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Mr Brain

GCE O Level Pure Chemistry

Summary of Catalytic Processes

Typical mechanism

Catalysts generally react with one or more reactants to form an intermediate that subsequently

give the final reaction product, in the process regenerating the catalyst. The

typical reaction scheme, where C represents the catalyst, A and B are reactants, and D is the

product of the reaction of A and B:

A + C → AC (1)

B + AC → ABC (2)

ABC → CD (3)

CD → C + D (4)

Although the catalyst (C) is consumed by reaction 1

so for the overall reaction:

A + B → D

Catalysts and reaction energetics


GCE O Level Pure Chemistry

Summary of Catalytic Processes


give the final reaction product, in the process regenerating the catalyst. The following is a


product of the reaction of A and B:

Although the catalyst (C) is consumed by reaction 1, it is subsequently produced by reaction 4,

Catalysts and reaction energetics

Page 1


following is a


, it is subsequently produced by reaction 4,


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Generic potential energy diagram showing the effect of a catalyst in an hypothetical exothermic

chemical reaction. 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. The effect of this is that more molecular collisions have the

energy needed to reach the transition state. Hence, catalysts can perform reactions that, albeit

thermodynamically feasible, would not run without the presence of a catalyst, or perform them

much faster, more specific, or at lower temperatures.

Catalysts cannot make energetically unfavorable reactions possible — they have no effect on

the chemical equilibrium of a reaction because the rate of both the forward and the reverse

reaction are equally affected. The net free energy change of a reaction is the same whether a

catalyst is used or not; the catalyst just makes it easier to activate.

Types of catalysts

Catalysts can be either heterogeneous or homogeneous. Biocatalysts are often seen as a

separate group. Biocatalysis can be defined as utilization of natural Catalysts, such as protein

Enzymes, to perform chemical transformations on Organic compounds.

Heterogeneous catalysts are present in different phases from the reactants (for example, a

solid catalyst in a liquid reaction mixture), whereas homogeneous catalysts are in the same

phase (for example, a dissolved catalyst in a liquid reaction mixture).

a) Heterogeneous catalysts

A simple model for heterogeneous catalysis involves the catalyst providing a surface on which

the reactants (or substrates) temporarily become adsorbed. For example, in the Haber process

to manufacture ammonia, finely divided iron acts as a heterogeneous catalyst.

Other heterogeneous catalysts include vanadium(V) oxide in the contact process, nickel in the

manufacture of margarine, alumina and silica in the cracking of alkanes and platinum, rhodium

and palladium in catalytic converters.

b) Homogeneous catalysts

Homogeneous catalysts are in the same phase as the reactants.

In homogeneous catalysis the catalyst is a molecule which facilitates the reaction. Examples of

homogeneous catalysts are:


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1) The ion H+(aq) which acts as a catalyst in esterification, as well as in the inverse reaction -

hydrolysis of esters such as methyl acetate is catalysed by H+

2) Chlorine free radicals in the break down of ozone. These radicals are formed by the action of

ultraviolet radiation on chlorofluorocarbons (CFCs).

Exploration of major catalytic processes

Case-1) Haber process for synthesis of ammonia

By far the major source of the hydrogen required for the Haber-Bosch process is methane from

natural gas, obtained through a heterogeneous catalytic process, which requires far less

external energy than the process used initially by Bosch at BASF: the electrolysis of water. Far

less commonly, in some countries, coal is used as the source of hydrogen through a process

called coal gasification. The source of the hydrogen is of no consequence in the Haber-Bosch

process.

a. Synthesis gas (H2) preparation

The methane is first cleaned, mainly to remove sulfur oxide and hydrogen sulfide impurities

that would poison the catalysts.

The clean methane is then reacted with steam over a catalyst of nickel oxide. This is called

steam reforming:


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CH4 + H2O → CO + 3 H2

Secondary reforming then takes place with the addition of air to convert the methane that did

not react during steam reforming:

2 CH4 + O2 → 2 CO + 4 H2

CH4 + 2 O2 → CO2 + 2 H2O

Then the water gas shift reaction yields more hydrogen from CO and steam:

CO + H2O → CO2 + H2

The gas mixture is now passed into a methanator which converts most of the remaining CO into

methane for recycling:

CO + 3 H2 → CH4 + H2O

This last step is necessary as carbon monoxide poisons the catalyst. (Note, this reaction is the

reverse of steam reforming). The overall reaction so far turns methane and steam into carbon

dioxide, steam, and hydrogen.

b. Ammonia synthesis – Haber process

The final stage, which is the actual Haber process, is the synthesis of ammonia using an iron

catalyst promoted with K2O, CaO and Al2O3

N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g) (ΔH = −92.22 kJ·mol−1

)

This is done at 15–25 MPa (150–250 bar) and between 300 and 550 °C, as the gases are passed

over four beds of catalyst, with cooling between each pass so as to maintain a reasonable

equilibrium constant. On each pass only about 15% conversion occurs, but any unreacted gases

are recycled, and eventually an overall conversion of 97% is achieved.

The steam reforming, shift conversion, carbon dioxide removal, and methanation steps each

operate at absolute pressures of about 2.5–3.5 MPa (25–35 bar), and the ammonia synthesis

loop operates at absolute pressures ranging from 6–18 MPa (59–178 atm), depending upon

which proprietary design is used.


