SURFACE CHEMISTRY
Adsorption Substances which accelerate the rate of reaction and remain
Accumulation of molecular species at the surface rather than in the
Catalysis
bulk of a solid or liquid. chemically and quantitatively unchanged after the reaction are
Surface phenomenon known as catalysts and phenomenon is know as catalysis.
Concentration on the surface of adsorbent different Homogeneous Catalysis
from that in bulk.
Reactants and catalyst are in same phase.
(oxidation of SO2 to SO3 by NO as catalyst)
ADSORBATE SORPTION ADSORBENT
Hetrogenous Catalyst
Both adsorption & Material on the
Molecular species
surface of which
Reactants and catalyst are in different phases.
which concentrates absorption takes
place simultaneously the adsorption (Oxidation of SO2 to SO3 by Pt as catalyst)
at the surface.
takes place.
I
Adsorption Theory
Y S
Diffusion of reactants to surface of catalyst
P H
Adsorption of reactant molecules on the
surface of catalyst.
Physisorption
•Adsorption when accumulation of gas on the surface Chemical reaction on the surface of catalyst
of solid occurs due to weak van der Waals'forces.
through formation of intermediate.
•Non-specific
•Depends on nature of adsorbate Desorption of products creating
•Reversible surface for further reaction.
L L A
•Increases with increases in surface area. Diffusion of products away from
WA
•Low enthalpy of adsorption. catalyst surface.
types Chemisorption
•Adsorption when gas molecules or atoms are
held to surface by chemical bonds. Enzyme catalysis
Enzymes that catalyse many life processes in bodies of
• Highly specific plants and animals are termed as Biochemical catalysts
and phenomenon is known as Biochemical catalysis
• Irreversible (Inversion of sugar, Conversion of milk into curd)
• Increases with increase of surface area Mechanism
Step 1:
• High enthalpy of adsorption Binding of enzyme to substrate to form an
activated complex.
E + S ES
Step 2: Decomposition of activated complex to form
Features product..
ES E + P
• G, H and S are all negative.
Shape Selective catalysis
• Extent of adsorption increase with Catalytic reaction that depends upon pore structure of
surface area catalyst and size of reactant and product molecules.
(Zeolites)
Adsorption Substances which accelerate the rate of reaction and remain
Accumulation of molecular species at the surface rather than in the
Catalysis
bulk of a solid or liquid. chemically and quantitatively unchanged after the reaction are
Surface phenomenon known as catalysts and phenomenon is know as catalysis.
Concentration on the surface of adsorbent different Homogeneous Catalysis
from that in bulk.
Reactants and catalyst are in same phase.
(oxidation of SO2 to SO3 by NO as catalyst)
ADSORBATE SORPTION ADSORBENT
Hetrogenous Catalyst
Both adsorption & Material on the
Molecular species
surface of which
Reactants and catalyst are in different phases.
which concentrates absorption takes
place simultaneously the adsorption (Oxidation of SO2 to SO3 by Pt as catalyst)
at the surface.
takes place.
I
Adsorption Theory
Y S
Diffusion of reactants to surface of catalyst
P H
Adsorption of reactant molecules on the
surface of catalyst.
Physisorption
•Adsorption when accumulation of gas on the surface Chemical reaction on the surface of catalyst
of solid occurs due to weak van der Waals'forces.
through formation of intermediate.
•Non-specific
•Depends on nature of adsorbate Desorption of products creating
•Reversible surface for further reaction.
L L A
•Increases with increases in surface area. Diffusion of products away from
WA
•Low enthalpy of adsorption. catalyst surface.
types Chemisorption
•Adsorption when gas molecules or atoms are
held to surface by chemical bonds. Enzyme catalysis
Enzymes that catalyse many life processes in bodies of
• Highly specific plants and animals are termed as Biochemical catalysts
and phenomenon is known as Biochemical catalysis
• Irreversible (Inversion of sugar, Conversion of milk into curd)
• Increases with increase of surface area Mechanism
Step 1:
• High enthalpy of adsorption Binding of enzyme to substrate to form an
activated complex.
E + S ES
Step 2: Decomposition of activated complex to form
Features product..
ES E + P
• G, H and S are all negative.
Shape Selective catalysis
• Extent of adsorption increase with Catalytic reaction that depends upon pore structure of
surface area catalyst and size of reactant and product molecules.
(Zeolites)
