Prøveforelesning
Se prøveforelesningBedømmelseskomité
Dr. Lioubov Kiwi-Minsker, Ecole Polytechnique Federale de Lausanne, Sveits
Professor Klaus-J. Jens, Høgskolen i Telemark, Porsgrunn
Professor Mats Tilset, Kjemisk institutt, Universitetet i Oslo
Leder av disputas: Professor Carl Henrik Gørbitz
Veileder: Prof. Unni Olsbye (UiO), Dr. Erling Rytter (StatoilHydro)
Sammendrag
Light alkenes constitute one of the most important classes of base chemicals for the chemical industry. Increasing demand for light alkenes and their derivatives observed in recent years has led to an increased interest in processes allowing for selective production of light alkenes, e.g. by catalytic dehydrogenation of the corresponding light alkanes.
The present work has focused on investigation of the correlation between surface properties and catalytic activity/selectivity for one of the most promising catalysts for selective dehydrogenation of light alkanes, Pt,Sn/Mg(Al)O. The surface properties of the Pt,Sn metal phase and of the Mg(Al)O support of the Pt,Sn/Mg(Al)O catalyst have been characterized using in situ XPS and FT-IR spectroscopy of adsorbed molecules, under conditions as close as possible to the industrial dehydrogenation conditions and during activation pretreatment. Mechanistic aspects of ethane dehydrogenation and byproduct formation have been investigated by catalytic activity/selectivity measurements and by isotopic labeling experiments using 13C monolabeled ethane and deuterium.
The experimental work has shown that the characterization results are in general agreement with the catalytic measurements. The following other main conclusions can be drawn: (i) In a model Pt/Mg(Al)O catalyst, the presence of terrace Pt sites and low-coordinated Pt sites (i.e. steps, corners, edges and defects) were revealed. In a model and a semicommercial Pt,Sn/Mg(Al)O catalysts the low-coordinated sites were covered by Sn. Catalytic testing of the same materials revealed an increased ethene selectivity for Pt,Sn/Mg(Al)O compared to Pt/Mg(Al)O. It was concluded that the terrace sites are active for dehydrogenation, whereas the low-coordinated sites are active for C-C bond scission. The Pt sites that interact with the basic sites of the support were found to further promote the dehydrogenation selectivity. (ii) The increase in dehydrogenation activity during activation of the semicommercial Pt,Sn/Mg(Al)O catalyst is accompanied by a marked increase in the amount of exposed Pt. (iii) Ethane dehydrogenation over the semicommercial Pt,Sn/Mg(Al)O catalyst can be described by the Horiuti-Polanyi reaction mechanism with ethane adsorption being the rate determining step of reaction. Both methane and ethyne, which are byproducts of the ethane dehydrogenation, are formed via ethene, and not directly from ethane.
Kontaktperson
For mer informasjon, kontakt Raul Boris Briceno.