Preparation Of Modified Sba-15 And Its Application In Co Oxidation Reaction

Ordered mesoporous silica material SBA-15 can be excellent catalyst supporters due to their excellent performance such as large surface area, uniform pore size and high hydrothermal stability etc. However, the pure-silica mesoporous material SBA-15 lacks active sites, which result poor ion exchange capacity, weak surface acidity and even hinder their applications. At present, several methods are developed to broaden the applications of SBA-15 in catalysis by introducing Lewis acid & Bronsted acid sites and oxidation & reduction centers. However, reported procedures usually have different drawbacks; i.e. the synthesis of SBA-15 was time-consuming, the active metal particle size of SBA-15 based catalyst prepared via impregnation method was not small enough, the grafting routes always relatively complicated, in some cases the process has to be carried out under conditions that do not include water and oxygen, and most noble metals were not suit for preparing SBA-15 based catalyst via deposition-precipitation procedure because of their anion characteristics. Base on these realities, we propose an improved method to synthesize SBA-15 and to prepare SBA-15 based catalyst with the Pt loading. In this thesis, for preparing Pt/SBA-15 with highly catalytic activity and stability, we studied the influence of various factors on the catalytic activity by using the CO oxidation reaction as a model. The main context of this thesis is described as following:By using the nonionic triblock co-polymer surfactant EO20PO70EO20 (P123) and tetraethyl orthosilicate (TEOS) as template and silicon source respectively, mesoporous silicon material SBA-15 was synthesized rapidly via microwave assistant method. XRD, N2 physisorption, HRTEM, IR etc. were carried out to characterize the obtain samples. The best catalyst supporter was selected based on CO oxidation reaction. We also studied the relation between the catalytic activity and the introducing of different agents, dopants. There are some imperative experimental results:1, High ordered mesoporous material SBA-15, with 2D hexagonal symmetry structure, was rapidly synthesized within 6 hours. The pore size of SBA-15 can be regulated via manipulating the temperature of crystallization. 2, Pt/SBA-15 catalyst was prepared based on the synthesized SBA-15, and be used for the CO oxidation reaction. The result indicated that the SBA-15 obtained by controlling the crystallizing temperature at 100℃, possess high surface area and suitable pore size (620 m2g-1,5.1 nm). The catalyst prepared based on this support has better catalytic activity and therefore more suitable as supporter in CO oxidation reaction.3, Traditional metals (Fe, Co and Ni agents) can improve the dispersion of metal loading; therefore can promote the catalytic activity. Comparing with the stepwise impregnation method, the co-impregnation was more benieficial to reaching higher CO oxidation activity. Ni promoter was superior in the catalytic reaction, and a complete converting of CO of PtNi/SBA-15 was at 190℃. The improved activity was a result of the strong bimetal interaction cooperation fact.4, Ce-SBA-15 can be obtained when the pH of gel system ranged from 2 to 7. Specifically, at pH=2, the obtained Ce-SBA-15 has higher surface area (692.28 m2g-1) and better textural structure. Suitable amount Ce species introduced into SBA-15 via impregnation method using cerium nitrate can also preserve the highly ordered structure of SBA-15.5, Modified SBA-15 with Ce dopant was more favour for the dispersion of Pt particles. However, the catalytic activity of Pt/Ce-SBA-15 catalyst was not outweigh that of PtCe/SBA-15. The catalytic activity can be promoted deeply when both Ce species (Ce loading and Ce dopant) were introduced into the catalyst. The prepared PtCe/Ce-SBA-15 has the highest catalytic activity over the CO conversion reaction that complete conversion at 120℃. Study indicated that the promoted catalytic activities were due to the improvement of Pt dispersions and the strong metal-support interactions created by the cerium loading.