The document discusses the principles and characteristics of catalysts. It begins by defining catalysts as substances that accelerate chemical reactions by lowering activation energy without being consumed. It then discusses several key points about catalysts, including that they: (1) provide alternative reaction pathways with lower activation energies; (2) are regenerated after reactions and only small amounts are needed; and (3) do not change chemical equilibrium but help reactions reach equilibrium faster. The document also outlines general characteristics of catalysts such as specificity, inability to initiate reactions, and achieving maximum activity at an optimum temperature.

1. 1
INTRODUCTION
The systematic study of the effect of various foreign substances on the rates of
chemical reactions was first made by Berzelius in 1835. He suggested the term
catalyst for such substances. In Greek, kata = wholly, lein = to loosen.
CATALYST:
Substances, which accelerate the rate of a chemical reaction and themselves
remain chemically and quantitatively unchanged after the reaction, are known as
catalysts. For example, MnO2 acts as a catalyst for the following reaction
The phenomenon of increase in the rate of a reaction that results from the addition
of a catalyst is known as catalysis. The action of the catalyst can be explained on
the basis of intermediate complex theory.
According to this theory, a catalyst participates in a chemical reaction by forming
temporary bonds with the reactant resulting in an intermediate complex which
decomposes to yield product and the catalyst.
It is believed that the catalyst provides an alternative pathway or reaction
mechanism by reducing the activation energy between reactants and products and
hence lowering the potential energy barrier, and the reaction rate is increased .

2. 2
Although a catalyst lowers the activation energy Ea for a reaction, it does not
affect the energy difference ΔH between the products and reactants. It is clear
from Arrhenius equation, lower the value of activation energy (Ea) faster will be
the rate of a reaction.
(Note: Arrhenius equation is K = A e-Ea/RT, where A is the Arrhenius factor or
the frequency factor, R is gas constant, Ea is activation energy.)

3. 3
OBJECTIVE
The objective of writing this project is to clarify the basic concept of
“Catalysis”.
It involves briefly discussed topics on:-
 Catalyst
 Types of Catalyst (based on the effect of rate‟s of reations)
 Types of Catalytic Reactions
 Discussing past date introduction dates i.e., its “History”,
Principals ruling the mechanism of Catalysis and Background
involving past reactions from which the very concept of
“Catalysis” started and is field of application in Organic to In-
organic reactions as explained in the examples.
The later part of the project clarifies the concept of “Biocatalyst-
Enzymes”. It is an important topic and has been added in this project
because of its wide application in Organic macro to small molecule
synthesis to achieving the “Goals of Green Chemistry”.
* The section of Enzymes answer the following questions:-
What are Enzymes? Are Enzymes similar to catalyst? Is the nature of
Enzymes similar to Proteins? Mechanism of Enzymatic Reactions?

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MOTIVATION
The motivation to work on this Dissertation Topic Entitled “Catalysis”
was my own keen interest on understanding the basic concepts of
Catalyst, its efficient working mechanism in the reactions, its nature and
characteristics.
TECHNICAL PERSPECTIVE
In the presence of a catalyst, less free energy is required to reach the transition
state, but the total free energy from reactants to products does not change. A
catalyst may participate in multiple chemical transformations. The effect of a
catalyst may vary due to the presence of other substances known as inhibitors
or poisons (which reduce the catalytic activity) or promoters (which increase the
activity and also affect the temperature of the reaction).
Catalyzed reactions have a lower activation energy (rate-limiting free energy of
activation) than the corresponding uncatalyzed reaction, resulting in a higher
reaction rate at the same temperature and for the same reactant concentrations.
However, the detailed mechanics of catalysis is complex. Catalysts may affect the
reaction environment favorably(like heat), or bind to the reagents to polarize
bonds, e.g. acid catalysts for reactions of carbonyl compounds, or form specific
intermediates that are not produced naturally, such as osmate esters in osmium
tetroxide catalyzed dihydroxylation of alkenes, or cause dissociation of reagents to
reactive forms, such as chemisorbed hydrogen in catalytic hydrogenation.
Kinetically, catalytic reactions are typical chemical reactions; i.e. the reaction rate
depends on the frequency of contact of the reactants in the rate-determining step.
Usually, the catalyst participates in this slowest step, and rates are limited by
amount of catalyst and its "activity". In heterogeneous catalysis, the diffusion of
reagents to the surface and diffusion of products from the surface can be rate
determining. A nanomaterial-based catalyst is an example of a heterogeneous
catalyst. Analogous events associated with substrate binding and product
dissociation apply to homogeneous catalysts.
Although catalysts are not consumed by the reaction itself, they may be inhibited,
deactivated, or destroyed by secondary processes.
In heterogeneous catalysis, typical secondary processes include coking where the
catalyst becomes covered by polymeric side products. Additionally,
heterogeneous catalysts can dissolve into the solution in a solid–liquid system or
sublimate in a solid–gas system.

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BACKGROUND
The production of most industrially important chemicals involves catalysis.
Similarly, most biochemically significant processes are catalysed. Research into
catalysis is a major field in applied science and involves many areas of chemistry,
notably organometallic chemistry and materials science. Catalysis is relevant to
many aspects of environmental science, e.g. the catalytic converter in automobiles
and the dynamics of the ozone hole. Catalytic reactions are preferred in
environmentally friendly green chemistry due to the reduced amount of waste
generated, as opposed to stoichiometric reactions in which all reactants are
consumed and more side products are formed. Many transition metals and
transition metal complexes are used in catalysis as well. Catalysts
called enzymes are important in biology.
A catalyst works by providing an alternative reaction pathway to the reaction
product. The rate of the reaction is increased as this alternative route has a
lower activation energy than the reaction route not mediated by the catalyst.
The disproportionate of hydrogen peroxide creates water and oxygen, as shown
below.
2 H2O2 → 2 H2O + O2
This reaction is preferable in the sense that the reaction products are more stable
than the starting material, though the uncatalysed reaction is slow. In fact, the
decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions
are commercially available. This reaction is strongly affected by catalysts such
as manganese dioxide, or the enzyme peroxidase in organisms. Upon the addition
of a small amount of manganese dioxide, the hydrogen peroxide reacts rapidly.
This effect is readily seen by the effervescence of oxygen. The manganese dioxide
is not consumed in the reaction, and thus may be recovered unchanged, and re-
used indefinitely. Accordingly, manganese dioxide catalyses this reaction.

