Resumen de presentación

Transcription

1 TÍTULO: Theretical study f the gemetrical, electrnic and catalytic prperties f metal clusters and nanparticles. AUTOR: Estefanía Fernández Villanueva, esfervi@dctr.upv.es PROGRAMA DE DOCTORADO: Química Sstenible. DIRECTOR DE TESIS: Mercedes Brnat Zaragza, brnat@itq.upv.es Institut de Tecnlgía química, UPV-CSIC, Universidad Plitécnica de Valencia - Cnsej Superir de Investigacines Científicas.Avda. de ls Naranjs s/n, 460 Valencia, Spain Resumen de presentación Transitin metal nanparticles with diameter between and 5 nm have imprved catalytic prperties with respect t bulk metals,. Furthermre, subnanmetric clusters have als been fund t be respnsible fr the catalityc activity in sme imprtant reactins 3,4. This different size-based behavir has n straightfrward cause, but these findings made the research f transitin metals clusters and nanparticles becme a very interesting subject industrially, due t the pssible discvery f new catalysts. Indeed, the general aim f the thesis is t study the reactivity f transitin metal clusters and nanparticles f increasing size by means f a theretical mdelling f the systems, in rder t help in the design f new catalysts. Cpper nanparticles catalyze imprtant industrial prcesses 5-6, and recently small clusters have als shwn catalytic activity 7. In additin, cpper has the industrial advantage f being a cheap resurce. Due t all this, we chse cpper t start ur investigatin n transitin metal clusters. Hwever, transitin metal systems are nt easy t handle cmputatinally. In fact, the apprpriate methds t use are nly applicable t the smallest systems, and ne has t switch t a cmpletely different theretical methd when systems get larger. Due t this, a first difficult gal was t stablish an apprpriate methdlgy t be able t study systems f increasing size and, hpefully, be able t cmpare their results. The next research stages cnsist in the study f the clusters ismers f different sizes and their interactin with cmmn mlecules. Mre specifically, they include: The mst stable structures f neutral clusters per size. The different adsrptin patterns f cmmn mlecules n the mst stable ismer per cluster size. The catalytic activity f the clusters in certain reactins f interest, which in turn includes: Transitin states (TS) studies thrugh Ptential Energy Surface scans. Activatin energy (E act ) evaluatin as the difference between TS and reactants: E act = E TS E R.

2 Reactin prducts (P) calculatins. Reactin energy (E reac ) evaluatin as the difference between P and reactants: E reac = E P E R. We started with the study f the adsrptin and dissciatin f the xygen mlecule n the cpper clusters. In the future, similar stages are t be fllwed with ther reactins such as: CO xidatin with xygen CO O Water Gas Shift reactin (WGS) Cun CO Prpene epxidatin CO H O n Cu CO H O n Cu In additin, larger systems will be studied and ther transitin metals r bimetallic systems will be included. Finally, spectra simulatin is meant t be dne and cmpared with experimental results if the latter are available. As a matter f fact, the future cllabratin with experimental grups at the ITQ will prvide further understanding f the subject. Indeed, the synthesis f small clusters and nanparticles is nt easy and the attempts are cstly, thus remarking the imprtance f theretical studies, which can explre many mre pssibilities and either suggest best candidates r discard thers, as well as explain the reasns underneath. The ultimate gal f this theretical research, therefre, is t assist in the design f new catalysts, which hpefully will be either cheaper, mre efficient, mre selective r mre envirnmentally friendly than thse currently used fr the crrespnding reactin, and thus will have ptential industrial applicability. References [] J. Catal. 993, 44, [] J. Catal. 0, 78, [3] Nature Chemistry 03, 5, 775. [4] PCCP 04, 6, [5] Angewandte Chemie-Internatinal Editin 005, 44, [6] Nature 04, 508, 504 [7] Acs Catalysis 03, 3, 8

