Zeolites, Catalysis, Colloids Properties
Here we will discuss about,
Zeolites
Catalysis
Homogenous catalysis
Heterogenous catalysis
Enzyme catalysis
Shape selective catalysis by zeolites
Properties of colloids
Zeolites
By
definition, a zeolite is a "boiling stone." This is due to the fact
that they are stones with very high heat retention rates. They are incredibly
porous and have the capacity to hold water, thus when heated, a lot of steam is
released from their surface.
Commercial
manufacturing of zeolites with specific structural and chemical characteristics
allows for the exploitation of zeolite qualities. Hydrocarbon separation, such
as in “the refinement of petroleum, drying of gases and liquids, and the
prevention of pollution through selective molecule adsorption are a few
examples of commercial usage”.
Natural
zeolites are found as cavity fills in mafic volcanic rocks, most likely as a
result of liquid or vapour deposition. They develop a wide variety of
crystalline formations with enormously regular open holes. There are roughly 40
naturally occurring zeolites, and many artificial or synthetic zeolites have
also been created.
The
ability of their structure to contain other molecules is by far its most
intriguing characteristic. They feature structures resembling honeycombs, which
makes them effective shape-selective catalysts.
Due to
structural and chemical variations, reversible dehydration and cation exchange
are made possible by the framework's ease of ion and water movement. The type
of dehydration differs depending on how the structure's water is bound.
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| Zeolite |
Shape Selective Catalysis (ZEOLITES)
In
shape-selective catalysis, catalysis and the molecular sieve effect are
combined. Here, the shape or size of the reactant or substrate causes the
catalyst to display preference or selectivity towards it. The size or form of
the substrates and products, as well as the catalyst's pore structure, all
affect these catalytic reactions. Zeolites are a good illustration of this kind
of catalyst.
By
transition state selectivity or by excluding competing reactants depending on
their molecular size, they function as shape-selective catalysts. Reactant
shape selectivity occurs when some of the reactant molecules are too big to diffuse
into the zeolite pores. On the other hand, product shape selectivity occurs
when only items with the right dimensions may diffuse out of the zeolite pores.
Zeolites,
which are crystalline aluminosilicates, are the most popular molecular sieves
utilised for catalytic applications. The Bronsted acid (proton)-containing
zeolite pore shown in Figure, it is the catalytically active site for acid-catalyzed
processes such aromatics alkylation with olefins. It has 10 tetrahedral atoms
arranged in a ring. The silicate structure gains one negative charge when one
tetrahedral Si (+4 in its oxidation state) is swapped out for one a-l-, (+3 in
its oxidation state), which must be counterbalanced by a positive charge, often
an alkali metal cation like Na.
Proton
form zeolite can be produced by the subsequent ion-exchange with NH 4 or
protonic acid, followed by heat treatment, as shown in Figure. In molecular
sieve structures, partial substitution of tetrahedral Al or Si molecules by
other atoms (such as Fe, Ga, etc.) can result in the formation of
metallosilicates, which have recently discovered some significant catalytic
uses.
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Shape Selective Catalysis (ZEOLITES) |
Catalysis
A "catalyst" is anything that
helps to speed up a process; the word comes from the Greek letter v, which
means "to annul," "to untie," or "to pick up."
"The prefix kata, which means
"an intensifying prefix," Additionally λύω
(lúō, "loosen")."
Based on her innovative work in
oxidation-reduction experiments, chemist Elizabeth Fulhame established the
concept of catalysis and detailed it in a book in 1794. Gottlieb Kirchhoff, who
discovered the acid-catalyzed conversion of starch to glucose, explored the
first chemical process in organic chemistry to involve a catalyst in 1811. Later,
in 1835, Jöns Jakob Berzelius coined the term "catalysis" to refer to
processes that are sped up by components that do not change after the reaction.
Prior to Berzelius, Fulhame conducted reduction experiments using water rather
than metals.
Catalyst
Chemical reactions do not start because
of a catalyst. The reaction does not use up a catalyst. As they react with
reactants to produce intermediates, catalysts also help the final reaction
product to be produced. A catalyst is capable of regeneration after the entire
procedure.
