Catalyst activation

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1. Topic Catalyst Activation

2. Catalyst: A catalyst is a substance which increases the rate of chemical reaction but remains chemically unchanged at the end of reaction. There are two classes. 1. Positive catalyst - increase the rate of the reaction. 2. Negative catalyst- decrease the rate of the reaction .

3. Catalyst activation: Such a substance which promotes the activity of catalyst is called “promotor” or “activator”.it is also called “catalyst for a catalyst”. such phenomenon is catalyst activation. Examples: Hydrogenation of vegetable oil to vegetable ghee is accelerated by nickel. the catalytic activity nickel is increased by using copper and tellurium. In the manufacture of ammonia in Haber process iron is used as a catalyst. If small amount of some high melting oxides like aluminium oxide or chromium oxides are added they increase the activity of iron catalyst. In the formation of alcohols chromium oxide is added into zinc oxide to increase its activity.

4. Auto catalyst activation: In some of reactions a product formed acts as a catalyst , this phenomenon is called as auto catalyst activation. Example: When a copper is react with nitric acid the reaction is slow in beginning. After some time it becomes faster due to formation of nitrous acid in the reaction which accelerates the process.

5. Catalytic Activity: A catalyst should be able to pass through the catalytic cycle multiple times. Higher the number of times the catalyst passes through this cycle, higher is the activity of the catalyst. The number of times that a catalyst can go through this cycle converting substrate molecule to product molecules is defined as the “turnover number”. In homogeneous systems, the “turnover frequency” is defined as the number of molecules of substrate converted into product per second. It depends upon adsorption of reactants on the surface of catalyst.

6. Catalytic Stability: A good catalyst should resist to deactivation, caused by the presence of impurities in feed and thermal deterioration. A solid catalyst should have reasonably large surface area needed for reaction (active sites). This is usually achieved by making the solid into a porous structure.

7. Catalyst activation enhance by two methods: Modify catalyst Modify process Change material(different promotors) optimize catalyst(promotor level , density , strength) Change reaction conditions(temp , pressure , flowrate) modify reactor(geometry , type)

8. Why we use catalyst activation in industrial process: I n industries we are mainly concerned with yield and time issues so we want the product to be formed as soon as possible. It decreases the activation energy required for a particular reaction. It speed u p the reaction and work at comparatively lower temperature. It fullfill our economic and environmental demand.

9. Factors affecting catalyst activation: Temperature Pressure Physical state Concentration of reactant

10. Advantages of catalyst activation: It increases rate of reaction. It reduces energy which is good for sustainable development. It saves time. It saves money.