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Yasukazu Kobayashi, [Hiroshi Mizoguchi](https://orcid.org/0000-0002-0992-7449), Koharu Yamamoto, Ryo Shoji

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[Chemical synthesis of Zr-/Ce-/Sm-containing intermetallic compounds catalyzing NaBH                    <sub>4</sub>                    -assisted hydrogenation of 4-nitrophenol](https://mdr.nims.go.jp/datasets/cfbfd50e-85f9-465a-a188-6e4c7e2c920c)

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Chemical synthesis of Zr-/Ce-/Sm-containing intermetallic compounds catalyzing NaBH4-assisted hydrogenation of 4-nitrophenolDaltonTransactionsPAPERCite this: Dalton Trans., 2026, 55,6876Received 2nd March 2026,Accepted 13th April 2026DOI: 10.1039/d6dt00513frsc.li/daltonChemical synthesis of Zr-/Ce-/Sm-containingintermetallic compounds catalyzing NaBH4-assisted hydrogenation of 4-nitrophenolYasukazu Kobayashi, *a Hiroshi Mizoguchi,b Koharu Yamamotoc and Ryo Shoji cZr-/Ce-/Sm-containing intermetallic compounds, specifically ZrZnNi4, CeNi5, CeAlNi4, CeNi4Si, Ce(NiSi)2,SmNi3, SmNi4Si, and Sm(NiSi)2, were synthesized by reducing the metal oxides using a CaH2 reducingagent within molten LiCl. The resultant nanopowders exhibited high specific surface areas: ZrZnNi4(42.0 m2 g−1), CeAlNi4 (66.9 m2 g−1), and Sm(NiSi)2 (25.0 m2 g−1). They were subsequently tested for theireffectiveness in the NaBH4-assisted hydrogenation of 4-nitrophenol. When compared to the preparedcatalysts, including a conventional CeO2-supported Ni catalyst, ZrZnNi4 demonstrated the highest cata-lytic activity. Based on experimental results and density functional theory calculations, it was proposedthat enhanced performance could be attributed to the formation of electron-rich Ni species in ZrZnNi4.IntroductionNitrophenols are commonly utilized in various industrialapplications, such as dyes, pesticides, herbicides, and pharma-ceuticals. However, nitrophenols and their derivatives are toxicand present significant risks to both ecosystems and humanhealth with prolonged exposure.1,2 The conversion of nitro-phenols into less harmful aminophenols via heterogeneouscatalysts is a well-established method for degradation. Thereduction of 4-nitrophenol (4NP) to 4-aminophenol (4AP)using NaBH4 as a reducing agent has attracted considerableinterest as a model reaction for assessing catalytic activity.3The proposed reaction mechanism follows the Langmuir–Hinshelwood model,4 commencing with the hydrolysis ofNaBH4, generating B(OH)4− and H2 gas or reactive hydrogen(H) adsorbed on the metal surface (M) as represented in eqn(1)–(6).5NaBH4ðSÞ ! Naþ þ BH4� ð1Þ2Mþ BH4� $ M–BH3� þM–H ð2ÞM–BH3� $ BH3 þM� ð3ÞBH3 þ OH� ! BH3ðOHÞ� ð4ÞM� þH2O ! M–Hþ OH� ð5ÞM–HþM–H ! 2MþH2ðgÞ ð6ÞThe product BH3(OH)− generated in eqn (4) is thought toexhibit reactivity similar to that of BH4− and undergoes reac-tion steps akin to eqn (2)–(4), leading to the formation ofBH2(OH)2−. This species can engage in further reactions result-ing in BH(OH)3− and, ultimately, B(OH)4−. In the second step,the adsorbed reactive hydrogen reacts with the 4NP that isadsorbed onto the metal surface to produce 4AP, as depictedin eqn (7)–(9) through a direct pathway.6Mþ 4NP ! M–4NP ð7Þ6M–HþM–4NP ! M–4APþ 2H2O ð8ÞM–4AP ! Mþ 4AP ð9ÞThe rate-determining step in this process is the surfacereduction of adsorbed 4NP to adsorbed 4AP (eqn (8)).4Consequently, it is crucial to utilize catalysts that facilitate thehydrogenation of 4NP to 4AP (eqn (8)) to enhance the overallefficiency of the process.Precious metal nanoparticles, such as Au and Ag, are recog-nized for their high catalytic performance in NaBH4-assistedhydrogenation.7,8 However, low-cost catalysts comprising Ni,Co, and Fe have also been developed to reduce catalystexpenses.9,10 To enhance the activity of these economicalmetal catalysts, the incorporation of other metals into the cata-lyst structure has been investigated.11 Low work function (WF)metals, such as W (4.55 eV), Cr (4.5 eV), and Mn (4.1 eV),12have the ability to readily donate electrons to higher WFmetals, such as Ni (5.15 eV) and Co (5.0 eV), as long as there isaRenewable Energy Research Center, National Institute of Advanced IndustrialScience and Technology, 2-2-9 Machiikedai, Koriyama, Fukushima 963-0298, Japan.E-mail: yasu-kobayashi@aist.go.jpbResearch Center for Materials Nanoarchitectonics (MANA), National Institute forMaterials Science (NIMS) Tsukuba, Ibaraki 305-0044, JapancDepartment of Chemical Science and Engineering, National Institute of Technology,Tokyo College, 1220-2 Kunugida, Hachioji, Tokyo 