Effects of Metal-Support Interactions and Interfaces on Catalytic Performance over M<sub>2</sub>O<sub>3</sub>- (<span class="nowrap"><svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-0.2379999pt" id="M1" height="11.6374pt" version="1.1" viewBox="-0.0657574 -11.3994 53.8828 11.6374" width="53.8828pt"><g transform="matrix(.017,0,0,-0.017,0,0)"><path id="g113-78" d="M962 650H795L470 145L347 650H176L170 622C268 613 275 606 244 503L190 322C150 188 132 126 118 91C102 50 80 33 18 28L12 0H245L251 28C175 35 170 48 174 93C177 128 191 180 220 284L292 542H294C331 392 383 150 409 4H432L774 555H776L714 137C700 40 694 34 612 28L606 0H868L874 28C793 34 784 37 797 137L849 533C859 612 863 616 956 622L962 650Z"/></g><g transform="matrix(.017,0,0,-0.017,21.699,0)"><path id="g117-34" d="M535 323V373H52V323H535ZM535 138V188H52V138H535Z"/></g><g transform="matrix(.017,0,0,-0.017,36.567,0)"><path id="g190-77" d="M495 163C480 117 462 85 444 65C421 39 387 34 332 34C290 34 256 36 236 47C218 57 213 77 213 131V526C213 612 222 616 301 622V650H40V622C122 616 128 611 128 526V126C128 41 120 34 36 28V0H489C498 31 519 126 525 157L495 163Z"/></g><g transform="matrix(.017,0,0,-0.017,46.057,0)"><path id="g190-98" d="M433 39L423 65C413 59 399 54 387 54C370 54 352 69 352 114V299C352 352 342 392 307 422C285 440 255 449 225 449C168 437 102 399 75 379C56 365 44 353 44 339C44 315 69 296 87 296C101 296 111 303 116 319C124 349 133 371 145 385C156 397 171 404 190 404C241 404 275 364 275 291V274C253 256 180 229 120 209C65 190 39 159 39 110C39 47 88 -12 159 -12C189 -12 237 25 277 52C282 35 288 21 301 8C312 -3 333 -12 348 -12L433 39ZM275 84C256 65 221 48 195 48C164 48 124 73 124 124C124 161 146 180 185 198C206 208 254 229 275 240V84Z"/></g></svg>,</span> Al-) Supported Ni Catalysts

Xiao, Zhourong; Li, Peng; Zhang, Senlin; Gu, Jianmin; Wang, Desong

doi:https://doi.org/10.1155/2023/6504914

International Journal of Energy Research

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Abstract Introduction Methods Results and Discussion Conclusions Data Availability Conflicts of Interest Authors’ Contributions Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 6504914 | https://doi.org/10.1155/2023/6504914

Effects of Metal-Support Interactions and Interfaces on Catalytic Performance over M₂O₃- (, Al-) Supported Ni Catalysts

Zhourong Xiao,¹Peng Li,¹Senlin Zhang,¹Jianmin Gu,¹and Desong Wang^1,2

Academic Editor: Rafael M. Santos

Received19 Oct 2022

Revised06 Nov 2022

Accepted08 Nov 2022

Published09 Feb 2023

Abstract

The metal-support interactions and their interfaces have showed great influence on catalytic activity and stability. Herein, different support of M₂O₃- (, Al-) supported Ni catalysts was prepared by a citric acid-assisted sol-gel method. The physical structure and chemical properties of the As-prepared catalysts were systematically characterized by various technologies. The catalytic performance was evaluated for hydrogen or syngas production by ethanol steam reforming and methane dry (CO₂) reforming, respectively. The results showed that compared with Al₂O₃ support, the nickel supported on La₂O₃ possessed a smaller particle size of nickel even after high-temperature reduction. In addition, the La₂O₃-supported nickel catalyst had stronger metal-support interaction and higher nickel electron density as a result of higher ethanol conversion activity and stability. The ethanol conversion was maintained at 87.8% after a 3000-minute test, and the hydrogen production was as high as 6500 μmol/min. Moreover, the Ni-La₂O₃ catalyst also showed good activity for methane dry reforming. The initial conversion of methane and carbon dioxide was close to 90%, and the ratio of H₂/CO reached 0.94. The better catalytic performance of the Ni-La₂O₃ catalyst was ascribed to smaller particle size of Ni, rich metal-support interfaces, more nickel electron densities, abundant strong basic sites, and strong metal-support interactions.

