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Description
Using the formation of ethane from ethylene and hydrogen as an example, the mechanisms of heterogeneous and homogeneous catalysis are examined.
Using the formation of ethane from ethylene and hydrogen as an example, the mechanisms of heterogeneous and homogeneous catalysis are examined.
| Module code and title: | ST294, Principles of chemical processes |
|---|---|
| Item code: | ST294; 14 |
| First transmission date: | 08-09-1975 |
| Published: | 1975 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:23:57 |
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| Producer: | Barrie Whatley |
| Contributors: | Ian Boustead; Charles Harding; Joan Mason |
| Publisher: | BBC Open University |
| Keyword(s): | Arrehenius A factor; Desorption; Ethane formation; Heterogenous/homogenous catalysis; Rates of reaction; Surface reaction |
| Footage description: | Ian Boustead introduces the programme. He refers to the necessity of using catalysts in certain reactions and the desirability of knowing how the mechanism works. Joan Mason demonstrates a simple example of catalysis in the hydrogenation process. She ignites a jet of hydrogen, first with a match then with a piece of platinum gauze. Mason lists the two properties essential for a catalyst and then goes on to explain that the above demonstration is one of heterogeneous catalysis. Using a molecular model of a metal surface, Joan Mason briefly discusses the adsorption process which can bind other molecules to the surface. An animated film demonstrates, at the molecule level, the two kinds of adsorption taking place on a metal surface - physical adsorption and chemisorption. Commentary by Joan Mason explains the process in detail. In the animation an H2 molecule is broken and the hydrogen atoms are bonded to the nickel surface. Joan Mason uses the molecular model of the metal surface to demonstrate some of the properties of a surface metal hydride. Charlie Harding explains the energy relationships for the reaction of ethylene with hydrogen to produce ethane. He uses a graph which gives the variation with temperature of the equilibrium constant plotted as log Kp. Harding explains why this reaction needs a catalyst. Joan Mason briefly explains why nickel is chosen as the catalyst for this reaction. An animated film shows the adsorption of an ethylene molecule on a nickel surface. Joan Mason then uses the molecular model to demonstrate what is happening on the nickel surface. An animated film shows how the carbon-nickel bond is weakened by the carbon-hydrogen bond. Commentary by Mason. She then uses the surface molecular model to show the rotation of the methyl group on the metal surface. She explains why this is important to the process. An animated film shows, at the molecular level, the transition state, the formation of ethane and desorption of ethane to the gas stage. Charlie Harding considers reasons why the catalytic mechanism leads to faster reactions. He does this in terms of the Arrhenius equation but concentrates on activation energy rather than the A factor. Harding looks first at a potential energy diagram for the uncatalysed reaction of ethylene and hydrogen to form ethane. Harding explains what happens to the overall activation energy when a nickel catalyst is used. He then constructs a potential energy diagram for the above reaction showing just three activated steps - adsorption, reaction and desorption. The diagram shows why the catalysed reaction is faster that the uncatalysed one. Joan Mason begins a discussion of homogeneous catalysis. She uses a model of a Rhodium complex (Wilkinson's catalyst) as an aid. An animated film sequence shows the catalytic process at the molecular level. Commentary by Joan Mason explains what is happening. The reaction is, as before, the hydrogenation of ethylene. Charlie Harding looks at the potential energy diagram for this homogeneous catalysis reaction. While discussing the reaction, he also refers to a molecular model of the Rhodium complex. Joan Mason discusses the A factor in catalysed and uncatalysed gas reactions. She refers to molecular models as she talks. |
| Master spool number: | 6HT/71420 |
| Production number: | 00525_1166 |
| Videofinder number: | 754 |
| Available to public: | no |