193-0997, Japan6876 | Dalton Trans., 2026, 55, 6876–6885 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineView Journal  | View Issuehttp://rsc.li/daltonhttp://orcid.org/0000-0001-5438-321Xhttp://orcid.org/0000-0003-4451-7872http://crossmark.crossref.org/dialog/?doi=10.1039/d6dt00513f&domain=pdf&date_stamp=2026-04-29http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fhttps://pubs.rsc.org/en/journals/journal/DThttps://pubs.rsc.org/en/journals/journal/DT?issueid=DT055017tight contact between the two, leading to the creation of elec-tron-rich Ni and Co species. Since the rate-determining step(eqn (8)) can be accelerated by increasing the surface concen-tration of reactive hydrogens (H) generated on these electron-rich metals (eqn (5)), designing improved catalysts thatcontain electron-rich active metals is a strategic approach inthe NaBH4-assisted hydrogenation of 4NP.In this study, we developed Ni-based intermetallic com-pound catalysts featuring very low WF metals like Zr (4.05 eV),Ce (2.9 eV), and Sm (2.7 eV).12 The oxidation of these metals toform oxides poses a significant challenge in the preparation ofalloy catalysts with nanoscale morphologies, which are essen-tial for achieving high surface areas. This issue was addressedby employing a CaH2-assisted molten salt synthesis method,allowing for the reduction of metals by CaH2 to occur in anoxygen-free molten LiCl environment,13 thus preventing oxi-dation. The versatility of this synthesis method was confirmedby the successful production of ZrZnNi4, CeNi5, CeAlNi4,CeNi4Si, Ce(NiSi)2, SmNi3, SmNi4Si, and Sm(NiSi)2 from therespective metal oxide precursors. The catalysts ZrZnNi4,CeAlNi4, and Sm(NiSi)2, which possess high surface areas,were then evaluated in the context of the NaBH4-assistedhydrogenation of 4NP.ExperimentalPreparation of intermetallic compound nanopowdersZr-/Ce-/Sm-containing intermetallic compounds were syn-thesized by reducing metal oxides with CaH2 as a reducingagent in molten LiCl at 600 °C. Initially, metal oxide precur-sors were prepared using the following citric acid method. ForZrZnNi4, CeNi5, CeAlNi4, and SmNi3, metal nitrate salts suchas ZrO(NO3)2·2H2O (97.0%, Wako Pure Chem. Corp.), Zn(NO3)2·6H2O (99.9%, Wako Pure Chem. Corp.), Ni(NO3)2·6H2O(98.0%, Wako Pure Chem. Corp.), Ce(NO3)3·6H2O (98.0%,Wako Pure Chem. Corp.), Al(NO3)3·9H2O (98.0%, Wako PureChem. Corp.), Sm(NO3)3·6H2O (99.5%, Wako Pure Chem.Corp.) were dissolved in distilled water to obtain the stoichio-metric molar ratios of ZrZnNi4, CeNi5, CeAlNi4, and SmNi3.For CeNi4Si, Ce(SiNi)2, SmNi4Si, and Sm(NiSi)2, the aforemen-tioned metal nitrate salts were dissolved in distilled water andmixed with SiO2 nanoparticles (99.5%, 10–20 nm, Sigma-Aldrich Co. LLC.) to achieve the stoichiometric ratios necessaryfor CeNi4Si, Ce(NiSi)2, SmNi4Si, and Sm(NiSi)2. Subsequently,citric acid was incorporated into the solutions at a molar ratioof total metals/citric acid = 1/1.2. After thorough mixing, theresultant solution was evaporated on a hot plate at 110 °C over-night. The resulting dried powder was initially heated in air at250 °C for 2 hours and then gently ground in a mortar tocreate a homogeneous powder. Lastly, the powder was heatedin air at 500 °C for 2 hours to produce the metal oxideprecursors.Next, the metal oxide precursor, CaH2 (94.0%, JUNSEIChem. Co.), and LiCl (99.0%, Wako Pure Chem. Corp.) wereblended in a mortar in a weight ratio of 2/6/3 of metal oxideprecursor/CaH2/LiCl. This mixed powder was placed in a stain-less-steel container filled with Ar gas and heated at 600 °C for2 hours. The reduced precursors were then crushed in amortar and rinsed multiple times with a 0.4 M NH4Cl aqueoussolution, followed by distilled water. The final dried productswere designated as ZrZnNi4, CeNi5, CeAlNi4, CeNi4Si, Ce(NiSi)2, SmNi3, SmNi4Si, and Sm(NiSi)2.The ZrNi5 ingot for WFs measurement was prepared by arcmelting a stoichiometric mixture of Zr and Ni elements on awater-cooled Cu hearth under a high-purity argon atmosphere.Annealing was subsequently conducted at 1000 °C for20 hours to produce the single phase.Characterization of intermetallic compound nanopowdersThe crystal structure was analyzed utilizing X-ray diffraction(XRD; SmartLab, 3 kW, Rigaku Corporation) with CuKα radi-ation at 40 kV and 30 mA. Porosity was assessed through N2adsorption and desorption at −196 °C (BELLSORP mini-II,Microtrac-BEL). The pore size distribution was derived fromthe measured adsorption isotherms using the Barrett, Joyner,and Halenda (BJH) method for all samples. Prior to measure-ment, the samples were pretreated