The Effect of Calcination Temperature on Various Sources of ZrO₂ Supported Ni Catalyst for Dry Reforming of Methane

Abstract

Dry reforming of methane (DRM) over an Ni-based catalyst is an innovative research area due to the growing environmental awareness about mitigating global warming gases (CH₄ and CO₂) and creating a greener route of synthesis. Herein, 5% Ni supported on ZrO₂ obtained from various sources was prepared by the impregnation method. The catalysts were calcined at 600, 700, and 800 °C. Furthermore, Ni-RC stabilized with MgO, SiO₂, TiO₂, and Y₂O₃ were tested. Characterization techniques employed comprise the N₂ physisorption, infrared spectroscopy, Raman, thermogravimetric analysis, XRD, and TEM. The results of the present study indicated that the ZrO₂ support source had a profound effect on the overall performance of the process. The best catalyst Ni-RC gave an average conversion of CH₄ and CO₂ of 61.5% and 63.6% and the least deactivation of 10.3%. The calcination pretreatment differently influenced the catalyst performance. When the average methane conversion was higher than 40%, increasing the calcination temperature decreased the activity. While for the low activity catalysts with an average methane conversion of less than 40% the impact of the calcination temperature did not constantly decrease with the temperature rise. The stabilization of Ni-RC denoted the preference Y₂O₃ stabilized catalyst with average values of CH₄ and CO₂ conversion of about 67% and 72%, respectively. The thorough study and fine correlation will be advantageous for technologically suitable Ni-15Y-RC catalysts for DRM.

1. Introduction

Almost 85% of the total world’s energy comes from fossil fuels. Nevertheless, the combustion of various types of fossil fuels over a period of one and a half centuries, has caused numerous problems, denoted as global warming, caused by the release of greenhouse gases. In other words, the utilization of fossil fuels, covering the energy requirements of the world, is accompanied by intolerable air pollution due to the generation of greenhouse gases [1,2,3]. The world’s population is continuously increasing, and the burning of fossil fuels highly promotes the amount of atmospheric carbon dioxide and other heat-catching gases, resulting in climate change issues. CH₄ gas is a greenhouse gas that contributes to global world warming [4,5]. Dry reforming of methane (DRM) is a catalytic conversion method that reduces the emission of greenhouse gases CO₂ and CH₄ and transforms them into useful products. The product of the DRM CO and H₂ gases with an optimum H₂/CO ratio near to one is therefore beneficial for liquid hydrocarbon production via the Fischer–Tropsch synthesis [6,7]. The main reaction for DRM reaction is displayed in Equation (1), whereas the accompanying side reactions are given in Equations (2)–(4) [8]. Equation (2) represents the disproportionation, while Equation (3) denotes the methane cracking. Equation (4), commonly termed as reverse water–gas shift reaction, is the key method for the H₂O formation. Currently, DRM is the preferable research topic, as it displays outstanding performance in its capacity to reduce greenhouse gases [9]. DRM is an endothermic process that entails the use of high temperatures, which favors rapid catalyst deactivation and thus lowers its industrial applications.

This aspect renders the CH₄ to decompose and the coke to form, as shown in Equations (2) and (3). Supported metallic catalysts are usually employed for DRM. Transitional metals such as Ni are practically used [10,11,12]. Though noble metals perform pronounced activity and stability, their utilization is avoided, owing to their scarcity and high prices [13]. The supporting interactions and dispersion of active species determine the efficiency of the supported catalysts. The adjustment of Ni-based catalysts by various supports is an effective technique to diminish carbon formation and promote the lifetime of the catalyst:

$${\mathrm{CH}}_4+{\mathrm{CO}}_2\leftrightarrow 2{\mathrm{H}}_2+2\mathrm{CO}\hspace{1em}\Delta {\mathrm{H}}_{298\mathrm{K}}^0=247.31\frac{\mathrm{kJ}}{\mathrm{mol}},$$

(1)

$$2{\mathrm{CO}}_{}\leftrightarrow {\mathrm{C}\mathrm{O}}_2+\mathrm{C}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}{\Delta \mathrm{H}}_{298\mathrm{K}}^0=-172.44\frac{\mathrm{kJ}}{\mathrm{mol}},$$

