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Article

Egg-Shell-Type MgAl2O4 Pellet Catalyst for Steam Methane Reforming Reaction Activity: Effect of Pellet Preparation Temperature

by
Yeon Jeong Yu
,
Eunkyung Cho
and
Chang Hyun Ko
*
School of Chemical Engineering, Chonnam Nation University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, Republic of Korea
*
Author to whom correspondence should be addressed.
Catalysts 2022, 12(12), 1500; https://doi.org/10.3390/catal12121500
Submission received: 12 October 2022 / Revised: 15 November 2022 / Accepted: 21 November 2022 / Published: 23 November 2022
(This article belongs to the Special Issue Catalysis on Stable Molecules (CO2, CO, CH4, N2, NH3) Activation and Their Transformation)
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Abstract

:
A pellet catalyst was prepared to be used in a large-scale steam methane reformer. Hydrotalcite powder (MG30) was used as a precursor to prepare MgAl2O4 pellet supports at different calcination temperatures. Ni-supported catalysts with egg-shell-type distribution were prepared on these pellet supports: Ni/sup-x (where x is the calcination temperature of the support with x = 1273, 1373, and 1473 K). Among them, Ni/sup-1473, which experienced the highest calcination temperature (1473 K), showed the highest methane conversion and lowest weight loss owing to carbon deposition. As a result, when the calcination temperature increased, the egg-shell thickness decreased, and the reducibility of the catalyst was enhanced. Although a small amount of Ni (3.5 wt%) was used, the egg-shell-type catalyst had superior catalytic activity and coke resistance. Therefore, the egg-shell-type catalyst using Ni as the active material and MgAl2O4 calcined at high temperature as the support is expected to be appropriate for large-scale industrial steam methane reforming reactions.

1. Introduction

The primary reason for global warming is the use of fossil fuels, which causes the emission of CO2 into the atmosphere [1]. To reduce global warming, hydrogen, which generates only H2O during combustion, can be used as a substitute for fossil fuels. However, the supply of hydrogen, as an energy carrier, is insufficient. At present, the only inexpensive method that can supply a large amount of hydrogen is to produce hydrogen through the steam methane reforming (SMR) reaction [2]. SMR is a reaction in which methane and steam react at high temperatures to produce hydrogen. The role of the catalyst is important for stable and efficient production of hydrogen in the SMR reaction [3]. When using a catalyst, suppressing coke generation is necessary to prevent catalyst deactivation [4,5]. Therefore, the catalyst should exhibit both high catalytic activity and resistance to coke deposition. SMR catalysts with these abilities have been extensively studied as powder-type catalysts, but not as pellet-type catalysts [6,7,8,9]. Furthermore, the conversion process of a powder catalyst into a pellet catalyst for large-capacity reformers has rarely been investigated. When preparing a pellet catalyst, many factors, such as productivity, reproducibility, size to prevent pressure drop, shape, and strength, should be considered. Commercial catalysts for the SMR reaction already exist; moreover, catalysts based on alumina supports, Ni, and various metal additives have been fabricated. Owing to the extremely fast reaction rate, the effectiveness factor of commercial catalysts was only 0.03–0.07 [10,11]. This implies that less than 10% of the total pellet volume was used because the reactant only reached the outside of the pellet and did not diffuse inside it. To overcome this problem, egg-shell-type pellet catalysts, in which the active metal (Ni or Ru) is concentrated on the surface of the pellet supports, have been proposed [12,13,14,15]. Egg-shell catalysts loaded with Ni or Ru on Al2O3 pellets showed excellent catalytic activity, but tended to be deactivated by carbon deposition due to the acidic sites of Al2O3. To lower the number of acid sites on the Al2O3 support, Cho et al. studied the synthesis of an egg-shell-type catalyst using MgAl2O4 with Mg as a support [16]. Owing to the alkali element, Mg could neutralize Al2O3 acid sites and be used to reduce carbon formation during hydrocarbon reforming reaction [17,18]. This effect also appeared when MgAl2O4 formed a spinel structure with Mg and Al2O3 [19]. The egg-shell-type catalyst, intensively impregnated with less than 5 wt% of Ni on the outer MgAl2O4 commercial pellet support (4 mm height, 4 mm diameter, and 2 mm inner hole diameter), had superior activity to the homo-type catalyst, which had a relatively high concentration of Ni. These egg-shell-type catalysts are resistant to carbon deposition and exhibit excellent catalytic activity at high space velocities in the SMR reaction. However, the MgAl2O4 support used in that study was not suitable for application to large-sized reformers because their small size may cause a pressure drop.
In this study, we developed large-sized MgAl2O4 pellets with inner holes (8 mm height, 8 mm diameter, and 3 mm inner hole diameter) not only for a low pressure drop, but also for egg-shell-type catalysts with remarkable physicochemical properties. The role and effect of the egg-shell-type catalyst were investigated by varying the strength and porosity of the support according to the calcination temperature. In addition, we studied the interaction between the MgAl2O4 support and Ni as the active material in the SMR reaction, depending on the calcination temperature of MgAl2O4. The egg-shell-type catalysts showed higher catalytic activity at a higher space velocity and lower coke deposition compared to that of the commercial catalyst with the same size and shape under various reaction conditions.