1. Introduction

Nowadays, the hypersonic aircraft has become a hot spot in the field of aerospace development. However, it will generate a lot of pneumatic heat in flight, which may cause the surface temperature of aircraft higher than the material tolerance and will lead to decay of the life-span or even destroy the material [1]. Therefore, controlling the surface temperature lower than the material tolerance is highly desirable for dealing with the problem of vehicle cooling with liquid hydrocarbon fuel [2]. Due to the high temperature of hypersonic flight vehicle cooling requirements and the shortcomings of liquid hydrogen fuel such as low density and low boiling point, endothermic hydrocarbon fuel is a good way for response to problems of hypersonic flight vehicles [3]. For endothermic hydrocarbon fuel process, three aspects including steam reforming, catalytic dehydrogenation, and cracking have been extensively investigated [4, 5]. Compared with the cracking or dehydrogenation process, fuel steam reforming process can provide a higher heat sink and can meet the actual requirements of hypersonic missiles with flight speed up to Mach 10 [3]. Adding water/ethanol to fuel was based on a two-step reaction involving the low-temperature prereforming of fuel to produce methane and carbon dioxide, and then the methane and carbon dioxide (dry) reforming under high-temperature conditions with strong endothermic effect [6]. Therefore, fuel steam reforming such as ethanol steam reforming and methane carbon dioxide reforming is expected to provide a fundamental data for improving the heat absorption capacity of fuel. Furthermore, ethanol steam reforming and methane carbon dioxide reforming are important reactions for production of hydrogen and syngas, which have become one of the hot spots [7–12].

Whether ethanol steam reforming or methane carbon dioxide reforming, the key to achieve high conversion is the design high-efficiency catalysts [13, 14]. Among them, nickel-based catalysts were regarded as the most promising catalysts for reforming reactions because of the high activity, abundant resource, and low price [15]. However, there are still some shortcomings for nickel-based catalysts, such as easy carbon deposition on the surface of nickel, which reduces the activity and stability of the catalysts [16]. Moreover, due to the low Taman temperature of nickel metal, it tends to agglomerate under high-temperature reaction conditions, which further greatly reduces the activity and stability of the catalyst. Therefore, it is an urgent problem to improve the carbon deposition resistance and sintering resistance of nickel-based catalysts [17]. Based on previous report, increasing the dispersion of nickel, reducing the particle size of nickel, and enhancing the interaction strength between nickel metal and support are efficient methods to improve the activity and stability for nickel-based catalysts [18, 19]. Xiao et al. [20] reported that the Ni-CePr_x catalyst prepared by the sol-gel method achieves stable hydrogen production by ethanol steam reforming. The catalyst prepared by the sol-gel method has higher activity and anticarbon deposition performance than the catalyst prepared by the impregnation method, which was attributed to the strong interaction between nickel metal and support and the high nickel dispersion. Further, they also reported that Ni-CeO₂ catalysts modified by valence states of different doping elements can achieve stable hydrogen production by ethanol steam reforming [21]. In particular, the La-doped catalyst has higher activity and stability, which was attributed to the greater nickel dispersion and oxygen vacancy concentration of the trivalent La-doped catalyst. La₂O₃ and Al₂O₃ were excellent support for supporting nickel catalysts, which have strong interaction with metal nickel and can form high-temperature sintering-resistant perovskite [22] or nickel-aluminum spinel structure [23].