(2)

$${\mathrm{CH}}_4\leftrightarrow 2{\mathrm{H}}_2+\mathrm{C}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\Delta {\mathrm{H}}_{298\mathrm{K}}^0=74.87\frac{\mathrm{kJ}}{\mathrm{mol}},$$

(3)

$${\mathrm{H}}_2+{\mathrm{CO}}_2\leftrightarrow {\mathrm{H}}_2\mathrm{O}+\mathrm{CO}\hspace{1em}\hspace{1em}\Delta {\mathrm{H}}_{298\mathrm{K}}^0=-41.17\frac{\mathrm{kJ}}{\mathrm{mol}}.$$

(4)

Many investigators synthesized appropriate catalysts by using numerous supports such as Al₂O₃, SiO₂, ZrO₂, etc. [14]. Basic supports like ZrO₂ are found to accelerate the CO₂ adsorption and decomposition, giving a strong metal-support interaction for reduced coke deposition [15]. Another property of catalyst support, which was found to be very useful for reforming methane, is oxygen storage capacity. The supporting merit in DRM is to give a stable, wide surface area to efficiently disperse the active phase and inhibit its sintering, and to contribute to the reaction mechanism through activation of CO₂ [16,17]. ZrO₂ is among the most universally used zirconium compounds in nature. Its phases of crystallization comprise cubic, monoclinic, and tetragonal [18,19,20] at ambient pressure. The major phase depends rigorously on parameters such as temperature, doping, sample preparation method, oxygen vacancy, and crystallite size [21,22].

The calcination pretreatments modify the structures of the supports [23,24]. Several investigations were performed to display the influences of this parameter during the catalyst formulation [25,26,27,28,29,30,31,32]. Low calcination temperature might cause incomplete decomposition of the metal salt precursor, thereby reducing the active component, whereas high-temperature sinters the active species, reduces the specific surface area, and deforms the carrier structure [29]. The Fischer–Tropsch activities of the catalysts were examined with and without previous calcination. It was found that the calcination in the air increased the liquid product selectivity of all the catalysts towards the diesel fraction. On the other hand, Sun et al. elaborated the catalytic performance of DRM over nitrogen doped activated carbon (Co/AC-N) catalysts, focusing on the calcination temperature effects [33]. Their result displayed that the catalytic activity was influenced by the calcination temperature as it altered the Co²⁺/Co³⁺ molar ratio and the content of nitrogen functional groups.

In this investigation, we elaborated on the impact of different sources of zirconia support with amphoteric nature and the influence of different calcination temperatures on the overall catalyst efficiency towards the dry reforming CH₄ reaction. Thus, we synthesized 5% Ni supported on ZrO₂ via the impregnation technique and applied it to DRM. The ZrO₂ was obtained from diverse sources. We sorted the broad effects of calcination, on the performance of 5%Ni/ZrO₂ catalyst. The substantial alterations in the catalyst structure and surface effects ascribed to the calcination were fully elaborated. The catalysts were calcined at 600 °C, 700 °C, and 800 °C.

2. Results and Discussion

Figure 1 presents the N₂ physisorption profiles of the catalysts. The N₂ physisorption isotherms of catalysts indicate the type IV isotherm with an H1 hysteresis loop at higher relative pressure, which is in line with the International Union of Pure and Applied Chemistry (IUPAC) classification, which designates that most of the pores are cylindrical in shape with an ordered mesoporous framework. The figure displays an intense rise at P/Po = 0.75 in the second half of the isotherm, owing to capillary condensation in inter particular mesopores/macropores. This matches the state where the adsorbate critical temperature is higher than the adsorption temperature. Mesoporous supports would also help the formation of active carbon, which has a habit of prompt gasification. The N₂-physisorption, of Ni-RC and Ni-ZH catalysts showed similar trends and the extent of N₂-physisorption decreased with the calcination temperature in accordance with the surface area measurement. The strong loss of surface area on the increasing calcination temperature is very common with the ZrO₂ system due to the sintering of strong ZrO₂ crystallite into bigger and denser aggregate [34,35]. Chan et al. carried out different calcination temperatures in preparation of ZrO₂ and found very similar results to our ZrO₂ supported Ni catalyst [34]. Chan et al. also found that phase transformation had an insignificant role in the decrease of surface area at high temperatures [34]. Figures S2–S4 display the pore size distribution of the catalysts at different calcination temperatures. The result indicates that the pore sizes are mesoporous, and that the higher calcination temperature increases the porosity. The catalysts displayed pore volume rise along with the pore size at lower pore size values.