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GENERAL PRINCIPALS
Units
Catalytic activity is usually denoted by the symbol z and measured in mol/s, a
unit which was called katal and defined the SI unit for catalytic activity since
1999. Catalytic activity is not a kind of reaction rate, but a property of
the catalyst under certain conditions, in relation to a specific chemical reaction.
Catalytic activity of one katal (Symbol 1 kat = 1 mol/s) of a catalyst means an
amount of that catalyst (substance, in Mol) that leads to a net reaction of one Mol
per second of the reactants to the resulting reagents or other outcome which was
intended for this chemical reaction. A catalyst may and usually will have different
catalytic activity for distinct reactions. There are further derived SI units related to
catalytic activity, see the above reference for details.
Typical mechanism
Catalysts generally react with one or more reactants to form intermediates that
subsequently give the final reaction product, in the process regenerating the
catalyst. The following is a typical reaction scheme, where C represents the
catalyst, X and Y are reactants, and Z is the product of the reaction of X and Y:
X + C XC -------------------- 1
Y + XC XYC -------------------- 2
XYC CZ -------------------- 3
CZ C + Z -------------------- 4
Although the catalyst is consumed by reaction 1, it is subsequently produced by
reaction 4, so it does not occur in the overall reaction equation:
X + Y → Z
As a catalyst is regenerated in a reaction, often only small amounts are needed to
increase the rate of the reaction. In practice, however, catalysts are sometimes
consumed in secondary processes.
The catalyst does usually appear in the rate equation. For example, if the rate-
determining step in the above reaction scheme is the first step
X + C → XC, the catalyzed reaction will be second order with rate equation v =
kcat[X][C], which is proportional to the catalyst concentration [C]. However [C]

7. 7
remains constant during the reaction so that the catalyzed reaction is pseudo-first
order: v = kobs[X], where kobs = kcat[C].
As an example of a detailed mechanism at the microscopic level, in 2008 Danish
researchers first revealed the sequence of events
when oxygen and hydrogen combine on the surface of titanium dioxide (TiO2,
or titania) to produce water. With a time-lapse series of scanning tunneling
microscopy images, they determined the molecules
undergo adsorption, dissociation and diffusion before reacting. The intermediate
reaction states were: HO2, H2O2, then H3O2 and the final reaction product (water
molecule dimers), after which the water molecule desorbs from the catalyst
surface.
Reaction energetics
Generic potential energy diagram showing the effect of a catalyst in a hypothetical
exothermic chemical reaction X + Y to give Z. The presence of the catalyst opens
a different reaction pathway (shown in red) with a lower activation energy. The
final result and the overall thermodynamics are the same.
Catalysts work by providing an
(alternative) mechanism involving a
different transition state and
lower activation energy. Consequently,
more molecular collisions have the
energy needed to reach the transition
state. Hence, catalysts can enable
reactions that would otherwise be
blocked or slowed by a kinetic barrier.
The catalyst may increase reaction rate
or selectivity, or enable the reaction at
lower temperatures. This effect can be
illustrated with an energy
profile diagram.
In the catalyzed elementary reaction, catalysts do not change the extent of a
reaction: they have no effect on the chemical equilibrium of a reaction because the
rate of both the forward and the reverse reaction are both affected (see
also thermodynamics). The second law of thermodynamics describes why a
catalyst does not change the chemical equilibrium of a reaction. Suppose there
Figure:- Generic potential energy diagram showing the
effect of a catalyst in a hypothetical exothermic
chemical reaction X + Y to give Z. The presence of the
catalyst opens a different reaction pathway (shown in
red) with a lower activation energy. The final result and
the overall thermodynamics are the same.

8. 8
was such a catalyst that shifted an equilibrium. Introducing the catalyst to the
system would result in a reaction to move to the new equilibrium, producing
energy. Production of energy is a necessary result since reactions are spontaneous
only if Gibbs free energy is produced, and if there is no energy barrier, there is no
need for a catalyst. Then, removing the catalyst would also result in reaction,
producing energy; i.e. the addition and its reverse process, removal, would both
produce energy. Thus, a catalyst that could change the equilibrium would be
a perpetual motion machine, a contradiction to the laws of thermodynamics.
If a catalyst does change the equilibrium, then it must be consumed as the reaction
proceeds, and thus it is also a reactant. Illustrative is the base-
catalysed hydrolysis of esters, where the produced carboxylic acid immediately
reacts with the base catalyst and thus the reaction equilibrium is shifted towards
hydrolysis.
The SI derived unit for measuring the catalytic activity of a catalyst is the katal,
which is moles per second. The productivity of a catalyst can be described by
the turnover number(or TON) and the catalytic activity by the turn over
frequency (TOF), which is the TON per time unit. The biochemical equivalent is
the enzyme unit. For more information on the efficiency of enzymatic catalysis,
see the article on enzymes. The catalyst stabilizes the transition state more than it
stabilizes the starting material. It decreases the kinetic barrier by decreasing
the difference in energy between starting material and transition state. It does
not change the energy difference between starting materials and products
(thermodynamic barrier), or the available energy (this is provided by the
environment as heat or light).
Materials
The chemical nature of catalysts is as diverse as catalysis itself, although some
generalizations can be made. Proton acids are probably the most widely used
catalysts, especially for the many reactions involving water, including hydrolysis
and its reverse. Multifunctional solids often are catalytically active,
e.g. zeolites, alumina, higher-order oxides, graphitic carbon, nanoparticles,
nanodots, and facets of bulk materials. Transition metals are often used to
catalyze redox reactions (oxidation, hydrogenation). Examples are nickel, such
as Raney nickel for hydrogenation, and vanadium(V) oxide for oxidation of sulfur
dioxide into sulfur trioxide by the so-called contact process. Many catalytic
processes, especially those used in organic synthesis, require "late transition
metals", such as palladium, platinum, gold, ruthenium, rhodium, or iridium.

