Propane Oxidation over Pt/SrTiO3 Nanocuboids

Automotive exhaust is one of the main generators of air pollutants. This problem is expected to worsen as the demand for privately owned vehicles increases. Internal combustion engines utilizing gasoline and diesel generate harmful pollutants such as nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (HC), particulates, and sulfur oxides (SOx). Liquefied petroleum gas (LPG), an alternative cleaner burning fuel, is gaining ground for use in internal combustion engines. Liquefied petroleum gas has a higher octane rating and produces considerably lower CO, HC, CO2 and particulate matter emissions compared to gasoline, provided the vehicle is retrofitted for LPG use. However, tailpipe emissions fromLPG fueled vehicles still contain high concentrations of light alkanes.Up to 80%of theHCemissions are produced in the first 60 to 90 s following a cold-start because of the catalytic converter’s inability to oxidize HCs at low temperatures (between 200 to 300 C). The aim of this work is to develop and characterize low light-off platinum-based HC oxidation catalysts in an effort to reduce tailpipe HC emissions. The study focuses on propane oxidation since propane is the main component in LPG and is found in automotive exhaust. Platinum is one of the most active materials for HC oxidation. There is some debate in the literature about whether the platinum particle size or shape affects the catalyst activity. While some studies show that the reaction rate per platinum atom does not significantly change with particle size or dispersion, the reaction rate per surface platinum atom increases for larger platinum particle sizes. 8 Conversely, it has even been observed that nanoscale platinum clusters show entirely different catalytic behavior than larger platinum particles, producing partially oxidized products. One explanation put forth for the increased activity of larger particles is that metallic platinummay be the active phase, and in an oxidizing environment smaller particles contain more PtO or PtO2 and less metallic platinum. If such is the case, the challenge would be to maintain platinum in a reduced state with high dispersion under an oxidizing atmosphere. Yoshida and co-workers reported that the total electrophilic and electrophobic properties obtained from the support and additives control the oxidation state of platinum. More electrophilic character would result in less oxidized platinum, thus higher catalytic activity. 12 Acidic supports and highly electronegative additives promoted Pt stabilization in the metallic phase. Perovskite-based materials (ABO3) have been investigated since the 1970s as promising automotive exhaust catalysts to replace the existing noble metal-based catalysts. These materials are attractive for deep oxidation because of their surface redox properties, high bulk oxygen mobility, and good thermal stability. 17 However, perovskites are generally less active for hydrocarbon oxidation than noble metal catalysts. To improve the oxidation activity, noble metals such as Pt and Pd were partially substituted into position B of the LaMnO3-based catalysts. 18,19 However, the activity of volatile organic compound oxidation for such catalysts was similar to the original perovskite. Incipient wetness was used to deposit noble metals on the surface instead of metal substitution