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Article

Facile Synthesis of Uniform NiO Nanoparticles Exclusively Confined in Mesoporous SBA-15 with High Loading for Ammonia Decomposition

by
Yun Xu
1,†,
Tianfa Tang
2,†,
Pengyao Wang
2,
Chunlei Zhang
1,
Jianbo Zhao
3,
Ke Zhuang
1,* and
Changjin Tang
2,4,*
1
State Key Laboratory of Low-Carbon Smart Coal-fired Power Generation and Ultra-Clean Emission, China Energy Science and Technology Research Institute Co., Ltd., Nanjing 210023, China
2
School of Environment, Nanjing Normal University, Nanjing 210093, China
3
School of Materials and Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou 450007, China
4
Jiangsu Province Engineering Research Center of Environmental Risk Prevention and Emergency Response Technology, Nanjing 210023, China
*
Authors to whom correspondence should be addressed.
†
These authors contribute equally to this work.
Catalysts 2025, 15(11), 1016; https://doi.org/10.3390/catal15111016
Submission received: 18 September 2025 / Revised: 14 October 2025 / Accepted: 27 October 2025 / Published: 29 October 2025
(This article belongs to the Special Issue Feature Papers in "Industrial Catalysis" Section, 2nd Edition)
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Abstract

The fabrication of highly loaded and uniformly dispersed metal oxide nanoparticles (NPs) is much desired but still remains a great challenge. Herein, the NiO NPs exclusively confined in mesoporous silica SBA-15 were obtained by using nickel nitrate hydrate as a precursor through a facile solvent-free preparation method, which comprised manual grinding of Ni(NO3)2·6H2O with SBA-15 and subsequent air calcination. Characterization results from X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed that aggregation-free NiO nanoparticles with sizes of 3–5 nm were obtained at loading as high as 20 wt.% (weight%). Further increasing the NiO loading to 30 wt.% led to partial agglomeration of discrete nanoparticles to rod-like particles, while no external particles were observed. By comparing the sample derived from nickel acetate with exclusively external NiO particles, it was established that the pore confinement provided NiO nanoparticles with high thermal stability. Lastly, the catalytic performance of the prepared sample was evaluated in the model reaction of ammonia decomposition to COx-free H2, and the stable NH3 conversion of 93.7% was achieved at the weight hourly space velocity (WHSV) value of 30,000 mL·g−1·h−1 and at high temperature of 650 °C for 60 h, demonstrating the great potential of the solvent-free method in preparing thermally stable and robust supported catalysts.

Graphical Abstract

1. Introduction

The fabrication of supported metal oxides with high loading and fine dispersion is of significant importance, mainly because of the obtainment of sufficient exposed sites and hence excellent performance in areas like adsorption and catalysis [1,2,3,4,5]. Nickel-based catalysts are among the most widely explored because of their rich reserves and superior activities in many industrially important (de)hydrogenation reactions [6,7,8]. Conventionally, to maximize the utilization of active sites, the nickel precursors are deposited onto a rigid support like SiO2 or activated carbon. Compared to solid supports, supports with porous or hollow structures are highly expected, mainly due to the possession of a large surface area for immobilization of guest species. More importantly, it is anticipated that these peculiar structures could offer a confined environment for outstanding performance [9].
As a famous mesoporous silica, SBA-15 is widely explored in the context of guest species dispersal [10]. Thus, extensive attentions have been paid to encapsulate nanoarchitectures (nanoparticle, nanowire and nanorod) into the channels of SBA-15 [11,12,13,14,15]. For application in catalysis, the exclusive formation of discrete nanoparticles with the maximum number of exposed atoms is of great interest. Until now, several strategies have been developed to construct pore-confined NiO nanoparticles in SBA-15. Richards et al. reported a so-called grafting method to prepare well-dispersed NiO nanoparticles [16]. It was established that the surface reaction between the precursor (Bis(1,5-cyclooctadiene) nickel) and surface silanol allowed for the preparation of uniform NiO nanoparticles of sizes smaller than 5 nm. However, it was noticeable that due to the limited silanol available on the surface of SBA-15, the NiO loadings were restricted, and the final value was lower than 3 wt.%. A similar phenomenon was also reported by Lu et al. during the preparation of Ni/silica catalyst with nickel acetylacetonate as a metal precursor through the use of a grafting method [17]. Alternatively, Yi and colleagues devised an in situ encapsulation method for anchoring NiO on SBA-15 by introducing PEO into the synthetic process of SBA-15 [18]. They found that the NiO loadings were intimately related to the PEO/P123 ratios and the highest loading value reached 8.5 wt.%. Nevertheless, in consideration of the large pore volume (~1 cm3 g−1) of SBA-15, the theoretic loading capacity can be roughly calculated by employing a solution of nickel precursor with a density of 1.578 g cm−3, resulting in a value of 21.26 wt.%, which considerably exceeds the above values [19]. Thus, the utilization efficiency of mesopores is still poor, and concerted efforts are needed to extend the loadings.
As the most used technique for the fabrication of supported catalysts, the impregnation of a porous support with a soluble metal precursor (e.g., nitrate or acetate) solution exhibits the merits of simple operation and the ability to handle a wide range of loadings. However, the commonly employed wet impregnation route always induces random distributions of guest species, generating particles both inside and outside of the pores. This disadvantage was recently resolved by two independent groups via modified impregnation methods. Based on a method of controlled thermal decomposition that was achieved by varying the category of calcination gases, de Jong and colleagues demonstrated that the strategy was effective in synthesizing moderately small Ni particles (~4 nm) at high loading (24 wt.% in terms of NiO) in a reductive calcination atmosphere [20]. However, the additive requirement needed for the NO/He atmosphere would inevitably limit its application on a larger scale. Another strategy was reported by Cheng and colleagues [19]. In their work, the formation of discrete and highly loaded (18.55 wt.%) NiO nanoparticles confined in SBA-15 was achieved by a so-called hydrophobic encapsulation process. By introducing a Pechini process during the complexing of Ni2+ with citric acid and the removal of outer precursor solutions with a hydrophobic solvent, the final NiO nanoparticles with small sizes (~3 nm) were found to be exclusively located in the mesopores and displayed excellent activity during methanation reaction. Although it approached the goal of high loading and good dispersion, drawbacks such as its tedious operational process and the leaching of the precursor were encountered, and the latter may simultaneously add environmental burden. Therefore, a facile and efficient synthesis of highly dispersed NiO nanoparticles confined in SBA-15 with high loadings continues to be of great importance but its achievement remains a challenge.
To insert guest species into a porous support, it is necessary for the precursor to first be translated into a mobile phase. As a unique property of many transitional metal nitrates, they will present as molten salts at temperatures higher than their melting points. In a previous study [21], Yue et al. successfully fabricated a family of mesoporous single crystals (Co3O4, NiO, CeO2, and Cr2O3) by using mesoporous silica as a hard template and metal nitrates as precursors through a so-called solid–liquid route. The result revealed that molten salts can be introduced into mesopores at large amounts. However, it is still unclear whether this method holds true for the fabrication of highly dispersed nanoparticles, without the coexistence of rod-like particles in the pore channels and external particles, and no related studies have been reported. On the other hand, the simple, cost-effective and environmentally benign features of this novel method encourage further exploration of its possible applications. Hence, in the present study, the efficiency of a solvent-free method for preparing highly loaded NiO nanoparticles confined in SBA-15 was investigated. The exclusively homogeneous dispersion of guest species in the pore channels derived in the absence of a solvent was subsequently emphasized. Moreover, the confinement of mesopores on the decomposition and coarsening of guest species was explored. Lastly, the advantage of encapsulated NiO in heterogeneous catalysis is exemplified by the reaction of NH3 decomposition in the production of COx-free H2, which is usually accomplished at relatively high temperatures and is thus suitable for exploring both the reactivity and sintering resistance of the prepared catalyst.

