Preparation Of Ruthenium-based Catalysts Supported On Carbon Materials And Its Catalytic Performance For Glycerol Hydrogenation

Biodiesel is an ideal renewable resource,and in recent years its substantial production has brought about new problems and challenges.Glycerol as the largest by-product during biodiesel process has a chronic oversupply in our market,the focus on the conversion of glycerol to value-added chemicals,such as 1,2 or1,3-propanediol,n-propanol and isopropanol is a promising strategy,which is conductive to stimulate the whole biodiesel industry.Thus,the preparation of catalyst with the desired conversion and high C3 alcohol selectivity is critical to achieving this strategy.In this work,we developed a novel hierarchically Ru-based catalyst for liquid phase hydrogenation of glycerol by introducing transition metal and acid promoters,which can effectively regulate the conversion of glycerol C-O/C-C and the reaction path,so as to obtain high conversion and selectivity of C3 alcohol products,especially the selectivity of 1,3-propanediol.During our work,different catalyst supports（carbon materials and metal oxides）,acid promoters and transition metal promoters have been screened.A kind of inorganic composites（PW-C）was prepared by modifying activated carbon phosphotungstic acid,which was further supported by Ru-Mo bimetal nanoparticles to prepare the Mo/Ru/PW-C catalysts with high catalytic performance.The introduction of phosphotungstic acid and metal Mo promoter not only improved the dispersion of ruthenium,but also promoted the dehydration-hydrogenation process of glycerol.By adjusting the metal deposition order of Ru and Mo and the amount of Mo,we found that MoO_x could migrate and cover the surface of Ru particles,moreover,the low valence MoO_x could enhance the C-O adsorption selectivity of glycerol molecules,thus inhibiting the cleavage of C-C catalyzed by Ru.The catalyst Ru/PW-C after 1%Mo-modification showed highest catalytic performance under the optimal reaction conditions(T=200℃、P_H2=5 MPa、t=6 h),the conversion of glycerol is 59.6%,the total selectivity of C3 alcohol is 96.1%,including 94.9%for propylene glycol and 20.7%for 1,3-propanediol.The changes of glycerol conversion and products selectivity are not obvious for five run times.A clear mechanism understanding shows that glycerol molecules can be adsorbed on both MoO_x-Ru interface and PW-C interface.Thus,the direct hydrogenation and dehydration hydrogenation co-exist in the liquid phase hydrogenation of glycerol when Mo/Ru/PW-C was used as catalyst.In order to further improve the selectivity of 1,3-propanediol,we have prepared Ru-Mo/CNTs by supporting Ru and Mo on the carbon nanotubes（CNTs）via co-impregnation method,and conducted it on the catalytic hydrogenation of glycerol after adding phosphotungstic acid.Due to the graphitization of CNTs support,more low-valent Mo⁴⁺oxides were formed in the catalyst,leading to the improvement of C-O adsorption.The size of Ru nanoparticles has a great effect on the selectivity of the products.Ru-1%Mo/CNTs showed highest catalytic performance under the optimal reaction conditions(T=200℃、P_H2=6 MPa、t=6 h and 0.12 g phosphotungstic acid),the conversion of glycerol is 58.0%,the total selectivity of C3 alcohol is 98.0%,including 80.0%for propylene glycol and 29.0%for 1,3-propanediol.A clear structure-activity relationship shows that the catalytic dehydration and hydrogenation of glycerol is favorable route in the presence of phosphotungstic acid.Besides,it should be pointed out that the stability of the Ru-Mo/CNTs catalyst is poor,due to the easier aggregation of active metal centers.