Interfacial Catalysis Overview

Interfacial Catalysis

• Definition:
  • Reactions occurring at the interface between two immiscible phases
  • Interface is a thin and poorly defined layer where all matter and energy exchanges occur
  • The interface is in a unique state, also called a phase boundary
• Types of Interfaces:
  • Solid-Solid
  • Solid-Liquid
  • Solid-Gas
  • Liquid-Liquid
  • Liquid-Gas
• Reactivity at the Interface:
  • The reaction conditions of a molecule adsorbed at an interface are different from those in the bulk phases.
  • Higher Concentrations: Molecules concentrate at the interface, influencing reaction rates
  • Different Permittivity: Unique solvent properties at the interface, affecting reactivity
  • Defined Molecular Orientations: Specific molecular arrangements at the interface, leading to selectivity in reactions
  • This molecular organization resembles those in biological systems, like cell membranes
• Advantages of Interfacial Catalysis:
  • Milder/safer reaction conditions
  • Increased rates for slow reactions
  • Higher product yields and purity
  • Enhanced reactivity and selectivity
  • Simplified procedures
  • Easy product separation due to initial partitioning
  • Scalability
  • Low energy consumption and investment cost
  • Minimization of industrial waste
• Examples of Application:
  • Ruhrchemie/Rhône–Poulenc hydroformylation of propene (the oxo process)
    • Produces over 450,000 tons/year of aldehydes
  • Aqueous biphasic catalysis:
    • Uses water-soluble phosphines for high activity and selectivity
    • Easy separation by decantation
• Concepts for Interfacial Catalysis:
  • Two main approaches:
    • Macroscopically Heterogenous Media:
      • Phase-transfer catalysis: Uses catalysts to transfer reactants between immiscible phases
      • Pickering emulsions: Emulsions stabilized by solid particles
    • Microscopically Heterogenous Media:
      • Lyotropic phases: Self-assembling lipid structures
      • Micellar catalysis: Uses micelles for catalysis
        • Micelles: Spherical structures of surfactants in solution
        • Vesicles: Lipid bilayer structures
        • Microemulsions: Stable dispersions of oil, water, and surfactants
        • Kinetic Effects: Increase the rate of reactions
        • Nano/micro-compartments: Provide environments similar to biological systems

Phase-Transfer Catalysis

• Uses Crown Ethers:

Micellar Catalysis

• Onion-like Structure:

Emulsion Catalysis

• Pickering-Assisted Catalysis:

Microemulsion Catalysis

• Salts: