Selective Hydrodeoxygenation Of Guaiacol Catalyzed By Nanoporous Nickel

In recent years,the increasing demand for fuel and environmental problems caused by greenhouse gas emissions has received strong attention.Due to the scarcity of fossil resources,researchers increasingly pay attention to the development and utilization of renewable resources.Lignocellulose is the most abundant renewable resource among biomass resources and can be used to produce high-quality,high-energy-density biofuels.It is a simple and quick way to convert biomass into bio-oil by fast pyrolysis,but bio-oil has high oxygen content and poor stability,and cannot be used directly as fuel.In this paper,lignin-derived guaiacol is used as the model compound,and nanoporous nickel is used to catalyze its hydrodeoxygenation.Nanoporous nickel modified by precious metals and non-precious metals was prepared by mechanical alloying,in which MnO₂ modifier can significantly promote the hydrodeoxygenation of guaiacol.The characterization results show that the nanoporous NiMnO₂ modified by MnO₂ has a high amorphous structure,but the electronic structure of the active metal has not changed significantly.During the reaction,hydrodeoxygenation of guaiacol includes hydrogenation of benzene ring and C-O bond hydrogenolysis,which are parallel and competing processes.Hydrogenation of the benzene ring generate2-methoxycyclohexanol,which cannot be further converted;the preferential hydrogenolysis of the C-O bond can achieve the deoxygenation of guaiacol.Experimental data show that high temperature and low pressure conditions are conducive to C-O bond breakage and improve the selectivity of the deoxygenated product cyclohexanol.At the optimal reaction condition of150?and 0.5 MPa H₂,the selectivity of cyclohexanol was 95.6%when guaiacol was completely converted.After 6 cycles,the activity of the catalyst fluctuated only slightly.This work provides a simple and effective method to decompose nanoporous nickel into smaller amorphous fragments,which may be beneficial to improve the catalytic activity of nanoporous metals.Based on the above work,in situ hydrodeoxygenation of guaiacol on nanoporous metals and supported catalysts using water as hydrogen donor under nitrogen atmosphere,of which only nanoporous nickel has catalytic activity.In order to clarify that water is the hydrogen supply agent of the catalytic system,the comparative experiment was carried out using cyclohexane,which has no hydrogen supply capability,as the solvent.The study found that water and isopropanol have the same effect and can provide hydrogen for the reaction,that is,water is the hydrogen source of the reaction system,not the catalyst.The isotope experiment with D₂O as the solvent also verified the experimental results.Nanoporous metal dealloyed to form porous and ligament structure,easy to form platform,step active site,which may be an important reason why nanoporous nickel has catalytic activity.The electronic structure information of the catalyst before and after the reaction indicated that the catalyst was oxidized,and the nitrogen atmosphere did not affect the reaction.