2. Results and Discussion

2.1. Analysis of Supports

To prepare thermally stable catalyst supports, it is necessary to convert MG30 with a hydrotalcite structure into MgAl2O4 with a spinel structure. The minimum temperature of first calcination was 973 K because MG30 was not converted into MgAl2O4 and separated into MgO and Al2O3 at this temperature [20]. Subsequently, the first calcination temperature of MG30 was changed from 973 to 1173 K. Before calcination, as shown Figure 1a, MG30 was a mixture of Al-CO3-OH, AlO(OH), MgAl2(OH)12CO3·3H2O, and Mg6Al1(CO3)(OH)16·4H2O. When MG30 was heat-treated at 973 K (Figure 1b), broad XRD peaks of MgAl2O4 and MgO appeared simultaneously. The MgAl2O4 diffraction peaks of the spinel structure appear at 31.4°, 36.9°, 38.5°, 44.8°, 55.7°, 59.4°, and 65.3° (JCPDS #21-1152). MgO existed as cubic magnesium oxide with weak and broad peaks located at 42.9° and 62.3° (JCPDS #45-0946). The weak and broad peaks mainly come from the segregation of MgO on MgAl2O4. As the calcination temperature increased, the spinel peaks became sharper and their intensity increased, whereas the MgO peaks became sharpwithout increasing intensity, as shown in Figure 1b–d. MgO is expected to suppress coke deposition because it is a basic oxide that neutralizes the acid sites of the Al2O3 support. Hence, MG30 was chosen as the precursor for the pellet support. Then, the calcined MgAl2O4 powder was placed in a mold and compressed into a pellet. These tableted MgAl2O4 pellets were calcined once more (second calcination) above 1173 K to improve their physicochemical stability. Figure 2 shows that the crystallinity of MgAl2O4 was enhanced after the second calcination. The XRD pattern of MG30 was used to compare the intensity and sharpness of the MgAl2O4 peaks with those of MG30, as shown in Figure 1a. The peaks of MgO, which were prominently confirmed during the first calcination, were difficult to observe in Figure 2. Compared with the peaks of MG30, the peak intensity of MgAl2O4 significantly increased after the second calcination. As shown in Figure 1, the peak intensity increased with increasing calcination temperature. The crystallinity and grain size of MgAl2O4 were determined depending on the final calcination temperature, which means that the characteristics of the support could be changed according to the support heating temperature.
As the SMR reaction in the bulk reactor was a highly endothermic reaction, the temperature gradient inside the reactor increased [21,22]. The reactor temperature could partially rise to ≥1073 K, maintaining the reactor at ≥973 K; hence, the catalyst used must maintain its structure even above 1073 K. The fabricated pellet, obtained by heating twice above 1173 K, is expected to be suitable for this reaction condition.
Nitrogen adsorption–desorption isotherms and corresponding analyses were performed to determine the porosity of the supports, which affected the catalytic activity. Although previous studies have indicated that powder-type MgAl2O4 could have a large specific surface area of up to 300 m2/g aftercalcination at lowtemperature [23,24], the prepared MgAl2O4 pellet used in this study had a narrow specific surface area and small pore volume, as shown in Figure 3 and Table 1. The MgAl2O4 pellets had smaller surface area and pore volume than the MgAl2O4 powder because they were not only calcined at high temperatures, but also molded using the high-pressure tableting method. As the calcination temperature was increased, the specific surface area and pore volume decreased. When the second calcination temperature was increased from 1273 K to 1473 K (Sup-1273 vs. Sup-1473), the specific surface area and pore volume of Sup-1473 were reduced by half and onethird (1/3), respectively, compared with those of Sup-1273.

