Infrared studies of gas phase and surface processes of the enhancement of catalytic methane decomposition by low temperature plasma

Abstract

Catalyst enhancement by atmospheric pressure plasma is a recently emerging field of research that embodies a complex system of reactive species and how they interact with surfaces. In this work we use an atmospheric pressure plasma jet integrated with a nickel on Al2O3/SiO2 support catalyst material to decompose methane gas by partial oxidation reaction. We use Fourier-transform Infrared spectroscopy analysis of the gas phase post reaction to measure the loss of methane and the production of CO, CO2, and H2O and diffuse reflectance Fourier-transform Infrared spectroscopy (DRIFTs) in situ analysis of the catalyst surface as a function of both catalyst temperature and plasma operating parameters. We find reduction of methane by both plasma alone, catalyst alone, and an increase when both plasma and catalyst were simultaneously used. The production of CO appears to be due primarily to the plasma source as it only appears above 2.5 W plasma dissipated power and decreases as catalyst temperature increases. CO2 production is enhanced by having the catalyst at high temperature and H2O production depends on both plasma power and temperature. Using DRIFTs we find that both heating and plasma treatment remove absorbed water on the surface of the catalyst. Plasma treatment alone however leads to the formation of CO and another IR spectral feature at 1590 cm−1, which may be attributed to carboxylate groups, bonded to the catalyst surface. These species exhibit a regime of plasma treatment where they are formed on the surface and where they are significantly removed from the catalyst surface. We see the formation of a new spectral feature at 995 cm−1 and discuss the behavior and possible origins of this feature. This research highlights the potential for plasma regeneration of catalyst materials as well as showing enhancement of the catalytic behavior under low temperature plasma treatment.

Plasma-Catalytic Partial Oxidation of Methane on Pt(111): A Microkinetic Study on the Role of Different Plasma Species

“…Only a few mechanistic studies are available on the surface chemistry of the plasma-catalytic oxidation of CH 4 . Knoll et al investigated the POX of CH 4 by an Ar/O 2 atmospheric pressure plasma jet (APPJ) in the presence of Ni on an Al 2 O 3 /SiO 2 support using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The authors found that CO 2 formation is enhanced at higher temperatures and that CO is likely to be converted to CO 2 on the catalyst surface.…”

“…The authors found that CO 2 formation is enhanced at higher temperatures and that CO is likely to be converted to CO 2 on the catalyst surface. However, they also suggested the presence of carboxylate groups or COO – , which are likely precursors to CO 2 . Zhang et al investigated the decomposition and oxidation of CH 4 exposed to a Ni catalyst on an Al 2 O 3 /SiO 2 support and an Ar or Ar/O 2 APPJ using time-resolved DRIFTS.…”

Tuning plasma parameters to control reactive species fluxes to substrates in the context of plasma catalysis

“…Comparatively, the atmospheric pressure plasma jet (APPJ) might be a suitable alternative for fundamental plasma-catalysis studies as it allows decoupling the plasma and catalyst. APPJ like approaches have been explored by a few groups [14][15][16]. APPJs can operate remotely with convective transport of reactive species to the catalytic surface, which offers opportunities for tuning the reactive species fluxes and related plasma-induced effects.…”

Plasma‐Assisted Reforming of Methane

“…[ 331 , 332 ] In addition, when the plasma and catalyst are coupled, the CO selectivity can be improved by suppressing the formation of CH n on the catalyst surface. [ 333 , 334 ] In the study, the catalyst could be placed in the plasma region (DBD) or downstream of the plasma (MW and GA) depending on the geometry of the plasma reactor, discharge pattern, plasma temperature, and thermal stability of the catalyst. [ 55 ] Placing the catalyst in the plasma region is not feasible for thermal plasmas (e.g., MW torches, RF torches, and gliding arcs) because of the high plasma temperature (thousands of °C).…”