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2.
Angew Chem Int Ed Engl ; 59(6): 2289-2293, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-31773819

RESUMO

Chemical synthesis of amino acids directly from biomass feedstock is rare. Reported here is a one-step protocol to convert crude glycerol, from the biodiesel industry, into 43 % alanine over a Ru1 Ni7 /MgO catalyst. The multifunctional catalytic system promotes glycerol conversion into lactic acid, and then into alanine. X-ray absorption spectroscopy and scanning transmission electron microscopy revealed the existence of bimetallic RuNi species, whereas density-functional theory calculations suggested Ni-doped Ru substantially decreased the Ea of C-H bond dissociation of lactate alkoxide to form pyruvate, which is the rate-determining step. The catalytic route established in this work creates new opportunities for glycerol utilization and enriches the substrate scope of renewable feedstock to access value-added amino acids.

3.
ACS Appl Mater Interfaces ; 11(41): 37875-37884, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31550116

RESUMO

Sr1.6K0.37Na1.43Ta5O15, which belongs to the Na-substituted Sr2KTa5O15 series of compounds with a tetragonal tungsten bronze structure, was fabricated using a flux mixture of KCl and NaCl (KCl/NaCl molar ratio = 55:45). It exhibited higher CO formation rate (94.6 µmol h-1), better selectivity for CO evolution (85.5%), and better stability of the photocatalytic activity than those of bare Sr2KTa5O15 and other Na-substituted Sr2KTa5O15 samples synthesized from flux mixtures with different KCl/NaCl ratios. X-ray photoelectron spectroscopic studies revealed that the surface atomic Sr/Ta ratio of Sr1.6K0.37Na1.43Ta5O15 was larger than that of Sr2KTa5O15. To clarify the factor responsible for the improvement in the photocatalytic activity facilitated by Na substitution, as well as to elucidate the reaction mechanism, the surface species were characterized by in situ Fourier transform infrared spectroscopy. It was observed that the bicarbonate species (HCO3-) adsorbed on the active Sr sites of Sr1.6K0.37Na1.43Ta5O15 was reduced to CO via the formate species during photoirradiation. The plot of the CO formation rate vs. the surface atomic Sr/Ta ratio for tetragonal tungsten bronze-type Sr-K-Ta-O complex oxides had the summit, indicating that Sr atoms on the surface enhance the photocatalytic activity, while an excessive amount of Sr on the surface leads to the decrease in the photocatalytic activity. Hence, it can be concluded that while the presence of Sr on the surface has a determining effect on the adsorption of CO2 and eventually on the photocatalytic activity, excess Sr on the surface that exists as SrCO3 or Sr2Ta2O7 suppresses the photocatalytic activity. Thus, Sr1.6K0.37Na1.43Ta5O15 showed higher CO formation rate than Sr2KTa5O15 did.

4.
ACS Appl Mater Interfaces ; 11(30): 26985-26993, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31262168

RESUMO

The development of NOx-trapping catalysts for automobiles is highly desired to meet the current strict exhaust emission regulations. This study demonstrates that NOx oxidation and storage reactions proceed over Pt-free Sr3Fe2O7-δ with a Ruddlesden-Popper-type layered perovskite structure. Two types of Sr-Fe perovskite with oxygen storage capacity, namely, SrFeO3-δ and Sr3Fe2O7-δ, are studied as NOx-trapping catalysts. Sr3Fe2O7-δ shows higher NOx storage capacity than SrFeO3-δ; its activity is comparable to that of Pt/Ba/Al2O3 calcined at 1273 K. NOx temperature-programmed desorption and diffuse reflectance infrared Fourier transform experiments confirm the superior NOx-trapping ability of Sr3Fe2O7-δ over SrFeO3-δ. In addition, NO temperature-programmed reactions and O2 temperature-programmed desorption experiments reveal that these catalysts operate through a novel NO oxidation mechanism involving the consumption of their lattice oxygens and topotactic structural changes at a temperature of around 350-400 K. The reduction performance of trapped NOx on Pd-modified Sr-Fe perovskites is investigated by lean-rich cycle experiments using H2 as the reductant. Pd/Sr3Fe2O7-δ shows significantly high NOx removal efficiency over the entirety of each lean-rich period. Modifying Sr3Fe2O7-δ with Pd is also effective for NOx storage in the presence of H2O and CO2 and the regeneration of the catalyst following SOx sorption. Sr3Fe2O7-δ, with both NOx adsorption and NO oxidation capabilities, acts as a Pt-free NOx-trapping catalyst, exhibiting both high NOx storage capacity and high thermal tolerance.