at 150 °C for 60 minutesunder vacuum. Scanning electron microscopy (SEM;JSM-7400F, JEOL Ltd) was employed to observe the mor-phology, with energy dispersive X-ray spectrometry (EDX) uti-lized for elemental analysis. X-ray fluorescence (XRF; ZSXPrimusII, 3 kW, Rigaku Corporation) was conducted in air todetect elements within the samples, except for lighterelements such as H, He, Li, N, and O. The chemical states andsurface composition of the prepared sample were analyzedusing X-ray photoelectron spectroscopy (XPS; PHI X-tool,ULVAC-PHI), operated with AlKα radiation. The chemical shiftswere calibrated by fixing the C1s peak of surface carbonaceouscontaminants at 284.5 eV. Photoemission yield spectra wererecorded in air to estimate the WFs using a RIKENKEIKI AC-2spectrometer, which collected photoelectrons emitted fromthe polished surface of ZrNi5 ingots upon UV light excitationthrough O2 molecule mediation.Catalytic test with intermetallic compound nanopowdersThe catalytic reactions were performed in 20 mL glass bottlesfollowing previously documented protocols. In the catalytictests, a 1 mL solution of p-nitrophenol (4NP) at 14 mM wascombined with 10 mg of catalyst powder, 1 mL of NaBH4 solu-tion (0.42 M), and 7 mL of distilled water as the solvent. Toensure pseudo first-order reaction kinetics, the initial concen-tration of NaBH4 (0.047 M) was set 30 times greater than thatof 4NP (1.6 mM). The reactions were carried out under stirringat room temperature (25 °C) for 60 minutes. An aluminumheat sink on a hot plate was used to maintain a constant solu-tion temperature. A small aliquot (100 μL) of the reaction solu-tion was extracted to evaluate concentration changes through-out the reaction. The conversion of 4NP to p-aminophenol(4AP) was monitored using an ultraviolet-visible spectrometer(Shimadzu, UV-1280), through the corresponding absorbancechanges at 401 and 315 nm.Dalton Transactions PaperThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 6876–6885 | 6877Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fFor comparison, a 12 wt% NiO or 10 wt% Ni catalyst sup-ported on commercial CeO2 nanopowder (30 m2 g−1, <50 nm,Sigma-Aldrich Co. LLC) was prepared using a conventionalimpregnation method. Initially, Ni(NO3)2·6H2O was dissolvedin distilled water, and a suspension was created with CeO2 toachieve a 12 wt% NiO loading. The resulting suspension wasthen evaporated on a hot plate at 110 °C overnight. The driedpowder was subsequently heated in air at 500 °C for 2 hours toyield the 12 wt%NiO/CeO2 catalyst. The metallic state nickel-loaded catalyst, denoted as 10 wt%Ni/CeO2, was obtained aftera reduction treatment of the NiO/CeO2 catalyst at 400 °C undera H2 flow at 100 mL min−1 for 2 hours.Electronic structure calculationsDensity functional theory (DFT) periodic calculations wereconducted using the generalized gradient approximation andthe Perdew–Burke–Ernzerhof functional14 and, along with theprojected augmented plane wave method15 implemented inthe Vienna Ab initio simulation package.16 An energy cutoff of600 eV was applied, and a gamma-centered k-mesh of 10 × 10× 10 was utilized. A Wigner–Seitz radius of 0.146 nm wasemployed for the site projections of all atoms. Atomic chargeswere determined through Bader charge analysis,17 and thecrystal structures were visualized with the VESTA software.18Results and discussionPreparation of intermetallic compound nanopowdersEight intermetallic compounds—ZrZnNi4, CeNi5, CeAlNi4,CeNi4Si, Ce(NiSi)2, SmNi3, SmNi4Si, and Sm(NiSi)2—were syn-thesized by reducing metal oxides with a CaH2 reducing agentin molten LiCl. Fig. 1 and Fig. S1–S5 display the XRD patternsof the metal oxide precursors, each identified in blue abovethe corresponding figure. Peaks associated with NiO (PDF01-071-1179) were present in all oxide precursors. Additionally,CeO2 (PDF03-065-5923) was also detected in the oxide precur-sors of CeNi5, CeNi4Si, and Ce(NiSi)2. Other metal oxides,including ZrO2, ZnO, SiO2, and Sm2O3, were not observed,suggesting they may exist in an amorphous form. The metaloxide precursors were subsequently reduced and washed toyield intermetallic compound nanopowders. The XRD patternsof the intermetallic compounds, shown in Fig. 1 and Fig. S1–S5 are described in orange below each figure. The peaks fromthe metal oxide precursors were absent, while the expectedpeaks for the intermetallic compounds ZrZnNi4, CeNi5,CeAlNi4, CeNi4Si, Ce(NiSi)2, SmNi3, SmNi4Si, and Sm(NiSi)2appeared in the reduced samples. The peaks assigned to themetallic Ni were not observed in the reduced samples.Impurity peaks