Investigating Vanadium Supported Zeolite for Direct Air Capture of CO2

Direct Air Capture (DAC) of CO2 is an engineering challenge that has been studied for about two decades. The process is primarily motivated as a possible rectification to the anthropogenic increase in atmospheric CO2. Catalytically converting the captured CO2 to value-added products further incentivises CO2 capture for a more sustainable economic trajectory. Finding an ideal DAC sorbent involves navigating through thermodynamic and kinetic impediments such as minimizing energy input for regeneration and maximizing the rate of CO2 adsorption given the low (400 ppm) concentration of CO2 in air. Materials such as CaO, amines, hydroxides, and metal organic frameworks have been studied, but there is still room for improving working capacity and energy efficiency, in particular during the CO2 desorption step.

To address these challenges, it is hypothesized that vanadium dispersed in a zeolite may be a material that exhibits desirable properties for DAC of CO2. Vanadium offers facile access to multiple oxidation states, has a nucleophilic surface, and can generate oxygen atom defects, all of which assist in binding and activating CO2. However, vanadium atoms in solid state materials have been shown to migrate, agglomerate, and volatilize. Stabilizing vanadium in a zeolite matrix could prevent these problems, but vanadium is known to catalyze dealumination which destroys the alumino-silicalite zeolite framework. Much of the sorbent would also remain inaccessible to the CO2 because of diffusion limitations within the micropores. To this end, it is proposed that dispersing vanadium in a boron-silicalite zeolite with meso/macro porosity is a potential candidate for DAC. By replacing aluminum with boron, it is expected that the same advantages of stabilizing the metal on a zeolite matrix are achieved, and the zeolite framework is also protected from potential degradation by vanadium. By introducing meso/macro porosity, the material can be tuned for CO2 adsorption, thereby decreasing the barrier to diffusion. Additionally, CH4 oxidation can be catalyzed on or nearby the active site where CO2 is adsorbed. A controlled CH4 oxidation would release heat into the system where CO2 is bound, effectively making the system able to convert a potent greenhouse gas CH4 into a lesser potent CO2 and meanwhile reducing the energy input for catalyst regeneration. Thereby, the proposed structure presents itself as a promising sorbent for direct air capture of CO2.