Decoupling Mass Transport and Catalytic Effects in the Plasma-Driven Reduction of CO₂ to CO on Heterogeneous Catalysts Formed by Atomic Layer Deposition

Plasma catalysis has been traditionally used for processes such as the removal of volatile organic compounds (VoC’s) from industrial waste streams and the production of ozone. Recently, significant work has studied the use of heterogeneous plasma catalysis for CO₂ conversion. This process can be used to generate chemical fuels from CO₂, such as CO, CH₄ and alcohols. The role of the heterogeneous catalyst to CO₂ reduction in a plasma system is typically the convolution of a number of simultaneous effects. In considering the performance of a catalyst, the effects of surface catalysis, mass transport due to multiscale structure, and local electric field enhancements can each contribute to the overall chemical transformation. The complex nature of these reactors makes it difficult to determine the true reason for differences in performance. Atomic layer deposition (ALD) is a technique capable of depositing layers of catalyst materials with nearly atomic precision in the layer composition. By controlling the composition of nanometer-scale thin films of catalyst onto high surface area scaffolds, we decouple the effects of mass transport and catalysis while having atomically precise control over their composition. Here we intend to develop an experimental scheme for comparing the catalytic effects of plasma CO₂ reduction catalysts without the introduction of significant structural variability. We will describe recent work to use ALD-derived plasma CO₂ reduction catalysts onto high surface area scaffolds. We show how to decouple the mass transport and catalytic effects in these catalyst-scaffold systems using gas chromatography and optical emission spectroscopy. Finally, we compare this approach to more traditional synthesis and coating methods such as sol-gel and wet impregnation methods. As a result, we can unambiguously identify the role that heterogeneous catalysis in plasma-driven transformations of CO₂.