الفهرس 
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Abstract
Nanocrystalline materials are showing great prospects in industry and technology. This is mainly because they have some unique properties which are not shown by the bulk crystalline materials. Nanomaterials represent almost the ultimate in increasing surface area. Substances with high surface area have enhanced chemical, mechanical, optical and magnetic properties, and this can be exploited for a variety of structural and non-structural applications.
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than any other material. These cylindrical carbon molecules have novel properties, making them potentially useful in many applications in nanotechnology, electronics, optics, and other fields of materials science.
Automotive exhaust gases formed in the gasoline engines contain many environmentally harmful compounds and with the industrialization of the Third World, the number of automobiles in the world is expected to increase even more dramatically
A catalytic converter (colloquially, ”cat” or ”catcon”) is a vehicle emissions control device which converts toxic byproducts of combustion in the exhaust of an internal combustion engine to less toxic substances by way of catalyzed chemical reactions.
In this work, Nano-sized CuO-CeO2, CuO-Fe2O3 -CeO2, Fe2O3 -CeO2 and CuO-Fe2O3 were prepared by co-precipitation route and Al2O3 was used as support using wet impregnation technique whereas nano-sized CuO-Fe2O3 -CeO2-Al2O3 was prepared by physical mixing of one mole of CuO-CeO2-Al2O3 with one mole of CuO-Fe2O3.
The Synthezied nanocatalysts were used to remove some of the exhaust gases and for catalytic oxidation of carbon monoxide.
The catalytic hydrocarbon and carbon dioxide decomposition over nanostructured materials in order to remove hydrocarbon gases, remove carbon dioxide and produce carbon nanotubes (CNTs.) have been also studied.
The effect of process parameters as temperature, gas flow rate ,catalyst composition and catalyst weight on catalytic oxidation of carbon monoxide , catalytic hydrocarbon and carbon dioxide decomposition were studied.
Microstructure and morphology of the synthesized catalyst and CNTs, were identified and characterized by X-ray phase analysis, scanning electron microscope, optical microscope connected with digital camera and transmission electron microscope.
Throughout this work it was found that:
• Nano-sized CuO-CeO2, CuO-Fe2O3 -CeO2, Fe2O3 -CeO2 and CuO-Fe2O3 were successfully prepared by co-precipitation route and Al2O3 was used as support using wet impregnation technique whereas nano-sized CuO-Fe2O3 -CeO2-Al2O3 was prepared by physical mixing of one mole of CuO-CeO2-Al2O3 with one mole of CuO-Fe2O3.
• It was found that ceria containing catalysts give the highest efficiency in oxidation of CO to CO2 at all the catalytic temperature .
• It was observed that the rate of CO oxidation to CO2 increased by increasing catalytic temperature and at relatively lower temperature (300 oC), the maximum CO oxidation occurs over CuO-CeO2-Al2O3, CuO-CeO2 and CuO-CeO2-Fe2O3-Al2O3 and with increasing temperature to 450 and 500oC the CO conversion % decrease again and this may be due to the sintering effect .
• It was also observed that CO conversion % over CuO-CeO2-Al2O3 increases with the decrease of CO and also CO conversion % increase with increasing catalyst weight and this is attributed to that with increasing the weight of catalyst the number of active sites available for CO catalytic oxidation reaction increases and consequently the catalytic activity increases.
• The study of the effect of temperature over the most promising catalysts (CuO-CeO2-Al2O3 and CuO-CeO2-Fe2O3-Al2O3 ) using the optimum catalyst weight and the optimum CO% shows that the CO oxidation increases with increasing catalytic oxidation temperature .
• The experimental data shows that the catalytic oxidation of CO probably proceeded by adsorption mechanism where the reactants are adsorbed on the surface of the catalyst with breaking O–O bonds, then CO picks up the dissociated O atom forming CO2
• It was found that ceria containing catalysts give the lowest efficiency in hydrocarbon decomposition and that the rate of hydrocarbon decomposition increased by increasing catalytic temperature. The maximum hydrocarbon decomposition occurs over CuO-CeO2-Fe2O3-Al2O3 and CuO- Fe2O3 . With the increasing of temperature, the increase in hydrocarbon decomposition is maintained
• The small value of activation energy (11.9 and 17.2 kJ mol-1 for Fe2O3-CuO and CuO-CeO2-Fe2O3-Al2O3 respectively) indicates that the two catalysts are very active toward acetylene decomposition.
• With increasing catalyst weight hydrocarbon decomposition increase till a certain weight (1g ) and after that it decrease again, because this metal loading exhibit the formation of CNTs having highest resistance to oxidation and also catalytically active sites are introduced in the system,with more increasing on the catalyst weight ,CNTs formed have more tendency for oxidation and consequently the carbon deposited will decrease and the conversion percent decrease
• The hydrocarbon decomposition percent increase with decreasing hydrocarbon flow rate from 150-50 ml/min, this is due to that with increasing acetylene flow rate the CNTs yield is very high at the beginning of the reaction, covering and poisoning the active sites on the catalyst surface and consequently HC conversion percent decrease.
• The SEM image shows that some catalytic nanoparticales are also observed at the tips of the carbon nanotubes indicating that CNTs formation occurs via tip growth mechanism .
• The results also show that nanocrystallite CuO-Fe2O3-CeO2-Al2O3 can be recommended as promising catalysts for hydrocarbon decomposition.
• Following the reduction behavior of metal oxides nanoparticles shows that all the prepared catalyst are completely reduced at 500oC.
• Re-oxidation for samples reduced in H2 flow at 500 oC and re-oxidized in CO2 flow at the same temperature shows that all the prepared catalyst are completely re-oxidized and CO2 decomposes on the surface of metallic phase.
• Studing Re-oxidation kinetics and mechanisms shows that interfacial chemical reaction is the main rate controlling mechanism at the initial stages of re-oxidation and the solid-state diffusion becomes the rate controlling mechanism at intermediate and final stages of reoxidation.