Nanostructured materials as catalysts for the production of green fuels and platform chemicals

Abstract

A range of nano-structured materials were prepared and utilised in this work as catalysts for the production of biofuels and platform chemicals. Titanosilicate (ETS-10), Linde type-zeolite A, faujasites (FAU), zeolite MAP and sepiolite, were synthesised or modified with potassium containing compounds using ion-exchange or impregnation. In addition, several commercially available zeolites, for instance, FAU, mordenite (MOR), beta (BEA) and MFI (ZSM-5) as well as Linde type-zeolite L (LTL) were exposed to a variety of acid and base treatments accompanied by surfactant templating approach, which led to the introduction of intracrystalline mesoporosity. The resulting materials were characterised in detail by the variable temperature in situ X-ray diffraction, N2 adsorption-desorption, transmission electron microscopy with energy dispersive X-ray analysis, temperature-programmed desorption (CO2-TPD), solid-state NMR and in situ FTIR spectroscopy using adsorption-desorption of different probe molecules in order to evaluate their structure - catalytic performance relationship in the conversion of feedstocks via different reactions. A wide range of parameters was utilised in order to optimise the reaction conditions. Although a high yield of fatty acid methyl esters was achieved in transesterification reactions in the presence of K-containing sepiolite, this system showed significant deactivation due to its structural degradation and loss of the active component during the reaction and regeneration cycles. In contrast, zeolite K-MAP and other K-form materials demonstrated a significant improvement in catalytic performance in the methanolysis of bio-oil compared to other materials, which can be attributed to its nano-particle morphology and high basicity. The strength of basic sites has a greater impact on the activity of the catalyst than their accessibility in the transesterification reactions.
The superamolecular templating approach was successfully applied to generate catalysts with tunable porosity for the microporous materials with the pores constructed by 12- (large pores) member ring windows in their pore topologies. It was found that the removing of oleic acid from grapeseed oil can be enhanced with acid sites and ideal pore size of zeolites. Furfural conversion over hierarchical zeolites was increased compared with the parent form. Nevertheless, basic zeolites exhibit high selectivity toward the desired reaction products in the aldol condensation reaction. In addition, mesostructured FAU zeolite demonstrated significant improvement in catalytic activity for both reactions as a result of increasing the accessibility of such molecules to the zeolite acid sites where the reaction takes place.This study suggested that the introduction of secondary pores systems in the zeolites might be the effective route for improved accessibility of active sites and enhanced catalytic activity.