3 Theretical study f the gemetrical, electrnic and catalytic prperties f metal clusters and nanparticles. Dctrad en Química Sstenible Estefanía Fernández Villanueva esfervi@dctr.upv.es Directr de tesis: Mercedes Brnat Zaragza brnat@itq.upv.es Institut de Tecnlgía química, UPV-CSIC Universidad Plitécnica de Valencia - Cnsej Superir de Investigacines Científicas Avda. de ls Naranjs s/n, 460 Valencia, Spain

4 Thesis main gal T study the reactivity f transitin metal (TM) clusters and nanparticles f increasing size and different structure by means f a theretical mdelling f the systems, in rder t help in the design f new catalysts. Cu atm cluster nanparticle bulk < nm 5 nm Increasing size

5 Backgrund and mtivatin TM nanparticles (-5 nm) are better catalysts than bulk: CO xidatin f Au supprted n TiO, α-fe O 3 and C 3 O 4 increases when particle size is < 4nm. Alchl xidatin ver Au/MgO is maximum at ~3nm particle size. Subnanmetric clusters (<nm) als catalyze imprtant reactins: Thiphenl (Ph-SH) xidatin t disulfide ((S-Ph) ) is maximum with Au clusters with 5-0 atms 3. Subnanmetric Ag clusters stabilize O and easily frm hydrperxides as reactin intermediates, while smaller clusters (n=3, 5) d nt 4. The causes fr these differences vary frm ne reactin t anther and are nt clear. Understanding them is key fr the synthesis f new catalysts. Similarly, cpper nanparticles catalyze imprtant industrial prcesses such as alchl syntheis 5 r the CO electrreductin t liquid fuels 6, and recently small clusters have als shwn catalytic activity 7. In additin, cpper has the industrial advantage f being a cheap resurce. [] J. Catal. 993, 44, [] J. Catal. 0, 78, [3] Nature Chemistry 03, 5, 775. [4] PCCP 04, 6, [5] Angewandte Chemie-Internatinal Editin 005, 44, [6] Nature 04, 508, 504 [7] Acs Catalysis 03, 3, 8

6 Research stages A first gal is t stablish an apprpriate methdlgy and then, in general, t study transitin metal systems f increasing size cmputatinally: The mst stable structures f neutral clusters per size, starting with Cu. The different adsrptin patterns f cmmn mlecules n the mst stable ismer per cluster size, starting with O. The catalytic activity f the clusters in certain reactins f interest, starting with O dissciatin, which includes: Transitin state (TS) study thrugh Ptential Energy Surface scans. Activatin energy (E act ) evaluatin as the difference between TS and reactants: E act = E TS E R. Reactin prducts (P) calculatins. Reactin energy (E reac ) evaluatin as the difference between P and reactants: E reac = E P E R.

7 Mdels and first results Neutral cpper clusters are planar up t n=6. Cu 3 Cu 4 Cu 5 Cu 6 Cu 7 Cu 8 Cu 3 Cu 38 The activatin energy fr xygen dissciatin decreases with cluster size as a cnsequence f the mrphlgy change.

8 Future wrk Similar stages will be fllwed at the B3PW9/Def-TZVP level with ther reactins: CO xidatin with xygen: CO + CO + O Water Gas Shift reactin (WGS): Prpene epxidatin: H Cun CO n O Cu CO + H + n O Cu Larger systems will als be studied with the p-pw9 methd. Other transitin metals r bimetallic systems will be included. Spectra simulatin is meant t be dne and cmpared with experimental results if the latter are available.

9 Cllabratin and applicatins Experimentally: Synthesis attempts. Spectrscpic characterizatin. Catalyst evaluatin. NEW OR IMPROVED CATALYSTS Theretically: Further understanding f results n bth sides. Structure cntrl, but many mre pssibilities. Characterizatin. Catalyst evaluatin.

