*2.3. Idling Conditions*

In addition to the extreme temperature gradient of the heaters, a stable idling condition was also simulated under the assumption of discontinuous power supply. The activity of the catalyst can be maintained by maintaining stable idling conditions. By applying an effective idling operation to the process, the reaction may not be completely terminated, which would shorten the preparation time for restarting the operation.

Figure 8 shows temperatures recorded along the SRM reaction followed by idling operation and the restart process. In a typical starting procedure, the reactor containing a reduced catalyst was heated to the reaction temperature (800 ◦C, region (1) in Figure 8b) prior to feeding the reactants. After stabilizing the reactor temperature, the SRM reaction was initiated by feeding the reactants (region (2)). After completion of the reaction, the three heaters were maintained at 500 ◦C, and nitrogen flowed inside the reactor at a rate of 1 L/min (region (3)). When the reforming reaction proceeded again, the reactor temperature was heated (region ((4)) followed by feeding of the reactants (region (5)). As shown in Table 3, no significant changes in catalytic performance were observed before or after the idling operation.

**Figure 8.** (**a**) Schematic of a catalytic layer for idling operation, (**b**) temperature recorded before (1, 2), during (3), and after idling (4, 5).

**Table 3.** Comparison of temperature, methane conversion, and hydrogen production before and after idling.


Reaction conditions: steam/methane ratio = 3, feed composition of CH4/H2O/N2 = 1/3/1, reaction pressure = 0.6 MPa, GHSV = 2.0 L CH4/(h·gcat), catalytic layer = 82 cm length, catalyst weight = 80 g, dilution agen<sup>t</sup> weight = 1220 g, and physical mixing.

#### **3. Materials and Methods**
