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  • 1
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    Coking- and sintering-resistant palladium catalysts achieved through atomic layer deposition (2012)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2012-03-10
    Description: We showed that alumina (Al(2)O(3)) overcoating of supported metal nanoparticles (NPs) effectively reduced deactivation by coking and sintering in high-temperature applications of heterogeneous catalysts. We overcoated palladium NPs with 45 layers of alumina through an atomic layer deposition (ALD) process that alternated exposures of the catalysts to trimethylaluminum and water at 200 degrees C. When these catalysts were used for 1 hour in oxidative dehydrogenation of ethane to ethylene at 650 degrees C, they were found by thermogravimetric analysis to contain less than 6% of the coke formed on the uncoated catalysts. Scanning transmission electron microscopy showed no visible morphology changes after reaction at 675 degrees C for 28 hours. The yield of ethylene was improved on all ALD Al(2)O(3) overcoated Pd catalysts.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lu, Junling -- Fu, Baosong -- Kung, Mayfair C -- Xiao, Guomin -- Elam, Jeffrey W -- Kung, Harold H -- Stair, Peter C -- New York, N.Y. -- Science. 2012 Mar 9;335(6073):1205-8. doi: 10.1126/science.1212906.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Energy Systems Division, Argonne National Laboratory, Argonne, IL 60439, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22403386" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Identification of active sites in CO oxidation and water-gas shift over supported Pt catalysts (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-09-05
    Description: Identification and characterization of catalytic active sites are the prerequisites for an atomic-level understanding of the catalytic mechanism and rational design of high-performance heterogeneous catalysts. Indirect evidence in recent reports suggests that platinum (Pt) single atoms are exceptionally active catalytic sites. We demonstrate that infrared spectroscopy can be a fast and convenient characterization method with which to directly distinguish and quantify Pt single atoms from nanoparticles. In addition, we directly observe that only Pt nanoparticles show activity for carbon monoxide (CO) oxidation and water-gas shift at low temperatures, whereas Pt single atoms behave as spectators. The lack of catalytic activity of Pt single atoms can be partly attributed to the strong binding of CO molecules.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ding, Kunlun -- Gulec, Ahmet -- Johnson, Alexis M -- Schweitzer, Neil M -- Stucky, Galen D -- Marks, Laurence D -- Stair, Peter C -- New York, N.Y. -- Science. 2015 Oct 9;350(6257):189-92. doi: 10.1126/science.aac6368. Epub 2015 Sep 3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, Northwestern University, Evanston, IL 60208, USA. ; Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA. ; Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208, USA. ; Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106, USA. ; Department of Chemistry, Northwestern University, Evanston, IL 60208, USA. Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439, USA. pstair@northwestern.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26338796" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of CH3I adsorbed on MgO(100): Theory and experiment (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5168-5176 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical and experimental results are compared for the 257 nm photolysis of methyl iodide adsorbed on an MgO(100) crystal. Molecular-dynamics calculations treat CH3I as a pseudodiatomic molecule and describe the geometry and the vibrational and librational frequencies of ground state CH3I on the surface of a solid at 125 K. The simulations modeled the photodissociation dynamics of the adsorbed species. The photoexcitation of CH3I at 257 nm is to the 3Q0 state which is, in turn, coupled to the 1Q1 state. The electronic surface coupling allows for two dissociation pathways, producing either ground- or excited-state iodine atoms in concert with ground-state methyl radicals. The I*/I branching ratio and the velocity and angular distributions of both photofragments are predicted by the theory. A comparison is made between these predictions and experimental observation of the I*/I branching ratio, the velocity distribution of the methyl fragment, and the internal state distribution of the methyl. A substantial lowering of the I*/I ratio as compared to data from the gas-phase photodissociation studies is both predicted by theory and seen experimentally. Theoretical simulations attribute this change to efficient trapping of the I* photofragments by the surface. Further comparisons between the theoretical predictions and the experimental data support a model where the molecule is aligned perpendicular to the surface and the escape of iodine atoms from the surface following the photodissociation of adsorbed methyl iodide involves collisions with the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463815
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  • 4
    Electronic Resource
    Electronic Resource