Mr Brain

Reaction rate and equilibrium

There are two opposing considerations in this synthesis: the position of the equilibrium and the

rate of reaction. At room temperatu

the temperature. This may increase the rate of the reaction but, since the reaction is

exothermic, it also has the effect, according to

reaction and thus reducing the amount of product, given by:

As the temperature increases, the

drops dramatically according to the

temperature is to be used and some other means to increase rate. However, the catalyst itself

requires a temperature of at least 400 °C to be efficient.

Pressure is the obvious choice to favour the forward reaction because there are 4 moles of

reactant for every 2 moles of product (see

alters the equilibrium concentrations to give a profitable yield.

Economically, though, pressure is an expensive commodity. Pipes and reaction vessels need to

be strengthened, valves more rigorous, and there

atm. In addition, running pumps and compressors takes considerable energy. Thus the

compromise used gives a single pass yield of around 15%.

Another way to increase the yield of the reaction would be to remove the product (i.e.

ammonia gas) from the system. In practice, gaseous ammonia is not removed from the reactor

itself, since the temperature is too high; but it is removed from the equilibr

leaving the reaction vessel. The hot gases are cooled enough, whilst maintaining a high pressure,

for the ammonia to condense and be removed as liquid. Unreacted hydrogen and nitrogen

gases are then returned to the reaction vessel to u

Catalysts

The catalyst has no effect on the position of

alternative pathway with lower activation energy

remaining chemically unchanged at the end of the rea

chambers used osmium and ruthenium

the BASF researcher Alwin Mittasch

is still used today. Part of the industrial production now takes place with a ruthenium rather

than an iron catalyst (the KAAP process), because this more active catalyst allows reduced

operating pressures.



. At room temperature, the reaction is slow and the obvious solution is to raise


has the effect, according to Le Chatelier's principle, of favouring the reverse

reaction and thus reducing the amount of product, given by:

ature increases, the equilibrium is shifted and hence, the amount of product

drops dramatically according to the Van't Hoff equation. Thus one might suppose that a low


requires a temperature of at least 400 °C to be efficient.

is the obvious choice to favour the forward reaction because there are 4 moles of

reactant for every 2 moles of product (see entropy), and the pressure used (around 200 atm)

alters the equilibrium concentrations to give a profitable yield.


be strengthened, valves more rigorous, and there are safety considerations of working at 200


compromise used gives a single pass yield of around 15%.



itself, since the temperature is too high; but it is removed from the equilibrium mixture of gases



gases are then returned to the reaction vessel to undergo further reaction.

has no effect on the position of chemical equilibrium; rather, it provides an

activation energy and hence increases the reaction rate, while

remaining chemically unchanged at the end of the reaction. The first Haber–Bosch reaction

ruthenium as catalysts. However, under Bosch's direction in 190

Alwin Mittasch discovered a much less expensive iron-based catalyst

t of the industrial production now takes place with a ruthenium rather


Page 5


re, the reaction is slow and the obvious solution is to raise


, of favouring the reverse

is shifted and hence, the amount of product

. Thus one might suppose that a low


is the obvious choice to favour the forward reaction because there are 4 moles of

), and the pressure used (around 200 atm)


are safety considerations of working at 200




ium mixture of gases



; rather, it provides an

and hence increases the reaction rate, while

Bosch reaction

as catalysts. However, under Bosch's direction in 1909,

based catalyst that

t of the industrial production now takes place with a ruthenium rather



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In industrial practice, the iron catalyst is prepared by exposing a mass of magnetite, an iron

oxide, to the hot hydrogen feedstock. This reduces some of the magnetite to metallic iron,

removing oxygen in the process. However, the catalyst maintains most of its bulk volume

during the reduction, and so the result is a highly porous material whose large surface area aids

its effectiveness as a catalyst. Other minor components of the catalyst include calcium and

aluminium oxides, which support the porous iron catalyst and help it maintain its surface area

over time, and potassium, which increases the electron density of the catalyst and so improves

its activity.

The reaction mechanism, involving the heterogeneous catalyst, is believed to be as follows:

1. N2 (g) → N2 (adsorbed)

2. N2 (adsorbed) → 2 N (adsorbed)

3. H2(g) → H2 (adsorbed)

4. H2 (adsorbed) → 2 H (adsorbed)

5. N (adsorbed) + 3 H(adsorbed)→ NH3 (adsorbed)

6. NH3 (adsorbed) → NH3 (g)

Reaction 5 occurs in three steps, forming NH, NH2, and then NH3. Experimental evidence points

to reaction 2 as being the slow, rate-determining step.

Review Questions:

1. Why NH3 BP is lower than H2 & N2 ? (What kind of bonding between the atoms?)

2. Why the Haber process need to set at high pressure and temperature ?

Case-2) Contact process for converting SO3 to H2SO4


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The process can be divided into five stages:

1. combining of sulphur and oxygen;

2. purifying sulphur dioxide in the purification unit;

3. adding excess of oxygen to sulphur dioxide in presence of catalyst vanadium oxide;

4. sulphur trioxide formed is added to sulphuric acid which gives rise to oleum (disulphuric

acid);

5. the oleum then is added to water to form sulphuric acid which is very concentrated.

Purification of air and SO2 is necessary to avoid catalyst poisoning (i.e. removing catalytic

activities). The gas is then washed with water and dried by sulphuric acid.

To conserve energy, the mixture is heated by exhaust gases from the catalytic converter by

heat exchangers.

