Modifikation kovalenter triazinbasierter Netzwerke mit Ruthenium und ihre Anwendung als Katalysatoren in der selektiven Oxidation von 5-Hydroxymethylfurfural

• Modification of covalent triazine-based frameworks with ruthenium and their application as catalysts in the selective oxidation of 5-hydroxymethylfurfural

Artz, Jens; Palkovits, Regina (Thesis advisor); Rueping, Magnus (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2015)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2015

Abstract

A novel method for the preparation of nano-particulate catalysts stabilized on covalent triazine-based frameworks (CTFs) has been investigated. A broad range of CTFs were accessible from trimerization of aromatic dinitriles in molten ZnCl$_2$. The material properties such as porosity, specific surface areas and nitrogen content could be tuned by variation of the monomer and a shift to shorter synthesis times at elevated temperatures of 400 and 600 °C. All materials are highly temperature stable up to 400 °C and insoluble in most common solvents including acids and bases. The porous CTF materials containing numerous triazine functionalities allow coordination of different molecular catalysts. In this study, the coordinating functionalities were used to immobilize a RuCl$_3$∙xH$_2$O precursor prior to reduction to finely dispersed metal nanoparticles. This approach allows for both a molecular dispersion of metal species on the solid catalyst support as well as very narrow particle size distribution of the Ru-species formed upon reduction. Furthermore, the nitrogen functionalities provide a stabilizing effect and therefore minimize agglomeration, leaching and subsequent catalyst deactivation.The Ru/CTF catalyst systems obtained via this approach showed increased activity compared to Ru/C in the selective aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran under mild reaction conditions in MTBE. Synthetic air could be used as an environmentally benign and sustainable oxidant. At 80 °C and 20 bar of air productivities of up to 25.4∙10$^{-3}$ mol g$^{-1}$ h$^{-1}$ could be achieved, which is about seven times higher than the productivity obtained utilizing Ru/C under the same conditions. Increasing the temperature to 140 °C and exchanging the organic solvent with water, HMF could be converted to 2,5-furandicarboxylic acid much faster compared to Ru/C under comparable conditions. The Ru/CTF system showed good activities when compared to typical oxidation catalysts based on platinum or palladium. Additionally, especially the low costs of ruthenium make it an attractive alternative when used in large scale catalytic processes. In recycling studies of all ruthenium based catalysts minor deactivation over five catalytic cycles occurred but activity could be regained by reactivation under H$_2$-atmosphere.