Lanthanum–Cerium-Modified Nickel Catalysts for Dry Reforming of Methane

Abstract

The catalyst MNi_0.9Zr_0.1O₃ (M = La, Ce, and Cs) was prepared using the sol–gel preparation technique investigated for the dry reforming of methane reaction to examine activity, stability, and H₂/CO ratio. The lanthanum in the catalyst LaNi_0.9Zr_0.1O₃ was partially substituted for cerium and zirconium for yttrium to give La_0.6Ce_0.4Ni_0.9Zr_0.1−xY_xO₃ (x = 0.05, 0.07, and 0.09). The La_0.6Ce_0.4Ni_0.9Zr_0.1−xY_xO₃ catalyst’s activity increases with an increase in yttrium loading. The activities of the yttrium-modified catalysts La_0.6Ce_0.4Ni_0.9Zr_0.03Y_0.07O₃ and La_0.6Ce_0.4Ni_0.9Zr_0.01Y_0.09O₃ are higher than the unmodified La_0.6Ce_0.4Ni_0.9Zr_0.1O₃ catalyst, the latter having methane and carbon dioxide conversion values of 84% and 87%, respectively, and the former with methane and carbon dioxide conversion values of 86% and 90% for La_0.6Ce_0.4Ni_0.9Zr_0.03Y_0.07O₃ and 89% and 91% for La_0.6Ce_0.4Ni_0.9Zr_0.01Y_0.09O₃, respectively. The BET analysis depicted a low surface area of samples ranging from 2 to 9 m²/g. The XRD peaks confirmed the formation of a monoclinic phase of zirconium. The TPR showed that apparent reduction peaks occurred in moderate temperature regions. The TGA curve showed weight loss steps in the range 773 K–973 K, with CsNi_0.9Zr_0.1O₃ carbon deposition being the most severe. The coke deposit on La_0.6Ce_0.4Ni_0.9Zr_0.1O₃ after 7 h time on stream (TOS) was the lowest, with 20% weight loss. The amount of weight loss increases with a decrease in zirconium loading.

1. Introduction

Research based on CO₂ absorption and H₂ production to solve global warming has led to the use of methane dry reforming (DRM) [1,2,3]. Methane dry reforming compared to partial oxidation and steam reforming in syngas generation produces a H₂/CO ratio near unity, which is appropriate for generating liquid hydrocarbons using the Fischer–Tropsch method [4,5,6]. The mole ratio of syngas is less than one due to side reaction; the reverse water gas shift (RWGS) step could take place in CH₄ reforming [7,8,9].

CO₂ + H₂ → CO + H₂O

(1)

Hydrogen produced from greenhouse gases can decarbonize the electricity and transport sectors when substituted for fossil fuels such as coal, diesel, gasoline, and natural gas [10,11]. Due to the highly endothermic inherent features of the DRM reaction, it is performed at high temperatures (973 K–1173 K), giving rise to possible complications which affect catalyst stability and can cause the sintering of active sites [12,13].

The dry reforming of the methane reaction sequence first involves methane adsorption [14]. Generally, methane is adsorbed in a dissociated form on metals to give H and CH_x species in which the numerical value of x ranges between zero and four, which is dependent on temperature and the metal substrate [7]. When the value of x is zero, this shows that coke is formed at the metal surface. Carbon dioxide dissociation and adsorption on transition metal are controlled by electron transfer and require the creation of an anionic CO²⁻ precursor [7]. The deactivation of catalysts by carbon formation, originating from CH₄ cracking and/or CO disproportionation (Boudouard) reaction, hinders the use of dry reforming methane.

Boudouard reaction: 2CO ↔ CO₂ + C   ΔH⁰ = −173 kJ mol⁻¹

(2)

Methane cracking: CH₄ ↔ 2H₂ + C    ΔH⁰ = +75 kJ mol⁻¹

(3)

Though noble metal catalysts such as Rh, Ru, Pt, and Pd possess good catalytic activity and better coke resistance for DRM reaction, costly prices and less availability hinder their usage [15,16,17,18,19]. In the dry reforming of methane, nickel-based catalysts, which are low cost, are widely used [20,21,22,23]. However, they are prone to swift deactivation due to the sintering of nickel sites and coke formation during the DRM reaction [24,25].

