Behavior of Pt Atoms on Oxide Supports During Reduction Treatments at Elevated Temperatures,Characterized by Aberration Corrected Stem Imaging

Abstract  

Aberration-corrected scanning transmission electron microscopy at the sub-?ngstr?m resolution allows imaging the structure of catalytic materials at the single atom level and permits fundamental studies of the behavior of heavy metal catalytic species as a result of elevated temperature gas-treatments. The present study is aimed at understanding the development of clusters and nanoparticles of Pt on γ-alumina during reduction treatments of a pre-oxidized highly dispersed catalyst. A special built ex situ reactor and a specimen holder allowing cyclic anaerobic transfer between the reactor and microscope were used for the study. The number of atoms in a nascent cluster can be determined along with the general shape of the cluster. Reduction experiments without air exposure of the sample showed that although clusters are formed at 500 °C, many Pt atoms are not associated with the cluster and are still dispersed on the catalyst support. After a 700 °C reduction, all of the Pt atoms are associated with the clusters. Movement of the clusters on the catalyst support is different depending upon the catalyst support.     

The influence of tillage and cropping-intensity on cereal response to nitrogen,sulfur, and phosphorus

Efficient fertilizer use is a prerequisite for achieving optimum crop yield while avoiding environmental contamination. Cereal response to nitrogen (N), sulfur (S), and phosphorus (P) were determined for 6 years under differing tillage [conventional-till (CT) vs. no-till (NT)] and intensity of cropping (cereal/fallow vs. cereal/cereal). Semidwarf white winter wheat (Triticum aestivum L.) alternated yearly with either fallow or spring cereal [barley (Hordeum vulgare L.) or spring wheat] on a Typic Haploxeroll soil in a 415 mm rainfall zone. Fertilizer treatments were no fertilizer (None), N only (N), N plus S (NS), and N plus S plus P (NSP). Average application rate, when applied, was 109 kg N, 18 kg S, and 11 kg P ha^–1. Average cereal yield without fertilizer was 1.82 t ha^–1. Nitrogen increased grain yield in 6 of 6, S in 4 of 6, and P in 3 of 6 years, with P and S response significant the remaining years at the 10% probability level. Average yield increases were 1.11 t ha^–1 for N, 0.93 t ha^–1 for S, and 0.47 t ha^–1 for P. The NT/CT yield ratio was 0.60, 0.75, 0.93, and 0.95 with None, N, NS, and NSP addition, respectively, indicating that N and S deficiency were more severe in no-till. Limited increase in the NT/CT ratio with P addition indicated that P deficiency was less affected by tillage. Winter wheat always yielded less under NT than CT regardless of fertility, whereas spring cereals reached equality when fertilized with NSP. Annually-cropped wheat yielded 52, 67, 89, and 90% of wheat after fallow with None, N, NS, and NSP, respectively. Thus N and S, but not P, deficiency was more intense with increased frequency of cropping. Adequate fertility was a prime prerequisite for efficient yield in all systems.     

Synthesis of Submicrometer Mullite Powder via High-Temperature Aerosol Decomposition

High-purity mullite powders (3Al₂O₃.2SiO₂) have been prepared using a high-temperature aerosol decomposition technique yielding submicrometer (0.6 μm average) particles of spherical morphology with no hard agglomerates using aluminum nitrate and fumed silica as precursors. Depending upon the reaction conditions used, the powders range from amorphous to crystalline with no evidence of secondary-phase formation. This mullite synthesis approach has the advantages of not requiring postsynthesis milling, the ability to use a wide range of precursor systems, and enhanced control over chemical homogeneity and particle size/shape.     

Reactive Laser Ablation Synthesis of Nanosize Alumina Powder

An aluminum (Al) target was laser ablated in an oxygen (O₂) atmosphere, producing nanosize alumina (Al₂O₃) powder. The powder surface area decreased (and the particle size increased) with both increasing oxygen pressure and laser fluence. All powders produced had surface areas between 135 and 250 m²/g, corresponding to primary particle sizes ranging from 7 to 3 nm in radius. Phase evolution with temperature was studied via X-ray diffraction. These powders showed a direct transformation from γ- to α-alumina at approximately 1200°C, bypassing other transition alumina phases, while still maintaining small particle size ( 30 nm). Despite the nanosize particles, green densities equal to 54% of the skeletal density (i.e., true density of the solid phase) were obtained by uniaxial pressing at 40 MPa.     

