Preparation Of SiO₂\PAM\Nylon66Supported Platinum Catalysts And Their Catalytic Properties For Hydrosilylation

Hydrosilylation, the addition of silicon and hydrogen across a multiple bond, isnot only an important reaction type in organic synthesis and polymer chemistry, butalso an effective method for synthesizing organosilicon compounds. Chloroplatinicacid is a common catalyst in hydrosilylation, but the reaction is a homogeneoussystem. When the reaction is finished, the noble metal catalyst remains in the product,which may have a negative impact on the quality of the product, so the application ofchloroplatinic acid in hydrosilylation is restricted. Supported platinum catalystsstudied in this paper can effectively solve the above problems. The cheap and readilyavailable inorganic oxide SiO₂and organic polymers （polyacrylamide and nylon66）are emplyed as carriers to prepare supported platinum catalyst with a simple and easymethod, and then the prepared catalysts are used in the hydrosilylation respectively toexamine their catalytic activity. The main results are summarized below:1. Chitosan was supported on the surface of large particle silicas with the size of3mm or5mm, and platinum was coordinated with chitosan to preparesilica-supported chitosan-platinum complex which was characterized by IR andSEM respectively. The hydrosilylation of styrene with triethoxidesilane wasstudied as a model reaction. The effects of the size of carrier, reaction temperature,the amount of catalyst and added order of reactants on catalytic activity wereinvestigated. The optimized reaction condition was obtained when the diameter ofthe carrier was3mm and temperature was60℃with0.041%of catalyst. Theconversion of styrene reached to99.5%in6.0h. The catalyst was filtrated andreused for3times without significant loss of activity and also showed a highcatalytic activity after being placed for6months.2. Chloroplatinic acid was dissolved in the aqueous solution of polyacrylamide（PAM） to obtain a sol-like substance, which was then adhered to the surface ofsilica with the particle diameter being3mm to form a PAM film-coated platinum catalyst. The catalyst was characterized by IR and SEM, respectively. Thehydrosilylation of styrene with triethoxidesilane was studied as a model reaction.The results showed that the catalytic activity of this catalyst was similar toSpeier’s catalyst. When the reaction temperature was60℃with0.017%ofcatalyst, the conversion of styrene could reach the best. The catalyst could bereused for3times without significant loss of activity and showed a high stabilityand catalytic activity after being placed for5months.3. Using nylon66fibers of stable performance as carrier, platinum was coordinatedwith oxygen atom on amide groups of nylon66molecules by a simple ethanolreduction method to prepare nylon66-Pt which was characterized by SEM andEDS respectively. The hydrosilylation of styrene with triethoxidesilane wasstudied as a model reaction. The effects of the platinum loading amount, reactiontemperature, the quantity of catalyst and added order of reactants on catalyticactivity were investigated. The optimized reaction condition was obtained whenthe loading amount was2.7×10-5mol/g, which made a reasonable usage ofplatinum to avoid the waste of noble metal, and temperature was90℃with0.019%of catalyst. The catalytic activity began to decrease after being used fortwice, and also showed a high catalytic activity after being placed for6months.4. The reaction mechanism for the hydrosilylation of styrene with triethoxysilanecatalysted by the supported catalysts was discussed.5. The catalytic kinetics of hydrosilylation of styrene with triethoxidesilanecatalyzed by the synthesized three kinds of catalysts was studied, indicating thatthe reaction followed the second-order kinetics law. Meanwhile the activationenergy of the reaction was calculated, which may reflect different properties of thethree supported catalysts.