2.2. Egg-Shell-Type 3.5 wt% Ni/MgAl2O4Pellet Catalysts

The properties of the catalysts with a 3.5 wt% Ni impregnated only on the outer surface of the pellet were analyzed. Figure 4 shows cross-sectional photographs of the synthesized catalysts. Although the Ni loading of 3.5 wt% was loaded in the same method, the thickness of the egg-shell (Ni deposition part) was different depending on the second calcination temperature. The egg-shell thickness of Ni/sup-1473, whose support had the smallest specific surface area and pore volume, was the thinnest. In addition, the Ni/sup-1473 interface between the egg-shell and the inside of the pellet without Ni became more distinct than the others. The following equation was used to quantify the degree of the Ni concentration gradient:
R = rNi/rpellet,
where R is the egg-shell ratio and the values of RNi/sup-1273, RNi/sup-1373, and RNi/sup-1473 were 0.30, 0.24 and 0.19, respectively. This implies that egg-shell thickness is affected by the porosity of the support.
Figure 5 shows the XRD patterns of all catalysts prepared by the egg-shell-type. The amount of Ni loaded was very low (3.5 wt%) compared to that of commercial catalysts (~15 wt%). However, Ni species were concentrated on the outer region of pellet. To examine the status of Ni species accurately, only the outer region of pellet, where Ni was present, was scraped off; then, the XRD analysis was performed. As shown in Figure 5, the main peaks indicate that the spinel structure of MgAl2O4 was the main component. When Ni was impregnated, the MgAl2O4 peaks became broad and the peak intensities decreased (Figure 5a,b compared with Figure 2b,c). Conversely, Ni/sup-1473 (Figure 5c) maintained excellent sharpness and intensity of the MgAl2O4 peaks. As shown in Figure 5, NiO showed peaks at 43.3° and 62.3° (JCPDS #44-1159), which are very close to the peaks of MgO 42.9° and 62.3°. Considering that the MgO peaks disappeared before loading Ni in Figure 2, the observed peaks can be assigned to NiO. In addition, the intensity of NiO peaks was low because the small amount of Ni was well distributed on the pellet. To further confirm that the peaks at 43.3° and 62.3° in Figure 5 could be attributed to MgO, the catalysts were reduced and the XRD analysis was performed. After reduction, the NiO peaks disappeared and a peak appeared at 51.8° corresponding to metallic Ni (JCPDS #04-0850) in Figure 6. This peak had very low intensity and was flat. It indicates that metallic Ni was highly dispersed on MgAl2O4 surface. Although the specific surface area of the support was small, the size of metallic Ni particles is expected to be very small.
H2-TPR analysis was performed to determine the reducibility of the NiO supported on each catalyst. The MgAl2O4 support was also analyzed simultaneously, as shown in Figure 7a. The amount of H2 consumed by the support was much smaller than the amount of H2 used by Ni-based catalysts. Thus, the amount of H2 consumed bythe support can be ignored in the Ni-based catalyst reduction. In many studies, the reduction of NiO has been the only pathway from ionic species (Ni2+) to metallic Ni (Ni0) [25]. Therefore, all the peaks in Figure 7 indicate that NiO was reduced. The TPR profile of Ni/sup-1273 shows a single peak at 1020 K, whereas those of Ni/sup-1374 and Ni/sup-1473 show three reduction peaks including that at 1020 K. The reduction peaks are related to the interaction between the Ni species and the support. The peaks at 750, 880, and 1020 K can be assigned to weak, medium, and strong interactions between the Ni species and the support, respectively [26,27]. Other studies reported that Ni2+ reduction above 1000 K occurred in NiAl2O4 to Ni0 or in the MgO–NiO solid solution [26,28,29]. As the synthesized support already had an excess of MgO, the strong interaction between the Ni species and the support may come from the excess MgO [30]. Therefore, most of the NiO on Ni/sup-1273 (Figure 7b) had strong interactions. Conversely, in Figure 7c,d, the second calcination temperature of the support increased the amount of NiO with weak and medium interactions at low temperatures. The reducibility of Ni can be controlled by the properties of the support, although the calcination temperature after Ni impregnation was the same. As Ni reduction occurred at temperatures above 700 K, the three synthesized catalysts appeared to have well-dispersed NiO because the reduction of bulk NiO occurred below 700 K [31]. Therefore, the reducibility of well-dispersed NiO improved with increasing calcination temperature of the MgAl2O4 support.

