C atalysis. Sunny S urana b.Tech 1 st year u101112fbt145. What is catalysis???. A Catalyst is a substance that initiates or accelerates a chemical reaction without itself being affected. Catalysts provide an alternative reaction mechanism with a lower activation energy.
b.Tech 1st year
A Catalyst is a substance that initiates or accelerates a chemical reaction without itself being affected.Catalysts provide an alternative reaction mechanism with a lower activation energy.
Catalyst provide an alternative path for a reaction to proceed it does not lower the activation energy of the reaction.
---Catalyst is in the same phase as reactants
---Increase rate of reaction caused by catalyst allowing for reaction to occur with alternative mechanism with lower activation energy
---Catalyst is consumed at one stage in the mechanism and reformed at a later stage
---Catalyst is in different phase to reactants
---Catalyst provides reactive surface where reaction can take place; reactants are absorbed onto the surface
---This process weakens the bonding in molecules and brings them into close contact; reaction occurs on the surface and the products are desorbed; this frees the surface for further reaction
---Solid/Gas PhaseTypes of catalysis
Advantages---easily removed from products by filtration, easily recycled
Disadvantages---only effective on the surface, reaction mechanisms are poorly understood in general, poorly defined active site
Advantages---all the catalyst is exposed to the reactant, easily modified, reaction mechanisms are well understood by scientists, easy process of diffusion and heat transfer, well defined active site
Disadvantages--- can be difficult to remove from the products for reuse
After the adsorption the reaction takes place on the surface of the catalyst and these reactions are known as surface reactions
The two molecules A and B both adsorb to the surface. While adsorbed to the surface, the A and B "meet," bond, and then the new molecule A-B desorbs.Langmuir-Hinshelwood mechanism
One of the two molecules, A, adsorbs to the surface. The second molecule, B, meets A on the surface, having never adsorbed to the surface, and they react and bind. Then the newly formed A-B desorbs.Rideal-Eley mechanism
One of the two molecules, A, is adsorbed on the surface. The second molecule, B, collides with the surface, forming a mobile precursor state. The molecule B then collides with A on the surface, they react, bind and the new molecule desorbs.Precursor mechanism.
Dr. Khan has a doctorate degree in Heterogeneous Catalysis from Indian Institute of Chemical Technology (IICT), Hyderabad.
Materials/solid catalysts: zeolites, mesoporous materials, AlPO , redox molecular sieves, metal oxides