Green catalysts are catalysts designed to increase reaction efficiency while minimizing environmental and health impacts. They follow the principles of green chemistry by being non-toxic, recyclable, energy-efficient, and derived from abundant or renewable resources.
Here’s a breakdown of examples and types:
1. Biocatalysts (Enzymes)
- What they are: Proteins that speed up reactions under mild conditions.
- Examples: Lipases, oxidases, proteases, cellulases.
- Applications: Pharmaceutical synthesis, food processing, biodiesel production.
- Why green: Biodegradable, highly selective (reduces waste), operate at low temperature and pressure.
2. Heterogeneous Catalysts
- What they are: Solid catalysts that can be separated from the reaction mixture and reused.
- Examples:
- Zeolites (used in petrochemical refining)
- Supported metal catalysts (Pd/C, Pt/C)
- Metal oxides like TiO₂, Al₂O₃, or CeO₂
- Why green: Recyclable, reduce need for solvents, and minimize energy consumption.
3. Organocatalysts
- What they are: Small organic molecules that catalyze reactions without metals.
- Examples: Proline (amino acid), DMAP, cinchona alkaloids.
- Applications: Asymmetric synthesis, esterifications, Michael additions.
- Why green: Metal-free, biodegradable, often used in mild conditions.
4. Photocatalysts
- What they are: Catalysts activated by light, often visible or UV.
- Examples: TiO₂, ZnO, graphitic carbon nitride (g-C₃N₄).
- Applications: Water purification, pollutant degradation, hydrogen production.
- Why green: Utilize sunlight, reduce chemical waste, often reusable.
5. Electrocatalysts
- What they are: Catalysts that facilitate electrochemical reactions.
- Examples: Transition metal phosphides, carbides, or nitrogen-doped carbon materials.
- Applications: Water splitting, fuel cells, CO₂ reduction.
- Why green: Enable clean energy conversion, often using abundant materials.
6. Supported Ionic Liquids
- What they are: Ionic liquids immobilized on solid supports.
- Applications: Catalysis in organic synthesis.
- Why green: Low volatility, reusable, tunable properties.
Summary:
Green catalysts are mainly enzymes, solid reusable metals, organocatalysts, photocatalysts, or electrocatalysts. The common goal is high efficiency, low toxicity, recyclability, and reduced energy usage.