Perovskites are metal oxides generally represented as ABO₃, with A and B representing the cations of two metals. The commonly used perovskites for the DRM reaction are those with Ni in the B site and A as rare-earth metals in their structure [26]. B site metal stands for the active site, whereas A site metal gives stability and augments catalytic performance [26]. The substitution of either a B or A ion with heterovalent metal ions could change the catalyst structure, generating oxygen vacancies or valence states of the original metal cation which could promote both redox properties and oxygen mobility [27]. The oxides of rare-earth metals allow for an excellent dispersion of nickel. Lanthanum shows higher stability in the DRM reaction for Ni-based catalysts [28,29]. The addition of La augments the medium-strength basicity and nickel accumulation on the catalyst surface [30]. Lanthanum was found to augment the reforming reaction by increasing the presence of NiO sites, thereby enhancing the reducibility of Ni species and carbon gasification, leading to an overall lower carbon deposit [31]. The LaNiO₃ catalyst was prepared for the steam and CO₂ reforming of methane and it was found that Ni was highly dispersed and resistant to coke deposition [32].

Ce-substituted perovskites possess enough capacity for oxygen storage and high mobility of lattice oxygen to improve catalytic behavior [33,34]. CeO₂ can create oxygen vacancies, which can eliminate carbon deposition by activating species of oxygen [34]. The ceria redox cycle between Ce³⁺ and Ce⁴⁺ helps to exude carbon deposited on the catalyst via oxygen vacancies [35]. Additionally, it was reported that CeO₂ can increase catalytic activity by enhancing the dispersion of surface-active components and the strong interaction between Ni and CeO₂ inhibits crystal growth [36,37]. Cesium minimizes nickel size by enhancing Ni dispersion [38]. The redox chemistry, heat stability, and oxygen-transporting capability of Zr can significantly enhance the catalytic behavior of nanocatalysts [39,40].

The objective of this research work is to evaluate the effect of the partial substitution of lanthanum in the catalyst LaNi_0.9Zr_0.1O₃ for cerium and zirconium for yttrium and to determine the catalytic activity and stability of each of the prepared catalysts for the CO₂ reforming of methane.

2. Results and Discussion

2.1. BET (Brunauer–Emmett–Teller) Analysis

The specific surface area of the catalysts based on the BET method range from 2 to 9 m²/g as shown in

Table 1. Specific surface area (SSA), Pore volume (Pv), and Pore diameter (Pd) of the fresh catalyst samples.

Samples	SSA, m2/g	Pv, cm3/g	Pd, nm
CsNi0.9 Zr0.1O3	5.19	0.029	25.33
LaNi0.9 Zr0.1O3	5.33	0.027	25.82
CeNi0.9 Zr0.1O3	9.35	0.031	12.12

and

Table 2. Specific surface area (SSA), Pore volume (Pv) and Pore diameter (Pd) of the fresh catalyst samples.

Samples	SSA (m2/g)	Pv (cm3/g)	Pd (nm)
La0.6Ce0.4Ni0.9Zr0.1O3	8.36	0.065	35.32
La0.6Ce0.4Ni0.9Zr0.05Y0.05O3	3.24	0.01	16.02
La0.6Ce0.4Ni0.9Zr0.03Y0.07O3	2.47	0.011	26.62
La0.6Ce0.4Ni0.9Zr0.01Y0.09O3	2.64	0.011	22.43

. The specific surface area of the samples is low due to the exposure of the precursor oxides to high temperatures; this is comparable with reported values in the literature [41]. From Table 2, the increase in the amount of yttrium does not significantly affect the surface area of the catalysts. Based on the IUPAC (International Union of Pure and Applied Chemistry) classification, the hysteresis loop of CeNi_0.9 Zr_0.1O₃ is comparable to the H3 type, as shown in Figure 1. The isotherms of yttrium-containing samples shown in Figure 2 are similar in shape and comparable to type III. The surface area of CeNi_0.9 Zr_0.1O₃ is slightly higher than La_0.6Ce_0.4Ni_0.9 Zr_0.1O₃ and exhibits the highest surface area among the samples, with an isotherm comparable to type IV. The samples have particle sizes ranging from 12 to 35 nm. The isotherm curves shown in Figure 1 and Figure 2 suggest that the materials are mesoporous with a pore diameter greater than 2 nm but less than 50 nm [40].

