Synthesis And Catalytic Performance Of Tin-substituted Co-containing Polyoxometalate/SBA-15 Hybrid Material

Polyoxometalates(POM)is a kind of catalytic materials with excellent functions,which is widely used as acid catalyst,oxidation-reduction catalyst and photocatalytic material.The POM containing Co is widely used in the field of catalysis because of its high catalytic performance in oxidation catalysis and acid catalysis,mainly used for alcohols'oxidation,olefins' oxidation and acetal reaction and so on.So POM with Co as the central atom(TBACo?W11SnOH)was synthesized and its catalytic oxidation performance was studied by applying it to catalyze benzyl alcohol to benzaldehyde.Meanwhile,the reaction conditions,such as temperature,reaction time,amount of H2O2,amount of solvent and catalyst were discussed and the best reaction condition was determined.Then different catalysts' catalytic activity for benzyl alcohol's oxidation were investigated.But there are many problems like low surface area,easy dissolution in polar solvent and difficult recycle when POM was used as catalyst.It' s a good way to solve these problems by making POM load on high surface area carrier.The most common way is impregnation method.Due to lack of strong force between the POM and the carrier,and the POM only relied on physical adsorption to adsorb on the carrier,so in the reaction the POM was easy to lose.So we thought of anchoring POM on high-surface-area mesoporous molecular sieve SBA-15 by the way of covalent linkage.So the mesoporous hybrid materials(TBACo?W11SnOH/SBA-15)with excellent catalytic performance was synthesized with second grafting method.The influence of reaction conditions,such as amount of POM precursor and calcination temperature,on the synthesis of hybrid materials' composition and structure was studied.Moreover,the hybrid materials' catalytic activity for acetal reaction was investigated.1.Synthesis of Keggin type Sn-substituted Co-containing POM derivatives and study of its catalytic activity for benzyl alcohol's oxidationSn-substituted Co-containing TBACo?W11SnOH was synthesized by direct method and indirect method.The structure and composition of TBACo?W11 SnOH were comprehensively characterized by IR,UV-Vis,ICP,AAS and TG-DTA.The result revealed that the POM was Keggin structure and the Co lied in the center of the tetrahedron,While the SnOH entered into the position of octahedron.Then,compound's catalytic oxidation activity was investigated in the reaction of benzyl alcohol's oxidation.Reaction conditions,such as temperature,reaction time,amount of H2O2,amount of solvent(H2O)and catalyst were discussed and the best reaction condition was determined.Then the catalytic activity of different kinds of catalysts for benzyl alcohol's oxidation was compared,and the reason why these catalysts showed different catalytic activity was also analyzed.The result revealed that TBACo?W11SnOH showed high catalytic activity and selectivity for the oxidation of benzyl alcohol to benzaldehyde.2.Synthesis of TBACo?W11SnOH/SBA-15 hybrid materials and Study of its catalytic activity for acetal reactionWe used TBACo?W11SnOH as precursor,SBA-15 as carrier,and then synthesized TBACo?W11SnOH/SBA-15 mesoporous hybrid materials with second grafting method.The hybrid materials were characterized by IR,BET,XRD and ICP.The results demonstrated that TBACo?W11SnOH was covalently linked to SBA-15 by the reaction between SnOH and SiOH on the surface of SBA-15.The results also showed that in the hybrid materials,TBACo?WSnOH still remained Keggin structure,and the hybrid materials also retained hexagonal symmetry mesoporous structure.The influence of amount of POM precursor and calcination temperature on hybrid materials was discussed.Characterization results showed that with the increase of the ratio of precursor and SBA-15,the load of hybrid materials increased,too.But when the ratio was more than 3:1,the load tended to saturate.On the other hand,with the rise of calcination temperature,hybrid materials' load also increased.Besides,with the increase of POM precursor or calcination temperature,the hybrid materials' pore plugging became more and more serious,the uniformity of pore size reduced,surface area and pore volume decreased.The hybrid materials' catalytic activity for Benzaldehyde 1,2-propanediol acetal reaction was investigated.The reaction condition:Benzaldehyde and 1,2-propylene glycol(molar ratio of 1/1.6),cyclohexane as water-carrying agent,reaction temperature 97-102 ?,reaction time 90min.The results showed that with non-load TBACo?W11SnOH as catalyst,the catalyst's catalytic activity was lower than that of the hybrid materials.In addition,the catalyst was partially soluble in the reaction system,so it was difficult to recycle.But with the hybrid materials as catalyst,the reaction showed excellent catalytic activity(5:1TBACo?W11SnOH/SBA-15(200 ?),acetal yield:88%,acetal selectivity:100%).and the catalyst could be easily recycled.Futhermore,The hybrid materials' load and calcination temperature had a significant impact on acetal reaction.The catalyst's catalytic activity was substantially unchanged after reused 5 times without any treatment.