An investigation of gauze supported platinum alumina and cobalt supported oxide oxidation catalysts
Ronane, Michael James (2005) An investigation of gauze supported platinum alumina and cobalt supported oxide oxidation catalysts. Master of Science thesis, Dublin City University.
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The aim of this research involved preparation and optimisation of Pt/Al203 gauze supported catalysts with high thermal stability and surface area with a well-dispersed layer of Pt. Preparation involved nucleation/whiskering of an FeAl metallic alloy substrate forming hair like crystal of AI2O3, followed by application of alumina washcoat support onto the crystals. The washcoated substrate support was then impregnated with an active phase material (i.e. Pt metal). Evaluation and characterisation of the metallic substrate support (i.e. gauze material) onto which the alumina support and Pt were impregnated were investigated with a view to developing, optimizing and scale up of the process to pilot plant for commercial scale. Catalysts characterisation was carried out using AAS, BET surface area (N2 physisorption) to determine metal loadings and surface area of the substrate and alumina washcoat supports. Metal surface area, Pt dispersion and metal particle size together with activity of the Pt supported catalysts were measured using Pulse chemisorption and combustion activity techniques. In addition particle size measurement of alumina (i.e. Puralox powders) employed in the washcoat support were investigated using Malvern Mastersize Analyser, in a view to discover if a correlation between surface area and thermal stability of the washcoat support existed. It was found a smaller particle size washcoat solution produce a more thermally stable support material. Finally the use of Scanning electron microscopy (SEM) and Energy dispersive X-ray analysis (EDX) was used in the surface and subsurface characterisation of both the whiskered gauze (including whiskering under different atmospheres and conditions) and final Pt/Al20 3 prepared catalysts.
The second area of research involved preparation and characterisation of various PP rted and unsupported single metal oxide combustion catalysts as alternatives to the more expensive noble metal catalysts. The investigation reports on the potential use of supported unsuPported coball oxides for the combustion of methane. Particular
emPhasis is placed on the role played by various thermal analysis techniques in the elucidation of factors which affect catalyst performance.
Two combined thermal analysis-mass spectroscopy techniques have been used to ascertain the effects of various support materials on the preparation and subsequent combustion activity of supported cobalt oxide catalysts. Both techniques used involved small sample masses in order to minimise temperature and pressure gradient throughout the sample during reaction as the sample temperature was increased at a linear heating rate. Temperature programmed reduction (TPR) techniques employed not only reveal reduction, but also distinguish it from the adsorption (or evolution) of the H2 and the loss of adsorbed water. The thermal induced decomposition of supported and unsupported cobalt nitrate hexahydrate was studied using solid insertion probe mass spectrometer (SIP-MS) system operating under high vacuum. The support material was found to affect the decomposition process significantly. In particular, the decomposition of cobalt nitrate dispersed on y-A^Os occurred via a markedly altered process in comparison with the unsupported nitrate. The ZrC>2 and CeC>2 supports both exhibited a less pronounced effects on the decomposition process. After calcinations of the dispersed cobalt nitrate species, methane combustion activity was found to be much lower for the aluminasupported samples relative to the other supports used. A combined temperatureprogrammed reduction-mass spectrometry (TPR-MS) technique was used to elucidate a correlation between the catalysts activity and reducibility. Constant thermal rate analysis (CRTA) was also used to investigate the reduction of Co304/Ce02.
The main conclusion from the research found the use of cobalt as a viable alternative to, noble metal combustion catalysts. Deactivation problems due to sintering of the active C03O4 phase and reaction with the alumina support forming inactive mixed oxides (i.e. C0AI2O4 spinel) were also establish. Cobalt oxide supported on ceria or zirconia as well as cerium support were shown to be a highly active catalyst for the combustion of CH4. However, in both cases deactivation was observed upon exposure to the reaction mixture which maybe associated with sintering or the conversion of C03O4 to a less active CoO phase. However, despite such problems with the existing formulation, research into the use of C03O4 may provide a greater understanding of the origins to low-temperature combustion activity and design of new automotive exhaust applications in the drive to develop new catalytic technologies.
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