2.2. Temperature-Programmed Reduction (TPR)

The active sites for the catalyst MNi_0.9Zr_0.1O₃ (M = La, Ce, and Cs) samples are Ni and Zr. The reducibility was determined as shown in Figure 3 and Figure 4. The reduction peaks are shown in the lower and moderate temperature regions. The TPR plot suggests that there was more than one element undergoing reduction. The peaks in the moderate temperature region can be attributed to the reduction of Ni³⁺ to Ni²⁺. Generally, the reduction becomes easier when the energy of the metal-oxygen bond decreases [41]. The cerium catalyst was reducible at lower temperatures than the lanthanum catalysts (Figure 3). The addition of yttria to lanthanum and cerium catalysts tends to move the reduction peak to the lower temperature region, with one reduction peak shown in Figure 4.

2.3. X-ray Diffraction (XRD) Analysis

The XRD peaks of the catalysts are depicted in Figure 5. The XRD peaks confirmed the formation of a monoclinic phase of zirconium at 2θ = 35.3° [41]. Peaks observed from the XRD include CeO₂, NiO, and ZrO₂ oxides. The rhombohedral phase of LaNiO₃ (JCPDF 34-1028) is in agreement with peaks 2θ = 23.6°, 32.9°, 47.3°, and 60.0° [13]. For the CeNi_0.9Zr_0.1O₃ catalyst, the intensity of the peaks at 2θ = 45.2° is higher, indicating that the substitution of La by Ce resulted in the formation of discrete crystalline phase of CeO₂. The Ni in the Ce-Ni systems exists as NiO at the surface of the ceria and Ni²⁺ ions in the CeO₂ lattice [13].

2.4. Scanning Electron Microscope (SEM) Analysis

Figure 6 shows the SEM images of fresh MNi_0.9Zr_0.1O₃ (M = La, Ce, and Cs) catalysts. CeNi_0.9Zr_0.1O₃ and LaNi_0.9Zr_0.1O₃ catalysts appear to have irregularly shaped particles since both Ce and La belong to the same group in the periodic table. CsNi_0.9Zr_0.1O₃ appears to have a less coarse surface.

2.5. Transmission Electron Microscope (TEM) Analysis

The TEM analysis for both the fresh and spent catalysts are illustrated in Figure 7, Figure 8, Figure 9 and Figure 10 at 100 and 200 nm magnifications. For the used La_0.6Ce_0.4Ni_0.9Zr_0.01Y_0.09O₃ catalyst, the particles look dispersed with the carbon aggregating on a particular spot, while for the CeNi_0.9Zr_0.1O₃ catalyst, clumsy particles are shown with the carbon spreading across the surface. The nickel particle size distribution expressed in nanometers is plotted for each of the TEM images, with that of the spent catalyst higher than the fresh catalyst samples. From

Table 3. Nickel particle size derived from TEM analysis.

Catalyst Names	Ni Particle Size
Fresh CeNi0.9Zr0.1O3	9.44 nm
Used CeNi0.9Zr0.1O3	11.68 nm
Fresh La0.6Ce0.4Ni0.9Zr0.01Y0.09O3	5.68 nm
Used La0.6Ce0.4Ni0.9Zr0.01Y0.09O3	8.05 nm

, the La modification of catalysts significantly reduced the crystalline nickel size from 9.44 nm to 5.68 nm, which further proves the influence of uniform Ni distribution by La, which enhances the catalyst activity.

2.6. Catalyst Activity

The CH₄ conversion was >75%, CO₂ conversion >85%, and H₂/CO >0.90, as shown in Figure 11 for the CeNi_0.9Zr_0.1O₃ catalyst. The CsNi_0.9Zr_0.1O₃ catalyst displayed CH₄ conversion >70%, CO₂ conversion >80%, and H₂/CO >0.90, while the LaNi_0.9Zr_0.1O₃ catalyst displayed CH₄ conversion >65%, CO₂ conversion >75%, and H₂/CO >0.90 for the DRM reaction performed at 1073 K for 7 hours’ time on stream. CeO₂ modifies the catalytic features of nickel-based catalysts in DRM based on its redox features and enables it to support CO₂ activation (Ce₂O₃ + CO₂ → 2CeO₂ + CO) [42,43]. The value of the H₂/CO ratio theoretically equals one but side reactions in the DRM experiment influence its actual value. The H₂/CO ratio values for the tested catalyst are slightly greater than one; hence, the Boudouard reaction is predominant [18]. The CeNi_0.9Zr_0.1O₃ catalyst shows better activity due to the abundance of oxygen vacancies, thereby creating more active sites. Studies have suggested that surface oxygen vacancy is responsible for the activation of methane. Cerium possesses a high enough capacity for oxygen storage and high mobility of lattice oxygen to improve catalytic behavior. An investigation of the influence of cerium on nickel-based catalysts for hydrogen production suggests that the addition of the right amount of cerium can increase oxygen vacancy formation, which can activate oxygen-containing compounds to react with a carbon species as soon as it forms. Lanthanum improved catalytic stability in the dry reforming of methane. The availability of La could lead to La₂O₂CO₃; coke deposited on the interface between Ni and La₂O₂CO₃ can be gasified via the reaction La₂O₂CO₃ + C → La₂O₃ + 2CO. This reaction effectively suppresses coke formation on the catalyst.