9. 9
Some so-called catalysts are really precatalysts. Precatalysts convert to catalysts
in the reaction. For example, Wilkinson's catalyst RhCl(PPh3)3 loses one
triphenylphosphine ligand before entering the true catalytic cycle. Precatalysts are
easier to store but are easily activated in situ. Because of this preactivation step,
many catalytic reactions involve an induction period.
Chemical species that improve catalytic activity are called co-
catalysts (cocatalysts) or promotors in cooperative catalysis.
GENERAL CHARACTERISTICS OF CATALYST
1. The catalyst remains unchanged at the end if the reactions-
The amount of catalyst remains chemically unchanged at the end of the reaction ,
though there may be change in the physical state such as particle state or change
in the colour of the catalyst , etc. This does not mean that the catalyst does not
take part in the reaction. In fact , it is essential for the catalyst to take part in the
reaction. To understand this apparent contradictions , consider the formation of
sulphur trioxide in the lead chamber process for the manufacture of sulphuric acid
, where sulphur dioxide and air are mixed with oxides of nitrogen. The catalyst is
nitric oxide which first reacts with oxygen to form nitrogen peroxide as:
NO(g) + ½ O2(g) NO2(g)
The nitrogen peroxide then reacts with sulphur dioxide to from sulphur trioxide
and nitric oxide is regenerated. Thus, although reacting chemically , the nitric
oxide is not used up.
NO2(g) + SO2(g) NO2 + SO3(g)
2. Only a small amount of the catalyst is generally needed-
A small amount of the catalyst can catalyse a large amount of reactants. For
example, 1 g of metallic platinum is sufficient to decompose 108 liters of H2O2.
while, some catalysts are required in relatively large amount to be effective.
For example, In Friedel-Crafts reaction, anhydrous aluminium chloride catalyst is
required to the extent of 30% of the mass of benzene.
3. Activity –
The activity of a solid catalyst is enhanced with increase in its surface area. Thus,
finely divided nickel is a better catalyst than lumps of nickel. Although the
meaning of activity can be explained as-

10. 10
(i) The ability of a catalyst to increase the rate of a chemical reaction is called
activity. A catalyst may accelerate a reaction to as high as 10^10 times.
(ii) Catalyst has an ability to increase the rate of reaction . This ability of
catalyst is known as the activity of catalyst. It depends upon adsorption of
reactants on the surface of catalyst.
(iii) Chemisorption is the main factor governing the activity of catalysts. The
bond formed during adsorption between the catalytic surface and the reactants
must not be too strong or too weak.
(iv) It must be strong enough to make the catalyst active whereas , not so strong
that the reactant molecules get immobilized on the catalytic surface leaving no
futher space for the new reactants to get adsorbed .
4. Catalyst is specific in its action.while a particular catalyst can be used for
one reaction, it will not necessarily work for another reaction. For example,
decomposition of KClO3 is catalyzed by MnO2 but not by platinum. Sometimes,
for the same substrate different catalyst yield different products.
However , transition metals are able to catalyse reactions of different types.
5. Catalyst cannot initiate a reaction. In most cases, it accelerates the reaction
already in progress.
6. Catalyst does not change the equilibrium constant of a reaction. It helps in
attaining the equilibrium faster, that is, it catalyses the forward as well the
backward reactions to the same extent so that the equilibrium state remains same
but is reached earlier.
7. Maximum activity of a catalyst is obtained at a particular temperature called
as optimum temperature.

11. 11
8. Catalyst does not change the enthalpy of reaction (∆H), i.e. it does not
affect the energy difference ∆H between the products and reactants.
9. A catalyst does not alter Gibbs energy, ∆G of a reaction.It catalyses the
spontaneous reactions but does not catalyse non-spontaneous reactions.
TYPES OF CATALYST
Positive Catalysts
The majority of catalysts are "positive catalysts." Positive catalysts speed up
chemical reactions. They are also referred to in science as "promoters."
Ex- Platinum is a catalyst in the contact process for the manufacture of sulphuric
acid .
Negative Catalyst
"Negative catalysts" slow down chemical reactions. These are used less
commonly than positive catalysts. A negative catalyst is referred to as an
"inhibitor."
Ex-Acetanilide retards the decomposition of hydrogen peroxide.
** Both negative and positive catalysts are used in very small amounts, as they are
reusable.
For both positive and negative catalysts, when the reaction has finished, you
would have exactly the same mass of catalyst as you had at the beginning.
TYPES OF CATALYTIC REACTIONS
Catalysts can be divided into two main types - heterogeneous and homogeneous.
In a heterogeneous reaction, the catalyst is in a different phase from the reactants.
In a homogeneous reaction, the catalyst is in the same phase as the reactants.
What is a phase?
If you look at a mixture and can see a boundary between two of the components,
those substances are in different phases. A mixture containing a solid and a liquid
consists of two phases. A mixture of various chemicals in a single solution
consists of only one phase, because you can't see any boundary between them.

12. 12
You might wonder why phase differs from the term physical state(solid, liquid or
gas). It includes solids, liquids and
gases, but is actually a bit more
general. It can also apply to two
liquids (oil and water, for example)
which don't dissolve in each other.
You could see the boundary between
the two liquids.
Heterogeneous catalysis
In heterogeneous catalysis , the catalyst used is in a different phase from the
reactants.
Typical examples involve a solid catalyst with the reactants as either liquids or
gases.
How the heterogeneous catalyst works (in general terms)?
Most examples of heterogeneous catalysis go through the same stages:
One or more of the reactants are adsorbed on to the surface of the catalyst at active
sites.
Adsorption is where something sticks to a surface. It isn't the same as absorption
where one substance is taken up within the structure of another. Be careful!
An active site is a part of the surface which is particularly good at adsorbing
things and helping them to react. There is some sort of interaction between the
surface of the catalyst and the reactant molecules which makes them more
reactive. This might involve an actual reaction with the surface, or some
weakening of the bonds in the attached molecules. The reaction happens.
At this stage, both of the reactant molecules might be attached to the surface, or
one might be attached and hit by the other one moving freely in the gas or liquid.
The product molecules are desorbed.

13. 13
Desorption simply means that the product molecules break away. This leaves the
active site available for a new set of molecules to attach to and react.
A good catalyst needs to adsorb the reactant molecules strongly enough for them
to react, but not so strongly that the product molecules stick more or less
permanently to the surface.
Silver, for example, isn't a good catalyst because it doesn't form strong enough
attachments with reactant molecules. Tungsten, on the other hand, isn't a good
catalyst because it adsorbs too strongly.
Metals like platinum , iron , copper and nickel make good catalysts because they
adsorb strongly enough to hold and activate the reactants, but not so strongly that
the products can't break away.
Some of the important examples of the heterogeneous catalysis are:
(i) Heterogeneous Catalysis involving Solid Reactants:
This type of reactions are not large in number. Decomposition of potassium
chlorate in presence of manganese dioxide as catalyst is an important of this type.
2KClO3(s) MnO2(s)
2KCl(s) + 3O2 (g)
(ii) Heterogeneous Catalysis involving Liquid Reactants:
Decomposition of hydrogen peroxide and hypochlorites in aqueous solution are
two important examples of heterogeneous catalysis involving liquid reactants.
2H2O2 (aq) 2H2O + O2
Ca(ClO)2 CaCl2 + O2
(iii) Heterogeneous Catalysis involving Gaseous Reactants:
In case of gaseous reactants , heterogeneous catalysis is more effective . Few
examples of them are:
(a.) Haber’ process for manufacture of ammonia in which nitrogen and
hydrogen in the ratio 1:3 are passed over heated iron catalyst having some
molybdenum as promoter.
N2 + 3H2 2NH3
(b.) Contact process for manufacture of sulphuric acid involves the oxidation of
SO2 to SO3 in the presence of platinum(Pt) catalyst.
SO2 + ½ O2 SO3
(c.) Hydrogenation of oils in presence of nickel catalyst.
R-CH=CH-R‟ + H2 RCH2CH2R‟(fat)
Unsaturated oil Saturated oil

