Characterization of flame synthesized Pd–TiO2 nanocomposite catalysts for oxygen removal from CO2-rich streams in oxy combustion exhausts

Abstract

Pd–TiO₂ catalysts with five Pd loadings were synthesized using a flame aerosol reactor. Studies of the initial and spent catalysts demonstrate that Pd loading impacted the size of Pd sub-nano clusters/nanoparticles and the fraction of Pd (metallic Pd, PdO, PdO_x). Increased size of Pd on catalysts' surface due to sintering, and the reduction of PdO to metallic Pd and/or PdO_x were observed during the reaction. Fractions of the total surface area of different Pd species and correlations to the apparent reaction rate constants were evaluated. Apparent kinetic constants are linearly proportional to fractions of total surface areas of metallic Pd and/or reduced Pd oxide, representing the intrinsic active site. The linear correlation between the O₂ reaction rate and the CO₂ concentration in the initial gas stream was also observed exhibiting the possible autocatalytic effect or a surface coverage effect.