2. Results and Discussion

Figure 1 displays the small-angle XRD pattern of a representative sample (20Ni-NO3-550) from the solvent-free method, and the pattern of pristine SBA-15 is registered for comparison. For SBA-15, four peaks (noted as 100, 110, 200, 210) indexed to the hexagonally arranged structures are observable, indicating the obtainment of highly ordered mesopores. After NiO introduction, the (210) reflection vanishes but the other peaks are still present, despite their disturbed intensity when compared to the pristine SBA-15. This tells us that the ordered framework does not suffer severe damage during grinding and the subsequent process of air calcination. Notably, when considering the introduction of guest species, the weakening of reflections can be reasonably ascribed to poorer scattering contrasts between the silica walls and the encapsulated mesopores, which is a well-reported phenomenon in occluded mesoporous materials [22].
The effect of manual grinding on the size and morphology of the final product is examined by scanning electron microscope (SEM). For pristine SBA-15 (Figure 2a), its macroscopic morphology is represented by rope-like domains with relatively uniform sizes of 2–3 μm in length and 0.5 μm in width, which are aggregated into wheat-like microstructures. Because of the homogeneous condensation of siliceous species onto the soft template, the surface of SBA-15 is smooth, and no bumps appear. This result is consistent with Zhao’s investigation [10]. Interestingly, after manual grinding, distinct changes are observed on the size and morphology of the primary particles. The rope-like domains are transformed into irregular particles, and their sizes decrease to the sub-micrometer level. On the other hand, the surface of the particles is no longer smooth, and tiny bumps are observed. Notably, most of these bumps are smaller than one hundred nanometers. In concerning of the amorphous nature and relatively poor mechanical stability of the silica matrix [23], the decrease in the size of the mesoporous matrix is probably due to the cutting effect from manual grinding, which is also supported by the partial reduction in textual parameters (Table S1). The concomitant small bumps can thus be interpreted as the silica fragments. This unexpected finding is of certain significance. As is well acknowledged, the nanochannels of SBA-15 run along the long axis and their length is in the scale of micrometers. Molecular diffusion through the lengthy pore channels is one of the main concerns when applying these materials for sorption and catalysis. Hence, the present solvent-free method in terms of manual grinding can “cut” the lengthy pores into short ones, which will in turn provide greater pore accessibility and facilitate molecular diffusion.
The efficiency of the solvent-free method when fabricating highly loaded NiO particles on SBA-15 is comprehensively investigated by selecting two loads (20 wt.% and 30 wt.%) and choosing two kinds of commonly used nickel precursors, i.e., nickel nitrate hydrate (Ni(NO3)·6H2O) and nickel acetate hydrate (Ni(CH3COO)2·3H2O). The results of wide-angle XRD are displayed in Figure 3. For comparison purposes, the pattern of the sample prepared via the conventional impregnation method is also presented. In general, all samples display the peaks (2θ = 37.2°, 43.2° and 62.8°) which can be indexed to the diffractions of (111), (200) and (220) planes of a face-centered cubic crystalline NiO (JCPDS 75-0269), and no reflections from other nickel species demonstrate the complete conversion of precursors into NiO. In addition, the broad peak centered at around 2θ = 23 originated from the amorphous silica matrix. Noticeably, the intensity of diffraction peaks for NiO varies greatly with different methods and precursors, indicating that the state (size, location) of the synthesized NiO may be different. For the samples prepared using the solvent-free method with nickel nitrate as a precursor, the line broadening of profiles is obvious, as compared to the reference sample of 20NiO/SBA-15. It reveals the formation of NiO particles of nanometric dimensions and verifies that the solvent-free method can disperse guest species well on the mesoporous support, even at the highest reported metal oxide loading value of 30 wt.%. This result is of great interest and significant importance, especially concerning the facile operation and the lack of demand for special facilities and expensive reagents. Further screening of the XRD peak shapes shows that there are bimodal crystal-size distributions in the pattern of 30Ni-NO3-550, which are similar to the results for the sample calcined in helium atmosphere [20], indicating that the slight aggregation of NiO particles may take place at higher loadings. On the other hand, for the sample prepared with nickel acetate as a precursor, it is interesting to note that the intensity of NiO diffraction peaks is much sharper than that of 20Ni-NO3-550 and 20NiO/SBA-15 when at the same loading value, suggesting that the properties of precursors exert a predominant influence on the final dispersion and size of NiO.
The formation of NiO of different particle sizes can be reflected by its interaction with the silica support. As such, H2-TPR measurement is performed. It can be seen from Figure 4 that the samples display distinctly different reduction profiles. For 20Ni-Ac-550, most of the reduction is accomplished at the temperature range of 200–400 °C, revealing that the facile reduction in bulk NiO is due to the limited interaction with silica support. For the other two samples, in addition to the low temperature peak, another reduction between 400 and 550 °C is obvious, suggesting the existence of NiO in strong interactions with SBA-15.
As reported elsewhere, the NiO particles outside of the mesopores usually exhibit large sizes under elevated thermal treatment [24,25]. Thus, it is presumed that the varied grain sizes of NiO that have been derived from different methods and precursors are related to their altered locations in SBA-15. To prove this assumption, further characterization via transmission electron microscope is operated. The representative TEM images of 20Ni-NO3-550 are displayed in Figure 5. To fully elucidate the location and dispersion of the NiO particles on the porous support, both images viewed from the directions perpendicular to (Figure 5a) and parallel to (Figure 5c,d) the pore channels are displayed. As for support, the alternating clear and dark stripes are visible (Figure 5a), indicating the preservation of ordered mesostructures and supporting the small-angle XRD result. Noticeably, apart from the presence of the bulk silica matrix with sizes in the sub-micrometer range, there are also some smaller silica fragments present (indicated by arrows in Figure 5a), which is in accordance with the SEM result. Thus, the darker area circled can be well-explained by the deposition of silica fragments on the bulk silica matrix. When it comes to guest species, the selected area electron diffraction (SAED) pattern (inset in Figure 5a) confirms that they are NiO crystallites. It can be clearly observed that the NiO particles are homogeneously dispersed on the support and no aggregation to large particles is found, and this corresponds with the wide-angle XRD result. The corresponding particle size distribution (PSD) that were statistically analyzed by the counting of about 200 particles is shown in Figure 5b and demonstrates that the present solvent-free method is fairly effective in preparing monodisperse NiO nanoparticles with narrow PSD. The histogram shows that most of the NiO nanoparticles (>80%) are centered at 3–5 nm. Based on Figure 5a, the dispersion of NiO is clearly established. However, the evidence is not very persuasive regarding the determination of these fine particles in the mesopores. Complementarily, the image viewed from the direction parallel to pore channels is displayed. To analyze the inner part of the pores, it is preferential for the electron beam to be oriented in the direction parallel to the mesopores, and it is then possible to illuminate the content of the mesopores [26,27]. In Figure 5c, still no aggregated particles are observed to have been deposited on the surface of the silica. Meanwhile, we can observe that some of the white spots representing pore channels are replaced by dark spots, and the enlarged image (Figure 5d) reveals the dark spots to be crystalline NiO that is packed in a hexagonal arrangement, which convincingly confirms the NiO nanoparticles are essentially studded in the pore channels of SBA-15. The encapsulation of NiO in mesopores can also be evidenced by the analysis of the N2 sorption result (Table S1).
The dispersions of NiO in other samples are also characterized by TEM. As can be seen from Figure 6a, the silica fragments are still present in 30Ni-NO3-550, verifying the proposed cutting effect made by manual grinding. In addition, most of the NiO nanoparticles are well scattered on the silica support with sizes of 4–5 nm. Typically, no bulk NiO is observed on the external surface of the support, powerfully demonstrating the advantage of the solvent-free method in preparing exclusive pore confined nanoarchitectures. Nevertheless, in certain areas, as framed in the image, rod-like particles appear. It suggests that partial aggregation of small nanoparticles into nanorods occurs when overwhelming amounts of metal precursor are introduced, which is in agreement with the wide-angle XRD result. In most cases, the appearance of nanorods is indicative of the blocking of mesopores, which is not favorable for molecular diffusion in the pores. For the reference sample of 20NiO/SBA-15 (Figure 6b), the dispersion of NiO particles is not good. That is, bulk particles with sizes of 20–100 nm are detected, and they are expected to disperse on the exterior of SBA-15. Meanwhile, rod-like particles are also observable, suggesting the difficulty in controlling the proper distribution of guest species on SBA-15 through wet impregnation. To further examine the effect of different precursors on the dispersion of NiO, the TEM images of 20Ni-Ac-550 are shown in Figure 6c,d. From the low magnification image (Figure 6c), the most severe aggregation of NiO is observed among the three samples, as evidenced by the presence of aggregated NiO particles at sizes of hundreds of nanometers. The majority of NiO particles are either completely separated from the silica matrix or just in loose contact with the fringe of SBA-15. In the high magnification image (Figure 6d), the agglomeration of bulk NiO particles is clearly observed and no particles are actually confined in the pore channels, even in the form of aggregated nanorods. The result reveals that the solvent-free method is not an innate technique for the fabrication of pore confined NiO particles and its successful encapsulation is much dependent on the properties of the selected precursors.
On the basis of the combined analyses from wide-angle XRD, N2 physisorption and TEM, the dispersion and location of NiO from different methods and precursors are confirmed. The results show that both the preparation method and precursors have great influence on the final state of NiO. For the conventional wet impregnation method, it is generally achieved by the impregnation of the porous support with a solution of metal precursor, followed by the evaporation of the solvent (drying step) and calcination. As seemingly facile as the practical execution is, the fundamental phenomena underlying impregnation and drying are extremely complex. Therefore, many intensive studies are carried out to investigate the influences of each individual step in preparing supported catalysts. Generally, the soluble precursor can be homogeneously dispersed onto the support in the impregnation step, and in certain cases, with the assistance of ultrasonic treatment. For SBA-15, it is reported the precursor is introduced into the pores during this step, resulting in its homogenous distribution. Subsequently, in the drying step, owing to the limited interactions between precursor and inert support, the diffusion of surface species with solvent evaporation results in the redistribution of the active phase [20]. For mesoporous silica as a support, the diffusion of the precursor out of the pores always takes place and conforms to the result showing heterogeneous distributions of NiO particles in 20NiO/SBA-15.
