AdvMat:AL Flashcards
4 types of chemical arrangemnet in bimetallics?
alloy
segregated
core@shell
onion
what influences species mixing?
- Bond strengths
- Surface energies
- size
- electronegativity
- ligands and supports
- Electronic/magnetic properties
- Temperature/Pressure
- Preparation methods
What structures are favoured by small nanoparticles
Icosahedron (Ih) more spherical. This is the most stable for small structures as it minimises surface area with (111) planes. The planes have close packing.
What structures are favoured by large nanaoparticles
As volume increase, it is more important to have no internal strain so a low SA isnt important anymore (V increases, SA decreases). FCC (100) structure is therefore favoured.
How to increase the work of adhesion
-Increase surface energy of metal by lowering the wetting angle
-Increase the surface energy of the support by adding defects (corners, less coordinated, higher energy, pinpoint to join to)
lowering the interface energy (Epitaxial & non epitaxial)
Predominant Crystal facet?
Ratio of surface energies = ratio of relative facet distances. Internal facet most stable.
Deviation from surface structure to lower surface energy
- Surface contraction(shortens bonds)
- Increase coordination number
Effect of reducible oxide and non reducible support on the nanoparticle.
Reducible oxides can become involved in reactions or encapsulate
nanoparticles (SMSI). Non-reducible oxides do not become involved
in the same way, and carbon is comparably inert.
Types of reactivity over nanoparticles
- Langmuir- Hinshelwood (LH)
- Eley-Ridel (ER)
- Mars Van Krevelen (MvK)
How temperature can influence structure
- Coalescence/Sintering
- Ripening
- Melting
- Recrystallisation
How to characterise metal surface
CO heavily used for surface characterisation
Q factor BCC
=2 if h+k+l=even
=4 otherwise
Q factor FCC
=1 h,k,l=odd
=2 otherwise