5.
Phys Chem Chem Phys ; 21(35): 18816-18822, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31187809

RESUMO

Ni-Cu alloy supported on γ-Al2O3 catalysts prepared by high-temperature hydrogen reduction exhibit high catalytic activity and durability for a three-way catalytic reaction under both oxidative and reductive conditions because of their self-regenerating feature. DFT calculations showed that Ni-oxide was reduced to Ni metal by CO in the presence of Cu metal because of the Ni-Cu alloy effect but was not in the absence of Cu metal.

6.
J Am Chem Soc ; 141(20): 8185-8197, 2019 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-31030515

RESUMO

Unlike nanostructured metal catalysts, supported single-atom catalysts (SACs) contain only atomically dispersed metal atoms, hinting at much more pronounced metal-support effects. Herein, we take a series of polyoxometalate-supported Pt catalysts as examples to quantitatively investigate the stability of Pt atoms on oxide supports and how the Pt-support interaction influences the catalytic performance. For this entire series, we show that the Pt atoms prefer to stay at a 4-fold hollow site of one polyoxometalate molecule and that the least adsorption energy to obtain sintering-resistant Pt SACs is 5.50 eV, which exactly matches the cohesive energy of bulk Pt metal. Further, we compared their catalytic performance in several hydrogenation reactions and simulated the reaction pathways of propene hydrogenation by density functional theory (DFT) calculations. Both experimental and theoretical approaches suggest that despite the Pt1-support interactions being different, the reaction pathways of various Pt1-polyoxometalate catalysts are very similar and their effective reaction barriers are close to each other and as low as 24 kJ/mol, indicating the possibility of obtaining SACs with improved stability without compromising activity. DFT calculations show that all reaction elementary steps take place only on the Pt atom without involving neighboring O atoms and that hydrogenation proceeds from the molecularly adsorbed H2 species. Pt SACs give a weaker H2 adsorption energy than Pt clusters or surfaces, resulting in small adsorption equilibrium constants and small apparent activation barriers, which agree between experiment and theory.

7.
Nat Commun ; 10(1): 1330, 2019 03 22.
Artigo em Inglês | MEDLINE | ID: mdl-30902990

RESUMO

Single-atom catalysts have recently been applied in many applications such as CO oxidation. Experimental in situ investigations into this reaction, however, are limited. Hereby, we present a suite of operando/in situ spectroscopic experiments for structurally well-defined atomically dispersed Rh on phosphotungstic acid during CO oxidation. The identification of several key intermediates and the steady-state catalyst structure indicate that the reactions follow an unconventional Mars-van Krevelen mechanism and that the activation of O2 is rate-limiting. In situ XPS confirms the contribution of the heteropoly acid support while in situ DRIFT spectroscopy consolidates the oxidation state and CO adsorption of Rh. As such, direct observation of three key components, i.e., metal center, support and substrate, is achieved, providing a clearer picture on CO oxidation on atomically dispersed Rh sites. The obtained information are used to engineer structurally similar catalysts that exhibit T20 values up to 130 °C below the previously reported Rh1/NPTA.

8.
Chem Rec ; 19(7): 1420-1431, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30663225

RESUMO

This paper describes a systematic study of the spectra and local structures of lanthanide (Ln) L-edge XANES. We found that Ln L1 and L3 -edge XANES spectra exhibit characteristic features correlated to their local symmetry through experimental and theoretical simulations. We also propose a simple local structure index criterion for a combination of XANES study and theoretical simulation. Possible solutions of intrinsic problems such as low resolution of characteristic features in the Ln L-edge XANES and site distributions are also discussed.

