Katalytisk förädling av koldioxid till metangas

Sammanfattning

This study explores catalytic methanation of carbon dioxide as a part of CCU technologies to enablea carbon cycle. The aim of this project was to design, synthesise and evaluate catalysts containingpalladium dispersed on a carrier consisting of cerium and zirconium (CexZr1−xO2). By varying thecomposition of the carrier material (0, 2.5, 5 and 10 wt% Zr) and the temperature of the calcination (400 °C and 600 °C) the influence of these factors on catalytic activity and selectivity was examined.The carrier materials were made through two rounds of co-precipitation, where revisions of thesynthesis method were applied to maintain desirable pH and effective filtration of the sample. All carriermaterials were characterized by X-ray diffraction, confirming the formation of a homogenous solidsolution with zirconium successfully incorporated into the crystal structure of cerium oxide. Also, X-rayfluorescence showed that the compositions of the samples were within the desired range. Furthermore,gas adsorption was used to characterize the surface area highlighting the samples calcinated at 400°Cto have a significantly larger surface area (up to 138 m2/g) compared to samples calcinated at 600 °C,following thermically induced sintering.Reactor trials were carried out between 150 °C and 350 °C, with hydrogen gas and carbon dioxide diluted in argon in a flow reactor. The results displayed that the conversion of carbon dioxideincreased with temperature to a maximum of 20 %, but that the selectivity of methane was very low.Instead the formation of carbon monoxide and water dominated, probably through the reverse watergas shift reaction. The high selectivity of carbon monoxide is believed to depend on a combinationof a too low reaction temperature and a too high dispersion of palladium on the large surface areas,something that favours desorption of carbon monoxide over further hydrogenation to methane.The project’s conclusions are that future attempts should focus on increasing the calcination temperature of the carrier material to decrease the dispersion of the metal, and to enable a higher reactiontemperature to favour the formation of methane.