assigned to CaCO3 were observed in CeNi5 andCe(SiNi)2, probably due to the incomplete removal of Caspecies from the samples. The peak shift was observed inCeNi4Si, indicating the formation of deformed structure prob-ably due to the deviation of composition in the synthesizedsample. These results indicate that the reduction of the metaloxide precursors using the CaH2 reducing agent in moltenLiCl effectively formed the intermetallic compounds. Theidentified crystal types and crystallite sizes, calculated usingthe Scherrer equation based on the main peaks detected at 2θ,are summarized in Table 1. The calculated sizes ranged from12.2 to 52.5 nm, indicating the formation of nanoscalemorphologies.For representative samples, we briefly outline their crystalstructure features. CeNi5 adopts the CaCu5-type crystal struc-ture (hexagonal, P6/mmm, Z = 1),19 as illustrated in Fig. 2(a).This structure consists of alternating layers of Ni3 kagomelayer (A) and a closed-packed layer of CeNi2 (B), stacked alongthe [001] direction in an ABAB sequence. In this arrangement,the larger Ce ion is nestled between two Ni6 hexagons of thekagome layer. Conversely, ZrNi5 exhibits the AuBe5-type crystalstructure (cubic, F4̄3m, Z = 4),20 as presented in Fig. 2(b). Inthis case, Ni3 kagome layer (A) and ZrNi2 closed-packed layer(B) are stacked in an alternating fashion along the 〈111〉 direc-tion, following the sequence of (AB)(AB)′(AB)″(AB)(AB)′(AB)″.Due to the smaller size of the Zr ion, the ZrNi2 closed-packedlayer displays a buckled structure, resulting in the formationFig. 1 XRD patterns for the oxide precursors (blue) and the reduced samples (orange) of (a) ZrZnNi4, (b) CeAlNi4, and (c) Sm(NiSi)2. The main peaksobserved in the reduced samples are described with their index values.Paper Dalton Transactions6878 | Dalton Trans., 2026, 55, 6876–6885 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fof a Frank–Kasper polyhedron around the Zr atoms.Consequently, the packing density of Ni in ZrNi5 is enhancedcompared to that in CeNi5. The stacking arrangement observedin ZrNi5 is reminiscent of the cubic Laves-type crystal structure(XY2, Fd3̄m, Z = 8),21 where the Y3 kagome layer (A) and X2Yclosed-packed layer (B) are also alternately stacked along the〈111〉 direction in the same pattern. In ZrNi5, there are two dis-tinct crystallographic sites for Ni (4c and 16e). The formationof Zr(ZnNi4) involves substituting Ni (4c site) with Zn, leadingto a 1.5% increase in the cubic lattice constant.22The electronic structure of ZrNi5, which serves as a parentcompound to ZrZnNi4, was examined using DFT calculations.Fig. 3(a) and (b) illustrate the electronic structures of ZrNi5and ZrZnNi4, including the energy–wave vector (E–k) diagramand the projected density of states (DOS). The energy scale isset such that the Fermi energy (EF) is at zero. Several energybands intersect EF, suggesting a metallic nature of the elec-tronic structure. A significant DOS is observed primarily fromthe Ni 3d orbitals in the energy range of −3.0 to +0.3 eV.Notably, there is a pseudo bandgap around +1.9 eV, as indi-cated in the E–k diagram. The contribution of Zr 4d characteris apparent in the unoccupied band with a narrow bandwidtharound +2.5 eV. According to the Badar charge analysis, theatomic charges are estimated as Zr+1.58Ni−0.325 for ZrNi5 andZr+1.60Zn+0.11Ni−0.434 for ZrZnNi4. This pattern of chargesaligns well with those derived from electronegativity values (Zr1.22, Zn 1.66, Ni 1.75).23 Negatively charged late transitionmetal ions, such as Niδ−, typically play an important role inhydrogenation processes for hydrogen storage applications.24The substitution of Zn, which has a relatively positive charac-Table 1 Summary of the measured properties, including BET surface area (SA), pore volume (Vp), crystallite size, and elemental composition. Thecrystallite sizes were calculated using the Scherrer equation applied to the main peaks detected at 2θ as described in the tableSampleCrystalstructureCrystallinity Porosity CompositionCrystallite size[nm]2θ[degree]BET SA [m2g−1]Vp [cm3g−1] SEM-EDX [mol%] XRF [mol%] XPS [mol%]ZrZnNi4 AuBe5 12.2 44.3 42.0 0.094 Zr/Zn/Ni = 19.7/8.1/72.2Zr/Zn/Ni = 22.4/7.9/69.8Zr/Zn/Ni = 48.7/19.2/32.1CeNi5 CaCu5 52.5 43.3 31.3 0.131 — — —CeAlNi4 CaCu5 49.1 42.7 66.9 0.089 Ce/Al/Ni = 17.3/26.5/56.1Ce/Al/Ni = 18.6/14.5/66.9Ce/Al/Ni = 5.8/47.1/47.1CeNi4Si DyNi4Si 15.7 43.9 16.7 0.099 — — —Ce(NiSi)2 Th(CrSi)2 21.9 36.7 33.4 0.187 — — —SmNi3 PuNi3 41.9 36.0 6.8 0.038 — — —SmNi4Si DyNi4Si 19.9 37.0 14.7 0.138 — — —Sm(NiSi)2Th(CrSi)2 45.0 45.2 25.0 0.179 Sm/Ni/Si = 