14. 14
(d.) Ostwald process for the manufacture of nitric acid involves the oxidation of
nitrogen to nitric acid in presence of Pt catalyst.
N2 + O2 2NO
A general representation of hydrogenation of C=C ( carbon double bond carbon )
present in ethene in presence of nickel catalyst .
Ethene molecules are adsorbed on the surface of the nickel. The double bond
between the carbon atoms breaks and the electrons are used to bond it to the
nickel surface.
Hydrogen molecules are also adsorbed on to the surface of the nickel. When this
happens, the hydrogen molecules are broken into atoms. These can move around
on the surface of the nickel.
If a hydrogen atom diffuses close to one of the bonded carbons, the bond between
the carbon and the nickel is replaced by one between the carbon and hydrogen.

15. 15
That end of the original ethene now breaks free of the surface, and eventually the
same thing will happen at the other end.
As before, one of the hydrogen atoms forms a bond with the carbon, and that end
also breaks free. There is now space on the surface of the nickel for new reactant
molecules to go through the whole process again.
Homogeneous catalysis
This has the catalyst in the same phase as the reactants. Typically everything will
be present as a gas or contained in a single liquid phase. The examples contain one
of each of these . . .
Examples of homogeneous catalysis
(i) The reaction between persulphate ions and iodide ions:
This is a solution reaction that you may well only meet in the context of catalysis,
but it is a lovely example!
Persulphate ions (peroxodisulphate ions), S2O8
2-
, are very powerful oxidising
agents. Iodide ions are very easily oxidised to iodine. And yet the reaction
between them in solution in water is very slow.If you look at the equation, it is
easy to see why that is:

16. 16
The reaction needs a collision
between two negative ions. Repulsion is going to get seriously in the way of that!
The catalysed reaction avoids that problem completely. The catalyst can be either
iron(II) or iron(III) ions which are added to the same solution. This is another
good example of the use of transition metal compounds as catalysts because of
their ability to change oxidation state.For the sake of argument, we'll take the
catalyst to be iron(II) ions. As you will see shortly, it doesn't actually matter
whether you use iron(II) or iron(III) ions.
The persulphate ions oxidise the iron(II) ions to iron(III) ions. In the process the
persulphate ions are reduced to sulphate ions.
The iron(III) ions are strong enough oxidising agents to oxidise iodide ions to
iodine. In the process, they are reduced back to iron(II) ions again.
Both of these individual stages in the overall reaction involve collision between
positive and negative ions. This will be much more likely to be successful than
collision between two negative ions in the uncatalysed reaction.What happens if
you use iron(III) ions as the catalyst instead of iron(II) ions? The reactions simply
happen in a different order.
(ii) The destruction of atmospheric ozone
This is a good example of homogeneous catalysis where everything is present as a
gas.
Ozone, O3, is constantly being formed and broken up again in the high atmosphere
by the action of ultraviolet light. Ordinary oxygen molecules absorb ultraviolet
light and break into individual oxygen atoms. These have unpaired electrons, and
are known as free radicals. They are very reactive.

17. 17
The oxygen radicals can then combine with ordinary oxygen molecules to make
ozone.
Ozone can also be split up again into ordinary oxygen and an oxygen radical by
absorbing ultraviolet light.
This formation and breaking up of ozone is going on all the time. Taken together,
these reactions stop a lot of harmful ultraviolet radiation penetrating the
atmosphere to reach the surface of the Earth.
The catalytic reaction we are interested in destroys the ozone and so stops it
absorbing UV in this way.
Chlorofluorocarbons (CFCs) like CF2Cl2, for example, were used extensively in
aerosols and as refrigerants. Their slow breakdown in the atmosphere produces
chlorine atoms - chlorine free radicals. These catalyse the destruction of the
ozone.
This happens in two stages. In the first, the ozone is broken up and a new free
radical is produced.
The chlorine radical catalyst is regenerated by a second reaction. This can happen
in two ways depending on whether the ClO radical hits an ozone molecule or an
oxygen radical.
If it hits an oxygen radical (produced from one of the reactions we've looked at
previously):
Or if it hits an ozone molecule:

18. 18
Because the chlorine radical keeps on being regenerated, each one can destroy
thousands of ozone molecules.
(iii) Decomposition of Acetic acid to ketone :-
The decomposition of acetic acid to ketone at 650˚C catalyzed by
triethylphosphate is another example of reactions in gaseous phase .
CH3COOH CH2CO + H2O
(iv) Oxidation of CO by Nitric acid:-
Nitric oxide gas also acts as a catalyst in the combination of CO with oxygen.
2CO + O2(g) 2CO2
Inhibitors, poisons, and promoters
Substances that reduce the action of catalysts are called catalyst inhibitors if
reversible, and catalyst poisons if irreversible. Promoters are substances that
increase the catalytic activity, even though they are not catalysts by themselves.
Inhibitors are sometimes referred to as "negative catalysts" since they decrease the
reaction rate. However the term inhibitor is preferred since they do not work by
introducing a reaction path with higher activation energy; this would not reduce
the rate since the reaction would continue to occur by the non-catalyzed path.
Instead they act either by deactivating catalysts, or by removing reaction
intermediates such as free radicals.
The inhibitor may modify selectivity in addition to rate. For instance, in the
reduction of alkynes to alkenes, a palladium (Pd) catalyst partly "poisoned"
with lead(II) acetate(Pb(CH3CO2)2) can be used. Without the deactivation of the
catalyst, the alkene produced would be further reduced to alkane.
The inhibitor can produce this effect by, e.g., selectively poisoning only certain
types of active sites. Another mechanism is the modification of surface geometry.
For instance, in hydrogenation operations, large planes of metal surface function
as sites of hydrogenolysis catalysis while sites catalyzing hydrogenation of
unsaturates are smaller. Thus, a poison that covers surface randomly will tend to
reduce the number of uncontaminated large planes but leave proportionally more