Herein, La₂O₃- and Al₂O₃-supported nickel catalysts were synthesized by a sol-gel method. The structures and properties of the two catalysts were characterized by wide-angle X-ray diffraction (XRD), nitrogen adsorption and desorption isotherm, transmission electron microscopy (TEM), CO₂ temperature-programmed desorption (CO₂-TPD), X-ray photoelectron spectroscopy (XPS), and a hydrogen temperature-programmed reduction (H₂-TPR). The results showed that the nickel catalysts supported on the two kinds of support have different performances for ethanol steam reforming and methane dry reforming. Furthermore, TEM and thermogravimetric analysis (TG) were performed on the spent catalyst. The La₂O₃-supported nickel catalyst showed better catalytic activity and stability as well as anticarbon deposition performance on account of its strong metal-support interaction, rich metal-support interaction interface, and smaller particle size of nickel.

2. Experimental Materials and Methods

2.1. Reagents and Materials

Nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O, Beijing Huawei Ruike, AR), lanthanum nitrate hexahydrate (La(NO₃)₂·6H₂O, Tianjin Guangfu Fine Chemical Research Institute, AR), aluminum nitrate ninehydrate (Al(NO₃)₃)·9H₂O, Tianjin Guangfu Fine Chemical Industry Research Institute, AR), absolute ethanol (C₂H₅OH, Tianjin Guangfu Fine Chemical Industry Research Institute, AR), methane carbon dioxide mixture (, Tianjin Taiya Gas Company), nitrogen (high purity), and helium (high purity) were purchased from Six Party Gas Company, deionized water.

2.2. Preparation of Catalyst

The catalyst was prepared by a sol-gel method as reported by our previous work [24, 25]. For the synthesis of Ni-La₂O₃, a certain amount of lanthanum nitrate hexahydrate and nickel nitrate hexahydrate were weighed, then dissolved in 17 mL deionized water. Then, citric acid with molar ratio to metal ion set at 2 : 1 was added into the above solution. After stirring for 6 h, the above mixed solution was transferred into oven under 120°C for 12 h. The obtained solid was ground to a powder and then transferred to a muffle furnace at 600°C for 4 h. To prepare the reduced catalyst, a certain amount of calcined catalyst was put in a quartz ark and reduced at 780°C for 1 h under 10% vol H₂/Ar mixture gas. The reduced catalyst was prepared, named as Ni-La₂O₃, and the weighted percentage of Ni was kept at 10 wt%. Similarly, the Ni-Al₂O₃ catalyst was prepared by the same method, and the precursor of aluminum used was aluminum nitrate nonahydrate.

2.3. Characterization

The phase structure of the prepared catalyst and the reduced catalyst was analyzed by the Rigaku D8 Focus X-ray diffractometer (XRD). The test conditions of XRD were as follows: Cu target, K_α ray (), tube voltage of 40 kV, tube current of 200 mA, scanning speed set at 8°/min, and scanning range from 10° to 80°. The instrument JEM-F200 was used to observe the nickel particles and carbon deposition of the prepared catalyst. At the same time, selected electron diffraction and crystal structure analysis could be provided, and the surface distribution analysis of the sample elements could be analyzed with the energy spectrometer. The test conditions were as follows: acceleration voltage of 200 kV, , and . Micromeritics Tristar 3000 was used to analyze the pore structure of the material under nitrogen atmosphere at -196°C. The samples were needed to be degassed and dehydrated for 3 h at 300°C before the test. H₂-TPR was carried out on an AMI-300. Firstly, a certain amount of catalyst samples were weighed and pretreated at 400°C in Ar atmosphere for 1 h. After cooling to 50°C, 10% vol H₂-Ar-mixed gas was added and the temperature was increased from 50°C to 800°C with the heating rate of 10°C/min. CO₂-TPD was carried out on an AMI-300. A powder sample (100 mg) was pretreated at 300°C with Ar under a flow of 30 mL/min for 1 h and then cooled to 100°C. CO₂ was introduced (30 mL/min) for 0.5 h at 100°C; and then, He stream was fed until the completely remove physically adsorbed CO₂. The chemically adsorbed CO₂ was determined by increasing the temperature up to 800°C with a heating rate of 10°C/min. The carbon deposition of the spent catalyst was characterized by HCT-1 comprehensive thermal analyzer. About 10 mg of the sample was weighed and placed in a porcelain crucible, kept at 30°C for 20 minutes, and then the temperature was increased from 30°C to 800°C in the air atmosphere with a heating rate of 10°C/min. The weight loss curve of the sample was obtained, and DTG data was obtained by first-order differentiation of the weight loss curve.