2.3. Catalytic Activity

2.3.1. Evaluation of the SMR Reaction According to Space Velocity

To compare the catalytic activities of the synthesized egg-shell-type catalysts, the SMR reaction was performed at a constant temperature of 1073 K with different space velocities ranging from 2500 to 10,000 h−1. A commercial catalyst (Com-catalyst: same size and shape as the synthesized catalysts) was used as the reference catalyst. As shown in Figure 8, at a higher space velocity, the catalyst with a thinner egg-shell had a higher methane conversion. The H2 yield also followed the same trend. In the case of the Com-catalyst, in which the active material was uniformly located inside the pellet, the conversion was lower even when the space velocity was low. As the conversion decreased, the H2 yield also decreased. Considering that the Ni loading of the Com-catalyst was approximately 15 wt%, which was four times higher than that of the egg-shell catalyst, the difference in methane conversion increased with increasing space velocity. In the case of egg-shell-type catalysts, all the methane conversions were over 90%, and Ni/sup-1474 had the best conversion among them at all space velocities. Although Ni/sup-1474 had the lowest specific surface area and pore volume, it exhibited remarkable catalytic activity because of the thinnest eggshell (RNi/sup-1473 = 0.19). The mass transfer limitation is a critical factor in controlling the SMR reaction [32,33,34]. However, the vigorous reaction on the outer catalyst was more important than the mass transfer to the inner catalyst in the large SMR reaction using a pellet catalyst. Therefore, an egg-shell-type catalyst is suitable when all reactants have a fast reaction rate and a high space velocity.

2.3.2. Evaluation of Durability and Resistance to Carbon Deposition

In addition to the conversion of reactants, the lifetime of the catalyst is also important. The major reason for the deactivation of the catalyst is carbon deposition and the consequent breakage of the catalyst pellets. A method to evaluate the deactivation and breakage of the catalyst by carbon deposition for a short time was applied, and the egg-shell-type catalyst and Com-catalyst were compared in terms of these two parameters. To evaluate the lifetime of the catalyst, the S/C ratio was set to 0.5 (GHSV = 6000 h−1 at 973 K) to accelerate coke deposition [35]. The results are shown in Figure 9. Although the ratio of steam was very low, all four catalysts maintained their methane conversion. Considering the catalyst lifetime, the extent of carbon deposition seems to be a more important factor than conversion. When carbon was deposited, the activity of the catalyst was reduced, and the inside of the reactor was blocked, causing a pressure drop. After the SMR reaction under harsh conditions that induced carbon deposition, the catalysts were analyzed by thermogravimetric analysis (TGA) to measure the amount of coke deposited. Figure 10 showed the result of TGA. The amount of coke deposition on the Com-catalyst, Ni/sup-1273, Ni/sup-1373, and Ni/sup-1473 were 37%, 9.5%, 6.7%, and 4.5%, respectively. The weight loss below 600 K can be assigned to moisture, amorphous carbon, and other impurities, whereas the weight loss above 600 K can be attributed to crystalline carbon [36,37,38]. Although there was no significant difference in the methane conversion, there was a large difference in the amount of carbon deposition. As the second calcination temperature of the MgAl2O4 pellets increased, the amount of coke deposition decreased.
The measurement of strength of the catalyst after this reaction revealed that Ni/sup-1473, with the thinnest egg-shell, was the strongest (Table 2). The lowest amount of coke deposition might be the main reason for the highest pellet strength of the catalyst. In the case of the Com-catalyst, it was difficult to remove the used catalyst after this reaction because it broke during this reaction. The high concentration of Ni present inside the Com-catalyst pellet seems to be the main reason for pellet breakage. The egg-shell-type catalyst did not contain Ni inside the pellet; therefore, carbon deposition occurred only on the pellet surface [39]. As there were no cracks induced by the deposited coke inside the egg-shell pellet, it could maintain the catalyst shape. If Ni was uniformly impregnated inside the pellet like Com-catalyst, carbon deposition would occur in all sections of the pellet, inducing cracks inside the pellet. Cho et al. also reported similar results in that study [16]. Based on these results, the thinner the egg-shell, the better the methane conversion and coke deposition resistance, even under conditions of high space velocity. As the egg-shell-type catalyst was resistant to carbon deposition inside the pellet, internal cracking by carbon could be suppressed. Therefore, the egg-shell-type catalyst exhibits excellent durability and resistance to carbon deposition.

