Correlation of light-off activity for full size and cored catalyst samples
Summary (2 min read)
1 Introduction
- Regulations concerning automotive exhaust emissions are becoming more and more stringent, requiring the development of more efficient and durable catalytic control systems.
- Commercially used three-way catalysts are often a bimetallic combination of precious metals, such as Pt/Rh or Pd/Rh, as rhodium is known to be an efficient catalyst for NOx reduction, whereas platinum and palladium are effective catalysts for the oxidation of carbon monoxide and hydrocarbons (Aitani and Siddiqui, 1995; Gandhi et al., 2003).
- Sintering of the washcoat can also occur, with a decrease in surface area and a loss of internal pore structure.
- Research conducted by Zanon Zotin et al. (2005) showed that the deactivation of catalyst samples, aged on an engine bench, was not due to one factor, but a combination of thermal, chemical and mechanical deactivation.
- There are no published results of laboratory analysis on full size commercial catalysts.
2 Experimental
- Four commercial three-way catalysts were used throughout this study.
- For each test in the Labcat, the sample was stabilised at a temperature of 150°C before applying the light-off ramp.
- Both the Horiba MEXA-7000 and the Horiba MEXA-6000 FTIR exhaust gas analysers were used to measure the gas concentrations.
- Samples of 36 mm length were then taken from the front and rear of these centre cores and labelled CF and CR respectively.
- In the SIGU, only the catalyst inlet and outlet temperatures are measured, as it is difficult to measure the catalyst bed temperature without interfering with the flow through the small samples.
3 QUB global catalyst model
- The QUB global catalyst model was first developed by McCullough (1997) as a Fortran code and has been considerably enhanced as a Microsoft Excel VBA based model over the past few years.
- The model simulates the catalyst activity based on these parameters.
- The model has been developed for 18 reactions (Stewart et al., 2102), which represent the full set of reactions that typically occur in a three-way automotive catalyst.
- Heat transfer in the model uses the laws of conduction and convection.
- The catalyst mesh defines the profile of the catalyst, with the catalyst monolith, matting and steel casing all included.
4 Results and discussion
- CO light-off tests were performed for each of the canned full size catalysts on the Labcat.
- Differences between cored samples and full size catalyst light-off performance may be due to thermal ageing, which may vary in the axial and radial directions throughout the brick, however, no trends were seen to prove this.
- The values of dispersion percentage and heat transfer factor required to match the simulation results with the experimental test results are shown in Table 2.
- Figure 16 shows the temperature profiles of the light-off ramps for each of the front core CO light-off tests, all plotted on one graph.
- With the changed values of precious metal dispersion and external heat transfer factor it can be seen that for each catalyst the simulated light-off temperature for the full size catalysts and the cores are almost identical, with the exception of Catalyst 3.
5 Conclusions
- CO activity tests performed on full size three-way catalysts and cored samples, along with simulations performed using the QUB global catalyst model, have shown that correlation between the full size and cored samples is generally good.
- Light-off tests have shown that variation exists between ‘identical’ full size bricks.
- Experimental analysis was not conducted to confirm the actual precious metal dispersion in this study.
- This study successfully conducts the performance testing of full size catalysts under laboratory conditions, and correlates the results to cored samples.
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Citations
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Cites methods from "Correlation of light-off activity f..."
...The procedure for the CO light-off tests conducted using the SIGU is described by Blades et al.[15] The gas concentrations used were, 10 % CO2, 1 % O2, 0.5 % CO, 5 % H2O and balance N2....
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...A study carried out by Blades et al.[15] showed how the QUB global catalyst simulation model, which was first developed by McCullough[16] and later enhanced by Stewart,[17] could accurately simulate the light-off behaviour of catalyst samples for tests conducted on two different laboratory catalyst test rigs....
[...]
...The procedure for the CO light-off tests conducted using the SIGU is described by Blades et al.([15]) The gas concentrations used were, 10 % CO2, 1 % O2, 0....
[...]
