Barium Promoted Palladium Catalysts for the Emission Control of Natural Gas Driven Vehicles and Biofuel Combustion Systems

Pd/ and Pd–Ba/alumina catalysts were prepared and tested for their activities in the removal of pollutants released from stoichiometrically operated natural gas vehicles (NGVs) and from the combustion of biofuels in small-scale stoves. The addition of barium to the Pd/alumina catalyst resulted in improved fresh and aged activities by widening the lambda window in NGV applications and by lowering the T50% for methane in biofuel combustion applications. An attempt to slow down the detrimental effect of sulfur toward methane oxidation was carried out by arranging Pd–Ba/alumina, Ba/alumina, and Pd/alumina in three separate layers. Ba species were believed to act as a sulfur sink or trap, leaving the active PdO partially free for methane oxidation. XPS technique was used to investigate the nature of sulfur species on the catalyst as well as the state of the precious metal. In addition, the catalysts were characterized by means of XRD, XRF, H2-adsorption, N2-physisorption, SO2/O2/C10H8-TPD, and CH4-TPR.