Modeling Catalytic Steps on Extra-Framework Metal Centers in Zeolites. A Case Study on Ethylene Dimerization

Abstract

In a case study of organometallic catalytic reactions, this work benchmarks density functional theory calculations on zeolite-supported transition metal complexes. Elementary steps of ethylene dimerization and hydrogenation reactions involving the complex [Rh(C2H4)2(H2)]+, supported on faujasite, were examined by comparing explicit QM (quantum mechanics) cluster models as well as QM/MM (molecular mechanics) embedded models to plane-wave periodic models as reference. Two QM cluster models, 1T and 5T where T refers to tetrahedral units of zeolite, as well as four QM/MM cluster models were explored. For the MM region, the UFF force field was found preferable to the semiempirical method PM6. The embedded cluster models reproduce barriers of C–C and C–H bond formation with deviations from the reference of at most 10 kJ mol–1. With variations of similar size, the effect of embedding on the energetics of the reactions under study is moderate, likely because of the small nonpolar reactants. For elucidating such catalytic reactions at transition metal species in zeolites, cluster models appear equally well-suited as periodic models but computationally advantageous.

Assessing the stability of Pd-exchanged sites in zeolites with the aid of a high throughput quantum chemistry workflow

“…The QM region includes on average 54 atoms, excluding hydrogen atoms used to terminate the Si atoms. The QM regions used here are larger than used in previous work [11,[32][33][34][35] and we found it to be more than sufficient for the calculations to converge (Figure S4). Finally, for the calculations of NO adsorption in Pd-CHA, the number of QM atoms was extended as needed to account for potential interactions of NO with other Si/O atoms in the framework.…”

Ethene Conversion at a Zeolite‐Supported Ir(I) Complex. A Computational Perspective on a Single‐Site Catalyst System

“…In the same spirit, we used an 83T cluster, [22] taken from the zeolite lattice, to model the ethene conversion activity at a Ir(I) center anchored in FAU. This cluster model comprises a supercage unit with additional sodalite cages and hexagonal prisms, with 278 atoms in total, Figure S1a of the Supporting Information.…”

“…Within this 83T cluster, we used a QM partition of 5T centers which contains the AlO 4 moiety carrying the metal complex, surrounded by 4 neighboring Si units, Figure S1b of the Supporting Information. This hybrid QM/MM 5/83T model was treated with the ONIOM approach, [23] a strategy which was reported [22] to be equally well‐suited as periodic models for describing the catalytic reactions addressed in the present study.…”

“…The remainder of the 83T atoms was assigned as low‐level (MM) partition, surrounding the QM zeolite partition, and treated with the universal force field (UFF) [28] . This combined theoretical method ONIOM(PBE:UFF) was applied to the considered 5/83T embedded cluster model [22] . The geometry optimizations were carried out without symmetry constraints.…”

CPMD/GULP QM/MM interface for modeling periodic solids: Implementation and its application in the study of Y‐zeolite supported Rhn clusters

“…The reverse hydrogen spillover reactions on Rh 6 and other late‐transition metal clusters supported by zeolites have been studied in detail . Benchmark studies of QM/MM calculations have been reported for C–C coupling and hydrogenation reactions involving zeolite‐supported [Rh(C 2 H 4 ) 2 (H 2 )] . Structure and properties of protonated Rh n clusters in Y‐zeolite were also investigated using periodic DFT …”