1. Chemsheets AS006 (Electron arrangement)
24/02/2019
CATALYSIS
&
TRANSITIONAL
METALS
1 minute chem channel Ethanol to ethene with Al2O3

2. CATALYSTS - lower Ea Catalysts work by providing…
“AN ALTERNATIVE REACTION PATHWAY WHICH HAS A LOWER ACTIVATION ENERGY”
WITHOUT A CATALYST
WITH A CATALYST
A GREATER PROPORTION OF PARTICLES WILL HAVE ENERGIES
IN EXCESS OF THE MINIMUM REQUIRED SO MORE WILL REACT

3. MAXWELL-BOLTZMANN DISTRIBUTION
DUE TO THE MANY COLLISONS TAKING PLACE IN GASES, THERE IS A SPREAD OF MOLECULAR ENERGY AND VELOCITY
NUMBER OF MOLECUES WITH
A PARTICULAR ENERGY
EXTRA NUMBER OF MOLECULES WITH SUFFICIENT ENERGY TO OVERCOME THE ENERGY BARRIER
MOLECULAR ENERGY Ea
The area under the curve beyond Ea corresponds to the number of molecules with sufficient energy to overcome the energy barrier and react.
Lowering the Activation Energy, Ea, results in a greater area under the curve after Ea showing that more molecules have energies in excess of the Activation Energy

4. Heterogeneous Catalysis
3min
Heterogeneous Catalysis
Catalysts are in a different phases, the surface of a solid and the gas which adsorbs onto the surface forming weak bonds with metal atoms.
There are 3 stages...
Adsorption
Dissimilar surfaces cling together. Incoming a gas lands
on an active site (a solid), often a transitional metal.
Ex. (Pt)
Reaction
Adsorbed gases are held in just the right orientation for a reaction to occur. This increases the chances of favourable collisions taking place (satisfying both tenants (parts) of the Collision Theory.
Desorption
products are then
released from the metal

5. HETEROGENEOUS CATALYSTS
Example reaction – V2O5 in Contact Process. Which is catalyst and which is reaction intermediate?
Step 1: V2O5 + SO2  V2O4 + SO Fast
Step 2 : V2O4 + ½ O2  V2O5
Slow
Overall: SO2 + ½ O2  SO3

6. Heterogeneous Catalysis
ANIMATION

7. HETEROGENEOUS CATALYSTS
1) Reactants adsorbed onto surface (onto active sites). W
weakens bonds
brings molecules closer
more favourable orientation
2) Reaction takes place.
3) Products are desorbed (leave the surface).
Too strong (e.g. W)
Reactants cannot move round surface and products cannot desorb.
Too weak (e.g. Ag)
Reactants not adsorbed.
Ideal (e.g. Ni, Pt)

8. HETEROGENEOUS CATALYSTS
Chem Channel (1min)
Nature of catalyst
Large surface area.
Spread thinly over ceramic honeycomb.
Catalytic Poisons :
Some substances may block active sites (i.e. they adsorb and will not come off). Can ruin catalyst.
e.g. Pb in catalytic converters

9. Note it can be done with H2O
Homogeneous Catalysis
Catalyst and reactants are in the same phase and transition with metal ions
Example: Acids Catalyst in Esterificaton where all are (aq)
CH3COOH C2H5OH CH3COOC2H H2O
1(min)
No H+ catalyst
SLOW step
With H+ catalyst
FASTER.
Note it can be done with H2O
but much slower
H2O

10. HOMOGENEOUS CATALYSTS
Transition metal catalyst
works by metal varying oxidation state
Mn2+
e.g. 2 MnO H+ + 5 C2O42- → 2 Mn H2O + 10 CO2
the reaction is catalysed by one of the products (Mn2+) so is autocatalysis