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Catalysts for Complete Oxidation of Gaseous Fuels p£x-F£-' 3oV Catalysts for Complete Oxidation of Gaseous Fuels Ahmad Kalantar Neyestanaki Academic Dissertation Thesis for the Degree of Doctor of Technology to be presented with due permission of the Department of Chemical Engineering at Abo Akademi for public criticism in the Stina Auditorium of the Axelia Building, Biskopsgatan 8, on August 25, 1995 at 12 noon. The opponent appointed by the Department of Chemical Engineering is Professor Zinfer R. Ismagilov from the Department of Environmental Catalysis, Boreskov Institute of Catalysis, Novosibirsk, Russia. Laboratory of Industrial Chemistry Department of Chemical Engineering Abo Akademi University Abo 1995 DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Catalysts for Complete Oxidation of Gaseous Fuels Catalysts for Complete Oxidation of Gaseous Fuels Ahmad Kalantar Neyestanaki Laboratory of Industrial Chemistry Faculty of Chemical Engineering Abo Akademi University Abo 1995 ISBN 951-650-584-8 Abo Akademis tryckeri Abo 1995 1 Preface This research work was carried out at the Laboratory of Industrial Chemistry at Abo Akademi University during the years 1991-1995, under the guidance of Professor Lars-Eric Lindfors. First and foremost, I wish to express my gratitude to Professor Lars-Eric Lindfors, head of the Laboratory of Industrial Chemistry, for fruitful discussions and inspiring advice. His constructive criticism and scientific ideas have been of great help. I am also extremely thankful to my colleagues from the Laboratory for their help and understanding. My special thanks go to our skillful Laboratory Engineer, DI Kari Eranen, whose technical assistance was of great help. I would like to express my sincere thanks to TkL Narendra Kumar, for fruitful discussions and valuable advice. I am also grateful to the collective of theKemira Oulu Research Laboratory, Catalyst Section for their assistance. The financial support from Kemira Ltd, Abo Akademi University, the Foundation of Abo Akademi University Research Institute, Finnish Technology Development Centre (TEKES) and the Graduate School in Chemical Engineering is gratefully acknowledged. Last, but not the least, I would like to thank my family for continuous support throughout the years. Turku, April 1995 Ahmad Kalantar Neyestanaki 11 Abstract Catalytic combustion is considered to be an effective approach in controlling the emissions of hydrocarbons, carbon monoxide and nitric oxides. This thesis presents a study on the complete oxidation of propane, natural gas and the conversion of car exhaust gases over two types of catalysts: a) knitted silica-fibre supported catalysts and b) metal-modified ZSM zeolite catalysts. A hybrid textile made up of an organic-inorganic hybrid fibre containing 70% cellulose and 30% silicic acid was used as the raw material for preparation of the fibre support for combustion catalysts. The hybrid textile was burnt to obtain a knitted silica-fibre. The changes in the surface area, pore volume and the crystallinity of the obtained support were studied as a function of burning temperature. The stability of the support in steam-rich atmospheres was tested. Theknitted silica-fibre obtained by burning the hybrid textile at 1223 K was found to have sufficient strength and high BET specific surface area (140 m2/g) to be used as a catalyst support A series of knitted silica-fibre supported metal oxides (oxides of Co, Ni, Mn, Cr and Cu) and combinations of them, platinum-activated metal oxides (Pt-Co 304, Pt-NiO, Pt-Mn0 2 and Pt-Cr203) as well as noble metal (Pt, Pd) catalysts were prepared. The location of the metal oxides on the catalyst was studied by SEM equipped with EDXA. The metal oxide was found to be located mostly inside the pores rather than on the exterior surface of the silica-fibre. The catalysts were characterized by XRD, N2-physisorption, 02-TPD and the chemisorption of propane, carbon monoxide and hydrogen. The activity of the catalysts was tested in the combustion of propane, natural gas and in the conversion of automobile exhaust gases. The effect of residence time and stoichiometry on the conversion behaviour of the catalysts was studied. The results indicated that high combustion efficiencies can be achieved by using base metal oxides. In each series, an increase in the metal oxide content of the catalysts resulted in an improved combustion efficiency and reduced light-off temperatures. The activity pattern in terms of light-off temperatures and final conversions was established. Co 304 was found to be the most active single metal oxide in propane combustion whereas NiO was the most active in natural gas combustion. Combination of metal oxides generally resulted in improved final conversions but not the light-off temperatures. Platinum-activated metal oxides, with the exception of Cr203, exhibited a better light-off and conversion behaviour as compared to the component catalysts. The Pd-catalysts were found to be more active in natural gas than in propane combustion, as compared to the Pt and Pt-activated