*3.3. Characterization*

PXRD analysis was carried out to study the crystal phases. The instrument used in the PXRD tests was a D/MAX 2500 X-ray di ffraction analyzer manufactured by RIGAKU. Analysis conditions were Cu target, scintillation counter tube (SC) detector, tube voltage 40 kV, tube current 200 mA, continuous scanning measurement, time constant 2, scan range 5~90◦, and scan speed 5◦/min. TG-MS was carried out under air conditions and a nitrogen atmosphere with a flow rate of 50 mL/min, and the temperature ranged from 30 ◦C to 700 ◦C with a heating rate of 10 ◦C/min.

In this study, the morphology of the catalysts was observed and analyzed using a Nanosem 430 scanning electron microscope manufactured by FEI. The instrument parameters were resolution 1 nm, acceleration voltage 0.1~30 kV, magnification 20~800,000, low vacuum, and low voltage deceleration mode. TEM was carried out on a Tecnai G2 F20 instrument made in America. The instrument parameters were accelerating voltage 200 kV, point resolution 0.248 nm, line resolution 0.102 nm, and magnification 1.05 × 10<sup>6</sup> times. FTIR was utilized to study the surface group of the catalysts on a Nicolet 6700 FTIR infrared spectrometer. The scans were taken 32 times and the scanning wave number was 400~4000 cm<sup>−</sup><sup>1</sup> with a resolution of 4 cm<sup>−</sup>1.

### *3.4. Catalytic Activity*

Low-temperature SCR catalytic performance of the as-prepared samples was tested in a fixed-bed reactor at atmosphere pressure. In a typical reaction test, 0.2 g of the samples and 0.4 g of quartz sand were loaded into the reactor tube. Before the activity test, the samples had to be pretreated under an N2 atmosphere to remove the solvent and ge<sup>t</sup> activated. The pretreated conditions were as follows: 200 ◦C, 3 h, and heating rate 2 ◦C/min. After the pretreatment, the samples were tested for a temperature range of 80–280 ◦C under ambient conditions. The total flow rate of the feed gas was 100 mL/min, while the gas hourly space velocity (GHSV) was about 50,000 h−1. The composition of the gas flow was as follows: 500 ppm NO, 500 ppm NH3, 5% O2, 5 vol.% H2O (when used), and Ar as a balance gas.

The concentration of outlet NO and NO2 were determined using KM9106 Quintox Kane International Limited, a flue gas analyzer. The concentrations of the products N2 and N2O were monitored by gas chromatography (Agilent GC-6820) at 30 ◦C when e ffluent gases passed through it. A 5 Å molecular sieve column and Porapak Q column were used, respectively. The calculation methods used were

$$X = \frac{[NO\_x]\_{in} - [NO\_x]\_{out}}{[NO\_x]\_{in}} \times 100\%$$

$$S = \frac{[N\_2]\_{out}}{[N\_2]\_{out} + [N\_2O]\_{out}} \times 100\%$$

In the formulas, *X* represents the conversion of NOx, S represents the N2 selectivity, [x] represents the concentration of each gas, in represents the inlet gas, and out represents the outlet gas. In our work, the N2 selectivity of our catalysts was 100%.
