A Direct Fourier Transform Infrared Spectroscopic Comparison of the Plasma- and Thermally-Driven Reaction of CO2 at Macor

Abstract

This paper reports the appraisal of two in situ Fourier Transform InfraRed plasma cells with respect to the interrogation of the glow of a non-thermal plasma (using a transmission cell), and the non-thermal plasma/solid (i.e. dielectric/catalyst) interface (with a reflectance cell). The paper also reports, for the first time, a direct comparison of the IR spectroscopy of plasmaand thermally-driven chemistry. The system chosen for study was the reduction of CO 2 as there is a wealth of data in the literature for comparison. The catalyst was Macor, a ceramic material comprising primarily Al, Si and Mg oxides. In both the thermal and plasma experiments, rotationally-excited CO 2 (CO Ã 2 ) was observed: in the plasma system, rotationally-excited CO (CO*) was produced via the reduction of CO 2 . Using the transmission cell, the conversion of CO 2 to CO was estimated and found to be up to 9% at energy efficiencies of ca. 1-2%, in line with the literature. No reaction of CO 2 was observed in the thermal system. The data obtained using the reflectance cell were similar to those obtained with the transmission cell, with the minor differences reflecting the longer residence time and higher specific input energy. Interestingly, two plasma-induced bands were observed in the reflectance experiments which increased in intensity with time and input power: these may be due transverse and longitudinal optical modes of SiO 2 and did not appear to participate in the observed chemistry.

The Production of Ketene and C5O2 from CO2, N2 and CH4 in a Non-thermal Plasma Catalysed by Earth-Abundant Elements: An In-Situ FTIR Study

“…The transmission NTP cell [37], see Fig. S1(a), was designed and fabricated in-house and was made from a 15 cm long, cylindrical polytetrafluoroethylene (PTFE) tube with an outer diameter of 6.3 cm and an inner diameter of 2.5 cm.…”

“…The reflectance NTP cell [37] is shown in Fig. S1(b): the IR beam passed through a 3 mm CaF 2 plate window and a 5 mm gap before being incident on the surface of a 3 cm 9 3 cm 9 0.5 cm Macor plate covered by a Ti mesh (50% open area) electrode at an angle of 24 degrees.…”

“…features are detailed in the previous paper [37]. , referenced to N 2 gas at the same flow rate, at 25°C.…”

“…It is clear from the figure that the fundamental bands are saturating and hence cannot be employed for any quantitative measurements; hence it was decided to employ the integrated areas of the CO 2 combination bands between 3491 and 3769 cm -1 to estimate the CO 2 conversion, the absorption coefficient employed was 6.5 9 10 5 cm mol -1 [37]. Using the thermal FTIR system, it was found that this value remained constant over the temperature range from 25 to 150°C [37].…”

“…Recently, we published in situ FTIR studies comparing the plasma-and thermallydriven reaction of CO 2 at Macor, the first such direct comparison of plasma and thermal chemistries [37]. We showed that, in both the thermal and plasma experiments, rotational excitation of the CO 2 (CO 2 *) took place in the plasma glow.…”