On the Accuracy of Density Functional Theory in Zeolite Catalysis

Abstract

Zeolites are porous materials that are typically studied using periodic density functional theory (DFT). In this work we benchmark commonly used density functionals using cluster models for Brønsted acidic as well as copper substituted SSZ‐13 (H‐SSZ‐13 and Cu‐SSZ‐13). We find that for acid‐catalyzed reactions with relevance for the methanol‐to‐olefins process, barriers are the main challenge as they are commonly underestimated by DFT. For reactions involving Cu‐SSZ‐13 (commonly used for the selective catalytic reduction of NOx, SCR), reaction energies are already a challenge for most density functionals. Our results show that the widely used PBE‐D3 functional leads to mean absolute errors larger than 40 kJ/mol for barrier heights. Hybrid functionals show significant improvements with the best tested functional herein M06 having an error of only 7 kJ/mol.

Including dispersion in density functional theory for adsorption on flat oxide surfaces, in metal–organic frameworks and in acidic zeolites

“…For example, for the methylation of ethene, propene, and t-butene-2 in zeolite H-MFI, without any dispersion included, PBE yields (apparent) barriers that are 16, 36 and 57 kJ mol À1 , respectively, too high, 16 whereas after the D2 term is added, the barriers are systematically too low by 12 to 21 kJ mol À1 . 17 For 17 elementary steps of the methanol-to-olefins process, PBE-D3 was found to underestimate energy barriers by 42 kJ mol À1 , whereas with the hybrid functionals B3LYP-D3 and PBE0-D3 the underestimation is reduced to 27 and 17 kJ mol À1 , respectively, 42,59 in agreement with a reduced SIC for hybrid functionals. For 38 molecular hydrogen atom transfer reactions Zhao and Truhlar had reported systematic underestimation of energy barriers by PBE and B3LYP with 39 and 17 kJ mol À1 , respectively.…”

A Supramolecular View on the Cooperative Role of Brønsted and Lewis Acid Sites in Zeolites for Methanol Conversion

“…Due to the huge amount of calculations performed within this study, hierarchical cluster approaches relying on high level wave function based methods are beyond the scope for the current study. 84,86−90 Furthermore, the projector augmented wave (PAW) method, a plane-wave cutoff of 600 eV, and a self-consistent field (SCF) convergence criterion of 10 –5 eV are used. 91,92 During the VASP calculations, the Brillouin zone is restricted to the Γ-point.…”

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

“…Theoretical studies have been employed to calculate reaction free energy barriers of possible initiation and C-C coupling steps to shed light on plausible reaction mechanisms [43][44][45][46][47][48][49][50][51][52][53][54][68][69][70]. Using H-SSZ-13 as the catalyst we recently proposed a viable mechanism of the initiation reaction based on DFT calculations that have been corrected using second order Møller Plesset perturbation theory (MP2) [71] thus comprising highly accurate reaction barriers [72]. This is crucial since non-hybrid DFT calculations, particularly those using PBE-D3 [73,74], give rise to significantly underestimated activation barriers, effectively making reaction mechanisms appear more favorable than they actually are [68,72].…”

“…Using H-SSZ-13 as the catalyst we recently proposed a viable mechanism of the initiation reaction based on DFT calculations that have been corrected using second order Møller Plesset perturbation theory (MP2) [71] thus comprising highly accurate reaction barriers [72]. This is crucial since non-hybrid DFT calculations, particularly those using PBE-D3 [73,74], give rise to significantly underestimated activation barriers, effectively making reaction mechanisms appear more favorable than they actually are [68,72]. The key steps that we have identified for the initiation reaction starting from MeOH or DME using DFT:MP2 [68] are (1) the oxidation of MeOH to formaldehyde (FA) and subsequent oxidation to carbon monoxide (CO) and (2) the methylation of CO to methyl acetate (MA) forming the first C-C bond (see Fig.…”