*2.2. Catalyst Analysis*

The thermogravimetric curves (TG-DTG) of the dried precursors, from ambient temperature to 1000 ◦C under nitrogen flow (100 mL min−1) at a heating rate of 20 ◦C min−1, were recorded on Mettler-Toledo TGA/SDTA851e thermal analyzer, (Schwerzenbach Switzerland). All techniques mentioned below were employed on calcined powders. X-ray reflection patterns from 10–80◦ at a scan rate of 0.2◦ min−<sup>1</sup> were recorded on a Shimadzu XRD-6000 diffractometer (Columbia, MD, USA) with monochromatic radiation of CuK (λ = 1.5406 Å). The specific surface area was measured by nitrogen adsorption on a Quantachrome NOVA 2000e BET system (Boynton Beach, FL, USA) and the pore size was measured by the BJH method. Temperature programmed reduction (TPR) experiments were carried out on a semiautomatic Micromeritics 2920 apparatus (Norcross, GA, USA). Samples of about 30 mg were placed in a U-shaped quartz tube, first purged in a synthetic air stream of 50 mL min−<sup>1</sup> at 300 ◦C for 1 h and then cooled to ambient temperature. Reduction profiles were then recorded by passing a 10% H2/Air flow over the samples at a rate of 25 mL min−1, while heating at a rate of 10 ◦C min−<sup>1</sup> from ambient temperature to 900 ◦C. Temperature programmed oxidation (TPO) was performed on the catalysts after the dry reforming stability tests, using the same instruments with which the TPR was performed, to verify the carbon formation. Transmission electron microscopy (TEM) was carried out using a JEOL JEM-1011 microscope (Tokyo, Japan)with an accelerating voltage of 80 kV. The samples were then placed in a copper grid where the liquid phase was evaporated. They were then used to analyze the morphology of the fresh and used catalysts for the estimation of deposited carbon.

## *2.3. Catalyst Activity Measurements*

The dry reforming of methane was carried out in a tubular fixed-bed stainless steel reactor (i.d. 10 mm, catalytic bed length 3 mm) coupled to a gas chromatograph (Shimadzu HP5890 series II, Kyoto, Japan) with a thermal conductivity detector. The reaction conditions were: 700 ◦C, 0.05 g of catalyst, a gas mixture CH4:CO2:N2 (30:30:10, 70 mL/min), a space velocity of 84,000 mLgcat.−1h−1, and at 1 atm pressure. Prior to the catalytic activity tests, the catalysts were reduced in a 10% H2/N2 mixture (40 mL/min) at 700 ◦C for 120 min. Then, the H2 flow was replaced by a He flow (60 mL/min), and the system was heated (10 ◦C/min) to the reaction temperature. Stability runs were carried out at 700 ◦C for periods of 440 min time-on-stream. The products of reactions were analyzed on-line by a VARIAN GC 3800 gas-chromatograph (Varian, Santa Clara, CA, USA), equipped with two thermal conductivity detectors and columns packed with Porapak N and 13X Molecular sieves (Varian, Santa Clara, CA, USA). The reproducibility of the gas phase composition was checked in replica experiments. In most experiments, the error was within 5%.

### **3. Results and Discussion**

#### *3.1. Characterization of As-Synthesized Catalysts*

#### 3.1.1. Thermal Decomposition of Precursors

Figure 1 shows the TG and DTG thermal decomposition curves of the precursors which are used to determine the final calcination temperature for the formation of crystalline products. Figure 1 shows that during the decomposition process, many phases are formed, but overall CeNiO3 exhibits a two step, and SrNiO3 a three step, decomposition. For CeNiO3, the weight loss (~8%) started slowly at about ~75 ◦C, reached a maximum rate at ~150 ◦C (T1) and was finally completed at ~300 ◦C. The weight loss below this temperature was caused by the removal of the water left over from crystallization and the release of gases. The weight loss (~21%) from 300 to 550 ◦C with a maximum rate at 420 ◦C (T2 in DTG curve), may be regarded as a result of the decomposition and burning of the remaining

organic matter. Further heating caused negligible weight loss with the release of minute gaseous products in the form of CO2 and formation of the perovskite phase.

**Figure 1.** TG-DTG curves versus temperature of SrNiO3 and CeNiO3 perovskites.

On the contrary, for SrNiO3, three step decomposition was observed at different intervals of temperature. The initial weight loss below 125 ◦C was attributed to the loss of water and some adsorbed gases. The other two steps of decomposition were attributed to the combustion of organic matter present in the precursor. Therefore, from the TG-DTG curves of the fabricated samples, it can be inferred that the perovskite phase forms above 700 ◦C.

## 3.1.2. X-ray Diffraction (XRD)

The XRD profiles of the as-synthesized SrNiO3 and CeNiO3 perovskites are presented in Figure 2. Upon analyzing diffraction data using MDI Jade® software (version 6.5, Materials data Inc., Newtown Square, PA, USA), it was found that diffraction peaks corresponding to 2θ values of 28.6◦, 33.2◦, 37.3◦, 43.3◦, 47.5◦, 56.4◦, 62.9◦, 69.5◦, and 76.7◦ are assigned to crystal planes (111), (200), (111), (200), (220), (111), and (110) of CeNiO3, respectively [34,35]. The peaks appearing at 2θ = 28.6◦, 33.2◦, 47.5◦, and 56.4◦ are related to cubic CeO2 corresponding to crystal planes (111), (200), (220), and (311), respectively (JCPDS 81–0792). The peaks observed for cubic NiO were found to be at 2θ = 37.3◦, 43.3◦, and 62.9◦, corresponding to crystal planes (111), (200), and (220), respectively (JCPDS 75–0197). Additionally, peaks ascribed to SrO and SrCO3, as labelled in Figure 2, are also observed for SrNiO3 perovskite [36].
