Hydrogenation of levulinic acid to γ-valerolactone using carbon nanotubes supported nickel catalysts

Abstract Carbon nanotubes (CNT) supported (10 wt.%) nickel catalysts were evaluated for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) using a trickle-bed reactor at 180 °C and 30 bar. The effect of nature of the nickel precursors salts (NiNIT- Ni(NO3)2.6H2O, NiACET- Ni(CH3COO)2.4H2O) and NiHYD- Ni(OH)2) and the preparation method on the distribution of Ni particles inside (CNTIN) and outside (CNTOUT) of the carbon nanotubes were investigated. The nickel catalysts were synthesized by incipient wetness impregnation method without opening or functionalization of CNTs. The difference between the preparation of Ni/CNTIN and Ni/CNTOUT catalysts was the pre-filling of the pores of the CNT with p-xylene before the impregnation of the nickel salts for the Ni/CNTOUT samples. These methodologies led to the complete deposition of Ni particles outside of pores for Ni/CNTOUT samples, but partial deposition of Ni particles inside of CNTs for Ni/CNTIN samples, regardless of the nickel precursor salt. It was estimated by TEM only 30 % of Ni particles inside CNTs for NiNIT/CNTIN. The Ni/CNTOUT catalysts prepared from nickel nitrate and nickel hydroxide salts showed the highest activity for LA hydrogenation, compared to those prepared from nickel acetate salts, which is likely due to the higher metal dispersion.