Infoscience

Thesis

Carbon dioxide hydrogenation to methanol at low pressure and temperature

The measurements obtained were used to investigates the methanol synthesis reaction from pure carbon dioxide and hydrogen over binary (CuO/ZrO2) and ternary supported catalysts (CuO/ZnO/Al2O3). A comparison of different catalysts is presented. The influence of the most important reaction parameters, i.e. temperature, pressure, space velocity and feed gas composition is examined at moderate temperatures (≤ 300 °C) and pressures (≤ 20 bar). The influence of the partial pressures of hydrogen, carbon dioxide, carbon monoxide, water and methanol are studied in detail with the most efficient catalyst. According to the results, water has a decisive effect on the catalyst activity and performance. The measured results were used to derive a possible Langmuir-Hinshelwood kinetic model of the methanol synthesis reaction. The catalyst surface is analyzed by in situ diffuse reflectance Fourier transform infrared spectroscopy. The identification and evolution of intermediates on CuO/ZnO/Al2O3 catalysts confirm that the reaction proceeds by prior formation of the carbonate on the copper, followed by hydrogenation of the carbonate to the formate and thereafter to methoxy and methanol. For CuO/ZrO2 catalysts results demonstrate that the methanol formation occurs via π – bound formaldehyde and methoxy. Responses of sine shape variation applied to the reactants are also examined. The conversion of CO2 with hydrogen to methanol is investigated in dielectric-barrier discharges with and without catalysts at low temperatures (≤ 100 °C) and pressures (≤ 10 bar). The combination of discharges and catalysts lower the activation energy of the reaction resulting in a decrease in the catalyst optimum temperature. The presence of the catalyst in the discharge increases the methanol yield and selectivity by more than a factor of 10. Electrochemical reduction of carbon dioxide is briefly investigated by using TiO2/Ni complex and TiO2/Ru complex thin film electrodes. A considerable decrease in overvoltage is achieved together with respectable current densities.

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