Spatially resolving CO and C3H6 oxidation reactions in a Pt/Al2O3 model oxidation catalyst

Abstract

Spatially resolved Fourier transform infrared spectroscopy (SpaciIR) was used to measure gas phase concentration profiles during CO and C 3 H 6 oxidation reactions over a Pt/Al 2 O 3 monolith supported catalyst. The reaction conditions were selected as representative of certain low temperature combustion (LTC) engine exhaust conditions, where in this study higher concentrations of CO, C 3 H 6 and lower concentrations of NO x were used relative to standard engine exhaust. CO and C 3 H 6 oxidation and NO X reduction reactions were examined individually and in combination via temperature programmed oxidation (TPO) experiments. Significant NO X reduction occurred right at CO and C 3 H 6 light off, and NO oxidation only occurred after the oxidation of CO and C 3 H 6. C 3 H 6 oxidation was not observed until after most of the CO oxidized, as CO was more strongly adsorbed to the active site surface at low temperature. During the TPO of CO and C 3 H 6 , the conversion versus temperature profiles did not monotonically increase; two inflections were observed where the rate of conversion change as a function of temperature slowed over a small temperature range before again accelerating with temperature. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used in order to characterize intermediates that were present on the surface at the temperatures where these steps were noted. Surface ethylene and formate species were present during the first step, with acetate and formate in the second step. The inhibition steps were therefore attributed to the partial oxidation of propylene to ethylene, and then the subsequent partial oxidation of ethylene to acetate.

Heterogeneous catalyst design: Zoned and layered catalysts in diesel vehicle aftertreatment monolith reactors

“…The complex feed conditions included a heavier hydrocarbon and contained 3000 ppm CO, 1500 ppm C 3 H 6 , 250 ppm C 12 H 26 , 50 ppm NO, 14 % O 2 , 5 % CO 2 , 5 % H 2 O, and balance N 2. The Spaci‐IR technique was used to measure concentrations at the midpoint of the reactor …”

“…[28,29] The Spaci-IR technique was used to measure concentrations at the midpoint of the reactor. [31] In evaluating the temperatures at which 50 % CO conversion (T 50 ) was achieved over these catalysts, listed in Table 1, the zoned Pd/Pt monolith reactor resulted in slightly better performance under simple feed conditions as compared to the uniform 1:1 Pt:Pd catalyst for both CO and hydrocarbon oxidation. For CO conversion versus temperature, shown in Figure 5a, the slope of conversion versus temperature curve for the Pd/Pt zoned reactor is less steep than the uniform 1:1 Pt:Pd system; however, the zoned design reached $50 % CO conversion at a lower temperature.…”

Kinetic and mechanistic study of bimetallic Pt-Pd/Al2O3 catalysts for CO and C3H6 oxidation

“…DRIFTS was used to characterize CO interactions with the catalyst surfaces during adsorption and TPO experiments, using a similar approach to that taken with a monometallic Pt catalyst. [22] The DRIFTS spectra obtained after sample exposure to CO and O2 at 80°C for 1 hour are shown in Figure 4 a), and the species represented by the spectral features are labeled based on literature results. The small feature at ~2200 cm -1 corresponds to CO on Lewis acid sites 2190-2200 cm -1 , [23] and is not considered catalytically important.…”

The Effect of Pt Particle Size on the Oxidation of CO, C3H6, and NO Over Pt/Al2O3 for Diesel Exhaust Aftertreatment

“…Even though a typical diesel exhaust contains a variety of 173 hydrocarbon components, propene (C3H6) was used as a model compound for hydrocarbon oxidation, 174 following common practice [5,10,11,23,24,46]. The propene conversion was determined based on the CO2 175 concentrations measured in the product gas, using the same analyzer as for CO oxidation, and the 176 stoichiometry of the reaction equation, forming three CO2 molecules per C3H6 molecule.…”