(638b) Energy Efficient Methane Reforming Enabled By Continuous Manufacturing of Porous Titania Microparticles

Despite the recent energy boom, due in part to the newfound ability to reach shale oil deposits, global population growth and ever-growing energy consumption demand the development of new, sustainable energy sources. With continued use of hydrocarbon fuels, additional attention must be devoted to mitigation of harmful emissions related to energy generation and other human activities including waste disposal and raising livestock on an industrial scale. Over the past decade, controlling emissions from waste disposal and livestock farming have attracted interest, as both produce enormous quantities of carbon dioxide (CO₂) and methane (CH₄), which are both known to contribute to global climate change. Interestingly, CO₂ and CH₄ can be used for syngas production through dry reforming of methane (DRM)/ CO₂ reforming of methane (CRM) processes.

Despite the attractiveness of the DRM/CRM processes, the energy barrier that must be overcome to successfully conduct this reaction, even with catalysts, is prohibitive, typically requiring temperatures ranging from 1000K to 1500K (reaction enthalpy = 247 kJ/mol). One method that has been explored to reduce the energy required for DRM has been the integration of visible-light photocatalysts with thermocatalytic coatings.¹ However, the unfavorable size dispersity and nano-meter size scale of Degussa P25 titanium oxide (TiO₂), limits its applicability as a visible-light photocatalyst in flow reforming reactors due to high pressure drops. Therefore, it is desirable to produce monodisperse photocatalytic microparticles that may be used in flow reforming with a variety of thermocatalysts at various loadings.

This project focuses on the production of hollow (and porous) TiO₂ microspheres via a microfluidic strategy for use as a dual-functionality substrate in photothermal bi-reforming reactions. The porous microspheres are produced via flow-focusing droplet formation in a custom-designed glass-based microfluidic reactor. The inner tapered- tip glass capillary delivers the oil-phase precursor into an outlet with a constricted tip, resulting in droplet break-up in a dripping regime. The continuous phase (formamide with 1 wt% Pluronic F108) is fed into the reactor by co- and counter- annular flows with independently controlled flow rates. The oil-phase precursor contains the titanium precursor (i.e., titanium butoxide), toluene, a photocurable polymer, and a radical photoinitiator. The droplets then exit the reactor into DI water where the titanium precursor is hydrolyzed, forming an amorphous TiO₂ shell. This method effectively decouples the droplet formation and the hydrolysis reaction by which the titania shells are formed following a monodispersed droplet formation stage. After collection, the droplets are UV cured, washed, dried, and calcined to form hollow TiO₂ microspheres. In the next step, the hollow titania microspheres are impregnated with 0.45 wt% rhodium as a thermocatalyst and are reduced under hydrogen to produce black titania. Using these novel photocatalytic microparticles without simulated sunlight illumination at 550°C, we have achieved methane reforming yields approximately three orders of magnitude greater than those previously reported at similar temperatures.¹ These results provide a new, promising direction for reduction of the DRM energy barrier and a potential method by which DRM may become viable both energetically and economically.

1. “Efficient Visible Light Photocatalytic CO₂ Reforming of CH₄.” Han, B.; Wei, W.; Chang, L.; Cheng, P.; Hu, Y. H. ACS Catal. 6, pp 494-497, 2016.