2.4. Catalyst Evaluation

Hydrogen production by ethanol steam reforming was carried out in a stainless-steel tubular-fixed bed reactor. Before reaction, the calcined catalyst was pressed into tablets with the pressure of 10 MPa, and then was sieved into mesh number of 20~40. For ethanol steam reforming, 0.25 g of catalyst and 1.2 g of quartz sand were mixed uniformly and then filled in a stainless-steel tubular with a diameter of 6 mm. The temperature was raised to 780°C in nitrogen, then the gas was switched to 10% vol H₂/Ar. After reducing for 1 h, the temperature was stabilized to the reaction temperature (600°C) by nitrogen, and the reaction pressure was set at 0.1 MPa. A constant quantity of ethanol aqueous solution (0.255 mL/min) was introduced into the gasifier by a high-pressure metering pump, then gasification at 300°C with nitrogen (60 mL/min). The partial pressure of ethanol vapor and nitrogen in the mixture were 15.73 vol% and 21.33 vol%, respectively. During the reaction, the gas hour space velocity (GHSV) of ethanol-water vapor was 55920 mL/g_cat·h. After the reaction, the gas product was condensed, dried, and passed through Micro GC 490 (Agilent) for online analysis. The gas chromatographic with a TCD detector was equipped with three columns: an activated alumina column for the detection of hydrocarbon molecules C₃ and above, a PPU column for the detection of CO₂, ethane, and ethylene, and a 5 Å MS column for the detection of H₂, N₂, CH₄, and CO. The conversion of ethanol was calculated according to Equation (1). The gas product rate and the composition of gas were calculated based on Equations (2) and (3). Similar to ethanol steam reforming, methane dry reforming was carried out in the same reactor. The 0.15 g of catalyst and 1.2 g of quartz sand were evenly mixed and loaded into a tube reactor, and then prereduced in 10% vol H₂/Ar mixture at 780°C for 1 h. The temperature was stabilized to 700°C under a nitrogen atmosphere. Then the mixture of methane, carbon dioxide, and nitrogen gas with a ratio of 1 : 1 : 2 was passed into the reaction tube; and nitrogen was used as the carrier gas and internal standard gas. The gas phase products were analyzed by GC490, and the gas production rate, reactant conversion, and H₂/CO molar ratio were calculated by using Equations (2), (4), and (6). , , and represent the total number of C₁ products at the outlet of the reaction tube (mol/min). For Equation (2), , namely, nitrogen flow rate, and represent the peak area and response factor of H₂, respectively. and represent the peak area and response factor of N₂, respectively. Here, Equation (3), (H₂) (excluding nitrogen) was the percentage of hydrogen in the dry gas (without nitrogen).

