Development of a New Combinatorial Approach to Multifunctional Catalysts: Metal Silsesquioxanes as Precursors to Microporous Metallosilicates

Abstract

IntroductionThe emergence of d i n a t o r i a l approaches for high-volume materials research promises to revolutionize materials discovery. In order for heterogeneous catalysis research to benefit fully from the use of automated parallel synthesis and high thmughput screening systems, mutes to micmpomus materials should be developed that preferably use air-stable, soluble and well defined pre-CUIS~IS. Silsesquioxanes and metal complexes thereof seem to ideally meet with these criteria. ' 31'ceptly as precursors for synthesis of micropomus metallosilicates as well as a scherhatic image of the chmosilicate 4 resulting from calcination of chrwnium silsesqUioxane complex 3 are presented in Fig. 1. An interesting finding is that the resulting amorphous materials have a very m w pore size distribution ammd 0.6 m.' Arelatively high loading ( up to w = 10% of metal) of monodisped metal oxide could be realized as well. We have now embarked on a large investigation on the use of silsesquioxane metal complexes as precursors for porous metallosilicates. Ln this communication, we access aspects of this new methdology that are relevant for the area of catalysis. These involve: optimization and scope of the method of calcination, the possibility to adjust the texture of metallosilicates and the dispersion of metal oxide by chang~ng the calcination conditions, the extent to which the structure of the S i U M skeleton in the precursor complex is retained in the resulting metallosilicate and whether the Si--0-M skeleton determines the pore size and its size distribution.Other important issues that will be addmeed should determine whether it is possible to prepare metallosilicates that are exclusively Lewis or Brilnsted acids or to get well dispersed supported metal particles when the precursor complex contains no direct Si-0-M ExperimentalThe incompletely condensed silsesquioxane 5 , was prepared by the hydrolytic condensation of cyclopentyltrichlomilane. 'Ihe disilanol 6 was prepared by silylation of 5 with MqSiCl using a procedure reported elsewhere."he magnesium silsesquioxane complex 7 was prepared by reacting the trisilanol silsesquioxane 5 with the Grignard reagent CH3MgCl in THF solvent using a recipe reported earlier. ' Aluminium silsesquioxane complexes 8 and 9 were 32Metal silsesquioxanea MAXIM et al. prepared by reacting AEt3 with trisilanol silsesquioxane 5 in THF and disilanol silsesquioxane 6 in toluene, respectively, using well known procedures.* Structures of magnesium and aluminium silsesquioxane complexes were checked out using 'H and l3 C NMR as well as solid state MAS %i NMR.Small portions of 0.5 g of metal containing oligosilsesquioxane 7, 8 and 9 as well as metal free 2400.For the nitrogen physisorption +ysi9 all the samples were pretreated just before the measurement in vacuum at 200°C for 2 h. l'ke measurements were performed on an ASAP 2OOO Micmeritics apparatus using an equilibriation interval of 5 seconds and a low pressure dose of 3 .oO cm3/g Srp. I n f o d o n about surface area, pore volume an...

Ti-bridged silsesquioxanes as precursors of silica-supported titanium oxide catalysts for the epoxidation of cyclooctene

“…While the formation of micropores by the calcination of POSS molecules has been previously reported [32][33][34][35][36][37][38][39][40][41][42][43][44], an increase in the BET surface area by the calcination of silica-supported POSS was not recognized from the results shown in Table 4, probably because of a low loading level of POSS.…”

“…In addition to their activities as homogeneous catalysts, their application to heterogeneous catalysis using metal-containing POSS as precursors has been examined [10,13,15,[24][25][26][27][28][29][30][31]. The preparation of microporous silicas containing well-dispersed metal oxide species by the controlled calcination of metal-containing POSS has been reported [32][33][34][35][36][37][38][39][40][41][42].…”