Introduction

In the contemporary landscape of energy sustainability, the imperative to transition away from finite fossil fuels and mitigate environmental degradation has propelled intensive research into alternative fuel production and chemical transformations [1, 2]. Central to this endeavor are catalysts, which serve as accelerators for chemical reactions, enhancing efficiency and minimizing undesirable byproducts. Among the plethora of alternatives, hydrogen (H2) stands as a beacon of clean energy, offering vast potential for both power generation and chemical synthesis. Thus, the quest for sustainable methods of H2 acquisition and storage has risen to the forefront of scientific inquiry [3,4,5].

One widely explored avenue for H2 production involves the utilization of metal boron hydrides and chemical hydrides [6, 7]. Foremost among these is sodium borohydride (NaBH4), esteemed for its stability and non-flammable nature. The hydrolysis of NaBH4, occurring spontaneously in aqueous solutions under mild conditions of temperature and pressure, serves as a principal route for H2 generation [8]. NaBH4 is a solid chemical compound extensively studied for its potential as a hydrogen storage material and its role in hydrogen generation through hydrolysis. The hydrolysis of NaBH4 involves its reaction with water to produce hydrogen gas (H2) and sodium hydroxide (NaOH) as shown in the Eq. (1) [9,10,11]:

$${{\text{NaBH}}}_{4}+2{{\text{H}}}_{2}{\text{O}}\to {\text{NaOH}}+4{{\text{H}}}_{2}$$
(1)

This reaction is exothermic and can occur spontaneously in aqueous solutions, particularly at elevated temperatures. The process is typically catalyzed to enhance reaction rates and improve efficiency.

While NaBH4 offers advantages such as high hydrogen content and relatively low toxicity compared to other chemical hydrides, challenges remain in terms of its regeneration and recycling, as well as the need to develop efficient catalysts to facilitate the hydrolysis process at lower temperatures and pressures [12,13,14].

However, while NaBH4 presents promise for H2 transportation and storage, its efficient recovery often necessitates considerable energy inputs, posing a significant challenge. Addressing this challenge demands the development of advanced catalytic systems [15]. Bimetallic catalysts, in particular, have garnered attention for their potential to diversify reaction pathways and enhance catalytic activity through judicious selection of metal combinations [16, 17]. In this context, Al2O3-supported nanobimetallic Co-La-B catalysts emerge as compelling candidates for H2 storage and recovery applications. Cobalt (Co) [18] and lanthanum (La) [19] are recognized for their pivotal roles in H2 storage reactions, while boron (B) serves as a supportive element, enhancing surface properties and catalytic activity. The incorporation of aluminum oxide (Al2O3) [20] further bolsters stability, owing to its high surface area and exceptional thermal resilience.

This study endeavors to develop an Al2O3-supported nanobimetallic Co-La-B (Al2O3@Co-La-B) catalyst tailored for H2 generation via NaBH4 hydrolysis, with a keen focus on elucidating its kinetic behavior. The efficacy of the catalyst in H2 generation and recovery, shaped by factors such as preparation methods, catalyst composition, crystal structure, and surface properties, will be rigorously assessed. By providing a detailed account of the catalyst's preparation steps and evaluating its performance, this article aims to furnish invaluable insights into its potential applications in NaBH4 hydrolysis, thereby enriching the discourse on sustainable energy production and storage.

Ultimately, as the global imperative for sustainable energy solutions grows ever more pressing, this study aspires to contribute to future advancements by championing the development and utilization of efficient catalysts.

Experimental section

Chemicals

Aluminum oxide (Al2O3, 99.9%, Sigma-Aldrich), cobalt chloride hexahydrate (CoCl2·6H2O, 99.9%, Merck), lanthanum nitrate hexahydrate (La(NO3)3·6H2O, 99.9%, Sigma-Aldrich), sodium borohydride (NaBH4, 99.9%, Merck), anhydrous ethanol (C2H5OH, > 99.8%, Sinopharm Group) and sodium hydroxide (NaOH, 99.9%, Scharlau Company) were purchased and used as received.

