Abstract
Carbon-based materials find many applications in today’s life due to their versatile properties that arise from their structural flexibility regarding hybridization, morphology, or hetero-element substitution. In this thesis, carbon-based materials are designed and investigated as catalysts as well as supports for environmentally benign processes. Structure-activity correlations of these carbon materials for the respective reactions are proposed and discussed. First, the conversion of CO and Cl2 into phosgene over activated carbons as industrial catalysts is studied as a potential way to utilize exhaust gas emissions from steel plants as new feedstock for the chemical industry. For this purpose, several porous and high surface area carbon materials are designed through a soft-templating approach and chemical activation of biomass waste. The interactions of those prepared materials with Cl2 are investigated in a CO and Cl2 adsorption/desorption set-up as a possible catalytic indicator. As an outcome, correlations between the physicochemical properties of the carbon materials and their interaction with Cl2 have been revealed. Hypotheses of the correlation between Cl2 interaction and catalytic activity of the carbon materials are stated, which are based on the degree of graphitization and the porosity as well as the surface area of the carbon materials. Following these results, carbon catalysts with improved performances can be designed to recycle emitted CO from point sources and convert it into valorized products.Second, electrocatalysis provides means for using renewable electrical energy for chemical transformation reactions like water splitting. This reaction enables the storage of renewable energy in form of H2 that can be used as fuel for diverse needs or chemical reagent. To increase the efficiency of this process, the kinetics of the accompanied oxygen evolution reaction (OER) needs to be improved by an effective electrocatalyst. Two different synthetic approaches for the design of transition metal-based nanoparticles supported on carbon as catalysts are investigated. On the one hand, a soft-templating method is explored to obtain an ordered mesoporous carbon material as a model system with confined Co nanoparticles. Variation of synthesis parameters, such as Co loading, pyrolysis atmosphere, and pyrolysis temperature, allows for the identification of ideal material properties for an active catalyst. Crucial factors are the high dispersion of transition metal nanoparticles and conductive carbon supports. In the next step, these desired material properties are obtained by a new synthesis method by using waste biomass as cheaper and abundant carbon support. Easy and scalable impregnation steps combined with activation during pyrolysis and appropriate post-treatments result in a diverse class of carbon-supported Co-based nanoparticles with high apparent specific surface areas, defined crystal structures of the Co-based nanoparticles, and different degrees of carbon functionalization. Both discussed synthesis methods produce materials that are more active than mesostructured reference pristine Co3O4 catalysts and thus can be applied to design improved catalysts for the conversion of renewable electrical energy into H2. The results of this thesis clearly show the potential of carbon-based catalysts for industrial applications as well as in environmentally benign chemical transformations. The physicochemical properties of the materials were tailored to achieve the optimized catalytic performance for the respective reaction, thus establishing structure-activity correlations of carbon-based materials in catalysis. With these design concepts for carbon-based materials, catalysts can be synthesized with improved performances under the new dynamic environment of a sustainable chemical industry.
