High-purity nitrogen and oxygen were adjusted to the total gas flow with a ratio of 79:21. A gas scrubber (Figure ① ) filled with paraformaldehyde particles of a certain quality was heated in water bath pot, and the volatilized paraformaldehyde vapor was carried by nitrogen into the pyrolysis furnace (Figure ④ ), paraformaldehyde steam was depolymerized into formaldehyde gas at the temperature of 160°C. Subsequently, the formaldehyde gas was catalytically degraded in a tube furnace. In addition, the calculation of RE of catalyst requires a formaldehyde calibration curve. The procedure for absorbance determination of formaldehyde standard solution with the calibration curve obtained after the determination is plotted in Figure and S1, respectively. The concentration of formaldehyde gas at the inlet and outlet of reactor was measured according to the above operating procedure, and the RE of formaldehyde ( ) was calculated from: