Computational insights into the zeolite-supported gold nanocluster-catalyzed ethanol dehydrogenation to acetaldehyde.

Zeolite-supported gold nanoclusters play increasingly important roles in heterogeneous catalysis and exhibit unique catalytic properties for ethanol dehydrogenation to acetaldehyde. Nevertheless, the reaction mechanism and potential roles of the zeolite-encapsulated gold nanoclusters during the catalytic process remain unclear. Herein, computational studies were carried out to gain mechanistic insights into ethanol dehydrogenation to acetaldehyde under both aerobic and anaerobic conditions catalyzed by a silicalite-1 zeolite-encapsulated Au3 cluster cation (Au3+-S1). The presence of O2 can significantly promote the ethanol dehydrogenation catalyzed by Au3+-S1. A feasible mechanistic pathway could be initiated via the O2 induced H-atom transfer (HAT) step from the hydrogen of the hydroxyl group to afford ethoxy and OOH radical species. Subsequently, the OOH induced second HAT from α-C-H of the ethoxy intermediate could follow to afford the acetaldehyde product. Moreover, the possible confinement and stabilization effect of the zeolite channels on the ethanol dehydrogenation reaction was discussed.

Electrosynthesis of Hydrogen Peroxide Enabled by Exceptional Molecular Ni Sites in a Graphene-Supported Nickel Organic Framework.

Electrosynthesis of hydrogen peroxide (H2O2) from 2e- transfer of the oxygen reduction reaction (2e--ORR) is a potential alternative to the traditional anthraquinone process. Two-dimensional (2D) metal-organic frameworks (MOFs) supported by carbon are frequently reported as promising 2e--ORR catalysts. Herein, a graphene-supported 2D MOF of Ni3(2,3,6,7,10,11-hexahydrotriphenylene)2 is synthesized through a common hydrothermal method, which exhibits high 2e--ORR performance. It is discovered that except for emerging MOFs, exceptional molecularly dispersed Ni sites coexist in the synthesis that have the same coordination sphere of the NiO4C4 moiety as the MOF. The molecular Ni sites are more catalytically active. The graphene support contains a suitable amount of residual oxygen groups, leading to the generation of those molecularly dispersed Ni sites. The oxygen groups exhibit a moderate electron-withdrawing effect at the outer sphere of Ni sites to slightly increase their oxidation state. This interaction decreases overpotentials and kinetically improves the selectivity of the 2e- reaction pathway.

Long-Term and Stable Dental Therapies via an In Situ Spontaneous Medicine Delivery System.

Chronic oral diseases are boring, long-term, and discomfort intense diseases, which endanger the physical and mental health of patients constantly. Traditional therapeutic methods based on medicines (including swallowing drugs, applying ointment, or injection in situ) bring much inconvenience and discomfort. A new method possessing accurate, long-term, stable, convenient, and comfortable features is in great need. In this study, we demonstrated a development of one spontaneous administration for the prevention and therapy on a series of oral diseases. By uniting dental resin and medicine-loaded mesoporous molecular sieve, nanoporous medical composite resin (NMCR) was synthesized by a simple physical mixing and light curing method. Physicochemical investigations of XRD, SEM, TEM, UV-vis, N2 adsorption, and biochemical experiments of antibacterial and pharmacodynamic evaluation on periodontitis treatment of SD rats were carried on to characterize an NMCR spontaneous medicine delivery system. Compared to existing pharmacotherapy and in situ treatments, NMCR can keep a quite long time of stable in situ medicine release during the whole therapeutic period. Taking the periodontitis treatment as an instance, the probing pocket depth value in a half-treatment time of 0.69 from NMCR@MINO was much lower than that of 1.34 from the present commercial Periocline ointment, showing an over two times effect.

Continuous Homogeneous Catalytic Oxidation of C-H Bonds by Metal-Free Carbon Dots with a Poly(ascorbic acid) Structure.

The activation of the C-H bond, a necessary step to get high-value-added compounds, is one of the most important issues in modern catalysis. Combining the advantages of both homogeneous and heterogeneous catalysis, a certain continuous homogeneous process should be one of the ideal routes for the catalytic activation of C-H bonds. Here, through machine learning (ML), we predicted and fabricated metal-free carbon dot (C-Dot) homogeneous catalysts for C-H bond oxidation. These C-Dots have an ascorbic acid unit based polymer-like structure with a polymerization degree in the range of 3-10. With C-Dots as the catalyst, three groups (aliphatic, aromatic, and cycloalkanes) of 10 hydrocarbon molecules were tested, proving its generality for the catalytic oxidation of the C-H bond. A typical example of cyclohexane that was selectively oxidized to adipic acid (AA) by using a circulation and phase-transfer process demonstrates its critical advantages, such as the continuous and large-scaled producing ability of the homogeneous catalysis process. The one-pass conversion efficiency of cyclohexane to AA reaches 77.49% with selectivity up to 84.24% in 4 h. The yield of 16.32% per hour is about 4 times over that of modern technology. Theoretical calculations suggested that the O2 activation on C-Dots plays a crucial role in determining the reaction rate of the entire catalytic oxidation process of cyclohexane.

