# Trapping and Methanation of CO\({}_{2}\) in a Domestic Microwave
## 2 Materials and Methods  
ZrO\({}_{2}\) (monoclinic, 131 m\({}^{2}\) g\({}^{-1}\)) was provided by MEL Chemicals and characterized in detail elsewhere [23]. Fe\({}_{3}\)O\({}_{4}\) (10 m\({}^{2}\) g\({}^{-1}\)) was bought from Alfa Aesar (lot X08G023). SiC (120 grit, ca. 137 \(\upmu\)m particles) was purchased from Alfa Aesar (batch #10179265). A silica-supported ruthenium methanation catalyst (6.8 wt.% Ru measured with ICP, Ru dispersion = 22% measured using H\({}_{2}\) chemisorption, corresponding to 4 nm particles) was prepared via dry impregnation using RuCl\({}_{3}\)\(\cdot\)H\({}_{2}\)O precursor. High purity gases N\({}_{2}\), H\({}_{2}\), O\({}_{2}\) and CO\({}_{2}\) from Air Liquide were used without any further purification. The experimental setup is illustrated in Figure 1A,B. The gas flow rates were controlled using Brooks electronic mass flow controllers. A commercial 800 W MW domestic oven (Sharp, model YC-MS01E-W) was modified as described elsewhere [22]. The MW oven power was always set to the maximum when used. Two quartz tubes were placed in the oven to accommodate the sorbent and catalyst beds, using PTFE (Teflon(r), Wilmington, NC, USA) Swagelok fittings. Sorbent and catalyst beds were held with quartz wool plugs. Gases were flown through polyethylene tubing passing through 2 mm holes drilled in the oven cavity. Figure 1: (**A**) Schematic representation of the catalytic setup used for CO\({}_{2}\) trapping and methanation. Gases were fed through mass flow controllers (MCs). The feed could be sent through a 4-way valve (4-W) to the sorbent and catalytic beds located in the MW oven first or directly into the FT-IR gas analyzer. (**B**) Picture of the sorption and catalyst beds located in the MW oven. (**C**) Examples of FT-IR transmission spectra showing the typical signals of methane, CO and CO\({}_{2}\) measured with the IR gas cell. The feed could be sent through the sorbent and catalytic beds first or directly into the IR gas analyzer, which consisted of a 10 cm pathlength IR gas cell (from Harrick) fitted in a Bruker Tensor 27. The gas cell was kept at 80 \({}^{\circ}\)C and 8 scans were averaged at a resolution of 4 cm\({}^{-1}\). A typical FT-IR transmission spectrum showing methane, CO and CO\({}_{2}\) bands are given in Figure 1C. IR Band assignment was ascertained via comparison to the NIST database [24; 25; 26]. CO\({}_{2}\) and product concentrations were derived from calibration curves, using the area of the bands located at 670 cm\({}^{-1}\) (for CO\({}_{2}\)), 3015 cm\({}^{-1}\) (for methane) and 2145 cm\({}^{-1}\) (for CO). The conversion of CO\({}_{2}\) was calculated as the ratio between reacted CO\({}_{2}\) and the inlet CO\({}_{2}\), the reacted CO\({}_{2}\) being the difference between the measured CO\({}_{2}\) and the inlet CO\({}_{2}\). The signal of the inlet CO\({}_{2}\) was measured by by-passing the reactor. The yield of CO (or CH\({}_{4}\)) was calculated as the concentration of CO (or CH\({}_{4}\)) divided by that of reacted CO\({}_{2}\). Zones in which an effective MW absorption by the materials occurred were determined from sample black body radiation, since it is difficult to measure temperatures in multimode MW ovens and because of the likely presence of strong temperature gradients within long (several centimeters) beds [27; 28]. Two positions associated with intense MW fields were found, shown in Figure 1B, expressed by the distance (in mm) from the oven center and height: (50; 30) and (115; 60), respectively. Figure 2 shows typical brilliances obtained from a mixture of SiC and Fe\({}_{3}\)O\({}_{4}\) placed in the catalyst bed.