2007 Spring Symposium

 
Vic­tor S.-Y. Lin
Depart­ment of Chem­istry and U.S. DOE Ames Lab­o­ra­to­ry
Iowa State Uni­ver­si­ty
Ames, Iowa 50011–3111
vsylin@​iastate.​edu

Abstract — We have devel­oped a syn­thet­ic strat­e­gy for mul­ti­func­tion­al­iza­tion of meso­porous sil­i­ca nanopar­ti­cle (MSN) mate­ri­als. This method allows us to tune the rel­a­tive ratio of dif­fer­ent func­tion­al groups and the result­ing par­ti­cle mor­phol­o­gy of MSNs. By intro­duc­ing two organoalkoxysi­lanes as pre­cur­sors in the co-con­den­sa­tion reac­tion, we can uti­lize one pre­cur­sor with stronger struc­ture-direct­ing abil­i­ty to cre­ate the desired pore and par­ti­cle mor­phol­o­gy and employ the oth­er for selec­tive immo­bi­liza­tion of cat­a­lysts. As a proof of prin­ci­ple, we have syn­the­sized and report­ed a series of bifunc­tion­al­ized MSN-based het­ero­ge­neous cat­a­lysts for a vari­ety of car­bonyl acti­va­tion reac­tions, such as aldol, Hen­ry and cyanosi­ly­la­tion reac­tions. By vary­ing the sec­ondary group in the bifunc­tion­al­ized MSN cat­a­lysts, we dis­cov­ered that the selec­tiv­i­ty of a nitroal­dol reac­tion of two com­pet­ing ben­zalde­hy­des react­ing with nitromethane could be sys­tem­at­i­cal­ly tuned sim­ply by vary­ing the physic­o­chem­i­cal prop­er­ties of the pore sur­face-bound sec­ondary groups, i.e. polar­i­ty and hydropho­bic­i­ty.

Fur­ther­more, we have report­ed a bio­mimet­ic coop­er­a­tive cat­alyt­ic sys­tem com­prised of a series of bifunc­tion­al­ized MSN mate­ri­als with var­i­ous rel­a­tive con­cen­tra­tions of a gen­er­al acid and a base group. We were inspired by the fact that enzymes engaged in car­bonyl chem­istry often employ both gen­er­al acid and base cat­alyt­ic residues in the active sites to coop­er­a­tive­ly acti­vate spe­cif­ic sub­strates. In this sys­tem, we have demon­strat­ed that the gen­er­al acid func­tion­al­i­ty could coop­er­a­tive­ly acti­vate sub­strates with the basic group in cat­alyz­ing var­i­ous reac­tions that involve car­bonyl acti­va­tion. By fur­ther uti­liz­ing this approach, we have devel­oped a mixed oxide cat­a­lyst that con­tains both Lewis acidic and basic sites for the syn­the­sis of biodiesel from var­i­ous free fat­ty acid (FFA)-con­tain­ing oil feed­stocks. We have demon­strat­ed that the acid and base func­tion­al­i­ties could coop­er­a­tive­ly cat­alyze both the ester­i­fi­ca­tion of FFAs and the trans­es­ter­i­fi­ca­tion of oils with short-chain alco­hols (e.g. methanol and ethanol) to form alkyl esters (biodiesel). We envi­sion that these mul­ti­func­tion­al­ized MSNs could serve as new selec­tive cat­a­lysts for many oth­er impor­tant reac­tions.