The N₂ physisorption results and crystalline size of 5%Ni/ZrO₂ catalysts for different calcination temperatures are displayed in

Table 1. N₂ physisorption results and crystalline size of 5%Ni/ZrO₂ catalyst for different calcination temperatures.

Catalyst	Calcination Temp. (°C)	BET (m2/g)	VPore (cm3/g)	DPore (nm)
Ni-MK	600	3.5	0.02	29.9
	700	3.2	0.02	41.4
	800	2.7	0.02	34.9
Ni-ZH	600	43.2	0.16	15.5
	700	9.8	0.05	24.8
	800	10.0	0.05	24.8
Ni-DK	600	19.6	0.16	39.7
	700	14.8	0.12	39.2
	800	13.2	0.12	49.7
Ni-EN	600	24.4	0.21	37.5
	700	15.5	0.13	38.6
	800	16.0	0.13	37.6
Ni-RC	600	50.4	0.27	21.5
	700	17.7	0.12	31.7
	800	18.7	0.12	31.1

.

The 5%Ni/ZrO₂ calcined catalysts and pristine supports were examined via FT-IR to pinpoint different kinds of bonds. Figure 2 exhibited bands positioned around 510 and 580 cm⁻¹ characteristics for Ni-O and Zr-O widening vibrations [34], whereas ZrO₂ was ascribed to the band around 730–750 cm⁻¹.

The performance of the catalysts for various calcination temperatures was carried out in terms of methane and carbon dioxide conversions (Figure 3). The deactivation factor was also calculated.

Table 2. The performance evaluation of catalysts.

Catalyst	Calcination Temperature (°C)	Conversion (%)				Carbon Deposits (%)	Deact. Factor (DF) (%)
		CH4		CO2
		Initial	Final	Initial	Final
Ni-MK	600	21.9	20.1	32.6	30.1	12.7	8.2
	700	46.0	36.3	54.2	46.4	46.7	21.1
	800	36.5	22.9	39.6	34.0	14.0	37.3
Ni-ZH	600	59.3	44.9	61.3	55.5	75.0	24.3
	700	62.2	45.3	69.5	57.9	38.1	27.2
	800	55.0	38.5	55.1	49.2	61.2	30.0
Ni-DK	600	52.3	36.1	57.7	49.2	48.5	31.0
	700	50.6	32.7	49.3	45.0	63.4	35.4
	800	47.5	34.7	57.2	48.6	53.3	26.9
Ni-EN	600	44.6	30.3	53.2	42.1	17.3	30.5
	700	42.3	31.9	52.8	43. 9	25.1	24.6
	800	45.1	28.3	52.6	39.3	27.8	37.25
Ni-RC	600	67.6	46.5	66.8	61.7	60.6	1.63
	700	67.4	46.5	68.4	58.2	65.8	31.0
	800	64.4	76.4 *	66.8	59.5 *	68.7	−1.7

Coke = obtained from TGA after 7 h reaction time; % DF after 7 h reaction time = (Starting methane conversion—Last methane conversion)/Starting methane conversion × 100; Initial = 20 min; Final = 420 min; * final = 280 min.

provides the results of the performance. The result indicates that the catalysts possess different activities with respect to the source type. Conversions of methane and carbon dioxide declined with time during the reaction as a result of deactivation. The relatively higher conversion of CO₂ is attributed to the reverse water gas shift reaction, which further consumed CO₂ to generate CO, in accordance with Equation (4).