Sulphur dioxide and oxygen then react as follows:

2 SO2(g) + O2(g) ⇌ 2 SO3(g) : ΔH = −197 kJ mol−1

According to the Le Chatelier's principle, a lower temperature should be used to shift the

chemical equilibrium towards the right, hence increasing the percentage yield. However, too

low of a temperature will lower the formation rate to an uneconomical level. Hence to increase

the reaction rate, high temperatures (450 °C), medium pressures (1-2 atm), and vanadium(V)

oxide (V2O5) are used to ensure a 96% conversion. Platinum would be a more effective catalyst,

but it is very costly and easily poisoned. The catalyst only serves to increase the rate of reaction

as it does not change the position of the thermodynamic equilibrium. The mechanism for the

action of the catalyst comprises two steps:

1. Oxidation of SO2 into SO3 by V5+

:

2 SO2 + 4V5+

+ 2 O2-

→ 2 SO3 + 4V4+

2. Oxidation of V4+

back into V5+

by oxygen (catalyst regeneration):

4 V4+

+ O2 → 4 V5+

+ 2 O2-

Hot sulphur trioxide passes through the heat exchanger and is dissolved in concentrated H2SO4

in the absorption tower to form oleum:

H2SO4(l) + SO3(g) → H2S2O7(l)

Note that directly dissolving SO3 in water is impractical due to the highly exothermic nature of

the reaction. Acidic vapor or mists are formed instead of a liquid.


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Oleum is reacted with water to form concentrated H2SO4.

The average percentage yield of this reaction is around 30%.

H2S2O7(l) + H2O(l) → 2 H2SO4(l)

Case-3) Catalytic Convertor for Vehicles

The catalytic converter consists of several components:

1. The catalyst core, or substrate. For automotive catalytic converters, the core is usually a ceramic

monolith with a honeycomb structure. Metallic foil monoliths made of FeCrAl are used in some

applications. This is partially a cost issue. Ceramic cores are inexpensive when manufactured in

large quantities. Metallic cores are less expensive to build in small production runs. Either

material is designed to provide a high surface area to support the catalyst washcoat, and

therefore is often called a "catalyst support".[citation needed]

The cordierite ceramic substrate used in

most catalytic converters was invented by Rodney Bagley, Irwin Lachman and Ronald Lewis at

Corning Glass, for which they were inducted into the National Inventors Hall of Fame in 2002.

2. The washcoat. A washcoat is a carrier for the catalytic materials and is used to disperse the

materials over a high surface area. Aluminum oxide, Titanium dioxide, Silicon dioxide, or a

mixture of silica and alumina can be used. The catalytic materials are suspended in the washcoat

prior to applying to the core. Washcoat materials are selected to form a rough, irregular surface,

which greatly increases the surface area compared to the smooth surface of the bare substrate.

This maximizes the catalytically active surface available to react with the engine exhaust.

3. The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is

widely used, but is not suitable for all applications because of unwanted additional reactions

and high cost. Palladium and rhodium are two other precious metals used. Rhodium is used as a

reduction catalyst, palladium is used as an oxidation catalysts, and platinum is used both for

reduction and oxidation. Cerium, iron, manganese and nickel are also used, although each has

its own limitations. Nickel is not legal for use in the European Union (because of its reaction with

carbon monoxide into nickel tetracarbonyl). Copper can be used everywhere except North

America,[clarification needed]

where its use is illegal because of the formation of dioxin.


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A two-way (or "oxidation") catalytic converter has two simultaneous tasks:

1. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

2. Oxidation of hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide and water:

CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O (a combustion reaction)

This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and

carbon monoxide emissions. They were also used on gasoline engines in American- and

Canadian-market automobiles until 1981. Because of their inability to control oxides of nitrogen,

they were superseded by three-way converters.

Since 1981, "three-way" (oxidation-reduction) catalytic converters have been used in vehicle

emission control systems in the United States and Canada; many other countries have also

adopted stringent vehicle emission regulations that in effect require three-way converters on

gasoline-powered vehicles. The reduction and oxidation catalysts are typically contained in a

common housing, however in some instances they may be housed separately. A three-way

catalytic converter has three simultaneous tasks:

1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2

2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2


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3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2]O2 →

xCO2 + (x+1)H2O.

These three reactions occur most efficiently when the catalytic converter receives exhaust from

an engine running slightly above the stoichiometric point. This point is between 14.6 and 14.8

parts air to 1 part fuel, by weight, for gasoline. The ratio for Autogas (or liquefied petroleum gas

(LPG)), natural gas and ethanol fuels is each slightly different, requiring modified fuel system

settings when using those fuels. In general, engines fitted with 3-way catalytic converters are

equipped with a computerized closed-loop feedback fuel injection system using one or more

oxygen sensors, though early in the deployment of three-way converters, carburetors equipped

for feedback mixture control were used.

Three-way catalysts are effective when the engine is operated within a narrow band of air-fuel

ratios near stoichiometry, such that the exhaust gas oscillates between rich (excess fuel) and

lean (excess oxygen) conditions. However, conversion efficiency falls very rapidly when the

engine is operated outside of that band of air-fuel ratios. Under lean engine operation, there is

excess oxygen and the reduction of NOx is not favored. Under rich conditions, the excess fuel

consumes all of the available oxygen prior to the catalyst, thus only stored oxygen is available

for the oxidation function. Closed-loop control systems are necessary because of the conflicting

requirements for effective NOx reduction and HC oxidation. The control system must prevent

the NOx reduction catalyst from becoming fully oxidized, yet replenish the oxygen storage

material to maintain its function as an oxidation catalyst.