Fabrication of Al2O3@Co-La-B catalyst

The specific procedure for preparing the Co-La-B catalyst has been detailed in earlier research studies. A Co-La-B catalyst with a La content of around 4% was employed. In the preparation process, a certain quantity of CoCI2.6H2O and La(NO3)3·6H2O were dissolved in 50 ml of ethanol. Following this, the appropriate amount of Al2O3 was added, allowing the metals to adhere to the Al2O3 at room temperature for a duration of 24 h. Subsequently, the ethanol within the solution was evaporated at 50 °C, and a solution containing 50 mL of distilled water was introduced to the Al2O3 impregnated with metals. Under an N2 atmosphere, a 0.1 M solution of NaBH4 (50 mL) was carefully added drop by drop to the metal-loaded Al2O3. The resultant catalyst underwent a thorough washing process using pure water and ethanol, and was then subjected to filtration. The synthesized catalyst was then dried under an N2 atmosphere at 80 °C for a span of 6 h. The final catalyst was stored within a sealed container for utilization in the hydrolysis of NaBH4.

Characterization techniques

An X-ray diffractometer (D8 Bruker) was employed to perform X-ray diffraction (XRD) analysis on the resulting catalyst using Cu Ka radiation (α = 1.54 Å), scanning across the range of 0 to 70 degrees. Functional group information of the resulting catalyst was acquired through Fourier transform infrared (FT-IR) analysis using a Perkin-Elmer spectrometer. The composition and chemical formation of the catalyst was determined by energy dispersive X-ray spectroscopy (EDX, Zeiss EVO Model), The determination of catalyst surface area was carried out using a Brunauer–Emmett–Teller (BET) surface area analyzer (Micromeritics ASAP 2000). To investigate the surface morphology of the catalyst, a scanning electron microscopy (SEM, Zeiss EVO Model) was utilized.

H2 production via NaBH4 hydrolysis experimentations and recyclability tests

For the H2 generation via NaBH4 hydrolysis tests, an Al2O3@Co-La-B catalyst (0.05 g) was introduced to a mixture comprising 10 mL of 0.31 wt% aqueous NaBH4 solution and 3 wt% NaOH solution. The reaction flask, which was used throughout the experiments, was immersed in a water bath to maintain the desired reaction temperature. The measurement of H2 volume produced was accomplished using the water displacement method. Following the NaBH4 reaction completion with the catalyst, the supported catalyst was isolated from the reaction medium and subjected to several rounds of thorough cleaning with distilled water. The catalyst was then placed in a fresh 10 mL solution of NaBH4 and subjected to five consecutive recyclability tests to validate its performance.

The H2 generation rate (H2GR) via NaBH4 hydrolysis was calculated by Eq. (2).

$${H}_{2}GR=\frac{{V}_{{H}_{2}}}{t\times {m}_{cat}}$$
(2)

where H2GR (mLH2 min−1 gcat−1) is the H2 generation rate, VH2 (mL) is the H2 volume, t (min) is the reaction time, mcat (g) is the amount of Al2O3@Co-La-B catalyst.

Kinetic models

The nth-order [21] and Langmuir–Hinshelwood [21, 22] models given by Eqs. (3)-(5) and Eqs. (5)-(6) were used to study the kinetics of H2 generation via NaBH4 hydrolysis.

nth-order model:

$$-^{r_A}=\frac{-d\left[NaBH_4\right]}{dt}=k\left[NaBH_4\right]^n$$
(3)

where [NaBH4] (ppm) is the concentration of NaBH4, rA is the rate of the reaction, and k is the rate constant of the reaction. By integrating Eq. (4), Eqs. (5) and (6) are obtained:

$$-\underset{\left[NaB{H}_{4}\right]}{\overset{\left[NaB{H}_{4}\right]}{\int }}\frac{d\left[NaB{H}_{4}\right]}{{\left[NaB{H}_{4}\right]}^{n}}=k\underset{0}{\overset{t}{\int }}dt$$
(4)
$$\frac{1}{\left(1-n\right)}\left(\frac{1}{{\left[NaB{H}_{4}\right]}^{n-1}}-\frac{1}{{\left[NaB{H}_{4}\right]}^{n-1}}\right)=kt\left(n\ne 1\right)$$
(5)

