Catalyst activation involves using a substance called a promotor or activator to increase the activity of a catalyst. This allows reactions to proceed faster and at lower temperatures. Some examples given include using copper and tellurium to increase the activity of nickel in hydrogenating vegetable oil, and adding aluminum oxide or chromium oxide to increase the activity of iron in the Haber process for ammonia synthesis. Catalyst activity can also be increased or auto-catalyst activated by products formed in the reaction itself, such as nitrous acid increasing the rate of a copper-nitric acid reaction. Modifying the catalyst material or process conditions such as temperature, pressure or flow rate can enhance catalyst activation for industrial processes where high yields and short time
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. Catalyst activation enhance by two methods:
1. Modify catalyst
2. Modify process
1. Change material(different promotors)
optimize catalyst(promotor level , density , strength)
2. Change reaction conditions(temp , pressure , flowrate)
modify reactor(geometry , type)
9. Why we use catalyst activation in industrial process:
In 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 up the reaction and work at comparatively lower temperature.
It fullfill our economic and environmental demand.
10. Factors affecting catalyst activation:
Temperature
Pressure
Physical state
Concentration of reactant
11. Advantages of catalyst activation:
It increases rate of reaction.
It reduces energy which is good for sustainable development.
It saves time.
It saves money.