Oxide-supported noble metal catalysts have been extensively studied for decades for the water gas shift (WGS) reaction, a catalytic transformation central to a host of large volume processes that ...variously utilize or produce hydrogen. There remains considerable uncertainty as to how the specific features of the active metal-support interfacial bonding-perhaps most importantly the temporal dynamic changes occurring therein-serve to enable high activity and selectivity. Here we report the dynamic characteristics of a Pt/CeO
system at the atomic level for the WGS reaction and specifically reveal the synergistic effects of metal-support bonding at the perimeter region. We find that the perimeter Pt
- O vacancy-Ce
sites are formed in the active structure, transformed at working temperatures and their appearance regulates the adsorbate behaviors. We find that the dynamic nature of this site is a key mechanistic step for the WGS reaction.
Uniform color distribution is essential for the packaging of light emitting diodes (LEDs). The Monte Carlo ray tracing method is applied to analyze the color distribution of white LEDs. Five ...packaging methods are investigated and the location of phosphor layer is varied. Results reveal that the packaging method is the primary factor affecting the color distribution and a nonreflector packaging method presents better color uniformity. The location of phosphor has a small impact on the color uniformity but remote location, if too far, can reduce the uniformity significantly. The reduction of color uniformity may exceed 88%.
This study develops a 'Pathways to De-dollarization' framework and applies it to analyze the institutional and market mechanisms that BRICS (Brazil-Russia-India-China-South Africa) countries have ...created at the BRICS, sub-BRICS, and BRICS Plus levels. This title is also available as Open Access on Cambridge Core.
A water boost for methanol synthesisModel catalysts based on metals and metal oxides can dissociate methane (CH4) at room temperature, converting it directly to methanol (CH3OH). Liu et al. show that ...for one of these catalysts, an “inverted” CeOx-Cu2O oxide on Cu(111), water tunes the selectivity from forming CO and CO2 to forming surface CH3O groups, as revealed by ambient-pressure x-ray photoelectron spectroscopy. Theoretical modeling showed that adsorbed water blocks O2 dissociation and O2 instead oxidizes the reduced catalyst. Hydroxyl groups from water generate the CH3O species from dissociated CH4, and water then goes on to form and displace CH3OH to the gas phase.Science, this issue p. 513Highly selective oxidation of methane to methanol has long been challenging in catalysis. Here, we reveal key steps for the promotion of this reaction by water when tuning the selectivity of a well-defined CeO2/Cu2O/Cu(111) catalyst from carbon monoxide and carbon dioxide to methanol under a reaction environment with methane, oxygen, and water. Ambient-pressure x-ray photoelectron spectroscopy showed that water added to methane and oxygen led to surface methoxy groups and accelerated methanol production. These results were consistent with density functional theory calculations and kinetic Monte Carlo simulations, which showed that water preferentially dissociates over the active cerium ions at the CeO2–Cu2O/Cu(111) interface. The adsorbed hydroxyl species blocked O-O bond cleavage that would dehydrogenate methoxy groups to carbon monoxide and carbon dioxide, and it directly converted this species to methanol, while oxygen reoxidized the reduced surface. Water adsorption also displaced the produced methanol into the gas phase.
A novel gas sensor was fabricated using ZnO nanowalls vertically grown on rGO thin film as sensing materials for detection of NO2 operating at room temperature. The obtained ZnO/rGO hybrids exhibited ...enhanced performance to 50ppm NO2 (9.61), fast response and recovery behavior (25s, 15s).
Display omitted
•A gas sensor was fabricated using ZnO nanowalls decorated rGO nanosheets.•The ZnO/rGO hybrids exhibited enhanced performance to 50ppm NO2 (9.61), fast response and recovery behavior (25s,15s).•The mechanism of NO2 gas sensing was discussed.