19.8/36.2/44.0Sm/Ni/Si = 24.8/44.1/31.1Sm/Ni/Si = 24.1/6.3/69.5Fig. 2 (a) The crystal structure of CeNi5, which includes the Ni3 kagome layer and the CeNi2 closed-packed layer, and (b) the crystal structure ofZrNi5, composed of the Ni3 kagome layer and a buckled ZrNi2 closed-packed layer.Dalton Transactions PaperThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 6876–6885 | 6879Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fter, promotes the reduction of the remaining Ni ions, resultingin an increase in EF energy. This shift in energy is confirmedby the unoccupied Zr 4d band, which is situated around +1.7eV within the total DOS of ZrZnNi4 (Fig. 3(b)). A subtle indi-cation of Zn substitution can be seen in the Zn 3d10 bandlocated approximately at −7.2 eV, which does not contribute tothe electronic structure near EF (not shown in Fig. 3(b)). Now,let’s consider the changes brought about by alloying Zr withNi. We show calculated DOS of metallic Ni in Fig. 3(c), as areference. The addition of Zr into Ni leads to two effects. Oneis the redox reaction, that is, electron transfer from Zr to Ni.The energy levels of the Zr bands are pushed lower due to theoxidation of Zr, while the Ni bands are elevated because ofincreased electron repulsion resulting from the reduction ofNi. Consequently, the WF of ZrNi5 decreases compared to thatof Ni metal, since the DOS at EF in ZrNi5 is dominated by theNi 3d bands. This prediction is supported by the measuredWF value of 4.2 eV, which is considerably lower than that of Nimetal (4.9 eV). The energy shift of WF (0.7 eV) is consistentwith the shift (∼0.8 eV) of unoccupied Zr 4d band mentionedabove. Another effect of addition of Zr is drastic decrease ofDOS(EF). Metallic Ni has large DOS(EF), which often inducesmagnetic ordering, because of the (3d4s) electronic configur-ation. Electron-doping into Ni by Zr fills remaining unoccu-pied 3d band, resulting in the decrease of DOS(EF), whereasthe WF decreases. Thus, catalytic activity due to the electron ofNi 3d band has the tradeoff relation.Subsequently, the porosity of the prepared intermetalliccompound nanopowders was assessed through nitrogenadsorption/desorption experiments. Fig. 4 and Fig. S6–S10display the nitrogen adsorption/desorption isotherms alongwith the corresponding pore size distributions. The measuredBET surface areas and pore volumes are collated in Table 1. Adistinct hysteresis in the isotherms, with pore formation occur-ring at 3.8 nm, was evident in ZrZnNi4. A negligible hysteresiswas observed in CeAlNi4, also featuring pore formation at3.8 nm. This pore creation likely contributes to the high BETsurface areas of 42.0 m2 g−1 for ZrZnNi4 and 66.9 m2 g−1 forCeAlNi4. Conversely, other samples such as CeNi5, CeNi4Si, Ce(NiSi)2, SmNi3, SmNi4Si, and Sm(NiSi)2 did not exhibit hyster-esis, indicating no small pore formation below 10 nm.The morphologies of representative samples ZrZnNi4,CeAlNi4, and Sm(NiSi)2, which contain Zr, Ce, and Sm, respect-ively, were examined via SEM (Fig. S11–S13). Numerous fineparticles measuring less than a micrometer were distinctlyvisible across all samples, and the surfaces appeared topossess nanoscale structures, leading to elevated specificsurface areas. Fig. 5 presents the elemental mappings for theconstituent elements of ZrZnNi4, CeAlNi4, and Sm(NiSi)2. Theconstituent elements appeared well-distributed among the par-ticles, with overlapping distributions indicating a thoroughmixture of the components. It is noted that the ideal sphericalparticles were observed in CeAlNi4, which are enclosed by rec-tangles in Fig. 5(b). According to the elemental mappings, thecore of the particles had dense concentrations of Ni, whereasCe was distributed in the shell. Thus, the results indicated thatthe formation of core–shell structures.The compositions of ZrZnNi4, CeAlNi4, and Sm(NiSi)2 wereanalyzed using SEM-EDX and XRF, with the results summar-ized in Table 1. The spectra obtained from SEM-EDX and XRFare shown in Fig. S14 and S15–S17, respectively. In the case ofZrZnNi4, the molar ratio of Zn was lower than the stoichio-metric ratio expected for the AuBe5-type intermetallic com-pound with a Ni site substituted by Zn, indicating that the Nisite was not fully occupied by a Zn atom, resulting in a partialdeficiency of Zn. For CeAlNi4, the molar ratio of Ni was slightlyless than what would be expected for the CaCu5-type interme-tallic compound with an Al atom substituted for Ni, suggestingFig. 