To obtain a supported catalyst with a uniform distribution of surface species, it is essential to control the unfavorable redistribution of precursors during the drying step. In brief, there are mainly two strategies to approach the goal. The first is based on the creation of strong interactions between the support and the precursor. In line with this idea, methods like grafting and strong electrostatic adsorption are developed. By preliminarily grafting functional groups like -NH2 onto the support or directly utilizing the surface hydroxyl, the anchoring sites can bind well to the precursor. As a result, the redistribution of precursors during drying is inhibited, which in turn ensures the high dispersion of active species. As an alternative, the synthesis of well dispersed guest species on silica via electrostatic adsorption is demonstrated [28,29]. Due to the presence of SEA, the diffusion of the precursor is prevented and as a result, highly dispersed metals are obtained. To reduce the redistribution of precursors, another strategy is to increase the diffusion resistance of the impregnated solution. This way is mainly based on the employment of chelating salts or the addition of viscosity-increasing agents to aqueous metal nitrate solutions [30,31]. With the evaporation of the solvent, the steep increase in viscosity is apparent, and will significantly inhibit the redistribution of precursors during drying. From this point of view, the preparation of highly loaded NiO with good dispersion, as reported by Cheng et al. [19], can be well explained, as the introduction of citric acid favors the formation of viscous nickel citrate solution.
From the discussion above, it is apparent that the redistribution of precursors during drying is one of the most decisive factors in the poor dispersion of guest species on an inert support. As a matter of fact, redistribution is induced by the diffusion of precursors with the evaporation of the solvent under certain temperatures. Thus, if there is no solvent present and the precursor can be automatically introduced into the mesopores, the redistribution of precursors can be greatly overcome. Moreover, it is assumed that the solvent can exert a competitive adsorption on the support and disturb the host–guest interactions, which in turn hinders the dispersion and anchoring of active components on supports [32]. This proposition is supported by the experimental result indicating that the dispersion of noble metals (Pd, Au) grafted on SBA-15 is influenced by the use of different solvents [33]. On the other hand, concerning the filling degree of active species within a single step, the deposition process without the use of a solvent has merit, as it can make full use of the pores without the void space needing to be occupied by a solvent.
As proved elsewhere, the dry salts can be introduced into the pore channels of SBA-15 [34]. These dry salts are metal nitrates and will turn into molten salt phase in certain temperature ranges. Apart from its unique property of mobility, the molten salts are also viscous, and both of these properties are supposed to be crucial for determining the dispersion of NiO particles. When the temperature is elevated, nickel nitrate starts to become meltable (evidence is provided by thermogravimetry-differential thermal analysis (TG-DTA) and the direct digital picture, Figures S1 and S2) and the filling of mesopores begins. Thus, under the driver of capillary imbibition, the molten salt can be easily sucked into the pore channels. As a sharp contrast to the wet impregnation preparation, the simultaneous lack of solvent evaporation and possession of high viscosity of molten salt phase significantly prevents the redistribution of guest species under thermal treatment. As a result, uniform NiO nanoparticles confined in the pore channels are produced when the temperature reaches and then surpasses the decomposition temperature. In terms of nickel acetate as a precursor, due to the thermal property of direct decomposition without involving an intermediate molten salt phase, it cannot be diffused into the pores. Consequently, it displayed bulk NiO particles exclusively outside of the mesopores.
Since the discovery of the ordered mesoporous silica, the expected confinement effects of the pores have attracted tremendous interest. However, there are only few reports concerning the systematic investigation of pore confinement on the properties of guest species. Normally, to fully explore the confinement effect, comparison of the behaviors of guest species exclusive inside and outside of the mesopores is favored. In the present case, the samples prepared from nickel nitrate and nickel acetate via the solvent-free method only just meets this requirement. As most of the catalytic reactions are high-temperature processes, the thermal stability of active species is an important parameter needed to evaluate the catalysts. Hence, the confinement effect of mesopores on the thermal stability of nickel species is investigated by XRD under different calcination temperatures. Owing to the different thermal stabilities, the decomposition processes of the two nickel precursors into NiO are not the same. After being air calcined at 250 °C for 4 h, almost all of the nickel acetate is converted into NiO, as evidenced by the absence of conspicuous diffraction peaks related to nickel species other than NiO (Figure 7a). Likely because of the relatively low thermal treatment temperature, the line broadening of diffraction peaks is obvious and the coarsening of NiO is not severe. However, for nickel nitrate (Figure 7b), only partial decomposition of precursor has occurred, as indicated by the presence of a series of diffraction peaks centered at 2θ = 12.8°, 25.8° and 33.6°, attributable to Ni3(NO3)2(OH)4 (JCPDS 22-0752). The compound had been previously reported as an intermediate between nickel nitrate and the final decomposed product NiO [22]. By comparing the pattern of 20Ni-NO3-250 with that of direct decomposed nickel nitrate at 250 °C (for simplicity, denoted as Ni(NO3)2-D), it can be assumed that the decomposition of Ni3(NO3)2(OH)4 into NiO is much retarded, possibly as a result of pore confinement. By increasing the calcination temperatures, the line broadening of diffraction peaks for nickel acetate gradually disappears, indicating the significant sintering of NiO particles under elevated temperatures. For the samples prepared from nickel nitrate, the complete conversion of Ni3(NO3)2(OH)4 to NiO is observed at 350 °C (Figure 7c). Strikingly, even after increasing calcination temperatures to 650 °C, the line broadening of diffraction peaks is still obvious, and no distinct changes are detected as compared to the sample air calcined at the lower temperature (350 °C). To quantify the confinement effect, the average grain size calculated by the Sherrer equation as a function of calcination temperature for different precursors is plotted in Figure 7d. Owing to the incomplete conversion to NiO, the 20Ni-NO3-250 is missing. All the guest species represented by hollow and solid squares are NiO and the comparison is thus reasonable. The smallest size of NiO is only ca. 2.7 nm, which is obtained from the 20Ni-Ac-250 sample with exclusive external particles. The result indicates that the fine particles are not an inherent property of pore confined NiO, and at low temperatures, it is the temperature rather than the location of guest species that determines the particle size. The size of NiO gradually increases to ca. 5 nm at temperatures below 350 °C. Severe sintering of NiO particles takes place when the temperature is further increased, as evidenced by the sharp increase in sizes to 15 nm and 25 nm at 450 °C and 550 °C, respectively. In contrast, for confined NiO samples (20Ni-NO3-T), the average grain size of NiO is around 5 nm and almost unchanged within the operated temperature range. The result clearly demonstrates that with the aid of pore confinement, the nanosized NiO particles are highly thermally stable. As a result, the highly dispersed NiO nanoparticles are obtained even at a high calcination temperature (650 °C).
In order to explore the catalytic performance of the prepared samples, the reaction of ammonia decomposition is adopted, in view of the high reaction temperature. Additionally, this reaction has recently been subject to an increasing level of attention due to the possibility of ammonia being used as a hydrogen storage medium in possible hydrogen economy. Compared to conventional processes involving hydrogen production, like stream reforming and partial oxidation of methane, the ammonia decomposition route has the merit of the production of COx-free hydrogen, which is highly desirable in current proton-exchange membrane fuel cells (PEMFCs). The supported Ni/silica catalyst is reported to be active for ammonia decomposition, making the evaluation meaningful. Since metallic Ni is well acknowledged to be the active site, the catalyst is subjected to H2 treatment at 550 °C before activity testing, and most of the NiO can be transformed into metallic Ni at this temperature, in reference to the temperature-programmed reduction by H2 (H2-TPR)result and high resolution transmission electron microscopy (HRTEM) characterization (Figure S3).
To make a reliable comparison, the effects from internal and external mass diffusion are first explored. The reaction rates were compared over the 20NiO-NO3-550 with varied granule sizes (20–40, 40–60, 60–80, 80–100 mesh) and at different dilution ratios with SiC (3:1, 1:1, 3:7, 1:9) while maintaining the same contact time at 400 °C. As can be seen from Figure S4a, the NH3 conversion showed similar rates when particle size was smaller than 20–40 mesh. In addition, the reaction rates were kept constant over the explored SiC dilution experiment (Figure S4b). These results suggested that the mass transfer limitations of catalysts during reactions could be eliminated under the employed reaction conditions. As such, it can be safely concluded that the differences in catalytic behavior accurately reflect the varied reactivity of the active sites.
From Figure 8, it is evident that significant variation in NH3 conversion are exhibited. That is, the catalytic activity of 20Ni-Ac-550 exhibits the worst performance, with the highest value of 55.0% at 650 °C. For the sample derived from wet impregnation, due to the improvement in NiO dispersion, the conversion efficiency receives distinct enhancement, with the maximum value of 82.1% obtained at 650 °C. Notably, the reaction efficiency is further improved when the catalyst is prepared by using the novel solvent-free method. The value of NH3 conversion (93.7% at 650 °C) exhibits a much higher value than the counterpart catalysts of 20Ni-Ac-550 and 20NiO/SBA-15. Remarkably, when compared with the literature reports, this value is among the best performance for Ni-base catalysts [35,36], and is likely related to both high loading and good dispersion of NiO. On the other hand, the catalyst also reveals superior stability, since the activity is almost the same even after successive running of 60 h at 650 °C (Figure 8b). The result demonstrates the present solvent-free method is powerful in preparing thermally stable and robust supported catalysts, which is supported by the results of XRD and TEM for the spent catalyst of 20Ni-NO3-550 (Figure 8c,d).

