discussed. 相似文献
Unmodified (LDH) and modified (mLDH) layered double hydroxides have been added to gum and ZnO‐cured carboxylated nitrile rubber (XNBR). It was observed that both LDH and mLDH inhibit the formation of ionic cross‐links between XNBR and ZnO quite significantly, as is evident from DMA and FT‐IR studies. The suppression of ionic cross‐links formation was also reflected in the mechanical properties of the resulting composites. A tentative sketch has also been suggested for the possible mechanism involved in the inhibition of ionic cross‐links by LDHs. X‐ray diffraction and STEM studies were performed to see the dispersion of LDH's in the elastomer matrix.
