(453g) A Microkinetic Model for Methyl Cyclohexane Dehydrogenation Combining Experimental Kinetics and First Principles Calculations with Co-Adsorbate Interactions

Methyl cyclohexane (MCH), a promising liquid organic hydrogen carrier, undergoes dehydrogenation to toluene catalysed by Pt-based nanoparticles [1]. Utilizing a cubo-octahedral Pt55 nanoparticle as a model, we conducted a density functional theory (DFT)-based microkinetic analysis. We determined the intrinsic activation barriers and thermodynamic barriers of elementary steps at clean Pt surfaces (Figure a), employing a lumped microkinetic model for reaction kinetics simplification. This approach, combining six dehydrogenation steps into one, mitigates numerical stiffness and enhances the numerical accuracy of the model. Crucially, our work highlights the necessity of simulating reaction kinetics under experimental conditions to bridge the gap between theoretical models and experimental observations. DFT studies on small adsorbates indicated sensitivity of reactivity and selectivity to surface coverage [2], yet the impact of adsorbate-adsorbate interactions on large hydrocarbon molecules remained elusive due to complex multidentate interactions. Calculating the adsorbate-adsorbate interaction at both Pt (100) and (111) facets, our findings illustrate that adsorbate-adsorbate interactions significantly affect adsorption energies (one example can be found in Figure b), while leaving activation barriers of elementary steps nearly unchanged. We incorporated the effects of these co-adsorbate interactions on reaction energies via a pairwise model into our microkinetic simulation (Figure b, c). We are calibrating the turnover frequencies and surface coverages of reaction intermediates determined using the model with experiments. This inclusion of the adsorbate-adsorbate interaction significantly enhances the model's predictive accuracy with selectivity and reactivity, offering a closer quantitative alignment with experimental data.

[1] Y. Okada, Extended abstracts of the 9th Tokyo Conference on Advanced Catalytic Science and Technology, Fukuoka, KL14, (2022).

[2] W. Xie, J. Xu, J. Chen*, H. Wang*, and P. Hu*, Acc. Chem. Res. 2022, 55, 9, 1237–1248