Slide 1: Surface Chemistry - Catalyst and types of catalysts

  • Surface chemistry is the branch of chemistry that deals with the study of the chemical phenomena occurring at the interface of two phases, such as solid-gas, solid-liquid, or liquid-gas.
  • Catalysts are substances that increase the rate of a chemical reaction by providing an alternative reaction pathway with lower activation energy.
  • They do not undergo any net change and are not consumed during the reaction.
  • Catalysts can be classified into two types: homogeneous catalysts and heterogeneous catalysts.

Slide 2: Homogeneous Catalysts

  • Homogeneous catalysts are those which are present in the same phase as the reactants.
  • They form an intermediate complex with the reactants and facilitate the reaction.
  • Examples of homogeneous catalysts are transition metal complexes in solution, such as chloroplatinic acid (H2PtCl6) used in the hydration of propene.

Slide 3: Heterogeneous Catalysts

  • Heterogeneous catalysts are those which exist in a different phase from the reactants.
  • They act by adsorbing the reactant molecules onto their surface and providing a favorable environment for the reaction to occur.
  • Examples of heterogeneous catalysts include finely divided metals like platinum (Pt), nickel (Ni), and catalysts like zeolites, which are used in the petroleum industry.

Slide 4: Types of Catalysts

  1. Homogeneous Catalysts:
    • Transition metal complexes
    • Acid-base catalysts
  1. Heterogeneous Catalysts:
    • Metals (e.g., platinum, nickel)
    • Metal oxides (e.g., iron oxide)
    • Zeolites
    • Enzymes

Slide 5: Transition Metal Complex Catalysts

  • Transition metal complexes are widely used as homogeneous catalysts due to their ability to undergo redox reactions.
  • They often involve the formation of coordination complexes with the reactants.
  • These catalysts can be tailored to have high selectivity towards desired products.
  • An example is the use of Wilkinson’s catalyst, [(Ph3P)3RhCl], which is used for hydrogenation reactions.

Slide 6: Acid-Base Catalysts

  • Acid-base catalysts are homogeneous catalysts that facilitate reactions by donating or accepting protons (H+).
  • Acids donate protons, while bases accept protons.
  • These catalysts are commonly used in organic reactions, such as esterification and hydrolysis.
  • Sulfuric acid (H2SO4) and sodium hydroxide (NaOH) are common examples of acid and base catalysts, respectively.

Slide 7: Metal Catalysts

  • Metal catalysts are heterogeneous catalysts that can be in the form of finely divided metals.
  • They provide a surface for reactant adsorption and promote reactions.
  • Examples include platinum (Pt), which is used in the catalytic converters of automobiles to convert harmful gases, and nickel (Ni), which is used in the hydrogenation of fats and oils.

Slide 8: Metal Oxide Catalysts

  • Metal oxide catalysts are heterogeneous catalysts that consist of metal atoms bonded to oxygen atoms.
  • These catalysts primarily promote redox reactions.
  • Examples include iron oxide (Fe2O3), which is used in the Haber process for ammonia synthesis, and titanium dioxide (TiO2), which is used in the photocatalytic degradation of pollutants.

Slide 9: Zeolite Catalysts

  • Zeolite catalysts are heterogeneous catalysts composed of a framework of silica (SiO2) and alumina (Al2O3) with pores of defined sizes and shapes.
  • These catalysts have a high surface area and specific pore structure, allowing them to selectively adsorb and catalyze certain reactions.
  • They are commonly used in the petroleum industry for cracking reactions and as shape-selective catalysts.

