Abstract A series of mesoporous nickel catalysts with different molar ratios of citric acid and nickel nitrate were synthesized via a simple two-step method by solid-state grinding and in-situ reduction; these catalysts were further employed for the catalytic transfer hydrogenation of levulinate esters to γ-valerolactone (GVL) with 2-propanol as the hydrogen donor. The effects of C6H8O7/Ni molar ratios, catalyst dosage, reaction temperature and time on the catalytic performance were investigated. An excellent GVL selectivity of 99.1% and an ethyl levulinate (EL) conversion of 100% could be achieved at 180 °C in 6 h over Ni-1.0 catalyst with a 1.0:1 M ratio of C6H8O7/Ni. The characterization results showed that the Ni-1.0 catalyst was composed of mesoporous metallic Ni bulk and a surface Ni–NiO composite, and the acid sites of NiO played a synergistic catalytic role in producing GVL from EL. The superior mesoporous structure and large surface area of Ni-1.0 increased the atomic utilization rate of nickel metallic active centers. Moreover, Ni-1.0 catalyst could be easily separated and reused ten times, with an EL conversion above 95% remaining in each recycle. This work provids a highly efficient and environmentally friendly catalytic procedure for the conversion of biomass into GVL, a fuel additive compound.

中文翻译：

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通过无载体介孔镍催化转化生物质衍生的乙酰丙酸酯高效合成γ-戊内酯

摘要 通过固态研磨和原位还原两步法合成了一系列不同柠檬酸和硝酸镍摩尔比的介孔镍催化剂；这些催化剂进一步用于以2-丙醇作为氢供体的乙酰丙酸酯催化转移氢化为γ-戊内酯（GVL）。考察了C6H8O7/Ni摩尔比、催化剂用量、反应温度和反应时间对催化性能的影响。在 C6H8O7/Ni 的比例为 1.0:1 M 的 Ni-1.0 催化剂上，在 180 °C 和 6 小时内可实现 99.1% 的出色 GVL 选择性和 100% 乙酰丙酸乙酯 (EL) 转化率。表征结果表明，Ni-1.0 催化剂由介孔金属 Ni 块体和表面 Ni-NiO 复合物组成，NiO 的酸性位点在从 EL 生产 GVL 中起到了协同催化作用。Ni-1.0优越的介孔结构和大表面积提高了镍金属活性中心的原子利用率。此外，Ni-1.0 催化剂可以很容易地分离和重复使用 10 次，每次循环的 EL 转化率都保持在 95% 以上。这项工作为将生物质转化为 GVL（一种燃料添加剂化合物）提供了一种高效且环保的催化程序。