Effect of porosity on catalytic performance of HKUST-1 in Knoevenagel condensation

Abstract

Abstract Hierarchically porous HKUST-1 materials ( A and B ) were synthesized via a cooperative template-directed strategy enabling controlled introduction of mesoporosity while preserving the characteristic original framework ( 1 ). Structural, spectroscopic, and textural characterization confirmed retention of the intrinsic HKUST-1 structure together with high specific surface areas of 1788, 1554, and 1690 m 2 g − 1 for activated 1’ , A’ , and B’ , respectively. The hierarchical materials exhibited pore size distributions extending from intrinsic micropores to mesopores. The catalytic performance was evaluated in the Knoevenagel condensation of benzaldehyde derivatives with malononitrile. Under optimized conditions (toluene, 80°C, 50 mg catalyst, 60 min), conversions of 93% and 98% were achieved for A’ and B’ , respectively. Arrhenius analysis yielded a lower effective activation energy for B’ (43.9 ± 5.2 kJ mol − 1 ) compared to A’ (53.6 ± 3.1 kJ mol − 1 ), indicating more favorable reaction kinetics. High conversions (~ 96–98%) were obtained for electron-withdrawing substituents, whereas bulky alkyl-substituted substrates showed lower conversions (~ 6–16% for B’ , ~ 5–11% for A’ ), confirming diffusion limitations. Recyclability tests showed only moderate activity loss after five cycles (17% for A’ , 15% for B’ ). Post-catalysis analysis confirmed preserved framework structure and crystallinity, while infrared and thermogravimetric analyses indicate residual species in the pores.