Titanium(IV)-induced cristobalite formation in titanosilicates and its potential impact on catalysis

Abstract

Cristobalite, a crystalline form of silica, is shown to be formed within an amorphous titanosilicate, at previously unknown conditions. Mesoporous titanosilicate microspheres (MTSM) were synthesized as efficient catalysts for the epoxidation of cyclohexene with tert-butyl hydroperoxide. High-resolution transmission electron microscopy revealed the presence of crystals in this predominantly amorphous material, after calcination at 750 °C. When calcined at 800 °C, the crystals were identified via PXRD as predominantly cristobalite, which possibly marks its first observation in titanosilicates at such a low temperature, without adding any alkali metals during synthesis. Catalytic experiments conducted with MTSM materials calcined at temperatures varying from 650 to 950 °C, reveal that the amount of cristobalite formed increases with temperature, and that it has a significant impact on the pore structure, and, remarkably, correlates with the catalytic activity of titanosilicates.Electronic supplementary materialThe online version of this article (10.1007/s10853-018-2869-0) contains supplementary material, which is available to authorized users.

A non-doped microporous titanosilicate for bimodal adsorption-photocatalysis based removal of organic water pollutants

“…Whilst most of the microbeads are isolated and spherical, some amalgamation of material in the form of a fusion of beads are evident. SEM micrographs also show micron sized pores, suggesting the presence of the oil/surfactant templating mixture prior to calcination, leaving behind a complex mesoporous/microporous structure, which will shift (in this case, to a predominantly microporous structure) based on homogenizing conditions, similar to previous reports [24,33].…”

“…Templating with a surfactant/oil mixture was investigated as a cost-effective, facile technique to improve material porosity. This method has successfully been used previously to develop various types of titanosilicates with a wide range of structural properties and advanced pore structures to catalyse industrially relevant reactions [24,33,34].…”

Silica-Coated ZnS Quantum Dots for Multicolor Emission Tuning from Blue to White Light

“…From 1400 to 4000 cm –1 , in the uninterest range the signals are related to solvent and surfactant residues during the capping process, such as O–H vibrations of the water and ethanol or C–H vibrations of trapped CTAB (3000–4000 and 2850–2910 cm –1 , respectively), and they decrease as the temperature increases until they disappear. Into the interest range (500–1400 cm –1 ) where the vibrational modes of silica appear, it is possible to observe a small position shifting in the main band around 1075 cm –1 , the enhancement of the intensity and definition as the temperature increases of a signal around 900 cm –1 related commonly with crystalline structures of silicon oxide (SiO x , x = 4 normally) and the appearing of a couple of signals around 600 cm –1 since 700 °C and higher temperatures, that has been reported for the Zn–O–Si vibrations for zinc (and other transition metal ions like titanium) orthosilicate (ZnSiO 4 ) and induced cristobalite formation. − …”

A Study on the Utilization of Coal Fly Ash Derived Grog in Clay Ceramics

“…Although kaolin clay has a substantial amount of quartz, the quartz was not transformed to cristobalite during firing at 1200 • C. The quartz from kaolin clay only changes to cristobalite upon firing at temperatures between 1200 • C and 1400 • C [24]. On the other hand, quartz from CFA has a higher ability to transform to cristobalite at temperatures below 1200 • C. This is attributed to the alkali metal oxides found in CFA that can accelerate the devitrification rate of silica into cristobalite [25]. This explained the high content of quartz in kaolin-rich samples and high content of cristobalite in CFAG-rich samples.…”

“…On the other hand, quartz from CFA has a higher ability to transform to cristobalite at temperatures below 1200 °C. This is attributed to the alkali metal oxides found in CFA that can accelerate the devitrification rate of silica into cristobalite [ 25 ]. This explained the high content of quartz in kaolin-rich samples and high content of cristobalite in CFAG-rich samples.…”