Mechanism of methylene oxidation on Pt catalysts: A DFT study

Study on the mechanism of acid treatment La0.8Sr0.2Mn0.8Cu0.2O3 to improve the catalytic activity of formaldehyde at low temperature

To address the issue of surface enrichment of A-site ions in perovskite and the resulting suppression of catalytic activity, the La0.8Sr0.2Mn0.8Cu0.2O3 was modified by treatment with dilute nitric acid (2 mol/L) and dilute acetic acid (2 mol/L). The results show that the effect of dilute nitric acid treatment on the morphology and catalytic activity of the catalyst is more significant. The specific surface area of the catalyst after dilute nitric acid treatment (268.78 m2/g) is seven times higher than before treatment (37.55 m2/g). The low-temperature catalytic oxidation activity of HCHO of the catalyst after dilute nitric acid treatment is significantly improved, achieving a 50% HCHO oxidation efficiency at 80 °C, while the original sample requires 127 °C to achieve a 50% HCHO conversion. The excellent catalytic activity of the catalyst after dilute nitric acid treatment is related to its large specific surface area, high surface-active site density, and abundant Mn4+ ions. Stability and water resistance experiments show that the catalyst after dilute nitric acid treatment has excellent reaction stability and good water resistance ability. The mechanism of the formaldehyde oxidation reaction is that formaldehyde is first oxidized to a dioxymethylene (DOM) intermediate and DOM dehydrogenation reaction is responsible for the formation of formate species (HCOO-).

Oxygen Atom Function: The Case of Methane Oxidation Mechanism to Synthesis Gas over a Pd Cluster

A dimer model Pd2 was established to study the adsorption of CHx (x = 1–4) and CH4 dehydrogenation, as well as syngas formation using density functional theory (DFT) at the atomic level. Meanwhile, insight into understanding the role of the oxygen atom on the partial oxidation of methane (POM) was also calculated based on a trimer model of Pd2O. For the adsorption of CHx, results showed that the presence of an oxygen atom was a disadvantage to the adsorption of CHx (x = 1–3) species. For CH4 dissociation, the process of CH2→CH + H was found to be the rate-limiting step (RSD) on both Pd2 and Pd2O. H2 was formed by the reaction of CH2 + 2H→CH2 + H2. For CO formation, it was primarily formed in the process of CH + O→CHO→CO + H on both the Pd2 and the Pd2O catalyst. Thermodynamic and kinetic calculations revealed that formation and maintainance of the oxygen atom on the Pd surface could promote a POM reaction to achieve high H2 and CO yield and selectivity. Our study provides a helpful understanding of the effect of an adsorbed oxygen atom on a POM reaction with a Pd catalyst.

One-Step Reforming of CO2 and CH4 into High-Value Liquid Chemicals and Fuels at Room Temperature by Plasma-Driven Catalysis

The conversion of CO₂ with CH₄ into liquid fuels and chemicals in a single‐step catalytic process that bypasses the production of syngas remains a challenge. In this study, liquid fuels and chemicals (e.g., acetic acid, methanol, ethanol, and formaldehyde) were synthesized in a one‐step process from CO₂ and CH₄ at room temperature (30 °C) and atmospheric pressure for the first time by using a novel plasma reactor with a water electrode. The total selectivity to oxygenates was approximately 50–60 %, with acetic acid being the major component at 40.2 % selectivity, the highest value reported for acetic acid thus far. Interestingly, the direct plasma synthesis of acetic acid from CH₄ and CO₂ is an ideal reaction with 100 % atom economy, but it is almost impossible by thermal catalysis owing to the significant thermodynamic barrier. The combination of plasma and catalyst in this process shows great potential for manipulating the distribution of liquid chemical products in a given process.

Recent application of calculations of metal complexes based on density functional theory

Recent application of density functional theory (DFT) for metal complexes is reviewed to show the achievements of DFT and the challenges for it, as well as the methods for selecting proper functionals.