Nickel-promoted copper–silica nanocomposite catalysts for hydrogenation of levulinic acid to lactones using formic acid as a hydrogen feeder

• Levulinic acid hydrogenation using formic acid as H2 source was studied over Ni-Cu/SiO2.
• Ni(20)-Cu(60)/SiO2 continuously produced γ-valerolactone with 97% yield.
• Ni-Cu/SiO2 showed its stability up to 200 h without any loss of catalytic activity.
• Metallic dispersion in Ni-Cu/SiO2 is mainly responsible for superior catalytic activity.

Highly active, thermally stable nickel-promoted copper–silica nanocomposite catalysts were prepared via a deposition–precipitation method and used for hydrogenation of levulinic acid (LA) using formic acid (FA) as H2 feeder. Ni(20)Cu(60)-SiO2 (3:1 weight ratio of Cu to Ni, 80 wt% metal content) showed better activity for vapor-phase formation of γ-valerolactone (GVL) from LA with FA as a hydrogen source. The catalyst selectively converts 99% of LA into 96% of GVL; the remaining 4% is angelica-lactone (AL). The effect of different concentrations of Ni promoted on Cu-silica and different LA to FA molar ratios on the catalyst activity affecting the hydrogen-free hydrogenation of LA was studied. The catalyst Ni(20)Cu(60)-SiO2 exhibited long-term stability (200 h) without loss in activity. Characterization using TEM, XPS, TPR, XRD and N2O titration was performed to find the most active phase for LA hydrogenation to GVL and the reason for the long-term stability. It was found that Ni-promoted well-dispersed metallic Cu species were the most active phases in hydrogenation, and the nanocomposite nature of the catalyst helped in providing long-term stability to the active phase.

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