(261g) Beyond the Active Site: Controlling the Local Chemical Environment of Active Sites to Achieve Improved Catalytic Performance

I will discuss our recent work on developing multifunctional catalytic materials that allow for not only the control over the structure of the active catalytic site but also over the environment in which this active site resides. By controlling the environment, we are able to control the chemical potential of reactive species and therefore direct chemical transformations in specific (desired) directions.

I will illustrate the phenomena using examples of developing catalyst/membrane multifunctional systems for oxidative coupling of methane (OCM) and propane dehydrogenation (PDH). OCM is a direct route for converting methane into ethylene and ethane (C₂). When performed in conventional packed bed reactors (PBRs) this process suffers from significant thermodynamic and kinetic limitations in the selectivity towards the desired products over almost all explored catalysts. We will show that a membrane/catalyst system with distributed oxygen feed (i.e. an O^2- conducting membrane reactor) can give significantly higher C₂ selectivity and yield compared to a PBR. We will discuss our work on identifying the O^2- conducting membranes and catalysts that are selective for OCM and that can be integrated in a membrane/catalyst system. We will discuss the OCM activity and selectivity on these membrane/catalysts systems as well as the long-term stability of the system. The conversion in the PDH reaction is equilibrium limited. We will show how membrane/catalyst systems allow us to in-situ remove H₂ from the product stream and by taking advantage of the Le Chatelier's principle remove the equilibrium limitations on the reaction conversion.