...A study carried out by Blades et al.([15]) showed how the QUB global catalyst simulation model, which was first developed by McCullough([16]) and later enhanced by Stewart,([17]) could accurately simulate the light-off behaviour of catalyst samples for tests conducted on two different laboratory catalyst test rigs....
[...]
1 citations
References
49 citations
"Correlation of light-off activity f..." refers background in this paper
...Another form of catalyst deactivation is mechanical deactivation, were the decrease in catalytic activity is caused by loss of catalyst material due to fractures in the ceramic monolith (Zanon Zotin et al., 2005)....
[...]
...…available to reactant gases and therefore reducing the catalyst activity (Harris, 1995; Heck et al., 2002; Martin et al., 2003; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; Polvinen et al., 2004; Tanabe et al., 2008; Winkler et al., 2010; Yang et al., 2008; Zanon Zotin et al., 2005)....
[...]
...Research conducted by Zanon Zotin et al. (2005) showed that the deactivation of catalyst samples, aged on an engine bench, was not due to one factor, but a combination of thermal, chemical and mechanical deactivation....
[...]
...Poisoning results in a reduced number of active sites available to the reactant gases and therefore causes reduced catalyst activity (Heck et al., 2002; Zanon Zotin et al., 2005)....
[...]
...…from the gamma phase, γ-Al2O3, through delta, δ-Al2O3 and theta, θ-Al2O3, to the stable alpha alumina, α-Al2O3, with loss of surface area and hence loss of catalyst activity (Heck et al., 2002; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; More et al., 1997; Zanon Zotin et al., 2005)....
[...]
45 citations
"Correlation of light-off activity f..." refers background in this paper
...At high temperatures, the precious metal particles agglomerate, decreasing the surface area of catalyst available to reactant gases and therefore reducing the catalyst activity (Harris, 1995; Heck et al., 2002; Martin et al., 2003; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; Polvinen et al., 2004; Tanabe et al., 2008; Winkler et al., 2010; Yang et al., 2008; Zanon Zotin et al., 2005)....
[...]
...…available to reactant gases and therefore reducing the catalyst activity (Harris, 1995; Heck et al., 2002; Martin et al., 2003; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; Polvinen et al., 2004; Tanabe et al., 2008; Winkler et al., 2010; Yang et al., 2008; Zanon Zotin et al., 2005)....
[...]
40 citations
"Correlation of light-off activity f..." refers background in this paper
...Moldovan et al. (2003) showed that, after automobile ageing, the loss of precious metal particles, and therefore a reduction in dispersion, was much greater at the front face of a three-way catalyst than in any other region of the brick....
[...]
39 citations
"Correlation of light-off activity f..." refers background in this paper
...At high temperatures, the precious metal particles agglomerate, decreasing the surface area of catalyst available to reactant gases and therefore reducing the catalyst activity (Harris, 1995; Heck et al., 2002; Martin et al., 2003; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; Polvinen et al., 2004; Tanabe et al., 2008; Winkler et al., 2010; Yang et al., 2008; Zanon Zotin et al., 2005)....
[...]
...The washcoat undergoes irreversible phase changes, with the alumina washcoat transforming from the gamma phase, γ-Al2O3, through delta, δ-Al2O3 and theta, θ-Al2O3, to the stable alpha alumina, α-Al2O3, with loss of surface area and hence loss of catalyst activity (Heck et al., 2002; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; More et al., 1997; Zanon Zotin et al., 2005)....
[...]
...A study by Meyer Fernandes et al. (2008) showed that thermal effects were the major contributor to catalyst deactivation....
[...]
...…available to reactant gases and therefore reducing the catalyst activity (Harris, 1995; Heck et al., 2002; Martin et al., 2003; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; Polvinen et al., 2004; Tanabe et al., 2008; Winkler et al., 2010; Yang et al., 2008; Zanon Zotin et al., 2005)....
[...]
...…from the gamma phase, γ-Al2O3, through delta, δ-Al2O3 and theta, θ-Al2O3, to the stable alpha alumina, α-Al2O3, with loss of surface area and hence loss of catalyst activity (Heck et al., 2002; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; More et al., 1997; Zanon Zotin et al., 2005)....
[...]