Langmuir–Hinshelwood model:

$$\frac{d\left[NaB{H}_{4}\right]}{dt}=-{r}_{CA}=-k\frac{{K}_{a}\left[NaB{H}_{4}\right]}{1+{K}_{a}\left[NaB{H}_{4}\right]}$$
(6)
$$\left({\left[NaBH_4\right]}_0-\left[NaBH_4\right]\right)+\frac1{K_a}\text{ln}\left(\frac{{\left[NaBH_4\right]}_0}{\left[NaBH_4\right]}\right)=kt$$
(7)

From Eq. (5), plot \(\frac{A=\pi {r}^{2}}{\left(1-n\right)}\left(\frac{1}{\left({\left[NaB{H}_{4}\right]}^{n-1}\right)}-\frac{1}{{{\left[NaB{H}_{4}\right]}_{0}}^{n-1}}\right)\) against t, estimating the n-value corresponding to the highest R2 value, and the slope represents the k constant. From Eq. (7), plot \(\left({\left[NaB{H}_{4}\right]}_{0}-\left[NaB{H}_{4}\right]\right)\) against t, and the slope represents the k constant.

The activation energy (Ea) for H2 generation via NaBH4 hydrolysis was calculated from Arrhenius Eq. (8) using the k-values obtained at different temperatures from the nth-order and Langmuir–Hinshelwood kinetic models. The Arrhenius equation provides valuable insights into the temperature dependence of reaction rates and helps elucidate the energy barriers associated with chemical processes [21].

$$Ink=In {k}_{0}-\frac{{E}_{a}}{RT}$$
(8)

Results and discussion

Characterization of Al2O3@Co-La-B catalyst

The characterizaiton of the as-prepared Al2O3@Co-La-B catalyst were studied by various techniques including XRD, FT-IR, EDX, BET and SEM.

XRD analysis

The XRD analysis of the Al2O3@Co-La-B catalyst, as illustrated in Fig. 1a, showcases a distinctive pattern with three discernible diffraction peaks. The positions of these peaks, with 2 theta values of 37.56, 45.82, and 66.86 degrees, respectively, correspond to the (311), (400), and (440) crystallographic planes. This information indicates the crystal structure within the catalyst. The alignment of these diffraction peaks with the spinel structure of Al2O3 [23] suggests that the crystalline framework within Al2O3 is well-preserved in this catalyst, and the incorporation of the CoLaB component has not significantly disrupted the main structural integrity. This underscores the chemical and structural stability of the catalyst. The absence of a discernible peak corresponding to the La element in the XRD pattern is attributed to its low quantity. This signifies that the proportion of La within the catalyst is limited, and therefore, it does not yield a prominent peak in the XRD analysis [24,25,26,27]. Such occurrences are common in the characterization of components with low abundance.

Fig. 1
figure 1

XRD pattern (a) and FT-IR spectrum (b) of Al2O3@Co-La-B catalyst

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FT-IR analysis

The FT-IR analysis of the Al2O3@Co-La-B catalyst, as depicted in Fig. 1b, reveals distinct peaks that provide valuable insights into its composition. The peaks observed below 1200 cm−1 can be attributed to the presence of Al2O3, signifying the substrate's contribution. Additionally, a pronounced peak at 1401 cm−1 indicates the occurrence of C-H stretching, suggesting the involvement of hydrocarbon moieties within the catalyst structure. Notably, the appearance of a peak at 2388 cm−1 is indicative of the presence of -OH hydroxyl groups, possibly hinting at surface hydroxylation or interactions with water molecules [28]. These FT-IR spectral features collectively offer a comprehensive understanding of the Al2O3@Co-La-B catalyst's molecular components and potential functional groups. Further investigations and correlations with catalytic performance could shed light on the catalytic pathways and mechanisms facilitated by these distinctive features.

EDX analysis

The composition and chemical formation of the Al2O3@Co-La-B catalyst was determined by EDX analysis. The qualitative and quantitative analysis results are reported in Fig. 2a. Spectral signals at 0.85 keV, 7.5 keV and 8.3 keV indicate the presence of the elements B, O, Co, Al and La elements in the Al2O3@Co-La-B catalyst. From the quantitative EDX analysis result (mass composition, %) embedded in Fig. 2b, it can be seen that the Al2O3@Co-La-B catalyst obtained is of high purity.

