Excessive use of fossil fuels shall result in the significant energy problems in the coming century and causes global warming by CO2 emission. Use of petroleum in transportation constitutes the dominant part of total petroleum use. Researches on non-petroleum based, environmentally friendly alternative fuels have been ascended in last decades. Among the alternative fuels, DME has been considered as an attractive fuel alternate due to high cetane number, low PM (particulate matter) and low NOx emission. Synthesis of DME is possible with gasification of biowastes or coal and steam reforming of natural gas. DME is produced in two different methods. In the first method, methanol is formed from the synthesis gas, followed by methanol dehydration to DME. In the second method, called as direct synthesis of DME from synthesis gas, methanol formation and dehydration occurs simultaneously at the same location within the reactor. For the direct synthesis of DME, bi-functional catalysts must be used / one site is responsible for methanol synthesis and other site is responsible for methanol dehydration. Throughout this thesis work, several catalysts were prepared to be used as methanol synthesis component or methanol dehydration component of bi-functional direct DME synthesis catalyst and bi-functional catalysts were also prepared for the direct synthesis of DME from synthesis gas. Materials were characterized by XRD, EDS, SEM, N2 physisorption, and DRIFTS characterization techniques. Activity tests were conducted in a high pressure, fixed bed flow reactor at 50 bar and for the feed gas compositions of H2:CO=50:50 and H2:CO: CO2=50:40:10. Addition of zirconia and alumina promoters, long aging time, calcination temperature of 550 &deg / C and reduction at 250 &deg / C were found to be beneficial in methanol synthesis from the equimolar composition of CO and H2. Precipitated catalysts were usually active and selective to methanol. However, bi-functional co-precipitated catalyst was not successful in situ conversion of methanol into dimethyl ether. Furthermore, tungstosilisic acid impregnated SBA-15 was physically mixed with commercial methanol reforming catalyst and activity results revealed that high DME yield and selectivity were obtained. By physically mixing commercial methanol synthesis and reforming catalysts with &gamma / -Al2O3 and TRC-75(L) in appropriate proportions or by preparing the reactor bed in a sequential arrangement, very high DME yields were obtained and superiority of direct synthesis to conventional two step synthesis was proven. Presence of CO2 in the feed stream not only enhanced the catalytic activity but also utilization of the most important greenhouse gas was accomplished. It was seen that synthesized catalysts are very promising in the direct synthesis of dimethyl ether from synthesis gas.

Metal alkoxides are easily available and versatile precursors for functional materials, such as solid catalysts. However, the poor solubility of metal alkoxides in organic solvents usually hinders their facile application in sol–gel processes and complicates access to complex carbonate or oxidic compounds after hydrolysis of the precursors. In our contribution we have therefore shown three different solubilization strategies for metal alkoxides, namely the derivatization, the hetero-metallization and CO2 insertion. The latter strategy leads to a stoichiometric insertion of CO2 into the metal–oxygen bond of the alkoxide and the subsequent formation of metal alkyl carbonates. These precursors can then be employed advantageously in sol–gel chemistry and, after controlled hydrolysis, result in chemically defined crystalline carbonates and hydroxycarbonates. Cu- and Zn-containing carbonates and hydroxycarbonates were used in an exemplary study for the synthesis of Cu/Zn-based bulk catalysts for methanol synthesis with a final comparable catalytic activity to commercial standard reference catalysts.