metal oxide (Pt-Co and Pt-Ni) catalysts. The propane oxidation over Pd/Si0 2 was found to be structure sensitive and the reaction was found to take place over the PdO phase. The dependency of the rate of propane iii combustion over the catalysts containing noble metals was found to be zero with respect to oxygen and one with respect to propane. The reaction orders for metal oxides were fractional. Different Cu-ZSM (Cu-ZSM-5, -11 and -48) catalysts as well as Pt- and Pd-ZSM-5 catalysts were prepared and tested for their activities in propane and natural gas combustion. The zeolites were modified by the ion-exchange technique and by introduction of the metal during the process of zeolite synthesis. The effect of basicity of the ion- exchange mixture on the metal uptake was studied. The prepared catalysts were characterised by SEM, XRD, N2-physisorption, TPD of oxygen, carbon monoxide and ammonia. The redox capacity of the copper-modified zeolites was determined by subjecting the catalysts to redox cycles in a microbalance. The prepared metal-modified zeolites were tested for their activity in propane and natural gas combustion. The effect of stoichiometry and contact time on the light-off and conversion behaviour of these catalysts was studied. The kinetic parameters (reaction orders, activation energies and the pre-exponential factors) of propane combustion over the prepared zeolites were determined. The modified zeolites exhibited higher activities in oxidation reactions as compared to the corresponding Cu-, Pt- and Pd/alumina catalysts. Among the Cu-ZSM zeolites, ion-exchanged Cu-ZSM-5 was the most active in complete oxidation reactions. Increase in the pH of the ion-exchange mixture results in increased copper uptake and, consequently, in increased catalytic activity. Temperature programmed desorption of oxygen and carbon monoxide as well as microbalance measurements of the redox cycles indicated the important influence of the extra lattice oxygen on these catalysts. Cu-ZSM-5 tends to stabilise the copper as Cu2+ and Cu-O-Cu species while on the ZSM-11 and ZSM-48, the copper is present as CuO. The ion-exchanged Pd-ZSM-5 exhibited lower, low-temperature activities in propane combustion, compared to the Cu-ZSM-5 catalysts, while the final conversions were close. The Pd-ZSM-5 catalysts, on the other hand, were found to be most active in natural gas combustion. The activity of these catalysts was correlated to theiroxygen carrier capacity. The method of introducing the metal into the zeolite was found to be very important in determining the oxidation activities of the ZSM-5 catalysts. The introduction of Cu and Pd into the zeolite during the process of the hydrothermal zeolite synthesis, although very convenient, resulted in a less active catalyst. The Pt-ZSM-5 catalysts in which the platinum was introduced to the zeolite during the process of zeolite synthesis, however, exhibited high activity in propane combustion. The high activity of the Pt-ZSM-5 in propane combustion is most probably due to the activity of the platinum itself, rather than the mutual effect of the platinum and zeolitic structure. IV List of Publications This thesis is a summary of the following papers, referred to in the text by their corresponding Roman numerals. I Kalantar Neyestanaki, A. and Lindfors, L.-E., "Catalytic Combustion of Propane Over Silica Fibre Supported Pt-Co Oxide Catalysts", 7th International Symposium on Heterogeneous Catalysis, Bourgas, Bulgaria, Part 2, 673 (1991). II Neyestanaki, A. K. and Lindfors, L.-E. "Catalytic Combustion Over Transition Metal Oxides and Platinum-Transition Metal Oxides Supported on Knitted Silica Fibre", Combustion Science and Technology , 121, 97 (1994). m Kalantar Neyestanaki, A. and Lindfors, L.-E. "Catalytic Combustion of Propane and Natural Gas over Silica-Fibre Supported Catalysts", Combustion Science and Technology (submitted, 1995). VI Kalantar Neyestanaki, A., Kumar N. and Lindfors, L.-E. "Catalytic Combustion of Propane over Pt and Cu Modified ZSM-5 Zeolite Catalysts", Fuel, 690, 74, 5 (1995). V Kalantar Neyestanaki, A., Kumar N. and L.-E. Lindfors, "Catalytic Combustion of Propane and Natural Gas over Cu and Pd Modified ZSM Zeolite Catalysts", Applied Catalysis B: Environmental (accepted, 1995). V The topic of the present thesis has also been presented in the following international conferences, report and patent: 1 Kalantar Neyestanaki, A. and Lindfors, L.-E., "Catalytic Combustion of Propane Over Cobalt Oxide Catalysts Supported on Knitted Silica-Fibre", Oral presentation at the 4th Nordic Symposium on Catalysis, Trondheim, Norway, October 3-4,1991. 2 Kalantar Neyestanaki, A., Paren, A. and Heidari, S., "New Development in Catalyst Supports", Technical Information, Kemira Ltd., January 1992. 3 Lindfors, L.-E. and Kalantar Neyestanaki, A., "Catalytic Combustion of Natural Gas", Poster presentation at the Twenty-Fourth International Symposium on Combustion", Sydney, Australia. July 5-10, 1992. 4 Salanne, S., Kalantar Neyestanaki, A., Lindfors, L.-E., and Vapaaoksa, P.
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