CuO-based Supported And Composite Porous Nanocatalysts For Low-temperature Carbon Monoxide Oxidation

As the major air pollutant, carbon monoxide is usually emitted from many industrial process, transportation and domestic activities. It is harmful to human health and environment. In order to control the toxic emission, catalytic oxidation of CO is an efficient way. During the last decades, a number of catalysts have been studied, in which precious metal catalysts have been demonstrated to be bery effective. Although the precious metal catalysts have high activity for CO oxidation, the high cost and limited availability discourage their extensive applications. Much attention has thus recently been paid to base metal as catalysts, especially copper oxide, for the purpose to find an alternative catalytic component to reduce using or enen replace the noble metal. Furthermore, the physical and chemical properties of materials depend not only on the chemical composition but crucially also on their porosity and shape, and much effort has been focused on tailoring the pore size and external morphology of the materials. In the fields of catalysts, porous oxides have recently attracted great interest for the use as catalyst and catalyst support, since the porous supports have remarkably large surface areas and narrow pore size distributions so as to give rise to well dispersed and stable metal particles on the surface and as consequence would show an improved catalytic performance.However, to the best of our knowledge, there are few reports on the study of porous metal oxides support CuO for CO oxidation at low temperature. It is still a challenge to develop high surface area and porous metal oxides catalysts for the application of enhancing catalytic performance. In the dissertation, the preparation process of the copper-based porous metal oxide catalysts, the synergistic effect, and the catalytic mechanism for CO oxidation were systematically investigated, aiming at developing new catalyst system for the abatement of CO at low temperature. The following results and conclusions have been obtained:1. The surfactant-assisted method of nanocrystalline particle assembly was employed to prepare the high-surface area mesoporous CuO/Ce_0.8Zr_0.2O₂ and CuO-Fe₂O₃ composite catalysts in the presence of the cationic surfactant CTAB for the first time. All the as-prepared samples were characterized by X-ray diffraction (XRD), N₂-sorption, thermogravimetry-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and other techniques. Their catalytic behavior for low-temperature CO oxidation was studied by using a microreactor-GC system. XRD and TEM analysis indicated that the catalysts particles were nanoscaled. N₂ adsorption-desorption isotherms realved a mesoporous nanocatalyst system with high-surface area and uniform pore-size distribution. The results of catalytic activity measurements showed that these mesoporous nanostructured CuO/Ce_0.8Zr_0.2O₂ and CuO-Fe₂O₃ composite catalysts were very active for low-temperature CO oxidation. The catalytic behavior depended on the CuO loading amount, the calcination temperature, the surface area, the particles size and the synergistic effect of the catalysts. Especially, for the CuO/Ce_0.8Zr_0.2O₂ catalyst system, the influences of the prepared method and the Ce/Zr ratio on the catalytic performance were investigated in detail. The results indicated that the surfactant-assisted method prepared catalysts show the highest catalytic activity and the Ce_0.8Zr_0.2O₂ is the best Ce/Zr ratio for the catalyst in the application of CO oxidation.2. Porousα-Fe₂O₃ nanorods were prepared by a surfactant-assisted method in the presence of the cationic surfactant CTAB. The structure and morphology of obtained products were characterized and the CO oxidation activities were investigated. Theα-Fe₂O₃ nanorods possess a mesostructure with a pore size distribution in the range of 5-12 nm and high surface area, exhibiting high catalytic activity for CO oxidation. The mechanism for the CTAB-assisted synthesis of porousα-Fe₂O₃ nanorods is proposed. CuO nanocrystals with size about 6 nm were loaded on the surface of porousα-Fe₂O₃ nanorods by a deposition-precipitation (DP) method, which retained the mesoporosity ID structure and exhibited superior activity for catalytic oxidation of CO, as compared with that on commercialα-Fe₂O₃ powders. The enhanced catalytic activity of the CuO/α-Fe₂O₃NRs nanocatalysts was attributed to the strong interaction between CuO nanocrystals and the porous nanorods support, supported by the H₂-TPR and XPS analysis results. The active site of the CuO/α-Fe₂O₃NRs nanocatalysts was Cu₂O, identified by the anaylsis results. And the scheme of CO oxidation over CuO/α-Fe₂O₃NRs nanocatalyst was proposed.3.Hierarchically mesoporous-macroporous titanium dioxide (MMTD) was synthesized by the hydrolysis of tetrabutyl titanate in the absence of surfactant and autoclaving at 60℃, which exhibits a porous hierarchy of wormhole-like mesostructure in the framework of macrochannels. Different contents of CuO nanoparticles were supported on the MMTD by a deposition-precipitation method, retaining the high surface areas and hierarchical porosity. The prepared MMTD support and resulted CuO/MMTD nanocatalysts were characterized and their catalytic behavior for low-temperature CO oxidation was studied by using a microreactor-GC system. The CuO/MMTD catalyst with 8 wt.% CuO content and calcined at 400℃was found to have the highest catalytic activity. The comparative study of the influence of the hierarchically porous structure on the catalytic activity was employed. The catalytic activity depended on the CuO loading amount, the precalcination temperature, the meso-macroporous framework, the surface area and the particle size of the CuO/MMTD catalysts. The active site of the CuO/MMTD nanocatalysts was Cu₂O, identified by the anaylsis results.4. Fiber-like high-surface-area attapulgite (APT) clay was used as the support of CuO nanoparticles for the first time, and the texural and structural properties of the prepared CuO/APT nanocatalysts were characterized by XRD, SEM, TEM, N₂ sorption analysis and XPS techniques. The catalytic behavior of the prepared CuO/APT catalysts for low-temperature CO oxidation was investigated, indicating interesting catalytic activity that comparable to the previously reported metal oxide supported CuO catalysts. Due to the unique property and the feature of much low cost and easy availability, the use of APT clay renders a great promise to be the catalyst support for the applications in various catalytic reactions including the low-temperature CO oxidation.