3. Experimental

3.1. Preparation of SBA-15

All chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China (except P123 from Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China) and used as received. Synthesis of SBA-15 follows Zhao’s process [10]. Basically, the soft template of P123 (4 g) was added to HCl aqueous solution (2 M, 120 mL) with stirring, followed by introduction of 30 mL H2O. After the dissolvation of surfactant, 9 g of TEOS (tetraethyl orthosilicate) was added and the solution was kept stirring for 24 h at 40 °C. Then the solution was transferred into an autoclave, sealed and aged at 100 °C statically for 24 h. The resulting precipitate was thoroughly washed with de-ionized water and ethanol for several times. The rinsed powder was dried and received calcination in air at 550 °C for 5 h under a ramp rate of 1 °C min−1.

3.2. Synthesis of Mesopore Confined NiO Nanoparticles

The solvent-free method to pore confined NiO nanoparticles was a simple and time-conserving process, as it only comprised manual grinding of the mixture of nickel precursor and SBA-15 and the subsequent air calcination. In a typical synthesis, calculated amount of Ni(NO3)2·6H2O was manually ground with SBA-15 in an agate mortar for about 10 min at ambient temperature and pressure. Then the homogeneous powder was transferred into a crucible, which was placed in the muffle furnace. The thermal treatment in air started at room temperature with a ramp of 1 °C min−1 to certain temperature and maintained at that temperature for 4 h, then cooled naturally. The obtained sample was denoted as mNiO-NO3-T, where m and T represented the loading in terms of weight percentage (wt.%) and the corresponding calcination temperature.
To determine the intrusion mechanism of guest species into the mesoporous and at the same time investigate the effect of pore confinement on the coarsening of NiO, the NiO derived from nickel acetate was also prepared under different calcination temperatures. In line with the above notation, these samples with 20 wt.% NiO loading were named as 20NiO-Ac-T.
As a comparison, the conventional wet impregnation route to supported NiO sample was employed. The precursor, loading and calcination parameters were identical to those of 20Ni-NO3-550 and the final product was denoted as 20NiO/SBA-15.

3.3. Characterization

Both small-angle and wide-angle XRD patterns were collected on a Philips X’pert X-ray diffractometer (PANalytical B.V., Almelo, The Netherlands) operated with Ni-filtered Cu Kα radiation (λ = 0.15418 nm) at 40 kV and 40 mA. The average grain sizes were determined from XRD line broadening measurements using the Scherrer equation, d = Kλ/βosθ where λ is the X-ray wavelength, θ is the diffraction angle, K is the particle shape factor, usually taken as 0.89, and β is full width at half maximum in radians. SEM images of samples were obtained with Hitachi S4800 (Hitachi High-Technologies Corporation, Tokyo, Japan) microscopes at an acceleration voltage of 10 kV. TEM images were taken on a JEM-2100 (JEOL Ltd. Tokyo, Japan) instrument at an acceleration voltage of 200 kV. The samples were crushed and dispersed in A.R. grade ethanol and the resulting suspensions were allowed to dry on carbon film supported on copper grids.
H2-temperature programmed reduction (H2-TPR) experiments were performed with H2 as a reductant in a quartz U-type reactor, and 100 mg sample was used for each measurement. Prior to the reduction, the sample was pretreated in a high purified N2 stream at 300 °C for 1 h and then cooled to room temperature. After that, the H2-Ar mixture (6.9% H2 by volume) was switched on, and the measurement started from room tempeature to target temperature with rate of 10 °C·min−1. The consumption of H2 was monitored by using a thermal conductivity detector (TCD).
The catalytic testing was carried out in a continuous-flow quartz reactor (catalyst: 100 mg, 60–80 mesh) under pure NH3 (flow rate: 50 mL/min; GHSVNH3: 30,000 mL/(h gcat)). Before reaction, the catalyst was reduced in situ in a 25% H2/Ar flow at 550 °C for 2 h, then purged with a flow of pure Ar. The acquisition of activity data at a particular temperature was conducted after the establishment of steady state. Product analysis was performed on an on-line gas chromatograph (Shimadzu, Corporation, Kyoto, Japan) equipped with thermal detector and Poropak Q column, using Ar as a carrier gas.

