29 Questions
What is the main purpose of phase transfer catalysts?
To increase rates of reactions where reactants are in different phases
Which type of catalyst is specifically useful for destroying harmful waste and water clean-up?
Photocatalysts
What is a key feature of heterogeneous catalysis mentioned in the text?
High surface area
How do phase transfer catalysts help in improving mass transport limitations?
By transporting reactants/reagents from one phase into another
Which factor influences the efficiency of a catalyst related to its nature and structure?
Pore size affecting rate of diffusion
What is the purpose of the regeneration process in catalytic cracking?
To burn off coke deposited on the catalyst
What determines the nature of a synthetic zeolite?
The composition of the base used in synthesis
Which method of cracking heavy oil fractions is known for being more energy efficient?
Fluid Catalytic Cracking (FCC)
Which characteristic is NOT associated with Zeolites?
Large pore size around 0.8 nm
What is the primary function of Zeolites in the bulk chemical industry?
Removal of heavy metals and odors
What is the role of desorption in the catalytic cycle of heterogeneous catalysts?
To facilitate the diffusion of reactants to the surface
What contributes to significant waste generated by industries using homogeneous catalysts?
Neutralization
In the context of homogeneous catalysts, what is the maximum number of metal-ligand bonds based on the 18 electron rule formula?
n + 2(CN)
What type of orbitals do transition metals have that make their electrons ready to transfer?
d orbitals
Which type of ligands are described as coordinatively unsaturated in the context of homogeneous catalysis?
Phosphine ligands
What is the cobalt catalyst HCo(CO)4 commonly used for in homogeneous catalysis?
Hydroformylation reactions
Which Lewis acids are highly water sensitive and not recovered, as mentioned in the text?
$BF_3$
What is the pore aperture size of ZSM-5 zeolite?
0.55 nm
In the Mobil MTG process, what reaction does ZSM-5 catalyze?
Alkylation of benzene with ethene
Why are many zeolites not stable at high temperatures in the presence of water?
Due to dealumination process
How is cyclohexanol traditionally prepared?
Catalytic hydrogenation of benzene followed by air oxidation using Co catalyst
What is the main product obtained through the use of H-ZSM-5 in toluene alkylation with methanol?
p-xylene
What type of reaction yield and selectivity are greatly enhanced by High Silica Zeolites in bulk chemical industries?
Aromatic substrate transformations
What is the advantage of using H2O2 for oxidation reactions?
It replaces waste generating peroxides like peracetic acid.
What role does phase transfer catalysis play in oxidation using H2O2?
Facilitates the transfer of the oxidant to the organic phase.
What is the significance of cysteine amino acids in enzyme structures?
They form stable disulfide linkages that hold the structure in place.
How do amino acids contribute to enzyme catalysis in green chemistry?
By acting as acid or base catalysts.
What is true about the oxidation of thiol functional group in cysteine?
It forms stable disulfide linkages to create cystine.
Which metal ions found in the body can enhance the scope of enzyme activity?
Fe2+ and Zn2+
Study Notes
Homogeneous Catalysis
- Transition metals have partially filled d orbitals, which are high-energy electrons ready to transfer.
- Ligands bond with transition metals through partially filled d orbitals.
- The maximum number of metal-ligand bonds is 18 (18 e- rule: n + 2(CN)max = 18).
- Complexes with less than maximum number of ligands are described as coordinatively unsaturated and make good catalysts.
- Phosphine ligands are very good electron donors and significantly influence reaction rates.
- Carbonyl ligands are used in hydroformylation reactions, such as the carbonylation of methanol to acetic acid.
- Wilkinson's catalyst (RhCl(PPh3)3) is highly valuable for alkene hydrogenation and is carried out at ambient temperature and pressure.
Lewis Acids
- Lewis acids are highly water sensitive and not recovered.
- Greener Lewis acids are being developed to replace waste-generating peroxides.
- Phase transfer catalysis facilitates oxidation using H2O2 by transferring the oxidant to the organic phase.
Biocatalysis
- Enzymes are complex proteins made from 100 to 400 amino acids.
- Enzyme activity depends on the sequence of amino acids and their 3D structure.
- Cysteine amino acids are important for forming stable disulfide linkages that hold the structure in place.
- Amino acids can act as acid or base catalysts.
- Enzyme catalysis is enhanced by coordination with metal ions found in the body, such as Mg2+, Fe2+, Fe3+, Ca2+, and Zn2+.
Heterogeneous Catalysis
- Heterogeneous catalysts have a catalytic cycle involving surface chemisorption, physisorption, reaction, diffusion, and desorption.
- Metal oxides impregnated with silica and/or alumina are used in heterogeneous catalysis.
- Zeolite Beta has a large pore size of around 0.7mm.
Zeolites
- Zeolites are 3D frameworks of crystalline hydrated aluminosilicates consisting of TO4 (T: tetrahedral, Si or Al).
- Zeolites have well-defined microporous structures and are hydrated, which imparts significant Brønsted acidity.
- There are 45 naturally occurring zeolites, including mordenite, clinoptilolite, and chabazite.
- Zeolites are used in the removal of heavy metals, odors, and building materials.
Zeolites and Bulk Chemical Industry
- Synthetic zeolites are synthesized by mixing a source of silica, a source of alumina, and a base, and then heating up to 200°C under autogenous pressure.
- Tuned pore sizes and acidities can be achieved by adjusting the reaction conditions and silica to alumina ratio.
- Zeolite Y has a large pore size of 0.8 nm and is used in fluid catalytic cracking (FCC).
Catalytic Cracking
- Catalytic cracking is used to produce gasoline from heavy oil fractions.
- Zeolite-based catalysts are used in fluid catalytic cracking (FCC) to improve efficiency and selectivity.
Commercial Uses of ZSM-5
- ZSM-5 has a 10-membered ring-pore aperture of 0.55 nm and is used in selective transformations on small aromatic substrates.
- ZSM-5 is used in the production of p-xylene through toluene alkylation with methanol, xylene isomerization, and toluene disproportionation.
- ZSM-5 is also used in the Mobil MTG process, which converts methanol to gasoline.
High Silica Zeolites
- High silica zeolites are prepared by adjusting the Si/Al ratio or by stabilization with silica after dealumination.
- High silica zeolites have improved stability and are used in bulk chemical industries.
Other Classifications of Catalysts
- Photocatalysts harness sun energy for carrying out chemical transformations.
- Phase transfer catalysts transport reactants/reagents from one phase into another, improving reaction rates and selectivity.
Learn about various types of catalysts such as photocatalysts and phase transfer catalysts, their classifications, and applications in chemical transformations. Understand how catalysts can improve reaction rates and facilitate mass transport in different phases.
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