Catalysts come in three different forms:
solid, liquid, and gaseous. Metals or their oxides, such as halides and sulphides,
are among the solid catalysts. As catalysts, semi-metallic substances including
silicon, aluminium, and boron are also employed. The same is true for the
employment of pure liquid and gaseous elements as catalysts. These substances
are occasionally combined with the appropriate solvents or carriers.
A catalytic reaction is one in which
their system contains a catalyst.
Types
of Catalyst
Positive
catalyst
Increase rate of reaction, for example, Iron
oxide serves as a positive catalyst in Haber's process to create NH3,
increasing the output of ammonia despite less nitrogen reacting with it.
Negative catalyst
Decrease the rate of reaction, for
example, Acetanilide, which functions as a
negative catalyst to slow down the rate of decomposition of hydrogen peroxide,
retards the breakdown of hydrogen peroxide into water and oxygen.
Promoters
Increase the catalytic activity of
catalyst, for example,
Molybdenum or a
combination of potassium and aluminum oxides function as Promoters in Haber's
process.
Inhibitors
Decrease the catalytic activity of
catalyst, for example,
the catalyst palladium
is poisoned with barium sulphate in quinolone solution to block the
hydrogenation of alkyne to an alkene at the alkene level. The catalyst is also
called the Lindler catalyst, used to prepare cis alkene from alkyne.
Homogenous catalysis
It is a type of catalysis in which
physical state of reactant and catalyst are same.
Examples,
NO, H2SO4,Mno2 these are used as catalyst.
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| Homogenous catalysis |
Heterogeneous catalysis
Physical state of catalyst and reactant
are different.
Examples,
Ni / pt and Fe act as catalyst.
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| Heterogeneous catalysis |
Enzyme catalysis
The speeding up of a process by a
biological molecule known as a "enzyme" is known as enzyme catalysis.
The majority of these processes, including most enzymes, involve chemical
reactions. Catalysis often takes place at a specific location inside the enzyme,
known as the active site.
Proteins, either one protein chain or
multiple chains in a multi-subunit complex, make up the majority of enzymes.
Properties of colloids
In nature, colloids are comparatively
stable. The dispersed phase's particles continue to move continuously and are
suspended in the solution. Colloids are referred to as heterogeneous in nature
since they are made up of two phases, the dispersed phase and the dispersion
medium. Colloids provide the impression of being a homogeneous solution even
though they are heterogeneous in nature and comprise suspended particles. This
is the case because the suspended particles are so small that the human eye
cannot see them.
Ultrafilters, a type of specialized filter, are needed for filtration of colloids. They effortlessly filter through common filter papers without leaving behind any waste.
Brownian Motion of Colloids
The Brownian movement is a crucial
characteristic of the scattered particles found in a colloidal solution. An
ultramicroscope image of a colloidal solution reveals the colloidal particles
to be moving continually in a zigzag pattern.
The colloidal particles are continuously
attacked from all sides by the moving molecules of the dispersion medium. The
Brownian movement gives the sol stability. It works against colloidal
particles' gravitational pull and prevents them from settling, keeping the sol
stable.
Tyndall Effect
The Tyndall effect, which is shown by
colloids, was first noticed by Tyndall in 1869. A bluish light illuminates the
path of the beam when it passes through a colloidal solution that has been kept
in darkness. The 'Tyndall effect and Tyndall cone' are terms used to
describe the phenomena of light scattering by colloidal particles. Dispersed
colloidal particles cause emissions that are analogous to ultraviolet and visible
radiations when light strikes them. These reflected rays are lighted.
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| Tyndall Effect |
Colloidal solutions' electrical characteristics
The dispersion medium has an equal and
opposite charge to that of the colloidal solution's particles, which all carry
the same kind of charge. The solution as a whole is electrically neutral
because the charge on the dispersion medium balances the charge on the
dispersed particles.
A colloid's scattered particles oppose
one another because they have identical electric charges, which keeps them from
settling and preserves the sol's stability. The colloidal sols can be divided
into positive and negative charged sols depending on the type of charge.
See More
Surface Chemistry
Emulsion, Adsorption and Adsorption Isotherm
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