4. Conclusions

A facile and efficient solvent-free method for the synthesis of pore confined NiO particles was reported in this work. It was found that under manual grinding, the grain size of silica matrix decreased to sub-micrometer levels, which would provide greater pore accessibility and facilitate molecular diffusion. The exclusive formation of pore confined NiO with high loading was prepared by using nickel nitrate as a precursor, whereas the particles obtained from nickel acetate were exclusively observed on the external surface of the mesopores. For 20 wt.% loading, the NiO nanoparticles were highly dispersed and no aggregation was discerned. Upon further increasing of the loading to 30 wt.%, most of the particles were still discrete and partial aggregation of NiO to rod-like architecture occurred simultaneously. For the mechanism of the formation process of pore confined nanoparticles with good dispersion, it was proposed that the mobility and viscosity of molten salt enabled the encapsulation and homogeneous distribution of NiO in the mesopore, respectively. The high thermal stability of NiO was enabled by the pore confinement. Owing to the properties of high loading, good dispersion and high thermal stability, the synthesized material displayed excellent activity and superior stability in the model reaction of ammonia decomposition. The preliminary catalytic result demonstrated in the present solvent-free method was powerful in preparing thermally stable and robust supported catalysts.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal15111016/s1, Table S1: The textural parameters of various samples; Figure S1: The TG/DTA curve of Ni(NO3)2·6H2O; Figure S2: digital picture of the two employed nickel salts at 100 °C; Figure S3: The HRTEM image of spent 20Ni-NO3-550 catalyst; Figure S4: Influence of (a) pellet size and (b) SiC dilution on the reaction rate of 20Ni-NO3-550. The reaction temperature is controlled at 400 °C.

Author Contributions

Y.X.: methodology, validation, formal analysis and writing—original draft; T.T.: data curation, methodology, validation and formal analysis; P.W.: formal analysis and methodology; C.Z.: investigation and data curation; J.Z.: data collection and formal analysis; K.Z.: conceptualization, methodology, formal analysis and funding acquisition; C.T.: conceptualization, methodology, formal analysis, writing—review and editing, supervision, project administration and funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Open Project Program of State Key laboratory of Low-carbon Smart Coal-fired Power Generation and Ultraclean Emission (D2023FK095), the Natural Science Foundation of Jiangsu Province (BK20230007), the National Natural Science Foundation of China (22276097).

Data Availability Statement

The data supporting the conclusions and findings are provided in the article and supplemental information.