A highly sensitive NO2 gas sensor based on ZnO nanowalls decorated rGO nanosheets was fabricated using a thermal reduction and soft solution process. The highly developed interconnected microporous networks of ZnO nanowalls were anchored homogeneously on the surface of reduced graphene oxide (rGO). Sensors fabricated with heterojunction structures achieved a higher response (S=9.61) and shorter response-recovery (25s, 15s) behavior at room temperature to 50ppm level NO2 effectively in contrast to those sensors based on net ZnO nanowalls or rGO layers. The stability and selectivity of ZnO/rGO heterojunction were carried out. Meanwhile, the effects of humidity on ZnO/rGO heterojunction gas sensor were investigated. The more preferable sensing performance of ZnO/rGO heterojunction to NO2 was discussed. It can be surmised that this NO2 gas sensor has potential for use as a portable room temperature gas sensor.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Mass customization (MC) is a crucial strategy for manufacturers to gain competitive advantages. Enterprise resource planning (ERP) systems are widely adopted in manufacturing. This study applied the ...dynamic capabilities view (DCV) to explore how firms leverage ERP systems to facilitate the implementation of MC. This study examined the effect of ERP assimilation (ERPA) and organizational agility (OA) on mass customization capability (MCC), the mediating role of OA, and the moderating role of absorptive capacity (AC). Data were collected using a self-administered questionnaire survey that yielded 166 responses in Jiangsu province, China. The partial least square structural equation modelling (PLS-SEM) approach was employed to test the study hypotheses. Results revealed that ERPA affects OA, and OA also affects MCC. However, no significant relationship was found between ERPA and MCC. Again, data supported the mediating effect of OA between ERPA and MCC and the moderating effect of AC between ERPA and OA.
Precise optical modeling of blue light-emitting diodes (LEDs) is constructed by reasonable optical parameters and Monte Carlo ray-tracing with the capability of precisely predicting light extraction ...and radiation pattern for both bare LED and packaged LED. Refractive indices and absorption coefficients of LED materials are determined by abundant references and comparisons between simulations and experiments. Surface roughness is considered in the optical model to improve the simulation precision. The simulation precisions are excellent for both bare blue LEDs (>96.5% for light extraction and >99% for radiation pattern) and packaged blue LEDs (>98.5% for both light extraction and radiation pattern).
The role of the interface between a metal and oxide (CeOx-Cu and ZnO-Cu) is critical to the production of methanol through the hydrogenation of CO2(CO2+ 3H2→ CH3OH + H2O). The deposition of ...nanoparticles of CeOx or ZnO on Cu(111), Θoxi< 0.3 monolayer, produces highly active catalysts for methanol synthesis. The catalytic activity of these systems increases in the sequence: Cu(111) < ZnO/Cu(111) < CeOx/Cu(111). The apparent activation energy for the CO2→ CH3OH conversion decreases from 25 kcal/mol on Cu(111) to 16 kcal/mol on ZnO/Cu(111) and 13 kcal/mol on CeOx/Cu(111). The surface chemistry of the highly active CeOx-Cu(111) interface was investigated using ambient pressure X-ray photoemission spectroscopy (AP-XPS) and infrared reflection absorption spectroscopy (AP-IRRAS). Both techniques point to the formation of formates (HCOO-) and carboxylates (CO2δ-) during the reaction. Our results show an active state of the catalyst rich in Ce3+ sites which stabilize a CO2δ- species that is an essential intermediate for the production of methanol. The inverse oxide/metal configuration favors strong metal-oxide interactions and makes possible reaction channels not seen in conventional metal/oxide catalysts.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
A combination of time-resolved X-ray diffraction (TR-XRD), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and diffuse reflectance infrared Fourier transform spectroscopy was used to ...carry out in situ characterization of Cu/CeO2 nanocatalysts during the hydrogenation of CO2. Morphological effects of the ceria supports on the catalytic performances were investigated by examining the behavior of copper/ceria nanorods (NR) and nanospheres. At atmospheric pressures, the hydrogenation of CO2 on the copper/ceria catalysts produced mainly CO through the reverse water–gas shift (RWGS) reaction and a negligible amount of methanol. The Cu/CeO2-NR catalyst displayed the higher activity, which demonstrates that the RWGS is a structure-sensitive reaction. In situ TR-XRD and AP-XPS characterization showed significant changes in the chemical state of the catalysts under reaction conditions, with the copper being fully reduced and a partial Ce4+ → Ce3+ transformation occurring. A more effective CO2 dissociative activation at high temperature and a preferential formation of active bidentate carbonate and formate intermediates over CeO2(110) terminations are probably the main reasons for the better performance of the Cu/CeO2-NR catalyst in the RWGS reaction.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
PDF