The calculated deactivation factors of CH₄ conversion over Ni-MK, Ni-ZH, Ni-DK, Ni-EN, and Ni-RC are 22.2%, 27.2%, 31.1%, 10.3%, and 10.3%, respectively. The results of Table 2 show the TGA values of the catalysts. It is apparent that the less active catalysts Ni-Mk and Ni-EN provide an average low value of TGA. This could be related to the poor performance, which causes less carbon to accrue [23,35]. The calcination pretreatment affects the catalyst performance differently. For instance, for the relatively high activity catalysts with an average methane conversion higher than 40% such as Ni-RC, Ni-ZH, and Ni-DK, increasing the calcination temperature decreases the activity. While for the low activity catalysts with average temperatures lower than 40%, the calcination impact fluctuated. For example, the Ni-MK catalyst’s activity increases from 600 °C to 700 °C calcination and then drops from 700 °C to 800 °C, while for Ni-EN catalyst, the activity increases when increasing the calcination temperature from 600 °C to 700 °C and then decreases from 700 °C to 800 °C. The variation of the catalyst with calcination temperatures may be related to the changes in ZrO₂ morphologies, which could show the various oxygen mobility and diverse capacity of metal-support synergies. The aspects of zirconia influenced coke removal and thermal sintering of Ni. The study of the effects of zirconia source and the calcination temperature resulted in the superiority of the Ni-RC catalyst calcined at 700 °C. The Raman instrument offers further evidence about the graphitization degree and the kind of carbon on the used catalysts. Figure 4 displays the Raman spectra of the used catalysts. The spectra are divisible into zones. Zone I lies between 1250 and 1650 cm⁻¹ and zone II occurs between 2400 and 3000 cm⁻¹. In the range between 1250 and 1650 cm⁻¹, the dominant characteristic peaks, D-band and G-band, are situated at 1341 cm⁻¹ and at 1568 cm⁻¹, respectively. The D-band is attributed to carbon deposits with imperfect structures that are disordered (amorphous) [36] and the G-band represents graphite. Because of the unification and implications of the band of zone I, the 2D band appears at 2666 [36]. The extent of carbon crystallinity formed during the reaction is appropriately assessed from the relative intensity sizes of the G and D bands (ID/IG). Minor ratios specify the supremacy of crystallinity owing to the graphitized carbon. For the examined catalysts, the readings of ID/IG were 0.50, 0.92, 0.92, 0.87, and 0.53 for the Ni−MK, Ni−ZH, Ni−EN, Ni−RC, and Ni-DK, in that order. The Ni−Mk and Ni-ZH catalysts exhibited the highest (ID/IG) ratios, indicating low crystallinity owing to the deficiency of graphitized carbon Therefore, the crystallinity of the Ni−Mk and Ni-ZH catalyst is less pronounced than other catalysts, and its graphitization degree was evidently diminished. The degree was obviously diminished.

The thermogravimetric analysis (TGA) was performed on the catalysts after reaction to evaluate the amount of carbon formed on the catalysts. As depicted in Figure 5, the weight loss that started at about 550 °C arises from the removal of different types of carbon species. The amount of carbon deposited for Ni-RC is as follows: 60.0%, 65.8%, and 68.8% for calcination temperatures of 600, 700, and 800 °C, respectively, denoting the rise of calcination temperature, which increases the carbon formation and hence reduces the stability. The TGA values for all catalysts are recorded in Table 2.

Further studies were performed by stabilizing the Ni-RC catalyst and calcining it at 700 °C. The stabilizers used include MgO, SiO₂, TiO₂, and Y₂O₃. The activity and stability results of the Ni supported on stabilized zirconia (RC) catalysts calcined at 700 °C are displayed in Figure 6. The Y₂O₃ stabilized catalyst outperforms the other catalysts, and it gave average conversions of CH₄ and CO₂ of 67.2% and 72%, respectively. The stability investigation of the best catalyst obtained (Ni-15Y-RC) is given in Figure S5. The performance of Ni-15Y-RC appears to be promising when compared to literature data obtained by other research teams on ZrO₂-based catalysts.

Table 3. Performance comparison of the present result with that of other studies.

Catalyst	Reaction Temperature (°C)	GHSV (mL/(g·h))	Average * CH4 Conversion (%)	Ref.
5%Ni/La+Zr	700	8000	66	[36]
0.1%Ni/Ce+Zr	850	3000	38	[37]
15%Ni/perlite+Zr	700	60,000	79	[38]
15%Ni+Co/Al+-Zr-I	850	24	72	[39]
5%Ni+Co/Al+Zr	550	24	18	[40]
5%Ni/PO4+Zr	800	13,000	45	[12]
Ni/Al2O3	700	42,000	53	[41]
Ni/MCM-41	800	39,000	85	[42]
Ni/SiO2	700	24,000	41	[43]
3Ni/SBA-15	800	15,000	72	[44]
Ni/La+Zr	700	8000	70	[36]
10 wt.% Ni/SA-5239	700	680	70	[8]
5%Ni/Y+Zr	700	42,000	67	Present work

* The mean of initial and final conversions.

displays the performance comparison to literature data.