Conflicts of Interest

Authors Yun Xu, Chunlei Zhang and Ke Zhuang were employed by State Key Laboratory of Low-carbon Smart Coal-Fired Power Generation and Ultra-Clean Emission, China Energy Science and Technology Research Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Zhou, Z.; Wang, S.; Zhou, W.; Wang, G.; Jiang, L.; Li, W.; Song, S.; Liu, J.; Sun, G.; Xin, Q. Novel Synthesis of Highly Active Pt/C Cathode Electrocatalyst for Direct Methanol Fuel Cell. Chem. Commun. 2003, 9, 394–395. [Google Scholar] [CrossRef]
  2. Huang, Z.; Cui, F.; Kang, H.; Chen, J.; Zhang, X.; Xia, C. Highly Dispersed Silica-Supported Copper Nanoparticles Prepared by PrecipitationGel Method: A Simple but Efficient and Stable Catalyst for Glycerol Hydrogenolysis. Chem. Mater. 2008, 20, 5090–5099. [Google Scholar] [CrossRef]
  3. Liu, N.; Zhang, J.; Cai, Y.-L.; Zhang, J.-G.; Ouyang, D.-J.; Wang, S.-B.; Xu, Q.-M.; Hu, J.-J.; Chen, D.-M.; Wang, G.-W.; et al. Modification of Biochar Catalyst Using Copper for Enhanced Catalytic Oxidation of VOCs. Toxics 2025, 13, 503. [Google Scholar] [CrossRef] [PubMed]
  4. Ma, Y.; Mu, B.; Zhang, X.; Zhang, H.; Xu, H.; Qu, Z.; Gao, L.I. Hierarchical Ag-SiO2@Fe3O4 Magnetic Composites for Elemental Mercury Removal from Non-Ferrous Metal Smelting Flue Gas. J. Environ. Sci. 2019, 79, 111–120. [Google Scholar] [CrossRef]
  5. Wang, H.; Zhang, B.; Yang, H.; Bao, Q.; Wu, B.O. New Insights on the Effects of SO2 on NO Oxidation from Flue Gas with H2O2 Vapor over Fe2O3/SiO2. Process. Saf. Environ. Prot. 2022, 165, 138–150. [Google Scholar] [CrossRef]
  6. Ermakova, M.A.; Ermakov, D.Y.; Kuvshinov, G.G. Effective Catalysts for Direct Cracking of Methane to Produce Hydrogen and Filamentous Carbon Part I. Nickel Catalysts. Appl. Catal. A Gen. 2000, 201, 61–70. [Google Scholar] [CrossRef]
  7. Cho, Y.S.; Park, J.C.; Lee, B.; Kim, Y.; Yi, J. Preparation of Mesoporous Catalyst Supported on Silica with Finely Dispersed Ni Particles. Catal. Lett. 2002, 81, 89–96. [Google Scholar] [CrossRef]
  8. Zhang, X.; Rui, N.; Jia, X.; Hu, X.; Liu, C.-J. Effect of Decomposition of Catalyst Precursor on Ni/CeO2 Activity for CO Methanation. Chin. J. Catal. 2019, 40, 495–503. [Google Scholar] [CrossRef]
  9. Zheng, R.; Liu, Z.; Wang, Y.; Xie, Z. Industrial Catalysis: Strategies to Enhance Selectivity. Chin. J. Catal. 2020, 41, 1032–1038. [Google Scholar] [CrossRef]
  10. Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G.H.; Chmelka, B.F.; Stucky, G.D. Triblock Copolymer Syntheses of Mesoporous Silica with Periodic 50 to 300 Angstrom Pores. Science 1998, 279, 548–552. [Google Scholar] [CrossRef]
  11. Zhu, J.I.; Kónya, Z.; Puntes, V.F.; Kiricsi, I.; Miao, C.X.; Ager, J.W.; Alivisatos, A.P.; Somorjai, G.A. Encapsulation of Metal (Au, Ag, Pt) Nanoparticles into the Mesoporous SBA-15 Structure. Langmuir 2003, 19, 4396–4401. [Google Scholar] [CrossRef]
  12. Laugel, G.; Arichi, J.; Guerba, H.; Molière, M.; Kiennemann, A.; Garin, F.; Louis, B. Co3O4 and Mn3O4 Nanoparticles Dispersed on SBA-15: Efficient Catalysts for Methane Combustion. Catal. Lett. 2008, 125, 14–21. [Google Scholar] [CrossRef]
  13. Zhang, Z.; Dai, S.; Blom, D.A.; Shen, J. Synthesis of Ordered Metallic Nanowires inside Ordered Mesoporous Materials through Electroless Deposition. Chem. Mater. 2002, 14, 965–968. [Google Scholar] [CrossRef]
  14. Audoit, G.; Kulkarni, J.S.; Morris, M.A.; Holmes, J.D. Size Dependent Thermal Properties of Embedded Crystalline Germanium Nanowires. J. Mater. Chem. 2007, 17, 1608–1613. [Google Scholar] [CrossRef]
  15. Li, Z.; Kübel, C.; Pârvulescu, V.I.; Richards, R. Size Tunable Gold Nanorods Evenly Distributed in the Channels of Mesoporous Silica. Acs Nano 2008, 2, 1205–1212. [Google Scholar] [CrossRef] [PubMed]
  16. Zhu, K.; D’Souza, L.; Richards, R.M. Planting of Bis(1,5-Cyclooctadiene) Nickel Upon Silica to Harvest NiO (<5 nm) Nanoparticles in a Silica Matrix. Appl. Organomet. Chem. 2005, 19, 1065–1069. [Google Scholar] [CrossRef]
  17. Lu, B.; Ju, Y.; Abe, T.; Kawamoto, K. Grafting Ni Particles onto SBA-15, and Their Enhanced Performance for CO2 Methanation. RSC Adv. 2015, 5, 56444–56454. [Google Scholar] [CrossRef]
  18. Park, Y.; Kang, T.; Kim, P.; Yi, J. Encapsulation Method for the Dispersion of NiO onto Ordered Mesoporous Silica, SBA-15, Using Polyethylene Oxide (PEO). J. Colloid Interface Sci. 2006, 295, 464–471. [Google Scholar] [CrossRef]
  19. Cheng, M.-Y.; Pan, C.-J.; Hwang, B.-J. Highly-Dispersed and Thermally-Stable NiO Nanoparticles Exclusively Confined in SBA-15: Blockage-Free Nanochannels. J. Mater. Chem. 2009, 19, 5193–5200. [Google Scholar] [CrossRef]
  20. Sietsma, J.R.A.; Meeldijk, J.D.; Den Breejen, J.P.; Versluijs-Helder, M.; Van Dillen, A.J.; De Jongh, P.E.; De Jong, K.P. The Preparation of Supported Nio and Co3O4 Nanoparticles by the Nitric Oxide Controlled Thermal Decomposition of Nitrates. Angew. Chem. Int. Ed. Engl. 2007, 46, 4547–4549. [Google Scholar] [CrossRef]
  21. Yue, W.; Zhou, W. Synthesis of Porous Single Crystals of Metal Oxides via a Solid-Liquid Route. Chem. Mater. 2007, 19, 2359–2363. [Google Scholar] [CrossRef]
  22. Chen, S.; Ciotonea, C.; Ungureanu, A.; Dumitriu, E.; Catrinescu, C.; Wojcieszak, R.; Dumeignil, F.; Royer, S. Preparation of Nickel (Oxide) Nanoparticles Confined in the Secondary Pore Network of Mesoporous Scaffolds Using Melt Infiltration. Catal. Today 2019, 334, 48–58. [Google Scholar] [CrossRef]
  23. Chytil, S.; Haugland, L.; Blekkan, A. On the Mechanical Stability of Mesoporous Silica SBA-15. Microporous Mesoporous Mater. 2008, 111, 134–142. [Google Scholar] [CrossRef]
  24. Carrero, A.; Calles, J.A.; Vizcaíno, A.J. Hydrogen Production by Ethanol Steam Reforming over Cu-Ni/SBA-15 Supported Catalysts Prepared by Direct Synthesis and Impregnation. Appl. Catal. A Gen. 2007, 327, 82–94. [Google Scholar] [CrossRef]
