Design of Ferromagnetic Nanomaterials for CO2 Hydrogenation to Light Olefins

A useful solution to the accumulation of carbon dioxide in the atmosphere is to utilize CO₂ to produce fuels and essential chemicals in a thermochemical process such as the conversion CO₂ to light olefins. The process of converting of CO₂ to light olefins can be achieved in two steps: first, by converting CO₂ to methanol at temperatures between 230^oC to 270^oC, followed by the conversion of methanol to light olefins at a higher temperature range, between 350^oC to 450^oC. This two-step process has been achieved using a bifunctional catalyst composed of indium oxide (In₂O₃) supported on zirconia (ZrO₂) and the zeolite SAPO-34 which has produced 80% selectivity of olefins, when reacted at a median temperature. However a higher selectivity of light olefins could be achieved if the required dual temperatures were provided to each of the catalysts within the same reactor. As a solution, induction heating, which uses alternating current run through coils can be used to heat ferromagnetic materials to achieve dual temperatures in the above catalysts.

In this work, Maxwell-Ampere’s law, heat diffusion and momentum transfer equations have been solved to attain the temperature profile of the two catalyst beds heated with induction heating. The two catalyst beds are modeled as a cluster of circular pellets of uniform sizing in the micron scale, heated by ferromagnetic materials mixed into each catalyst bed, represented as pellets of the same radius. The amounts of heating material used is varied by changing the number of pellets assigned as ferromagnetic. The different types of ferromagnetic materials such as iron, nickel and cobalt and steel are considered. Initial work has been performed in H₂ gas flow.

Our results indicate that the temperature decreased radially from the center to the walls of the reactor for both catalysts, with an average temperature difference of 40^oC. A smaller variance of temperatures was observed along the length of the reactor due to H₂ flow. Less uniform temperatures were observed by the In₂O₃/ZrO2 catalyst bed compared to the SAPO-34 catalyst due to differences in thermal conductivity. By changing the amounts of heating pellets, a temperature difference of 100^oC was observed between the two catalysts. Of the different ferromagnetic materials tested, steel provided the highest temperatures in both catalysts. The presented results will guide the future experimental design of ferromagnetic materials.