The modification of Pt–based nanostructured and nanoporous catalysts for carbon compounds conversion into value-added products using theoretical study

Researcher studied the conversion of carbon compounds into value-added chemicals by Pt-based nano-structured and nanoporous catalysts employing Density Functional Theory(DFT). There were two reaction mechanisms studied: 1.) CO2 hydrogenation on a platinum catalyst doped on boron nitrite nanosheets (Pt-BNNSs) and 2.) n-hexane isomerization on Pt-FAU zeolites. For the CO2 hydrogenation reaction, Pt adatoms can be effectively stabilized at boron vacancy sites (Pt-BV). Our investigation demonstrated that the reaction mechanisms of CO2 hydrogenation over Pt-BV can be found in three possible reaction pathways: (i) co-adsorption, (ii) H2 dissociation, and (iii) H2 dissociation followed by CO2 hydrogenation pathways. Co-adsorption together with H2 dissociation provides the most favorable pathway among these three proposed mechanisms. The important finding of our study is that the presence of CO2 at the stage of hydrogen dissociation plays an important role in producing formic acid (FA) on the Pt-BV catalyst. In addition, we found that the hydrogenation of CO2 via carboxylate (COOH) has a rate-determined step of 0.63 eV in the process of hydrogen dissociation. Furthermore, the microkinetic modelling suggests that the COOH route is found to be more energetically and kinetically feasible over the formate route (HCOO) at a reaction temperature of 350 K at a pressure of 5 bar. The results of our calculations provide important information for developing Pt-BV catalysts and may guide the experimental design of novel Pt-BV catalysts for CO2 hydrogenation and the conversion of greenhouse gases into value-added products. HY zeolites have typically proven to be active hydrocarbon-cracking catalysts for n-hexane isomerization. The challenge has been to find an effective catalyst that favors the isomerization of n-alkanes without excessive cracking of product substances. In this work, adding Pt atoms to HY zeolite provided an enhanced multifunctional catalyst for converting n-alkanes to branched hydrocarbons. The isomerization reaction on Pt-HY selectively produces primary and secondary products i.e. 2-methylpentane (2MP) and 3-methylpentane (3MP) respectively, on high cracking products including C1, C2, C3, C4, and C5. To understand the effect of Pt on zeolite for the isomerization of the n-hexane process, we investigated the reaction mechanism of n-hexane isomerization to 2MP and 3MP by using a cluster of 30T HY zeolite modeled by B3LYP+3D calculations. Calculations found that the 2MP and 3MP can oceur via route A1 (C3-C4 bond activation) and B2 (C2-C3 bond activation), with activation energies for rate-determining steps of 0.97 and 1.20 eV, respectively, consistent with the experimental data. Furthermore, the presence of Pt on HY zeolite plays an important role in C-C bond formation and C-C bond activation on the Pt-HY catalyst. Finally, the Pt-HY zeolite can be used to enhance petroleum efficiency by improving the octane number in both catalytic performance and product selection by isomerizing straight chain alkanes to its branched-chain isomers.