Highly selective liquid-phase hydrogenation of furfural over N-doped carbon supported metallic nickel catalyst under mild conditions

In this work, N-doped activated carbon supported metallic nickel (Ni/NAC) catalysts were fabricated by two-step calcination method in N 2 atmosphere for liquid-phase hydrogenation of furfural (FAL). It was found that the pyrolysis temperature and amount of melamine as N doping source have important influence on N doping content and type in activated carbon (AC) support, resulting in the subsequently formed Ni nanoparticles on N-doped AC with different sizes and thus affording different catalytic hydrogenation activities. The results demonstrated that using N-doped AC with 1.0   g melamine at 1073   K in N 2 atmosphere as support, the obtained Ni/NAC at 873   K in N 2 atmosphere with Ni nanoparticle sizes of ∼13.1   nm (denoted as Ni/NAC-1-1073) exhibits a N doping content of 3.65   at.% and a surface area of 561.2   m 2   g −1 with a microporous structure. As catalyst for FAL hydrogenation, Ni/NAC-1-1073 demonstrated the best catalytic performance among all investigated catalysts, achieving almost 100% selectivity of tetrahydrofurfuryl alcohol (THFOL) with a complete FAL conversion at 353   K after 3   h reaction, while only 76.7% selectivity of THFOL with a FAL conversion of 86.4% was obtained using Ni/AC catalyst without N doping under the identical experimental conditions. Furthermore, it was found that almost 100% conversion of FAL to furfural alcohol (FOL) can be reached by transfer hydrogenation pathway in 2-proponal solvent using Ni/NAC-1-1073 at 413   K after 5   h reaction, whereas Ni/AC without N doping can only afford 30.2% conversion of FAL to FOL under the same conditions. The superior catalytic performance of Ni/NAC-1-1073 could be ascribed to a synergistic effect of nanosized Ni providing catalytic active sites, suitable N doping content and type in AC to promote catalytic performance, and advantageous structure characteristics of high surface area and porous structure favourable for the exposure of catalytic active sites and mass transport.