Synthesis Of Supported Pt-Al/MCM-41 Catalyst And Its Catalytic Property For Hydrosilylation

Organosilicon surfactants are widely used in agriculture because of their excellent wettability,spreadability and significantly reducing surface tension of solution,it can effectively reduce the spray water,dosage of pesticide and environmental pollution,which plays an important role in the agricultural sustainable development in our country.And this surfactant is synthesized through hydrosilylation reaction catalyzed by supported platinum catalyst.It could solve some problems of homogeneous catalysts through cattering metal active component in the stationary phase,for instance,the platinum metal existed in catalyst is difficult to remove and the catalyst can’t be recycled easily.However,the agglomeration of the platinum metal existed in catalyst would happen,which brings bad effects to the catalytic activity of catalyst.To conquer above difficulty,supported Pt-Al/MCM-41 catalysts were studied in this paper.Furthermore,this catalyst is applied to the hydrosilylation reaction of heptamethyltrisiloxane(MDHM)and allyl polyether(PGAE).The main contents of the thesis are as the following:(1)Supported Pt-Al metallic catalyst was prepared by impregnation method.The results show that,Pt/Al-MCM catalyst with the six-party porous structure has best order degree,and its order decreased with the increase of dosage of Al.In addition,the introduction of Al can improve the dispersion of platinum particle.The particle diameter of platinum decreases prior to increasing as the increase of dosage of Al,and dispersion of platinum particle is best when the molar ratio of Pt and Al is 1:2.The introduction of aluminum can improve the catalytic activity of catalyst,Pt1Al2-MCM catalyst shows excellent catalysis.Its mass content of platinum and aluminum is respectively 0.73% and 1.34%.(2)The interaction mechanism of platinum and aluminum was investigated.The results indicate that,introduction of a small amount of aluminum grafting onto the carrier with the interaction of hydroxyl improves the dispersion of platinum particle via "isolation" effect and "anchor" effect.Moreover,with weakening of reunion of platinum particles and increasing of active surface area,catalytic activity and sulfur resistance are improved due to the Pt-Al interaction.However,when the content of aluminum is added more than 1.34%,"anchor" effect is so strong that promoting the reunion between the particles and reducing the catalytic activity.(3)Organosilicon surfactants(NSS)was synthesized by the hydrosilylation reaction of allyl polyether and heptamethyltrisiloxane catalyzed by homemade Pt1/Al2-MCM catalyst.It was found that this reaction is mainly about β-addition reaction described by secondary dynamic model and the apparent activation energy is73.28 kJ/mol.By using single factor experiment and orthogonal experiment method,the optimal preparation condition at which the conversion(94.1%)is obtained: the reaction time is 4 h,the temperature is 100℃,the mole ratio of PGAE and MDHM is1.1:1 and dosage of catalyst was 0.5%.The order of significance of the effect of different reaction conditions on the conversion is reaction time > temperature > the mole ratio of reactants > dosage of catalyst.Furthermore,Pt1/Al2-MCM catalyst shows excellent stability and reusability,and the conversion of MDHM is still above90% when it is used for six times.Some parameters of NSS was tested: the critical micelle concentration is 6.81×10-4 mol/L,γCMC is 20.82 mN/m and HLB value is 14.13.And it exhibited the worst stability under acid condition due to hydrolysis,while it is relatively stable under neutral condition.(4)Using polygonum lapathifolium var.salicifolium as target organism,the spraying experiment of starane herbicide was investigated with the addition of organic silicone surfactants.The results show that,while spraying the mixed liquid including0.5 g/Kg starane and 0.05% NSS,it can significantly reduce water content and chlorophyll content of weeds.Moreover,the synergistic mechanism of NSS is by reducing the surface tension of the starane,increasing its expanding diameter and maximum retention on the leaf.