A Direct Route for Upcycling Electronic Waste Into High-Performance Palladium Catalysts

Abstract

Conversion to a circular economy needs efficient methods to recover critical metals from electronic waste. Here, we demonstrate a two-step, purification-free process to transform palladium contained in waste multilayer ceramic capacitors (MLCCs) into highly active heterogeneous catalysts. After acid leaching, Pd(II) was selectively extracted (97%–100% yield) using di-n-octyl sulfide (DOS) or N,N,N′,N′-tetrahexylmalonamide (THMA), then directly impregnated onto γ-Al₂O₃. The resulting catalysts—containing residual Ag or Bi—showed activity at the level of a commercial reference (1 wt% Pd on γ-Al₂O₃) in methane oxidation (T₅₀ = 325°C–327°C) and hindered olefin hydrogenation (quantitative conversion during the first cycle at 185°C/20 bar), suggesting reasonable tolerance to metallic impurities. Notably, DOS-extracted catalysts retained full activity despite sulfur content (0.5–0.6 wt%), while THMA-derived systems showed three times higher intrinsic activity than the reference catalyst at 350°C. HRTEM-EDS revealed well-dispersed Pd or Pd/Ag nanoparticles. This approach eliminates the need for complete Pd purification, offering a sustainable route to upcycle complex e-waste into value-added materials for industrial catalysis.