Continuous hydrogenation of ethyl levulinate to γ-valerolactone and 2-methyl tetrahydrofuran over alumina doped Cu/SiO2 catalyst: the potential of commercialization.

Hydrogenation of levulinic acid (LA) and its esters to produce γ-valerolactone (GVL) and 2-methyl tetrahydrofuran (2-MTHF) is a key step for the utilization of cellulose derived LA. Aiming to develop a commercially feasible base metal catalyst for the production of GVL from LA, with satisfactory activity, selectivity, and stability, Al2O3 doped Cu/SiO2 and Cu/SiO2 catalysts were fabricated by co-precipitation routes in parallel. The diverse physio-chemical properties of these two catalysts were characterized by XRD, TEM, dissociative N2O chemisorptions, and Py-IR methods. The catalytic properties of these two catalysts were systematically assessed in the continuous hydrogenation of ethyl levulinate (EL) in a fixed-bed reactor. The effect of acidic property of the SiO2 substrate on the catalytic properties was investigated. To justify the potential of its commercialization, significant attention was paid on the initial activity, proper operation window, by-products control, selectivity, and stability of the catalyst. The effect of reaction conditions, such as temperature and pressure, on the performance of the catalyst was also thoroughly studied. The development of alumina doped Cu/SiO2 catalyst strengthened the value-chain from cellulose to industrially important chemicals via LA and GVL.

Polymer-based stimuli-responsive recyclable catalytic systems for organic synthesis.

The introduction of stimuli-responsive polymers into the study of organic catalysis leads to the generation of a new kind of polymer-based stimuli-responsive recyclable catalytic system. Owing to their reversible switching properties in response to external stimuli, these systems are capable of improving the mass transports of reactants/products in aqueous solution, modulating the chemical reaction rates, and switching the catalytic process on and off. Furthermore, their stimuli-responsive properties facilitate the separation and recovery of the active catalysts from the reaction mixtures. As a fascinating approach of the controllable catalysis, these stimuli-responsive catalytic systems including thermoresponsive, pH-responsive, chemo-mechano-chemical, ionic strength-responsive, and dual-responsive, are reviewed in terms of their nanoreactors and mechanisms.

Selective adsorption of DNA on chiral surfaces: supercoiled or relaxed conformation.

The right fit: Plasmid DNA molecules show chirality-dependent interaction with gold surfaces modified by L and D N-isobutyrylcysteine. Relaxed DNA molecules have a stronger interaction and adsorption on the L surface, while their counterparts on the D surface maintain a supercoiled conformation, indicating a weak interaction (see picture).

Stereoselective interaction between DNA and chiral surfaces.

ssDNA exhibits much different adsorption behaviors on enantiomer modified surfaces, which can be explained by the stereoselective H-bond interaction between DNA and the chiral surfaces. This effect not only may help to understand the stereospecific cell/substrate interaction and the origin of the chiral preference in nature but also brings novel insights to the study of DNA properties and the application in biochemical devices.

One-step controllable synthesis for high-quality ultrafine metal oxide semiconductor nanocrystals via a separated two-phase hydrolysis reaction.

A one-step synthesis method is described to prepare high-quality ultrafine inorganic semiconductor nanocrystals via a two-phase interface hydrolysis reaction under hydrothermal conditions. With the synthesis of ZrO2 quantum dots as an example, we show that the prepared nanocrystals have good monodispersity and high crystallinity, as well as other related superior properties, e.g., strong photoluminescence and excellent photocatalytic activities. Also the crystal size can be conveniently adjusted in the range below 10 nm through controlling the reaction temperature. Besides that, this method also shows other distinct advantages compared with other methods reported previously. First, the preparation process is simple and cheap and does not contain any complicated posttreatment procedure. Second, products (without coating) can be collected from the organic phase which effectively avoids grain aggregation induced by the capillary concentration in the water environment. Third, the production yield is very high (almost 100%) and the organic and water phases after reaction can be easily recycled for next reaction. Therefore, it provides a promising strategy for the large-scale industrial production of different kinds of high-quality inorganic nanocrystals.