New opportunities for ultrafast time resolved 2D-IR spectroscopy in zeolite catalysis research Paul Donaldson 1 , Russell F. Howe 1 , Alex P. Hawkins 2 , Gregory M. Greetham 2 1 University of Aberdeen, UK, 2 STFC Rutherford-Appleton Laboratory, UK Understanding chemical transformations in solid acid zeolite catalysts has been a fundamental area of catalysis research for many decades. Impacting on issues such as energy, sustainability, pollution control and industrial scale feedstock generation, an incredible amount of work is being done globally towards zeolite preparation, characterization and above all, understanding the chemistry of these important catalysts. Infrared (IR) spectroscopy plays a fundamental role in zeolite research and is well suited to in-operando monitoring of the evolution of the great diversity of hydroxyl, hydrocarbon and framework species present in zeolite systems. The limitations of IR spectroscopy are often quickly reached in practical work however, as IR bands can be hard to assign, difficult to obtain species concentration information from and of indeterminate lineshape origin. In an analogous way to the improvement of nuclear magnetic resonance (NMR) via multiple pulse / multidimensional approaches, the information content of both IR and Raman spectra 1,2 can be substantially improved upon by using femtosecond laser-based pulsed two-dimensional (2D) techniques. These report structural and picosecond-timescale dynamical information not available in ordinary IR and Raman measurements, and can also be used stand-alone to recover concentration and absorption coefficient information. 3 Zeolites are ripe for 2D-IR exploration, but as they are optically scattering powders of micron-sized crystals, they present practical challenges for the acquisition of 2D-IR data under conditions suitable for catalysis studies. In this contribution, we present 2D-IR spectra of pressed pellets of zeolites and under variable gas flow and temperature. We will discuss an experimental approach that supports routine collection of high quality 2D-IR spectra in the presence of intense pump laser scattering. 4 Using this approach, we have explored in-depth the 2D-IR spectroscopy of a range of zeolites in gas flows of D 2 O, HOD/H 2 O and MeOD over wide temperature ranges (20 °C- 540°C. From this ‘encyclopedia’ of spectra gathered, we will present several observations and procedures for which the uniqueness of zeolite 2D-IR spectroscopy delivers high value information of importance to contemporary catalysis research. References 1. Hamm, P.; Zanni, M. " Concepts and Methods of 2D Infrared Spectroscopy" ; Cambridge University Press, 2011 2. Donaldson, P. M. " Photon Echoes and Two Dimensional Spectra of the Amide I Band of Proteins Measured by Femtosecond IR-Raman Spectroscopy" . Chemical Science. 2020 , 11 (33), 8862–8874 3. Donaldson, P. M. " Spectrophotometric Concentration Analysis without Molar Absorption Coefficients by 2D-IR and FT-IR Spectroscopy" . Analytical Chemistry. 2022 , 94 (51), 17988–17999 4. Donaldson, P. M.; Howe, R. F.; Hawkins, A. P.; Towrie, M.; Greetham, G. M. " Ultrafast 2D-IR Spectroscopy of Intensely Optically Scattering Pelleted Solid Catalysts" . Submitted to Journal of Chemical Physics, 2022 .
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