Low-temperature oxidative removal of gaseous formaldehyde by an eggshell waste supported silver-manganese dioxide bimetallic catalyst with ultralow noble metal content

Under dark/low temperature (DLT) conditions, the oxidative removal of gaseous formaldehyde (FA) was studied using eggshell waste supported silver (Ag)-manganese dioxide (MnO2) bimetallic catalysts. To assess the synergistic effects between the two different metals, 0.03%-Ag-(0.5-5%)-MnO2/Eggshell catalysts were prepared and employed for DLT-oxidation of FA. The steady-state FA oxidation reaction rate (mmol g(-1) h(-1)), when measured using 100 ppm FA at 80 ?C (gas hourly space velocity (GHSV) of 5308 h(-1)), varied as follows: Ag-1.5%MnO2/Eggshell-R (9.4) > Ag-3%-MnO2/Eggshell-R (8.1) > Ag-1.5%-MnO2/Eggshell (7.5) > Ag-5%-MnO2/Eggshell-R (7.2) > Ag-1.5%-MnO2/CaCO3-R (6.8) > MnO2-R (6) > Ag-0.5%-MnO2/Eggshell-R (3.2) > Ag/Eggshell-R (2.6). (Here, R' denotes hydrogen-based thermochemical reduction pretreatment.) The temperature required for 90% FA conversion (T90) at the same GHSV exhibited a contrary ordering: Ag/Eggshell-R (175 ?C) > Ag-0.5%-MnO2/Eggshell-R (123 degrees C) > Ag-5%-MnO2/Eggshell-R (113 degrees C) > MnO2-R (99 degrees C) > Ag-1.5%MnO2/Eggshell (96 degrees C) > Ag-3%-MnO2/Eggshell-R (93 degrees C) > Ag-1.5%-MnO2/Eggshell-R (77 degrees C). The eggshell catalyst outperformed the ones made of commercial calcium carbonate due to the presence of defects in the former. The MnO2 co-catalyst enhances the catalytic activities through the capture and activation of atmospheric oxygen (O2) with rapid catalytic regeneration. Also, MnO2 favorably captures the hydrogen of the adsorbed FA molecules to make the oxidation pathway thermodynamically more favorable.

Automated summary

The study demonstrated that the silver-manganese dioxide bimetallic catalyst supported by eggshell waste shows promising efficiency in oxidizing formaldehyde under dark/low temperature conditions. The synergistic effects between silver and manganese enhance catalytic activities, while the eggshell catalyst outperforms commercial calcium carbonate-based catalysts due to its defects.