Experimental Research On The Biomass Molecule Catalytic Conversion During The Nickel-based Catalysts

Because of the increasing pressure on the environment due to the excessive dependence of fossil fuels,research on renewable energy sources,such as the catalytic conversion of biomass,has gradually risen in recent years.Nickel-based catalysts have shown good activity in the catalytic conversion reaction of biomass.Compared with precious metal catalysts,nickel-based catalysts are less cost.On the other hand,the activity of nickel-based catalysts could be as good as precious metal catalysts.This dissertation has carried out a series of researches on nickel-based catalysts in the field of catalytic conversion of biomass.The details are as follows.1.The paper investigated effects of the different nickel precursors?Ni?NO₃?₂,NiCl₂,NiSO₄,Ni?CH₃COO?₂,Ni?NH₂SO₃?₂?on the catalytic behaviors of Ni/Al₂O₃ catalysts in steam reforming of acetic acid,aiming to understand the fundamental influences nickel metal precursors on catalytic behaviors of nickel-based catalyst.The catalysts were characterized with TPR,TPO,TPR-MS,TPO-MS,XRD,TG-MS,FT-IR,FT-Raman,BET method,element analysis,TEM and SEM.The results revealed the substantial influence of the nickel precursors on properties of the Ni–based catalysts.The use of NiSO₄ and Ni?NH₂SO₃?₂ as the precursors led to the low activity of the catalyst due to the formation of Ni₃S₂ during the reduction of the catalyst.The sulfur species were removed in the form of SO₂ during calcination of the catalyst precursor in air and in the form of H₂S during the reduction in hydrogen.NiCl₂/Al₂O₃ showed a negligible activity as the chlorine poisoned the catalyst and was difficult to be removed from the surface of the catalyst.Furthermore,chlorine could also accelerate sintering of alumina.In comparison,Ni?CH₃COO?₂ as precursor could effectively suppress the formation of NiAl₂O₄.Ni?CH₃COO?₂/Al₂O₃ catalyst showed comparable activity with that of Ni?NO₃?₂/Al₂O₃,but the resistivity towards coking was higher.In addition,the coke species produced over the catalysts have both the large and the small aromatic rings with the morphology of both amorphous and fibrous structures.2.This study investigated the effects of a series of additives ranging from alkali,alkali earth,transition and rare earth metals?Na,Mg,K,Ca,Sc,Cr,Mn,Fe,Co,Cu,Zn,Zr,La,Ce?on catalytic behaviors of Ni/Al₂O₃ in steam reforming of acetic acid.The addition of alkali and alkaline metals led to the sintering of alumina and nickel species.Cr,Ce or Zr addition filled pores,while Mn addition enhanced the specific area by creating more pores.Cu and Zn addition probably led to merging of small pores.In addition,K or Na promoted reduction of nickel oxides,promoting the catalytic activity.La,Ce or Co also enhanced activity of the catalysts,while Mg,Ca,Sc,Cu,Zn or Zr decreased the activities.The K or Na modified catalysts was much more stable than that of the La or Ce modified catalysts,although the coking was more serious.The coke formed in K or Na modified catalysts was mainly in fibrous form?probably the catalytic coke?,while that in La or Ce modified catalysts was mainly amorphous form?probably the polymeric coke?.The fibrous coke did not lead to the fast deactivation of the nickel catalysts as the amorphous coke did.The TG-MS and DRIFTS study showed that the coke contained the aliphatic structures with the functionalities such as methyl group,carbonyl groups,carboxylic structures as well as the structures of aromatic rings.The amorphous coke formed in La or Ce modified catalysts contained more aliphatic structures.The in situ DRIFTS study of steam reforming of acetic acid showed that a number of reaction intermediates including the-OH,C=O,aliphatic C=C,aromatic C=C,COO,=C-H,-CH₃,aliphatic C-O-C structure,and absorbed CO₂ involved in the reforming reaction.3.Cyclopentanone?CPO?is a platform molecule for manufacturing other value-added chemicals,production of which from furfural requires the catalyst with balanced distribution of acidic sites and hydrogenation sites.In this study,Ni/C and Ni/SBA-15 catalysts with varied catalytic efficiency for hydrogenation and acid-catalysis were evaluated for conversion of furfural to CPO.The Ni/C catalyst with a small specific area and big nickel crystallites showed the lower activity for hydrogenation of furfural.However,the abundant strong acidic sites in Ni/C suppressed the further hydrogenation of furfuryl alcohol?FA?to tetrahydrofurfuryl alcohol?TFA?,while,in converse,guided the selective conversion of FA to CPO.Ni/SiO₂catalyst with a much bigger specific area,small nickel crystallites and weak acidic sites possessed a superior activity for hydrogenation of both the carbonyl functionality and furan ring in furfural to TFA,which prevented CPO formation,even with aid of externally added Br?nsted acid catalyst and Lewis acid catalyst.In comparison,the externally added Lewis acid catalyst showed superior capability to coordinate with Ni/C catalyst to facilitate the conversion of furfural to CPO.4.The conversion of furfural to cyclopentanone?CPO?involves not only hydrogenation but also acid-catalysis reactions.The step of the acid-catalysis might be catalyzed by Lewis acid or Br?nsted acid or both,which was investigated in this study by employing Ni/SiC,a catalyst with“clean”surface containing negligible amounts of acidic sites.Lewis acid?nitrate salts and chloride salts?or Br?nsted acid?D008,a solid acid resin catalyst?with externally added to the reaction medium.The results showed that both Lewis acid and Br?nsted acid could catalyze the conversion of furfural to CPO.The further hydrogenation of furfuryl alcohol?FA?to tetrahydrofurfuryl alcohol was main side reaction,which could be suppressed more effectively with the Lewis acid like CrCl₃.The yield of CPO could be up to ca.88.1%with the Ni/SiC-CrCl₃ catalytic system.The chelation of CrCl₃ with FA stabilized the C=C bond in the furan ring and the hydroxyl group,preventing the side reactions while facilitating CPO formation.The synergistic effects between the cation and anion was essential for the conversion of FA to CPO as the varied nitrate salts or chloride salts chelated with furfural,FA or other reaction intermediates in distinct ways,determining distribution of the products.