19. 19
smaller sites free, thus changing the hydrogenation vs. hydrogenolysis selectivity.
Many other mechanisms are also possible.
Promoters can cover up surface to prevent production of a mat of coke, or even
actively remove such material (e.g., rhenium on platinum in platforming). They
can aid the dispersion of the catalytic material or bind to reagents.
AUTO CATALYSIS:
When one of the products formed during the course of reaction itself act as a
catalyst for that reaction the phenomenon is called as autocatalysis. In normal
reaction, the rate of reaction decreases with the passage of time. However, in
autocatalysis, as the reaction proceeds, concentration of catalytic product increases
and so the rate of reaction increases.
Examples: (1) Hydrolysis of methyl acetate is catalysed by H+ ions furnished by
acid. As the reaction proceeds, concentration of catalyst (H+ ) increases and
hence, the rate of reaction increases.
(2). In the titration of oxalic acid (H2C2O4) with acidified potassium
permanganate (KMnO4), the reaction is slow in the beginning but becomes fast
as the reaction progresses. Manganese sulphate or Mn2+ ions produced during
the reaction acts as autocatalyst for the reaction. As the concentration of Mn2+
ions increases with time, the rate of reaction increases with time. Hence, the time
required for decolourisation of first drop of KMnO4 is much higher and it goes
on decreasing with time.

20. 20
SPECIFICITY (Qualitative treatment)
A catalyst is generally specific in its action. A particular catalyst can catalyst only
specific reaction and can‟t be used for every reaction. Ex- Manganese Dioxide can
catalyses the decomposition of Potassium Chlorate but not that of Potassium
Nitrate or Potassium Perachlorite. However, transition metal catalyzes reactions of
different types. Also the activity of a catalyst depends upon the strength of
chemisorptions to a large extent. the reactant must get adsorbed strongly onto the
catalyst to became active the adsorbed portion should not be so that strong they
are immobilized and other reactant are left with no space on the catalyst surface
for adsorption. It may be noted that for hydrogenation reaction the catalyst activity
increases from Grp5 to Grp11 metals. The maximum activity is shown by
elements of Grp7-9 in the periodic table.
2H2 (g) + O2 Pt
2H2O(l)
SELECTIVITY (Quantitative treatment)
The selectivity of a catalyst is its ability to direct a reaction to yield a particular
product. Consider the combination of hydrogen and carbon mono-oxide using
different catalyst to form different products.
(I) When the nickel used as catalyst methane is formed.
CO (g) + 3H2 (g) Pt CH4 (g) + H2O (g)
Carbon Monoxide Methane
(II) When oxide of zinc and chromium along with copper is used as catalyst .
CO (g) + 2H2 (g) ZnO-Cr2O3 CH3OH (g)
(III) When copper is used as catalyst then formaldehyde results.
CO (g) + H2 (g) Cu HCHO (g)

21. 21
Thus we can say that the action of catalyst is highly selective in nature. It means
that a given substance can act as catalyst only in a particular reaction and not for
all reactions. In others words, a substance which act as a catalyst may fail to
catalyse another reaction.
Certain reactions depend upon the pores and structure of the catalyst and the size
of the reactant and the product molecules. This are called Shape Selective
Catalyst. Zeolites are good shape selective catalyst due to their honey –comb like
structures. They are microporous aluminosilicate with three dimensional network
of silicate in which some silicon atoms are replaced by aluminuim atom giving
Al-Si-O frame work. The reactions which take place in zeolites depend upon the
size and shape of reactant and product molecules as well as open the pores and
cavities of the zeolites . These are found in nature and also synthesized for catalyst
selectivity. These are widely used as catalyst in petrochemical industries for
cracking of hydrocarbons and isomerisation. ZSM-5 is an important zeolite
catalyst used in petrochemical industries. The catalyst converts alcohols directly
in to gasoline or petrol by dehydrating them to give a mixture of hydrocarbons.
EFFECT OF A PARTICLE SIZE AND EFFIENCY OF NANO-
PARTICLES AS CATALYST:-
The modern adsorption theory of catalysis explains the efficiency of finely
divided catalyst. Finely divided colloidal catalyst particles have large surface area.
Ex-surface of a block of 1cm3 becomes 10000times when broken down to
particles having a size of 1(10-4cm) and 1 million times if ground to particulate
size of 1m. Nano-particles provided still efficient then the solid catalyst. This
explains why finely divided nickel is more efficient in hydrogenation of oils and
finely divided platinum more effective in oxidation of SO2 to SO3. In contact
process for the manufacture of sulphuric acid.

22. 22
SIGNIFICANCE
Estimates are that 90% of all commercially produced
chemical products involve catalysts at some stage in the
process of their manufacture. In 2005, catalytic
processes generated about $900 billion in products
worldwide. Catalysis is so pervasive that subareas are
not readily classified. Some areas of particular
concentration are surveyed below.
Energy processing
Petroleum refining makes intensive use of catalysis
for alkylation, catalytic cracking (breaking long-chain
hydrocarbons into smaller pieces), naphtha reforming
and steam reforming (conversion
of hydrocarbons into synthesis gas). Even the exhaust
from the burning of fossil fuels is treated via
catalysis: Catalytic converters, typically composed
of platinum and rhodium, break down some of the more
harmful byproducts of automobile exhaust.
2 CO + 2 NO → 2 CO2 + N2
With regard to synthetic fuels, an old but still important
process is the Fischer-Tropsch synthesis of hydrocarbons from synthesis gas,
which itself is processed via water-gas shift reactions, catalysed by
iron. Biodiesel and related biofuels require processing via both inorganic and
biocatalysts.
Fuel cells rely on catalysts for both the anodic and cathodic reactions.
Catalytic heaters generate flameless heat from a supply of combustible fuel.
Bulk chemicals
Some of the largest-scale chemicals are produced via catalytic oxidation, often
using oxygen. Examples include nitric acid (from ammonia), sulfuric
acid (from sulfur dioxide to sulfur trioxide by the contact process), terephthalic
acid from p-xylene,
and acrylonitrile from propane and ammonia.
Many other chemical products are generated by large-scale reduction, often
via hydrogenation. The largest-scale example is ammonia, which is prepared via
the Haber process from nitrogen. Methanol is prepared from carbon monoxide.
Bulk polymers derived from ethylene and propylene are often prepared
via Ziegler-Natta catalysis. Polyesters, polyamides, and isocyanates are derived
via acid-base catalysis.
Figure 1:-Left: Partially caramelised cube
sugar, Right: burning cube sugar with ash as
catalyst
Figure 2:-A Ti-Cr-Pt tube (~40 μm long)
releases oxygen bubbles when immersed in
hydrogen peroxide (via catalytic
decomposition), forming a micropump

