Boosting catalytic reduction of hexavalent chromium over PdNi alloy by electron injection into unoccupied Pd d-band

Abstract

Hexavalent chromium (Cr(VI)) in industrial wastewater presents a severe environmental threat. Using formic acid for Cr(VI) reduction offers an efficient and sustainable chromium remediation. While Pd reduces the energy barrier for formic acid dissociation to produce H*, the formation of strong PdH bonds hinders subsequent Cr(VI) reduction due to elevated energy levels and an increased proportion of unoccupied states in the Pd 4d bands. To address this challenge, we developed a PdNi/TiO₂ nanofibrous catalyst designed to optimize hydrogen adsorption through intermetallic electron transfer within the alloy. Experimental and theoretical results confirm that electrons from Ni are injected into the unoccupied portion of the Pd d-band, downshifting the d-band center upon alloy formation. This electron injection optimizes the electronic states of the Pd active sites, lowering the energy barrier for formic acid dissociation while weakening the PdH interaction, thereby facilitating the release of H* species. The optimized Pd₆Ni₄/TiO₂ achieves an improved turnover frequency (TOF) of 164.8 min⁻¹ for Cr(VI) reduction, outperforming most previous Pd-based catalysts.