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Volumn 309, Issue , 2014, Pages 397-407

Thermochemistry and micro-kinetic analysis of methanol synthesis on ZnO (0 0 0 1)

Author keywords

Catalysis; DFT; Kinetics; MeOH; Phase diagram; Zinc oxide

Indexed keywords

ACTIVATION BARRIERS; DFT; KINETIC MODELING; MEOH; METHANOL SYNTHESIS; MICRO-KINETIC ANALYSIS; TEMPERATURE AND PRESSURES; WATER-GAS SHIFT REACTION (WGS);

EID: 84888103199     PISSN: 00219517     EISSN: 10902694     Source Type: Journal    
DOI: 10.1016/j.jcat.2013.10.015     Document Type: Article
Times cited : (57)

References (63)
  • 1
    • 84868477113 scopus 로고    scopus 로고
    • Methanol synthesis
    • 10.1007/s10562-012-0905-2
    • K.C. Waugh Methanol synthesis Catalysis Letters 142 10 2012 1153 1166 10.1007/s10562-012-0905-2
    • (2012) Catalysis Letters , vol.142 , Issue.10 , pp. 1153-1166
    • Waugh, K.C.1
  • 4
    • 0001214149 scopus 로고
    • Synthesis of methanol
    • P.H. Emmett, Reinhold New York
    • G. Natta Synthesis of methanol P.H. Emmett, Catalysis vol. 3 1955 Reinhold New York 349 409
    • (1955) Catalysis , vol.3 VOL. , pp. 349-409
    • Natta, G.1
  • 5
    • 0026869374 scopus 로고
    • Methanol synthesis
    • K.C. Waugh Methanol synthesis Catalysis Today 15 1992 51 75
    • (1992) Catalysis Today , vol.15 , pp. 51-75
    • Waugh, K.C.1
  • 6
    • 0542406651 scopus 로고
    • Electronic structures of active sites on metal oxide surfaces: Definition of the copper-zinc oxide methanol synthesis catalyst by photoelectron spectroscopy
    • E. Solomon, P. Jones, and J. May Electronic structures of active sites on metal oxide surfaces: definition of the copper-zinc oxide methanol synthesis catalyst by photoelectron spectroscopy Chemical Reviews 93 1993 2623 2644
    • (1993) Chemical Reviews , vol.93 , pp. 2623-2644
    • Solomon, E.1    Jones, P.2    May, J.3
  • 8
    • 0035252871 scopus 로고    scopus 로고
    • The role of ZnO in Cu/ZnO methanol synthesis catalysts morphology effect or active site model?
    • 10.1016/S0926-860X(00)00712-2
    • Y. Choi, K. Futagami, T. Fujitani, and J. Nakamura The role of ZnO in Cu/ZnO methanol synthesis catalysts morphology effect or active site model? Applied Catalysis A: General 208 1-2 2001 163 167 10.1016/S0926-860X(00)00712-2
    • (2001) Applied Catalysis A: General , vol.208 , Issue.12 , pp. 163-167
    • Choi, Y.1    Futagami, K.2    Fujitani, T.3    Nakamura, J.4
  • 9
    • 0344552817 scopus 로고    scopus 로고
    • On the issue of the active site and the role of ZnO in Cu/ZnO methanol synthesis catalysts
    • J. Nakamura, Y. Choi, and T. Fujitani On the issue of the active site and the role of ZnO in Cu/ZnO methanol synthesis catalysts Topics in Catalysis 22 3-4 2003 277
    • (2003) Topics in Catalysis , vol.22 , Issue.34 , pp. 277
    • Nakamura, J.1    Choi, Y.2    Fujitani, T.3
  • 12
    • 0001533312 scopus 로고    scopus 로고
    • Methanol synthesis and reverse water gas shift kinetics over Cu (1 1 0) model catalysts: Structural sensitivity
    • J. Yoshihara, and C. Campbell Methanol synthesis and reverse water gas shift kinetics over Cu (1 1 0) model catalysts: structural sensitivity Journal of Catalysis 782 0240 1996 776 782
    • (1996) Journal of Catalysis , vol.782 , Issue.240 , pp. 776-782
    • Yoshihara, J.1    Campbell, C.2
  • 13
