Chemsheets AS006 (Electron arrangement) 24/02/2019 CATALYSIS & TRANSITIONAL METALS 1 minute chem channel Ethanol to ethene with Al2O3 https://www.youtube.com/watch?v=uudOD44TFZU

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

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

Heterogeneous Catalysis 3min https://www.youtube.com/watch?v=R27PkAWqSTc 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

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

Heterogeneous Catalysis ANIMATION

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)

HETEROGENEOUS CATALYSTS Chem Channel (1min) https://www.youtube.com/watch?v=6XxgiiA1e9s 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

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 CH3COOC2H5 + H2O 1(min) https://www.youtube.com/watch?v=1MoTHw1Rfxk No H+ catalyst SLOW step With H+ catalyst FASTER. Note it can be done with H2O but much slower H2O

HOMOGENEOUS CATALYSTS Transition metal catalyst works by metal varying oxidation state Mn2+ e.g. 2 MnO4- + 16 H+ + 5 C2O42- → 2 Mn2+ + 8 H2O + 10 CO2 the reaction is catalysed by one of the products (Mn2+) so is autocatalysis