Fig. 2
figure 2

EDX spectrum (a), corresponding EDX mapping (b) and SEM image (c) of Al2O3@Co-La-B catalyst

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SEM and BET analysis

The SEM image of the Al2O3@Co-La-B catalyst (Fig. 2c) reveals a porous and homogeneous structure, showcasing its unique characteristics. This structure is quite significant, as evidenced by the BET surface area value of 140.12 m2/g. This larger surface area is a notable advantage of the Al2O3@Co-La-B catalyst, particularly for electrochemical applications. The increased surface area translates to a higher number of active sites available for reactions to occur, which is crucial in electrochemical processes. The incorporation of Al2O3 in the Al2O3@Co-La-B catalyst further enhances its suitability for electrochemical applications. Beyond the increased surface area, the addition of Al2O3 contributes to improved stability and selectivity in electrochemical reactions. This implies that the catalyst can maintain its performance over extended periods and also favor the desired reactions over unwanted side reactions, making it a promising candidate for various electrochemical processes. The findings of this study underscore the significance of both morphological and surface area properties when designing catalysts for electrochemical reactions. The porous and homogeneous structure of the Al2O3@Co-La-B catalyst, coupled with its impressive surface area, highlights the potential for high activity and efficiency in electrochemical processes. Researchers and engineers can leverage this knowledge to develop more effective catalysts for a wide range of electrochemical applications. It's worth noting that the information from the SEM image and the BET surface area value collectively contributes to a comprehensive understanding of the catalyst's capabilities, opening up new avenues for the advancement of electrochemical technologies.

Catalytic performance of Al2O3@Co-La-B catalyst

Effect of La concentration on H2 generation rate

This part was conducted to evaluate the effect of La concentration on the H2 generation rate (H2GR) via NaBH4 hydrolysis. The obtained H2GR values shown in Fig. 3 were determined at different La concentrations. The recorded H2GR values for 0, 1, 2, 3, 4 and 5% La concentrations were 756.84, 1165.04, 1417.98, 1835.47, 3349.12 and 2400.72 mLH2 min−1 gcat−1, respectively. According to the obtained results, it is evident that the La concentration has a significant impact on the catalytic activity of the Co-La-B catalyst. As the La concentration increases, a noticeable enhancement in the H2GR is observed. This suggests that the presence of La element can enhance the catalytic ability of the active sites of the catalyst to facilitate H2 generation reactions. Higher La concentrations can potentially increase the surface area and reactive sites of the catalyst, thereby improving the efficiency of the hydrolysis reactions [29,30,31,32]. The obtained results indicate lower H2GRs at 0% and 1% La concentrations, whereas a significant increase is observed at 2% and 3% concentrations. However, it is noteworthy that the increase in H2GR at 4% and 5% La concentrations is more substantial than anticipated. This could be attributed to the potential influence of higher La concentrations on the reaction kinetics, leading to faster hydrolysis reactions. Nonetheless, it should be noted that high concentrations might also adversely affect the stability of the catalyst.

Fig. 3
figure 3

The effect of La concentration on the H2 generation rate (H2GR) (experimental conditions: catalyst amount = 25 mg, NaBH4 concentration = 1%, NaOH concentration = 2%, solution volume = 10 mL, temperature = 30 °C)

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Effect of Al2O3 support on H2 generation rate