Reactive Laser Ablation Synthesis of Nanosize Aluminum Nitride

An aluminum (Al) target was laser ablated in a nitrogen (N₂) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm² and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase-pure AlN by X-ray diffraction (XRD). The surface area of this powder is 82 m²/g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observations.     

Interleukin-2 mutants with enhanced {alpha}-receptor subunit binding affinity

Stimulation of T-cells by IL-2 has been exploited for treatmentof metastatic renal carcinoma and melanoma. However, a narrowtherapeutic window delimited by negligible stimulation of T-cellsat low picomolar concentrations and undesirable stimulationof NK cells at nanomolar concentrations hampers IL-2-based therapies.We hypothesized that increasing the affinity of IL-2 for IL-2R     

Decoding the Chemical Language of Motile Bacteria by Using High‐Throughput Microfluidic Assays

Motile bacteria navigate chemical environments by using chemoreceptors. The output of these protein sensors is linked to motility machinery and enables bacteria to follow chemical gradients. Understanding the chemical specificity of different families of chemoreceptors is essential for predicting and controlling bacterial behavior in ecological niches, including symbiotic and pathogenic interactions with plants and mammals. The identification of chemical(s) recognized by specific families of receptors is limited by the low throughput and complexity of chemotaxis assays. To address this challenge, we developed a microfluidic‐based chemotaxis assay that is quantitative, simple, and enables high‐throughput measurements of bacterial response to different chemicals. Using the model bacterium Escherichia coli, we demonstrated a strategy for identifying molecules that activate chemoreceptors from a diverse compound library and for determining how global behavioral strategies are tuned to chemical environments.     

Head‐to‐Head Prenyl Synthases in Pathogenic Bacteria

Many organisms contain head‐to‐head isoprenoid synthases; we investigated three such types of enzymes from the pathogens Neisseria meningitidis, Neisseria gonorrhoeae, and Enterococcus hirae. The E. hirae enzyme was found to produce dehydrosqualene, and we solved an inhibitor‐bound structure that revealed a fold similar to that of CrtM from Staphylococcus aureus. In contrast, the homologous proteins from Neisseria spp. carried out only the first half of the reaction, yielding presqualene diphosphate (PSPP). Based on product analyses, bioinformatics, and mutagenesis, we concluded that the Neisseria proteins were HpnDs (PSPP synthases). The differences in chemical reactivity to CrtM were due, at least in part, to the presence of a PSPP‐stabilizing arginine in the HpnDs, decreasing the rate of dehydrosqualene biosynthesis. These results show that not only S. aureus but also other bacterial pathogens contain head‐to‐head prenyl synthases, although their biological functions remain to be elucidated.     

A framework for ammonia supply chain optimization incorporating conventional and renewable generation

Ammonia is an essential nutrient for global food production brought to farmers by a well‐established supply chain. This article introduces a supply chain optimization framework which incorporates new renewable ammonia plants into the conventional ammonia supply chain. Both economic and environmental objectives are considered. The framework is then applied to two separate case studies analyzing the supply chains of Minnesota and Iowa, respectively. The base case results present an expected trade‐off between cost, which favors purchasing ammonia from conventional plants, and emissions, which favor building distributed renewable ammonia plants. Further analysis of this trade‐off shows that a carbon tax above $25/t will reduce emissions in the optimal supply chain through building large renewable plants. The importance of scale is emphasized through a Monte Carlo sensitivity analysis, as the largest scale renewable plants are selected most often in the optimal supply chain. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4390–4402, 2017     

DETECTION OF KNOWN PHOTOCHEMICAL DECOMPOSITION PRODUCTS OF PAH IN PARTICULATE MATTER FROM POLLUTION EPISODES IN SEOUL,KOREA