9.
Chempluschem ; 84(5): 442, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31943895

RESUMO

Invited for this month's cover is the group of Dr. Katsutoshi Sato and Prof. Dr. Katsutoshi Nagaoka (Kyoto University) and collaborators at Oita and Kyushu Universities. The cover picture shows the proposed mechanism for automotive exhaust purification over a Pt-Co alloy nanoparticle catalyst with an extremely low Pt/Co molar ratio. In the catalyst, the isolated electron-rich Pt atoms are present on the surface of the nanoparticles and play an important role in NOx capture and activation, which are important elementary steps in exhaust purification. Read the full text of the article at 10.1002/cplu.201800542.

10.
Chempluschem ; 84(5): 447-456, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31943901

RESUMO

There is interest in minimizing or eliminating the use of Pt in catalysts by replacing it with more widely abundant and cost-effective elements. The alloying of Pt with non-noble metals is a potential strategy for reducing Pt use because interactions between Pt and non-noble metals can modify the catalyst structure and electronic properties. Here, a γ-Al2 O3 -supported bimetallic catalyst [Pt(0.1)Co(1)/Al2 O3 ] was prepared which contained 0.1 wt % Pt and 1 wt % Co and thus featured an extremely low Pt : Co ratio (<1 : 30 mol/mol). The Pt and Co in this catalyst formed alloy nanoparticles in which isolated electron-rich Pt atoms were present on the nanoparticle surface. The activity of this Pt(0.1)Co(1)/Al2 O3 catalyst for the purification of automotive exhaust was comparable to the activities of 0.3 and 0.5 wt % Pt/γ-Al2 O3 catalysts. Electron-rich Pt and metallic Co promoted activation of NOx and oxidization of CO and hydrocarbons, respectively. This strategy of tuning the surrounding structure and electronic state of a noble metal by alloying it with an excess of a non-noble metal will enable reduced noble metal use in catalysts for exhaust purification and other environmentally important reactions.

11.
Shokuhin Eiseigaku Zasshi ; 59(4): 174-182, 2018.
Artigo em Japonês | MEDLINE | ID: mdl-30158396

RESUMO

Colchicum autumnale is a perennial, toxic plant that originated in Europe and North Africa. Although inedible, it is occasionally consumed accidentally because it resembles the edible Allium victorialis and other related species. This misidentification has led to episodes of food poisoning in Japan. However, determining the causative agent of a food poisoning outbreak by observing the sample visually or analyzing the chemical composition is challenging when dealing with small samples. Therefore, we developed a novel set of PCR primers that anneal to the internal transcribed spacer (ITS) region of C. autumnale ribosomal DNA, designed to detect the presence of C. autumnale in small samples. These primers successfully detected C. autumnale in all samples in which it was present, and did not give a positive PCR band in the 48 other distinct crop species tested, in which it was not present. Further, our method could amplify DNA from samples of C. autumnale that had been heat-treated and digested using artificial gastric fluids. Thus, this PCR strategy is highly specific and can be used to distinguish C. autumnale simply and rapidly from various other crops.


Assuntos
Colchicum/classificação , DNA de Plantas/isolamento & purificação , Doenças Transmitidas por Alimentos/diagnóstico , Primers do DNA , DNA Espaçador Ribossômico/genética , Humanos , Japão , Reação em Cadeia da Polimerase
12.
ACS Appl Mater Interfaces ; 10(26): 22182-22189, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29893121

RESUMO

Environmental catalysts are required to operate highly efficiently under severe conditions in which they are exposed to reductive and oxidative atmospheres at high temperatures. This study demonstrates that SrFe1- xTi xO3-δ-supported Pd catalysts exhibit high catalytic activities for NO reduction with C3H6 and CO in the presence of O2, which is a model reaction for the purification of automotive exhaust gases. Catalytic activity is enhanced with increasing Ti content, and the highest activity is observed for Pd/SrFe0.2Ti0.8O3-δ among the examined catalysts. The state of the loaded Pd species can be controlled by the Fe/(Fe + Ti) ratio in SrFe1- xTi xO3-δ, and highly active PdO nanoparticles are properly anchored on SrFe0.2Ti0.8O3-δ. The Ti-rich Pd/SrFe0.2Ti0.8O3-δ shows significantly higher catalytic activity and is more thermally stable than the conventional Pd/Al2O3, which has a high surface area. Since Fe-rich SrFe1- xTi xO3-δ has the high oxygen storage capacity, its response capabilities to atmospheric fluctuations were evaluated by changing the oxygen concentration during NO reduction. As a result, Fe-rich Pd/SrFe0.8Ti0.2O3-δ retains its high NO-reduction activity for longer times even under oxidative conditions, when compared to SrFeO3-δ or Ti-rich Pd/SrFe1- xTi xO3-δ. The oxygen storage properties of Pd/SrFe0.8Ti0.2O3-δ allow it to effectively act as an oxygen buffer for NO reduction. These properties ensure that the SrFe1- xTi xO3-δ support, with both high thermal stability and oxygen storage capacity, is a very useful environmental-catalyst material.

