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The Effect of Pretreatment on the Reactivity of Pd/Al2O3 in Room Temperature Formaldehyde Oxidation

A Pd/Al2O3 nanocatalyst was pretreated at 750 °C in air, Ar or H2O/Ar, respectively. The effect of these different pretreatments on the active species and reactivity of Pd/Al2O3 in formaldehyde oxidation at room temperature was investigated. The pretreatment was found to affect both the phase transformation of PdO to Pd metal and the Pd dispersion, leading to different catalytic performances. We found that the Pd/Al2O3 nanocatalyst pretreated in both Ar and H2O/Ar show 60 % and 100 % formaldehyde conversion at 25 °C, respectively, while the catalyst pretreated in air is not active under the same condition. Pretreatments in both Ar and H2O/Ar were found to facilitate the formation of metallic Pd on Pd/Al2O3 catalyst, confirmed by both experiments and calculation based on the function of the equilibrium oxygen pressure and temperature. We further found that the catalyst pretreated in H2O/Ar has higher Pd dispersion and more surface OH groups compared to that pretreated in Ar, leading to improved activity in formaldehyde oxidation.