Oxidation catalysts were the first catalysts used for air pollution control.
These emission control catalysts combine CO and gas phase organic compounds with oxygen in the air to form CO2 and water.
Catalyst is a substance that promotes certain reaction reactions but is not one of the original reactants or the final product.
Catalyst is not used in the reaction it produces.
Platinum group metals (PGMs), including platinum itself, palladium, and rhodium are commonly used in emission control catalysts.
Modern catalytic converters use a homogeneous honey substrate coated with PGM metal alloys and packaged in a stainless steel container.
Honey rod is made of ceramics or stainless steel foil.
Its structure of many small parallel channels offers a high catalytic contact area for exhaust gases.
As hot gases flow through the channel and interact with the catalyst, many pathway pollutants are converted into harmless substances.
Reactions:
The following reactions occur in oxidative catalysts:
[Hydrocarbons] + O2 = CO2 + H2O
CnH2m + (n + m/2)O2 = nCO2 + mH2O
2CO + O2 = 2CO2
Hydrocarbons in Oxidation Catalyst
The structure of the molecule determines the amount of activity and energy it needs to oxidize to CO2.
Non-graduated molecules such as formaldehyde, ethylene and propylene react easily at low temperatures.
Saturated molecules such as methane, ethane and propane are very stable and require very high temperatures to convert to CO2 and H2O.
The use of a catalyst to produce a reaction reduces energy, so they can take place at low temperatures.
Oxidation Catalysts:
Elements that are active for catalytic oxidation of air pollutants include precious metals such as Pt, Pd and Rh and many base metals.
Specifically, promoters and binders are added so as to have maximum catalytic activity and stability.
High levels of oxides are used to support precious metals and, together, these materials are coated on ceramic or metallic substances to produce emission control catalysts that flow through almost all industrial and combustible materials. Can be used to prevent air pollution from the process.
Metallic substrates: offer extremely low backpacks and can be braced for stability in applications where they suffer shock and vibration. Metal particles are formed at multiple cell densities, rectangular and round, and can be made in very large sizes.
Ceramic substrates: are manufactured at multiple cell densities with different wall thickness to meet the requirements of low backpressure. They are resistant to harsh chemical environments and can be cut and stored in large, custom-sized beds.