Structure and Surface Chemistry of Gold-Based Model Catalysts

Structure and Surface Chemistry of Gold-Based Model Catalyst

Selective Oxidation of Ethanol to Acetaldehyde on Gold

Selective Oxidation of Ethanol to Acetaldehyde on Gol

Oxygen Exchange in the Selective Oxidation of 2-Butanol on Oxygen Precovered Au(111)

Direct evidence for C−O bond cleavage in the partial oxidation of 2-butanol on oxygen precovered Au(111) is provided using temperature programmed desorption (TPD) and molecular beam reactive scattering (MBRS) under ultrahigh vacuum (UHV) conditions. The oxygen precovered Au(111) surface can promote the partial oxidation of 2-butanol into 2-butanone with near 100% selectivity at low oxygen coverages, while 2-butanol adsorbs and desorbs molecularly on the clean Au(111) surface. Both C2H5C16OCH3 and C2H5C18OCH3 are observed in TPD after 2-butanol (C2H5CH16OHCH3) was dosed onto Au(111) precovered with 18Oa. This oxygen exchange phenomenon serves as strong evidence for the C−O bond cleavage in 2-butanol partial oxidation to 2-butanone. Two surface intermediates are proposed for the selective oxidation of 2-butanol: 2-butoxide and η2-aldehyde. As oxygen coverage increases, full oxidation is activated in addition to selective partial oxidation

The Effect of Adsorbed Water in CO Oxidation on Au/TiO₂(110)

The effect of moisture on CO oxidation on Au/TiO2(110) model catalysts is investigated using temperature-programmed desorption and molecular beam reactive scattering under ultrahigh vacuum (UHV) conditions. Oxygen exchange is observed between adsorbed atomic oxygen and isotopically labeled water. Coadsorbed water (H218O) takes part in CO oxidation on Oa precovered Au/TiO2(110) model catalysts, leading to the formation of C16O18O and C16O16O. The amount of C16O18O produced increases with increasing water coverages; however, the total amount of CO2 produced decreases. Although coadsorbed Oa and H2O have a minimal influence on the initial adsorption probability of CO, the total uptake of CO decreases as H2O coverages increase. Interestingly, the adsorption of water induces desorption of predeposited molecularly chemisorbed O2. Thus, adsorbed water slightly inhibits CO oxidation on atomic oxygen precovered Au/TiO2(110) model catalysts under UHV conditions

Imaging Hindered Rotations of Alkoxy Species on TiO₂(110)

We present the first scanning tunneling microscopy (STM) study of the rotational dynamics of organic species on any oxide surface. Specifically, variable-temperature STM and dispersion-corrected density functional theory (DFT-D) are used to study the alkyl chain conformational disorder and dynamics of 1-, 2-, 3- and 4-octoxy on rutile TiO2(110). Initially, the geminate pairs of the octoxy and bridging hydroxyl species are created via octanol dissociation on bridging-oxygen (Ob) vacancy defects. The STM images provide time-averaged snapshots of octoxy species rotating among multiple energetically nearly degenerate configurations accessible at a given temperature. In the calculations we find that the underlying corrugated potential energy surface is a result of the interplay between attractive van der Waals dispersion forces, leading to weak attractive C···Ti and repulsive C···Ob interactions which lead to large barriers of 50−70 kJ mol−1 for the rotation of the octoxy alkyl chains across the Ob rows. In the presence of the geminate hydroxyl groups we find that the relative populations of the various conformations as well as the rotational barriers are perturbed by the presence of geminate hydroxyl due to additional C···hydroxyl repulsions

Coverage Effect on the Activity of the Acetylene Semihydrogenation over Pd–Sn Catalysts: A Density Functional Theory Study

The existence of acetylene impurities in ethylene feedstock is harmful to downstream polymerization reactions. The removal of acetylene can be achieved via semihydrogenation reaction, which is normally catalyzed by Pd-based catalysts. This paper describes the coverage effect on the activity of acetylene hydrogenation reactions over Pd and PdSn alloy surfaces. High-coverage models are presented to construct coverage-dependent adsorption energies of C₂H₂, C₂H₄, and H₂ on Pd(111) and Pd₃Sn­(111) surfaces. It has been validated that the downshift of d-band center caused by preadsorbed molecules makes the adsorption weaker along with the increase of coverage, and the geometric effect can be neglected. An iterative method has been applied to predict surface coverages of reaction intermediates. Previous calculations with low-coverage models indicate that alloying Pd with late or post-transition metals, in general, enhances ethylene selectivity, accompanied with lower hydrogenation activity. However, by applying a high-coverage model, we show that the predicted hydrogenation barriers are comparable over Pd(111) and Pd₃Sn­(111) surfaces

