Hydrodeoxygenation Of Lignin-derived Phenols Over Cobalt-based Catalysts

With the rapid development of human society,the consumption of the traditional fossil resources is faster,which brings about the worse greenhouse effect.It is necessary to develop the renewable resources to replace traditional fossil resources partially.Biomass resources derived from photosynthesis of green plants is the solely renewable organic carbon resource in nature.The development of conversion technology of the abundant biomass to replace traditional fossil resources has great significance.Lignin as an important part of lignocelluloses with 40%of biomass energy has a great potential for producing fuels and bulk chemicals.However,lignin depolymerization products are mainly methoxy-substituted phenols.These phenols contain high oxygen content,which are difficult to use directly.Therefore,hydrodeoxygenation(HDO)has been proposed to transform these compounds to chemicals and liquid fuels.Currently,the catalysts used in HDO of lignin-derived phenols are mainly noble-metal catalysts,such as Pd,Ru,Pt,etc.Although these catalysts showed good activity in HDO of lignin-derived phenols,the cost was high,which was adverse to industrial application.Non-noble metal Ni was also used in the reaction,but the reaction conditions was high.To solve the aforementioned problems,we developed the cobalt-based catalysts used in HDO of lignin-derived phenols.In our first work,a simple method with cellulose as the carbon source,cobalt nitrate as the metal source,and ammonia as nitrogen source has been proposed for preparation of CoNx@NC catalysts.Using eugenol as model compound,the catalyst prepared in 650 ℃(CoNx@NC-650)exhibited the best HDO activity for eugenol conversion.The yield of propylcyclohexanol from eugenol was>99.9%under 2 MPa H2 at 200 ℃ for 2 h.Moreover,a high yield of propylcyclohexane(99.1%)could be achieved when the solid acid HZSM-5 was added to the reaction system.Through the catalysts characterization,cobalt nitrides(CoNx)formed in ammonia atmosphere played an important role in the catalytic hydrodeoxygenation(HDO)reactions.Based on the mechanism investigation,the catalyst demonstrated a high selectivity to cleave the Caryl-OR bond under mild conditions.Based on the research of our first work,we developed a series of supported cobalt catalysts and studied the influence of different oxide supports for catalytic activity of cobalt-based catalysts.Among the catalysts,Co/TiO2 showed the best hydrodeoxygenation(HDO)activity.An equivalent of propylcyclohexanol(>99.9%)was achieved under 1MPa H2,200 ℃ for 2 h.According to the characterization results,the different interaction between Co and supports could be the main reason for the difference in catalytic activity.99%yield of propylcyclohexanol could even be obtained under 0.4 MPa H2,180 ℃ for 8 h.This should be the mildest condition that has been reported for HDO of eugenol to propylcyclohexanol catalyzed by non-noble metal catalyst.Based on the mechanism and substrates extension studies,Co/TiO2 showed high activity to cleave Caryl-OCH3 bond before the hydrogenation of the aromatic ring when the-OCH3 group substituted at ortho-position.