Adobe Scan 3 Feb 2025
2.4 Catalysis for Energy and Environmental Applications
Catalysis is essential in developing sustainable energy production pathways, addressing rising energy demands and environmental concerns.
High efficiency in advanced catalytic systems is critical for industrial applications.
The past fifty years have seen a surge in energy consumption due to population growth, urbanization, and improved living standards.
No universal solution exists for energy and environmental challenges, yet catalysis plays a pivotal role.
2.4.1 Catalytic Conversion of Fossil Fuels
Hydrogen Production:
Catalytic conversion from fossil fuels, particularly natural gas, is the most feasible method to produce hydrogen.
Noble metals are effective catalysts but costly; alternatives like nickel (Ni), cobalt (Co), and copper (Cu) alloys are explored.
Methods for Hydrogen Production:
Pyrolysis
Partial Oxidation
Autothermal Reforming
Steam Reforming
Ni/Al2O3 catalyst is regarded as cost-effective, reducing coke formation; combining hydrogen production with carbon capture is encouraged.
Hydrogen Types:
Green Hydrogen: Produced via water electrolysis/photolysis.
Gray Hydrogen: Derived from fossil fuels, extensively used due to established technology and environmental considerations.
Oil reforming is significant for hydrogen production, favoring light oils over heavy oils due to lower coke formation risks.
Hydrogen Production Techniques
Steam Reforming:
Endothermic reaction requiring an external heat source.
Produces syngas with a favorable H₂ to CO ratio (~3:1) but has the highest emissions.
Partial Oxidation (POX):
Converts hydrocarbons to hydrogen by combustion with oxygen.
Benefits include low methane slip, high sulfur tolerance, and favorable H₂ to CO ratios (1:1 to 2:1) but requires high temperatures (1,300-1,500°C).
Pyrolysis:
Hydrogen production via thermal decomposition without water or oxygen, avoiding CO/CO2 formation, offering reduced emissions and by-product carbon.
Autothermal Reforming (ATR):
Combines steam with catalytic partial oxidation, enables rapid starting/stopping, and provides a greater hydrogen yield.
Requires tight control of oxygen-to-fuel and steam-to-carbon ratios.
2.4.2 Catalysts for Pollution Control
Catalysts reduce gaseous pollutants and convert CO2 into useful products while degrading toxic organic compounds in water and air.
Catalytic Reduction of Greenhouse Gas Emissions
Non-CO2 GHGs: Combustion is effective for controlling methane emissions. Catalyst processes include various reforming methods.
Catalytic Control of N2O Emissions: Fe-ZSM-5 catalysts are effective in selective catalytic reduction of nitrogen oxides (NO, NO2, N2O).
Conversion of CO2: Catalytic routes for transforming CO2 into fuels/chemicals are crucial in addressing climate change.
Key CO2 Utilization Approaches
Reforming, Esterfication, Reverse Water-Gas Shift, Thermal, Electrochemical, Photocatalytic, Methanation: Various methods with their advantages and disadvantages outlined.
Commercial Catalysts for CO2 Conversion: A variety of catalysts listed for producing valuable chemicals from CO2.
2.4.2.2 Catalytic Dye Degradation
The increase in global pollution from dyes necessitates effective water purification. Organic dyes pose significant environmental threats.
Photocatalytic Dye Degradation: Involves advanced oxidation processes using reactive species for pollutant degradation, often hindered by challenges such as low adsorption efficiency.
Biocatalytic Degradation: Uses enzymes and microorganisms like algae for dye removal, addressing catalyst stability and efficiency issues.
Common Catalysts Used for Dye Degradation
Photocatalysts: TiO2, ZnO, SnO2, Graphene-gold composites, Ag-ZnO composites.
Biocatalysts: Enzymes (e.g. peroxidases, laccases) and algae species for dye degradation.
Exercises
Define catalyst and catalysis.
Differentiate between homogeneous and heterogeneous catalysis with examples.
Discuss the engineering features of catalysts and their design considerations.