Novel Ni-catalysts For The Hydrodeoxygenation Of Bio-lipids To Renewable Hydrocarbons

Inedible bio-lipids,an excellent renewable resource,can be converted into biofuels by esterification or transesterification.However,this biofuel exposes several disadvantages such as low heating value,poor low-temperature fluidity,and incompatibility with the engine due to its high oxygen content.Thus,it is necessary to remove oxygen by hydrodeoxygenation（HDO）to improve its ignition property to suit the existing diesel engine.Ni-based catalysts are widely used in this process because of their low cost and excellent hydrogenation activity.However,there are still some problems,such as quick deactivation due to Ni nanoparticles（NPs）agglomeration,low hydrodeoxygenation selectivity,poor anti-sintering property and so on.Thus,the precise design and synthesis of high-efficiency Ni-based catalysts for hydrocarbon fuels preparation by bio-lipids deoxygenation is a meaningful work.Long-chain fatty alcohol,an intermediate of fatty acid HDO reaction,is also an important renewable biomass clean resource.Though it has been reported that Ni-catalysts presents high activity for the synthesis of fatty alcohols,the reaction temperature is still high（>270℃）.Thus,it’s important to develop novel Ni-catalyst for catalyzing the hydrogenation of FAMEs to fatty alcohols under mild conditions.Although renewable hydrocarbon fuel can be obtained by bio-lipid HDO,the resulted alkanes seldom have branched/cyclic structure.Hence,the development of novel synthetic routes using biomass derivatives as raw material for hydrocarbon fuels production with branched/cyclic structure is of great importance.The precursors of aviation kerosene can be obtained by catalyzing the hydroxyalkylation of 2-methylfuran（2-MF）with aldehyde and ketone.The high-quality hydrocarbon fuel with branched/cyclic structure can be achieved by HDO of these precursors with HDO catalyst.However,the following problems still exist in the above route:（1）most of the catalysts used in hydroxyalkylation reaction are proton acid catalysts,which are prone to corrode equipment and are difficult to separate from the catalyst system.In contrast,solid acid catalysts are rarely reported.（2）sevely C-C bond cleavage is often encountered during the HDO reaction step,lowering the yield of target product.Aiming the aforementioned problems,the main research work of this paper is as follows:1.Hydrodeoxygenation of bio-lipids to hydrocarbons fuel over Ni Ce Al-EISA catalyst by one-pot synthesis of evaporation-induced self-assembly methodIn this chapter,Ni Ce Al catalysts with different Ce O₂NPs dispersion at high Ce O₂loading（20 wt.%）were prepared by EISA,impregnation and coprecipitation methods,namely Ni Ce Al-EISA,Ni Ce Al-WI and Ni Ce Al-CP.The effect of Ce O₂NPs dispersion on the activity of bio-lipid HDO to renewable alkanes was also studied.Based on the characterization data and experimental results,we reveal the relationship between Ce O₂NPs dispersion and tunable SMSI in Ni Ce Al system.In high temperature process（reduction and reaction）,when Ni NPs are loaded on Ce Al support with large-size Ce O₂NPs,Ni NPs are prone to sinter and aggregate.In contrast,when Ni NPs are anchored on Ce O₂NPs with high dispersion（<5 nm）,their hydrogenation activity and stability are greatly improved.The results showed that Ni Ce Al-EISA showed excellent activity in the catalytic deoxygenation of five fatty acid methyl esters,including methyl decanoate,methyl laurate,methyl myristate,methyl palmitate and methyl stearate.The molar yields of corresponding alkanes were97.8%（n-C₉）,98.7%(n-C₁₁),96.4%(n-C₁₃),94.3%(n-C₁₅)and 92.9%(n-C₁₇),respectively.After 11 consecutive cycles,the catalyst still remained high activity(96.4%ML conversion and 92.2%n-C₁₁yield).This excellent performance of Ni Ce Al-EISA catalyst is attributed to the following factors:（1）EISA method makes Ni Ce Al-EISA catalyst have high specific surface and appropriate pore size,which is conducive to the high dispersion of Ni NPs and Ce O₂NPs and the intimate contact between Ni NPs and Ce O₂NPs;（2）O_Vspecies and Ni^δ+-O_V-Ce O_xinterfacial sites on the catalyst surface not only stabilize Ni NPs and also promote the adsorption and activation of C=O/C-O bond;（3）SMSI in Ni Ce Al-EISA catalyst is switched from Ni-Al₂O₃to Ni-Ce O₂,which weakens the strong Ni-Al interaction,inhibiting the formation of inert and tough reductive Ni Al₂O₄species,improving Ni⁰dispersion and promoting the dissociation of H₂to produce active hydrogen.2.Effect of oxophilic metal promoter on the hydrodeoxygenation activity of Ni-M bimetallic catalysts to hydrocarbons fuelIn this chapter,Ni-M/Si O₂bimetallic catalysts modified by different oxophilic metal promoter were prepared by co-precipitation method.Compared with Ni/Si O₂and Ni-Fe/Si O₂,Ni-Mo/Si O₂and Ni-W/Si O₂catalyst showed better HDO activity.The ML conversion of the four Ni catalysts decreased in the order of Ni-Mo（98.7%）>Ni-W（93.8%）>Ni（87.7%）>Ni-Fe（81.8%）;while