3. Results and Discussion

3.1. Characterization of Structure and Metal-Support Interaction

The XRD patterns of the As-reduced catalysts are shown in Figure 1(a). For the Ni-Al₂O₃ catalyst, no obvious peak of Al₂O₃ was observed, which could be due to its amorphous structure [19]. The diffraction peaks with strong intensity appear at 44.5^o, 51.9^o, and 76.4^o were attributed to the characteristic diffraction peaks of nickel (JCPDF#01-1260), indicating that the high crystallinity of nickel in the reduced catalyst with the uneven distribution of large particles size of nickel. For the Ni-La₂O₃ catalyst, the peaks of La₂O₃ (JCPDF#83-1344) was mainly observed. There was no obvious characteristic peak of nickel, illustrating that the small particle size of nickel with uniform distribution. These results will be confirmed by H₂-TPR as shown in Figure 1(b). All the As-prepared catalysts have three reduction peaks. For the Ni-Al₂O₃ catalyst, the reduction peak of 391.1°C was attributed to the reduction of NiO with large particles or weak interaction with the support, and 484.1°C was assigned to the reduction of NiO with small particles or strong interaction with the support, and 695.4°C was attributed to the reduction of nickel-aluminum spinel [19]. For the Ni-La₂O₃ catalyst, the first peak appeared at 416.9°C, which can be attributed to the decrease of Ni²⁺ species on the surface. The second peak appeared at 609.3°C, possibly because LaNiO₃ was reduced to La₂Ni₂O₅ [26]. The third reduction peak was located at 767.7°C, which corresponds to the reduction of Ni²⁺ in LaNiO₃ to metal Ni⁰ [27]. The higher reduction temperature of the Ni-La₂O₃ catalyst indicates that it possessed a strong metal-support interaction, which is beneficial to inhibit the sintering of nickel and maintain the small particle size of nickel during the high-temperature reduction process.

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The nitrogen adsorption-desorption isotherms of the calcined catalyst are shown in Figure 1(c) with hysteresis loop indicating that the prepared catalyst was a mesoporous material. With the increase of the relative pressure, the adsorption capacity also increases, indicating that there was a certain amount of large pores in the material. The pore size showed double pore size distribution. The mesoporous pore was centered at 4 nm and the macroporous was around 60 nm. From Table 1, the specific surface area of the Ni-Al₂O₃ catalyst was 51.3 m²/g, the pore volume was 0.11 m³/g, and the average pore size was 7.8 nm (inset Figure 1(c)). For the Ni-La₂O₃ catalyst, the surface area and pore volume were decreased to 23.3 m²/g and 0.04 m³/g, respectively. The results indicate that the prepared catalyst has a porous structure and its specific surface area was relatively small.

In order to illustrate the alkaline site on different supports, the data of CO₂-TPD was collected as shown in Figure 1(d). For Ni-La₂O₃, the high intensity of CO₂ desorption peak was mainly centered on 782°C, which illustrates abundant and strong basic sites, while for the Ni-Al₂O₃, the main CO₂ desorption temperature was located at 167°C and 473°C, which means weak and few basic sites. The strong basic sites for Ni-La₂O₃ may play a positive influence on CO₂ adsorption during the methane dry reforming, thus exhibiting good activity and stability for methane dry reforming [17].

3.2. XPS Analysis of the Reduced Catalyst

XPS of the reduced catalyst is shown in Figure 2. For the Ni-Al₂O₃ catalyst, Al 2p_3/2 was detected, indicating that the Al element was trivalent. Similarly, La 3d_3/2 was detected on the Ni-La₂O₃ catalyst, indicating that the La element was also trivalent. For the Ni 2p, three peaks at 852, 856, and 861 eV could be assigned to Ni⁰, Ni²⁺, and satellite peak (Ni²⁺), respectively. Compared with Ni-Al₂O₃, the binding energy of Ni⁰ for Ni-La₂O₃ shifts towards low binding energy, indicating the increased electron density of Ni⁰, which may be explained by the enhanced metal-support interaction as verified by Figure 1(b). Jing et al. [28] pointed out that the enhanced electron density of nickel enhances the activation and dissociation of CO₂ and balances the formation rates of C and O species on the catalyst. In addition, the Ni⁰/(Ni⁰ + Ni²⁺) ratio was also calculated. The Ni⁰ ratios of Ni-La₂O₃ and Ni-Al₂O₃ were 59.9% and 56.9%, respectively, indicating that the ratio of nickel for two catalysts was similar.