Case-4) Hydrogenation of Alkenes to Alkanes


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Alkenes are relatively stable compounds, but are more reactive than alkanes due to the

presence of a carbon-carbon pi-bond. It is also attributed to the presence of pi-electrons in the

molecule. The majority of the reactions of alkenes involve the rupture of this pi bond, forming

new single bonds.

Alkenes serve as a feedstock for the petrochemical industry because they can participate in a

wide variety of reactions.

Alkenes react in many addition reactions, which occur by opening up the double-bond. Most

addition reactions to alkenes follow the mechanism of electrophilic addition. Examples of

addition reactions are hydrohalogenation, halogenation, halohydrin formation, oxymercuration,

hydroboration, dichlorocarbene addition, Simmons-Smith reaction, catalytic hydrogenation,

epoxidation, radical polymerization and hydroxylation.

Hydrogenation of alkenes produces the corresponding alkanes. The reaction is carried out

under pressure at a temperature of 200 °C in the presence of a metallic catalyst. Common

industrial catalysts are based on platinum, nickel or palladium. For laboratory syntheses, Raney

nickel (an alloy of nickel and aluminium) is often employed. The simplest example of this

reaction is the catalytic hydrogenation of ethylene to yield ethane:

CH2=CH2 + H2 → CH3-CH3

Review Questions:

1. Name another application of Nickel due to its ability to absorb hydrogen gas.

Case-5) Ozone Layer Depletion

Three forms (or allotropes) of oxygen are involved in the ozone-oxygen cycle: oxygen atoms (O

or atomic oxygen), oxygen gas (O2 or diatomic oxygen), and ozone gas (O3 or triatomic oxygen).

Ozone is formed in the stratosphere when oxygen molecules photo-dissociate after absorbing

an ultraviolet photon whose wavelength is shorter than 240 nm. This converts a single O2 into

two atomic oxygen ions. The atomic oxygen ions then combine with separate O2 molecules to

create two O3 molecules. These ozone molecules absorb UV light between 310 and 200 nm,

following which ozone splits into a molecule of O2 and an oxygen atom. The oxygen atom then

joins up with an oxygen molecule to regenerate ozone. This is a continuing process which


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terminates when an oxygen atom "recombines" with an ozone molecule to make two O2

molecules.

O + O3 → 2 O2 chemical equation

The overall amount of ozone in the stratosphere is determined by a balance between

photochemical production and recombination.

Ozone can be destroyed by a number of free radical catalysts, the most important of which are

the hydroxyl radical (OH·), the nitric oxide radical (NO·), the atomic chlorine ion (Cl·) and the

atomic bromine ion (Br·). All of these have both natural and man-made sources; at the present

time, most of the OH· and NO· in the stratosphere is of natural origin, but human activity has

dramatically increased the levels of chlorine and bromine. These elements are found in certain

stable organic compounds, especially chlorofluorocarbons (CFCs), which may find their way to

the stratosphere without being destroyed in the troposphere due to their low reactivity. Once

in the stratosphere, the Cl and Br atoms are liberated from the parent compounds by the action

of ultraviolet light, e.g.

CFCl3 + electromagnetic radiation → CFCl2 + Cl

The Cl and Br atoms can then destroy ozone molecules through a variety of catalytic cycles. In

the simplest example of such a cycle, a chlorine atom reacts with an ozone molecule, taking an

oxygen atom with it (forming ClO) and leaving a normal oxygen molecule. The chlorine

monoxide (i.e., the ClO) can react with a second molecule of ozone (i.e., O3) to yield another

chlorine atom and two molecules of oxygen. The chemical shorthand for these gas-phase

reactions is:

• Cl + O3 → ClO + O2 – The chlorine atom changes an ozone molecule to ordinary oxygen

• ClO + O3 → Cl + 2 O2 – The ClO from the previous reaction destroys a second ozone molecule

and recreates the original chlorine atom, which can repeat the first reaction and continue to

destroy ozone

The overall effect is a decrease in the amount of ozone. More complicated mechanisms have

been discovered that lead to ozone destruction in the lower stratosphere as well.


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A single chlorine atom would keep on destroying ozone (thus a catalyst) for up to two years

(the time scale for transport back down to the troposphere) were it not for reactions that

remove them from this cycle by forming reservoir species such as hydrogen chloride (HCl) and

chlorine nitrate (ClONO2).

On a per atom basis, bromine is even more efficient than chlorine at destroying ozone, but

there is much less bromine in the atmosphere at present. As a result, both chlorine and

bromine contribute significantly to the overall ozone depletion. Laboratory studies have shown

that fluorine and iodine atoms participate in analogous catalytic cycles. However, in the Earth's

stratosphere, fluorine atoms react rapidly with water and methane to form strongly bound HF,

while organic molecules which contain iodine react so rapidly in the lower atmosphere that

they do not reach the stratosphere in significant quantities. Furthermore, a single chlorine atom

is able to react with 100,000 ozone molecules. This fact plus the amount of chlorine released

into the atmosphere by chlorofluorocarbons (CFCs) yearly demonstrates how dangerous CFCs

are to the environment.

Review Questions:

1. Other than Cl, any other compound or Ions that act as catalyst to ozone depletion?

2. What are the common sources of CFC ? Why is fluorine not a concern in fluoro-hrdocarbon?


Mr Brain Page 14

Case-6) Hydrogen-Peroxide Decomposition

Hydrogen peroxide decomposes (disproportionate) exothermically into water and oxygen gas

spontaneously:

2 H2O2 → 2 H2O + O2

This process is thermodynamically favorable. It has a ΔHo of −98.2 kJ·mol

−1 and a ΔS of 70.5

J·mol−1

·K−1

. The rate of decomposition is dependent on the temperature (cool environment

slows down decomposition, therefore hydrogen peroxide is often stored in refrigerator) and

concentration of the peroxide, as well as the pH and the presence of impurities and stabilizers.

