Complete methanol oxidation in carbon monoxide streams over Pd/CeO2 catalysts: Correlation between activity and properties

Three different techniques, a hydrothermal process with impregnation, solution-combustion and common precipitation with impregnation, were employed for the synthesis of 1.5 wt% Pd/CeO2, and the resulting catalysts were denoted as Pd/HY, Pd/COM and Pd/PI, respectively. These catalysts have been investigated in terms of catalytic co-oxidation of CO and methanol and characterized by means of XRD, BET, SEM, STEM-EDS, CO chemisorption, XPS, Raman, O2-TPD, H2-TPR and CO-TPD measurements. Activity results show that a rapid catalytic oxidation of CO following the Mars-van Krevelen-type mechanism favors the complete methanol oxidation at low temperature. Consequently, the Pd/HY catalyst with the highest degree of defect sites connected with the mobility of activated oxygen shows the best catalytic performance. And the generation of more defect sites demonstrated by Raman is assumed for the low crystallinity and small crystallite size of CeO2 synthesized through a hydrothermal process while the high mobility of activated oxygen is evidenced by O2-TPD and H2-TPR. Additionally, the outstanding catalytic performance of Pd/HY is also associated with its high Pd dispersion and stable PdOx species as well as good redox behavior.

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► Three types of Pd/CeO2 were compared in the co-oxidation of CO and methanol.
► An easier CO oxidation facilitates the complete methanol oxidation.
► High degree of defect sites connected with activated oxygen mobility is the key.
► Pd dispersion, stable PdOx species and redox ability also affect the oxidation activity.