Unlimiting thermodynamic constraints in continuous catalytic transformation of carbon dioxide and methanol towards dimethyl carbonate

Identifier:  TDX:2465

Handle: https://hdl.handle.net/20.500.11797/TDX2465

Authors:  Stoian, Dragos Constantin

Abstract:
One of the major global challenges urged by the climate change and the desired paradigm shift from the fossil-fuels dependent society to a more sustainable one is the carbon management. This means how to efficiently utilize carbon dioxide (CO2) being emitted and accumulated in the atmosphere. In the last decades, catalytic transformation of CO2 into useful chemicals such as organic and inorganic carbonates via non-reductive CO2 transformations has been widely investigated. In this context, the present thesis targets the dimethyl carbonate (DMC) synthesis via methanol carboxylation reaction. The principal objective of the project is to find a catalytic system capable to perform the continuous DMC synthesis by direct transformation of CO2 over heterogeneous catalysts. Circumventing the thermodynamic limitations represents the most challenging part of the work. CeO2-based catalysts in cooperation with the proper organic dehydrating agent (2-cyanopyridine, 2-CP) are found to perform well in the reaction, yielding high methanol conversion and DMC selectivity. Catalyst poisoning and subsequent deactivation is one of the most encountered problems for any chemically relevant industrial process. Laboratory scale DMC production led, invariably, to the same conclusion. A series of strategies have been thought and tested to improve the catalyst lifetime and stability. It was found out the rare-earth metals promoted CeO2 materials can extend the catalyst life while keeping a high catalytic activity. The use of some in situ / operando spectroscopic techniques (i.e. Xanes, Raman, DRIFTS) offered new insights into the possible redox involvement of CeO2 materials in the methanol carboxylation reaction towards DMC. It is shown that along with acid-base catalysis, CeO2 redox properties play pivotal roles in the catalytic process.