After determining the optimum La concentration as 4%, NaBH4 hydrolysis experiments were conducted with an Al2O3/Co-La-B ratio of 10% to examine the activity of the support material (Al2O3) on the H2 generation rate (H2GR). The H2GR values were obtained under these conditions. Here, the value of 10% was chosen as a nominal value, solely to investigate how the efficiency of the catalyst changes in the presence of the support material. Figure 4 illustrates the obtained H2GR values for Co-La-B and Al2O3@Co-La-B catalysts. The recorded H2GR values were 3349.12 and 6057.27 mLH2 min−1 gcat−1 for Co-La-B and Al2O3@CoLaB catalysts, respectively. One of the possible reasons for the increase in H2GR value in the presence of the support material could be the surface characteristics and interaction of the Al2O3 support material. Al2O3 is a material with high surface area and can provide suitable active sites for catalytic reactions. This situation might allow better dispersion of the active components of the Co-La-B catalyst and better access to the reaction surface. The surface properties of Al2O3 can facilitate the participation of water molecules in the hydrolysis reaction, which could enhance the reaction rate [33]. Another possibility is that the Al2O3 support material could enhance the stability of the catalyst and prevent the formation of deactivating by-products [34]. In reactions like NaBH4 hydrolysis, by-products can reduce the catalyst's efficiency. In this case, the presence of Al2O3 support material might have prevented the erosion or poisoning of the active components, leading to an increase in the H2GR value. Careful determination of reaction conditions minimizes the formation of undesired by-products while efficiently yielding the desired product. Therefore, in this study, the presence of the Al2O3@Co-La-B catalyst was investigated regarding its effect on H2GR in relation to parameters such as catalyst amount, NaOH concentration, NaBH4 concentration, and temperature.

Fig. 4
figure 4

The effect of Al2O3 support on the H2 generation rate (H2GR) (experimental conditions: catalyst amount = 25 mg, NaBH4 concentration = 1%, NaOH concentration = 2%, solution volume = 10 mL, temperature = 30 °C)

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Effect of catalyst amount on H2 generation rate

Figure 5 displays the H2 generation rate (H2GR) values obtained via NaBH4 hydrolysis for different amounts of Al2O3@Co-La-B catalyst. The recorded H2GR values for 10, 15, 20, 25, 30, and 40 mg catalyst amount were 4659.44, 5047.73, 5267.19, 6057.27, 5506.61 and 5708.03 mLH2 min−1 gcat−1, respectively. According to the obtained data, it was observed that with an increase in catalyst amount, the H2GR values initially increased. This increase can be attributed to the potential rise in the catalyst's surface area and the number of active sites. However, intriguingly, a slowdown and even a decrease in H2GR values were observed after reaching a catalyst amount of 25 mg, specifically in the cases of 30 mg and 35 mg catalyst amounts. These results indicate a complex influence of catalyst amount on the reaction rate. As the catalyst amount increases, it is possible that an excessive amount of catalyst could restrict the beneficial reaction zones and lead to unwanted side reactions. Additionally, the interactions of the catalyst with reaction intermediates and products suggest that different mechanisms might be at play for different catalyst amounts [35].

Fig. 5
figure 5

The effect of catalyst amount on the H2 generation rate (H2GR) (experimental conditions: NaBH4 concentration = 1%, NaOH concentration = 2%, solution volume = 10 mL, temperature = 30 °C)

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Effect of NaOH concentration on H2 generation rate

The H2 generation rate (H2GR) values obtained via NaBH4 hydrolysis for different NaOH concentrations are shown in Fig. 6. The recorded H2GR values for 0, 1, 2, 3, and 4% NaOH concentration were 3884.19, 4661.03, 6057.72, 5507.02 and 5006.38 mLH2 min−1 gcat−1, respectively. The data presented in Fig. 6 indicate the effect of varying NaOH concentrations on H2GR values in the NaBH4 hydrolysis process. Notably, the H2GR values demonstrate a non-linear trend as the NaOH concentration increases. The results suggest that optimal NaOH concentration plays a crucial role in enhancing the H2GR. The observed increase in H2GR values with rising NaOH concentrations up to 2% is indicative of the promotion effect of alkali. Higher NaOH concentrations lead to an elevated concentration of hydroxide ions (OH-) in the reaction mixture, which, in turn, facilitates the hydrolysis reaction and enhances the H2 production rate. However, beyond a certain NaOH concentration (2–3%), a decline in H2GR values is noticeable. This phenomenon can be attributed to potential side reactions or an excessive concentration of hydroxide ions, which might induce unwanted reactions or impact the reaction equilibrium [36]. The decreasing trend at higher NaOH concentrations highlights the intricate balance between the beneficial catalytic effects and possible adverse reactions. Optimal NaOH concentration is vital for achieving the highest efficiency in the NaBH4 hydrolysis process (Fig. 7).

