Study On Super/preparation, Testing, Characterization And Application Of Pt-based Catalysts

Hydrogenation reduction is a crucial step in the preparation of dyes,pharmaceuticals and synthetic intermediates,which has a very important effect on people's daily life.At present,the catalyst used for the hydrogenation of Schiff bases in the process of synthesizing berberine is Raney Ni.Such catalyst not only generates a large amount of waste water and waste alkali in the preparation process,but also is easy to be naturally stored in the air and used Has brought great difficulty to people.Therefore,the development of a new type of hydrogenation catalyst to replace the traditional Raney Ni catalyst for the synthesis of berberine has important significance and application prospects.Using uniform precipitation method,ammonium bicarbonate and magnesium sulfate as raw materials,PEG6000 as a surfactant to prepare nano-MgO.The optimum conditions for the preparation of nano-MgO were determined by univariate analysis as follows:0.6 mol/L MgSO₄ solution and 1:2 NH₄HCO₃ concentration 1:2 reaction at 95?for 1 h,then filtered and washed to obtain Mg₂?OH?₂CO₃ solid,And then calcined in a muffle furnace at 600?for3 h.The resulting MgO showed a uniform petaloid structure with an average particle size of about 23 nm and a specific surface area of 107.8 m²/g.Compared with the commercial product MgO has a smaller particle size and large specific surface area,can be used as a catalyst carrier to improve the dispersion of active metals.The impregnation method was used to investigate the hydrogenation activity of Schiff bases on Pt-based catalysts.The differences of the hydrogenation activities of Schiff bases on single-metal Pt-based catalysts loaded with different supports??-Al₂O₃,MgO?were investigated.The results show that 0.5%Pt/MgO catalyst has better catalytic performance than 0.5%Pt/?-Al₂O₃ catalyst.The reaction is carried out at 110?and initial pressure of 4.0MPa under hydrogen pressure until the gauge pressure does not drop.The Schiff base conversion on the 0.5%Pt/MgO catalyst was 82.5%and the condensate yield was 81.6%.Therefore,select the active nano-MgO as a carrier.A series of catalysts of xPt/MgO?x=0.1%,0.5%and1.0%?were prepared by impregnation method,which were used to catalyze the activity sequence of hydrogenation of Schiff base0.5%Pt/MgO>1.0%Pt/0.1%Pt/MgO.The Schiff base conversion on the 0.5%Pt/MgO catalyst was 82.5%and the condensate yield was 81.6%.The catalysts were characterized by XRD,BET and H₂-TPR.The study found that when the Pt loading increased,too much Pt in the carrier agglomeration,resulting in decreased catalytic activity of the catalyst.Therefore,the choice of 0.5%Pt/MgO is more appropriate.A series of Pt-M/MgO?M=Ni,Cu?bimetallic catalysts were prepared by impregnation method.The catalytic activity of Pt-Ni/MgO>Pt-Cu/MgO,which Pt-Ni/MgO catalyst has a more catalytic activity.At 110?,the initial pressure of 4.0 MPa H₂ pressure reaction conditions until the pressure does not drop.The conversion of Schiff base on the 0.2%Pt-0.3%Ni/MgO catalyst was 92.5%,the yield of the condensate was 91.8%,the hydrogenation rate of Raney Ni catalyzed hydrogenation of Schiff base was 89.2%The catalytic activity of 0.2%Pt-0.3%Ni/MgO catalyst decreased by less than 10%after 90 times of recycle,showing a good stability.In comparison,0.2%Pt-0.3%Ni/MgO catalyst can replace Raney Ni catalyst.The crystal structure and grain size of the fresh catalyst and the post-reaction catalyst were determined by XRD.Pt-M bimetallic species were formed by the substitution of the metal atom M for the Pt atoms in the lattice randomly.TEM images showed that the size of Pt-M metal particles on the active nano-magnesia support was in the range of 2-5 nm,and the active components were uniformly dispersed.The synergistic effect of the formed Pt-M bimetal species enhanced the catalyst activity.