3. Conclusions

In summary, egg-shell-type pellet catalysts were prepared for the SMR reaction. In the preparation of MgAl2O4 pellet, which had outstanding thermal stability, hydrotalcite MG30 (70 wt% Al2O3 and 30 wt% MgO) was used as a precursor in a two-step calcination process. In the first calcination, the hydrotalcite structure of MG30 was converted into the spinel structure of MgAl2O4. In the second calcination, the calcination temperature controlled the porosity and crystallinity of the MgAl2O4 pellet, which affected the preparation of egg-shell-type catalysts with different Ni shell thicknesses. In the egg-shell-type catalysts, the active material is concentrated in the outer region of the pellet support. All three prepared catalysts (Ni/sup-1273, Ni/sup-1373, and Ni/sup-1473) with an egg-shell-type Ni distribution had the same Ni loading of 3.5 wt%. As the calcination temperature of the MgAl2O4 support increased, the egg-shell thickness decreased. These catalysts exhibited excellent catalytic activity in the SMR reaction under a flow rate, although the egg-shell-type catalysts used a small amount of Ni (3.5 wt%). The weight loss of the commercial catalyst was approximately 37% under accelerated carbon deposition (S/C = 0.5). In all three egg-shell-type catalysts, the weight loss was less than 10%. After the reaction, the egg-shell-type catalyst maintained its shape because less coke was deposited in the outer region of the pellet. The support calcination temperature controlled the thickness of the egg-shell. The thin Ni-shell enhanced the resistance to carbon deposition, as doesthe catalytic activity. Therefore, the egg-shell-type pellet catalyst is promising for a commercialized large-scale steam methane reformer.

4. Materials and Methods

4.1. Manufacturing Pellet Type Supports

A pellet-type support using MG30 as the support precursor was manufactured based on a commercial catalyst. The MG30 (Al2O3:MgO = 70:30) was purchased from SASOL. The pellet support was shaped like a cylinder with one hole in the middle and with dimensions of 8 mm × 8 mm × 3 mm (height × external diameter × hole diameter), considering the diameter of the reaction tube and flow rate of the reactant gas. After calcining MG30 at 1173 K, the MG30 hydrotalcite structure changed to the spinel phase MgAl2O4 to eliminate CO2 and H2O. The MgAl2O4 powder was then pressed into pellets using a mold. To maintain the shape, the molding was completed by calcining at temperatures (1273 K, 1373 K, and 1473 K) higher than 1173 K. The synthesized pellet was named according to the last calcination temperature (Sup-x, where x is the last calcination temperature). The schematic diagram of Figure 11 summarized the preparation procedures of the MgAl2O4 pellet. The image of Figure 12 showed prepared pellet.

