A catalytic architecture composed of titanium silicalite-1 and nanostructured support for oxime synthesis.

摘要

The objective of this Ph.D. thesis is to develop a supported titanium silicalite-1 (TS-1) composite for industrial ammoximation process. The synthesis and catalytic activity of the material developed were studied. Carbon nanofibers (CNFs) were first used as the catalyst support for SiO2-TiO 2 nanoparticles due to its potential in catalyst recovery. Although transmission electron microscopy (TEM) revealed that the amorphous nanoparticles could be transformed to TS-1 crystals on the CNF surface upon recrystallization, the CNF-based TS-1 catalyst was not suggested for industrial application due to the poor thermal and chemical stability of the support. Therefore, the catalyst design was then focused on using bentonite clay as an alternative to form the clay-based TS-1 composite. The synthesis, catalytic activity and reaction model were studied thoroughly for the cyclohexanone ammoximation.;It was found that submicron TS-1 could be formed on and between the clay structures by hydrothermal treatment which mimics the layered morphology of the clay. No agglomeration of TS-1 was observed in the clay-based composite after reuse, therefore the catalyst was proven to be durable. It was found that the presence of clay facilitated rapid crystallization of TS-1. Fourier transfom infrared (FT-IR) study showed that the Si defective sites were the exact location at which Ti was bonded. As a result, it was concluded that the formation of TS-1 on the bentonite was initiated by the prior formation of silicalite-1 structure, which is then followed by Ti incorporation. The preparation condition of the composite was optimized in terms of characteristics necessary for selective oxime synthesis. The catalytic composite is much superior to the ordinary TS-1 in terms of durability as it showed 90% cyclohexanone conversion and 84% selectivity in repeated reaction cycles. In addition, the composite also demonstrated improved settling ability compared with unsupported TS-1.;The intrinsic kinetic of the cyclohexanone ammoximation over the clay-based TS-1 composite was found to follow the Eley-Rideal mechanism according to the reaction model developed. The model results were in good agreement with the experimental data. With the reaction kinetic being formulated, together with the calculated activation energy and preexponential factor, this study provided a guideline for industrial design and showed conclusively that the clay-based TS-1 composite is applicable.