NANOSTRUCTURED OXIDES: NEW MATERIALS FOR ...Gianfranco Pacchioni – Dept. Materials Science –...
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NANOSTRUCTURED OXIDES: NEW MATERIALS FOR ENERGY AND ENVIRONMENT
http://www.mater.unimib.it/utenti/pacchioni
Quantum Chemistry Laboratory
Dipartimento di Scienza dei Materiali
Università Milano-Bicocca
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
THE GROUP AT UNIMIB
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Quantum Chemistry Laboratory
THREE MAIN RESEARCH LINES
Nanostructured oxides and thin films as model catalysts
(UHV, surface science)
Semiconducting oxides in photocatalysis
Band gap engineering
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Models of real catalysts
Concepts and interpretations
Nanostructured oxides and thin films
Model catalysts
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Real systems:
Au nano-catalyst on TiO2
TEM
Model systems:
Au nano-clusters on
MgO/Ag(100)
STM
Support
Noble metal
Diffusion
from gas
phase
Molecular
adsorption
Surface
diffusion
Product
desorption
Adsorbed
product
reaction
CO CO2
NO
N2
Dissociative
adsorption
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Density functional theory
Plane wave basis set
Pseudopotentials + Projector Augmented Wave (PAW, Blöchl)
DFT or DFT+U approach PW91, PBE, HSE functionals
vacuum
(1989-2012)
VASP (G. Kresse, J. Hafner (Technical Unv. of Vienna)
METHODS: DENSITY FUNCTIONAL THEORY
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Ricci, Bongiorno, GP, Landman, Phys. Rev. Lett. 97, 036106 (2006)
Sterrer, Risse, Heyde, Rust, Freund, Phys. Rev. Lett. 98, 206103 (2007)
GOLD NANOPARTICLES ON MgO ULTRATHIN FILMS
Electron transfer from oxide films to adsorbates (metal clusters, molecules) by electron tunneling
G. Pacchioni, 26/3/2015
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
STRUCTURAL CHANGE OF FeO/Pt(111) FILM UNDER O2 PRESSURE
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Giordano, Goniakowski, Shaikutdinov, GP, Freund et al. Angew. Chemie 49, 4418 (2010)
MAIN RESULTS
on ultrathin films spontaneous charging of supported clusters possible by direct tunneling; role of the metal/oxide work function
structural flexibility may lead to enhanced reactivity
Exploit nano-porosity to modify properties and generate assembly of ad-atoms and clusters
Doping of oxide films - charging can be induced by selective doping with TM atoms
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Semiconducting oxides in photocatalysis
Band gap engineering
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
R Abe, J.Photo-chem.Photobio.C.
2011, 11, 179.
A photon of suitable frequency excites an electron (e-) from VB to CB generating a hole (h+) in the valence band Recombination processes reduce efficiency Photon frequency needed for excitation depends on band gap value. The redox potential depends on the energy of e- (CB) and h+ (VB) with respect to the potential of the semi-reaction involved
Photoactivity: the mechanism
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
(1988-2009)
band structure theory
periodic supercell
Atomic orbital basis set
Allows one to treat exchange exactly (HF) and
to use hybrid DFT functionals (B3LYP)
Dovesi, Saunders, Roetti, Orlando, Zicovich-Wilson, Pascale, Civalleri, Doll, Harrison, Bush,
D’Arco, Llunell, CRYSTAL09 (University of Torino)
METHODS: DENSITY FUNCTIONAL THEORY
SEMICONDUCTING OXIDES: BAND GAP PROBLEM
TiO2 ZnO WO3 ZrO2
DOPED TiO2: B, C, N, F SUBSTITUTIONAL TO O
Paramagnetic defects
states in the gap
move down along the
series
F substitutional:
formation of Ti3+(3d1)
States are localized!
Systematic DFT-B3LYP calculations
Di Valentin, GP, Catal. Today 206, 12 (2013)
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
DOPED TiO2: B, C, N INTERSTITIALS
Interstitials more
stable than
substitutional
B and C interstitials act
as electron donors:
formation of Ti3+(3d1)
N forms “NO”
interstitials (proven by
EPR and XPS)
Defect states are
localized!
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Third generation photocatalysts Multi-photon excitations?
ZrO2, inert material as photocatalyst due to high band gap
Ce-doped ZrO2: under visible light material becomes active
e/h+ pairs generated by irradiation with visible light ( > 420 nm)
e/h+ pairs migrate to the surface
Ce introduces new states in the gap
Double excitation possible explanation
Gionco, Paganini, Giamello, Burgess, Di Valentin, GP, J. Phys. Chem. Lett. 5, 447 (2014)
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Oxygen vacancy in WO3: electrochromic windows
Charge state of O vacancy may explain effect; strong anisotropy of VO electronic structure
SEMICONDUCTING OXIDES: DEFECTS, DOPANTS, NANOSTRUCTURES
Doping of TiO2, ZnO WO3: photocatalytic water splitting
Dopants induce formation of VO and shifts VB and CB edges or introduce localized levels in the gap
(WO3)3 clusters on TiO2(110): heterogeneous catalysts
TiO2-x/WO3 interaction (charge transfer) determines reaction mechanism
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Models of real catalysts
Concepts and interpretations
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Au/TiO2 in CO oxidation at high temperature (FP7- CATSENSE project)
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
Oxide catalysts in biomass conversion
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
oxide surfaces
Ru, Ni particles
O reverse spillover
H spillover
ketonization
Hydro-deoxygention
Coke formation
H
H2O desorption
reduction
reaction
nanoparticles
Titania and zirconia in biomass conversion (FP7-CASCATBEL project)
P. Lievens
EXTERNAL COLLABORATIONS AND PROJECTS
Recent projects:
MIUR PRIN 2016-2019 – New materials for CO2 and H2 cataysis
MIUR FIRB 2011-2016 – Nanostructured oxides
Cariplo Foundation 2014-2017 – Oxides photocatalysis
DECORE – FP7 2012-2015 – Oxicarbides for fuel cells
CASCATBEL – FP7 2014-2018 – Oxide catalysts for biofuels
CATSENSE – FP7 2014-2018 – Metal clusters on oxides
COST CM1104 – 2013-2017 - Reducible oxides
HJ Freund N Nilius
Fritz Haber MPI Berlin
E Giamello
Univ. Torino
Univ. Leuven
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
G Granozzi
Univ. Padova J Behm
Univ. Ulm
REVIEW ARTICLES
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
REVIEW ARTICLES
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca
The University Milano Bicocca
Gianfranco Pacchioni – Dept. Materials Science – Univ. Milano Bicocca