Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid‐phase catalytic reactions (e.g., hydrogenation of biomass‐derived furfural in ...alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid‐phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X‐ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ‐Al2O3. Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under‐coordinated copper atoms on the nanoparticle surface.
Catalytic Armoring: Atomic layer deposition (ALD) of alumina overcoats has been employed to stabilize base metal catalysts against sintering and leaching in liquid‐phase conditions. Kinetic studies, characterization of the materials, and theoretical studies were used to elucidate the mechanism by which this stabilization of base metal nanoparticles is achieved.
Atomic layer deposition (ALD) has emerged as an interesting tool for the atomically precise design and synthesis of catalytic materials. Herein, we discuss examples in which the atomic precision has ...been used to elucidate reaction mechanisms and catalyst structure–property relationships by creating materials with a controlled distribution of size, composition, and active site. We highlight ways ALD has been utilized to design catalysts with improved activity, selectivity, and stability under a variety of conditions (e.g., high temperature, gas and liquid phase, and corrosive environments). In addition, due to the flexibility and control of structure and composition, ALD can create myriad catalytic structures (e.g., high surface area oxides, metal nanoparticles, bimetallic nanoparticles, bifunctional catalysts, controlled microenvironments, etc.) that consequently possess applicability for a wide range of chemical reactions (e.g., CO2 conversion, electrocatalysis, photocatalytic and thermal water splitting, methane conversion, ethane and propane dehydrogenation, and biomass conversion). Finally, the outlook for ALD-derived catalytic materials is discussed, with emphasis on the pending challenges as well as areas of significant potential for building scientific insight and achieving practical impacts.
To efficiently catalyze a chemical reaction, enzymes are required to maintain fast rates for formation of the Michaelis complex, the chemical reaction and product release. These distinct demands ...could be satisfied via fluctuation between different conformational substates (CSs) with unique configurations and catalytic properties. However, there is debate as to how these rapid conformational changes, or dynamics, exactly affect catalysis. As a model system, we have studied bacterial phosphotriesterase (PTE), which catalyzes the hydrolysis of the pesticide paraoxon at rates limited by a physical barrier--either substrate diffusion or conformational change. The mechanism of paraoxon hydrolysis is understood in detail and is based on a single, dominant, enzyme conformation. However, the other aspects of substrate turnover (substrate binding and product release), although possibly rate-limiting, have received relatively little attention. This work identifies "open" and "closed" CSs in PTE and dominant structural transition in the enzyme that links them. The closed state is optimally preorganized for paraoxon hydrolysis, but seems to block access to/from the active site. In contrast, the open CS enables access to the active site but is poorly organized for hydrolysis. Analysis of the structural and kinetic effects of mutations distant from the active site suggests that remote mutations affect the turnover rate by altering the conformational landscape.
The genome of soybean (Glycine max), a commercially important crop, has recently been sequenced and is one of six crop species to have been sequenced. Here we report the genome sequence of G. soja, ...the undomesticated ancestor of G. max (in particular, G. soja var. IT182932). The 48.8-Gb Illumina Genome Analyzer (Illumina-GA) short DNA reads were aligned to the G. max reference genome and a consensus was determined for G. soja. This consensus sequence spanned 915.4 Mb, representing a coverage of 97.65% of the G. max published genome sequence and an average mapping depth of 43-fold. The nucleotide sequence of the G. soja genome, which contains 2.5 Mb of substituted bases and 406 kb of small insertions/deletions relative to G. max, is ∼0.31% different from that of G. max. In addition to the mapped 915.4-Mb consensus sequence, 32.4 Mb of large deletions and 8.3 Mb of novel sequence contigs in the G. soja genome were also detected. Nucleotide variants of G. soja versus G. max confirmed by Roche Genome Sequencer FLX sequencing showed a 99.99% concordance in single-nucleotide polymorphism and a 98.82% agreement in insertion/deletion calls on Illumina-GA reads. Data presented in this study suggest that the G. soja/G. max complex may be at least 0.27 million y old, appearing before the relatively recent event of domestication (6,000∼9,000 y ago). This suggests that soybean domestication is complicated and that more in-depth study of population genetics is needed. In any case, genome comparison of domesticated and undomesticated forms of soybean can facilitate its improvement.
Heterogeneous electrochemistry induced by Martian dust activity is an important type of atmosphere‐surface interaction that affects geochemical processes at the Martian surface and in the Martian ...atmosphere. We have experimentally demonstrated that heterogeneous electrochemistry stimulated by mid‐strength dust events can decompose common chloride salts, which is accompanied by the release of chlorine atoms into the atmosphere and the generation of (per)chlorates (chlorates and perchlorates) and carbonates. In this study, we present quantitative analyses on the above products from 26 heterogeneous electrochemical experiments on chloride salts. Based on these quantifications, our calculation indicates that such atmosphere‐surface interaction during a portion of Amazonian period could accumulate the observed abundance of (per)chlorates, carbonates, and HCl by landed and orbital missions, and thus can be considered as a major driving force of the global chlorine‐cycle on Mars. This study emphasizes the importance of measuring the electrical properties of dust activity on Mars.