3 (a) The calculated band structure and projected density of states for ZrNi5. (b) The calculated total density of states for ZrZnNi4. (c) The calcu-lated total density of states of Ni. Magnetic ordering is not included. The calculations were performed on the primitive unit cell to reduce compu-tational time.Paper Dalton Transactions6880 | Dalton Trans., 2026, 55, 6876–6885 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fFig. 4 (a) The adsorption (blue) and desorption (orange) isotherms of nitrogen, as well as (b) the corresponding pore size distributions for ZrZnNi4,CeAlNi4, and Sm(NiSi)2.Fig. 5 SEM images and elemental mappings for (a) ZrZnNi4, (b) CeAlNi4, and (c) Sm(NiSi)2, with corresponding EDX spectra shown in Fig. S14.Dalton Transactions PaperThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 6876–6885 | 6881Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fa slight deficiency in Ni. For Sm(NiSi)2, the molar ratio of Sm/Ni/Si was nearly in accordance with the stoichiometric ratio forthe Th(CrSi)2-type intermetallic compound, indicating success-ful synthesis of Sm(NiSi)2. Detailed analysis through XRFrevealed very minimal amounts of impurities in ZrZnNi4,CeAlNi4, and Sm(NiSi)2 (Tables S1–S3). It is noteworthy thatthe detected amounts of Ca were minimal in all samples,suggesting that impurities originating from CaH2, includingCaH2, CaO, Ca(OH)2, and CaCl2, were effectively removedthrough washing with a weak acid solution during the prepa-ration process.Catalytic performance of intermetallic compoundnanopowdersThe NaBH4-assisted hydrogenation of 4-nitrophenol (4NP) to4-aminophenol (4AP) follows the Langmuir–Hinshelwoodmodel, making it crucial to examine the surface species thatdirectly facilitate this reaction. Consequently, surface-sensitiveXPS measurements were conducted on ZrZnNi4, CeAlNi4, andSm(NiSi)2. Fig. 6 presents the XPS spectra calibrated by align-ing the C1s peak of surface carbonaceous contaminants to284.5 eV (see Fig. S18). The resulting surface compositions aresummarized in Table 1.For ZrZnNi4 shown in Fig. 6(a), a prominent peak attributedto Ni 2p3/2 was detected at 855.5 eV. Previous studies indicatethat a peak associated with Ni(+2) in Ni(OH)2 appears at 856.2eV, while a peak for Ni(0) is found at 852.6 eV.25 Hence, theoxidation state of surface nickel in ZrZnNi4 is close to Ni(+2).Additionally, a peak corresponding to Zr 3d5/2 appeared at181.5 eV. As reported earlier, peaks linked to Zr(+4) in ZrO2and Zr(0) can be found at 182.75 eV and 178.52 eV, respect-ively.26 This suggests that the surface oxidation state of zirco-nium in ZrZnNi4 is Zr(+4>, >0), or greater than zero. A peakcorresponding to Zn 2p3/2 was observed at 1,021.1 eV.According to prior reports, Zn 2p lines are not highly sensitiveto chemical environments, making it challenging to differen-tiate between Zn(0) (1,021.4 eV) and Zn(+2) (1,021.7 eV).27These findings indicate that the surface components ofZrZnNi4 largely exist in higher oxidation states, such as Ni(+2)and Zr(+4>, >0). The measured surface composition of Zr/Zn/Ni = 48.7/19.2/32.1 deviated significantly from those obtainedby SEM-EDX and XRF, with the molar ratio of Ni being con-siderably lower than the stoichiometric ratio; thus, Zr–Zn–Ocomprised the primary surface components. Because no oxidephases were observed in the XRD measurement (Fig. 1(a)), thethickness of the surface oxide layers could be very thin or/andthe crystallinity was very low enough not to be detected byXRD.In the case of CeAlNi4, depicted in Fig. 6(b), the main peakcorresponding to Ni 2p3/2 was recorded at 856.2 eV, whichidentifies the oxidation state of surface nickel in CeAlNi4 as Ni(+2). A peak associated with Ce 3d5/2 was found at 881.3 eV.Previous studies identified peaks for Ce(+4) in CeO2 and Ce(+3) in CePO4 at 882.7 eV and 880.9 eV, respectively.28Therefore, the oxidation state of surface cerium in CeAlNi4approximates Ce(+3). A peak for Al 2p was detected at 73.5 eV,with prior reports indicating that peaks for Al(+3) in Al2O3 andAl(0) appear at 74.14 eV and 72.87 eV respectively.29,30Therefore, the oxidation state of surface Al in CeAlNi4 is Al(+3>, >0), or greater than zero. These results indicate that theFig. 