Low temperature plasmas provide unique capabilities which have already been leveraged for decades in some applications, such in the case of the semiconductor industry, while not being not fully understood in others. The young field of plasma catalysis falls into this last category. Several studies in the last few years have confirmed that plasmas can activate desired reactions at the surface of catalysts, with notable examples including the steam reforming of methane or the synthesis of ammonia from nitrogen and hydrogen in dielectric barrier discharge (DBD) reactors. Despite several promising studies, there is a fundamental lack of understanding of how plasmas activate catalytic reactions. The inherent complexity of these systems makes them difficult to probe experimentally, with plasmas generated in DBD reactors being particularly complex, as they are composed of transient and spatially non-uniform filamentary discharges. In our study we use a radio-frequency discharge sustained at lower pressure (few Torrs) to create a spatially uniform and steady plasma. The plasma-surface interaction is investigated by exposing a simple stainless steel mesh to the plasma, all while varying its electrostatic potential with respect of a reference electrode. This system allows performing a careful parametric study in which plasma parameters (density, temperature etc.) and the plasma-surface potential difference is varied in a controlled and reproducible way. Results related to the case of ammonia synthesis will be discussed.<br/>Another catalysis-related area of opportunity for low temperature plasmas is in the synthesis of active materials. The second part of the talk will focus on the synthesis and characterization of earth-abundant, alternative plasmonic materials such as titanium nitride (TiN) and zirconium nitride (ZrN). A radio-frequency non-thermal plasma reactor for their synthesis in nanoparticle form will be described in details. The optical properties of these structures are comparable with those of plasmonic gold and silver colloidal nanoparticles. Simple test reactions, such as the reduction of a metal salt at the particle surface upon visible light exposure, suggest that these materials can be made chemically active via a plasmon-mediated light-induced process.

Plasmas for catalysis: from surface chemistry activation to synthesis of novel nanomaterials

2019 Spring National Meeting

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