Preparation Of Nickel-based Nano-Catalysts For Dioctyl Phthalate Hydrogenation

Compared with the commercial phthalate?PAEs?plasticizers,cyclohexane 1,2-dicarboxylate plasticizers have the advantages of low biological toxicity,excellent plasticizing effect and been regarded as a class of environmentally friendly plasticizers.Direct hydrogenation of PAEs has some advantages such as high atom utilization and become the most practical method for the synthesis of cyclohexane 1,2-dicarboxylates.However,the benzene ring in the PAEs has two electron-withdrawing ester groups making it more chemically stable.It can be completely hydrogenated usually over noble metal catalysts.Therefore,it is of great research and application value to prepare efficient and low-cost catalysts for PAEs hydrogenation.In this paper,a series of highly active and stable nickel-based nano-catalysts was prepared and applied in the catalytic hydrogenation of dioctyl phthalate?DOP?to di?2-ethylhexyl?hexahydro-phthalate.Firstly,several Ni/Montmorillonite?MMT?catalysts were prepared by different methods and evaluated in the hydrogenation of DOP.It was found that the catalyst prepared by an ammonia evaporation method?Ni/MMT-AE?showed excellent catalytic activity and stability in this transformation,which can be recycled ten times without significant loss of its initial activity and selectivity under harsh reaction conditions.TEM,XPS and TPR results revealed that the active nickel species in Ni/MMT-AE catalyst were highly dispersed on the MMT support.The strong interaction between the active nickel species and the support can effectively inhibit the agglomeration and loss of the active species during the reaction,resulting in its excellent stability.Secondly,a nickel-based nano-catalyst NiAl-LDO was in-situ derived from the nickel-aluminum hydrotalcite,which was prepared by a hydrothermal co-precipitation method,by subsequent calcination and reduction.The obtained catalyst exhibited excellent catalytic performance in the hydrogenation of DOP.Under the optimal reaction conditions,the conversion of DOP was 99%.Notably,it can be reused 7 times,indicating its good stability.In contrast,the conversion of DOP was only 20%over the Ni/Al₂O₃ catalyst prepared by the impregnation method under the same conditions,and it decreased to 10%only after 3 times.Based on necessary characterizations,it was demonstrated that the formation of hydrotalcite precursor can improve the dispersion of the active Ni species,as well as the interaction between Ni and the support,accounting for its better catalytic performance.Finally,a composite nano-catalyst Ni₂Al₁-MMT with high thermal stability and activity was fabricated by firstly introducing Ni²⁺and Al³⁺between the montmorillonite laminates using an ion exchange method,and subsequently in-situ growing hydrotalcite using a hydrothermal co-precipitation method.The catalyst showed excellent catalytic performance in the hydrogenation of DOP.It can be reused 14 times without significant loss of its initial activity.This can be attributed to the double limitation effect of the montmorillonite laminate and the Ni-Al oxide derived from hydrotalcite can effectively improve the catalyst activity and stability.