Fundamental understanding of Fe and Co based catalysts for light olefin (C2-C4) production via the direct Fisher-Tropsch to olefins process

In this project we deal with fundamental issues related to the industrial exploitation of methane (the main component in natural gas) as a feedstock for petrochemical industries. Light olefins (alkenes) are key intermediates in the chemical industry, and are important building blocks for a range of materials (chemicals, polymers and plastics) with numerous applications. The long-term goal is to develop new technologies enabling the use of cheap feedstocks in the production of ethene, propene and butenes, products that today are made from crude oil fractions or LPG. The technology can also be applied in producing chemicals from biomass as part of a future renewable economy. We have addressed fundamental aspects of the technology, forming a basis for future technology developments. We have worked on the Fischer-Tropsch synthesis (FTS), where synthesis gas (also called syngas, a mixture of carbon monoxide and hydrogen) is converted to hydrocarbons and water over cobalt-based catalysts. The syngas can in principle be produced from any carbon-containing feedstock, such as natural gas (the purpose of this project) or coal or biomass. The Fischer-Tropsch technology is not new, but is under constant development. The key to develop improve or develop new processes is that the product distribution can be controlled and altered through the properties of the catalyst. Our goal was to develop the understanding of the link between the catalyst properties and the product selectivity, and through this develop new systems with a high selectivity to light olefins. We have used a number of techniques and tools in this work. The central method is synthesis and testing of heterogeneous catalysts. The key topic is the use of promoters, and we have confirmed that the addition of manganese (Mn) leads to an enhanced olefin selectitvity. At the same time the methane selectivity is reduced, and the chain growth properties are enhanced. This project has provided us with the possibility to improve the understanding of this change. Transient kinetics at stationary conditions (SSITKA; Steady State Isotopic Transient Kinetic Analysis) has been shown to be a useful tool in this work. We use this method to investigate the mechanism in detail, for example to look at changes in the adsorption of reactants and reaction of adsorbed intermediates on the catalyst surface. Another useful method is fundamental (first principles) quantum-chemical calculations, applied to study adsorption and reaction on the surface. The DFT-method (Density Functional Theory) is used in these calculations, which give us improved understanding of the link between the catalyst composition and structure, and the reactions occurring on the surface. The results are particularly useful when they are compared with experimental results, as we have done in this project. The main finding is that Mn changes the binding of reactants and intermediates on the surface, favouring the formation of light olefins. Different catalyst preparation routes were tried, but these gave very similar results. Mn influences the Co reducibility, which to some extent can be countered by adding a noble metal acting as a reduction promoter. By applying advanced spectroscopic techniques we have shown that the system is dynamic, and the composition of the surface changes through the different steps in the process. The main effect of Mn is that it changes the distribution of reaction intermediates on the surface. The surface has more carbon species (CHx) and less adsorbed hydrogen, leading to less methane formation, while olefin production and chain growth is favoured.

Prosjektet er et forskerprosjekt med kompetansebygging som formål. Hovedvirkningen er å bidra til utdanning av kandidater (2 PhD og 1 postdoc), som tar med seg sin kompetanse til forskningsinstitutter og norsk industri. Videre er det gjennom samarbeid med instituttsektoren bygget kompetanse - både hos de utdannede kandidatene og i SINTEF - i bruk av DFT i katalyse. For videre beskrivelse av resulatter og virkninger - se resultatrapporten.

Direct conversion of synthesis gas to olefins is a highly attractive process for the production of key petrochemical intermediates, the light olefins. This could provide a new and energetically efficient way to upgrade natural gas to high value chemicals. The present work will apply a multiscale approach, integrating first principles calculations, detailed mechanistic studies using transient kinetics, and advanced catalyst preparation, characterization and testing, to achieve a better understanding of the chain growth and termination in the Fisher-Tropsch to olefin (FTO) reaction as a function of catalyst properties. The project aims at applying these new scientific insights gained at the atomic level to manipulate the catalyst supports and surface compos itions to increase light olefin selectivity and reduce the methane selectivity. Moreover, the methods and kinetic models developed in the present project are highly applicable in the conventional F-T reaction using synthesis gas from natural gas, coal or biomass. The project involves training 1 PhD candidate, a postdoc for 2 years, and also includes 1 researcher for 1 person-year. The total funding applied for is 5902 kNOK.