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.
An ultrathin MgO coating was synthesized via atomic layer deposition (ALD) to improve the surface properties of the LiNi0.5Mn0.3Co0.2O2 (NMC) cathode. An in-situ quartz crystal sensor was used to ...monitor the “self-limiting” surface reactions during ALD process and estimate the density of the deposited film. The electrochemical performance of the MgO-coated NMC cathode was evaluated in a half-cell assembly and compared to other ALD-based coatings, such as Al2O3 and ZrO2. Cyclic voltammetry studies suggested that ALD MgO has a higher Li-diffusion coefficient which resulted in lower overpotential on the NMC cathode surface and improved Li-ion battery rate performance. MgO-coated NMC also yielded improved capacity retention over uncoated NMC in a long-range cycling test.
Well-defined Cu catalysts containing different amounts of zirconia were synthesized by controlled surface reactions (CSRs) and atomic layer deposition methods and studied for the selective conversion ...of ethanol to ethyl acetate and for methanol synthesis. Selective deposition of ZrO2 on undercoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced by UV–vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The concentrations of Cu and Cu-ZrO2 interfacial sites were quantified using a combination of subambient CO Fourier transform infrared spectroscopy and reactive N2O chemisorption measurements. The oxidation states of the Cu and ZrO2 species for these catalysts were determined using X-ray absorption near edge structure measurements, showing that these species were present primarily as Cu0 and Zr4+, respectively. It was found that the formation of Cu-ZrO2 interfacial sites increased the turnover frequency by an order of magnitude in both the conversion of ethanol to ethyl acetate and the synthesis of methanol from CO2 and H2.
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
An ultrathin MgO coating was synthesized via atomic layer deposition (ALD) to improve the surface properties of the LiNi
Mn
Co
O
(NMC) cathode. An in-situ quartz crystal sensor was used to monitor ...the "self-limiting" surface reactions during ALD process and estimate the density of the deposited film. The electrochemical performance of the MgO-coated NMC cathode was evaluated in a half-cell assembly and compared to other ALD-based coatings, such as Al
O
and ZrO
. Cyclic voltammetry studies suggested that ALD MgO has a higher Li-diffusion coefficient which resulted in lower overpotential on the NMC cathode surface and improved Li-ion battery rate performance. MgO-coated NMC also yielded improved capacity retention over uncoated NMC in a long-range cycling test.
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.
PDF