A varying amount of Y was used to modify the catalyst La_0.6Ce_0.4Ni_0.9Zr_0.1O₃ and the reaction was carried out at 1073 K to evaluate the effect of Y loading on the modified catalyst. The La_0.6Ce_0.4Ni_0.9Zr_0.1−xY_xO₃ (x = 0.05, 0.07, and 0.09) catalyst’s activity increases when the Y loading increases, as shown in Figure 12. The activity of La_0.6Ce_0.4Ni_0.9Zr_0.05Y_0.05O₃ is lower than the unmodified catalyst, hence the need to increase yttrium loading to 0.07 Y and 0.09 Y. The La_0.6Ce_0.4Ni_0.9Zr_0.1−xY_xO₃ catalyst’s activity increases with the increase in yttrium loading. The activities of the yttrium-modified catalysts La_0.6Ce_0.4Ni_0.9Zr_0.03Y_0.07O₃ and La_0.6Ce_0.4Ni_0.9Zr_0.01Y_0.09O₃ are higher than the unmodified La_0.6Ce_0.4Ni_0.9Zr_0.1O₃ catalyst, with the latter having methane and carbon dioxide conversion values of 84% and 87%, respectively, and the former having methane and carbon dioxide conversion values of 86% and 90% for La_0.6Ce_0.4Ni_0.9Zr_0.03Y_0.07O₃ and 89% and 91% for La_0.6Ce_0.4Ni_0.9Zr_0.01Y_0.09O₃, respectively. Yttrium results in the formation of oxygen vacancies that are believed to contribute to improved catalytic activity. Y₂O₃ as a basic carrier allows Ni catalyst to be easily reduced and have better activity. Yttrium led to smaller Ni crystallites and enhanced the dispersion of active sites. Furthermore, doping ceria with yttrium was reported to enhance the number of oxygen vacancies and oxygen mobility. Ions of Ce³⁺ (0.97 Å) can be replaced by Y³⁺ (1.04 Å) and form a solid solution due to their similar ionic radii. La improves the interaction between the active component and the carrier, causing the even distribution of the Ni, which can be determined from SEM/EDX analysis [44]. Cerium possesses a high enough capacity of oxygen storage and high mobility of lattice oxygen to improve catalytic behavior [45]. CeO₂ can create oxygen vacancies, which can eliminate carbon deposition by activating species of oxygen [35]. The ceria redox cycle between Ce³⁺ and Ce⁴⁺ helps to exude carbon deposited on the catalyst via oxygen vacancies [34]. Additionally, it was reported that CeO₂ can increase catalytic activity via enhancing the dispersion of the surface-active component and the strong interaction between Ni and CeO₂ inhibiting crystal growth [36,37].

Table 4. Comparison of the results of this work with those of the literature.

Catalyst Constituents	Operating Temperature	Product/Conversion	Ref.
La0.95Ce0.05NiO3	1023 K	CH4 = 50 CO2 = 60	[36]
La0.6Ce0.4NiO3	1023 K	CH4 = 47 CO2 = 58	[36]
La0.3Ce0.7NiO3	1023 K	CH4 = 30 CO2 = 36	[36]
La0.9Ce0.1Ni0.9Zr0.1O3	1073 K	CH4 = 40 CO2 = 60	[45]
La0.9Ce0.1Ni0.8Zr0.2O3	1073 K	CH4 = 60 CO2 = 80	[45]
La0.9Ce0.1Ni0.7Zr0.3O3	1073 K	CH4 = 10 CO2 = 20	[45]
La0.6Ce0.4Ni0.9Zr0.1O3	1073 K	CH4 = 84 CO2 = 87	[this work]
La0.6Ce0.4Ni0.9Zr0.05Y0.05O3	1073 K	CH4 = 80 CO2 =85	[this work]
La0.6Ce0.4Ni0.9Zr0.03Y0.07O3	1073 K	CH4 = 86 CO2 = 90	[this work]
La0.6Ce0.4Ni0.9Zr0.01Y0.09O3	1073 K	CH4 = 89 CO2 = 91	[this work]

exhibits the results of this work compared to the literature. This table denotes the suitability of the synthesized catalysts in this process. The addition of yttria to the catalyst system enhances the activity performance as compared to previous work without yttria.

