Preparation, characterization and testing of well-defined iron carbides for efficient CO2 hydrogenation to higher hydrocarbons

• Applicant: Professor Dr. Evgenii Kondratenko
• Subject Area: Technical Chemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553148345

The use of CO2, which is a key greenhouse gas, as a feedstock in the chemical industry is a promising way to close the carbon cycle and thus to contribute to sustainable development. In this context, the hydrogenation of CO2 to higher hydrocarbons (C2+-hydrocarbons) called as CO2 Fischer-Tropsch synthesis (CO2-FTS) should be mentioned as an alternative to oil-based cracking processes. Iron carbides are generally accepted to be responsible for the formation of the desired products in this reaction. Nevertheless, the mechanism and kinetics of their in situ formation and the influence of their structural/morphologic parameters on the kinetics of product formation, are still under debate. Moreover, the origins determining the resistance of iron carbides against irreversible oxidation to iron oxides by water under reaction conditions have not been elucidated. Such knowledge is very important to control the distribution of carbide from upstream to downstream catalyst layers as the concentration of water formed in CO2-FTS increases accordingly. To address these challenges, the primary objective of this project is to identify fundamental descriptors that influence the activity, selectivity, and stability of iron carbides in CO2-FTS. Particularly, we aim to establish (i) factors affecting the distribution of iron carbides along the catalyst bed under CO2-FTS conditions, (ii) the relationships between structural characteristics of iron carbides and (a) their ability to activate H2, CO and CO2 as well as (b) their resistance to oxidation by H2O. To achieve the project aims, we will follow a multidisciplinary approach consisting of the precise synthesis of iron carbides of certain structure/morphology, their detailed characterization by complementary techniques, mechanistic and kinetic (including segmental rate analysis) tests under steady-state and transient conditions. For catalyst preparation, our efforts on identifying the most relevant steps in synthesis of unpromoted and promoted iron carbides as well as their mixtures with iron oxides to control their phase composition, morphology, and redox properties. It is also important to understand factors (e.g. initial phase composition or morphology, kind of promoter) that influence the reaction-induced structural changes of such catalysts. To this end, microkinetic tests of activation of the feed components H2/CO2 and the reaction products CO and C2H4 with fresh and spent catalysts will be performed to identify reaction mechanism and to derive kinetic parameters, which will be correlated with structural catalyst properties.

• DFG Programme: Research Grants