Atık Bitkisel Yağların Etenolizi için Morfolojik Olarak Farklı Silika Jeller İçerisinde Hoveyda-Grubbs İkinci Nesil Katalizörünün Enkapsülasyonu

Abstract

Olefin metathesis is an efficient synthetic method for forming carbon-carbon double bonds. In parallel to the progress in the chemical industry, metathesis chemistry has gained tremendous interest within industry and academia in the last twenty years. Ruthenium-based metathesis catalysts play an important role in the transformation of petrochemicals and vegetable oils with high unsaturated hydrocarbon content to the desired products. Metathesis chemistry has progressed with the invention of high functional group tolerance and air/moisture stable Hoveyda-Grubbs first and second-generation ruthenium-based metathesis catalysts. Although Hoveyda-Grubbs type homogenous catalyst showed high performance in both metathetic and non-metathetic transformation reactions, non-reusability and separation problems emerge as important problems. In this context, the immobilization of HG2 catalyst on various support materials solves iv the reusability and recovery problems but the decrease in selectivity and the additional modification protocols such as covalent modification of catalyst structures limits performance. In the context of this thesis study, hybrid catalyst systems are developed where the advantages of homogenous and heterogenous catalytic systems are combined as an alternative to the catalytic systems in the literature. In this regard, hollow silica gels were synthesized via the hard-template method through the coating of iron (III) oxide cores with silica gels using the Stöber method. The hollow silica gel materials with higher surface area were obtained through etching the core template. Hoveyda-Grubbs second generation catalyst were loaded on silica gels with square, peanut and capsule morphology and encapsulated within the pore structures through post-pore size reduction using organosilicon derivatives. The pore size reduction allowed the reactants to diffuse easily through the pores while catalyst was confined within the pore structure. The obtained catalyst was characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption isotherms and scanning electron microscopy (SEM). The activity of the catalysts were tested on ring closing metathesis and ethenolysis reactions. The obtained catalysts showed high selectivity and performance in metatheis reactions and additionally, such as heterogenous system, the catalyst was separated easily from the reaction mixture and was used up to tenth turn in ring closing reactions.