Enhanced Surface Reaction Kinetics and Charge Separation of p–n Heterojunction Co₃O₄/BiVO₄ Photoanodes

Surface reaction kinetics and bulk charge separation are both critical to the efficiency of solar water splitting. In addition to the well-documented surface catalytic effect, the promotion of bulk charge separation upon loading of cocatalysts has rarely been reported. This paper describes the synergetic enhancement of surface reaction kinetics and bulk charge separation by introducing discrete nanoisland p-type Co₃O₄ cocatalysts onto n-type BiVO₄, forming a p–n Co₃O₄/BiVO₄ heterojunction with an internal electric field to facilitate charge transport. Being highly dispersed on the surface of photoanodes, the nanoisland cocatalysts could suppress the formation of recombination centers at the photoanode/cocatalyst interface. This cocatalyst-loading method achieved a charge separation efficiency of up to 77% in the bulk and 47% on the surface of catalysts. An AM 1.5G photocurrent of 2.71 mA/cm² at 1.23 V versus the reversible hydrogen electrode for water oxidation was obtained, which is the highest photocurrent yet reported for Co-catalyzed undoped BiVO₄ photoanodes, with a photoconversion efficiency of 0.659%

Long non-coding RNA MALAT1 aggravated liver ischemia-reperfusion injury via targeting miR-150-5p/AZIN1

Long non-coding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) plays a crucial role in the process of renal ischemia-reperfusion (IR) injury and myocardial IR injury. However, its mechanism in liver IR injury is not clear. IR and hypoxia/reoxygenation (H/R) model were built on C57BL/6 mice. Blood samples were obtained from the inferior vena cava of the model mice. MALAT1 expression was detected in IR model and H/R model. Supported by experimental results, the impacts of MALAT1 on viability, apoptosis, and inflammation of H/R model cells were detected. The correlation between MALAT1 and downstream genes was analyzed by mechanism assays. MALAT1 was detected to be upregulated in IR model and H/R model. MALAT1 knockdown had inhibitory effects on apoptosis and inflammatory reaction while promoting liver cell viability in H/R condition. Meanwhile, MALAT1 targeted miR-150-5p to regulate antizyme inhibitor 1 (AZIN1) in liver cells. Finally, MALAT1 regulated viability, apoptosis, and inflammatory reaction of liver cells by targeting miR-150-5p and AZIN1. To conclude, MALAT1 targeted miR-150-5p/AZIN1 to accelerate liver IR injury, suggesting that MALAT1 might be a novel target for liver IR injury.</p

Techno-Economic Analysis of a Hybrid Process for Propylene and Ammonia Production

Hydrogen as a large-scale byproduct from the propane dehydrogenation process is of great value for the downstream value-added chemical production. The paper describes a hybrid process which combines the production of propylene and ammonia using hydrogen produced from the propane dehydrogenation process. The utility consumption and economic cost of the hybrid process are investigated in comparison with the standalone propylene production and methane-to-ammonia processes. Due to the combination of the endothermic propane dehydrogenation process and exothermic ammonia synthesis process, the hybrid process can achieve a more efficient heat exchange capacity with lower utility requirement. The utility consumption of the hybrid process is 3.5% lower than the summation of standalone propylene production at 900 kt/year and ammonia production at 220 kt/year. The total production cost of the hybrid process is 13.6 M$/year lower at this production scale. Although the production costs of all processes increase with the increase of resource prices and decrease of produce scale, the hybrid process still shows higher economic performance than the summation of those of the two individual processes. This study can potentially instruct the efficient utilization of the byproduct hydrogen from the propane dehydrogenation process for downstream value-added chemical production processes

Imaging Hindered Rotations of Alkoxy Species on TiO₂(110)

We present the first scanning tunneling microscopy (STM) study of the rotational dynamics of organic species on any oxide surface. Specifically, variable-temperature STM and dispersion-corrected density functional theory (DFT-D) are used to study the alkyl chain conformational disorder and dynamics of 1-, 2-, 3- and 4-octoxy on rutile TiO2(110). Initially, the geminate pairs of the octoxy and bridging hydroxyl species are created via octanol dissociation on bridging-oxygen (Ob) vacancy defects. The STM images provide time-averaged snapshots of octoxy species rotating among multiple energetically nearly degenerate configurations accessible at a given temperature. In the calculations we find that the underlying corrugated potential energy surface is a result of the interplay between attractive van der Waals dispersion forces, leading to weak attractive C···Ti and repulsive C···Ob interactions which lead to large barriers of 50−70 kJ mol−1 for the rotation of the octoxy alkyl chains across the Ob rows. In the presence of the geminate hydroxyl groups we find that the relative populations of the various conformations as well as the rotational barriers are perturbed by the presence of geminate hydroxyl due to additional C···hydroxyl repulsions