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3.3. TEM Analysis of Reduced Catalyst

Apart from binding energy of Ni, the particle size of nickel is also play vital important role in catalytic performance. The TEM images of the reduced catalyst are shown in Figure 3. The distribution of nickel particles in the Ni-La₂O₃ catalyst was relatively uniform, and the average particle size was 13.5 nm (inset Figure 3(a)). It was found that some nickel particles were embedded in the support and showed strong interaction with the support and more metal-support interfaces, which was consistent with the results of H₂-TPR (Figure 1(b)). Moreover, according to HR-TEM, the lattice parameter of nickel particles was 0.201 nm, which corresponds to the Ni (111) crystal plane. The interaction interface between nickel particles and La₂O₃ support was large (Figure 3(b)). For the Ni-Al₂O₃ catalyst, agglomeration of nickel particles was observed and the average particle size was 45.2 nm (inset Figure 3(c)), indicating the contact interface between nickel particles and the support was small (Figure 3(d)). These results were consistent with the previous XRD and TPR results. According to literature, nickel particles have strong metal-support interaction, which makes them smaller particle sizes and rich interaction interfaces, leading to the better catalytic activity and sintering resistance [23].

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The element distribution of reduced Ni-La₂O₃ and Ni-Al₂O₃ catalyst are analyzed by the TEM-mapping technique. As shown in Figure 4(a), the high-angle dark field images showed that Ni nanoparticles were uniformly distributed on the La₂O₃ support (Figures 4(b)–4(e)). However, for the Ni-Al₂O₃ catalyst (Figures 5(a)–5(e)), the nickel particles were agglomerated, which was consistent with the previous TEM and XRD results. In high temperature (780°C) hydrogen atmosphere, the nickel particles of Ni-La₂O₃ catalysts remain uniformly dispersed, due to the strong metal-support interaction which help to inhibit the agglomeration of Ni particles.

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3.4. Catalytic Performance

The stability of ethanol steam reforming was studied at 600°C, the molar ratio of H₂O/C₂H₅OH was 4 : 1, and the GHSV of aqueous ethanol vapor was 55920 mL/g_cat∙h, under atmospheric pressure, as shown in Figure 6. Ni-La₂O₃ catalyst has higher ethanol steam reforming activity and stability than Ni-Al₂O₃ (Figure 6(a)). For Ni-Al₂O₃, the conversion rate of ethanol decreased rapidly from 50.2% to 15.1% within 360 min, and the conversion decreased by nearly 70% (Figure 6(b)). Similarly, the hydrogen production rate decreased from 4529.9 μmol/min to 1659.3 μmol/min. The rapid deactivation of Ni-Al₂O₃ in the steam reforming of ethanol may be related to weak metal-support interaction, which cause the serious metal sintering and carbon deposition. For Ni-La₂O₃, the conversion of ethanol increased to 93.9% and the hydrogen production rate was 6913.6 μmol/min after 75 min. After 3000 min, the conversion still remained at 87.8%, and the hydrogen production rate remained as high as 6579.4 μmol/min. The ethanol conversion rate of the Ni-La₂O₃ catalyst decreased by only 6.1%, which was much smaller than that of Ni-Al₂O₃. Meanwhile, the gas production composition (Figures 6(c) and 6(d)) were closed to balanced composition [20, 21].

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The high activity and stability of the Ni-La₂O₃ catalyst can be attributed to its strong metal-support interaction, rich metal-support interface, abundant nickel electron density, and small particle size of nickel [20, 21]. The relative low decrease of the ethanol conversion of Ni-La₂O₃ catalyst can be attributed to the enhancement of anticarbon deposition performance, which will be confirmed by the following XRD and TG results. Also, the catalyst performance was compared with these previous reported (Ref [29–38]) as summarized in Table 2. The Ni-La₂O₃ catalyst designed in this study has higher ethanol steam reforming activity, greater stability, and good carbon deposition resistance and will be used in future.