    • 0035250646 scopus 로고    scopus 로고
    • Structure-dependent kinetics for synthesis and decomposition of formate species over Cu(1 1 1) and Cu(1 1 0) model catalysts
    • 10.1021/jp002644z
    • H. Nakano, I. Nakamura, T. Fujitani, and J. Nakamura Structure-dependent kinetics for synthesis and decomposition of formate species over Cu(1 1 1) and Cu(1 1 0) model catalysts The Journal of Physical Chemistry B 105 7 2001 1355 1365 10.1021/jp002644z
    • (2001) The Journal of Physical Chemistry B , vol.105 , Issue.7 , pp. 1355-1365
    • Nakano, H.1    Nakamura, I.2    Fujitani, T.3    Nakamura, J.4
  • 15
    • 79953711473 scopus 로고    scopus 로고
    • 2 and CO hydrogenation
    • 10.1021/cs200055d
    • 2 and CO hydrogenation ACS Catalysis 1 4 2011 365 384 10.1021/cs200055d
    • (2011) ACS Catalysis , vol.1 , Issue.4 , pp. 365-384
    • Grabow, L.C.1    Mavrikakis, M.2
  • 17
    • 4644265529 scopus 로고    scopus 로고
    • Improved adsorption energetics within density-functional theory using revised Perdew-Burke-Ernzerhof functionals
    • 10.1103/PhysRevB.59.7413
    • B. Hammer, L. Hansen, and J.K. Nørskov Improved adsorption energetics within density-functional theory using revised Perdew-Burke-Ernzerhof functionals Physical Review B 59 11 1999 7413 7421 10.1103/PhysRevB.59.7413
    • (1999) Physical Review B , vol.59 , Issue.11 , pp. 7413-7421
    • Hammer, B.1    Hansen, L.2    Nørskov, J.K.3
  • 19
    • 1842816907 scopus 로고
    • Special points for Brillouin-zone integrations
    • H.J. Monkhorst, and J.D. Pack Special points for Brillouin-zone integrations Physical Review B 13 12 1976 5188 5192
    • (1976) Physical Review B , vol.13 , Issue.12 , pp. 5188-5192
    • Monkhorst, H.J.1    Pack, J.D.2
  • 20
    • 0001048838 scopus 로고    scopus 로고
    • Dipole correction for surface supercell calculations
    • 10.1103/PhysRevB.59.12301
    • L. Bengtsson Dipole correction for surface supercell calculations Physical Review B 59 19 1999 12301 12304 10.1103/PhysRevB.59.12301
    • (1999) Physical Review B , vol.59 , Issue.19 , pp. 12301-12304
    • Bengtsson, L.1
  • 21
    • 0037438010 scopus 로고    scopus 로고
    • Density-functional study of the structure and stability of ZnO surfaces
    • 10.1103/PhysRevB.67.035403
    • B. Meyer, and D. Marx Density-functional study of the structure and stability of ZnO surfaces Physical Review B 67 3 2003 035403 10.1103/PhysRevB.67.035403
    • (2003) Physical Review B , vol.67 , Issue.3 , pp. 035403
    • Meyer, B.1    Marx, D.2
  • 22
    • 34047152800 scopus 로고    scopus 로고
    • The chemistry and physics of zinc oxide surfaces
    • 10.1016/j.progsurf.2006.12.002
    • C. Woll The chemistry and physics of zinc oxide surfaces Progress in Surface Science 82 2-3 2007 55 120 10.1016/j.progsurf.2006.12.002
    • (2007) Progress in Surface Science , vol.82 , Issue.23 , pp. 55-120
    • Woll, C.1
  • 23
    • 79951777120 scopus 로고    scopus 로고
    • Methanol synthesis on ZnO(0 0 0 1). III. Free energy landscapes, reaction pathways, and mechanistic insights
    • 10.1063/1.3541826
    • J. Kiss, J. Frenzel, N.N. Nair, B. Meyer, and D. Marx Methanol synthesis on ZnO(0 0 0 1). III. Free energy landscapes, reaction pathways, and mechanistic insights The Journal of Chemical Physics 134 6 2011 064710 10.1063/1.3541826
