Catalysis and its Types Homogeneous Catalysis Advantages of Homogeneous Catalysis History of Homogeneous Catalytic Reactions Examples of Homogeneous Catalytic Reactions

1. SUBMITTED BY
HAMYAL AWAIS
MPHIL CHEMICAL ENGINEERING
SCME, NUST

2. HOMOGENEOUS
CATALYTC
REACTIONS

3. “Catalysis is the key process to accelerate the rate of a chemical reaction in the presence of a catalyst”
CATALYST
A catalyst is a chemical substance that accelerates the rate of a chemical reaction by providing a new path with a
low activation energy and is not chemically consumed and can be regenerated at the end of the reaction.
TYPES OF CATALYSIS
Catalysis can be divided into following two types
1. Homogeneous Catalysis
2. Heterogeneous Catalysis
CATALYSIS
https://www.energy.gov/science/doe-
explainscatalysts#:~:text=Catalysis%20is%20the%20process%20of,the%20atoms%20into%20new%20molecules.V

4. The word homogeneous divides into two categories
“Homo” mean “Same” & “Geneous” means “Phase”
FEATURES
In the homogeneous catalytic process:
 The reactants involved in the chemical reaction are in same phase
with the catalyst used
 The catalyst is distributed evenly with the reactants
 The reaction proceeds with the decrease in activation energy
 The reaction continues with the formation of intermediate molecules
 Multiple steps are usually involved in the catalytic process
HOMOGENEOUS CATALYSIS
https://en.wikipedia.org/wiki/Homogeneous_catalysis

5. HOMOGENEOUS VS HETEROGENEOUS
CATALYSIS
HOMOGENEOUS
HETROGENEOUS
https://www.chemguide.co.uk/physical/catalysis/introduction.html

6. HISTORICAL BACKGROUND OF
HOMOGENEOUS CATALYSIS
Contributions
of
Wilhelm
Ostwald
In the late 19th century, a
German chemist Wilhelm
Ostwald, made
pioneering contributions
in early catalytic
processes by his work on
the oxidation of
ammonia over platinum
catalyst
Emergence
of
Organometallic
Chemistry
In the early 20th century,
the organometallic
compounds containing
metal-carbon bonds
becomes increasingly
predominant, play a
pivotal role in
homogeneous catalysis
Contributions
of
Sabatier
&
Senderens
In the 20th century, the
foundational work of
French chemists Pau J.
Sabatier and Jean
Baptiste Senderens laid a
foundation of catalysis
by demonstrating the use
of finely divided soluble
transition metal
complexes for the
catalytic hydrogenation
of various organic
compounds, paving the
way of modern
homogeneous catalysis
Nobel
Laureates
in
Homogeneous
Catalysis
In 1963, Karl Ziegler and
Giulio Natta received Noble
Prize for their work on
catalytic polymerization.
In 1973, Ernst Otto Fischer
and Geoffrey Wilkison
received Noble Prize for their
contributions to
organometallic chemistry.
Wisniak, J. (2010). The history of catalysis. From the
beginning to Nobel Prizes. Educación química, 21(1), 60-69.

7. o Less time is required
o Economic and easy avalibility
o High yield is obtained
o Less conditions are required to fulfil
o Catalysts are more active and selective
o Pore diffusion limitations are not present as
catalysts are equally dispersed in the mixture
o Acidic catalysts are not affected by the
content or vice versa
o Chemistry and mechanism of reaction can
be studied more effeciently
o Not efficient way is present to separate the
reaction mixture
o Large amount of water is required for the
reaction
o Basic catalysts are affected by the content
o Bulk phase mass transfer limitations are
present
ADVANTAGES DISADVANTAGES
https://www.researchgate.net/figure/Advantages-and-disadvantages-of-homogeneous-and-heterogeneous-catalysts-in-biodiesel_tbl2_337389292