Fig. 6
figure 6

The effect of NaOH concentration on the H2 generation rate (H2GR) (experimental conditions: catalyst amount = 25 mg, NaBH4 concentration = 1%, solution volume = 10 mL, temperature = 30 °C)

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Fig. 7
figure 7

The effect of NaBH4 concentration on the H2 generation rate (H2GR) (experimental conditions: catalyst amount = 25 mg, NaOH concentration = 2%, solution volume = 10 mL, temperature = 30 °C)

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Effect of NaBH4 concentration on H2 generation rate

The results of H2 generation rate (H2GR) via NaBH4 hydrolysis conducted at varying NaBH4 concentrations are depicted in Fig. 6. The recorded H2GR values for 1, 2, 3, and 4% NaBH4 concentration were 6057.72, 5313.78, 5261.17 and 4916.82 mLH2 min−1 gcat−1, respectively. These recorded H2GR values offer valuable insights into the catalytic performance of the Al2O3@Co-La-B catalyst during the NaBH4 hydrolysis process. The results demonstrate a trend wherein the H2GRs exhibit variability as the amount of NaBH4 is modified. This trend suggests that the NaBH4 concentration plays a significant role in influencing the catalytic activity and overall reaction kinetics. The highest H2GR value of 6057.72 mLH2 min−1 gcat−1 is observed for the 1% NaBH4 concentration. This finding implies an optimal interaction between the catalyst and the reactant at this particular NaBH4 concentration, resulting in enhanced H2 generation. As the NaBH4 concentration increases to 2%, there is a decrease in H2GR, indicating a change in the reaction dynamics or a possible saturation of the catalytic sites. Interestingly, both the 3% and 4% NaBH4 concentrations exhibit comparable H2GR values, with only a slight difference between them. This suggests that increasing the NaBH4 concentration beyond a certain threshold might not significantly contribute to higher H2GRs, possibly due to limitations in available catalytic sites [37].

Effect of temperature on H2 generation rate

Figure 8 demonstrates the results of H2 generation rate (H2GR) via NaBH4 hydrolysis conducted at different temperatures. The recorded H2GR values for 30, 40, 50, and 60 °C temperature were 6057.72, 6724.06, 7598.19 and 8661.94 mLH2 min−1 gcat−1, respectively. The data presented in Fig. 8 offer valuable insights into the catalytic behavior of the Al2O3@Co-La-B catalyst under varying temperature conditions during NaBH4 hydrolysis. The results reveal a clear relationship between temperature and H2GRs, showcasing how temperature influences the reaction kinetics. At 30 °C, the H2GR value is 6057.72 mLH2 min−1 gcat−1, indicating the baseline H2GR under this temperature condition. As the temperature increases to 40 °C, there is a notable enhancement in H2GR to 6724.06 mLH2 min−1 gcat−1. This rise in H2GR suggests that the reaction kinetics are accelerated at higher temperatures, possibly due to increased reactant activity and improved catalyst-substrate interactions. Further elevating the temperature to 50 °C results in a more significant increase in H2GR to 7598.19 mLH2 min−1 gcat−1. This temperature-driven augmentation in H2GR underscores the catalytic activity enhancement facilitated by elevated temperatures, which can lead to faster reaction rates and higher H2 generation efficiency. Remarkably, the highest H2GR value of 8661.94 mLH2 min−1 gcat−1 is recorded at 60 °C. This outcome reinforces the positive correlation between temperature and catalytic performance, as higher temperatures provide more energy to drive the reaction forward, thereby yielding higher H2GRs [38].

Fig. 8
figure 8

The effect of temperature on the H2 generation rate (H2GR) (experimental conditions: catalyst amount = 25 mg, NaBH4 concentration = 1%, NaOH concentration = 2%, solution volume = 10 mL)

