Many catalytic processes suffer from deactivation of the catalyst through surface deposits that poison active sites or render them inaccessible, whereas other catalytic processes are characterized by long induction periods because the catalytically active surface species are generated only on stream. In this presentation, infrared and UV-vis spectroscopy are applied in situ to gain fundamental insights into the surface chemistries responsible for such effects. The overarching research objective is to identify surface species and understand their dynamics and, subsequently, use this knowledge to improve the catalytic process.
The first part of the talk will focus on catalysis by solid acids, which plays a central role in the conversion of petroleum- and biomass-derived feedstocks to chemicals and fuels. Methanol-to-olefins (MTO) conversion is emerging as a potentially sustainable pathway to produce small olefins for use as monomers. While MTO is commercialized, the process suffers from deactivation through coking of the catalyst and lack of selectivity control. Better insight into the mechanism could help remedy these issues. The MTO reaction presents an interesting case of organic-inorganic hybrid sites: Long-lived intermediates in the pores of the zeolite or zeotype catalysts, often referred to as “hydrocarbon pool”, are known to be essential for the catalytic cycle. The exact constitution and role of these species for product formation are under debate. Advances in the interpretation of IR and UV-vis spectra allow us to monitor transformations with unprecedented precision, and time-resolved spectra are used to extract kinetics and determine activation energies for in-the-pore transformations.
A shorter, second part will address the Phillips Cr(VI)/SiO2 catalyst for polyethylene manufacture. The induction period of this catalyst has been a mystery since its discovery in 1951. Spectroscopic data are one important piece in solving the puzzle of the active chromium site.