Role of Copper Species in Copper Phyllosilicate Catalysts for the Catalytic TransferHydrogenation of Furfural to __Valerolactone

Abstract

Copper phyllosilicate (CuPS) catalysts were synthesized and evaluated for the catalytic transfer hydrogenation of furfural to γ‐valerolactone (GVL). Various copper loadings (10‐30 wt.%) were studied to elucidate the impact of copper species on catalytic performance. Notably, a high dispersion of copper (%DCu ≈ 70%) and a substantial BET surface area (620 m²/g) were achieved, even at 30 wt.% copper loading. TR‐XANEs and XPS analyses identified two geometric structures of Cu²⁺ on the CuPS catalysts; square planar and octahedral alongside Cu⁺/Cu⁰ species formed upon reduction. The reduced 30%CuPS‐R catalyst, enriched in metallic Cu⁰, achieved complete conversion of furfural but exhibited low GVL selectivity. Conversely, the as‐synthesized 30%CuPS, predominantly composed of Cu²⁺, showed a lower furfural conversion but higher selectivity. The physical mixing of 30%CuPS‐R and 30%CuPS in a 50:50 ratio yielded the best catalytic performance, resulting in 100% furfural conversion and 86% GVL selectivity. The findings suggest that metallic Cu⁰ is essential for initiating the conversion of furfural, while Cu²⁺ plays a critical role in GVL formation. An optimal Lewis/Brønsted acidity ratio is determined to be 5.7 for the mixed catalysts. The proposed reaction mechanism underscores the complex interplay between different copper species and acid sites in CuPS catalysts.