Structure sensitivity of Cu supported on manganese oxide catalysts in levulinic acid hydrogenation

Abstract

Different synthesis methods were used to prepare a series of size-controlled copper nanoparticles supported on manganese oxide octahedral molecular sieve (OMS-2) catalysts. All Cu/OMS-2 catalysts, with average Cu nanoparticle sizes prepared in the range of 2–22 nm, were thoroughly characterised using X-ray diffraction (XRD), N₂ sorption, H₂ temperature programmed reduction (TPR), transmission electron microscopy (TEM), and ICP-OES elemental analyses. The catalytic activity of the size-controlled Cu/OMS-2 catalysts was investigated in liquid phase hydrogenation of levulinic acid as a model reaction to evaluate the nanoparticle size dependance and structure–activity relationship. The catalytic activity studies showed that the catalyst performance depends greatly on the catalyst preparation methodology and Cu nanoparticle size. Complete conversion of levulinic acid with a high γ-valerolactone yield, >99%, was observed using Cu/OMS-2 catalysts prepared by the precipitation–deposition (Cu nanoparticle size 2–3 nm) method. In comparison to wet-impregnated catalysts (Cu particle size 20–22 nm), the improved performance of precipitation–deposition catalysts was mainly attributed to the well-distributed, smaller Cu nanoparticles. The influence of Cu nanoparticle size is correlated with the turnover frequency (TOF, h⁻¹) for levulinic acid conversion, indicating the structure sensitivity of the levulinic acid hydrogenation reaction.