23. 23
Most carbonylation processes require metal catalysts, examples include
the Monsanto acetic acid process and hydroformylation.
Fine chemicals
Many fine chemicals are prepared via catalysis; methods include those of heavy
industry as well as more specialized processes that would be prohibitively
expensive on a large scale. Examples include the Heck reaction, and Friedel–
Crafts reactions.
Because most bioactive compounds are chiral, many pharmaceuticals are
produced by enantioselective catalysis (catalytic asymmetric synthesis).
Food processing
One of the most obvious applications of catalysis is the hydrogenation (reaction
with hydrogen gas) of fats using nickel catalyst to produce margarine. Many other
foodstuffs are prepared via biocatalysis.
Environment
Catalysis impacts the environment by increasing the efficiency of industrial
processes, but catalysis also plays a direct role in the environment. A notable
example is the catalytic role of chlorine free radicals in the breakdown of ozone.
These radicals are formed by the action
of ultraviolet radiation on chlorofluorocarbons (CFCs).
Cl·
+ O3 → ClO·
+ O2
ClO·
+ O·
→ Cl·
+ O2

24. 24
HISTORY
Generally speaking, anything that increases the rate of a process is a "catalyst", a
term derived from Greek καταλύειν, meaning "to annul," or "to untie," or "to pick
up." The concept of catalysis was invented by chemist Elizabeth Fulhame and
described in a 1794 book, based on her novel work in oxidation-reduction
experiments. The term catalysis was later used by Jöns Jakob Berzelius in 1835 to
describe reactions that are accelerated by substances that remain unchanged after
the reaction. Fulhame, who predated Berzelius, did work with water as opposed to
metals in her reduction experiments. Other 18th century chemists who worked in
catalysis were Eilhard Mitscherlich who referred to it as contact processes,
and Johann Wolfgang Döbereiner who spoke of contact action. He
developed Döbereiner's lamp, a lighter based on hydrogen and a platinum sponge,
which became a commercial success in the 1820s that lives on today. Humphry
Davy discovered the use of platinum in catalysis. In the 1880s, Wilhelm
Ostwald at Leipzig University started a systematic investigation into reactions that
were catalyzed by the presence of acids and bases, and found that chemical
reactions occur at finite rates and that these rates can be used to determine the
strengths of acids and bases. For this work, Ostwald was awarded the 1909 Nobel
Prize in Chemistry.
----------
Hence in order to conclude the topics covered in above chapter:
Catalyst‟s pre-structured definition, Catalyst‟s market importance, field of
application and countries researching on its advancement has been short noted as
below: Catalysts are supplementary chemicals compounds that are added in small
amounts to enhance the rate of chemical reaction. Catalyst does not undergo any
type of chemical changes in them. Catalyst reduces reaction time and energy
required to complete a chemical reaction. They are highly specific and selective
in action. With the advancement in molecular chemistry, the catalysis control
over the broad range of chemical reaction has been observed in past years.
Catalyst is one of the most important areas of chemical industry, where
increasing investment in research and development is observed even during the
economic slowdown.
Based on the product type, the global catalyst market can be broadly segmented
as, heterogeneous catalyst and homogeneous catalyst. And based on its catalytic
activity as, Positive and Negative Catalyst.
ADVANCEMENT: The global demand on catalysts in 2010 was estimated at
approximately 29.5 billion USD. Based on the various application of catalyst the
market can be segmented as refinery, chemical synthesis, polymer and
environment. Chemical compound has been the largest segment of the catalyst
market in 2014.

25. 25
ENZYME CATALYSIS
The first enzyme was synthesised in the laboratory in 1969.Enzymes are also
proteins which act as catalyst in many bio-chemical reactions this are the
important group of globular proteins which acts as essential biological catalyst in
living system. Enzymes are specific in action. They are specific activity is due to
specific structural arrangement by heating its specific form structural
arrangement is changed irreversibly. This results in conversation of enzyme into
fibrous or insoluble form , due to this irreversible change enzymes lose their
specific activity when heated .
Numerous reactions that occur in the bodies of animals and plants to maintain
the life process are catalyzed by enzymes. The enzymes are, thus, termed as
biochemical catalysts and the phenomenon is known as biochemical catalysis.
The following are some of the examples of common enzyme-catalyzed
reactions:
1. Inversion of cane sugar into glucose and fructose by invertase enzyme.
2. Conversion of glucose into ethyl alcohol and carbon dioxide by zymase
enzyme.
3. Conversion of starch into maltose by diastase enzyme.
4. Conversion of maltose into glucose by maltase enzyme.

26. 26
5. Decomposition of urea into ammonia and carbon dioxide by urease enzyme.
6.
7.
8.
6. In stomach, the pepsin enzyme converts proteins into peptides while in
intestine, the pancreatic trypsin converts proteins into amino acids by
hydrolysis.
7. Conversion of milk into curd: It is an enzymatic reaction brought about by
lacto bacillienzyme present in curd.

27. 27
NATURE OF ENZYMES:-
Enzyme are essential protein and show their catalytic properties. Enzymes are
defined as a protein with catalytic properties due to their specific activation.
Following are the point which prove the protein nature of enzyme:
(i) Composition:- Regarding elementary composition , enzymes show the
usual proportions of C,H,N,S as found in proteins. Some crystalline enzymes do
contain minute quantities of phosphorous and metal ions. On hydrolysis, such
enzymes produce amino acids.
(ii) Amphoteric nature:- Like proteins, enzymes behaves as ampholytes in the
electric field and their isoelectric points have also been found.
(iii) Denaturation:- Enzymes also get denatured like the proteins under
unfavourable conditions of pH and temperature.
(iv) Formation of anti-bodies:-It is found that many purified enzymes when
injected in the body produce specific antibodies.
CHARACTERISTICS OF ENZYME CATALYSIS:-
1. One molecule of an enzyme may transform one million molecules of the
reactant per minute.
2. Each enzyme is specific for a given reaction, i.e., one catalyst cannot catalyse
more than one reaction. For example, the enzyme urease catalyses the
hydrolysis of urea only.
3. The rate of an enzyme reaction become maximum at a definite temperature,
called the optimum temperature. On either side of the optimum temperature,
the enzyme activity decreases. The optimum temperature range for enzymatic
activity is 298-310K. Human body temperature being 310 K is suited for
enzyme-catalysed reactions.
4. The rate of an enzyme-catalysed reaction is maximum at a particular pH called
optimum pH, which is between pH values 5-7.
5. The enzymatic activity is increased in the presence of certain substances,
known as co-enzymes.
6. The inhibitors interact with the active functional groups on the enzyme surface
and often reduce or completely destroy the catalytic activity of the enzymes.