4.2. Preparation of Egg-Shell-Type Catalysts

For the synthesis of egg-shell-type catalysts, Ni was present only on the surface of the pellet, and the prepared pellet support was sonicated in ethylene glycol as a hydrophobic solvent [40]. After the pores of the pellet were filled with ethylene glycol, the unabsorbed solvent was removed. This pellet was immersed in a Ni nitrate aqueous solution corresponding to 3.5 wt% of Ni in distilled water. It was heated at 343 K until the water evaporated completely. Finally, the pellets were heated to 1073 K in air for 5 h and maintained at 1073 K for 2 h. Each synthesized catalyst was named according to final calcining temperature of the support (Ni/sup-x, x was the second calcination temperature 1273 K, 1373 K, and 1473 K).

4.3. Conditions for SMR Reaction

As the catalyst was pellet-type, the reaction was carried out in a 1-inch fixed reactor. Reduction was performed using 200 sccm of nitrogen and 50 sccm of hydrogen. The reduced temperature was increased to 1073 K for 2 h 30 min and maintained for 2 h. To evaluate the intrinsic activity of the egg-shell-type catalysts, the steam-to-carbon ratio (S/C) was 3.0, and the gas hourly space velocity (GHSV) was 2500, 5000, and 10,000 h−1 at 1073 K. In another reaction for estimating coke resistance, the reaction was S/C = 0.5 at 973 K in a 6000 h−1 reactant stream. There were no gases other than methane or steam during the SMR reaction. To measure the catalytic performance in these SMR reactions, methane conversion [CH4 conversion (%)] was calculated as follows:
CH4 conversion (%)= 100 × [(mole fraction of carbon monoxide and carbon dioxide in outlet)/(mole fraction of methane, carbon monoxide and carbon dioxide in outlet)]

4.4. Characterization

The structures of the prepared supports and catalysts were analyzed by X-ray diffraction (XRD) in the 2θ range using a 40 kV/40 mA X-ray. The instrument used was a goniometer Ultima3 theta-theta gonio. N2 adsorption and desorption analyses were performed to determine the specific surface area and pore volume using a Tristar II 3020 instrument from Micromeritics®. The N2-adsorption and desorption were preprocessed by holding the sample at 423 K for 3 h under vacuum. H2-temperature programmed reduction (H2-TPR) was performed using a chemisorption analyzer (BEL Japan Inc.). Cross-sectional images of the egg-shell catalysts were obtained using a Dino-Lite Premier Digital Microscope (AnMo Electronics Corp.). Thermogravimetric analysis (TGA) was carried out to measure the amount of carbon deposition on the used catalysts under an air atmosphere using a TGA2 by ETTLER TOLEDO.

