Synthesis of active supported gold catalysts for CO oxidation and light alkane activation.

Al-Sayari, Saleh Abdullah 2006. Synthesis of active supported gold catalysts for CO oxidation and light alkane activation. PhD Thesis, Cardiff University.

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Abstract

The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine important factors, such as selection of support material and preparation method, and preparation parameters, such as preparation temperature, pH, and ageing process. These factors control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. The two preparation methods differ in the manner in which the pH is controlled during coprecipitation, either constant pH throughout or variable pH in which the pH is raised from an initial low value to a defined end point. Non- calcined Au/ZnO catalysts prepared using both methods are very sensitive to pH and ageing time. Catalysts prepared at higher pH give lower activity. However, all catalysts require a short indication period during which the oxidation activity increases. In contrast, the calcined catalysts are not sensitive to preparation conditions. Non-calcined Au/Fe203 catalysts exhibit high activity when prepared at pH > 5. Active calcined Au/Fe2O3 catalysts can be prepared when the pH is controlled at pH 6-7, 8, whereas calcined catalysts prepared using the variable pH method are inactive. The study demonstrates the immense sensitivity of catalyst preparation methods on the performance. Catalysts exhibited excellent catalytic activity and stability compared with the pure supports, ZnO and Fe2O3, and the best preparation temperature was 80 C. Use of temperatures > 80 C led to inactive catalysts. The deposition-precipitation (DP) method was also employed using four different supports in this study (ZnO, Fe2O3, MgO, and MnO2). A comparison between these catalysts was taken rather than an investigation of the effect of the preparation parameters on catalysts prepared by DP method because they have been well studied previously. Several characterization techniques including AAS, BET surface area, XRD, TPR, and XPS, were utilised to investigate the physical and chemical properties of the prepared supported gold catalysts. Characterization results were combined with catalytic results for the low temperature CO oxidation reaction of catalysts in order to study the aforementioned factors that can affect either the properties of catalysts or their activities. Subsequently, several experiments at high GHSV were conducted to study the catalytic activities of these catalysts in-depth and to correlate data with alkane activation reactions. CH4 activation reaction using supported gold catalysts at light temperatures and the effect of the preparation parameters, types of supports on catalysts activities were investigated. The Au/Fe2O3 catalyst prepared by coprecipitation method B at pH 8 showed the highest catalytic activity for CO oxidation and CH4 activation reactions. The most active catalysts were also evaluated for C2H6 and C3H8 activation at low temperature. After this, a comparison between CO oxidation and alkane activation over supported gold catalysts was undertaken to investigate the relationship between the behaviour of supported gold catalysts for these two types of reactions. Activation energies and pre-exponential factors of many catalysts were calculated based on the Arrhenius equation either for CO oxidation or for alkane activation. The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine the important factors that control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. (Abstract shortened by UMI.)

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
ISBN:	9781303204616
Funders:	Saudi Basic Industries Corporation (SABIC)
Date of First Compliant Deposit:	30 March 2016
Last Modified:	09 Jan 2018 19:11
URI:	https://orca.cardiff.ac.uk/id/eprint/56051

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