28. 28
7. Effect of temperatue – Enzymes are very
efficient near body temperature. Above this
temperature, they lose their activity. At lower
temperature, the rate of enzyme-catalysed
reactions are slow because of kinectics
effects. In general, all chemical reactions
proceed faster with increase in temperature
but the rate of enzyme catalysed reaction first
increase , become maximum at about 35-
40˚C and then decrease at higher temperature.
8. Effect of pH- The effect of pH on the rate of
enzyme reaction is complex. The rate of an
enzyme catalysed reaction passes through a
maximum at an optimum pH. At higher or lower
pH than the optimum value, the enzymes
become less active.
FISCHER‟S LOCK AND KEY MODEL
According to this model, the union between the substrate and the enzyme takes
place at the active site more or less in a manner in which a key fits in a lock
results in the formation of an enzyme-substrate complex. The union depends on a
reciprocal fit between the molecular substrate of the enzyme and the substrate.
The enzyme-substrate(E-S) complex is highly unstable and almost immediately,
this complex breaks to produce the end-product of the reaction and to regenerate
the free enzyme releasing energy.
MECHANISM-
(i) The reactant molecule (substrate) binds itself to the enzyme (E) to form
a complex ES i.e., enzyme-substrate complex.
E + S ES
(ii) Product is formed in the complex.
ES EP
(iii) The enzyme product finally decomposes to give product molecules and
enzyme is regenerated.
EP E + P
Enzymes are highly specific in their action because the enzyme activity is present
only in certain specific regions on their surfaces, this sites are called as active sites

29. 29
or catalytic sites. The shape of the active site of any given enzyme is such that
only a particular substrate can fit into the particular active site.
KOSHLAND‟S INDUCED FIT MODEL
The unfortunate feature of Fischer‟s model (point a in the above fig.) is the
rigidity of the active site. The avtive site is presumed to be pre-shaped to fit the
substrate. Koshland modified this concept (as per the point b in the above fig.) and
stated that- “The enzyme molecule do not retain its original shape structure.” But
the contact of the substrate induces some configurational or geometrical changes
in the active site of the enzyme molecule. As a result, the enzyme molecule is
made to fit fit completely the configuration and active centers of the substrate. At
the same time, other amino acid residues may become buried in the interior of the
molecule. In the absence of substrate , the substrate binding and catalytic groups
are far apart from each other. But the proximity of the substrate induces a
conformational change in the enzyme molecule aligning the groups for both
substrate binding and catalysis. Simultaneously, the spatial orientation of other
regions is also changed so that the substrate and the active site are closer.

30. 30
MECHANISM OF ENZYME CATALYSIS:-
There are a number of cavities present on the surface of enzymes. These cavities
are of characteristic shape and possess active groups like -NH2, -COOH, -SH, -
OH, etc.
These are actually the active centres on the surface of enzyme particles. Molecules
of the substrate, which have complementary shape, fit into these cavities just like
a key fits into a lock.
Thus, the enzyme-catalysed reaction proceeds in two steps.
Step 1: Binding of enzyme (E) to substrate (S) forms enzyme substrate
complex(ES)
Step 2: Decomposition of the enzyme substrate (ES) complex to form product (P)

31. 31
KINETICS OF ENZYME CATALYSED REACTIONS:
MICHAELIS-MENTEN EQUATION
In 1913, Michaelis and Menten proposed a mechanism for the kinetics of enzyme
catalyzed reaction. It involves two steps:
Step I: The enzyme (E) reacts with the substrate (S) to form enzyme-substrate
complex(ES). This is a reversible process and equilibrium is established rapidly.
Step II: The ES complex undergoes dissociates to give product (P) and enzyme
(E).
Second step is the slow and rate determining step.
Thus, Rate of reaction = - d[S] = d[P] = K2[ES] .....(3)
dt dt
But, [ES] is not an experimentally measurable quantity.
Solve for intermediate [ES],
d[ES] = K1[E][S] – K-1[ES] – K2[ES]
dt
Use of steady state approximation for [ES]
We get, d[ES] = 0
dt
d[ES] = K1[E][S] – K-1[ES] – K2[ES] = 0 …..(4)
dt
Instead of solving for [ES] in terms of Free enzyme [E], solve for [ES] in terms of
Total enzyme [E]0.
Total enzyme [E]0 = Free enzyme [E] + Bound enzyme [ES]
[E] = [E]0 – [ES] …..(5)
Replace [E] = [E]0 – [ES] from equation (5) in equation (4)
d[ES] = K1{[E]0 –[ES]} [S] – K-1[ES] – K2[ES] = 0

32. 32
dt
d[ES] = K1[E]0 [S] – K1[ES] [S] – K-1[ES] – K2[ES] = 0
dt
Rearrange [ES] terms to one side of the equation
K1 [ES] [S] + K-1 [ES] + K2 [ES] = K1 [E]0 [S]
[ES] {K1 [S] + K-1 + K2} = K1 [E]0 [S]
[ES] = K1 [E]0 [S] …..(6)
K-1 + K2 + K1[S]
Dividing the numerator and denominator by K1
[ES] = K1 [E]0 [S] ÷ K1 = K1 [E]0 [S]
{ K-1 + K2 + K1 [S]} ÷ K1 K1 { K-1 + K2 + K1 [S]} ÷ K1
[ES] = K1 [E]0 [S] = [E]0 [S] …..(7)
K1 { K-1 + K2 + K1 [S]} { K-1 + K2} + {K1 [S]}
K1 K1 K1
Introduce new term Km (Michaelis-Menten constant) in equation (7)
Where, Km = K-1 + K2
K1
[ES] = [E]0 [S] …..(8) (Since, K-1 + K2 = Km )
[S] + Km K1
Substitute [ES] into equation (3)
(a) When [S] >> Km, then neglecting Km as compared to [S]
Rate of product formation = K2 [E]o [S] = K2 [E]0
[S] + Km (small and is neglected)
This is called Vmax.
Maximal rate = Vmax = K2 [E]0
(b) When [S] = Km, then
Rate of product formation = K2 [E]0 [S] = K2 [E]0 [S] = 1 K2 [E]0half
[S] + [S] 2[S] 2
Definition of Michaelis constant (Km) = concentration of [S] for which the rate is half-maximal.

