MOM 2006 journal for pdf.pmd - University of Michigan-Flint

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The computational tool is an alternative and/or support to the experimental research, but theoretical studies of bulky zeolites are limited by computer resources. With the recent development in theoretical methods, the cluster model can be used to represent the interaction between the adsorbed molecules (adsorbate) and the zeolite fragments. 18,19,20,21,22 The mechanism of adsorption-decomposition of NO x on Cu-ZSM-5 is complicated and involves many steps. 22 This study focused only on the initial adsorption of NO x – the first step in the adsorption-decomposition process. Only chemically bonded adsorption complexes may be stable enough to allow subsequent decomposition reactions. There are 5 possible NO 2 adsorption complexes and 3 possible NO adsorption complexes. Ab initio calculations of the structure of these complexes were performed to determine possible stable adsorption complexes and energy barriers. Approaches A cluster model was used to simulate zeolite structures in this project. Zeolite is treated as a small neutral cluster cut out of the bulky crystal structure. Hydrogen atoms terminate the resulting dangling bonds at the boundary. 23 Two types of clusters are examined – hydrogen terminated and hydroxyl terminated. The hydrogen terminated clusters result from the cluster being cut at the Si-O bond and terminated with hydrogen (Si-H end group). The hydroxyl terminated clusters result from the cluster being cut at the O-Si bond and being terminated with hydrogen (Si-O-H end group). Since the cluster model takes only a very small part of the zeolite structure, two important deficiencies exist. 24 First, the cluster model is different from the zeolite structure, because atoms near the cluster boundary, arbitrarily terminated by hydrogen/hydroxyl groups, are in different electronic environments. The second is potential deficiency. A potential is generated from the long-range electrostatic forces between the cluster model and the zeolite framework, which is missing in cluster calculations. Results obtained from cluster model investigations may give us a chance to examine the usage of the embedded cluster model. A recently developed embedded cluster model method can be used to avoid/alleviate aforementioned problems without significantly increasing the computational costs. 25,26,27 Computational Details Full optimizations of cluster models, from 1T to 10T models (Figure 1), were performed at the Hartree Fock (HF) and then the Density Functional Theory (DFT) levels with the 6-31G(d) basis set using the ab initio suite of GAMESS package. 28 Additionally, MacMolPlt, a 3D visualization package, was used to view the optimized geometries. 29 This work was partially supported by the National Center for Supercomputing Applications under CHE060031N and utilized the Copper and Tungsten systems. All other calculations were performed on a Mac Power cluster. Meeting of Minds 2006 70
1T 3T 5T Figure 1: The cluster models (X = H or OH) 10T Results There are five possible ways for NO 2 to adsorb on Cu-ZSM-5 (Figure 2). The first possibility is for nitrogen to bind to copper (A). Another possibility is for one of the oxygen atoms to bind to copper (B and C). In the B structure the second nitrogen is in line with the Cu-O bond, while in the C structure the second oxygen is located 90ˆ from the Cu-O bond. Another possibility is for both one of the oxygen atoms and the nitrogen to bond to copper forming a Cu-O-N ring (D). Finally the last possibility is for both of the oxygen atoms to bind to copper, thus forming a Cu-O-N-O ring (E). Since NO 2 is a polar molecule and the dipole moment points to N from O, different binding types should affect the bonding in NO 2 and the relative stabilities of the different adsorption complexes. The HF method was used to obtain an initial optimization of the geometry and orbitals for each adsorption complex. To include the correlation effects, optimizations at the DFT level were then performed using the HF results as a starting point. The optimized DFT geometries are listed in Table 1 and the relative energies are listed in Table 2. Although there are five possible structures, only 2 or 3 (depending on the cluster size) are stable adsorption complexes, ie. they represent local minima on the potential energy surface. The DFT results indicate that the E structure is the most stable adsorption complex regardless of the cluster size. The A, B, and D structures occur as local minima, though never all three with the same cluster. The C structure, however, never occurs as a local minimum. This is because the lone pairs of electrons on oxygen in this structure are in orbitals, whose orientation is not favorable for this complex. If the C structure were to exist, there would be a large strain on the Cu-O bond. If this strain were relieved by the reduction of the Cu-O-N bond angle, then the other oxygen in NO 2 would nearly overlap with an oxygen atom in the zeolite. Both of these situations are energetically unfavorable. Thus the C structure cannot be a stable complex. Meeting of Minds 2006 71
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Meeting of Minds XIV Journal of Und
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ABOUT THE MEETING OF MINDS: JOURNAL
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TABLE OF CONTENTS Preface Contribut
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DIFFERENCES IN TEACHING: INNER-CITY
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1995. The teacher believed they are
Page 11 and 12:
In studies of age related declines
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slightly smaller than the incongrue
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Since the requirements of surviving
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Table 2 Observed behaviors of Imara
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Figure 2 Relative frequencies of de
Page 21 and 22:
References Alexander, R. D. “The
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She goes for it. She proves to the
Page 25 and 26: Hypotheses The current study examin
Page 27 and 28: Previous fMRI research suggests tha
Page 29 and 30: [LDL’s] carry cholesterol from th
Page 31 and 32: for amounts in excess of 0.5 grams.
