Light-off temperature determination

Light-Off Temperature Determination of Oxidation Catalyst Using Fourier Transform IR Technique... 

In-situ FTIR technique was developed and demonstrated for the light-off temperature determination and the identification of reaction products of oxidation catalysts. 

Figure 3 compares the light-off temperatures determined on Rh/A and Rh/CeA catalysts. Ce02 is known to stabilize noble metals [18] and probably limits here the rhodium migration into the support. Nevertheless, contrary to what was observed on Rh/A, a reducing treatment increases the deactivation of Rh/CeA. The most probable explanation is that a RhCexOy mixed oxide could be... 

Sulfated catalyst activity was determined with the S02 free feedstream in the absence of water The light-off temperatures reported in Fig 3a for propene oxidation show that sulfation by SO2 induces the same effects on catalyst activity than SO2 in the feedstream in the course of the oxidation reaction (Fig 1b). Thus Pt-Rh catalyst activity is not affected by sulfation while monometallic platinum catalysts are far less active after sulfur storage with 20 ppm SC>2 We must note also that a small inhibiting effect appears after sulfur storage with 4 ppm SO2. 

Light-off temperatures of oxidation catalysts are considered as one of the important parameters for catalyst performance evaluation. In this study, the in-situ FTIR technique was developed and used to determine the light-off temperatures and reaction products of three three-way automotive catalysts with 20 torr monomethylamine in air at 0.5 1/min flow rate. Light-off temperatures were found to be 140, 143, and 170°C for Davison, Allied-Signal, and Degussa oxidation catalysts, respectively. CO, CO2, 1 0, and nitric acid were found to be the major oxidation products. The activation energies of formation of CO and CO2 on the catalysts were also determined. 

Light-off temperatures with 20 torr MMA for Davison, Allied-Signal, and Degussa three-way automotive catalysts were determined to be 140, 143, and 170°C in air with 0.5 1/min fLow rate, respectively. 

In order to determine the light off temperature the temperature of the catalyst was raised from 150°C at a rate of 9°C per minute and the increase in CO conversion was recorded. T q in Table 1 is defined as the temperature at which the CO conversion is 50%. 

The conversion was studied as a function of the temperature at R=1 to determine the light-off temperatures where at least 50% conversion of the reactants occurs, but also to test the resistance of the catalysts to high temperatures. 

Light-off temperatures for feed streams A and B determined under stoichiometric conditions (5 = 1.0)a,b... 

As metal concentration is increased particle size may increase, so support interactions will decrease. Variations in particle size are also associated with changes in the density of active sites, with associated effects on the catalysis. The concentration of the noble metal can affect both catalytic activity and resistance to deactivation, hence the amount of noble metal on a supported catalyst is of prime importance. The former is illustrated by Skoglundh [34], who noted that the overall noble metal content of a Pt-Pd catalyst (ratio 4/1) is of vital importance in determining the light off temperature for xylene oxidation, as the light off temperature markedly decreased as noble metal content increased in the range 5-20 pg mol These results are shown in figure 4. 

The turnover frequencies at various temperatures are summarized in Table 17.5. The dispersions determined by hydrogen chemisorption for the S-free catalysts were used to calculate the TOP, assuming that the number of Pt atoms exposed in the poisoned catalysts was the same as that in the S-free catalyst. The boldfaced values indicate reaction rate at 100% CO conversion, which can be calculated in the recycle reactor. For the silica-supported catalysts, the difference in the light-off temperature between the fresh and poisoned samples (ATjg) appears to depend on the average particle size (expressed as metal dispersion). For the catalyst with lowest dispersion... 

The remaining unit operations (secondary units), which are not associated with any identified objectives or constraints, are examined next to determine if they can be attached to a dominant unit of a candidate module on the basis that the secondary unit assists the primary unit to achieve its objectives. For example, if the explicit objective of a minimum light off temperature is associated with a reactor unit and a furnace precedes the reactor, the furnace can be incorporated into the candidate module with the reactor, since the furnace helps the reactor meet this objective. Once all of the secondary units have been assigned to the modules, the resulting set of modules represents the first iteration of the flowsheet decomposition. 

Although catalytic total oxidation reactions have been studied since 1817, the earliest work on catalytic combustors was first described by Pfefferle in 1917. Active interest in catalytic combustion for power generation increased during the early 1990s. For practical applications of catalytic combustion, the light-off temperature is a critical parameter that determines both system operation and system design as suggested by Pfefferle. ... 

Figure 9 shows a typical series of CO light-off curves measured under lean conditions. The first curve (squares) is for a simple feed of CO and 02 (plus C02 and water, with N2 as the balance). In reality, a series of these curves would be measured with different CO and 02 concentrations, to determine the concentration and temperature dependence of CO oxidation. By modelling this data, a rate expression for CO oxidation for this catalyst can be determined. 

The values of kinetic parameters (pre-exponential factors k0j and activation energies Ej of rate constants k and inhibition constant Kg) can for a particular catalyst be determined by weighted least squares method, Eq. (35), from the light-off or complete ignition-extinction curves measured in experiments with slowly varying one inlet gas variable—temperature or concentration of one component (cf., e.g., Ansell et al., 1996 Dubien et al., 1997 Dvorak et al., 1994 Kryl et al, 2005 Koci et al., 2004c, 2007b Pinkas et al., 1995). 

Other uses of lasers include eye surgery on detached retinas, spot welding, holography, isotope separation, accurate determination of the moon s orbit by reflection of laser light off a reflector placed on the moon s surface, and laser-guided bombs and missiles. Possible future uses include terrestrial and extraterrestrial communication, applications to computers, and production of the high temperatures needed for controlled nuclear-fusion reactions. 

---