    • (2011) The Journal of Chemical Physics , vol.134 , Issue.6 , pp. 064710
    • Kiss, J.1    Frenzel, J.2    Nair, N.N.3    Meyer, B.4    Marx, D.5
  • 24
    • 0036572216 scopus 로고    scopus 로고
    • An object-oriented scripting interface to a legacy electronic structure code
    • S.R. Bahn, and K.W. Jacobsen An object-oriented scripting interface to a legacy electronic structure code Computing in Science & Engineering 4 2002 56 66
    • (2002) Computing in Science & Engineering , vol.4 , pp. 56-66
    • Bahn, S.R.1    Jacobsen, K.W.2
  • 25
    • 77958072947 scopus 로고    scopus 로고
    • Reaction intermediates of methanol synthesis and the water gas-shift reaction on the ZnO(0 0 0 01) surface
    • 10.1016/j.susc.2010.06.025
    • K. Chuasiripattana, O. Warschkow, B. Delley, and C. Stampfl Reaction intermediates of methanol synthesis and the water gas-shift reaction on the ZnO(0 0 0 01) surface Surface Science 604 19-20 2010 1742 1751 10.1016/j.susc.2010.06.025
    • (2010) Surface Science , vol.604 , Issue.1920 , pp. 1742-1751
    • Chuasiripattana, K.1    Warschkow, O.2    Delley, B.3    Stampfl, C.4
  • 26
    • 84864425120 scopus 로고    scopus 로고
    • Theoretical study of syngas hydrogenation to methanol on the polar Zn-terminated ZnO (0 0 0 1) surface
    • Y. Zhao, R. Rousseau, J. Li, and D. Mei Theoretical study of syngas hydrogenation to methanol on the polar Zn-terminated ZnO (0 0 0 1) surface The Journal of Physical 116 2012 15952 15961
    • (2012) The Journal of Physical , vol.116 , pp. 15952-15961
    • Zhao, Y.1    Rousseau, R.2    Li, J.3    Mei, D.4
  • 27
  • 29
    • 79952361040 scopus 로고    scopus 로고
    • Initial steps in methanol steam reforming on PdZn and ZnO surfaces: Density functional theory studies
    • 10.1016/j.susc.2011.01.014
    • G.K. Smith, S. Lin, W. Lai, A. Datye, D. Xie, and H. Guo Initial steps in methanol steam reforming on PdZn and ZnO surfaces: density functional theory studies Surface Science 605 7-8 2011 750 759 10.1016/j.susc.2011.01.014
    • (2011) Surface Science , vol.605 , Issue.78 , pp. 750-759
    • Smith, G.K.1    Lin, S.2    Lai, W.3    Datye, A.4    Xie, D.5    Guo, H.6
  • 30
    • 78649760417 scopus 로고    scopus 로고
    • 2C for higher alcohols synthesis
    • 10.1016/j.cattod.2010.03.079
    • 2C for higher alcohols synthesis Catalysis Today 158 3-4 2010 241 245 10.1016/j.cattod.2010.03.079
    • (2010) Catalysis Today , vol.158 , Issue.34 , pp. 241-245
    • Wang, N.1    Fang, K.2    Jiang, D.3    Li, D.4    Sun, Y.5
  • 33
    • 33947469472 scopus 로고
    • A method for evaluating and correlating thermodynamic data
    • 10.1021/j150514a018
    • C.H. Shomate A method for evaluating and correlating thermodynamic data Journal of Physical Chemistry 58 4 1954 368 372 10.1021/j150514a018
    • (1954) Journal of Physical Chemistry , vol.58 , Issue.4 , pp. 368-372
    • Shomate, C.H.1
  • 35
    • 84883615398 scopus 로고    scopus 로고
    • On the effect of coverage dependent adsorbate-adsorbate interactions for CO methanation on transition metal surfaces
    • A.C. Lausche, A.J. Medford, T.S. Khan, T. Bligaard, F. Abild-Pedersen, J.K. Nørskov, F. Studt, On the effect of coverage dependent adsorbate-adsorbate interactions for CO methanation on transition metal surfaces, Journal of Catalysis, 307 (2013) 275-282. http://dx.doi.org/10.1016/j. jcat.2013.08.002.
