Solvent-Free Catalytic Hydrotreatment of Alcell Lignin Using Mono- and Bimetallic Ni(Mo) Catalysts Supported on Mesoporous Alumina

Abstract

Technical lignins are an attractive and renewable source for the production of aromatic chemicals. However, efficient depolymerization of technical lignins to valuable low-molecular-weight chemicals is challenging due to its recalcitrant nature. Here, we report the use of nonprecious metal-based, monometallic Ni (prereduced) and bimetallic NiMo (in situ sulfided) catalysts supported on mesoporous alumina, either as such or doped with Si, Mg, or Ti, for a solvent-free catalytic hydrotreatment (batch, 400 °C, 4 h reaction time, 100 bar initial H2 pressure) of Alcell lignin to obtain oils enriched in biobased chemicals like alkylphenols and the parent phenol. These are important building blocks in the chemical industry and are currently obtained from fossil resources. The catalysts were prepared by a one-pot evaporation-induced self-assembly (EISA) method and characterized by various techniques [N2 physisorption, X-ray diffraction (XRD), temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), and transmission electron microscopy (TEM)]. The best result was obtained using a monometallic Ni catalyst with an ordered mesoporous alumina support doped with Ti, giving an oil yield of 57 wt % with 10 wt % alkylphenols on lignin intake. By comparison, it was shown that the mesoporous structure of alumina is crucial for enhanced lignin oil yields.