High catalytic performance of nitrate reduction by synergistic effect of zero-valent iron (Fe0) and bimetallic composite carrier catalyst

Abstract

Nitrate pollution has attracted increasing attention due to the worsening of water pollution. This study focuses on the synergistic effects of zero-valent iron and bimetallic composite carrier catalyst for maximizing the catalytic reduction of nitrate in water to nitrogen gas. Compared with other conditional catalytic processes, this new technology exhibits a better catalytic efficiency with 70% of N2 selectivity and 0.42 mg/L‧g‧min of catalytic activity under the following conditions: 2 h reaction time, 4 g/L zero-valent iron, 3 g/L catalyst, 3:1 of palladium:tin, 2:1 of γ-aluminium oxide: diatomite, and 5.2 pH (catalyst: palladium-tin/γ-aluminium oxide-diatomite). In addition, a kinetic study indicates that this catalytic reaction is well illustrated by the first-order kinetics of the Langmuir-Hinshelwood model. A study on the catalytic rates of catalysts with six different composite carriers (γ-aluminium oxide-diatomite, γ-aluminium oxide-manganese dioxide, γ-aluminium oxide-kaolin, diatomite-kaolin, diatomite-manganese dioxide, and kaolin-manganese dioxide) shows that the physical-chemical properties of the carriers are an important factor that significantly influences the reaction process. Finally, the regeneration and reuse of six catalysts are further investigated. Acidic washing enhances the catalytic performance more than alkaline washing. However, except for palladium-tin/diatomite and palladium-tin/γ-aluminium oxide-diatomite, other catalysts after acidic washing remained improved catalytic performance, but, lower than their original catalysts.