Catalysis for Emission Control EA4550
Fall 2024 Exam #1
Kinetic rates, Mass transfer, Deactivation, Characterization
(25 points)
1. Each question is 1 point
a Why is it important to disperse the catalytic component onto a high surface area carrier material such as γAl2O3?
b What is a practical observation for determining the rate limiting step during testing of a catalyst?
c List at least 3 different processes than can lead to catalyst deactivation.
d Explain the characterization method(s) used to determine the extent of each deactivation for each process.
e What can you do to enhance the activity of a catalyst itself when it is controlled by chemical reaction
2. (total = 4 points)
A vehicle painting facility must abate toluene emissions (toluene is the solvent used to disperse the colored pigments). You are working for a catalyst company at a very high salary since you are a catalyst expert from Columbia. The company history suggests using 1%Pt on Al2O3 washcoated on the walls of a 400 cpsi/6.5 ceramic monolith is a good choice initially for your lab testing but you have the option to select a different monolith and dimensions. What different monolith and reactor dimensions (diameter, length while maintaining the same SV) would you adjust to enhance the rate for BMT control? Discuss why there are penalties for making these changes
3. (total = 6 points)
3a. (2 points) How are reaction orders for a HC and O2 determined in the rate equation below?
Consider Rate = k (HC)x (O2)y
3b. (2 points) How can you change the Rate of conversion knowing the reaction orders?
3c. (2 points) Show one experimental method to determine the activation energy for a reaction for which the order (s) are not known.
4. (total 6 points)
The first oxidation catalyst used in the US in 1975 for abating CO and HC emissions from the automobile exhaust (gasoline) was a combination of 2 1/2%Pt and 1%Pd dispersed on γ-Al2O3 on a monolith. In Brazil, where ethanol (derived from sugar cane) is often used as a fuel, The local catalyst companies first tried the same catalyst. The first laboratory tests conducted used a simulated emission of 2% ethanol in excess air and a conversion vs. temperature plot was made. The ethanol began converting at 150oC however, the product distribution (selectivity), especially at low temperatures showed undesirable acetaldehyde (CH3CHO) formation along with the desired CO2 and H2O.
4a. (2 points) Write the general rate equations for the formation of each product. Ignore the reverse reaction since the Ke is very large. The formation of acetaldehyde was determined to be first order in ethanol while for the CO2 path the ethanol order was 0.25. In both cases the O2 was pseudo zero order because it was present in large excess. How can you use these kinetic parameters to enhance the desired reaction?
4b. (2 points) The CO2 path has an activation of 80 kj/mol while the undesired path 45 Kj/mol. In the exhaust of the vehicle what could you consider doing to optimize the reactor design to minimize the undesired reaction?
4c. (2 points) Given that the Pt, Pd catalyst has worked for gasoline engines but has a not so well for ethanol fuel vehicles how would you prepare some simple variations the PtPd/ Al2O3 catalyst to minimize or eliminate acetaldehyde production completely?
5. (total 4 points)
2% Pd/ϒ-Al2O3 supported on a monolith is to be used to abate the organic pollutants from a natural gas-fired power plant. What characterization methods for each (a, b and c) would be used to determine the various modes of deactivation for each separate case listed below? Also suggest the shape of the conversion/temperature profile from your laboratory, generated conversion vs temperature plot of the deactivated catalyst using hexane as a model compound. In some cases, there may be more than one deactivation mode possible. Consider each separately.
a. (1 point) The data recorded over-night indicated the catalyst saw an excessively high temperature due to a failed heat exchanger upstream.
b. (1 point) It is known that some sulfur is present in the natural gas
c. (1 point) A heavy organic impurity (oil) is depositing and masking the catalyst causing deactivation. Sketch the conversion vs temperature profile you would observe when performing a lab test
d. (1 point) How might you remove the hydrocarbon from the catalyst (regeneration) and what techniques would you use to provide guidance?