Time-resolved temperature jump IR spectroscopy of heterogeneous catalysts from nanoseconds to seconds Alexander Hawkins 1 , Amy Edmeades 1 , Christopher Hutchison 1 , Russell F. Howe 2 , Gregory M. Greetham 1 . Michael Towrie 1 , and Paul M. Donaldson 1 1 Central Laser Facility, STFC Rutherford Appleton Laboratory, UK, 2 Department of Chemistry, University of Aberdeen, UK The product selective nature of heterogeneous catalysis in microporous materials such as zeolites has wide- ranging industrial applications across multiple chemical sectors.[1] Studying the chemistry and interactions of adsorbed molecules with microporous materials on timescales relevant to their reactions is vital for developing an improved understanding of the mechanisms of catalysis. To this end, pulsed-laser based time-resolved infrared (IR) spectroscopy can offer new possibilities to address these questions. Here, we report our work towards studying zeolites with time resolved temperature (T)-jump IR spectroscopy. IR spectroscopy is widely used for the study of microporous catalysts due to providing structural information from the vibrational modes of adsorbed hydrocarbons and catalytically active acid sites.[2] The use of pulsed- lasers allows the extension of IR spectroscopy into the ultrafast time domain (fs‑ms) associated with dynamical processes, such as molecular motion and intermediate species formation in reactions.[3] Pulsed laser heating offers the ability to trigger thermally activated processes with temperature jumps. We show here that by adopting a Time-Resolved Multiple Probe Spectroscopy (TRMPS) experimental approach [4] it is possible to heat a zeolite sample on nanosecond timescales and monitor its evolution across 8 decades of time into the hundreds of milliseconds time range, allowing heating-triggered reaction and diffusion processes to be followed. Using a custom-designed laser system at the Central Laser Facility to heat zeolites by pumping their O-H stretch modes along with the femtosecond ULTRA B 10kHz laser system as an IR probe, we have successfully applied T-Jump IR-TRMPS to study the dynamics of deuterated water in acid zeolites. Experiments were performed with solid zeolite samples in IR transmission under controlled gas flow and elevated sample temperature. Comparison with FTIR data and computational thermodynamic simulations of laser heating establish that temperature jumps as large as 110 K from the starting temperature are achievable. The rapid heating of the sample allows observation of the desorption behaviour of the water while the subsequent spectral evolution allows observation of the re-adsorption kinetics, both important parameters in the industrial use of zeolitic materials.[5] These results provide important information on aspects of adsorbate dynamics important to catalysis, and point the way toward achieving operando time-resolved IR observation of intermediate formation and evolution in catalytic reactions. References 1. A. Corma, Chem. Rev. 95 , 559 (1995). 2. S. Bordiga, et al. , Chem. Soc. Rev. 44 , 7262 (2015). 3. O. Kühn and L. Wöste, Analysis and Control of Ultrafast Photoinduced Reactions, 1st ed. (2007). 4. G.M. Greetham, et al. , Appl. Spectrosc. 74 , 720 (2020). 5. D.E. Resasco, et al. , Catal. Rev. 63 , 302 (2021).
P27
© The Author(s), 2023
Made with FlippingBook Learn more on our blog