X-Ray Photoelectron Spectroscopic Studies of Laboratory-Aged Natural Gas and Diesel Oxidation Catalysts 

Combustion engines are a major source of emissions such as various greenhouse gases and hazardous chemicals. Reducing these emissions is of major importance, and catalytic converters are one of the most prominent applications towards this end. In a catalytic converter, molecules in the exhaust gas undergo oxidation or reduction reactions enhanced by noble metal catalysts and form less harmful compounds. While in use, the catalytic converters and the active catalytic materials within are gradually deactivated. In chemical poisoning, unwanted particles adsorb on the active sites of the catalyst thus preventing adsorption and conversion of the desired molecules. In thermal deactivation, the active catalyst particles migrate to form larger particles, thus decreasing the active surface area of the catalyst. In this work, the effect of laboratory-scale deactivation treatments on diesel and natural gas oxidation catalysts are studied. All the catalysts feature platinum or palladium as the active metal and alumina, silica or zirconia as the solid support. In the deactivation treatments, the catalysts have been exposed to sulfur and phosphorus, significant catalytic poisons, as well as elevated temperatures. The effect of these treatments have been investigated with X-ray photoelectron spectroscopy, a non-destructive experimental method for chemical characterization. The atomic percentages of the chemical elements in each catalyst have been determined together with the chemical states of each element. With the help of complementary studies, the properties of the treated catalysts are discussed in detail.