Furthermore, our Ni-La₂O₃ can be used to convert methane and carbon dioxide under harsh reaction condition as shown in Figure 7. Under the same reaction condition, Ni-La₂O₃ catalyst showed higher activity and stability of methane dry gas reforming than that of Ni-Al₂O₃. The initial conversion rates of methane and carbon dioxide over Ni-La₂O₃ catalyst were 92.6% and 92.5%, respectively (Figures 7(a) and 7(b)). While, the initial conversion rates of methane and carbon dioxide over Ni-Al₂O₃ catalyst were 76.3% and 86.5%, respectively. After 140 min reaction, the conversion rates of methane and carbon dioxide were 84.4% and 82.2% for Ni-La₂O₃ catalyst, which were higher than those of Ni-Al₂O₃ catalyst. In addition, the H₂/CO ratio of the Ni-La₂O₃ catalyst remained at 0.94, while for the Ni-Al₂O₃ catalyst decreased to 0.85 after 140 min of reaction (Figure 7(c)). The hydrogen production rate (Figure 7(d)) of the Ni-La₂O₃ catalyst was maintained at 1.49 mmol/min, which was 1.37 times higher than that of the Ni-Al₂O₃ catalyst (1.09 mmol/min). These results indicate that Ni-La₂O₃ has higher catalytic activity and stability than Ni-Al₂O₃ during the methane dry reforming.

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3.5. XRD and TEM Analyses of Spent Catalyst

In order to illustrate the big difference of two catalysts in catalytic performance, the powder XRD results of catalysts after ethanol steam reforming and methane dry reforming are shown in Figures 8(a) and 8(b). The structure of the catalyst after the reaction was similar to that of the catalyst before the reaction. For the Ni-Al₂O₃ catalyst after reaction, a very strong diffraction peak of nickel could be observed, while the characteristic peak of nickel was not observed for the Ni-La₂O₃ catalyst. At the same time, a new diffraction peak appeared in the catalyst after the reaction at 26.1^o, which was attributed to the diffraction peak of graphite-carbon [39]. The intensity of the graphitic carbon diffraction peak of the Ni-Al₂O₃ catalyst was stronger than that of the Ni-La₂O₃ catalyst, which indicates that Ni-La₂O₃ has litter carbon deposition and better anticarbon deposition performance. This may be due to the Ni-La₂O₃ catalyst possessed smaller nickel particles size, rich electron density, and abundant strong basic sites.

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The TEM images for the spent catalysts were obtained. For Ni-La₂O₃, the average size of nickel particles was about 15.5 nm (inset Figure 9(a)), and no obvious carbon deposition was observed (Figure 9(b)). After the reaction, the average size of nickel particles in the Ni-Al₂O₃ catalyst was about 68.5 nm (inset Figures 9(c) and 9(d)), which was increased to a large extent compared with fresh sample, and the larger size of nickel particles reduces its catalytic activity [19]. This characterization result directly explains the reason for the significant reduction of ethanol reforming performance.

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3.6. Analysis of Carbon Deposition on the Spent Catalyst

The carbon deposition on the catalyst surface after the reaction were analyzed by TG and DTA, and the results are shown in Figures 10(a) and 10(b). The weight loss percentage of Ni-Al₂O₃ after ethanol steam reforming reaction was 21.7%, indicating that the proportion of carbon deposition in the catalyst after the reaction was 21.7%. For the spent Ni-La₂O₃ catalyst, the weight loss rate was significantly reduced. The better anticarbon deposition performance of the Ni-La₂O₃ catalyst is attributed to the smaller size of Ni particles, the abundant metal-support interface, and the abundant strong basic sites, which is beneficial to the inhibition of carbon deposition.

