Theoretical Investigation of zeolite-catalyzed transformations involving ketenes as intermediates

• Applicant: Dr. Philipp Pleßow
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434253773

In the second funding period of this project, the goal is to study several zeolite-catalyzed reactions that involve ketenes as intermediates and therefore share common reactivity. The theoretical investigations will be carried out with periodic density functional calculations (DFT) and ab initio calculations on cluster models of the zeolites. Reaction conditions (temperature and pressure) are accounted for when computing Gibbs free energies. Furthermore, reaction kinetics will be studied using suitable kinetic models based on computed rate constants. Ketenes are increasingly discussed as short-lived – but important – reaction intermediates in zeolite catalysis. Ketonic decarboxylation, investigated in the first funding period for H-SSZ-13, was found to proceed via ketene and we plan to extend the investigation of this reaction to H-ZSM-5 as well as Lewis acidic BEA zeolites. Another goal of this project is to clarify the reactions during the initiation of the methanol-to-olefins (MTO) process, where formation of carbon dioxide was observed experimentally. Here, we plan to further investigate the coupling of ketenes and formaldehyde and their role in initiating the hydrocarbon pool (HCP). Another focus of this project are the so-called oxide-zeolite-based composite (OXZEO) catalyzed processes. Here, syngas is directly converted to hydrocarbons by a physical mixture of a Brønsted acidic zeotype and a reducible oxide, where many materials such as ZnCrOx have been tested. The oxide is believed to catalyze the initial reaction between H2 and CO, perhaps resulting in the formation of methanol or formaldehyde. The zeolite then further converts these intermediates to hydrocarbons. Ketene was observed as an intermediate and was proposed to form at the oxide, but this may also result from the reaction of CO with methanol at the zeolite. In this proposal we focus only on the reactivity at the zeotype, where we will investigate H-SAPO-34, as a commonly used catalyst. Regarding the reactivity at the oxide, we will employ hypotheses in the literature, i.e. assume that it produces either ketene or methanol. That means we will investigate the reactivity of methanol or ketene in the presence of CO and H2. Here, we will furthermore compare with experimental studies that employed pure ketene as well as methanol with co-feeds of either CO or H2 or both.

• DFG Programme: Research Grants