  25. Park, J.G.; Ko, C.H.; Yi, K.B.; Park, J.-H.; Han, S.-S.; Cho, S.-H.; Kim, J.-N. Reactive Adsorption of Sulfur Compounds in Diesel on Nickel Supported on Mesoporous Silica. Appl. Catal. B-Environ. 2008, 81, 244–250. [Google Scholar] [CrossRef]
  26. Marceau, E.; Che, M.; Čejka, J.; Zukal, A. Nickel(II) Nitrate vs. Acetate: Influence of the Precursor on the Structure and Reducibility of Ni/MCM-41 and Ni/Al-MCM-41 Catalysts. ChemCatChem. 2010, 2, 413–422. [Google Scholar] [CrossRef]
  27. Vallet-Regí, M.; Manzano, M.; González-Calbet, J.M.; Okunishi, E. Evidence of Drug Confinement into Silica Mesoporous Matrices by Stem Spherical Aberration Corrected Microscopy. Chem. Commun. 2010, 46, 2956–2958. [Google Scholar] [CrossRef]
  28. He, C.; Li, P.; Wang, H.; Cheng, J.; Zhang, X.; Wang, Y.; Hao, Z. Ligand-Assisted Preparation of Highly Active and Stable Nanometric Pd Confined Catalysts for Deep Catalytic Oxidation of Toluene. J. Hazard. Mater. 2010, 181, 996–1003. [Google Scholar] [CrossRef]
  29. Wang, X.; Wang, J.; Liu, A.; Yu, Y.; Ji, J.; Guo, K.; Wan, H.; Tang, C.; Dong, L. Unravelling the Structure Sensitivity of CuO/SiO2 Catalysts in the No + Co Reaction. Catal. Sci. Technol. 2020, 10, 3848–3856. [Google Scholar] [CrossRef]
  30. Kim, B.M.; Qian, S.; Bau, H.H. Filling Carbon Nanotubes with Particles. Nano Lett. 2005, 5, 873–878. [Google Scholar] [CrossRef] [PubMed]
  31. Sun, J.; Ma, D.; Zhang, H.E.; Liu, X.; Han, X.; Bao, X.; Weinberg, G.; Pfänder, N.; Su, D. Toward Monodispersed Silver Nanoparticles with Unusual Thermal Stability. J. Am. Chem. Soc. 2006, 128, 15756–15764. [Google Scholar] [CrossRef] [PubMed]
  32. Shi, L.-Y.; Li, Y.-X.; Xue, D.-M.; Tan, P.; Jiang, Y.; Liu, X.-Q.; Sun, L.-B. Fabrication of Highly Dispersed Nickel in Nanoconfined Spaces of as-Made SBA-15 for Dry Reforming of Methane with Carbon Dioxide. Chem. Eng. J. 2020, 390, 124491. [Google Scholar] [CrossRef]
  33. Freeman, H.; Sferra, P. Innovative Hazardous Waste Treatment Technology; Technomic Publishing Co., Ltd.: Lancaster, PA, USA, 1990. [Google Scholar]
  34. Yang, Q.; Sun, P.Z.; Fumagalli, L.; Stebunov, Y.V.; Haigh, S.J.; Zhou, Z.W.; Grigorieva, I.V.; Wang, F.C.; Geim, A.K. Capillary Condensation under Atomic-Scale Confinement. Nature 2020, 588, 250–253. [Google Scholar] [CrossRef]
  35. Su, T.; Guan, B.; Zhou, J.; Zheng, C.; Guo, J.; Chen, J.; Zhang, Y.; Yuan, Y.; Xie, W.; Zhou, N.; et al. Review on Ru-Based and Ni-Based Catalysts for Ammonia Decomposition: Research Status, Reaction Mechanism, and Perspectives. Energy Fuels 2023, 37, 8099–8127. [Google Scholar] [CrossRef]
  36. Le, T.A.; Do, Q.C.; Kim, Y.; Kim, T.-W.; Chae, H.-J. A Review on the Recent Developments of Ruthenium and Nickel Catalysts for COx-Free H2 Generation by Ammonia Decomposition. Korean J. Chem. Eng. 2021, 38, 1087–1103. [Google Scholar] [CrossRef]
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Figure 1. The small-angle XRD patterns of SBA-15 (a) before and (b) after NiO encapsulation.
Figure 1. The small-angle XRD patterns of SBA-15 (a) before and (b) after NiO encapsulation.
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Figure 2. The typical SEM images of SBA-15 (a) before and (b) after manual grinding.
Figure 2. The typical SEM images of SBA-15 (a) before and (b) after manual grinding.
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Figure 3. The wide XRD patterns of various samples. (a) 20Ni-NO3-550, (b) 30Ni-NO3-550, (c) 20NiO/SBA-15 and (d) 20Ni-Ac-550.
Figure 3. The wide XRD patterns of various samples. (a) 20Ni-NO3-550, (b) 30Ni-NO3-550, (c) 20NiO/SBA-15 and (d) 20Ni-Ac-550.
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Figure 4. The H2-TPR profiles of various samples.
Figure 4. The H2-TPR profiles of various samples.
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Figure 5. The typical TEM images viewed from the directions (a) perpendicular to and (b) parallel to mesopore channels of 20Ni-NO3-550 sample and (b) the corresponding histogram for particle size distribution. (d) The enlarged image of the framed area in (c).
Figure 5. The typical TEM images viewed from the directions (a) perpendicular to and (b) parallel to mesopore channels of 20Ni-NO3-550 sample and (b) the corresponding histogram for particle size distribution. (d) The enlarged image of the framed area in (c).
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Figure 6. The typical TEM images for (a) 30Ni-NO3-550, (b) 20NiO/SBA-15 and (c,d) 20Ni-Ac-550 sample.
Figure 6. The typical TEM images for (a) 30Ni-NO3-550, (b) 20NiO/SBA-15 and (c,d) 20Ni-Ac-550 sample.
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Figure 7. Effect of calcination temperature on the sintering behavior of NiO on mesoporous SBA-15. (a–c) XRD patterns and (d) correlation of particle size with calcination temperature for NiO derived from acetate and nitrate precursors.
Figure 7. Effect of calcination temperature on the sintering behavior of NiO on mesoporous SBA-15. (a–c) XRD patterns and (d) correlation of particle size with calcination temperature for NiO derived from acetate and nitrate precursors.
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Figure 8. The (a) catalytic activity and (b) reaction stability of confined NiO in SBA-15 for NH3 decomposition. (c,d) XRD and typical TEM image of the spent catalyst after successive reaction at 650 °C for 60 h.
Figure 8. The (a) catalytic activity and (b) reaction stability of confined NiO in SBA-15 for NH3 decomposition. (c,d) XRD and typical TEM image of the spent catalyst after successive reaction at 650 °C for 60 h.
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MDPI and ACS Style

