Synergistic effect of acidity and active phases for nickel nanoparticles supported HZSM-5 catalysts on lignin-related model compounds hydrodeoxygenation performance under mild conditions

Abstract

The cleavage >C-O- bridge bonds and saturate aromatic rings of oxygen compounds from lignin is increasingly important in catalytic hydrodeoxygenation (HDO) for lignin upgrading and value-added utilization. Therefore, the catalytic behavior of a series of HZSM-5 (HZ-5) with different Si/Al ratios (n = 25, 50, 170, and 200) and acidity levels supported Ni nanoparticles (NPs) were prepared by modified deposition-precipitation method for catalytic HDO of lignin-related model compounds (LRMCs). The effects Ni loading, HZ-5 texture, and acid properties on catalytic activity, products distribution, and mechanism were systematically investigated. Furthermore, as-prepared catalysts were characterized by X-ray diffraction, N2 adsorption, scanning electron microscope, energy dispersive spectrometer, pyridine infrared, NH3-temperature programmed desorption, X-ray photoelectron spectrometer, and used for catalytic HDO of LRMCs with different >C-O- bridge bonds and aromatic rings, including oxydibenzene, oxybis(methylene)dibenzene, benzyloxybenzen, and oxydinaphthalene. These results indicate that Ni/HZ-5(n) can activate H2 to biatomic hydrogen (H‧‧‧H) and heterogeneously split H‧‧‧H to relatively mobile H+ and immobile H- with synergistic effect of Ni NPs, further leads to cleave the >Cal-O- and >Car-O- bridge bonds with different conversion through active hydrogen transfer. Additionally, effective modulate of catalytic HDO of LRMCs would be helpful to further maximize the target product yield on the basis of this mechanism at 160 °C for 5 MPa initial hydrogen pressure (mild conditions).