PhD Dissertation: Catalysis by design: Well-Defined Aluminium Tetra-coordinated Surface Ligand for Catalytic Applications

Nov 18 2018 10:00 AM - Nov 18 2018 12:00 PM

Abstract 

The surface organometallic chemistry (SOMC) is a conceptual tool allowing, in ideals cases, to overcome the gap between homogeneous and heterogeneous catalysis. This is achieved by the creation of identical active single sites regarding activity, selectivity and with ease recovery. The central part in surface organometallic chemistry is the support. In this field, the oxide surfaces are the most used in heterogeneous catalysis. They are well documented and present significant interest for several applications. But they are usually not enough defined e.g. in term of acido- basicity or redox properties. Typically an alumina surface contains various types of Lewis or even Bronsted centers. So that SOMC on alumina is not giving single sites systems. 

In order to overcome these limitations, and to broaden the area of SOMC, wide ranges of chemical transformation have been achieved by post­treatments to generate new sites with enhanced acido-basic, redox, electronic, magnetic properties of the surfaces and with a single site strategy. One of the most interesting approaches for modification of surface properties is the generation of a Lewis acid center on the oxide surfaces and to get single site Lewis centers by introducing central group elements such as aluminum (Al) in low coordination with surface organometallic strategy. 

After testing two types of aluminum alkyl precursors (TIBA) and (DIBAL), the reaction of TIBAL with dehydroxilated SBA-15700 leads mainly to a bipodal [(=Si-0-Si=)(=Si0)2Al-iBu) species with 3 differents types of aluminum coordinations (AIIV, AIV and AIVI). However, the reaction of OIBAL with dehydroxylated SBA-15700 and on KCC-1700 generates only AIIV-isobutyl. This grafting step was followed first, by Jl-H elimination leading to the generation of terminal aluminum hydride [(=Si-0-Si=)(=Si0-)2AI-HJ and then by oxidation generating aluminum hydroxide [(=Si-0-Si=) 

(=Si0-)2AI-OH]. The mechanisms involved and the structures obtained were fully elucidated by combining experimental data (FT-IR and advanced solid-state NMR spectroscopies (1 H, 13C, 29Si, 27 Al, and 20 multiple quanta), elemental and gas phase analysis) and OFT calculations. 

Interestingly, these new surfaces exhibit a unique structure for the immobilization of different organometallic complexes and were used for various catalytic applications including alkane metathesis, olefin metathesis and olefin polymerization reactions. 
First the grafting the 2nd generation of Hoveyda-Grubbs catalyst (HG-II) by the creation of an Al···Cl-[Ru)-type-interaction showing high activity in the non-functionalized olefin metathesis of propene. Second, the grafting of and Schrock Tungsten W(=CtBu)(CH2tBu)3 complex, giving monopodal [(=Si-0-Si=) (=Si-0-)2Al-0-W(H)2(=C-tBu)] sites. Its activity was evaluated in the propane metathesis reactions, where a TON of 800 was obtained, the highest value obtained for a SOMC monometallic catalyst.

First the grafting the 2nd generation of Hoveyda-Grubbs catalyst (HG-II) by the creation of an Al···Cl-[Ru)-type-interaction showing high activity in the non-functionalized olefin metathesis of propene. Second, the grafting of and Schrock Tungsten W(=CtBu)(CH2tBu)3 complex, giving monopodal [(=Si-0-Si=) (=Si-0-)2Al-0-W(H)2(=C-tBu)] sites. Its activity was evaluated in the propane metathesis reactions, where a TON of 800 was obtained, the highest value obtained for a SOMC monometallic catalyst.