Influence of Ag metal dispersion on the thermal conversion of ethanol to butadiene over Ag-ZrO2/SiO2 catalysts

Hydrated cation-π interactions of π-electrons with hydrated Mg2+ and Ca2+ cations

Hydrated cation-π interactions at liquid-solid interfaces between hydrated cations and aromatic ring structures of carbon-based materials are pivotal in many material, biological, and chemical processes, and water serves as a crucial mediator in these interactions. However, a full understanding of the hydrated cation-π interactions between hydrated alkaline earth cations and aromatic ring structures, such as graphene remains elusive. Here, we present a molecular picture of hydrated cation-π interactions for Mg2+ and Ca2+ by using the density functional theory methods. Theoretical results show that the graphene sheet can distort the hydration shell of the hydrated Ca2+ to interact with Ca2+ directly, which is water-cation-π interactions. In contrast, the hydration shell of the hydrated Mg2+ is quite stable and the graphene sheet interacts with Mg2+ indirectly, mediated by water molecules, which is the cation-water-π interactions. These results lead to the anomalous order of adsorption energies for these alkaline earth cations, with hydrated Mg2+-π < hydrated Ca2+-π when the number of water molecules is large (n ≥ 6), contrary to the order observed for cation-π interactions in the absence of water molecules (n = 0). The behavior of hydrated alkaline earth cations adsorbed on a graphene surface is mainly attributed to the competition between the cation-π interactions and hydration effects. These findings provide valuable details of the structures and the adsorption energy of hydrated alkaline earth cations adsorbed onto the graphene surface.

Porous ZrO2 encapsulated perovskite composite oxide for organic pollutants removal: Enhanced catalytic efficiency and suppressed metal leaching

Cobalt-based perovskite material, an effective activator of PMS, is widely employed for wastewater remediation, but still affected by the leakage of the cobalt ions. In this study, a porous core-shell structured perovskite LaFe_0.1Co_0.9O_3-λ/SiO₂ core @ZrO₂ shell (LFCS@ZrO₂) was fabricated and partially etched to enlarge channels to further enhance mass transfer ability. The well-designed core-shell structure can not only restrain metal ion leaching by changing the surface microenvironment but also provide an additional driving force attributed to the enriched concentration gradient, thus enhancing the catalytic oxidation performance. Results showed that the partially etched LFCS@ZrO₂ (eLFCS@ZrO₂) particles exhibited an increased pore size and showed an attractive catalytic performance as well as a suppressed cobalt ion leaching (3.61 to 0.67 mg/L). Over 99% of tetracycline hydrochloride (20 mg/L) could be degraded in 15 min, and the reaction rate increased 2 folds compared with pristine LaFe_0.1Co_0.9O_3-λ. Besides, quenching test and electron paramagnetic resonance analysis proved that sulfate radicals and singlet oxygen were the two predominant reactive oxygen species during the catalytic oxidation. This work provides a novel perspective for the fabrication of an environmentally friendly perovskite catalyst, which has a great potential application in organic pollutant degradation.

Hydrated cation-π interactions of π-electrons with hydrated Li+, Na+, and K+ cations

Cation-π interactions are essential for many chemical, biological, and material processes, and these processes usually involve an aqueous salt solution. However, there is still a lack of a full understanding of the hydrated cation-π interactions between the hydrated cations and the aromatic ring structures on the molecular level. Here, we report a molecular picture of hydrated cation-π interactions, by using the calculations of density functional theory (DFT). Specifically, the graphene sheet can distort the hydration shell of the hydrated K+ to interact with K+ directly, which is hereafter called water-cation-π interactions. In contrast, the hydration shell of the hydrated Li+ is quite stable and the graphene sheet interacts with Li+ indirectly, mediated by water molecules, which we hereafter call the cation-water-π interactions. The behavior of hydrated cations adsorbed on a graphene surface is mainly attributed to the competition between the cation-π interactions and hydration effects. These findings provide valuable details of the structures and the adsorption energy of hydrated cations adsorbed onto the graphene surface.

Recent Advances in Catalysts for the Conversion of Ethanol to Butadiene

Butadiene is an important monomer for synthetic rubbers. Currently, the annual demand of ∼16 million tonnes is satisfied by butadiene produced as a byproduct of steam naphtha cracking where ethylene and propylene are the main products. The availability of large amounts of shale gas and condensates in the USA since about 2008 has led to a change in the cracker feed from naphtha to ethane and propane, affecting the amount of butadiene obtained. This has provided the impetus to look into direct processes for butadiene production. One option is the eco-friendly conversion of (bio) ethanol to butadiene (ETB). This process had been developed in the 1930s in the then Soviet Union. It was operated on a large scale in USA during World War II but has since been abandoned in favour of petroleum-based processes. The current trend, driven both by the availability of the raw material and ecological considerations, may make this process feasible again, particularly if the catalytic systems can be improved. This critical review discusses recent catalysts for the ETB process with special focus on the development since 2014, benchmarking them against earlier systems with a large database of operational experience.

NWPEsSe: An Adaptive-Learning Global Optimization Algorithm for Nanosized Cluster Systems

Global optimization constitutes an important and fundamental problem in theoretical studies in many chemical fields, such as catalysis, materials, or separations problems. In this paper, a novel algorithm has been developed for the global optimization of large systems including neat and ligated clusters in the gas phase and supported clusters in periodic boundary conditions. The method is based on an updated artificial bee colony (ABC) algorithm method, that allows for adaptive-learning during the search process. The new algorithm is tested against four classes of systems of diverse chemical nature: gas phase Au₅₅, ligated Au₈²⁺, Au₈ supported on graphene oxide and defected rutile, and a large cluster assembly [Co₆Te₈(PEt₃)₆][C₆₀]_n, with sizes ranging between 1 and 3 nm and containing up to 1300 atoms. Reliable global minima (GMs) are obtained for all cases, either confirming published data or reporting new lower energy structures. The algorithm and interface to other codes in the form of an independent program, Northwest Potential Energy Search Engine (NWPEsSe), is freely available, and it provides a powerful and efficient approach for global optimization of nanosized cluster systems.

Ethanol-to-butadiene: the reaction and its catalysts

Catalytic conversion of ethanol is a promising technology for producing sustainable butadiene. This paper reviews the reaction and its catalysts, and discusses the challenges their development faces.