Interfacial electronic effects of palladium nanocatalysts on the by-product ammonia selectivity during nitrite catalytic reduction

Abstract

Catalytic denitrification is an emerging technology that can remove nitrate and nitrite from water. However, the undesirable formation of ammonia requires further suppression. By preparing three types of Pd-based nanocatalysts with different electronic structures as model catalysts, we demonstrate the interfacial electronic effects induced by ethanol (EtOH) and 1-dodecanethiol (C12T) modifications on the selectivity of nitrite catalytic reduction. XPS and in situ DRIFTS spectral characterization studies illustrate that the electron density of the Pd surface atoms increased with the ethanol modification and decreased with the 1-dodecanethiol modification. The nitrite reduction results show that the Pd–EtOH@MIL-101 catalyst (Pd^δ−) exhibited an unexpectedly low ammonia selectivity of 0.31%, while a higher value of 10.18% was obtained for the Pd–C12T@MIL-101 catalyst (Pd^δ+), which indicated that the electronic structure of Pd can control the ammonia selectivity during the nitrite reduction. Thermodynamics studies revealed that increasing the electron density of the Pd surface atoms reduced the nitrite reaction activation energy and changed the reaction pathways, which resulted in a significant decrease in the ammonia selectivity. The results in this paper may provide new insight into designing and optimizing Pd-based catalysts with low ammonia selectivity for nitrate and nitrite catalytic reduction.