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Ceria Supported Au Catalysts for Low-temperature CO Oxidation

Author: HuangXinSong
Tutor: CaoYong
School: Fudan University
Course: Physical and chemical
Keywords: Supported Gold Catalysts Cerium oxide Carrier structure Surface morphology CO oxidation
CLC: O643.32
Type: Master's thesis
Year: 2009
Downloads: 363
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Abstract


Gold catalysis in recent years has become a research hotspot. From the late eighties Haruta et al found that the load on the transition metal oxide gold nanoparticles in the CO oxidation reaction with high catalytic activity and exhibit unique humidity enhancement effect since the gold catalyst for research and development has become increasingly active . The attraction of gold catalysis nanometer effect that makes one kind traditionally been considered to be catalytically inert metal produced a qualitative change in the catalytic performance improved, so the size effect of Au nano-gold catalyst has been the focus of the study. In addition, it is also found that the catalytic deposits but also with the type of vector used. Generally used reducible transition metal oxide as a carrier, which is mainly due to such carriers not only produce a strong interaction with gold to enhance the stability of gold small scale, and can provide some reactant molecules (such as oxygen ) activation and directly contribute to the reaction. However, even on the same carrier, when using a different method of preparation, the activity of the resulting catalyst will have different, sometimes the difference of magnitude. The literature for preparing the most common method is to use gold catalysts NaOH as a precipitating agent deposition - precipitation (DP) method. Cerium oxide (CeO 2 ) is a widely used catalytic materials. Cerium oxide Ce 4 can easily be reduced to Ce 3 , in this process the surface of the cerium oxide lattice ions can be removed, thereby forming a large number of between CeO 2 and Ce2O 3 between the non-stoichiometric oxides, but the lattice itself remains the original fluorite structure and oxygen-rich conditions in quickly restored to CeO 2 . However, the literature contains cerium oxide gold catalysts for CO oxidation reaction performance reported is very inconsistent, even conflicting, reflecting the complexity of the catalytic system. In this paper, we used a variety of preparation methods and characterization methods detailed study of the structure and cerium oxide forms on the surface structure of supported gold catalysts, and the effects of these catalysts in CO oxidation at low temperature catalytic performance. In the structure-activity relation, based on the load on the gold nanoparticles of cerium oxide catalytic nature and activity center for a more in-depth discussion. The main contents are as follows: First, the product contained cerium oxide VP Adnano 50 gold catalyst structure and properties of the goods offered by the company Degussa ceria VP Adnano 50 as the carrier, using the DP gold catalyst synthesized to study the atmosphere of post-processing, gold loading and storage time on the gold cerium catalyst structure and performance, optimized for the subsequent study preparation conditions, preliminary exploration gold cerium catalyst properties. Study found that the CO oxidation reaction atmosphere most conducive to post-processing of gold cerium catalyst surface gold species highly dispersed, get the best catalytic performance. Lower gold loading more conducive to improving the utilization efficiency of gold to obtain a higher intrinsic activity. Au/VP50 catalyst also has excellent resistance to storage stability. Two different pre-calcination temperature ceria supported gold catalyst structure and properties of gold in advance before the load through a different temperature (673-1073 K) The method of vector control calcined cerium oxide structure and surface morphology, with sodium hydroxide deposition - Load 1% gold precipitated catalysts prepared and evaluated their activity for CO oxidation. Experimental results show that when the carrier pre-calcination temperature of 873 K when, Au / CeO 2 optimal activity of the catalyst. TEM results show that the pre-calcined at 873 K cerium oxide has good crystallinity, cerium oxide, {111} surface the angle between the surface is flattened at the same temperature to expose the thermodynamically metastable {100} crystal faces. Further characterized by the catalyst prebaked We found 873 K ceria mainly through improving the catalytic activity of both: a) {100} crystal faces have a stronger interaction with gold, so that Au / CeO 2 -873 higher dispersion of the gold; b) {100} crystal faces than the redox strong {111} crystal faces, the CO oxidation reaction of migration of reactive oxygen species better. At high space velocity (1,600,000 h -1 ) conditions, Au / CeO 2 -873 The intrinsic activity reached 98.8 mol CO · h < sup> -1 · g Au -1 and within 6h without significant deactivation. Third, cerium oxide nanorods supported gold catalyst structure and properties has been synthesized by hydrothermal method structured cerium oxide surface morphology and the nanorods as the carrier prepared by DP gold catalyst. Test results show that the activity of cerium oxide nanorods containing catalyst activity compared to gold nanoparticles of cerium oxide catalysts containing gold has increased significantly in the 278 K the intrinsic activity and were 4.02mol CO · h -1 · g Au -1 , the apparent activation energy of 15.9 kJ · mol -1 , and Gold nanoparticles of cerium oxide catalyst containing data 0.15 mol CO · h -1 · g Au -1 and 28.4 kJ · mol -1 . By XRD, TEM, H2-TPR, XPS, UV-Vis, DRIFTS characterizations indicate cerium oxide nanorod surface exposed {100} and {110} planes with gold exists between the stronger carrier - metal interaction (SMSI ), further supports the conclusion in two research also found that the presence of gold modification of the electronic structure of the carrier, the carrier improved redox ability.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
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