Hydrogen peroxide is incompatible with many substances that catalyse its decomposition,

including most of the transition metals and their compounds. Common catalysts include

manganese dioxide, silver, and platinum. The same reaction is catalyzed by the enzyme catalase,

found in the liver, whose main function in the body is the removal of toxic byproducts of

metabolism and the reduction of oxidative stress. The decomposition occurs more rapidly in

alkali, so acid is often added as a stabilizer.

The liberation of oxygen and energy in the decomposition has dangerous side-effects. Spilling

high concentrations of hydrogen peroxide on a flammable substance can cause an immediate

fire, which is further fueled by the oxygen released by the decomposing hydrogen peroxide.

High test peroxide, or HTP (also called high-strength peroxide) must be stored in a

suitable,vented container to prevent the buildup of oxygen gas, which would otherwise lead to

the eventual rupture of the container.


Mr Brain

Propellant

Rocket Belt hydrogen peroxide propulsion system used in a

High concentration H2O2 is referred to as HTP or

monopropellant (not mixed with fuel) or as the oxidizer component of a

Use as a monopropellant takes advantage of the decomposition of 70

hydrogen peroxide into steam and oxygen. The propellant is pumped into a reaction chamber

where a catalyst, usually a silver or platinum screen, triggers decomposition, producing steam

at over 600 °C (1,112 °F), which is expelled through a

monopropellant produces a maximum

it a low-performance monopropellant. Peroxide generates much less thrust than

Bell Rocket Belt used hydrogen peroxide monopropellant.

As a bipropellant H2O2 is decomposed to burn a fuel as an oxidizer. Specific i

350 s (3.5 kN·s/kg) can be achieved, depending on the fuel. Peroxide used as an oxidizer gives a

somewhat lower Isp than liquid oxygen, but is dense, storable, noncryogenic and can be more

easily used to drive gas turbines to give high p

be used for regenerative cooling of rocket engines. Peroxide was used very successfully as an

oxidizer in World-War-II German rockets (e.g.

Me-163), and for the low-cost British

In the 1940s and 1950s, the Walter

submerged; it was found to be too noisy and require too much maintenance compared to

diesel-electric power systems. Some

propellant, but this was dangerous and has been discontinued by most

peroxide leaks were blamed for the sinkings of

was discovered, for example, by the Japanese Navy in torpedo trials, that the concentration of

H2O2 in right-angle bends in HTP pipework can often lead to explosions in submarines and


Rocket Belt hydrogen peroxide propulsion system used in a jet pack

is referred to as HTP or High test peroxide. It can be used either as a

(not mixed with fuel) or as the oxidizer component of a bipropellant rocket

Use as a monopropellant takes advantage of the decomposition of 70–98+% concentration

gen peroxide into steam and oxygen. The propellant is pumped into a reaction chamber


at over 600 °C (1,112 °F), which is expelled through a nozzle, generating thrust.

monopropellant produces a maximum specific impulse (Isp) of 161 s (1.6 kN·s/kg), which makes

performance monopropellant. Peroxide generates much less thrust than

used hydrogen peroxide monopropellant.

is decomposed to burn a fuel as an oxidizer. Specific impulses as high as


than liquid oxygen, but is dense, storable, noncryogenic and can be more

easily used to drive gas turbines to give high pressures using an efficient closed cycle


II German rockets (e.g. T-Stoff, containing oxyquinoline stabilizer, for the

cost British Black Knight and Black Arrow launchers.

Walter turbine used hydrogen peroxide for use in submarines


power systems. Some torpedoes used hydrogen peroxide as oxidizer or

angerous and has been discontinued by most navies. Hydrogen

peroxide leaks were blamed for the sinkings of HMS Sidon and the Russian submarine


HTP pipework can often lead to explosions in submarines and

Page 15

. It can be used either as a

bipropellant rocket.

98+% concentration

gen peroxide into steam and oxygen. The propellant is pumped into a reaction chamber


. H2O2

/kg), which makes

performance monopropellant. Peroxide generates much less thrust than hydrazine. The

mpulses as high as


than liquid oxygen, but is dense, storable, noncryogenic and can be more

closed cycle. It can also


, containing oxyquinoline stabilizer, for the

submarines while


used hydrogen peroxide as oxidizer or

. Hydrogen

Russian submarine Kursk. It


HTP pipework can often lead to explosions in submarines and


Mr Brain

torpedoes. SAAB Underwater Systems is manufacturing the Torpedo 2000. This torpedo, used

by the Swedish navy, is powered by a piston engine propelled by HTP as an oxidizer and

kerosene as a fuel in a bipropellant system.

While rarely used now as a monopropellant for large engines, small hydrogen peroxide

control thrusters are still in use on some

and handle before launch than hydrazine thrusters. However,

spacecraft because of its higher

Review Questions:

1. 2H2O2 �2H2O + O2 , is this a redox reaction ?

2. Can you sketch the energy profile

3. Why is H2O2 a preferred fuel than fossil fuel as a rocket propellant?

Case-7) Cracking of hydrocarbon

Petroleum crude oil consists primarily of a mixture of hydrocarbons with small amounts of

other organic compounds containing sulfur,




as a fuel in a bipropellant system.

