3-D Mesoporous Architectures for Carbon-Conversion Photocatalysis: Block Copolymer-Templated Semiconductor Mesostructures Substantially Enhance Photocatalytic Dry Reforming of Methane

The recent discovery of low-temperature photocatalytic conversion of methane and carbon dioxide to syngas (photocatalytic dry reforming of methane; photo-DRM) transformed an expensive high-temperature process into an appealing sustainable process for carbon conversion. This simple reaction, which can proceed under illumination without external heating, could provide an alternative to crude oil for supplying the organic chemical precursors our modern world is built upon. While much attention has been paid to alternative photocatalyst support chemistries or exotic metallic promoters, the 3-D architecture of the semiconductor support itself has been largely overlooked. This has left a massively important variable space in photocatalyst support development largely unexplored.<br/><br/>By utilizing block-copolymer self-assembly templating of common semiconductor supports, we have studied TiO₂ and Ta₂O₅ photocatalyst supports in a range of architectures: from hexagonally packed cylinders to 3-D co-continuous gyroids to asymmetrically porous thin films. This mesoporosity provides enhanced activity across a wide range of volumetric flow rates, delivering record low-temperature performance beyond the expectations of enhanced surface area alone. Beyond surface area, the 3-D accessibility of co-continuous architectures greatly reduces tortuosity, leading to fast facile transport of reactive species through the structure.<br/><br/>Further, we developed novel TiO₂ thin film catalyst architecture derived from liquid filtration membranes that has a thin mesoporous top layer with macroporous support layer. This highly-active low-density membrane architecture delivers the highest reported activity per gram for low-temp photo-DRM to-date by supporting a thin active layer on a macroporous substructure, allowing rapid gas transport. These solution-based polymer processes for creating 3-D architectures are simple, low-cost and scalable routes to create world-class photocatalyst supports, applicable to a wide-range of gas-phase catalytic reactions.