2.7. Thermogravimetric Analysis of the Used Catalyst (TGA)

The amount of coke deposited on the catalysts was determined by TGA analysis after 7 h on stream, as depicted in Figure 13. The weight loss step is in the temperature range of 773 K–973 K, with the carbon deposition of CsNi_0.9Zr_0.1O₃ being severe. The amount of carbon deposited on the La_0.6Ce_0.4Ni_0.9Zr_0.1O₃ catalyst is the lowest, indicating that La improved carbon formation resistance [26]. Although, after adding La, carbon deposits exist in the form of filamentous carbon. Adding La does not only change the way carbon deposition occurs, but may also limit it to some extent [44].

2.8. RAMAN Analysis

Raman spectra of the used catalysts depict two bands with Raman shifts in the range of 950 ± 5 cm⁻¹ and 1100 ± 10 cm⁻¹, as shown in Figure 14A, and of 1574 ± 5 cm⁻¹ and 2650 ± 10 cm⁻¹, as shown in Figure 14B corresponding to D and G bands, respectively. The D band is related to coke deposits with imperfect or disordered structures (amorphous carbon), while the G band is a related to well-ordered structures (graphitic carbon). The value of the ID/IG ratio of the spent catalysts is relatively close. There is an increase in the Raman shift with the modified catalyst with yttrium.

3. Experimental Section

3.1. Catalyst Preparation

The catalysts were prepared by the sol–gel method with propionic acid acting as a solvent, to dissolve nitrates of each metal. In the preparation, La(NO₃)₃·6H₂O (Sigma), Ni(NO₃)₂·6H₂O (Sigma), Ce(NO₃)₃·6H₂O (Sigma), Cs(NO₃)₃·6H₂O (Sigma), Y(NO₃)₃·6H₂O (Sigma) ZrO(NO₃)₂·6H₂O (Sigma) and propionic acid (C₃H₆O₂, Sigma) were used. The nitrates were separately dissolved in propionic acid, stirred, and heated at T = 363 K with oil as a heating medium in a closed vessel. Afterward, the solutions were mixed and stirred continuously for about 2 h at T = 403 K. Thereafter, the propionic acid was evaporated using a rotary evaporator at T = 343 K until a gel was formed. The gel obtained was dried at T = 363 K overnight, and calcined at 998 K for 4 h. The calcined catalysts were ground into powder and used for the DRM reaction.

3.2. Catalytic Testing

The catalysts were tested for DRM at 1073 K reaction temperature under atmospheric pressure. A packed bed stainless-steel reactor (internal diameter, 0.0091 m; height, 0.3 m) was used to perform the experiments. A catalyst mass of 0.10 g was positioned in the reactor over a ball of glass wool. Stainless steel, sheathed thermocouple K-type, axially positioned close to the catalyst bed was used to determine the temperature during the reaction. Preceding the reaction, activation of the perovskite catalysts was achieved at 973 K in an atmosphere of H₂. This lasted for 60 min and the remnant H₂ was purged with N₂. During the dry reforming reaction, the feed volume ratio was kept at 3:3:1 for CH₄, CO₂, and N₂ gases, respectively, with a space velocity of 42 L/h·gcat. The outlet gas from the reactor was connected to an online Gas Chromatograph (GC) with a thermal conductivity detector to analyze its composition. The CH₄, CO₂ conversion, and H₂/CO (syngas ratio) were calculated using Equations (4)–(6):

$$\mathrm{Methane} \mathrm{conversion} \left(\%\right)=\frac{{\mathrm{CH}}_{4,\mathrm{in}}-{\mathrm{CH}}_{4,\mathrm{out}}}{{\mathrm{CH}}_{4,\mathrm{in}}}\ast 100$$

(4)

$$\mathrm{Carbon} \mathrm{dioxide} \mathrm{conversion} \left(\%\right)=\frac{{\mathrm{CO}}_{2,\mathrm{in}}-{\mathrm{CO}}_{2,\mathrm{out}}}{{\mathrm{CO}}_{2,\mathrm{in}}}\ast 100$$