Xu, Y.; Tang, T.; Wang, P.; Zhang, C.; Zhao, J.; Zhuang, K.; Tang, C. Facile Synthesis of Uniform NiO Nanoparticles Exclusively Confined in Mesoporous SBA-15 with High Loading for Ammonia Decomposition. Catalysts 2025, 15, 1016. https://doi.org/10.3390/catal15111016

AMA Style

Xu Y, Tang T, Wang P, Zhang C, Zhao J, Zhuang K, Tang C. Facile Synthesis of Uniform NiO Nanoparticles Exclusively Confined in Mesoporous SBA-15 with High Loading for Ammonia Decomposition. Catalysts. 2025; 15(11):1016. https://doi.org/10.3390/catal15111016

Chicago/Turabian Style

Xu, Yun, Tianfa Tang, Pengyao Wang, Chunlei Zhang, Jianbo Zhao, Ke Zhuang, and Changjin Tang. 2025. "Facile Synthesis of Uniform NiO Nanoparticles Exclusively Confined in Mesoporous SBA-15 with High Loading for Ammonia Decomposition" Catalysts 15, no. 11: 1016. https://doi.org/10.3390/catal15111016

APA Style

Xu, Y., Tang, T., Wang, P., Zhang, C., Zhao, J., Zhuang, K., & Tang, C. (2025). Facile Synthesis of Uniform NiO Nanoparticles Exclusively Confined in Mesoporous SBA-15 with High Loading for Ammonia Decomposition. Catalysts, 15(11), 1016. https://doi.org/10.3390/catal15111016

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