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Kinetic study

Kinetic studies are very important to elucidate the reaction processes. The nth-order and Langmuir–Hinshelwood models were employed to experimental data obtained at different temperatures (30–60 °C) to study the kinetics of H2 generation via NaBH4 hydrolysis. Based on the experimental data, the order of reaction (n-value) for the nth-order kinetic model was estimated to be 0.90 with a maximum correlation coefficient (R2) of 99%. Figure 9 shows the corresponding Arrhenius plots of ln (k) versus 1/T for the nth-order kinetic model and the Langmuir–Hinshelwood kinetic model. Both models fit the experimental data with high R2. The values of the activation energy (Ea) from the nth order kinetic model and the Langmuir–Hinshelwood kinetic model were found to be 51.38 kJ mol−1 and 49.33 kJ mol−1, respectively. Remarkably, calculated activation energy values for the reaction catalyzed by Al2O3@Co-La-B is notably lower than previously reported values [39,40,41]. The lower activation energy observed for the NaBH4 hydrolysis reaction catalyzed by Al2O3@Co-La-B suggests that the catalyst facilitates the reaction by providing an alternative reaction pathway with reduced energy requirements. This catalytic effect results in increased reaction rates even at relatively lower temperatures, which is crucial for energy-efficient and practical H2 generation processes.

Fig. 9
figure 9

The corresponding Arrhenius plots for the calculation of Ea values from nth-order (a) and Langmuir–Hinshelwood (b) kinetic models

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Recyclability of Al2O3@Co-La-B catalyst

The reusability and stability performance of the developed catalyst is the most important criterion for evaluating the practical applicability and process costs. In each cycle, the used catalyst was rinsed several times with distilled water prior to its subsequent use in the NaBH4 hydrolysis process. The results of the reusability tests are presented in Fig. 10, which shows the variation in H2GR values over five consecutive cycles. The H2GR values recorded for the 1st, 2nd, 3rd, 4th and 5th cycles were 6057.72, 5838.94, 5656.13, 5605.68 and 5550.17 mLH2 min−1 gcat−1, respectively. The data provide insight into the catalytic stability and durability of the Al2O3@Co-La-B catalyst under repeated use scenarios. The observed trend of decreasing H2GR values over successive cycles suggests that certain changes or deactivation mechanisms may occur within the catalyst structure over time. The initial H2GR value of 6057.72 mLH2 min−1 gcat−1 in the 1st cycle represents the baseline performance of the catalyst. However, subsequent cycles show decreasing H2GR values, indicating a gradual decrease in catalytic activity. This reduction in H2GR could potentially be due to catalyst fouling, active site blockage or changes in surface properties caused by repeated use and purging. It's important to note that despite the declining trend, the H2GR values remain relatively close over the cycles tested. This suggests that the Al2O3@Co-La-B catalyst maintains a degree of stability and retains a significant proportion of its catalytic activity throughout the reusability tests.

Fig. 10
figure 10

Reusability tests of Al2O3@Co-La-B catalyst for H2GR via NaBH4 hydrolysis (experimental conditions: catalyst amount = 25 mg, NaBH4 concentration = 1%, NaOH concentration = 2%, solution volume = 10 mL, temperature = 30 °C)

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Comparison with literature

Table 1 provides a brief comparison between the present study and those previously reported. Considering the recorded H2GR values via NaBH4 hydrolysis listed in Table 1, it is clear that Al2O3@Co-La-B has a significant potential compared to other catalysts reported in the literature. As a result, the Al2O3@Co-La-B catalyst exhibited superior H2GR, indicating its promising potential for the hydrolysis of NaBH4 in industrial processes.

Table 1 Comparison of H2 generation rate (H2GR) via NaBH4 hydrolysis of Al2O3@Co-La-B catalyst with literature
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Conclusions

In conclusion, the novel Al2O3-supported nanobimetallic Co-La-B (Al2O3@Co-La-B) catalyst has demonstrated exceptional performance in hydrogen generation via sodium borohydride hydrolysis. Characterized by its unique porous, cubic structure, the catalyst achieved remarkable hydrogen production rates, with a peak rate of 8661.94 mLH2 min−1 gcat−1 at 60 °C, and maintained over 91% catalytic activity after multiple cycles. These results highlight the catalyst's efficiency and stability, positioning it as a promising candidate for advancing hydrogen production technologies. Additionally, the activation energies calculated using nth-order and Langmuir–Hinshelwood models were 51.38 kJ mol−1 and 49.33 kJ mol−1, respectively, indicating the catalyst's effectiveness in lowering energy barriers. These findings underline the catalyst's potential in enhancing hydrogen production technologies.