Analysis of Flue Gas Oxidation in Catalytic Converters - ENGR 300

This assignment analyzes the oxidation of flue gases within catalytic converters, focusing on the reduction of pollutants like carbon monoxide, unburnt hydrocarbons, and nitrogen oxides. It details the operational principles of catalytic converters, including the role of catalysts such as platinum, rhodium, and palladium in facilitating redox reactions. The paper discusses the two main types of catalytic converters (two-way and three-way) and explains the phenomena of interphase mass transfer and intraphase diffusion. The interphase mass transfer involves the transfer of oxygen from the catalysts to the carbon monoxide molecules. The role of alumina as a washcoat material is also discussed. Furthermore, it delves into the significance of diffusion at the gas-washcoat interface, and how pore size impacts the process. The conclusion emphasizes the effectiveness of catalytic converters in combating pollution, highlighting the importance of continuous research and development to improve their design and functionality. References from sources like Libretexts and Explain That Stuff are included to support the analysis.

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OXIDATION OF FLUE GASES
THROUGH A CATALYTIC
CONVERTER

Introduction
As the time is changing the level of pollution is also changing. The negative footprint on the
environment is increasing, particularly on the air quality. The exhaust gases that are released
from the engine of an automobile contains many hazardous as well as pollution causing
agents such as Carbon Monoxide (CO), unburnt hydrocarbons and Nitrogen Dioxide and
Nitric Oxides. A catalytic converter reduces the level of pollution by converting these
harmful substances into a lesser harmful forms. The Nitrogen Dioxide and Nitric Oxides are
reduced to free nitrogen. CO gets oxidised to Carbon Dioxide (C02) and the hydrocarbons are
oxidised to get C02 and water vapour (H2O). This oxygen is basically extracted from the first
stage of reduction. This is carried out a reduction chamber in which other are plenty of
monolithic tubular structures so as to provide a large surface area that would help in better
oxidation. The catalyst used is Platinum and Rhodium. They reduce the Nitrogen Dioxide and
Nitric Oxides under heat which a catalyst converter is not deprived because a catalytic
converter is located near the engines. The next section is the oxidation in which Platinum and
Palladium is used as the catalysts. The free oxygen from the stage 1 is used to oxidise C0 and
unburnt hydrocarbons. Both the redox reactions require heat to be carried out and therefore
ceramic is used as a substrate material because it remains hot for a longer time. There are two
common types of catalytic converters, Two-Way (2-way) and the other one is a Three-way
catalytic converters (3-way). The two-way converter performs oxidation of CO and unburnt
hydrocarbons only while q three-way can perform reduction of Nitric Oxide and Nitrogen
Dioxide.

Task 1a:
The phenomenon of transportation that is being involved is basically divided into two
processes namely interphase mass transfer and intraphase diffusion In the case of interphase
mass transfer, there is a transfer of atoms belonging to oxygen from the catalysts to the
interface and then from the interface to the Carbon Monoxide molecule (CO) in the feeder
section. The phase of the catalyst being solid and that of C0 being gaseous therefore, here the
two phases are different. The mass of oxygen is transferred between them whose rate
depends on the concentration of oxygen in both the zones and this mass transfer continues to
occur until equilibrium is attained. Alumina is the most common material used as a washcoat.
Its surface area is quite high and it remains stable in a temperature range. It also depends on
the extent of purity in the given material as well as additives that are used. If the range is
misbalanced the phase of this alumina changes with a decreased surface area for the oxidation
of catalyst and the hazardous waste. Since, the material used in washcoat is porous, the
surface area that is in contact with the gas is not the same as that exposed to the solid phase of
the catalyst. The mass diffusion that happens at the gas and whitewash interface depends
upon the size of the pores. If the mean free path of molecules is less than than the diameter
of the Pores, the diffusion takes place in accordance to Fick’s Law. The mean free path would
tend to become more that the diameter when the pressure is low and pores are small in size.
In this case the collision of the molecules of CO among themselves will decrease while with a
wall it would be high (Woodford 2018), (Libretexts 2018).

Conclusion
Catalytic converter are very useful in order to combat pollution. It not only converts gaseous
products in to harmless gaseous forms. There are some redox reactions which have been
analysed along with the various aspects of a catalytic converters. The mass transfer and the
process of diffusion plays an important role in a catalytic converter. The velocity distribution,
methods in order to solve the governing equations and the concentration of Carbon
Monoxide. CO is extremely harmful because it is odourless and cannot be detected and so it
can be removed in the form of oxidation. The performance can be enhanced if these analysis
are undertaken.
Future holds for them who continuously change themselves according to the requirements.
Research and innovative steps needs to be encouraged and being implemented in a
sustainable way. Catalytic converters are not fully efficient. There is some amount of CO and
hydrocarbons generated and therefore their management is very necessary by using certain
methodologies. If steps are taken in the improvement of the designs as well as the
functioning, the level of pollution would decrease further.

References
Libretexts. 2018. Catalytic Converters. 18 May. Accessed November 5, 2018.
https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Te
xtbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/
Kinetics/Case_Studies%3A_Kinetics/Catalytic_Converters.
Woodford, Chris. 2018. Catalytic converters. 10 June. Accessed November 5, 2018.
https://www.explainthatstuff.com/catalyticconverters.html.