6 XPS spectra for (a) Zr 3p5/2, Zn 2p3/2, Ni 2p3/2 for ZrZnNi4, (b) Ce 3d5/2, Al 2p, Ni 2p3/2 for CeAlNi4, and (c) Sm 3d5/2, Si 2p, Ni 2p3/2 forSm(NiSi)2.Paper Dalton Transactions6882 | Dalton Trans., 2026, 55, 6876–6885 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fsurface compounds in CeAlNi4 primarily exist in higher oxi-dation states, such as Ni(+2), Ce(+3), and Al(+3>, >0). Themeasured surface composition of Ce/Al/Ni = 5.8/47.1/47.1showed significant deviation from SEM-EDX and XRF results,with the molar ratios of Al and Ni being considerably higherthan the stoichiometric ratio; consequently, Al–Ni–O emergedas the main surface components. Because no oxide phaseswere observed in the XRD measurement (Fig. 1(b)), the thick-ness of the surface oxide layers could be very thin or/and thecrystallinity was very low enough not to be detected by XRD.For Sm(NiSi)2, as shown in Fig. 6(c), a significant peakassigned to Ni 2p3/2 was noted at 856.2 eV, indicating that theoxidation state of surface Ni in Sm(NiSi)2 is Ni(+2). A peakcorresponding to Sm 3d5/2 appeared at 1082.8 eV. Previousreports indicate that the peaks for Sm(+3) and Sm(+2) arefound at 1084.0 eV and 1076.4 eV, respectively.31 Therefore, theoxidation state of surface Sm in Sm(NiSi)2 appears to be closeto Sm(+3). A peak corresponding to Si 2p was observed at 101.8eV, with previous reports showing that peaks for Si(+4) in SiO2and Si(0) are found at 103.8 eV and 99.8 eV, respectively.32Thus, the oxidation state of surface Si in Sm(NiSi)2 is Si(+4>,>0). These results point to surface compounds in Sm(NiSi)2mostly existing in higher oxidation states, such as Ni(+2), Sm(+3), and Si(+4>, >0). Additionally, the measured surface com-position of Sm/Ni/Si = 24.1/6.3/69.5 significantly differed fromthose obtained via SEM-EDX and XRF. The Ni molar ratio wasnotably smaller than the stoichiometric ratio, and thus Sm–Si–O was determined to be the main surface component. Becauseno oxide phases were observed in the XRD measurement(Fig. 1(c)), the thickness of the surface oxide layers could bevery thin or/and the crystallinity was very low enough not to bedetected by XRD.Next, the hydrogenation of 4-nitrophenol (4NP) to 4-amino-phenol (4AP) was facilitated by NaBH4 at room temperatureusing ZrZnNi4, CeAlNi4, and Sm(NiSi)2. The three intermetal-lics were chosen as representative catalysts containing very lowWF metals of Zr, Ce, and Sm, respectively, with high BETsurface areas available for the catalytic reactions. 12 wt%NiO/CeO2 and 10 wt%Ni/CeO2 were used as a reference. XRD ana-lysis revealed that the reference catalysts of NiO/CeO2 and Ni/CeO2 contained minuscule peaks of NiO and Ni, respectively,alongside significant peaks corresponding to CeO2 (Fig. S19),indicating that small particles of NiO and Ni were successfullydispersed on CeO2, respectively. In Fig. 7(a), the change inabsorbance of the reaction mixture is plotted over time withthe ZrZnNi4 catalyst. The absorbance at 401 nm, associatedwith the concentration of 4NP, rapidly decreased over time,while the absorbance at 315 nm, which corresponds to 4AP,increased as the reaction progressed. By converting theseabsorbance changes into concentration variations, the plotsshowing concentration changes of 4NP and 4AP were obtained,as illustrated in Fig. 7(b). It was confirmed that the conversionof 4NP to 4AP occurred in a nearly stoichiometric manner.Fig. 7(c) illustrates the normalized concentration changes (C/C0) of 4NP with ZrZnNi4, CeAlNi4, Sm(NiSi)2, and the referencecatalysts of 12 wt%NiO/CeO2 and 10 wt%Ni/CeO2. The concen-Fig. 7 (a) Changes in absorbance and (b) the concentration shifts of 4NP and 4AP over time in the reaction solution utilizing ZrZnNi4 catalyst. (c)Changes in normalized concentration (C/C0) of 4NP during the reactions and (d) the linear relationship of ln(C/C0) over time for 12 wt%NiO/CeO2(X), 10 wt%Ni/CeO2 (diamond), ZrZnNi4 (square), CeAlNi4 (circle), and Sm(NiSi)2 (triangle) catalysts.Dalton Transactions PaperThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 6876–6885 | 6883Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513ftrations showed a gradual decrease with CeAlNi4 and NiO/CeO2, achieving nearly 80% conversion in 60 minutes. In con-trast, ZrZnNi4, Sm(NiSi)2, and Ni/CeO2 achieved complete con-version within 60 minutes, with ZrZnNi4 reaching 100% con-version in just 10 minutes, indicating its superior catalyticactivity. In comparison with NiO/CeO2 and Ni/CeO2, it wassuggested that metallic state Ni was effective to achieve thequick complete conversion. From the plots of ln(C/C0) againstreaction time (Fig. 7(d)), the rate constants were determined as0.16 min−1 for ZrZnNi4, 0.04 min−1 for CeAlNi4, 0.08 min−1 forSm(NiSi)2, 0.04 min−1 for NiO/CeO2, and 0.06 min−1 for Ni/CeO2. Comparing these constants to our previous studies con-ducted under the same reaction conditions but with differentcatalysts (Table 2), ZrZnNi4 demonstrated a higher catalyticperformance than the alloy catalysts CrMnFeCoNi andAlCoCrFeNi, yet lower performance than 5 wt%Pd/ZnO andAl0.2Co1.5CrFeNi1.5Ti0.5.The reaction rates