While rarely used now as a monopropellant for large engines, small hydrogen peroxide

are still in use on some satellites.They are easy to throttle, and safer to fuel

and handle before launch than hydrazine thrusters. However, hydrazine is more often used in

spacecraft because of its higher specific impulse and lower rate of decomposition.

a redox reaction ?

2. Can you sketch the energy profile diagram for the above reaction?

fuel than fossil fuel as a rocket propellant?

) Cracking of hydrocarbon- Fluid Catalytic Cracking


containing sulfur, nitrogen and oxygen.

Page 16



While rarely used now as a monopropellant for large engines, small hydrogen peroxide attitude

tle, and safer to fuel

is more often used in

and lower rate of decomposition.



Mr Brain Page 17

Fig 1 Example of the catalytic cracking of petroleum hydrocarbons

The fluid catalytic cracking process breaks large hydrocarbon molecules into smaller molecules

by contacting them with powdered catalyst at a high temperature and moderate pressure

which first vaporizes the hydrocarbons and then breaks them. The cracking reactions occur in

the vapor phase and start immediately when the feedstock is vaporized in the catalyst riser.

Figure 1 is a very simplified schematic diagram that exemplifies how the process breaks high

boiling, straight-chain alkane (paraffin) hydrocarbons into smaller straight-chain alkanes as well

as branched-chain alkanes, branched alkenes (olefins) and cycloalkanes (naphthenes). The

breaking of the large hydrocarbon molecules into smaller molecules is more technically

referred to by organic chemists as scission of the carbon-to-carbon bonds.

As depicted in Figure 1, some of the smaller alkanes are then broken and converted into even

smaller alkenes and branched alkenes such as the gases ethylene, propylene, butylenes and

isobutylenes. Those olefinic gases are valuable for use as petrochemical feedstocks. The

propylene, butylene and isobutylene are also valuable feedstocks for certain petroleum refining

processes that convert them into high-octane gasoline blending components.

Catalysts- Aluminum oxides (Alumina) & SiO2 (Silica)

The desirable properties of an FCC catalyst are:

• Good stability to high temperature and to steam

• High activity

• Large pore sizes


Mr Brain Page 18

• Good resistance to attrition

• Low coke production

A modern FCC catalyst has four major components: crystalline zeolite, matrix, binder and filler.

Zeolites are hydrated Alumina silicate Minerals and have a micro-porous structure Zeolite is the

primary active component and can range from about 15 to 50 weight percent of the catalyst.

The zeolite used in FCC catalysts is referred to faujasite or as Type Y and is comprised of silica

and alumina tetrahedra with each tetrahedron having either an aluminum or a silicon atom at

the center and four oxygen atoms at the corners.

The catalytic sites in the zeolite are strong acids (equivalent to 90% sulfuric acid) and provide

most of the catalyst activity.

The matrix component of an FCC catalyst contains amorphous alumina which also provides

catalytic activity sites and in larger pores that allows entry for larger molecules than does the

zeolite. That enables the cracking of higher-boiling, larger feedstock molecules than are cracked

by the zeolite.

The binder and filler components provide the physical strength and integrity of the catalyst. The

binder is usually silica sol and the filler is usually a clay (kaolin).

Review Questions:

1. Name the ore used for electrolysis extraction of Aluminum?

2. Name another application of Al2O3.

Case-8) Making of Methanol from Methane Gas

Synthesis gas is most commonly produced from the methane component in natural gas rather

than from coal. Methane is a Chemical compound with the molecular formula. It is the simplest

Alkane, and the principal component of Natural gas. Natural gas is a Gaseous Fossil fuel

consisting primarily of Methane but including significant quantities of Ethane, Propane, Three

processes are commercially practiced. At moderate pressures of 1 to 2 MPa (10–20 atm) and

high temperatures (around 850 °C), methane reacts with steam on a nickel or nickel oxide

catalyst to produce syngas according to the chemical equation:

CH4 + H2O → CO + 3 H2


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This reaction, commonly called steam-methane reforming or SMR, is endothermic and the heat

transfer limitations place limits on the size of and pressure in the catalytic reactors used.

Methane can also undergo partial oxidation with molecular oxygen to produce syngas, as the

following equation shows:

2 CH4 + O2 → 2 CO + 4 H2

this reaction is exothermic and the heat given off can be used in-situ to drive the steam-

methane reforming reaction.

The carbon monoxide and hydrogen then react on a second catalyst to produce methanol.

Today, the most widely used catalyst is a mixture of copper, zinc oxide, and alumina first used

by ICI in 1966. At 5–10 MPa (50–100 atm) and 250 °C, it can catalyze the production of

methanol from carbon monoxide and hydrogen with high selectivity

CO + 2 H2 → CH3OH

Case-9) Fuel Cells-Electrodes are catalyst for redox electrons transfer

Fuel cells are different from batteries in that they consume reactant, which must be

replenished, whereas batteries store electrical energy chemically in a closed system. In

electronics a battery is a combination of two or more Electrochemical cells which store

chemical Energy which can be converted into electrical energy Additionally, while the

electrodes within a battery react and change as a battery is charged or discharged, a fuel cell's

electrodes are catalytic and relatively stable.


Mr Brain Page 20

In essence, a fuel cell works by catalysis, separating the component electrons and protons of

the reactant fuel, and forcing the electrons to travel though a circuit, hence converting them to

electrical power. The catalyst is typically comprised of a platinum group metal or alloy. Another

catalytic process takes the electrons back in, combining them with the protons and the oxidant

to form waste products (typically simple compounds like water and carbon dioxide).


