Controllable Preparation Of Ni/Mo Sulfides And Its Catalytic Performance For Oleic Acid Hydrogenation

With the increasing shortage of fossil energy,the aggravation of global environmental problems and the advancement of the technology on the utilization of spent oil resource,the catalytic hydrogenation technology has received more attention accompanying with the elimination of traditional regeneration technology.In this thesis,a series of nickel sulfide and molybdenum sulfide catalysts were synthesized by precipitation and solid phase methods using transition metal Mo/Ni as the active compounds.Ni/Mo sulfides with different crystal phases were obtained by adjusting the synthesis condition.Oleic acid with oxygen-containing acidic functional groups and unsaturated bonds is a typical model compound of spent oil.The hydrogenation performance of the catalyst has been systematically studied combining XRD,SEM,TEM,XPS,Raman and other characterization methods to explore the structure-activity relationship between the catalyst’s microscopic morphology,electronic structure and catalytic activity.The main conclusions are as follows:1.Two nickel sulfide catalysts with different morphologies and structures were obtained by changing the vulcanization temperature of prepared Ni particles.The Ni S prepared by the solid phase method at low temperature（300℃）possesses loose surface structure,which has higher specific surface area than granular Ni₃S₂obtained at high temperature（900℃）.It is beneficial for exposing more active sites to improving the catalytic performance of oleic acid hydrogenation.The results show that Ni S displays better catalytic performance in the saturation of C=C bonds and deoxygenation/decarboxylation reactions for oleic acid hydrogenation.The iodine value of oleic acid decreases from 88.52 to 36.28,suggesting the saturation rate of C=C bonds are 59%.And the acid value decreases from 203.46 to 108.37,corresponding 47% conversion rate on the deoxygenation/decarboxylation reactions.2.Ammonium tetrathiomolybdate was prepared by precipitation method as the precursor.The crystal structure of MoS₂could be controlled through the control strategy of solid phase combined with high temperature annealing introducing Na Cl as a structure guiding agent.The results show that ammonium tetrathiomolybdate is directly decomposed into both of amorphous and crystalline MoS₂mixture when the precursor was calcined at a low temperature（300℃）.As the calcination temperature rises to 900℃,the crystal structure of MoS₂changes from disorder to pure phase 2H type.When Na Cl as a structure guiding agent is added into the ammonium tetrathiomolybdate,it can induce the transformation of MoS₂crystal structure from 2H type to 3R type.The obtained MoS₂with 3R type has the best hydrogenation saturation performance for C=C bonds due to its high metal atom binding energy,high specific surface area from thin sheet thickness and strong lipophilicity.The iodine value of oleic acid decreases from 88.52 to 31.46,suggesting the saturation rate of C=C bonds is 64%.In contrast,the mixture of amorphous and crystalline MoS₂with defective structure is more favorable for the deoxygenation/decarboxylation reactions of oleic acid reaction.The acid value decreases from 203.46 to 95.87,corresponding 53%conversion rate on the deoxygenation/decarboxylation reactions.3.The bimetallic MoS₂/Ni S and MoS₂/Ni₃S₂catalysts were prepared.The results show that the contact angle of the two catalysts is significantly higher than that of the single nickel sulfide,suggesting improvement of lipophilicity of the catalysts.Both of them exhibit different catalytic effects in oleic acid hydrogenation.The activity of MoS₂/Ni S catalyst is higher than MoS₂/Ni₃S₂on the deoxygenation/decarboxylation reactions of oleic acid hydrogenation because the strong metal electron binding energy between MoS₂and Ni S.The acid value of oleic acid decreased from 203.46 to 107.04,while the MoS₂/Ni₃S₂prepared at high temperature is more conducive to the saturation of the C=C bonds of oleic acid.The iodine value of oleic acid decreases from 88.52 to 35.26 after hydrogenation,and the saturation rate of C=C bonds reaches 60.17%.