| dc.description.abstract | To move towards a more sustainable form of energy production, COx emissions need to be drastically
reduced. As renewable energy sources cannot yet provide for the growing demand, the thermal
catalytic decomposition of methane could be a promising intermediate. Apart from energy-rich
hydrogen, this reaction also adds value to the solid carbon by-product in the form of carbon
nanostructures. Promotion with alkali and alkaline earth metals of Ni-based catalysts was investigated
by following the carbon growth in-situ using a thermogravimetric analyzer. Nickel catalysts with Li, Na,
K, and Mg as promoters were tested. It was found that under similar reaction conditions, all the
promoters show different effects on the catalytic properties of the catalysts, with promotion by Na and
Mg showing a large increase in both activity and lifetime. K, on the other hand, shows a reduction in
both properties. For the Na-promoted catalysts a concentration dependency was found, suggesting
that lower promotion concentrations are needed when going down the alkali metals. On the other
hand, Mg-promotion showed a slight increase in catalytic performance when increasing the promoter
concentration, this might suggest that the promoter effect of Mg is different from that of the alkali
metals. Measurements performed at different temperatures found activation energies of 77, 83, and
102 kJ/mol for the tested Ni reference, Na-promoted, and Mg-promoted catalysts, respectively. Only
for the Mg-promoted catalysts an optimum in the catalytic lifetime was found at around 450 °C. While
the other two catalysts showed increasing lifetimes and total carbon yields with decreasing
temperatures, where this was not expected. The formed carbon structures seem mostly unaffected by
the introduction of the different promoters compared to the reference catalyst, suggesting limited
changes in the carbon growth mechanism upon promotion. | |