Slide 10: Enzyme Catalysts

  • Enzymes are biological catalysts that are highly specific and efficient.
  • They are protein molecules that facilitate biochemical reactions in living organisms.
  • Enzymes work by reducing the activation energy required for a reaction to occur, increasing reaction rates.
  • They exhibit high selectivity and can catalyze a wide range of reactions.
  • Examples of enzymes include amylase, which catalyzes the hydrolysis of starch, and catalase, which catalyzes the decomposition of hydrogen peroxide.
  1. Importance of Catalysts:
  • Catalysts play a crucial role in various industrial processes, including petroleum refining, chemical synthesis, and environmental remediation.
  • They enhance reaction rates, leading to improved efficiency and reduced energy consumption.
  • Catalysts also enable the production of desired products selectively, minimizing unwanted by-products.
  • Examples: Catalytic converters in car engines reduce harmful emissions, and catalysts in the production of ammonia increase efficiency.
  1. Factors Affecting Catalyst Activity:
  • Surface area: Catalysts with higher surface area provide more active sites for reactant adsorption, enhancing activity.
  • Temperature: Catalyst activity usually increases with temperature due to increased reactant energy and collision frequency.
  • Pressure: Some reactions are pressure-dependent, and catalyst activity may be affected by changes in pressure.
  • Reactant concentration: Higher reactant concentration can increase catalyst activity by increasing the number of collisions.
  • Presence of inhibiting substances: Certain substances may inhibit catalyst activity, affecting reaction rates.
  1. Mechanism of Catalysis:
  • Catalysts provide an alternative reaction pathway with lower activation energy.
  • They stabilize transition state complexes for reactions, facilitating the breaking and formation of chemical bonds.
  • Catalysts may involve interactions with reactant molecules through adsorption, coordination, or electrostatic interactions.
  • The catalytic cycle comprises several steps, including reactant adsorption, reaction, and product desorption.
  1. Specific Examples of Catalysts:
  • Platinum in catalytic converters: Converts harmful gases like carbon monoxide and nitrogen oxides into less harmful substances.
  • Enzymes in biological systems: Catalyze numerous biochemical reactions essential for metabolism and cellular processes.
  • Iron oxide in the Haber process: Catalyzes the synthesis of ammonia from nitrogen and hydrogen.
  • Zeolites in petroleum refining: Control the size and shape-selective cracking of hydrocarbon molecules.
  • Nickel in hydrogenation reactions: Catalyzes the addition of hydrogen to unsaturated compounds like oils and fats.
  1. Catalyst Deactivation:
  • Catalysts can experience deactivation, leading to a decrease in their activity and effectiveness.
  • Several reasons for catalyst deactivation include poisoning by impurities, fouling due to reactant adsorption, and sintering of catalyst particles.
  • Regeneration techniques like catalyst washing, heat treatment, and surface reactivation are applied to restore catalyst activity.
  1. Application of Heterogeneous Catalysts:
  • Heterogeneous catalysts find extensive use in industrial processing due to their stability and ease of separation from the reaction mixture.
  • Examples include the use of metal catalysts in hydrogenation, oxidation, and isomerization reactions.
  • Metal oxide catalysts are employed in catalytic cracking, catalytic reforming, and the removal of pollutants from exhaust gases.
  1. Application of Homogeneous Catalysts:
  • Homogeneous catalysts are useful in fine chemical synthesis and pharmaceutical industries.
  • Examples include transition metal complexes in organic synthesis, such as the Grubbs catalyst for olefin metathesis reactions.
  • Acid-base catalysts like sulfuric acid find application in esterification and hydrolysis reactions.
  1. Industrial Catalytic Processes:
  • Several industries rely on catalytic processes for the production of important chemicals.
  • Examples include the Haber-Bosch process for ammonia synthesis, the contact process for sulfuric acid production, and the catalytic cracking of petroleum.
  • Industrial catalysts are optimized for high efficiency, selectivity, and stability, taking into account economic and environmental factors.
  1. Environmental Applications of Catalysts:
  • Catalysts play a crucial role in environmental protection and sustainability.
  • They are used in pollution control technologies, such as exhaust catalysts in vehicles and catalytic converters to reduce air pollution.
  • Additionally, catalysts help in the treatment of wastewater and the removal of harmful pollutants from industrial effluents.
  1. Future Trends in Catalysis:
  • Ongoing research focuses on developing novel catalysts with improved properties, such as higher activity, selectivity, and stability.
  • Nanocatalysis, biocatalysis, and photocatalysis are emerging fields that hold great potential for future applications.
  • The use of sustainable and renewable catalysts is gaining attention, aiming to reduce environmental impact and reliance on scarce resources.
  • Reaction Rate: Catalysts increase the reaction rate by lowering the activation energy required for a reaction to proceed.
  • Example: The breakdown of hydrogen peroxide (H2O2) is slow in the absence of a catalyst, but with the presence of a catalyst like manganese dioxide (MnO2), the reaction occurs rapidly.
  • Selectivity: Catalysts can enhance the selectivity of a reaction by promoting specific pathways leading to desired products.
  • Example: In the conversion of ethanol to ethanoic acid, a catalyst like palladium (Pd) supported on carbon can selectively oxidize ethanol without further oxidation to carbon dioxide.
  • Enzymes: Enzymes are biological catalysts that greatly enhance reaction rates in living organisms.
  • They are highly specific and can catalyze a wide range of reactions.
  • Example: The enzyme amylase catalyzes the breakdown of starch into smaller sugar molecules.
  • Adsorption: Catalysts work through adsorption, where reactant molecules bind to the catalyst’s surface.
  • Adsorption can occur through different types of interactions, such as physical adsorption or chemisorption.
  • Example Equation: A + B on catalyst surface → AB (adsorbed complex)
  • Activation Energy: Catalysts lower the activation energy required for a reaction to occur by providing an alternative reaction pathway.
  • The activation energy is the energy barrier that reactant molecules must overcome to form products.
  • Example Equation: Reactants (A + B) + Catalyst → Activated Complex → Products
  • Active Sites: Catalysts have specific regions called active sites where reactant molecules bind and undergo chemical reactions.
  • The arrangement and accessibility of active sites greatly affect catalyst activity.
  • Example: Platinum catalysts have numerous active sites on their surface for promoting various reactions.
  • Catalyst Poisoning: Catalysts can get deactivated or poisoned by the presence of certain substances that block active sites or inhibit catalytic activity.
  • Common poisons include sulfur compounds and lead in some catalytic converters.
  • Example: Sulfur can poison catalysts used in the petroleum industry, reducing their effectiveness.
  • Catalyst Regeneration: Deactivated catalysts can be regenerated by removal of poisons or by physical or chemical treatment.
  • Regeneration restores the catalyst’s activity and improves its efficiency.
  • Example: Spent catalysts used in large-scale processes are often regenerated to recover their catalytic properties.
  • Factors Affecting Catalyst Performance: Several factors can influence the performance of a catalyst.
  • Temperature, pressure, reactant concentration, and the presence of inhibitors or promoters can affect catalytic activity.
  • Example: Higher temperatures generally increase catalyst activity by providing more energy for reactant molecules to overcome the activation energy barrier.
  • Catalysts in Everyday Life: Catalysts are present in many aspects of our everyday lives, beyond industrial applications.
  • Examples include enzymes in digestion, catalytic converters in vehicles, and catalysts used in laundry detergents.
  • Catalysts make numerous everyday processes more efficient, economical, and sustainable.