Study of hydrothermal aging impact on Na- and P-modified diesel oxidation catalyst (DOC)

Abstract The effects of hydrothermal aging (HT-aging), of a biodiesel oxidation catalyst in presence of Na and P impurities were studied. The synthesized reference-PtPd/CeZrO 2 /La-Al 2 O 3 and Na-, P-modified-PtPd/CeZrO 2 /La-Al 2 O 3 catalysts were HT-aged, characterized by several techniques and catalytically tested. The characterization results showed the loss of specific surface area due to the sintering of the catalyst. H 2 -TPR results evidenced the decrease of the catalytic redox activity. TEM results indicated that sodium impurities did not modified the catalyst structure while phosphates were formed. In general, lower reaction rates were found for CO, C 3 H 6 and NO involved reactions after HT-aging. The electronic changes induced by sodium species were attenuated after HT-aging due to the sintering of the catalyst. The lower metal-adsorbates charge transfer enhanced CO oxidation while had a negative effect for C 3 H 6 and NO involved reactions. Diffuse Reflectance Infrared Fourier Transform Spectroscopy experiments indicated that phosphates inhibited the intermediates adsorption on the catalyst surface.