Efficient and sustainable hydrogenation of levulinic-acid to gamma-valerolactone in aqueous solution over acid-resistant CePO4/Co2P catalysts

摘要

Developing a highly active, acid-resistant and low-cost catalyst which can perform well in aqueous solution has long been sought for practical and sustainable lignocellulosic biomass transformation. In this work, a series of Ce-P-Co heterogeneous catalysts were prepared by a convenient solvothermal method for catalytic hydrogenation of levulinic acid (LA) to gamma-valerolactone (GVL) in water. By comprehensive characterizations and catalytic measurements, the structure of the prepared Ce-P-Co samples was disclosed as (CePO4)(m)/Co2P composites with a modulated molar ratio (m) of 0.04-0.34. With the introduction of CePO4, the unique hydrogen activation on CePO4 markedly accelerated the reaction, with the GVL yield after 90 min on (CePO4)(m)/Co2P (45-97%) being much higher than on pure Co2P (26%), together with an attractive TOF of 0.27-0.61 s(-1) on (CePO4)(m)/Co2P (comparable to precious metal catalysts). Further analysis of the kinetic and acidic features indicated a Langmuir-Hinshelwood mechanism, initiated by activation of H-2 and LA on CePO4 and Co2P, respectively, followed by a surface reaction of the two activated species as the rate-determining step, as a plausible pathway for producing GVL from LA on (CePO4)(m)/Co2P. The consistent catalytic performance during recycling tests and the unchanged morphological, bulk and surface structure features of the used catalyst relative to the fresh catalyst confirmed that the (CePO4)(m)/Co2P structure was robust enough to endure the acidic aqueous environment for efficiently and sustainably converting LA to GVL. The advantages of high catalytic efficiency, stable, acid-resistant structure and low cost marked (CePO4)(m)/Co2P as a competitive and practical heterogeneous catalyst for sustainable, scaled-up lignocellulosic biomass transformation.