    • (2013) Journal of Catalysis , vol.307 , pp. 275-282
    • Lausche, A.C.1    Medford, A.J.2    Khan, T.S.3    Bligaard, T.4    Abild-Pedersen, F.5    Nørskov, J.K.6    Studt, F.7
  • 37
    • 78650509697 scopus 로고    scopus 로고
    • Ferromagnetic behavior of high-purity ZnO nanoparticles
    • 10.1016/j.ssc.2010.11.019
    • R. Escudero, and R. Escamilla Ferromagnetic behavior of high-purity ZnO nanoparticles Solid State Communications 151 2 2011 97 101 10.1016/j.ssc.2010. 11.019
    • (2011) Solid State Communications , vol.151 , Issue.2 , pp. 97-101
    • Escudero, R.1    Escamilla, R.2
  • 38
    • 40849097936 scopus 로고    scopus 로고
    • Bulk moduli of wurtzite, zinc-blende, and rocksalt phases of ZnO from chemical bond method and density functional theory
    • 10.1063/1.2895635
    • C. Fan, Q. Wang, L. Li, S. Zhang, Y. Zhu, X. Zhang, M. Ma, R. Liu, and W. Wang Bulk moduli of wurtzite, zinc-blende, and rocksalt phases of ZnO from chemical bond method and density functional theory Applied Physics Letters 92 10 2008 101917 10.1063/1.2895635
    • (2008) Applied Physics Letters , vol.92 , Issue.10 , pp. 101917
    • Fan, C.1    Wang, Q.2    Li, L.3    Zhang, S.4    Zhu, Y.5    Zhang, X.6    Ma, M.7    Liu, R.8    Wang, W.9
  • 39
    • 1042276607 scopus 로고    scopus 로고
    • Competing stabilization mechanism for the polar ZnO(0 0 0 1)-Zn surface
    • 10.1103/PhysRevB.68.245409
    • G. Kresse, O. Dulub, and U. Diebold Competing stabilization mechanism for the polar ZnO(0 0 0 1)-Zn surface Physical Review B 68 24 2003 245409 10.1103/PhysRevB.68.245409
    • (2003) Physical Review B , vol.68 , Issue.24 , pp. 245409
    • Kresse, G.1    Dulub, O.2    Diebold, U.3
  • 40
    • 1542344032 scopus 로고    scopus 로고
    • First-principles study of the polar O-terminated ZnO surface in thermodynamic equilibrium with oxygen and hydrogen
    • 10.1103/PhysRevB.69.045416
    • B. Meyer First-principles study of the polar O-terminated ZnO surface in thermodynamic equilibrium with oxygen and hydrogen Physical Review B 69 4 2004 045416 10.1103/PhysRevB.69.045416
    • (2004) Physical Review B , vol.69 , Issue.4 , pp. 045416
    • Meyer, B.1
  • 42
    • 33845378526 scopus 로고
    • Comparison of the chemical properties of the zinc-polar, the oxygen-polar, and the nonpolar surfaces of zinc oxide
    • S. Akhter, K. Lui, and H. Kung Comparison of the chemical properties of the zinc-polar, the oxygen-polar, and the nonpolar surfaces of zinc oxide The Journal of Physical Chemistry 89 1985 1958 1964
    • (1985) The Journal of Physical Chemistry , vol.89 , pp. 1958-1964
    • Akhter, S.1    Lui, K.2    Kung, H.3
  • 43
    • 0002990560 scopus 로고
    • Conversion of methanol, formaldehyde and formic acid on the polar faces of zinc oxide
    • J. Vohs, and M. Barteau Conversion of methanol, formaldehyde and formic acid on the polar faces of zinc oxide Surface Science 176 1986 91 114
    • (1986) Surface Science , vol.176 , pp. 91-114
    • Vohs, J.1    Barteau, M.2
  • 45
    • 0001384695 scopus 로고
    • Structure sensitivity in methanol decomposition on ZnO single-crystal surfaces
    • 10.1016/0021-9517(83)90200-2
    • W. Cheng Structure sensitivity in methanol decomposition on ZnO single-crystal surfaces Journal of Catalysis 82 2 1983 341 350 10.1016/0021-9517(83)90200-2
    • (1983) Journal of Catalysis , vol.82 , Issue.2 , pp. 341-350
    • Cheng, W.1
  • 47
    • 65149093190 scopus 로고    scopus 로고