Plain Language Summary
Frictional electrification is a common process in our solar system, with Martian dust activities known to be a powerful source of electrical charge buildup. Furthermore, the thin atmosphere on Mars makes the breakdown of accumulated electrical fields, in form of electrostatic discharge (ESD), much easier to occur (a hundred times easier than on Earth). ESD generates a huge amount of energetic electrons that collide with Martian atmospheric molecules and generate free radicals. These free radicals react with the Martian chlorides to generate new species. This study found the yields of (per)chlorates, carbonates, and chlorine from the ESD process, with the strength matching mid‐strength Martian dust activity, are at per thousand or percent levels (normalized to the starting chlorides). Based on these results, it is possible to calculate the total yields of those species produced from known chloride sources on Mars by global dust storms during defined durations in the Amazonian period. It was found that the contributions of Mars dust activity can account for the abundances of (per)chlorates, carbonates, and chlorine observed by past and current Mars missions. This study supports that Martian atmosphere‐surface interaction in dust events is a major driving force for the global chlorine‐cycle on Mars.
Key Points
Heterogeneous electrochemistry induced by Mars dust activity can decompose chloride, form (per)chlorate, carbonate, and release chlorine
This experimental study simulated mid‐strength Mars dust events and revealed the high yields of (per)chlorates, carbonates, and chlorine
A calculation based on the results supports Martian dust activity as the major driving force for the global Cl‐cycle in Amazonian period
Molybdenum disulfide (MoS2), which is composed of active edge sites and a catalytically inert basal plane, is a promising catalyst to replace the state‐of‐the‐art Pt for electrochemically catalyzing ...hydrogen evolution reaction (HER). Because the basal plane consists of the majority of the MoS2 bulk materials, activation of basal plane sites is an important challenge to further enhance HER performance. Here, an in situ electrochemical activation process of the MoS2 basal planes by using the atomic layer deposition (ALD) technique to improve the HER performance of commercial bulk MoS2 is first demonstrated. The ALD technique is used to form islands of titanium dioxide (TiO2) on the surface of the MoS2 basal plane. The coated TiO2 on the MoS2 surface (ALD(TiO2)‐MoS2) is then leached out using an in situ electrochemical activation method, producing highly localized surface distortions on the MoS2 basal plane. The MoS2 catalysts with activated basal plane surfaces (ALD(Act.)‐MoS2) have dramatically enhanced HER kinetics, resulting from more favorable hydrogen‐binding.
The catalytically inert basal plane of MoS2 is activated for the hydrogen evolution reaction (HER) by combining the atomic layer deposition (ALD) technique and an in situ electrochemical activation process. The basal plane activated MoS2 (ALD(Act.)‐MoS2) catalysts significantly improve the HER performance, resulting from more favorable hydrogen‐binding.
Satellite-based passive microwave remote sensing typically involves a scanning antenna that makes measurements at irregularly spaced locations. These locations can change on a day to day basis. Soil ...moisture products derived from satellite-based passive microwave remote sensing are usually resampled to a fixed Earth grid that facilitates their use in applications. In many cases the grid size is finer than the actual spatial resolution of the observation, and often this difference is not well understood by the user. Here, this issue was examined for the Soil Moisture Active Passive (SMAP) enhanced version of the passive-based soil moisture product, which has a grid size of 9-km and a nominal spatial resolution of 33-km. In situ observations from core validation sites were used to compute comparison metrics. For sites that satisfied the established reliability and scaling criteria, the impact of validating the 9-km grid product with in situ data collected over a 9-km versus a 33-km domain was very small for the sites studied (0.039 m3/m3 unbiased root mean square difference for the 9-km case versus 0.037 m3/m3 for the 33-km case). This result does not mean that the resolution of the product is 9-km but that for the conditions studied here the soil moisture estimated from in situ observations over 9-km is a close approximation of the soil moisture estimated from in situ observations over the 33-km resolution. The implication is that using the enhanced SMAP product at its grid resolution of 9-km should not introduce large errors in most applications.
•Comparison of SMAP soil moisture validation at 9-km and 33-km spatial scales.•In situ soil moisture at 9-km scale correlates well with soil moisture at 33-km.•Validation metrics similar at 9-km and 33-km scales for the SMAP product.•The SMAP product can be used at 9-km scale with most applications.
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