Lecture 2 - Heterogenous catalysts

Importance of Catalytic Processes

  • Approximately 85% of chemical processes utilize catalysis.

  • Benefits of Catalysis:

    • Sustainability: Enhances environmental safety and cleaner production.

    • Energy Efficiency: Processes require less energy.

    • Selectivity: Targeted reactions produce fewer byproducts.

    • Reduced Waste: Improved waste management.

Energy Efficiency and Selective Catalysis

  • Energy diagrams demonstrate:

    • Energy activation reduced by catalysts

    • Catalysts provide alternative pathways for reactions, resulting in product formation.

Waste Reduction Techniques

  • E-factor defined: ratio of kg waste/kg product

  • Indicates the environmental impact of a process, with lower values signifying more efficient processes.

Types of Catalysts Overview

  • Homogeneous: Catalysts dissolved in the same phase as reactants.

  • Heterogeneous: Catalysts in a different phase, often solid with liquid/gas reactants.

  • Biocatalysts: Enzymes and other biological catalysts.

Homogeneous Catalysts

  • Examples of acid/base catalysts: HCl, HNO3, H2SO4, NaOH.

  • Frequently comprise metal complexes: combine metal atoms/ions with ligands (including aromatic groups).

Organocatalysts in Homogeneous Catalysis

  • Organocatalysts, inspired by nature, facilitate reactions without metals.

  • Example: Decarboxylase enzyme influencing reactions of amino acids like Phenylalanine and phenethylamine.

Biocatalysts Types

  • Enzymes: Require external energy input.

  • Biotransformations: Occur in cells, needing additional feed for energy.

  • Fermentations: Self-sustaining processes utilizing part of the feed to generate energy.

Heterogeneous Catalysts

  • Example: Supported metal catalysts, commonly used for hydrogenation of unsaturated bonds in oils (e.g., vegetable oils).

  • Application: Healthier food choices via hydrogenation.

Catalyst Types Comparison

  • Activity per reactor volume and temperature effects.

  • Selectivity and ease of separation vary significantly between:

    • Chemocatalysts

    • Biocatalysts

  • Pros and Cons discussed:

    • Heterogeneous vs. homogeneous vs. biocatalysts with focus on selectivity, temperature performance, and separation difficulties.

Components of Heterogeneous Catalysts

  • Common components include:

    • Support: Material facilitating reaction services, e.g., oxides like SiO2 and Al2O3, activated carbon.

    • Active Phase: The active phase where reactions occur.

    • Promoter: Enhances catalyst performance without being directly active.

Function of Heterogeneous Catalyst Components

  • Active Site: Specific area where reaction locality occurs.

  • Support Role: Provides stability and enhances surface area for reaction.

Nanoparticle Usage in Catalysts

  • Importance of nanoparticle size for increased surface area and reactivity noted.

Support Requirements and Properties

  • Essential characteristics of supports:

    • High surface area

    • Dispersion of active phase

    • Thermal and mechanical stability

Types of Supports

  • Varieties of supports include:

    • Oxides: Silica (SiO2), alumina (Al2O3)

    • Carbons: Activated carbon, graphitic carbons

    • Zeolites: Useful for specific catalysis applications.

Silica (SiO2) Characteristics

  • Extraction methods: Natural and synthetic production.

  • Structure: Tetrahedral units of [SiO4].

Alumina (Al2O3) Characteristics

  • Comparison with silica:

    • Similarities in structure but richer chemistry observed.

Zeolite Properties

  • Functionality as solid acids with molecular sieve properties.

  • Composition involves Si and Al, providing unique catalytic properties.

Carbon-Based Catalysts

  • Comparison between activated carbon and graphite:

    • Activated carbon: High surface area and microporous structure, significant reactivity.

    • Graphite: Inert with low surface area, mainly structural purposes.

Challenges in Catalysis

  • Composition characteristics noted for successful transitions from fossil fuels to biobased feedstocks.

Catalyst Preparation Techniques

  • Two strategies presented:

    • Coprecipitation: Support and active phase synthesized together.

    • Deposition: Active phase deposited on pre-existing support.

Comparison of Deposition Techniques

  • Evaluates efficiency, loading capacity, and dispersion from various techniques including:

    • Adsorption/Ion Exchange

    • Incipient Wetness/Wet Impregnation

    • Deposition Precipitation