From Spent Catalysts to Smart Windows: Recovery of Vanadium for Use in Advanced Thermochromic Coatings

Abstract

Vanadium is a transition metal widely used in steel production, batteries, and catalysis. It is a critical material and its disposal poses significant environmental challenges, making recovery and reuse a necessity. This study presents an innovative approach for the recovery and reuse of vanadium from spent catalysts, transforming it into high-purity V2O5 as the precursor for advanced VO2-based thermochromic coatings for smart windows. A multistep process comprising reductive acid leaching, oxidation, and selective precipitation was employed to develop two recovery pathways, resulting either in high-purity vanadium pentoxide (total metallic impurities of 2.14 ppm; extraction yield = 26%) or in a high extraction yield of 72% (total metallic impurities = 1.78%). The material was subsequently converted to monoclinic VO2 and applied for the production of a thermochromic solar control coating for smart windows. Optical measurements revealed a visible transmittance of 55% and a solar modulation of 4.4%, consistent with values for state-of-the-art VO2 coatings prepared by chemical reduction of virgin V2O5. This process demonstrates the technical feasibility of recovering vanadium from spent catalysts and reuse it in functional materials for smart windows, contributing to resource efficiency and environmental sustainability.