    257 nm photoinduced chemistry of methyl iodide adsorbed on MgO(100) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9221-9232 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 257 nm photochemistry of CD3I adsorbed on MgO(100) has been investigated. The photofragments ejected along the surface normal were probed using resonantly enhanced multiphoton ionization spectroscopy coupled with time-of-flight mass spectrometry. Methyl radicals and atomic iodine fragments in both the ground I(2P3/2)≡I and spin–orbit excited I(2P1/2)≡I* states were observed as direct photofragments produced at the surface. Laser-induced desorption of methyl iodide competes with dissociation at the surface. The total cross section for removal of adsorbed CD3I from the surface at 257 nm is comparable to the gas phase cross section. A significant portion of the atomic iodine fragments remain trapped at the surface with preferential trapping of I*. Additionally, nonresonant I+ and I+2 signals were detected and initially observed to increase as a function of the irradiation time and then decrease with further irradiation. This behavior is shown to be indicative of photoinduced production and photoinduced removal of a surface intermediate. A surface reaction mechanism and the existence of a common precursor resulting from the interaction of adsorbed atomic iodine with adsorbed methyl iodide or methyl iodide clusters is postulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462232
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  • 5
    Electronic Resource
    Electronic Resource
    Resonance enhanced multiphoton ionization/time-of-flight measurements of the velocity and internal energy content of thermal and photochemical methyl radical sources (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2031-2036 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A single-stage time-of-flight mass spectrometer used in conjunction with resonance enhanced multiphoton ionization has been employed to study the dynamics of surface photodissociation processes as well as methyl radicals produced from a continuous source. By utilizing ion rather than neutral flight times, species that have an impressed velocity along the detection axis can be readily distinguished from species that exhibit an isotropic velocity distribution. This allows for experimental discrimination between photofragments produced from adsorbate photolysis and those produced as a result of probe laser photolysis of gas-phase species photodesorbed from the surface. For species generated in continuous sources, such as methyl radicals produced from azomethane pyrolysis, the same approach permits an unambiguous determination of the total-energy content, despite the presence of additional radicals within the ionizing volume that have scattered from the chamber walls. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148093
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  • 6
    Electronic Resource
    Electronic Resource
    Adsorption of boron on molybdenum(100) and its effect on chemisorption of carbon monoxide, ethene, propene, and 3,3,3-trifluoropropene (1987)
    s.l. : American Chemical Society
    Langmuir 3 (1987), S. 1015-1025 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00078a024
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular Orientation and Surface Morphology in Methyl Iodide Films Grown on MgO(100) Probed by Photodissociation (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 13042-13049 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100100a037
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  • 8
    Electronic Resource
    Electronic Resource
    Ultraviolet photodissociation dynamics of methyl iodide at 333 nm (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3787-3791 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ultraviolet (UV) photodissociation dynamics of methyl iodide at 333.45 nm has been studied using resonantly enhanced multiphoton ionization in conjunction with a time-of-flight mass spectrometer (REMPI-TOFMS). At this wavelength methyl iodide photolysis involves a transition with significant parallel and perpendicular character. Both ground (I) and spin–orbit (I*) excited iodine result from a parallel transition to the 3Q0 state. In contrast, the perpendicular transition, which most likely involves initial excitation to the 3Q1 state, leads exclusively to production of I. Based on data from this study, an upper limit for the conical intersection between the 3Q0 and 1Q1 potential surfaces is ∼30 500 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467495
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  • 9
    Electronic Resource
    Electronic Resource
    The role of adsorbate structure in the photodissociation dynamics of adsorbed species: Methyl iodide/MgO(100) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7267-7276 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 257 nm photodissociation dynamics of methyl iodide multilayers adsorbed on MgO(100) have been studied using resonantly enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) to detect both methyl and iodine photofragments. The photofragments result from direct photolysis of the methyl iodide adsorbate. Methyl fragments with a translational and internal energy content comparable to that found in the gas phase dissociation of the isolated molecule are produced. However, the measured I/I* branching ratio is modified in favor of ground state (I) iodine production. Collisionally slowed methyl fragments, characterized by a translational temperature close to that of the surface, are also observed. Iodine fragments with velocities in excess of the gas phase limit are produced as a result of collisional energy transfer between iodine and faster moving methyl photofragments. A small amount of laser induced photodesorption, leading to the production of molecular methyl iodide, was also detected. The observed photofragmentation dynamics can be accounted for based on the ordered antiparallel structure adopted by the adsorbate molecules that are preferentially aligned along the surface normal within the physisorbed layer. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469038
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  • 10
    Electronic Resource
    Electronic Resource
    The concept of Lewis acids and bases applied to surfaces (1982)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 104 (1982), S. 4044-4052 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00379a002
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