Correlating Vibrational Spectra to C1 Surface Species on Nickel-Based Hydrogenation Catalysts Using Density Functional Theory

Abstract

Understanding catalytic processes requires insights into the behavior of reactants, intermediates, and products at the surface of a solid catalyst. This is often studied via in situ or operando vibrational spectroscopy and by theoretical calculations. However, direct comparison between experimental and theoretical vibrational frequencies remains challenging and requires careful methodological treatment. Here, we present a systematic computational framework for calculating and scaling the fundamental vibrational frequencies of fourteen key intermediates involved in catalytic C1 reactions over nickel. Such intermediates were modeled on Ni(111), Ni(100), Ni(110), and Ni(211) crystal surfaces. Multiple density functional theory (DFT) methods and basis sets were benchmarked. Linear scaling equation (LSE) correction was applied to all computed wavenumbers. The result is a validated database of LSE-corrected vibrational frequencies, designed to aid experimentalists in infrared (IR) spectral interpretation. We illustrate its application with a phenomenological evaluation of the CO adsorption region, comparing calculated spectra to IR spectra from CO2 methanation over four Ni/SiO2 catalysts. For this analysis, we used a dual-model approach, computing CO∗ frequencies on both extended facets and a 1.439 nm Wulff-constructed nanoparticle to account for size-dependent effects. The analysis highlights how adsorption site and adsorbate interactions influence vibrational features, underscoring the need for both more complex models and complementary experiments to accurately capture effects, such as peak shifts, inhomogeneous broadening, and intensity transfer that govern the spectra of working catalyst surfaces.