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Computational Studies of Transition Metal Nanoalloys

:	Lauro Oliver Paz Borbón
:	Computational Studies of Transition Metal Nanoalloys
:	Springer-Verlag
:	9783642180125
:	1
:	CHF 85.40
:

:	Theoretische Chemie
:	English

:	156
:	Wasserzeichen
:	PC/MAC/eReader/Tablet
:	PDF

The focus of this thesis is the computational modelling of transition metal bimetallic (nanoalloy) clusters. More specifically, the study of Pd-Pt, Ag-Pt, Au-Au and Pd-Au as a few tens of atoms in the gas phase. The author used a combination of global optimization techniques - coupled with a Gupta-type empirical many-body potential - and Density Functional Theory (DFT) calculations to study the structures, bonding and chemical ordering, as well as investigate the chemisorptions of hydrogen and carbon monoxide on bimetallic clusters. This research is highly relevant to experimental catalytic studies and has resulted in more than seven publications in international journals.

	Computational Studies of Transition Metal Nanoalloys	4
	Supervisor’s Foreword	8
	Acknowledgments	9
	Contents	10
	1 Introduction	14
	1.1…Clusters: Overview and Applications	15
	1.2…Nanoalloys	16
	1.2.1 Homotops	17
	1.2.2 Segregation in Nanoalloys	17
	1.3…Experimental Background: From Synthesis to Cluster Characterisation	19
	1.4…Second and Third Rows Transition Metal Nanoalloys	20
	1.4.1 Pd--Pt Clusters	20
	1.4.2 Pd--Au Clusters	21
	1.4.3 Ag--Pt Clusters	21
	1.4.4 Ag--Au Clusters	22
	1.5…Chemisorption on Single Metal and Bimetallic Clusters	22
	References	24
	2 Theoretical Background and Methodology	27
	2.1…Modelling Metal Clusters and Nanoalloys	27
	2.1.1 Potential Energy Surfaces	28
	2.2…Theoretical Methods	28
	2.2.1 The Gupta Potential	28
	2.2.2 Early Density Functional Theory: Thomas Fermi Model	29
	2.2.3 Modern Density Functional Theory	31
	2.2.4 Functionals and Basis Sets	34
	2.3…Global Optimization Techniques	35
	2.3.1 The Birmingham Cluster Genetic Algorithm	35
	2.3.2 The Basin-Hopping Monte Carlo Algorithpotential energy surface (PES)m	38
	2.3.3 Shell Optimization Routine	39
	2.3.4 Combined EP-DFT Approach	39
	2.4…Energetic Analysis	40
	References	42
	3 34-Atom Pd--Pt Clusters	44
	3.1…Introduction	44
	3.2…Computational Details	44
	3.3…Results and Discussion	45
	3.3.1 Gupta Potential Calculations on PdmPt34	45
	minus	45
	m	45
	3.4…DFT Calculations	48
	3.4.1 Composition Pd24Pt10	49
	3.4.2 Segregation Effects for Pd17Pt17 Clusters	51
	3.4.3 Analysis of the Dh--cp(DT) Structure	52
	3.4.4 Conclusions	54
	References	55
	4 98-Atom Pd--Pt Nanoalloys	56
	4.1…Introduction	56
	4.2…Computational Details	56
	4.3…Results and Discussion	57
	4.3.1 Comparison of Global Minimum Structures for 98-Atom Pd--Pt Nanoalloys	57
	4.3.2 Analysis of the Leary Tetrahedron	61
	4.3.3 Onion-Like Structures	62
	4.3.4 Competition Between Different Structural Families	62
	4.4…Conclusions	63
	References	64
	5 38-Atom Binary Clusters	65
	5.1…Introduction	65
	5.2…Computational Details	67
	5.3…Results and Discussion	68
	5.3.1 Structural Families	69
	5.3.2 Composition Dependence of the Mixing Energy	72
	5.3.3 Pd--Pt Clusters	72
	5.3.4 Segregation Effects in Pd--Pt Clusters	74
	5.3.5 Ag--Pt Clusters	75
	5.3.6 Segregation Effects in Ag--Pt Clusters	75
	5.3.7 Pd--Au Clusters at Compositions 14--24 and 6--32	76
	5.3.8 Pd--Au Clusters at Compositions 24--14 and 32--6	78
	5.3.9 Segregation Effects in Pd--Au Clusters	79
	5.3.10 Ag--Au Clusters	79
	5.3.11 Segregation Effects in Ag--Au Clusters	81
	5.4…Conclusions	84
	References	85
	6 Chemical Ordering of 34-Atom Pd--Pt Nanoalloys	87
	6.1…Introduction	87
	6.2…Computational Details	90
	6.2.1 Genetic Algorithm	90
	6.3…Results and Discussion	92
	6.3.1 DFT Study of (Pd--Pt)N/2 Clusters (N = 2--20)	92
	6.3.2 Gupta Potential Study of (Pd--Pt)N/2 Clusters (N = 2--20) for Potentials Ia, Ib and Ic	95
	6.3.3 Gupta Potential Study of 34-Atom Pd34Pt34minusm Clusters for Potentials Ia, Ib and Ic	95
	6.3.4 Detailed Study of 34-Atom PdmPt34minusm Clusters for Variable Gupta Potential Weights	98
	6.3.5 Structural Motifs	99
	6.3.6 Segregation	104
	6.3.7 Study of Interfacial Areas in Segregated Bimetallic Clusters	104
	6.3.8 Derivation of the Interfacial Area Formulae	107
	6.3.8.1 Core--Shell Segregation	107
	6.3.8.2 Spherical Cap Segregation	108
	6.3.8.3 Ratio of Interfacial Areas	109
	6.4…Conclusions	109
	References	111
	7 Theoretical Study of Pd--Au Clusters	112
	7.1…Introduction	112
	7.2…Computational Details	113
	7.2.1 Genetic Algorithm	113
	7.2.2 Pd--Au Parameters	113
	7.3…Results and Discussion	115
	7.3.1 Gupta Potential Calculations on (Pd--Au)N/2 Clusters (N = 2--50)	115
	7.3.2 DFT Calculations on (Pd--Au)N/2 Clusters (N = 2--25)	119
	7.3.3 Structural Analysis	120
	7.4…34-Atom Pd--Au Clusters	120
	7.5…38-Atom Pd--Au Clusters	123
	7.6…DFT Investigation of Segregation in 34- and 38-Atom Pd--Au Clusters	131
	7.7…Large Pd--Au Nanoclusters, N = 98 Atoms	133
	7.7.1 Global Optimizations of 98-Atom Pd--Au Clusters	133
	7.7.2 Leary Tetrahedron Structure	135
	7.8…Conclusions	136
	References	141
	8 Chemisorption on Metal Clusters and Nanoalloys	142
	8.1…Introduction	142
	8.1.1 Experimental and Theoretical Studies on Chemisorption	142
	8.2…Chemisorption of CO and H on Pd, Pt and Au Nanoclusters	143
	8.2.1 Energetic Analysis	144
	8.2.2 Computational Details	146
	8.3…Results	147
	8.4…Chemisorption of CO and H on Bimetallic Clusters	153
	8.5…Conclusions	154
	References	155
	9 Conclusions and Future Work	157
	References	159
	Index	160