Search

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.

Conversion of carbon dioxide (CO2) to more valuable chemicals is nowadays receiving increasing attention from an environmental and industrial point of view. Herein, we computationally investigated CO2 hydrogenation to formic acid on Lewis acid zeolites by means of density functional theory (DFT) with the M06-L functional. The reaction proceeds in two steps, hydrogenation of CO2 to form the formate intermediate and hydrogen-abstraction to form formic acid. A defect zeolite seems to be favored over a perfect one, leading to its low rate determining step barrier of 5.2 kcal mol−1. We also considered the effect of the zeolite frameworks and found that the catalytic activities are in the order Sn-ZSM-5 ＞ Sn-BEA ＞ Sn-FAU. Finally, we performed catalytic activity screenings of tetravalent metals (Ge, Zr and Hf) substituted into the defect Sn-ZSM-5 zeolite. The order Hf ＞ Zr ＞ Sn ＞ Ge was found based on the rate determining step activation energy. The difference in activation energy can be explained by the difference in charge transfer from the catalytic site to the reacting molecules. [ABSTRACT FROM AUTHOR]

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 CO 2 hydrogenation on the metal(II)-hydride supported DUT-5 is presented. • The Eley-Rideal mechanism is more favored than Langmuir-Hinshelwood mechanism. • The supported DUT-5 stabilizes the intermediates and transition states of the reaction. • NiH-DUT-5 exhibits the highest catalytic activity compared to the other metals studied in this work. Conversion of carbon dioxide (CO 2) to value-added chemicals is achieving increased attention from an environmental and industrial perspective because it could reduce the dependency on petroleum as raw material and also its net emission into the atmosphere. We present mechanisms for the CO 2 hydrogenation on the aluminum-based metal-organic framework DUT-5 support transition metal(II)-hydride in a detailed using density functional (DFT) calculations. Two different pathways, namely, Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms are described. The ER mechanism requires activation barriers of 8.5 and 15.1 kcal/mol for the formation of formate and of formic acid steps, respectively. The first barrier is three times lower than in the LH mechanism (27.4 kcal/mol), thus favouring the ER mechanism. Supported DUT-5 MOFs are also found to have a stabilizing effect on the intermediates and transition states formed along the reaction coordinate. Finally, we screen the catalytic activities of different metals substituted into MH-DUT-5 (M = Mn, Fe, Co, Ni, and Cu) MOFs for the hydrogenation of CO 2 to formic acid. It is found that NiH-DUT-5 exhibits the highest catalytic activity, based on its barriers. [Display omitted] [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.)

Conversion of carbon dioxide (CO2) to more valuable chemicals is nowadays receiving increasing attention from an environmental and industrial point of view. Herein, we computationally investigated CO2 hydrogenation to formic acid on Lewis acid zeolites by means of density functional theory (DFT) with the M06-L functional. The reaction proceeds in two steps, hydrogenation of CO2 to form the formate intermediate and hydrogen-abstraction to form formic acid. A defect zeolite seems to be favored over a perfect one, leading to its low rate determining step barrier of 5.2 kcal mol-1. We also considered the effect of the zeolite frameworks and found that the catalytic activities are in the order Sn-ZSM-5 > Sn-BEA > Sn-FAU. Finally, we performed catalytic activity screenings of tetravalent metals (Ge, Zr and Hf) substituted into the defect Sn-ZSM-5 zeolite. The order Hf > Zr > Sn > Ge was found based on the rate determining step activation energy. The difference in activation energy can be explained by the difference in charge transfer from the catalytic site to the reacting molecules.