8. The mechanism of homogeneous catalysis involves a series of following steps through which a catalyst facilitates a
chemical reaction between reactants.
STEP I
CATALYST-SUBSTRATE INTERACTION
 The catalytic reaction begins when the catalyst interacts with the reactants to form an intermediate complex.
 The binding usually occurs through coordination bonds, where catalyst is used as a coordination center.
STEP II
REACTION INTERMEDIATES FORMATION
 The crucial step in the catalytic process is the transformation of catalyst-reactant complex into reactive intermediates.
 The reactivity of these intermediates is different than original reactant molecules, which allows the occurrence of
desired chemical transformation.
STEP III
CATALYTIC CYCLE
 This step includes different steps that facilitates the conversion of reactants into desired products; such as substrate
binding, activation, reaction process, and release of product.
MECHANISM OF HOMOGENEOUS CATALYSIS

9. STEP IV
REACTION FACILITATION
 The catalysts accelerates the chemical reaction by providing an alternate pathway that helps to stabilize the transition
states by lowering the energy of activation.
STEP V
CATALYST REGENERATION
 In the final step of catalytic process, after facilitating the reaction, the catalyst is regenerated.
STEP VI
MULTIPLE TURNOVERS
 The catalyst can efficiently facilitates the conversion of multiple sets of reactants into products, therefore can
repeatedly catalyzed same reaction without being consumed.
MECHANISM OF HOMOGENEOUS CATALYSIS
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CHE_103Chemistry_for_Allied_Health_%28Soult%29/Chapters/Chap
ter_11%3A_Properties_of_Reactions/11.6%3A_Rates_of_Reactions

10. Exothermic Reaction
Endothermic Reaction
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CHE_103Chemistry_for_Allied_Health_%28Soult%29/Chapters/Chap
ter_11%3A_Properties_of_Reactions/11.6%3A_Rates_of_Reactions

11.  Acid-Base Catalysis
 Transition Metal Complexes
 Organocatalysis
 Photocatalysis
 Enzymatic Catalysis
 Metathesis Catalysis
TYPES OF
HOMOGENEOUS
CATALYSIS

12. In acid catalysis,
 An acid catalyst donates proton(s) (H+) to the reactant molecules to facilitate the catalytic
reaction.
 An electrophilic specie is formed.
 A stable carbocation intermediate is formed.
EXAMPLES
 Hydrolysis of Ester or Amines
 Formation of Sulphur dioxide
 Formation of Ethyl acetate
ACID CATALYSIS

13. Acid catalyzed hydrolysis reactions involves the cleavage of chemical bonds by the addition of water molecule.
 In the hydrolysis of an ester, the (-OR) group of the ester is replaced by the hydroxyl (-OH) group from water,
which results in the formation of a carboxylic acid and an alcohol.
 CATALYSTS: Mineral acid e.g. dilute sulphuric acid (H2SO4) or dilute hydrochloric acid (HCl)
 MECHANISM:
Step 1: The acid catalyst protonated the
oxygen atom present on the carbonyl group.
The positively charged oxygen increases the
electrophilicity of the carbonyl carbon.
Step 2: The water molecule attacks the
electrophilic carbon of carbonyl group
Step 3: A tetrahedral intermediate is formed.
Step 4: The acid causes the protonation of
-OR group which causes its detachment.
Step 5: A molecule of carboxylic acid is
generated.
https://psiberg.com/hydrolysis-of-esters/
HYDROLYSIS OF ESTER

14. In base catalysis,
 A base catalyst donates proton(s) (H+) to the reactant molecules to facilitate the catalytic
reaction.
 An nucleophilic specie is formed.
 A stable carbanion intermediate is formed.
EXAMPLE
 Hydrolysis of Ester (Saponification)
BASE CATALYSIS

15. SAPONIFICATION
 Base catalyzed hydrolysis reactions involves the cleavage of chemical bonds by the addition of water
molecule.
 In the saponification process, the (-OR) group of the ester is replaced by the hydroxyl (-OH) group from
water, which results in the formation of a carboxylate ion and an alcohol.
 CATALYSTS: Strong alkali such as sodium hydroxide (NaOH)
 MECHANISM
Step 1: The hydroxide ion acts as a nucleophile
and attacks the electrophilic carbonyl carbon
to form a tetrahedral intermediate.
Step 2: The oxygen atom removes a -OR
group and forms a double bond which causes
the formation of carboxylic acid.
Step 3: The alkoxide ion cleaves the
proton by breaking acyl –oxygen bond to form
a carboxylate ion and an alcohol molecule.
https://psiberg.com/hydrolysis-of-esters/

