CH4 and CO2 utilisation by unsteady-state operation

CH4 and CO2 are ideal candidates in the context of C1 chemistry as alternatives to oil-based feedstocks for chemicals and fuels production, due to their abundancy, low cost and potential to develop a closed carbon cycle.Large scale utilisation of CO2 in the chemical industry is currently limited to a few applications (e.g. synthesis of urea, carboxylic acids, food industry) and generally requires high purity feedstock. Integrated processes that combine CO2 capture from diluted sources (e.g. industrial flue gases, air) and its conversion to value-added chemicals represent a solution to enhance the utilisation of CO2 and mitigate its emissions. CH4 is an abundant hydrocarbon with diversified sources ranging from fossil-based (natural gas, shale gas) to renewable ones (biomass, biogas), which can potentially substitute oil for the synthesis of valuable chemicals and fuels, including higher hydrocarbons. At the moment, however, CH4 utilisation is circumscribed to combustion for heat and energy production or energy-intensive production of H2 and syngas (H2 + CO) via steam reforming, resulting in a high carbon footprint.In general, the thermodynamic stability of CO2 and CH4 molecules imposes severe limitations to their exploitation as chemical feedstocks, in terms of low conversion efficiencies and control on the selectivity of products. Their efficient conversion requires harsh reaction conditions (high temperatures and pressures, highly chemically reactive substances) at which the stability of the desired products is threatened, resulting in low selectivity. In this scenario, catalysis is essential to identify functional materials and develop new catalytic processes able to maximise the selective conversion of CO2 and CH4 feedstocks to value-added products.Unsteady-state operation in catalysis is an option to overcome the thermodynamic constraints imposed by the conventional steady-state operation. Integrated CO2 capture and conversion, sorption-enhanced reactions, chemical looping combustion are examples of intrinsically unsteady-state catalytic processes that demonstrated enhanced performances compared to their steady state analogues. Moreover, the analysis of the transient catalytic behaviour developed in unsteady-state conditions leads to a deeper understanding of the catalytic processes in terms of identification of specific reactant-catalyst interactions, the steps involved in products formation and the mechanism of catalyst deactivation.This dissertation deals with the catalytic activation of CO2 and CH4 molecules targeting at their valorisation to important chemical commodities as CO (syngas) and light hydrocarbons. Unsteady-state catalysis is explored as a means to overcome thermodynamic constraints associated to the conventional CO2 and CH4 conversion routes....ChemE/Catalysis Engineerin