13.
Proc Natl Acad Sci U S A ; 115(20): 5093-5098, 2018 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-29712826

RESUMO

Amino acids are the building blocks for protein biosynthesis and find use in myriad industrial applications including in food for humans, in animal feed, and as precursors for bio-based plastics, among others. However, the development of efficient chemical methods to convert abundant and renewable feedstocks into amino acids has been largely unsuccessful to date. To that end, here we report a heterogeneous catalyst that directly transforms lignocellulosic biomass-derived α-hydroxyl acids into α-amino acids, including alanine, leucine, valine, aspartic acid, and phenylalanine in high yields. The reaction follows a dehydrogenation-reductive amination pathway, with dehydrogenation as the rate-determining step. Ruthenium nanoparticles supported on carbon nanotubes (Ru/CNT) exhibit exceptional efficiency compared with catalysts based on other metals, due to the unique, reversible enhancement effect of NH3 on Ru in dehydrogenation. Based on the catalytic system, a two-step chemical process was designed to convert glucose into alanine in 43% yield, comparable with the well-established microbial cultivation process, and therefore, the present strategy enables a route for the production of amino acids from renewable feedstocks. Moreover, a conceptual process design employing membrane distillation to facilitate product purification is proposed and validated. Overall, this study offers a rapid and potentially more efficient chemical method to produce amino acids from woody biomass components.


Assuntos
Aminoácidos/metabolismo , Biomassa , Nanopartículas/química , Nanotubos de Carbono/química , Aminoácidos/química , Catálise , Hidrogenação , Níquel/química , Rutênio/química
14.
Chem Commun (Camb) ; 54(9): 1053-1056, 2018 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-29231929

RESUMO

A core-shell structure of Ag-Cr dual cocatalyst loaded-Ga2O3 was found to significantly enhance the formation rate of CO and selectivity toward CO evolution for the photocatalytic conversion of CO2 where H2O is used as an electron donor.

15.
J Am Chem Soc ; 140(1): 176-184, 2018 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-29224338

RESUMO

The dynamic behavior of Rh species in 1 wt% Rh/Al2O3 catalyst during the three-way catalytic reaction was examined using a micro gas chromatograph, a NOx meter, a quadrupole mass spectrometer, and time-resolved quick X-ray absorption spectroscopy (XAS) measurements at a public beamline for XAS, BL01B1 at SPring-8, operando. The combined data suggest different surface rearrangement behavior, random reduction processes, and autocatalytic oxidation processes of Rh species when the gas is switched from a reductive to an oxidative atmosphere and vice versa. This study demonstrates an implementation of a powerful operando XAS system for heterogeneous catalytic reactions and its importance for understanding the dynamic behavior of active metal species of catalysts.

16.
Langmuir ; 33(49): 13929-13935, 2017 12 12.
Artigo em Inglês | MEDLINE | ID: mdl-29144762

RESUMO

Modification of the surface of Ga2O3 with rare-earth elements enhanced the evolution of CO as a reduction product in the photocatalytic conversion of CO2 using H2O as an electron donor under UV irradiation in aqueous NaHCO3 as a pH buffer, with the rare-earth species functioning as a CO2 capture and storage material. Isotope experiments using 13CO2 as a substrate clearly revealed that CO was generated from the introduced gaseous CO2. In the presence of the NaHCO3 additive, the rare-earth (RE) species on the Ga2O3 surface are transformed into carbonate hydrates (RE2(CO3)3·nH2O) and/or hydroxycarbonates (RE2(OH)2(3-x)(CO3)x) which are decomposed upon photoirradiation. Consequently, Ag-loaded Yb-modified Ga2O3 exhibits much higher activity (209 µmol h-1 of CO) than the pristine Ag-loaded Ga2O3. The further modification of the surface of the Yb-modified Ga2O3 with Zn afforded a selectivity toward CO evolution of 80%. Thus, we successfully achieved an efficient Ag-loaded Yb- and Zn-modified Ga2O3 photocatalyst with high activity and controllable selectivity, suitable for use in artificial photosynthesis.