    • The surface chemistry of ZnO nanoparticles applied as heterogeneous catalysts in methanol synthesis
    • 10.1016/j.susc.2008.09.063
    • J. Strunk, K. Kähler, X. Xia, and M. Muhler The surface chemistry of ZnO nanoparticles applied as heterogeneous catalysts in methanol synthesis Surface Science 603 10-12 2009 1776 1783 10.1016/j.susc.2008.09.063
    • (2009) Surface Science , vol.603 , Issue.1012 , pp. 1776-1783
    • Strunk, J.1    Kähler, K.2    Xia, X.3    Muhler, M.4
  • 48
    • 2542455919 scopus 로고    scopus 로고
    • Photoelectron spectroscopic and electronic structure studies of CH(2)O bonding and reactivity on ZnO surfaces: Steps in the methanol synthesis reaction
    • 10.1021/ic035252q
    • P.M. Jones, J.a. May, J.B. Reitz, and E.I. Solomon Photoelectron spectroscopic and electronic structure studies of CH(2)O bonding and reactivity on ZnO surfaces: steps in the methanol synthesis reaction Inorganic Chemistry 43 11 2004 3349 3370 10.1021/ic035252q
    • (2004) Inorganic Chemistry , vol.43 , Issue.11 , pp. 3349-3370
    • Jones, P.M.1    May, J.A.2    Reitz, J.B.3    Solomon, E.I.4
  • 49
    • 33747065298 scopus 로고    scopus 로고
    • On the mechanism of methanol synthesis and the water-gas shift reaction on ZnO
    • 10.1007/s10562-006-0088-9
    • J. Tabatabaei, B.H. Sakakini, and K.C. Waugh On the mechanism of methanol synthesis and the water-gas shift reaction on ZnO Catalysis Letters 110 1-2 2006 77 84 10.1007/s10562-006-0088-9
    • (2006) Catalysis Letters , vol.110 , Issue.12 , pp. 77-84
    • Tabatabaei, J.1    Sakakini, B.H.2    Waugh, K.C.3
  • 50
    • 0035803637 scopus 로고    scopus 로고
    • 2 to methanol by hybrid QM/MM embedding
    • 2 to methanol by hybrid QM/MM embedding Angewandte 23 2001 4437 4440
    • (2001) Angewandte , Issue.23 , pp. 4437-4440
    • French, S.1    Sokol, A.2
  • 51
    • 0346904024 scopus 로고    scopus 로고
    • Identification and characterization of active sites and their catalytic processes the Cu/ZnO methanol catalyst
    • S. French, A. Sokol, S. Bromley, C. Catlow, and P. Sherwood Identification and characterization of active sites and their catalytic processes the Cu/ZnO methanol catalyst Topics in Catalysis 24 1-4 2003 161 172
    • (2003) Topics in Catalysis , vol.24 , Issue.14 , pp. 161-172
    • French, S.1    Sokol, A.2    Bromley, S.3    Catlow, C.4    Sherwood, P.5
  • 52
    • 67249107184 scopus 로고    scopus 로고
    • Methanol synthesis on ZnO(0 0 0 1). I. Hydrogen coverage, charge state of oxygen vacancies, and chemical reactivity
    • 10.1063/1.3126682
    • J. Kiss, A. Witt, B. Meyer, and D. Marx Methanol synthesis on ZnO(0 0 0 1). I. Hydrogen coverage, charge state of oxygen vacancies, and chemical reactivity The Journal of Chemical Physics 130 18 2009 184706 10.1063/1.3126682
    • (2009) The Journal of Chemical Physics , vol.130 , Issue.18 , pp. 184706
    • Kiss, J.1    Witt, A.2    Meyer, B.3    Marx, D.4
  • 53
    • 61649102229 scopus 로고    scopus 로고
    • A density functional study of the methanol synthesis at an oxygen vacancy on the polar ZnO(0 0 0 1) surface
    • G. Rossmuller, V. Kleinschmidt, J. Kossmann, and C. Hättig A density functional study of the methanol synthesis at an oxygen vacancy on the polar ZnO(0 0 0 1) surface The Journal of Physical Chemistry C 113 2009 1418 1425
    • (2009) The Journal of Physical Chemistry C , vol.113 , pp. 1418-1425
    • Rossmuller, G.1    Kleinschmidt, V.2    Kossmann, J.3    Hättig, C.4
  • 54
    • 85008399371 scopus 로고
