The synergistic role of moisture and the silver-lead(II) oxide interface in room-temperature catalytic oxidation of gaseous formaldehyde

초록

Formaldehyde (FA), a carcinogenic oxygenated volatile organic compound, represents a principal challenge for indoor air quality management efforts. This study investigates the oxidation potential of lead(ii) oxide (PbO)-supported silver (Ag) catalysts against FA under dark and low-temperature conditions, including room temperature (RT) conditions. FA (100 ppm) conversion (X-FA) on Ag/PbO increases with increasing Ag content while being lowered with reduction pre-treatment (R). The RT X(FA )of these catalysts decreases (at gas hourly space velocity: 9436 h(-1)) as follows: 0.9%-Ag/PbO (83%) > 0.9%-Ag/PbO-R (56%) > 0.2%-Ag/PbO (39%) > 0.02%-Ag/PbO (35%). Interestingly, the 0.9%-Ag/PbO catalyst achieves 100%X(FA)at RT above 60% relative humidity, demonstrating exceptional FA removal efficiency. While complete mineralization to carbon dioxide requires a mild temperature increase to 80 degrees C, the catalyst effectively sequesters FA as surface-bound intermediates (e.g., dioxymethylene and carbonates) at RT, functioning as a transformative adsorptive sink. Density functional theory calculations and characterization results reveal that the Ag/PbO interface effectively activates molecular oxygen (O-2) and water (H2O) to generate reactive oxygen species (*O) and hydroxyl (OH) groups for the oxidation of FA molecules. Compared to Ag/PbO-R, the Ag/PbO surface exhibits a higher concentration of *O under oxidative operational conditions, as oxygen species preferentially accumulate at interfacial sites rather than being consumed to restore the lattice structure. Additionally, moisture plays a crucial role by facilitating the formation of *OH as well as the key *CH2(OH)(2 )intermediate. This study mechanistically dissects the charge-transfer dynamics at the Ag-PbO interface and the cooperative O-2/H2O chemistry that arises from this junction.

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