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The metal-support interaction of a dispersed Pt atom on H-ZSM-5 zeolite is investigated by using an embedded cluster and cluster models with the density functional theory/B3LYP functional method. It is found that the Madelung potential of the support is responsible for the observed small red shift of CO on the Pt-H-ZSM-5.

The ab initio embedded cluster methodology at the B3LYP level of theory is applied for systematically studying the adsorption of NO and CO in Cu-ZSM-5. It was found that the effects of the cluster size and Madelung potential were small for the adsorption energies of CO and NO.

The metal−support interaction of a dispersed Pt atom on H-ZSM-5 zeolite has been investigated by using an embedded cluster and cluster models with the density functional theory/B3LYP functional method. We found that the Pt atom interacts with a Brønsted proton and a nearby framework oxygen. Interaction with the framework oxygen causes electron transfer from the zeolite to the Pt atom. Concurrently, a Brønsted proton stabilizes the Pt atom on the zeolite surface by withdrawing excess electron density from the Pt atom. These charge transfers result in a zero net charge on the Pt atom while changing its orbital occupation. The binding energy of Pt on the Brønsted acid was 15 kcal/mol. Inclusion of the Madelung potential by Surface Charge Representation of the Electrostatic Embedded Potential method (SCREEP) had small effects on structure and charge density of Pt/H-ZSM-5 but it shifted the stretching mode of CO toward a higher frequency by almost 40 cm-1. The frequency shift of absorbed CO calculated with embedded cluster models was from 8 to 11 cm-1 red shift, compared to 20 cm-1 red shift from experiment. This implies that not only the electronic state of the Pt atom but also the Madelung potential of the support is responsible for the observed small red shift of CO on the Pt-H-ZSM-5. [ABSTRACT FROM AUTHOR]

An efficient synthesis of 5,7-dihydroxy-4-methylcoumarin from phloroglucinol with ethyl acetoacetate in the UiO-66-SO 3 H metal-organic framework is reported. The potential of UiO-66-SO 3 H as a solid catalyst was determined through optimized-condition experiments and quantum molecular calculations. The optimal conditions for the synthesis of 5,7-dihydroxy-4-methylcoumarin with UiO-66-SO 3 H were as follows: phloroglucinol/ethyl acetoacetate molar ratio = 1:1.6, reaction time = 4 h, and temperature = 140 °C, for which the reaction yield reached 66.0%. The reusability of UiO-66-SO 3 H catalysts for Pechmann condensation was examined. The activation energy of the reaction occurring on a sulfonic group of the UiO-66-SO 3 H catalyst was 12.6 kcal/mol, which was significantly lower than 22.6 kcal/mol of the same reaction on the UiO-66 catalyst. To comprehend the reaction mechanism, density functional theory with the ONIOM approach was applied for the synthesis of coumarin on the UiO-66-SO 3 H and UiO-66 clusters. A possible reaction mechanism was proposed involving three steps: a trans-esterification step, an intramolecular hydroxyalkylation step, and a dehydration step. The rate-determining step was suggested to be the first step which acquired an activation energy of 15.7 and 29.5 kcal/mol, respectively. Information from this study can be used as guidelines to develop more efficient catalytic metal-organic frameworks for various organic syntheses., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)