(5)

$$\mathrm{Syngas} \mathrm{Ratio}=\frac{\mathrm{mole} \mathrm{of} {\mathrm{H}}_2 \mathrm{produced}}{\mathrm{mole} \mathrm{of} \mathrm{CO} \mathrm{produced}}$$

(6)

3.3. Determination of Catalyst’s Physicochemical Properties

3.3.1. Nitrogen Physisorption

The catalyst’s surface area and the pore size distribution were measured by N₂ adsorption–desorption at 77 K using a Micromeritics Tristar II 3020 for porosity and surface area analyzer.

3.3.2. Temperature Programmed Reduction (TPR) Analysis

An amount of 70 mg of the sample was loaded inside the TPR sample holder of a Micromeritics apparatus. Thereafter, TPR measurements were performed at 423 K using Ar gas for 30 min. Afterward, the sample was cooled to ambient temperature. The next step involved heating by the furnace up to 1073 K ramping at 283 K min⁻¹, in an atmosphere of H₂/Ar mixture (1:9 vol. %) flowing at 40 mL/min. The thermal conductivity unit recorded the consumption of H₂ during the operation.

3.3.3. Thermo-Gravimetric Analysis (TGA)

The quantity of carbon deposited on the spent catalysts was measured by the TG analysis. Here, a platinum pan was filled with 10–15 mg of the used catalysts. Heating was carried out from room temperature up to 1273 K at 293 K min⁻¹ temperature ramp. Change in mass was constantly monitored as the heating progressed.

3.3.4. X-ray Diffraction (XRD) Analysis

The X-ray Diffraction patterns of the perovskite catalysts were recorded on a Miniflex Rigaku diffractometer that was equipped with Cu Kα X-ray radiation. The device was run at 40 kV and 40 mA.

3.3.5. Transmission Electron Microscopy (TEM)

Transmission electron microscopy (JEOL JEM-2100F) with high resolution to give larger magnification was used to carry out the TEM measurement of both the fresh and used catalysts. The electron microscope operated at 200 kV produces the active metal nickel particle sizes and depicts the morphology of carbon deposited on the used catalyst. Before the TEM measurement, the catalysts were first dispersed ultrasonically in ethanol at room temperature. Thereafter, the drop from the suspension was placed in a lacey carbon-coated copper grid to produce the images.

3.3.6. Laser Raman (NMR-4500) Spectrometer

Laser Raman (NMR-4500) Spectrometer (JASCO, Japan) was used to record Raman spectra of the spent catalyst samples. The wavelength of the excitation beam was set to 532 nm, and an objective lens of 100× magnification was used for the measurement. The laser intensity was adjusted to 1.6 mW. Each spectrum was received by averaging 3 exposures on 10 s. Spectra were recorded in the range 1200–3000 cm⁻¹ (Raman shift) and were processed by using Spectra Manager Ver.2 software (JASCO, Tokyo, Japan).

4. Conclusions

The activity of the LaNi_0.9Zr_0.1O₃ catalyst was significantly improved by partial substitution with cerium, which enhances catalyst activity due to the abundance of oxygen vacancies. The methane conversion activity of the best-modified catalyst (La_0.6Ce_0.4Ni_0.9Zr_0.01Y_0.09O₃) is significantly higher than the base catalyst (LaNi_0.9Zr_0.1O₃). La_0.6Ce_0.4Ni_0.9Zr_0.1O₃ activity is higher than the modified catalyst at 0.05 Y, but lower than 0.07 Y and 0.09 Y, which suggests that the activity of the modified catalyst increases above 0.05 Y. The catalyst activity increases with an increase in yttrium loading, with the La_0.6Ce_0.4Ni_0.9Zr_0.01Y_0.09O₃ catalyst having the best activity with a CH₄ conversion >89% and CO₂ conversion >91%. The Raman analysis suggests that carbon deposits on the catalysts are graphitic carbon. La_0.6Ce_0.4Ni_0.9Zr_0.1O₃ has the least carbon, indicating that La improved the carbon formation resistance since thermal resistance is controlled by A-cations. Furthermore, the amount of carbon deposited on the catalyst decreases with the increase in zirconium amount; hence, zirconium also enhances catalyst stability. Supplementary characterization has been explained in the Supplementary Materials.