Catalysts

Overview of Homogeneous and Hetergenous catalysts

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  • Created by: Maddie
  • Created on: 12-06-10 14:04

Hetrogeneous Catalysts

Catalytic Cracking- Zeolite Catalyst

Catalytic Converters- Platinum, Rhodium and palladium catalysts on a honeycomb structure to maximise surface area

Haber Process- Converting 3H2 + N2 -> 2NH3

Iron catalyst on aluminium oxide or iron oxide promoter

Contact Process - SO2 + 1/2O2 ---> SO3

V2O5 catalyst

V2O5 + SO2 ---> V2O4 + SO3

V2O4 + 1/2O2 ---> V2O5

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Hetrogeneous Catalysts

How do they work?

i) Aborption of reactants into active sites on surface + weak bonds form between catalyst + reactant

ii) Reaction - The bonds in the reactants are weakened + reactants held in correct orientation for reaction. Also increases local concentration so more collisions.

iii) Desorption of products from the nucleus- Weak bonds broken between product and catalyst. Products desorped from active site and diffuse away

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Homogenous Catalysts

They have variable oxidation states

Reaction of peroxdisulphate ions and iodide ions

S2O82- + 2I- ---> 2SO42- + I2

This is slow without a catalyst due to both of the ions being negatively charged and repelling each other

Fe2+ acts as a catalyst

S2O8 2- + 2Fe2+ ---> 2SO42- + 2Fe3+

2Fe3+ + 2I- ---> I2 + 2Fe2+

These are oppositely charged so attract each other

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Autocatalysis

Reaction between MnO4- and C2O42-

2MnO4- + 16H+ + 5C2O42- ---> 10CO2 + 2Mn2+ + 8H2O

This reaction is at first very slowdue to oppositely charged ions, however Mn2+ acts as a catalyst

4Mn2+ + MnO4- + 8H+ ---> 5Mn3+ + 4H2O

Mn3+ + C2O42- ---> 2CO2 + 2Mn2+

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Comments

KathrynSalvatore :)

Simple and to the point :) still have no idea how i'm gonna memorize the autocatalysis equations though, they're SO complicated :P

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