17.
Chem Sci ; 8(8): 5797-5801, 2017 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-28989619

RESUMO

Ammonium bicarbonate (NH4HCO3) was generated by the absorption of carbon dioxide (CO2) into an aqueous solution of ammonia (NH3). NH4HCO3 was successfully used to achieve highly efficient photocatalytic conversion of CO2 to carbon monoxide (CO). NH3 and/or ammonium ions (NH4+) derived from NH4HCO3 in aqueous solution were decomposed into nitrogen (N2) and hydrogen (H2). Stoichiometric amounts of the N2 oxidation product and the CO and H2 reduction products were generated when the photocatalytic reaction was carried out in aqueous NH4HCO3 solution. NH3 and/or NH4+ functioned as electron donors in the photocatalytic conversion of CO2 to CO. A CO formation rate of 0.5 mmol h-1 was obtained using 500 mg of catalyst (approximately 7500 ppm) in ambient conditions (303 K, 101.3 kPa). Our results demonstrated that NH4HCO3 is a novel inorganic sacrificial reagent, which can be used to increase the efficiency of photocatalytic CO production to achieve one step CO2 capture, storage and conversion.

18.
Nat Commun ; 8: 16100, 2017 07 27.
Artigo em Inglês | MEDLINE | ID: mdl-28748956

RESUMO

Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsaturated pentahedral Al3+ centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period.

19.
Phys Chem Chem Phys ; 19(21): 14107-14113, 2017 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-28524189

RESUMO

This study proves that a small amount of Pd loading (1 wt%) on Sr3Fe2O7-δ can dramatically enhance the oxygen-storage properties of Sr3Fe2O7-δ. The topotactic oxygen intake and release between Sr3Fe2O6.75 and Sr3Fe2O6 takes place in response to gas switching between an O2 flow and H2 flow, regardless of the presence or absence of Pd loading. The effect of Pd loading is significant for the oxygen-release process under H2 atmosphere; that is, highly dispersed Pd metal nanoparticles sized less than 1 nm formed on Pd/Sr3Fe2O7-δ to promote H2 dissociation, resulting in the improvement of the oxygen-release temperature and rate. Pd/Sr3Fe2O7-δ with a layered perovskite structure has a higher oxygen-release property at lower temperature than Pd/SrFeO3-δ with a perovskite phase without the layered structure. These facts indicate that the surface reaction as well as the crystal structure are responsible for the oxide ion mobility in perovskite structure, and also provide guidelines for designing novel oxygen-storage materials.

20.
Sci Total Environ ; 584-585: 88-95, 2017 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-28135617

RESUMO

To reveal the in planta behaviour of caesium (Cs), the stable isotope 133Cs was administered into 3-year-old Cryptomeria japonica seedlings by the application of 133CsCl aqueous solution to the bark surface. The administered 133Cs was quantified by ICP-MS measurements, which showed transportation of 133Cs in an ascending direction in the stem. Distribution of 133Cs was visualized using freeze-fixed C. japonica woody stem samples and cryo-time-of-flight secondary ion mass spectrometry/scanning electron microscopy (cryo-TOF-SIMS/SEM) analysis. Cryo-TOF-SIMS/SEM visualization suggested that 133Cs was rapidly transported radially by ray parenchyma cells followed by axial transportation by pith and axial parenchyma cells. Adsorption experiments using powdered C. japonica wood samples and X-ray absorption fine structure (XAFS) analysis suggested that 133Cs was in the hydrated state following its deposition into tracheid cell walls.


Assuntos
Isótopos de Césio/metabolismo , Cryptomeria/metabolismo , Caules de Planta/metabolismo , Madeira/metabolismo , Plântula , Espectrometria de Massa de Íon Secundário
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