10 Thank yu fr yur attentin!

11 j Theretical study f the gemetrical, electrnic and catalytic prperties f metal clusters and nanparticles. Dctrad en Química Sstenible Estefanía Fernández Villanueva, esfervi@dctr.upv.es Directr de tesis: Mercedes Brnat, brnat@itq.upv.es Institut de Tecnlgía química, UPV-CSIC, Universidad Plitécnica de Valencia Cnsej Superir de Investigacines Científicas, Avda. de ls Naranjs s/n, 460 Valencia, Spain Thesis main gal T study the reactivity f metal clusters and nanparticles f increasing size and different structure by means f a theretical mdelling f the systems, in rder t help in the design f new catalysts. Cu atm cluster nanparticle bulk Backgrund and mtivatin Transitin metal nanparticles with a diameter between and 5 nm have imprved catalytic prperties with respect t bulk metals. Subnanmetric clusters have been als identified as respnsible fr the catalytic activity in sme imprtant reactins. -4 The interest in understanding the causes fr this different behavir and the pssibility f discvering new effective catalysts fr different reactins is the main mtivatin f this thesis. [] Science 008, 3, [] Nature Mat. 009, 8, 3 [3] Science 0, 338, 45 [4] Nat. Chem. 03, 5, 775 < nm 5 nm Increasing size Cmputatinal details Research stages A first gal is t stablish an apprpriate methdlgy t study transitin metal systems f increasing size cmputatinally, specifically: The mst stable structures f neutral clusters per size. The different adsrptin patterns f cmmn mlecules n the mst stable ismer per cluster size. The catalytic activity f the clusters in certain reactins f interest. The methds emplyed are based n the Density Functinal Thery: Based n atm-centered gaussian rbitals DFT- Gaussian 09. Hybrid functinal B3PW9 with 6-3+G(d,p), LANLDZ and Def-TZVP basis sets and BPW9 functinal with Def-TZVP basis set (Cu atms). 6-3+G(d,p) basis set fr O atms. Atmic charges and MO distributins: NBO. Transitin states: PES scan. Plane-wave based peridic DFT VASP cde. Clusters placed in a 0x0x0 Å cubic cell. GGA PW9 functinal (labelled p-pw9) Cutff = 450 ev, PAW, Γ k-pint. Transitin states: DIMER Mdels and first results In rder t fulfill the previus research stages, we selected a variety f cmputatinal methds t study cpper clusters f size n=3-8, 3 and 38 alng with the adsrptin and dissciatin f ne xygen mlecule n them. Different ismers per cluster size are fund with energies clse t the grundstate structures: The activatin energy fr xygen dissciatin decreases with cluster size as a cnsequence f the mrphlgy change. Cu 3 Cu 4 Cu 5 Cu 6 Cu 7 Cu 8 Cu 3 Cu 38 Neutral cpper clusters are planar up t n=6. Future wrk Similar stages at the B3PW9/Def-TZVP level will be fllwed with ther reactins: CO xidatin with xygen: Water Gas Shift reactin (WGS): Prpene epxidatin: Spectra simulatin is meant t be dne and cmpared with experimental results if the latter are available. Larger systems will als be studied with the p-pw9 methd. Finally, ther transitin metals r bimetallic systems will be included. CO CO H O Cun CO O Cun CO H O Cu n Pssible applicatins The practical applicatin f this thesis relies upn the discvering and characterizatin f new catalysts based n small clusters f transitin metals and their prperties. Hpefully, the new catalysts fund will be either cheaper, mre efficient, mre selective r mre envirnmentally friendly than thse currently used fr the crrespnding reactin, and thus will have ptential industrial applicability. At the very least, this wrk will prvide sme insight n the behavir f transitin metal clusters and nanparticles and infrmatin that may aid in their future synthesis. Acknwledgement. We thank spanish MINECO fr financial supprt (prgrama Sever Ocha SEV-0-67 y Cnslider Ingeni Multicat CSD ). Red Españla de Supercmputación (RES) and Centre de Càlcul de la Universitat de València are gratefully acknwledged fr cmputatinal facilities and technical assistance. E. F. V. thanks spanish MINECO fr her fellwship SVP