Oxidation and disproportionation of carbon monoxide over Pd-ZrO2 catalysts prepared from glassy Pd-Zr alloy and by coprecipitation

Abstract

Palladium/zirconia catalysts prepared by oxidation of an amorphous PdZr 3 alloy were tested for the oxidation and disproportionation of CO. Their catalytic and structural properties were compared with those of a Pd/ZrO 2 catalyst of similar composition, prepared by conventional coprecipitation. For the preparation of Pd/ZrO 2 , the glassy PdZr 3 alloy was either oxidized in situ , i.e. under CO oxidation conditions or oxidation in air. The catalysts were characterized by thermal analysis (TG, DTA), XRD, electron microscopy, CO chemisorption and nitrogen physiorption measurements. In situ , oxidation of the Pd-Zr alloy led to significantly higher BET and palladium surface areas than oxidation in air. The catalysts derived from the glassy Pd-Zr alloy exhibited considerably higher activities for both oxidation and disproportionation of CO at low temperature than the coprecipitated Pd/ZrO 2 catalyst and palladium powder. The higher activities are attributed to the extremely large interfacial area of palladium and zirconia phases in the alloy-derived Pd/ZrO 2 compared to the coprecipitated catalyst. For both alloy-derived catalysts the apparent activation energy for CO oxidation was 58±3 kJmol −1 . In the absence of oxygen, disproportionation of CO with subsequent incorporation of carbon into the palladium lattice occurred with the alloy-derived catalysts readily at ca. 150°C, whereas no similar phenomenon was observed with the palladium powder up to 400°C. The interstitial carbon was found to be very reactive towards oxygen forming CO 2 . The storage of carbon by formation of a solid solution with Pd was found to influence significnatly the behaviour of the catalyst under forced cycling between CO and O 2 feed.