were observed in the following order:ZrZnNi4 > Sm(NiSi)2 > CeAlNi4, NiO/CeO2. XPS results indi-cated that a minimal quantity of Ce was present on the surfaceof CeAlNi4, with Al–Ni–O being the primary surface com-ponent. This suggests that the active Ni species may not haveeffectively interacted with Ce, limiting electron transfer fromCe to Ni and thereby resulting in reduced catalytic perform-ance for CeAlNi4. Conversely, XPS analysis showed that Zr andSm were predominantly present on the surfaces of ZrZnNi4and Sm(NiSi)2, respectively, implying that active Ni speciescould interact effectively with Zr and Sm. This efficient elec-tron donation from Zr and Sm to Ni likely activated the Nispecies, leading to higher catalytic performance in ZrZnNi4and Sm(NiSi)2. Notably, DFT calculations revealed thatZrZnNi4 acts as a reductive intermetallic compound with thecapability to release electrons, which aids in the generation ofreactive hydrogen and accelerates the rate-determining step(eqn (8)). Although it was suggested that the synthesizedZrZnNi4 had a core–shell structure that very thin oxide layerscovered the intermetallic-phase core, it is possible that theelectron-rich Ni species (Niδ−), suggested by DFT calculations,may be partially exposed on surface through the pit-hole of theoxide shell, or/and the crystallized intermetallic ZrZnNi4 exist-ing in the core may promote the surface reaction due to theelectron donation through the thin oxide shell. Therefore, theintermetallic compound ZrZnNi4 stands out as a distinct cata-lyst, with its electron-rich Ni species effectively facilitating theNaBH4-assisted hydrogenation of 4NP.ConclusionsEight intermetallic compounds containing Zr, Ce, or Sm weresynthesized through the reduction of metal oxides. The cata-lysts ZrZnNi4 (42.0 m2 g−1), CeAlNi4 (66.9 m2 g−1), and Sm(NiSi)2 (25.0 m2 g−1) were subsequently evaluated for their cata-lytic activity in the NaBH4-assisted hydrogenation process of4-nitrophenol. In comparison with the widely used Ni/CeO2catalyst, both ZrZnNi4 and Sm(NiSi)2 exhibited superior cata-lytic performance. Given that the WFs of Zr and Sm are con-siderably lower than that of Ni, which serves as the active sitefor hydrogenation, it was hypothesized that this high catalyticperformance arises from the generation of electron-rich Nispecies, particularly in the case of ZrZnNi4.Author contributionsYasukazu Kobayashi: conceptualization, supervision, fundingacquisition, investigation, methodology, data curation, writing– original draft, writing – review & editing. Hiroshi Mizoguchi:investigation, methodology, data curation, writing – review &editing. Koharu Yamamoto: investigation, methodology, datacuration, writing – review & editing. Ryo Shoji: methodology,writing – review & editing.Conflicts of interestThere are no conflicts to declare.Data availabilityThe authors declare that the data supporting the findings ofthis study are available within the paper and its supplementaryinformation (SI). Supplementary information is available. SeeDOI: https://doi.org/10.1039/d6dt00513f.Should any raw data files be needed in another format theyare available from the corresponding author, YasukazuKobayashi, upon reasonable request.AcknowledgementsThis work was supported by JSPS KAKENHI Grant Numbers24K08591 and 23K23440. A part of this work was supported by“Advanced Research Infrastructure for Materials andNanotechnology in Japan (ARIM)” of the Ministry ofEducation, Culture, Sports, Science and Technology (MEXT).Proposal Number JPMXP125NM5175. We acknowledge MrKoei Takagi for his help in review process.Table 2 The comparison of rate constants (k) for the hydrogenation of4NPCatalyst Conditionsk[min−1] Ref.ZrZnNi4 25 °C; 4-NP (1.6 mM);NaBH4 (47 mM); 10 mg-cat/9 mL0.16 ThisworkCeAlNi4 0.04Sm(NiSi)2 0.0812 wt%NiO/CeO2 0.0410 wt%Ni/CeO2 0.065 wt%Pd/ZnO 0.44 33Al0.2Co1.5CrFeNi1.5Ti0.5 0.29 34CrMnFeCoNi 0.11 35AlCoCrFeNi 0.03 36Paper Dalton Transactions6884 | Dalton Trans., 2026, 55, 6876–6885 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttps://doi.org/10.1039/d6dt00513fhttps://doi.org/10.1039/d6dt00513fhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513fReferences1 Z. Xiong, H. Zhang, W. Zhang, B. Lai and G. Yao, Chem.Eng. J., 2019, 359, 13–31.2 P. 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Hydrogen Energy, 2023, 48, 30963–30973.Dalton Transactions PaperThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 6876–6885 | 6885Open Access Article. Published on 17 April 2026. Downloaded on 5/6/2026 11:50:44 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d6dt00513f Button 1: