Preparation Of Reduced Metallic Catalysts And Study On Catalytic Hydrodeoxygenation Activity

Renewable biomass resource has attracted extensive attention because it can be used to produce chemicals and energy as a substitute for petroleum resource.Biomass resource cannot be directly used as engine fuel due to its high oxygen content and low calorific value.At present,the often used catalysts for deoxygenation of bio-oil are the vulcanized metal catalysts and noble metal catalysts.However,the vulcanized catalysts trend to deactivate due to the loss and oxidation of sulfur.Noble metal catalysts are scarce and expensive,and this limits its industrial applications.Therefore,it is necessary to develop sulfur-free,economical and efficient catalysts.In this thesis,the reduced catalysts were separately prepared by loading the transition metal Ni or Mo（as the main catalyst）and promoters on various supports.The catalytic hydrogenations of waste cooking oil（WCO）,bio-oil and their model compounds were conducted over these reduced catalysts.The relationships between the active metal components and the supports,and the major metal components and the promoters were investigated.The stability and regeneration of catalysts were discussed.We aim to explore a new way for catalytic conversion of bio-oil into liquid fuel over the reduced catalysts.The main research contents and results are given as follows:（1）Preparation of the reduced MoNi/Hβ-Al₂O₃ catalyst using conventional method.The composite support Hβ-Al₂O₃ was firstly prepared by the combination ofγ-Al₂O₃ andβ-zeolite.The oxidized MoNi/Hβ-Al₂O₃ catalyst（Cox）was prepared by traditional impregnation and calcination method.Then,the reduced MoNi/Hβ-Al₂O₃ catalysts（Cre）were obtained by H₂ reduction of Cox.The catalytic hydrogenation of stearic acid（SA）was carried out over Hβ-Al₂O₃,Cox and Cre catalysts,respectively.The results show that Cre catalysts reduced at 450°C achieved a complete SA conversion at 380°C,H₂ 3MPa for 3 h,which was much higher than SA conversion over support（22.9%）and Cox（64.3%）.High reaction temperature and H₂ pressure improved the catalytic activity.However,excessive reaction temperature promoted pyrolysis reaction,resulting in the formation of light products.After four catalytic reaction-regeneration cycles,the SA conversion decreased by 13.3%.（2）Preparation of the reduced NiMo catalyst using a new process.Ni（main metal component）and Mo were loaded on different supports（γ-Al₂O₃,β-zeolite（Hβ）,HZSM-5,activated carbon（AC）and bentonite（Bent））by incipient-wetness impregnation method,followed by H₂ reduction without undergoing calcination process.The catalytic activity was studied by hydrogenation of SA and WCO over these catalysts.It was found that when Ni²⁺is loaded on a support with weak acidity（such as AC）,Ni²⁺is easier to be reduced to metallic Ni,and is aggregated to form larger particles.When Ni²⁺is loaded on a support with strong acidity（such as HZSM-5）,Ni²⁺is more difficult to be reduced to form metallic Ni,and can be uniformly dispersed on support.The order of SA conversion over different catalysts was:Al₂O₃-C>Hβ-C>HZSM-C>Bent-C>AC-C,while the order of WCO conversion over different catalysts was:Al₂O₃-C>HZSM-C>Bent-C>Hβ-C>AC-C.Al₂O₃-C has suitable acidity and larger pore size,consequently showing the highest catalytic activity.Catalysts with weak acidity and high aggregation degree of Ni atoms promoted the formation of C17 hydrocarbons,while those with strong acidity and good dispersion of Ni atoms increased the selectivity of C18 hydrocarbons.Under the same reaction condition,WCO conversion was lower than that of SA.（3）Hydrothermal synthesis of mesoporous HZSM-5 zeolites and preparation of the reduced mesoporous NiMo/ZSM-5 catalysts.A series of HZSM-5 supports with different pore sizes were synthesized by hydrothermal method using hexadecyl trimethyl ammonium bromide（CTAB）and tetrapropyl ammonium hydroxide（TPAOH）as template.Ni and Mo were loaded on the prepared HZSM-5 supports by incipient-wetness impregnation method,and then reduced by H₂ to obtain mesoporous reduced NiMo/HZSM-5（HZ-xC-C）with different pore size（new process）.The catalytic activities were investigated through hydrogenation of SA and WCO over different HZ-xC-C.The results showed that with the increase of CTAB content from 0 to 1,the pore size of the support increased from 3.2 nm to 9.2 nm,the acidity decreased from 1.11mmol/g to 0.57 mmol/g,the degree on reducibility and aggregation of Ni component increased,consequently leading to conversion of SA and WCO improved,C18 decreased and C17 increased in the catalytic products.The conversion of SA and WCO was improved by increasing reaction temperature and hydrogen pressure.The prepared mesoporous catalyst HZ-1C-C（CTAB ratio was 100%）achieved SA and WCO conversion of 99.2%and 86.5%at300°C,H₂ 2 MPa,respectively,and the alkane selectivity in products was 96.7%and 87%,respectively.（4）Catalytic hydrogenation of furfural.Furfural was catalytically hydrogenated by using HZ-xC-C catalysts.Furthermore,the effects of metal promoters（Cu,Mo,Co）on the dispersity and reducibility of Ni component as well as the catalytic activity of the mesoporous Ni-based catalysts were investigated.When ethanol or heptanes was used as solvent,the main products of catalytic hydrogenation of furfural were 2-methyl furan,2-methyl tetrahydrofuran,furfuryl alcohol and tetrahydrofurfuryl alcohol.Furfural conversion and the selectivity to the above four components increased significantly with the increase in CTAB content.Among the three metal promoters,Mo showed the best synergistic catalytic effect.The NiMo catalyst achieved a complete furfural conversion at 180°C.（5）Catalytic hydrogenation of guaiacol.Guaiacol was catalytically hydrogenated using the HZ-xC-C catalysts.The effect of metal promoters（Cu,Mo,Co）on the catalytic activity was further discussed.The results showed that the increase in pore size and the decrease in acidity of catalysts promoted the hydrogenation of C=C bond in the bezene ring structure of guaiacol,consequently resulting in the increase in the selcvitity to aliphatic oxygen-contaning compunds.Among the three metal promoters,Co showed the best synergistic catalytic effect.The introduction of Co accelerated the decomposition of C-O bond,and thus improved the conversion of guaiacol.（6）Catalytic hydrogenations of biomass and bio-oil.Hemicellulose,lignin and bio-oil from eucalyptus sawdust were catalytically hydrogenated over the reduced Ni-based catalysts.The results showed that hemicellulose and lignin were mainly degraded（hydrolyzed）to small-molecular organic acids,alcohols,phenols and ketones in the presence of the reduced Ni-based catalysts.After undergoing catalytic hydrogenation reaction,black viscous bio-oil was converted to yellowish transparent liquid,indicating that macromolecular compounds in bio-oil may be decomposed significantly.