Ni/USY with Fine Stabilized Ni Nanoparticles for Lignin Hydrodeoxygenation

Cyclanes serve as crucial platform compounds for the production of polymers, chemicals, and biofuels. Utilizing renewable biomass to synthesize cyclohexane is imperative not only to mitigate dependence on fossil fuels but also to advance green development strategies. The use of metal catalysts in the hydrodeoxygenation (HDO) reaction is essential for obtaining biomass-derived cyclanes. During the HDO process, the size of the metal particles and the adsorption capacity of the substrate significantly impact the reaction. This study reports the preparation of a fine and stable Ni nanoparticle material for an efficient HDO process. A postconfinement strategy was employed to synthesize a three-dimensional confined Ni/USY catalyst with finely dispersed particles. Initially, the Ni precursor was introduced into the ultrastable Y (USY) chemical microenvironment to facilitate nucleation and growth. Subsequently, H2 reduction of Ni was within the three-dimensional confined scaffold at high temperatures. Compared with conventional Ni-based catalysts, these confined spaces restrict Ni aggregation, resulting in finer Ni particle sizes, increased exposure of active sites, and enhanced catalytic activity. To understand the mechanism for the HDO of soluble portion (SP), the catalytic activity of Ni/USY was investigated using 2,2-oxydinaphthalene (ODN) as lignin-related model compounds. As a result, ODN was completely converted to decalin at 160 °C under an initial hydrogen pressure of 2 MPa for 2.5 h, while the lignin was converted to soluble portion (SP) dominant by cyclanes and alkanes at 250 °C for 8 h over Ni/USY, and the yield of SP was about 83.3%. The characterization of Ni/USY and the time profiles of the product proved that Ni/USY can activate H2 to H···H, which subsequently cleaves into mobile H+ and immobile H–. The addition of H···H and H+ promoted the hydrogenation of benzene rings in the ODN and the removal of oxygen atoms, respectively. In addition, Ni/USY exhibits excellent reusability after 3 runs. In addition, the HDO properties and physicochemical properties of Ni loaded onto different kinds of zeolite supports were compared and used to reveal the reason for the good HDO performance of Ni/USY.