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Καταλυτική υδρογόνωση του CO2 σε υποστηριγμένους καταλύτες μετάλλων

Kapenekakis Chariton

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Summary

Nowadays one of the major issues that humanity has to deal with is the environmental crisis that occurs and involves the air pollution. The greenhouse effect has already been enhanced due to the uncontrollable use of fossil fuels and the general technological and industrial development. As a result there is increased CO2in the atmosphere which the main greenhouse gas that contributes to the increase in the average temperature of the planet. Therefore, various alternative and environmentally friendly solutions have been recommended for the reduction of CO2in the atmosphere. Among them the catalytic hydrogenation of CO2 seems to be promising, aiming to the transformation of CO2 andresulting in the production of useful gases such as CH4, CH3OH, HCOOH, CO, C2 hydrocarbons.The present thesis aims to study the catalytic behavior of promoted 0.5% Ru / TiO2 catalysts withCe, Ca, Zr, Ba and La as well as to study the effect of operating parameters (reaction time, space velocity,H2 / CO2 ratio in feed) in catalytic activity and selectivity of 5% Ni / CeO2 catalyst.Catalytic activity experiments were performed in a fixed bed reactor in the temperature range 180- 4500C, using a feed stream, consisting of 5% CO2, 20% H2 (in He). The effect of H2 / CO2 ratio on the catalytic behavior of 5% Ni / CeO2 was investigated in the H2 / CO2 ratio region of 4-8. Results showed that the conversion of CO2 to CH4 increases with decreasing space velocity and increasing the H2 / CO2 ratio in the feed stream. Moreover from the reinforced metals used, Ce exhibited the highest CO2 conversion. As shown, the nature of the enhancer greatly influences both the conversion of CO2 and the intrinsic reaction rate following the Ce ~ La ~ Ba>Zr> Ca sequence. With respect to the selectivityto CH4, it increases comparing to the non supported sample, but is not affected by the nature of the support.In the stability experiment carried out for the 5% Ni/CeO2 catalyst, it was observed that in addition to its excellent activity and selectivity to CH4, it also possessed remarkable stability for more than 30 hours of reaction, indicating that it is a promising catalyst for the CO2 hydrogenation reaction.

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