L’hydrogénation catalytique du CO2 est considérée comme l’une des voies de valorisation les plus prometteuses pour la production du méthanol. Cette synthèse, souvent accompagné par une formation de CO, a fait l’objet de nombreuses études dans la littérature. Cependant, les résultats obtenus sur des catalyseurs à base de Cu et de ZnO ont démontré que cette réaction n’est pas aussi simple qu’elle y paraissait. Il y a encore beaucoup de controverses et d’interrogations sur la nature des sites actifs et sur les différentes étapes réactionnelles mises en jeu lors de la réaction. L’objectif de ce travail est d’apporter des éléments de compréhension sur la nature des sites actifs et leur rôle sur l’activation du CO2 et de H2. L’étude sur des catalyseurs modèles (mélanges mécaniques et matériaux préparés par coprécipitation) a permis de mettre en évidence un effet de synergie entre Cu et ZnO lié à des phénomènes de migration. Ce travail a montré que la production de méthanol est étroitement liée à la création d’une phase oxyde de type CuxZn(1-x)Oy (lacunaire en oxygène) induit par un effet de Kirkendall à l’interface Cu-ZnO, favorisant l’épandage de l’hydrogène. Différents modèles mathématiques ont été développés afin de déterminer la concentration des contacts entre Cu et ZnO. Les résultats obtenus ont démontré qu’il est possible de corréler directement l’activité du catalyseur avec la concentration de contacts et que cela peut permettre ainsi de prédire la composition chimique idéale du catalyseur pour un design de matériau donné. L’expertise complète de la relation design-activité a permis le développement de matériaux Cu-ZnO de type cœur-coquille 100% sélectif en méthanol. / The catalytic CO2 hydrogenation is considered to be one of the most promising methods for methanol production. This synthesis, often accompanied by a CO formation, had been the subject of many studies in the literature. However, the results obtained on Cu and ZnO based catalysts demonstrated that the reaction is not as simple as it appear to be. There is still a lot of controversies and interrogations concerning the nature of the active sites and the different reactional steps involved during the reaction. The objective of this work is a better understanding of the nature of the active sites and their role on CO2 an H2 activation. A study on model catalysts (mechanical mixtures and materials prepared by coprecipitation) allowed to demonstrate that the synergetic effect between Cu and ZnO linked to a migration phenomenon. This work showed that the methanol production was closely linked to the CuxZn(1-x)Oy oxide phase creation (with oxygen vacancies) induced by a Kirkendall effect on Cu-ZnO interface, thereby promoting the hydrogen spillover. Different mathematical models were developed to determine the concentration of contacts between Cu and ZnO. The results obtained demonstrated that it is possible to directly correlate the catalyst’s activity with the concentration of contacts between Cu and ZnO, which in turn allowed predicting optimal catalyst chemical composition for a particular design of a material. The full expertise of the design-activity relationship allowed the development of Cu-ZnO core-shell type materials with a 100% selective to methanol.

Zur Entwicklung eines effizienten Verfahrens zur CO2-Hydierung im Dreiphasensystem erfolgten in dieser Arbeit Untersuchungen zur Optimierung des Katalysatorsystems, zum Screening nach neuen geeigneten Lösungsmitteln und zum Einfluss der Prozessführung. Durch Variieren des Trägersystems und der Präparationsmethode ergaben sich sieben Kupferkatalysatoren, welche sich in ihren Eigenschaften und ihrer katalytischen Aktivität unterschieden. Zudem gelang die Immobilisierung von Kupferkatalysatoren auf Aluminiumoxid und auf Glas. Es wurde eine kontinuierliche Anlage mit Rieselbettreaktor entwickelt und in Betrieb genommen, welche die Durchführung der CO2-Hydrierung in Gasphase und im Dreiphasensystem bei bis zu 90 bar ermöglicht. Im Batchversuch zeigte sich der Einfluss der Lösungsmittel auf die Effizienz des Katalysators. Vielversprechende Lösungsmittel wurden dann zur Methanolsynthese im kontinuierlichen Prozess eingesetzt, um den Einfluss der Prozessbedingungen zu untersuchen.

This report travels through multiple disciplines to seek innovative and sustainable energy solutions for wastewater treatment plants. The first subject is a report about increased global temperatures and an over-exploitation of natural resources that threatens ecosystems worldwide. The situation is urgent where the current trend is a 2°C increase of global temperatures already in 2040. Furthermore, the energy-land nexus becomes increasingly apparent where the world is going from a dependence on easily accessible fossil resources to renewables limited by land allocation. A direction of the required transition is suggested where all actors of the society must contribute to quickly construct a new carbon-neutral resource and energy system. Wastewater treatment is as required today as it is in the future, but it may move towards a more emphasized role where resource management and energy recovery will be increasingly important. This report is a master’s thesis in energy engineering with an ambition to provide some clues, with a focus on energy, to how wastewater treatment plants can be successfully integrated within the future society. A background check is conducted in the cross section between science, society, politics and wastewater treatment. Above this, a layer of technological insights is applied, from where accessible energy pathways can be identified and evaluated. A not so distant step for wastewater treatment plants would be to absorb surplus renewable electricity and store it in chemical storage mediums, since biogas is already commonly produced and many times also refined to vehicle fuel. Such extra steps could be excellent ways of improving the integration of wastewater treatment plants into the society. New and innovative electric grid-connected energy storage technologies are required when large synchronous electric generators are being replaced by ‘smaller’ wind turbines and solar cells which are intermittent (variable) by nature. A transition of the society requires energy storages, balancing of electric grids, waste-resource utilization, energy efficiency measures etcetera… This interdisciplinary approach aims to identify relevant energy technologies for wastewater treatment plants that could represent decisive steps towards sustainability.