16.  Conversion of unsaturated compounds (e.g. alkenes, alkynes or olefins) into saturated compounds (e.g.
alkanes) by the addition of hydrogen gas under the influence of transition metals catalysts.
 It reduces the unsaturation by converting the double or triple bonds into single bond of saturated compounds
 SUBSTRATE: alkenes, alkynes
 PRODUCT: alkanes
CATALYST: Nickel, Palladium, Platinum, Wilkinson's catalyst, Chlorotris-(triphenylphosphine) rhodium,
[(Ph3P)3RhCl]
 USE: Using this process, vegetable oils are converted into solid fats (ghee)
 EXAMPLES:
Hydrogenation of Alkenes
Hydrogenation of Alkynes
Hydroformylation Reaction
HYDROGENATION REACTIONS

17. HYDROGENATION OF ALKENES
 The double bond in alkenes is converted in single bond of alkanes by the addition of hydrogen in the presence
of Pd catalyst
 The mechanism of hydrogenation reaction is
shown below

18. HYDROGENATION OF VARIOUS HYDROCARBONS

19.  The hydroformylation process, also known as oxo-reaction, was developed by O. Roelen.
 In the hydroformylation process, branched or linear aldehyde molecules are synthesized in the industries by
the addition of a hydrogen atom and a formyl group in alkenes.
 CATALYSTS: tris rhodium carbonyl hydride & cobalt tetra carbonyl hydride
HYDROFORMYLATION REACTION
https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Inorganic_Chemistry_(LibreTexts)/14%3A_Org
anometallic_Reactions_and_Catalysis/14.03%3A_Organometallic_Catalysts/14.3.02%3A_Hydroformylation

20. MECHANISM
Step 1: The pre-catalyst Co2(CO)8 in converted into
actual catalyst HCo(CO)4 in the presence of H2. Then a molecule of
CO is removed from catalyst to give the 16-electronmolecule.
Step 2: The alkenes bind with resultant molecule to
form an molecule containing18-electrons
Step 3: The olefin molecule is inserted to form alkyl tricarbonyl.
Step 4: Another molecule of CO is added from catalyst to form
alkyl tetracarbonyl.
Step 5: The alkenes bind with resultant molecule to form an
molecule containing18-electrons
Step 6: Another molecule of CO is added to form an acyl molecue
containing16-electrons
Step 7: A molecule of hydrogen is added to form a di hydrido
complex
Step 8: In the end, a molecule of aldehyde is released by reductive
elimination process.
https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Inorganic_Chemistry_(LibreTexts)/14%3A_Organometallic_Reactions_and_Catalysis/14.03%3A_Organometallic_Cata
lysts/14.3.02%3A_Hydroformylation

21. Hydrosilylation or hydrosilation is a catalytic process in which organsilanes and organosilicones (alkyl silanes, vinyl
silanes and silyl ethers) are synthesized by the addition of a H-Si in a bond such as carbon-carbon, carbon-oxygen,
carbon-nitrogen, nitrogen-nitrogen and nitrogen-oxygen present in unsaturated compounds (alkenes, alkynes,
aldehydes and ketones) through transition metal catalyst, Lewis acid, or radical.
 CATALYST: Speier's catalyst (H2PtCl6), Karstedt's catalyst, Wilkinson's catalyst
 MECHANISM
A most recognized mechanism for metal
catalyzed hydrosilylation reaction is
Chalk-Harrod mechanism.
There are various modifications to this
mechanism.
Step 1: The Si-H bond is added to metal
catalyst by the process of oxidation.
Step 2: After that the alkene molecules
are inserted.
Step 3: The hydrogen atom is added to
the alkene molecule through beta-insertion
process.
Step 4: The adduct is obtained by the reduction of alkylsilyl Pd(II)
complex and the metal catalyst returns to its original oxidation state.
HYDROSILYLATION REACTION
,
https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and
_Websites_%28Inorganic_Chemistry%29/Catalysis/Catalyst_Examples/Hydrosilylation