The X-ray diffraction analysis of the fresh catalysts was done to determine their crystallinity and structure. The peaks of fresh catalysts are exhibited in Figure 7. The Ni diffractions are specked at two theta values of 37.6° and 42.8°. The peaks at 18.2°, 24.0°, 27.8°, 63.2°, 69.9°, 75.7°, and 82.6° are assigned to the monoclinic ZrO₂ (JCPDS file No. 81–1314). Alternatively, the tetragonal ZrO₂ diffraction peaks are situated at 29.9°, 34.3°, 35.1°, 50.6°, and 59.8° [37]. It is found that non-stabilized Ni-RC and that of Ti and Mg stabilized catalysts indicate the presence of small NiO peaks. This means the addition of Ti and Mg stabilizers did not affect the structural distribution of NiO, while on the other hand, the absence of NiO peaks for the Si and Y stabilizers indicates the high dispersion of species in the zirconia matrix.

The TEM analysis of the best stabilized Ni-15Y-RC catalyst was performed for a better understanding of the surface morphology and carbon formation on the surface. Figure 8a,a’ shows the fresh catalyst, illustrating that the catalyst has good scattering and smaller active metal particles size, while Figure 8b,b’ shows the used catalyst where sintering or agglomeration has been noted, and the thin layers of multiwall carbon nanotubes.

3. Experimental

3.1. Materials

Nickel nitrate hexahydrate [Ni(NO₃)₂.6H₂O, 98%, Alfa Aesar]. ZrO₂ supports were obtained from different sources: MK (Canada); RC (Japan); ZH (Japan); DK (Japan), and EN (China). All the chemicals were of analytical grade and used without further purification. A fixed Ni loading of 5 wt.% was adopted.

The catalysts were prepared via the wet-impregnation technique. First, the solution with a stoichiometric amount of [Ni (NO₃)₃ 9H₂O] was prepared in double-distilled water, then ZrO₂/or ZrO₂ stabilized support was impregnated with the previously prepared solution of active metal salt. Then, mixing was carried out under constant stirring at 80 °C for at least 3 h. The mixture was then dried overnight at 120 °C and followed by calcination at the desired temperature for 3 h. The 5%Ni/ZrO₂ catalysts are referred to as Ni-MK, Ni-RC, Ni-ZH, Ni-DK, and Ni-EN. While the Ni-RC stabilized with 15%M (M = Mg, Ti, Si, and Y) catalysts are referred to as Ni-15Mg-RC, Ni-15Ti-RC, Ni-15Si-RC, and Ni-15Y-RC.

Table 4. Textural properties of various ZrO₂ supports: BET specific surface area (BET), pore volume (P_v), and pore size (D_P).

Country of Origin	Product Brand-Name	Abbreviated Name	BET (m2/g)	Pore-Volume (cm3/g)	Pore-Diameter (µm)
Tokyo, Japan (Daiichi Kigenso Kagaku Kogyo Co., Ltd.)	RC-100 (zirconia oxide)	RC	100	0.38	7.2
	Z-1325 (zirconia hydroxide)	ZH	371	0.36	3.6
	DK-1 (zirconia oxide)	DK	25	0.20	28.4
Hefei, China (Anhui Elite Industrial Co., Ltd.)	ELTN (zirconia oxide)	EN	28	0.21	32.5
Canada	MKnano (zirconia oxide)	MK	4	0.10	19.2

shows the textural properties of various ZrO₂ supports. The mathematical equation below is used for calculating the conversion of reactants (CH₄ and CO₂).

$$Reactant conversion \%=\frac{mol {\left(R\right)}_{in}-mol {\left(R\right)}_{out}}{mol {\left(R\right)}_{in}}\times 100.$$

(5)

