Review on Plasma techniques for catalyst preparation, modification and regeneration
Part 1 concerns non-thermal plasma (NTP) techniques, which offer a green route for catalyst preparation and modification. The report describes the techniques with examples. Non thermal plasmas (plasmas with gas temperature of 298 – 473 K and electron temperature up to 10000 K) are applied to prepare supported metal catalysts, as well as to modify the catalyst surface and to regenerate coked catalysts. NPT treatments can increase particle dispersion and metal-support interaction, enrich the catalyst surface with the active element, remove the preparation precursor, reduce the oxidized particles, and increase the acidity of the catalyst.
Part 2 concerns thermal plasma applications for catalysts preparation. Thermal plasmas (up to 15000 K) are obtained via direct current arcs (dc/plasma jet arc) or via radiofrequency arc discharges. In Conventional Plasma Spray, solids injected into the plasma jet via a gas carrier, get heated up to melting and then impact the target surface or cool down forming powders. Suspension plasma spray is used to deposit powders onto supports as thin layers. An alternative method to produce agglomerated or nano powders and coatings is the Solution Precursors Plasma Spray method. The arc plasma deposition (APD) processes is a method to prepare metal supported catalysts with nano-sized particle distribution.
Part 3 concerns quantitative modelling the most relevant phenomena that occur in a non-thermal plasma (NTP) discharge, with and without a ceramic media. There are two main categories of reactors for exposing a packed-bed catalyst to non-thermal plasma: one-stage plasma reactors (Direct Barrier Discharge reactor and the Pin-to-Plate reactor) and two-stage plasma reactors. The synergistic effect of NTP on catalysis can be positive (VOC abatement, NOx reduction, decoking) or negative (Fischer Tropsch, steam reforming). The possible effects of plasma on the catalyst are discussed, followed by a kinetics and reactor model.