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Review Questions:

1. Write the redox half reaction equations at both electrodes. Derive the overall reaction

equation for H2/O2 fuel cell.

2. What is the advantage of fuel cell over the chemical cell in generating electricity?

Case-10) Production of Alcohol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile,

flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs.

Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers,

as a solvent, and as a fuel. In common usage, it is often referred to simply as alcohol or spirits.

Ethanol is produced both as a petrochemical, through the hydration of ethylene and, via

biological processes, by fermenting sugars with yeast. Which process is more economical

depends on prevailing prices of petroleum and grain feed stocks.

a) Ethylene hydration

Ethanol for use as an industrial feedstock or solvent (sometimes referred to as synthetic

ethanol) is made from petrochemical feed stocks, primarily by the acid-catalyzed hydration of

ethylene, represented by the chemical equation

C2H4 + H2O → CH3CH2OH

The catalyst is most commonly phosphoric acid, adsorbed onto a porous support such as silica

gel or diatomaceous earth. This catalyst was first used for large-scale ethanol production by the

Shell Oil Company in 1947. The reaction is carried out with an excess of high pressure steam at


Mr Brain Page 22

300 °C. In the U.S., this process was used on an industrial scale by Union Carbide Corporation

and others; but now only LyondellBasell uses it commercially.

b) Fermentation

Ethanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel is

produced by fermentation. When certain species of yeast (e.g., Saccharomyces cerevisiae)

metabolize sugar they produce ethanol and carbon dioxide. The chemical equations below

summarize the conversion:

C6H12O6 → 2 CH3CH2OH + 2 CO2

C12H22O11 + H2O → 4 CH3CH2OH + 4 CO2

Fermentation is the process of culturing yeast under favorable thermal conditions to produce

alcohol. This process is carried out at around 35–40 °C. Toxicity of ethanol to yeast limits the

ethanol concentration obtainable by brewing; higher concentrations, therefore, are usually

obtained by fortification or distillation. The most ethanol-tolerant strains of yeast can survive

up to approximately 15% ethanol by volume.

To produce ethanol from starchy materials such as cereal grains, the starch must first be

converted into sugars. In brewing beer, this has traditionally been accomplished by allowing the

grain to germinate, or malt, which produces the enzyme amylase. When the malted grain is

mashed, the amylase converts the remaining starches into sugars. For fuel ethanol, the

hydrolysis of starch into glucose can be accomplished more rapidly by treatment with dilute

sulfuric acid, fungally produced amylase, or some combination of the two.

Review Questions:

1. What are the uses of alcohol?

2. What are the advantages and disadvantages of using Alcohol as a fuel?

Case-11) Production of Esters

Fischer esterification or Fischer–Speier esterification is a special type of esterification by

refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst. The reaction was


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first described by Emil Fischer and Arthur Speier in 1895.Most carboxylic acids are suitable for

the reaction, but the alcohol should generally be a primary or secondary alkyl. Tertiary alcohols

are prone to elimination, and phenols are usually too unreactive to give useful yields.

Commonly used catalysts for a Fischer esterification include sulfuric acid, tosic acid, and Lewis

acids such as scandium(III) triflate.

Fischer esterification is an example of nucleophilic acyl substitution based on the

electrophilicity of the carbonyl carbon and the nucleophilicity of an alcohol. However,

carboxylic acids tend to be less reactive than esters as electrophiles. Additionally, In dilute

neutral solutions they tend to be deprotonated anions (and thus unreactive as electrophiles).

Though very kinetically slow without any catalysts (most esters are metastable), pure esters will

tend to spontaneously hydrolyse in the presence of water, so when carried out "unaided", high

yields for this reaction is quite unfavourable.

Several steps can be taken to turn this "unfavourable" reaction into a favourable one.

The reaction mechanism for this reaction has several steps:

1. Proton transfer from acid catalyst to carbonyl oxygen increases electrophilicity of carbonyl

carbon.

2. The carbonyl carbon is then attacked by the nucleophilic oxygen atom of the alcohol

3. Proton transfer from the oxonium ion to a second molecule of the alcohol gives an activated

complex

4. Protonation of one of the hydroxyl groups of the activated complex gives a new oxonium ion.

5. Loss of water from this oxonium ion and subsequent deprotonation gives the ester.

A generic mechanism for an acid Fischer esterification is shown below.


Mr Brain

Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is

the usual acid catalyst for the conversion of

making nylon. It is used for making

H2SO4 is used in petroleum refining, for example as a catalyst for the reaction of

isobutylene to give isooctane, a compound that raises the

The major use for sulfuric acid is in the "wet method" for the production of

used for manufacture of phosphate

more than 100 million tonnes are processed annually. This raw material is shown below as

fluorapatite, though the exact composition may vary. This is treated with 93% sulfuric acid to

produce calcium sulfate, hydrogen fluoride

hydrofluoric acid. The overall process can be represented as:

Ca5F(PO4)3 + 5 H2SO4 + 10

Ammonium sulfate, an important nitrogen fertilizer, is most commonly produced as a

byproduct from coking plants supplying the iron and steel making plants. Reacting the


uric acid is used for a variety of other purposes in the chemical industry. For example, it is

the usual acid catalyst for the conversion of cyclohexanone oxime to caprolactam

. It is used for making hydrochloric acid from salt via the Mannheim process

refining, for example as a catalyst for the reaction of

, a compound that raises the octane rating of gasoline

The major use for sulfuric acid is in the "wet method" for the production of phosphoric acid

phosphate fertilizers. In this method, phosphate rock is used, and

re processed annually. This raw material is shown below as

, though the exact composition may vary. This is treated with 93% sulfuric acid to

hydrogen fluoride (HF) and phosphoric acid. The HF is removed as

. The overall process can be represented as:

