Study of dry reforming of methane on Ni and Ru catalysts supported on mixed lanthanide oxides
Loading...
Date
2023-07-15
Authors
Λουκανάρης, Κωνσταντίνος
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Industrialization and rapid population growth, that characterize the modern era, have led to an increase in energy needs. However, the dependence on fossil fuels to satisfy these needs, has contributed significantly, among others, to the intensification of the greenhouse effect. A promising reaction that can be applied to limit greenhouse gas emissions is dry reforming of methane, which exploits the two main greenhouse gases (CH4 and CO2) to produce syngas (a mixture of H2 and CO).
This thesis studies Ni and Ru catalysts supported on CeO2, promoted with lanthanide oxides for the dry reforming of methane reaction. The mixed oxide carriers were prepared by the co-precipitation method using nitrate precursors, in such a way that the final composition of the carrier (mixed oxide), in each case, was 80% mol Ce and 20% mol Y, where Y: La, Pr, Nd, Eu, Gd, Tb, Dy, Er. Then, the 1 wt.% Ru/Ce0.8Y0.2Ox and 5 wt.% Νi/Ce0.8Y0.2Ox catalysts were prepared employing the liquid impregnation method. The structure of the synthesized catalysts was studied with the X-ray diffraction (XRD) method and the reducibility of the materials was investigated using the Temperature-Programmed Reduction with hydrogen (H2-TPD). The effects of the mature of the mixed oxide support on the bacisity of the catalysts was studied with Temperature-Programmed Desorption of CO2 (CO2-TPD).
Results obtained showed that in the case of ruthenium catalysts, the modification of the CeO2 carrier with lanthanide oxides, resulted in higher conversions of reactants and higher H2/CO ratios in the products compared to the unmodified Ru/CeO2 catalyst. Regarding the nickel catalysts, higher conversions were observed only in the case of the CePr-supported catalyst and higher H2/CO ratios only for the CeDy-supported sample. Results of long-term stability tests showed that Ru catalysts dispersed on mixed oxide supports were very stable under reaction conditions for 40 hours-on-stream. The conversions obtained over the latter catalysts were significantly higher than those of the unmodified Ru/CeO2 sample. In addition, the H2/CO ratio in the reaction products remained constant and reached fairly high value (0.95), except for the Ru/CePr catalyst which showed a very small gradual decrease from 0.85 to 0.8. On the other hand, the nickel catalysts were not stable under reaction conditions, as there was accumulation of a large amount of carbon on their surface, forcing in termination of the experiments.
The work presented in this thesis is divided into five chapters. In the 1st chapter, an introduction is made regarding the increased energy demands of the modern world and the need to find alternative sources of energy. Some ways of producing and using biogas and hydrogen are mentioned and methane reforming reactions that can contribute to syngas production are discussed. Chapter 2 deals with the thermodynamics of the dry reforming reaction of methane, the conditions under which it takes place, as well as the catalysts commonly used for this reaction. The 3rd chapter covers all the experimental procedures employed, including the preparation method and the techniques used for catalyst characterization, as well as the procedure followed in the catalytic activity and stability experiments. Finally, in the 4th chapter, the experimental results are analyzed and in the 5th chapter, the conclusions of the work are summarized and some suggestions for future work are presented.
Description
Keywords
Dry reforming of methane, Mixed lanthanide oxides, Ni catalysts, Ru catalysts, H2 production, Catalytic activity, Catalytic stability, Catalyst structure, TPR-H2, TPD-CO2, TPO, XRD