33. 33
Thus, in order to conclude the concept of “Enzyme Catalysis” it can be short
noted as- Enzymes (biocatalyst) are similar to proteins in nature and
characteristics. It acts as a catalyst in many biochemical reactions. There are
specific and selective in nature due to its specific structural arrangement in them.
They are sensitive to pH and temperature changes. The catalytic activities of
enzymes can be regulated by certain non-protein components.
Enzymes are considered as true catalysts because they are not consumed in the
process and keep working as long as the substrate reactant is present e.g. as long
sugar is left in an aqueous solution mixed with yeast.
Enzymes have been used by humans since the beginning of recorded history e.g.
use in fermentation to make wine.
Enzymes are becoming increasingly important in the “biotechnology” industry.
Enzyme reactions happen inside living cells. However, dead cells that have been
broken open to release their enzymes and used to let the process happen in test
tubes or for large scale industrial production situations.
Based on the various application of catalyst the market can be segmented as
refinery, chemical synthesis, polymer and environment. Chemical compound has
been the largest segment of the catalyst market in 2014. The segment is also
expected to witness considerable growth during the forecast period, attributed to
its cost-effective working capacity, as compared to other type of catalyst. Based
on the product type, heterogeneous catalyst has been the largest segment in 2014.
Rising demand for clean fuels is one of the most important driving factors for the
catalyst market in refineries. In addition, the growth of end user industries such as
polymer and chemical industries has also increased the demand of catalyst in
recent years. The rising demand from developing economies owing to the
increasing number of vehicles, growing purchasing power and rapid expansion of
oil refineries is expected to drive the catalyst market during the forecast period.
The development of innovative product portfolio in catalyst market is one of the
recent trends in the industry. However, the fluctuating prices of raw material are
one of the major hindrances for the global catalyst market .
Asia Pacific was the largest and fasted growing market of catalyst in 2014.
The market dominance of Asia Pacific is attributed to the presence of large
number of refineries in India and China: two major importer of crude oil in the
world. In addition, the rising number of vehicles and increasing demand of plastic
from the developing countries of Asia Pacific is also driving the catalyst market.
India, China and Japan are some of the major markets of catalyst in Asia Pacific.

34. 34
SUMMARY
In order to summaries the presented ideas and concept on “CATALYSIS”
following Questions, terms and their pre-structured definitions are enough.
What are Catalyst?
A catalyst would be that substance which gives an option of a shortcut, bypassing
that lengthy, energy consuming reaction pathways . By giving a new alternate
route, reaction can proceed going towards “A...saving time and energy process.”
In other words, a catalyst is a substance that increases the rate of a
reaction, without being used up itself. Remember that if it got used up, then it
would be a reactant.
This process is called 'Catalysis'.
Biocatalysts are called „Enzymes‟.
Depending upon the Catalyst nature i.e., whether it increases or decrease the rate
of reaction, it is of two types: POSITIVE AND NEGATIVE CATALYST as per
the name Positive(enhancing the rate) and Negative (decreasing the rate).
Similarly, the catalytic reactions are of two types: HETEROGENEOUS AND
HOMOGENEOUS CATALYTIC REACTIONS. Homogenous in case both ,
catalyst and reactants are of same physical state and different in Heterogeneous
catalytic reactions.
As for the nature and characteristics following points sum up all the attributes of
a Catalyst:-
i. Regenerated again at the end of the reaction.
ii. Needed in small amount.
iii. Do not alter the reaction equilibrium.
iv. It‟s not an initiator.
v. Specific and Selective in action
vi. Do not alter the nature of the product.
vii. It is Adsorbed not Absorbed on the surface of the reactant.
Now, in case of the Biocatalyst – Enzymes, its nature ( similar to proteins) and
characteristics can be summarized as:
i. Has usual proportions of C,H,N and S.
ii. Ampholytes in the electric field.
iii. Gets denatured under unfavorable temperature or pH.

35. 35
iv. Forms anti-bodies in bodies.
v. Lose their activities in presence of electrolytes and UV Rays.
Fischer‟s Lock and Key Model and Koshland‟s induced fit model theories help to
explain the mechanism of enzyme activity.
According to the Fischer‟s Lock and Key Model, the union between the reactant
(substrate) and the enzyme takes place at the site more or less in a manner in
which a key fits a lock results in the formation of the enzyme-substrate complex
which later undergoes chemical and conformational changes and breaks to give
enzyme and product.
Whereas, Koshland‟s induced fit model contradict the Fischer‟s model. The
unfortunate feature of the Fischer‟s model is the rigidity of the active site and its
presumed to be pre-shaped to fit the substrate. According to the Koshland‟s
model, the substrate induces conformational changes in the enzyme and it is
made to fit the substrate.
Lastly, the summary on Enzyme Kinetics as explained from Michaelis-Menten
Equation.
For enzymatically catalyzed reactions, if
a plot is drawn between the reaction rate
(V) against substrate concentration, then a
hyperbolic curve is obtained. The curve is
analogous to the oxygen-dissociation
curve of myoglobin. The plot shows that
the velocity increases with increase in
substrate concentration until a maximum
V(Vmax) is approached asymptotically.
Thereafter, larger concentrations of substrate do not significantly enhance the
reaction rate. In the lower regions of curve, the reaction approaches first order
kinetics. It shows that V is a direct function of [substrate] because the active sites
of the enzyme molecules are not saturated. At the upper portion of the plot, the
reaction reaches zero order kinetics because the active sites of all the enzyme
molecules are saturated and thus, the reaction rate is independent of further
increase in the concentration of the substrate. For the intermediate part of the
curve, the enzyme approaches substrate saturation, kinetic are mixed zero and
first order kinetics. Thus enzyme assays are designed to follow zero order
kinetics to avoid the influence of substrate concentration on reactions velocity.

36. 36
REFERENCE
 Masel, Richard I. (2001) Chemical Kinetics and Catalysis. Wiley-Interscience,
New York. ISBN 0-471-24197-0.
 “7 things you may not know about catalysis”. Louise Lerner, Argonne National
Laboratory (2011)
 Behr, Arno (2002) "Organometallic Compounds and Homogeneous Catalysis"
in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim.
 "Types of catalysis". Chemguide. Retrieved 2008-07-09.
 Sharma,Y.R.2017.Modern College Chemistry (Theory and Practical).Ludhyana
.Kalyani Publishers.
 Sharma,Y.R:Sharma,Dr.K.D. 2016. Modern College Chemistry(Theory and
Practical).Ludhyana. Kalyani Publishers.
Website Links:
https://simple.wikipedia.org/wiki/Enzyme
https://simple.wikipedia.org/wiki/Catalyst
https://www.quora.com/in
https://www.cbse.edu.in/chemistry/catalyst