    • Oxidations carried out by means of vanadium oxide catalysts
    • 10.1016/S0009-2509(54)80005-4
    • P. Mars, and D. van Krevelen Oxidations carried out by means of vanadium oxide catalysts Chemical Engineering Science 3 1954 41 59 10.1016/S0009-2509(54) 80005-4
    • (1954) Chemical Engineering Science , vol.3 , pp. 41-59
    • Mars, P.1    Van Krevelen, D.2
  • 55
    • 84855277677 scopus 로고    scopus 로고
    • CatApp: A web application for surface chemistry and heterogeneous catalysis
    • 10.1002/anie.201107947
    • J.S. Hummelshøj, F. Abild-Pedersen, F. Studt, T. Bligaard, and J.K. Nørskov CatApp: a web application for surface chemistry and heterogeneous catalysis Angewandte Chemie 51 1 2012 272 274 10.1002/anie. 201107947
    • (2012) Angewandte Chemie , vol.51 , Issue.1 , pp. 272-274
    • Hummelshøj, J.S.1    Abild-Pedersen, F.2    Studt, F.3    Bligaard, T.4    Nørskov, J.K.5
  • 56
    • 77953595060 scopus 로고    scopus 로고
    • Localized atomic basis set in the projector augmented wave method
    • 10.1103/PhysRevB.80.195112
    • A.H. Larsen, M. Vanin, J.J. Mortensen, K.S. Thygesen, and K.W. Jacobsen Localized atomic basis set in the projector augmented wave method Physical Review B 80 2009 195112 10.1103/PhysRevB.80.195112
    • (2009) Physical Review B , vol.80 , pp. 195112
    • Larsen, A.H.1    Vanin, M.2    Mortensen, J.J.3    Thygesen, K.S.4    Jacobsen, K.W.5
  • 60
    • 79952721118 scopus 로고    scopus 로고
    • Activation of carbon dioxide on ZnO nanoparticles studied by vibrational spectroscopy
    • 10.1021/jp102751t
    • H. Noei, C. Woll, M. Muhler, and Y. Wang Activation of carbon dioxide on ZnO nanoparticles studied by vibrational spectroscopy The Journal of Physical Chemistry C 115 4 2011 908 914 10.1021/jp102751t
    • (2011) The Journal of Physical Chemistry C , vol.115 , Issue.4 , pp. 908-914
    • Noei, H.1    Woll, C.2    Muhler, M.3    Wang, Y.4
  • 61
    • 42449098616 scopus 로고    scopus 로고
    • Mechanism of the water gas shift reaction on pt: First principles, experiments, and microkinetic modeling
    • 10.1021/jp7099702
    • L.C. Grabow, A.A. Gokhale, S.T. Evans, J.A. Dumesic, and M. Mavrikakis Mechanism of the water gas shift reaction on pt: first principles, experiments, and microkinetic modeling The Journal of Physical Chemistry C 112 12 2008 4608 4617 10.1021/jp7099702
    • (2008) The Journal of Physical Chemistry C , vol.112 , Issue.12 , pp. 4608-4617
    • Grabow, L.C.1    Gokhale, A.A.2    Evans, S.T.3    Dumesic, J.A.4    Mavrikakis, M.5
  • 62
    • 34249766677 scopus 로고
    • Micro- and macro-kinetics: Their relationship in heterogeneous catalysis
    • C.T. Campbell Micro- and macro-kinetics: their relationship in heterogeneous catalysis Topics in Catalysis 1 1994 353 366
    • (1994) Topics in Catalysis , vol.1 , pp. 353-366
    • Campbell, C.T.1
  • 63
    • 77952021985 scopus 로고    scopus 로고
    • Understanding trends in catalytic activity: The effect of adsorbateadsorbate interactions for CO oxidation over transition metals
    • 10.1007/s11244-010-9455-2
    • L.C. Grabow, B. Hvolbæk, and J.K. Nørskov Understanding trends in catalytic activity: the effect of adsorbateadsorbate interactions for CO oxidation over transition metals Topics in Catalysis 53 5-6 2010 298 310 10.1007/s11244-010-9455-2
    • (2010) Topics in Catalysis , vol.53 , Issue.56 , pp. 298-310
    • Grabow, L.C.1    Hvolbæk, B.2    Nørskov, J.K.3


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