Catalytic Selective Hydrogenation Of Phthalic Anhydride To Synthesize Phthalide Over Ni-Based Catalysts

As an important organic platform molecule,phthalide has been widely applied in the synthesis of fine chemicals such as pharmaceuticals,pesticides and synthetic dyes,etc.The selective hydrogenation of phthalic anhydride（PA）to synthesize phthalide over heterogenous catalysts has the advantages of being economical and practical.However,the catalytic hydrogenation of phthalic anhydride,in addition to the main product phthalide,produces a variety of possible by-products such as 2-methylbenzoic acid and2-methylcyclohexane-1-carboxylic acid.Therefore,the development of highly selective hydrogenation catalysts is one of the cornerstone technologies to catalyze the selective hydrogenation of phthalic anhydride to produce phthalide.Based on above discussions,we design and prepare a series of mono-and bimetallic loaded nickel-based catalysts for the catalytic hydrogenation of phthalic anhydride to synthesize phthalide,which can yield high conversion of phthalide and selectivity of phthalic anhydride,as follows:（1）A series of Ni/Ce O₂ catalysts with different loading capacities were prepared by impregnation method and applied in the selective hydrogenation of phthalic anhydride to synthesize phthalide.Under the optimal temperature（190 ^oC）and pressure（3 MPa）,the optimized catalyst 5%Ni/Ce O₂ shows PA conversion of 82%and phthalide selectivity of84%in 8 h.According to the results of XRD and TEM,the supported Ni/Ce O₂ catalysts exist in good crystal structure,and Ni O-Ce O₂solid solution is formed on the surface of Ni/Ce O₂ catalysts.Based on H₂-TPR experiments,the interaction between Ni O and Ce O₂in 5%Ni/Ce O₂is stronger than that of 3%and 7%Ni/Ce O₂ catalysts.Therefore,we believe that the reason for the catalytic performance of 5%Ni/Ce O₂ over other Ni/Ce O₂ catalysts is attributed to a good synergistic effect between the Ni O and the Ce O₂ sites.（2）A series of bimetallic Ni_xCu_y/Al₂O₃（x/y=10:0,9:1,7:3,5:5,3:7,1:9,0:10）catalysts were prepared by a deposition-precipitation method and applied in the selective hydrogenation of phthalic anhydride to synthesize phthalide.Under the optimal temperature（200 ^oC）and pressure（3 MPa）,the optimized Ni₉Cu₁/Al₂O₃ catalyst shows excellent PA conversion of 91%and high selectivity of phthalide up to 97%in 10 h.After5 cycles of this catalyst,only a slight decreases of PA conversion（from 54%to 53%）,while the selectivity of phthalide still keeps at about 98%without observing the obviously deactivation of catalysts.XRD and TEM results indicate the successfully doping of Ni into Cu with the formation of Cu Ni alloy and the uniform distribution of Ni-Cu alloy on alumina carrier.Based on XPS and H₂-TPR experiments,the interaction between Ni and Cu have been formed with the constructing of Ni Cu alloy,and the reduction of Ni O and Cu O species can be promoted with increasing the content of Ni in Cu.The superior catalytic performance of the Ni₉Cu₁/Al₂O₃ catalyst can be attributed to the synergistic interaction of the two metals in alloy and the interaction between Ni and Cu.In summary,the key to catalyze the highly selective hydrogenation of phthalic anhydride to produce phthalide is the construction of active metal sites with good synergistic effects on the catalyst.The work is expected to provide experimental basis for rational design of catalyst for in the selective hydrogenation of phthalic anhydride to synthesize phthalide,and to provide a new idea for rational design the catalyst for selective hydrogenation of C=O bonds.