Page 33 and 34: Dewey, David L. “Hydrogenated Oil
Page 35 and 36: These are the tranquillized Fifties
Page 37 and 38: The reader is thrust out of the mem
Page 39 and 40: WHEN THE SAINTS GO MARCHING OUT: CO
Page 41 and 42: What follows is a description of tw
Page 43 and 44: The ceiling of the church is adorne
Page 45 and 46: Against the back wall of the church
Page 47 and 48: Bibliography Bowen, John R. Religio
Page 49 and 50: (Gough, 1957). Because individuals
Page 51 and 52: References Bochner, A., di Salvo V.
Page 53 and 54: It is difficult for many critics, a
Page 55 and 56: It seems clear that Bishop is not a
Page 57 and 58: “SHE WAS ONLY A SLIP OF A THING B
Page 59 and 60: women are strong enough to care for
Page 61 and 62: had the luxury of doing business
Page 63 and 64: Chinese students regularly had as m
Page 65 and 66: The age of the participants ranged
Page 67 and 68: Table 3 illustrates the results of
Page 69 and 70: If I was to further this study, I w
Page 71 and 72: idomain conductivities (σ iL , σ
Page 73 and 74: Meeting of Minds 2006 67
Page 75: THEORETICAL INVESTIGATIONS ON ADSOR
Page 79 and 80: The N-O bond lengths also show a si
Page 81 and 82: The relative energies of the NO ads
Page 83 and 84: INVESTIGATION OF SUBSTITUTED CYCLOO
Page 85 and 86: were 9 possibilities from the X and
Page 87 and 88: 28 O O RSS NA 8.6 28 O O SSS NA 8.6
Page 89 and 90: As seen from the distance data abov
Page 91 and 92: continually touches her and plays w
Page 93 and 94: In the last scene, Act 5.4, the tra
Page 95 and 96: Tristan was the one who had her bef
Page 97 and 98: Bibliography Béroul. The Romance o
Page 99 and 100: given day one could observe a cheat
Page 101 and 102: Many countries have taken Latin Ame
Page 103 and 104: References and Works Cited Andaló,
Page 105 and 106: differentiates human beings from an
Page 107 and 108: has to beg the wind to help her. Th
Page 109 and 110: APOCALYPSE, WHEN? Joanne Chiu Facul
Page 111 and 112: Lowell’s energetic diction connec
Page 113 and 114: The apocalypse has come and as with
Page 115 and 116: RELIGION AS A MANIPULATIVE TOOL IN
Page 117 and 118: With a sense of his mastery of stra
Page 119 and 120: References Arenal, Electa and Stace
Page 121 and 122: constructed a visual lexicon aggres
Page 123 and 124: them as the hoods plot their next t
Page 125 and 126: The motivation behind Guston’s re
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LANGUAGE ACQUISITION: A PARADOX OF
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GUNTHER VON HAGEN’S GESTALT PLAST
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are borrowed directly from the visu
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In general, science museums do not
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The report suggests that war-crimes
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DATA MINING IN BIOINFORMATICS: USIN
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Zealand, which was ranked 77 th in
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THE JENSEN LANDSCAPE AT HENRY AND C
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number of Boxelder trees increased
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Figure 3. The distribution of Sugar
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THE EFFECT OF RETINOIDS ON REGENERA
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deparaffinized in xylene. After the
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A B C Figure 2 Photographs of tadpo
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IU/mL retinoids is the best concent
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