+ 10 H2O → 5 CaSO4·2 H2O + HF + 3 H3PO

, an important nitrogen fertilizer, is most commonly produced as a

supplying the iron and steel making plants. Reacting the

Page 24

uric acid is used for a variety of other purposes in the chemical industry. For example, it is

caprolactam, used for

Mannheim process. Much

refining, for example as a catalyst for the reaction of isobutane with

gasoline (petrol).

phosphoric acid,

. In this method, phosphate rock is used, and

re processed annually. This raw material is shown below as

, though the exact composition may vary. This is treated with 93% sulfuric acid to

. The HF is removed as

PO4

, an important nitrogen fertilizer, is most commonly produced as a

supplying the iron and steel making plants. Reacting the ammonia


Mr Brain Page 25

produced in the thermal decomposition of coal with waste sulfuric acid allows the ammonia to

be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-

chemicals industry.

Another important use for sulfuric acid is for the manufacture of aluminium sulfate, also known

as paper maker's alum. This can react with small amounts of soap on paper pulp fibers to give

gelatinous aluminium carboxylates, which help to coagulate the pulp fibers into a hard paper

surface. It is also used for making aluminium hydroxide, which is used at water treatment plants

to filter out impurities, as well as to improve the taste of the water. Aluminium sulfate is made

by reacting bauxite with sulfuric acid:

Al2O3 + 3 H2SO4 → Al2(SO4)3 + 3 H2O

Sulfuric acid is also important in the manufacture of dyestuffs solutions.

Review Questions:

1. What is the reaction between Conc H2SO4 and Copper?

2. What are other uses of H2SO4?

Case12- d-Block Transition Elements Complexes


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The transition metals are the group of metals in the middle section of the periodic table. They

are divided into three groups - the first row transition metals, the second row transition metals

and, guess what, the third row transition metals. The most commonly studied ones are the first

row transition metals, listed in the table below.

Symbol Name Atomic

Number

Electronic Configuration

Sc Scandium 21 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

1

Ti Titanium 22 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

2

V Vanadium 23 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

3

Cr Chromium 24 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

1, 3d

5

Mn Manganese 25 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

5

Fe Iron 26 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

6

Co Cobalt 27 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

7

Ni Nickel 28 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

8

Cu Copper 29 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s1, 3d

10


Mr Brain Page 27

Zn Zinc 30 1s2, 2s

2, 2p

6, 3s

2, 3p

6, 4s

2, 3d

10

Why are they called the transition metals? They are the metals which make the transition to

using the d-orbitals for their bonding. Hence they are sometimes called the d-block elements.

(The f-block elements are the ones which make the transition to using their f-orbitals for

bonding.)

All the transition metals have certain properties in common, and exams often ask you to list or

discuss some of these common properties.

• They have a partly filled d-shell either as the element or in their compounds (apart from

Zn).

• They are all metals.

• They are all shiny metals with the typical metallic grey / white colour, except gold, which

is gold coloured, and copper, which is copper coloured.

• They are all good conductors of heat and electricity.

• They have high melting and boiling points.

• Most transition metals form coloured compounds (apart from Sc and Zn).

• They have several stable oxidation states or valencies.

• Many are used as catalysts, either as the metal itself or as some of their compounds.

• They form complex ions, with various co-ordination numbers and geometries.

• Many form compounds which are paramagnetic (have unpaired electrons).


Mr Brain Page 28

Overall Summary Table to memorize for GCE O Level

Case Catalyst & conditions Application/Processes

1 Finely divided Iron, 450 degree C, High

pressure 250 atm

Haber process for the synthesis of

ammonia gas.

2 Temperatures (450 °C), medium pressures

(1-2 atm), and vanadium(V) oxide (V2O5) Use in 1

st step of Contact process for

making H2SO4 to convert SO2 to SO3.

3 Ceramic elements coated with Platinum

(OA & RA), rhodium(RA) & palladium (OA)

Use in 2/3 ways catalytic convertor of

automobile to remove exhaust gas

pollutants CO, NOx, CxHy

4 Temperature 200 degree C, Nickel Hydrogenation of Alkenes to Alkanes.

5 Free radicals of Chlorine, NO, Bromine

from CFC products in the presence of solar

UV radiation

Root-cause of Ozone layer depletion in

stratosphere

6 Manganese Oxide (MnO2) Decomposition of H2O2 in the

Laboratory to produce Oxygen gas

7 High Temperature 600 degree C,

Aluminum Oxide or Silicon(IV) Oxide

Cracking of heavy Alkanes to hydrogen,

smaller molecule Alkanes or Alkenes.

8 Moderate pressures 10–20 atm and high

temperatures (around 850 °C), Nickel or

Nickel Oxide

In 1st

step of synthesis gas production to

convert methane (natural gas) to CO &

H2 gases.

9 Platinum metal or alloy Used as Fuel cells electrodes’ coating

10 Phosphoric (V) acid, Temperature 300

degree C pressure 60 atm

Industrial process of Alcohol production

by reacting steam with Alkenes.

11 Concentrated Sulphuric Acid Esterification (condensation reaction) of

Alcohol and Carboxylic acid

12 Aqueous ions of Transition metals such as

Copper

Increase speed of reaction between

metals and acids.

------------------End of Summary-----------------

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