Over the past two decades, significant efforts have been expended to identify the photochemical decomposition products of the OH radical reactions of various polycyclic aromatic compounds (PAC), such as naphthalene, methylnaphthalenes, acenaphthene and phenanthrene (1 Lane, D. A. and Tang, H. 1994. Photochemical degradation of polycyclic aromatic compounds. I. Naphthalene.. Polycycl. Aromat. Comp, 5(1): 131–138. [Taylor & Francis Online] , [Google Scholar], 2 Bunce, N. J., Liu, L., Zhu, J. and Lane, D.A. 1997. Reaction of naphthalene and its derivatives with hydroxyl radicals in the gas phase.. Environ. Sci. Technol, 31(8): 2252–2259.  [Google Scholar], 3 Sasaki, J., Aschmann, S.M., Kwok, E.S.C., Atkinson, R. and Arey, J. 1997. Products of the gas-phase OH and NO3 radical-initiated reactions of naphthalene.. Environ. Sci. Technol, 31(11): 3173–3179.  [Google Scholar], 4 Sauret-Szczepanski, N. and Lane, D.A. 2004. Smog chamber study of acenaphthene: Gas/particle partition measurements of the products formed by reaction with the OH radical.. Polycycl. Aromat. Comp, 24(3): 161–172. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar], 5 Banceu, C. E., Mihele, C.M., Lane, D.A. and Bunce, N.J. 2001. Reactions of methylated naphthalenes with hydroxyl radicals under simulated atmospheric conditions.. Polycycl. Aromat. Comp, 18(4): 415–426. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar], 6 Wang, L., Atkinson, R. and Arey, J. 2007. Dicarbonyl products of the OH radical-initiated reactions of naphthalene and the C1- and C2-alkylnaphthalenes.. Environ. Sci. Technol, 41(8): 2803–2810.  [Google Scholar], 7 Lee, J. Y. and Lane, D.A. 2009. Unique products from the reaction of naphthalene with the hydroxyl radical. Atmos. Environ., 43: 4886–4893. [Crossref] , [Google Scholar]). Although these parent PAC are predominantly found in the gas phase, many of their oxidation products have been found largely in the particle phase (4 Sauret-Szczepanski, N. and Lane, D.A. 2004. Smog chamber study of acenaphthene: Gas/particle partition measurements of the products formed by reaction with the OH radical.. Polycycl. Aromat. Comp, 24(3): 161–172. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar], 7 Lee, J. Y. and Lane, D.A. 2009. Unique products from the reaction of naphthalene with the hydroxyl radical. Atmos. Environ., 43: 4886–4893. [Crossref] , [Google Scholar], 8 Mihele, C. M., Wiebe, H.A. and Lane, D.A. 2002. Particle formation and gas/particle partition measurements of the products of the naphthalene-OH radical reaction in a smog chamber. Polycycl. Aromat. Comp., 22: 729–736. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). These products include diones, hydroxy-, and nitrated products as well as many products resulting from ring-opening steps. It is, or should be, the goal of every laboratory study on atmospheric processes to apply the laboratory results to real world samples. To this end, we have obtained particulate matter air samples, as well as some smog episode samples, from Seoul Korea and have searched for the known decomposition products of the above mentioned PAC. To eliminate the use of chlorinated solvents used in the extraction and analysis of particulate matter samples, we have been utilizing the direct thermal desorption of small (4 mm diameter) punches of filters followed by Multidimensional Gas Chromatography-Time of Flight Mass Spectrometry (TD-GCxGC-TOFMS) for the analysis of the desorbed compounds. So far, we have detected 14 of the known decomposition products of naphthalene, acenaphthene and phenanthrene in the Seoul pollution episode samples. These include: 1-hydroxynaphthalene, (E) 2-formylcinnamaldehyde, phthalic anhydride, phthalide, 1,2-naphthalic anhydride, 9-hydroxyphenanthrene and dibenzopyrone.