the selectivity of n-C₁₂alkanes decreased in the order of Ni-Mo（79.7%）>Ni-W（28.2%）>Ni-Fe（19.6%）>Ni（5.7%）.The TOF value of Ni-Mo was much higher than the other three Ni catalysts:Ni Mo(657 h^-1)>Ni-W(364 h^-1)>Ni(310 h^-1)>Ni-Fe(272 h^-1).Through a series of characterization,Ni NPs on Ni-Mo and Ni-W catalysts are more uniformly dispersed,while Ni NPs on Ni-Fe catalyst agglomerated obviously.Ni-MO_xinteraction is formed in the three catalysts,and Ni-Mo has the strongest Ni-Mo O_xinteraction.During the reduction process,O_Vspecies formed on the catalyst surface accompanied by the formation of Ni^δ+-O_V-MO_xinterfacial sites.Through the in-situ FT-IR spectrum of CO adsorption,Ni electron density increased in the order of:Ni-Mo<Ni-W<Ni-Fe.Combined with XPS Ni 2P spectra,the Ni electron density in Ni-M catalyst is affected by both surface promoter metal site（M⁰）and partial reduced romoter oxide.In conclusion,there are more Ni⁰sites（low electron density）,surface O_Vspecies and Ni^δ+-O_V-MO_xinterfacial sites on Ni-Mo catalyst surface.They synergeticly promote ML HDO and achieve high ML conversion and HDO selectivity.In addition,the Ni-Mo catalyst shows good stability and excellent performance in the HDO of a series of fatty acid methyl esters（methyl decanoate,methyl laurate,methyl myristate,methyl palmitate and methyl stearate）and actual oils（Jatropha curcas oil and waste cooking oil）.3.Preparation of aliphatic alcohols by selective hydrogenation of bio-oils catalyzed over Ni/Mo₂C@CQDs assisted by carbon quantum dotsHigh activity,robust and cheap noble-free catalysts for selective hydrogenation of fatty acids to fatty alcohols are facing more and more demand because fatty alcohols are directly used in the production of surfactants and plasticizers.However,it is still a big challenge to develop selective hydrogenation catalysts with similar or even superior properties to noble metals,especially those that can work under mild conditions.Based on this,Ni/Mo₂C@CQDs catalyst was prepared by temperature programmed reduction（TPR）method using carbon Quantum dots（CQD）as carbon source.This catalyst shows superior activity in the hydrogenation of methyl stearate to.This catalyst affords 98.1%methyl stearate conversion and 95.7%octadecanol selectivity when the reaction was carried out at 180℃which is much lower than the reported in literature.Combined with experimental data and characterization results,it’s found that Ni-addition effectively promote the formation of Mo₂C species at relative low TPR temperature and form strong Ni-Mo₂C interaction,which weakens the strong adsorption of Mo₂C on active H species and thus enhances Ni NPs activity for H₂dissociation at low temperature.According to XPS characterization,it’s found that the Ni site on Ni/Mo₂C@CQDs catalyst is electron rich,whereas Mo₂C species is electron deficient due to the strong Ni-Mo₂C interaction.This promotion effect on Ni site electron density significantly promotes Ni NPs activity for H₂dissociation at low temperature.Meanwhile,Ni site with excess electron density promotes hydrogenation of fatty aldehyde intermediates to fatty alcohol rather than decarbonylation of fatty aldehyde intermediates to C_N-1alkanes.Moreoverm,the electron deficient Mo₂C species shows strong affinity towards O atom（C=O）containing lone pair electrons and promotes the adsorption and activation of C=O bond.Benefiting from the synergism between Ni and Mo₂C,the hydrogenation of methyl stearate has been greatly improved.More importantly,the catalyst shows excellent hydrogenation activity in the hydrogenation of a series of FAMEs（methyl decanoate,methyl laurate,methyl myristate,methyl palmitate and methyl stearate）and practical bio-lipids（jatropha curcas oil and waste cooking oil）.The as-prepared Ni/Mo₂C@CQDs catalyst has certain industrial application prospects.4.Preparation of aviation fuel by hydroxyalkylation of biomass derivatives catalyzed by Mo O_3/Ti O₂and Ni/MO₂C@CQDsSolid acidic Mo O₃/Ti O₂and Ni/Mo₂C@CQDS catalysts were prepared and used to catalyze the two-step preparation of aviation fuel from furfural and 2-methylfuran.Mo O₃/Ti O₂catalyst was used to catalyze the hydroxyalkylation/alkylation（HAA）of furfural with 2-MF.The 10wt%Mo O₃catalyst affords 100%furfural conversion and94.6%yield of HAA product under sepecial conditions（0.1 g catalyst,furfural/2-MF molar ratio=1/2.05,60℃and 6 h）.The characterization of Mo O₃/Ti O₂catalyst shows that the synergy between Lewis acidic site in Ti O₂and Br（?）nsted acidic site in Mo O₃accounted for the high HAA activity.The Ni/Mo₂C@CQDs catalyst was applied in catalyzing the HDO of HAA product and presented excellent performance.The 10wt%Mo O₃catalyst affords 100%conversion of HAA product and 97.1%yield of total alkanes,in which the yield of 6-butyl undecanone is 86.1%under 5 MPa at250℃for 10 h.The synergy between Ni and Mo₂C are the main reason for its high HDO activity.The high dispersion of Ni on Mo₂C avoids the cracking of C-C bond in the reaction.