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In addition, the differential thermal analysis of the catalyst after the reaction is shown in Figure 10(a). The temperature for oxidation of carbon on Ni-Al₂O₃ catalyst was concentrated at 594.9°C, which corresponds to the oxidation of the encapsulated carbon on the surface of nickel metal. For spent La₂O₃, the elimination temperature of carbon deposition on nickel surface moves to the low temperature (592°C) zone and the peak area was greatly reduced. The main carbon deposition oxidation temperature was 761.8°C, which was attributed to the oxidation of carbon nanotubes [40]. The activity and stability of the Ni-Al₂O₃ catalyst are reduced due to a large amount of carbon deposition on the surface of nickel, while the stability of the Ni-La₂O₃ catalyst was well maintained due to the small amount of carbon deposition on the surface of the nickel. The oxidation of carbon deposits after methane dry reforming exhibited a similar rule (Figure 10(b)). Large amounts of carbon deposition on the surface of nickel metal cause bad stability for Ni-Al₂O₃ which was consistent with the TEM results above (Figure 9).

4. Conclusions

In a word, La₂O₃- and Al₂O₃-supported Ni catalysts were prepared by the citric acid-assisted sol-gel method, and their structures, properties, and reactivity were systematically compared. Ni-La₂O₃ with small particle size of nickel, strong metal-support interaction, rich metal-support interface, and abundant strong basic sites were achieved as verified by XRD, H₂-TPR, TEM, and CO₂-TPD. The catalytic performance showed that compared with Ni-Al₂O₃, Ni-La₂O₃ catalyst had higher ethanol steam reforming activity, stability, and hydrogen production rate. Under the condition of 55920 mL/g_cat∙h of ethanol-water vapor at 600°C, the ethanol conversion remained at 87.8% after 3000 min of reaction. The hydrogen production rate was greater than 6500 μmol/min, and the resistance to carbon deposition was greatly improved. In addition, the Ni-La₂O₃ catalyst showed good activity in methane dry reforming with the initial conversion rate of methane and carbon dioxide was greater than 90%, and the H₂/CO ratio was close to 0.94. The better catalytic performance for Ni-La₂O₃ catalyst was attributed to the smaller size of metal nanoparticles, more metal-support interfaces, rich nickel electron density, abundant strong basic sites, and strong metal-support interaction.

Data Availability

The data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Authors’ Contributions

Zhourong Xiao and Peng Li contributed equally to this work.

Acknowledgments

This work was supported by the Cultivation Project for Basic Research and Innovation of Yanshan University (No. 2021LGQN028), the Key Research and Design Program of Qinhuangdao (No. 202101A005), and the Subsidy for Hebei Key Laboratory of Applied Chemistry after Operation Performance (No. 22567616H).

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Copyright © 2023 Zhourong Xiao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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International Journal of Energy Research

Effects of Metal-Support Interactions and Interfaces on Catalytic Performance over M2O3- (, Al-) Supported Ni Catalysts

Abstract

1. Introduction

2. Experimental Materials and Methods

2.1. Reagents and Materials

2.2. Preparation of Catalyst

2.3. Characterization

2.4. Catalyst Evaluation

3. Results and Discussion

3.1. Characterization of Structure and Metal-Support Interaction

3.2. XPS Analysis of the Reduced Catalyst

3.3. TEM Analysis of Reduced Catalyst

3.4. Catalytic Performance

3.5. XRD and TEM Analyses of Spent Catalyst

3.6. Analysis of Carbon Deposition on the Spent Catalyst

4. Conclusions

Data Availability

Conflicts of Interest

Authors’ Contributions

Acknowledgments

References

Copyright

Effects of Metal-Support Interactions and Interfaces on Catalytic Performance over M₂O₃- (, Al-) Supported Ni Catalysts