22.  The hydrocyanation process was developed by Arthur and Pratt in 1954.
 It is an industrial catalytic process for the conversion of unsaturated hydrocarbons (e.g. linear alkenes and
alkynes) to nitriles by the addition of hydrogen cyanide (HCN) to the metal complexes.
 SUBSTRATE: alkenes
 PRODUCT: nitriles
CATALYST: copper, palladium, nickel, phosphite (P(OR)3) complexes of nickel, chiral, chelating aryl diphosphite
complexes, Lewis acids such as B(C6H5)3, triphenylboron
 EXAMPLES:
HYDROCYANATION REACTION
Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic Chemistry; John Wiley & Sons: New York, 1999; pp. 244-6, 440, 1247-9

23. Following is the mechanism of industrial process for catalytic hydrocyanation of butadiene to adiponitrile, which was
developed by W. C. Drinkard.
MECHANISM
Step 1:
First Hydrocyanation
Butadiene is transformed into a mixture of
2-methyl-3-butenenitrile (2M3BM) and 3-pentenenitrile (3PN)
Step 2:
Isomerization
2M3BM (unwanted product) is converted to 3PN
Step 3:
Second Hydrocyanation
3PN is converted into adiponitrile using a Lewis acid such as
aluminium trichloride as a catalyst
https://www.sciencedirect.com/science/article/abs/pii/B9780080951676005176

24. ADVANTAGES
 The nitriles obtained as a result of hydrocyanation can be converted into a variety of industrially useful products
which includes amines, amides, carboxylic acids, esters.
 Adiponitrile serves as a precursor of hexamethylenediamine which is used in the synthesis of a variety of Nylon
https://www.sciencedirect.com/science/article/abs/pii/B9780080951676005176

25. HOMOGENEOUS
CATALYSTS
GAS
PHASE
LIQUID
PHASE

26. OXIDATION OF SULPHUR DIOXIDE
 The formation of sulphur trioxide is an example of gas phase homogeneous catalyzed reaction.
 In the lead chamber process, during the manufacturing process of sulphuric acid (H2SO4), nitric oxide
(NO) acts as a catalyst in the oxidation sulphur dioxide (SO2) to sulphur trioxide (SO3).
DECOMPOSITION OF ACETALDEHYDE
 The formation of sulphur trioxide is an example of gas phase homogeneous catalyzed reaction.
 During the normal decomposition of acetaldehyde (R-COH) into methane (CH4) and carbon monoxide
(CO), iodine vapors are used as a catalyst.
https://www.sciencedirect.com/science/article/abs/pii/S0010218073800628
https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1930.0096

27. OXIDATION OF CARBON MONOXIDE
 The degradation of two environmentally hazardous gases, CO and N2O, can be done through the
oxidation of CO by N2O in the presence of ruthenium hydride ((PNN)Ru–H) pincer complex under mild
conditions.
 During this reaction, an O-atom is transferred from N2O to Ru–H bond to form a Ru–OH intermediate, followed
by intramolecular attack of hydroxyl ion on the adjacent CO molecule, synthesizing two non hazardous gases,
carbon dioxide (CO2) and nitrogen (N2).
FORMATION OF ETHYLACETATE
 The synthesis of ethyl acetate is an example of liquid phase homogeneous catalytic reaction.
 During this reaction, ethanol and acetic acid react with each other in the presence of H2 SO4.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6502446/

28. CONCLUSION
&
FUTURE PERSPECTIVE
Homogeneous catalysis is a catalytic driven
approach that plays pivotal role in modern
chemistry, enabling more efficient and selective
chemical processes. By harnessing the
powerful, well-designed catalysts, we can
achieve more efficient and environmental
friendly chemical transformations both in
industries and laboratory research as well as
address pressing global challenges. Continued
research will pave the way to greener and more
sustainable chemical processes.

29. THANK
YOU