3.2. Catalytic Testing

Dry reforming of CH₄ over 5%Ni/ZrO₂ catalysts was performed at 700 °C and at atmospheric pressure in a vertical stainless steel fixed-bed tubular (i.d., 9.1 mm; length, 0.3 m) micro-reactor (PID Eng and Tech micro activity). The set-up for the experiment, as shown in Figure S1, consists of three sections: the feed section where the cylinders containing feed gas such as CH₄, CO₂, N₂ are situated; the reaction section assembly, which consists of a microtubular reactor. The reactor temperature is measured with the aid of a K-type-thermocouple touching the catalyst bed. The product gases from the reaction section were sent for analysis to estimate the catalytic activity; the analysis section, where the reaction products together with feed mixtures were analyzed using an online gas GC system. The thermal conductivity detector contained in the GC was used to analyze the gas composition. Activity tests were performed using 0.1 g of catalyst. A thermocouple, placed axially at the center of the catalyst bed measures the temperature during the reaction. Prior to each test, the catalysts were activated with H₂ (20 mL/min) for 1 h at 700 °C. Experiments were carried out using a feed gas mixture (CH₄, CO₂, and N₂) at a ratio of 30/30/10 and space velocity: 42,000 mL/(h·gcat). The outlet gas composition was analyzed by online gas chromatography (GC-2014 Shimadzu Corp., Kyoto, Japan) fitted out with a thermal conductivity detector. CH₄ and CO₂ conversions were computed:

CH₄ conversion (%) = (CH_4,in − CH_4,out )/CH_4,in × 100; CO₂ conversion (%) = (CO_2,in − CO_2,out)/CO_2,in × 100; The deactivation factor (DF) after 7 h reaction time is calculated: DF (%) = (Starting methane conversion − Last methane conversion)/Starting methane conversion × 100.

3.3. Catalyst Characterization

The catalysts were characterized. The specific surface area of catalysts was done by nitrogen physisorption at −196 °C. A Micromeritics Tristar II 3020 unit was employed to acquire the surface area by standard Brunauer–Emmett–Teller (BET). Thermogravimetric analysis in atmospheric air via an EXSTAR SII TG/DTA 7300 analyzer was used to calculate the amount of carbon formation on the surface of used catalysts. A laser Raman (NMR-4500) spectrometer (JASCO, Tokyo, Japan) was used to provide the graphitization degree and the type of carbon deposited over the used catalysts. An excitation beam with a 532 nm wavelength was used. The structure of the spent samples was seized using a transmission electron microscope (TEM) “120 kV JEOL JEM-2100F”. TEM micrographs were documented at 120 kV. The crystal structure and the phases of fresh catalysts were examined with the X-ray diffractometer. A Miniflex Rigaku diffractometer, which has Cu Ka X-ray radiation, functioned at 40 kV and 40 mA, was used for the test. Data gathering was performed using a 2 h angle span of 10–85° and a step magnitude of 0.01°.

4. Conclusions

The current work comprised the development of 5%Ni-ZrO₂ and its stabilized catalysts through the impregnation method for dry reforming of methane. ZrO₂ acquired from different sources was employed as support. The stabilizers used were MgO, TiO₂, SiO₂, and Y₂O₃. The examination focused on the impact of using supports attained from diverse sources such as Canada, Japan, and China. Then, the performance was tested. The obtained catalysts were calcined at 600, 700, and 800 °C. BET, FT-IR, Raman, XRD, TEM, and TGA characterizations were used to investigate spent and fresh catalysts. The BET results point out average values ranging between 3 and 29 m²/g and showed that generally increasing the calcination temperature decreased the BET values. The Ni-RC catalyst presented the highest surface area and the highest activity performance towards DRM and the lowest deactivation factor of 10.3%. Ni-MK and Ni-EN catalysts presented the lowest average weight loss of 24.3% and 23.4%. This was due to their low activity behavior. The results of the FT-IR displayed the relevant characteristic transmissions bands for the Zr-O and Ni-O stretching vibrations at their respective locations. The Raman bands of the used samples assessed the amount of crystallinity of the carbon formed in the reaction. The crystallinity of the Ni−MK is more noticeable than other catalysts, and its graphitization degree was markedly improved. The Ni stabilized zirconia catalyst revealed the preference of the Y₂O₃ stabilizer. The XRD of the fresh stabilized catalysts depicted the presence of both monoclinic and tetragonal phases of ZrO₂ besides the NiO. The TEM analysis of the best stabilized Ni-15Y-RC catalyst revealed good scattering and small size of Ni in the fresh catalyst and Ni sintering or agglomeration with thin layers of multiwall carbon nanotubes in the used catalyst. The RC-100 supported Ni catalyst calcined at 700 °C gave the best performance in the DRM process.