Author Contributions

Conceptualization, C.H.K. and Y.J.Y.; methodology, Y.J.Y.; investigation, Y.J.Y. and E.C.; data curation, Y.J.Y.; writing—original draft preparation, Y.J.Y.; writing—review and editing, Y.J.Y. and C.H.K.; visualization, Y.J.Y.; supervision, C.H.K.; project administration, C.H.K.; funding acquisition, C.H.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (Ministry of Science and ICT) (No. NRF-2021R1A2C1011778).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 12 01500 g001 550
Figure 1. XRD patterns of MgAl2O4 powders after the first calcination and MG30 before calcination.
Figure 1. XRD patterns of MgAl2O4 powders after the first calcination and MG30 before calcination.
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Catalysts 12 01500 g002 550
Figure 2. XRD patterns of MgAl2O4 pellets after the second calcination and MG30 powder after calcination at 1173 K.
Figure 2. XRD patterns of MgAl2O4 pellets after the second calcination and MG30 powder after calcination at 1173 K.
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Catalysts 12 01500 g003 550
Figure 3. N2 adsorption–desorption isotherms of each MgAl2O4 pellet.
Figure 3. N2 adsorption–desorption isotherms of each MgAl2O4 pellet.
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Catalysts 12 01500 g004 550
Figure 4. Cross-sectional image of the synthesized catalysts: (a) Ni/sup-1273, (b) Ni/sup-1373, and (c) Ni/sup-1473.
Figure 4. Cross-sectional image of the synthesized catalysts: (a) Ni/sup-1273, (b) Ni/sup-1373, and (c) Ni/sup-1473.
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Catalysts 12 01500 g005 550
Figure 5. XRD patterns of the egg-shell-type 3.5 wt% Ni/MgAl2O4 pellet catalysts.
Figure 5. XRD patterns of the egg-shell-type 3.5 wt% Ni/MgAl2O4 pellet catalysts.
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Catalysts 12 01500 g006 550
Figure 6. XRD patterns of the egg-shell-type 3.5 wt% Ni/MgAl2O4 pellet catalysts after reduction.
Figure 6. XRD patterns of the egg-shell-type 3.5 wt% Ni/MgAl2O4 pellet catalysts after reduction.
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Catalysts 12 01500 g007 550
Figure 7. TPR profile of MgAl2O4 support and the egg-shell-type Ni/MgAl2O4 pellet catalysts.
Figure 7. TPR profile of MgAl2O4 support and the egg-shell-type Ni/MgAl2O4 pellet catalysts.
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Catalysts 12 01500 g008 550
Figure 8. The methane conversion of Com-catalyst (purple line), Ni/sup-1273 (black line), Ni/sup-1373 (red line) and Ni/sup-1473 (blue line) according to space velocity.
Figure 8. The methane conversion of Com-catalyst (purple line), Ni/sup-1273 (black line), Ni/sup-1373 (red line) and Ni/sup-1473 (blue line) according to space velocity.
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Catalysts 12 01500 g009 550
Figure 9. The methane conversion of Com-catalyst (purple line), Ni/sup-1273 (black line), Ni/sup-1373 (red line) and Ni/sup-1473 (blue line) after the SMR reaction under harsh conditions.
Figure 9. The methane conversion of Com-catalyst (purple line), Ni/sup-1273 (black line), Ni/sup-1373 (red line) and Ni/sup-1473 (blue line) after the SMR reaction under harsh conditions.
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Figure 10. TGA curves after the SMR reaction under harsh conditions.
Figure 10. TGA curves after the SMR reaction under harsh conditions.
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Catalysts 12 01500 g011 550
Figure 11. Schematic diagram of the pellet making procedure.
Figure 11. Schematic diagram of the pellet making procedure.
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Figure 12. Image of the prepared pellet support.
Figure 12. Image of the prepared pellet support.
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Table
Table 1. Porosity of the MgAl2O4 pellet supports obtained by N2 adsorption and desorption analysis.
Table 1. Porosity of the MgAl2O4 pellet supports obtained by N2 adsorption and desorption analysis.
Pellet SupportsSurface Area (m2/g) 1Pore Volume (cm3/g) 2
Sup-127329.30.074
Sup-137325.00.057
Sup-147314.50.024
1 Specific surface area calculated by Brunauer–Emmett–Teller (BET) method. 2 Calculation using Barrett–Joyner–Halenda (BJH) method at the N2 desorption part.
Table
Table 2. Strength of the catalysts used.
Table 2. Strength of the catalysts used.
Catalyst Strength (N)
Ni/sup-127348
Ni/sup-1373123
Ni/sup-1473137
Com-catalystShattered
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Yu, Y.J.; Cho, E.; Ko, C.H. Egg-Shell-Type MgAl2O4 Pellet Catalyst for Steam Methane Reforming Reaction Activity: Effect of Pellet Preparation Temperature. Catalysts 2022, 12, 1500. https://doi.org/10.3390/catal12121500

AMA Style

Yu YJ, Cho E, Ko CH. Egg-Shell-Type MgAl2O4 Pellet Catalyst for Steam Methane Reforming Reaction Activity: Effect of Pellet Preparation Temperature. Catalysts. 2022; 12(12):1500. https://doi.org/10.3390/catal12121500

Chicago/Turabian Style

Yu, Yeon Jeong, Eunkyung Cho, and Chang Hyun Ko. 2022. "Egg-Shell-Type MgAl2O4 Pellet Catalyst for Steam Methane Reforming Reaction Activity: Effect of Pellet Preparation Temperature" Catalysts 12, no. 12: 1500. https://doi.org/10.3390/catal12121500

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