In-situ mesoporous silica pillared clay synthesis and effect of titanium and iron incorporation to structural properties

Abstract

Abstract Standard Wyoming SWy-2 mineral as a clay source was modified by use of cetyltrimethylammonium bromide as surfactant before Silica Pillared Clays (SPCs) synthesis, while octylamine (OA) was chosen as an auxiliary surfactant. Using tetraethyl orthosilicate as a silica source by ranging silica/modified clay (Si/C+) molar ratio within 20–150, SPC supports were synthesized keeping OA/C+ molar ratio as 20. Hydrothermal syntheses of titanium and iron containing SPC catalysts were carried out with M/Si molar ratios in between 0.03 and 0.15. Structural characterization results explained well the proposed mechanism for formation of MCM-41 like silica pillars between clay layers. With an increase of (001) peak reflection yielding basal spacing values up to 6.9 nm, polycrystalline structure observed in XRD patterns was confirmed by TEM images in SPCs. TEM also showed silica phase formations between clay bundles. Structural properties at Si/C+ molar ratio as 50 were the best with a surface area of 1874 m2/g. Titanium loading resulted in some decreases in surface area values while structural properties of iron incorporated catalyst at low iron content were found to be closer to that of the support. The highest Lewis and Bronsted acidities were observed by low titanium and iron incorporation to high silica containing support, respectively. TGA results showed that calcination temperature of 550 °C was sufficient for stable structures formation. ICP analysis and TEM images indicated that titanium species settled locally nearly 100% loading success and presence of titanium increased iron loading success. XPS results showed presences of TiO2 and mostly Fe2O3 forms.