# Fileset

[CoLa2O3_JPCL2025.pdf](https://mdr.nims.go.jp/filesets/3480c021-59c7-4c6d-a7b3-304b5ff78218/download)

## Creator

[Hiroshi Mizoguchi](https://orcid.org/0000-0002-0992-7449), [Shunqin Luo](https://orcid.org/0000-0002-1162-0200), Masato Sasase, Masaaki Kitano, [Hideo Hosono](https://orcid.org/0000-0001-9260-6728)

## Rights

[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

## Other metadata

[Ammonia Decomposition Catalyzed by Co Nanoparticles Encapsulated in Rare Earth Oxide](https://mdr.nims.go.jp/datasets/3eb7f2a8-a15a-4978-ba8a-4d5511e02e57)

## Fulltext

Ammonia Decomposition Catalyzed by Co Nanoparticles Encapsulated in Rare Earth OxideAmmonia Decomposition Catalyzed by Co NanoparticlesEncapsulated in Rare Earth OxideHiroshi Mizoguchi,*,§ Shunqin Luo,§ Masato Sasase, Masaaki Kitano, and Hideo Hosono*Cite This: J. Phys. Chem. Lett. 2025, 16, 796−801 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: We fabricated Co-based catalysts by the low-temperature thermal decom-position of R−Co intermetallics (R = Y, La, or Ce) to reduce the temperature of ammoniacracking for hydrogen production. The catalysts synthesized are nanocomposites of Co/ROxwith a metal-rich composition. In the Co13/LaO1.5 catalyst derived from LaCo13, Conanoparticles of 10−30 nm size are enclosed by the LaO1.5 matrix. The nanocompositeexhibited superior catalytic activity (91% at 500 °C), which was attributed to dual advantages;the low workfunction of the supporter, O-deficient LaO1.5‑x nanoparticles, promotes electrondonation to the Co catalyst in the interface, which leads to enhanced N−H bond dissociation.Moreover, such a composite structure is effective in suppressing the grain growth of Conanoparticles because the LaO1.5 layer works as a diffusion barrier against Co. The thermaldecomposition of intermetallics is a new route for the facile synthesis of catalysts having an electronically active support.For the realization of hydrogen economy, a technology forthe transport of hydrogen should be established.1a,b Ascandidates for hydrogen carriers, compressed gaseous hydro-gen in cylinders, liquid hydrogen, liquid ammonia (NH3), andorganic hydrides have been investigated thus far. Among these,ammonia has the advantage of being easy to liquefy andtransport in large volumes. However, the method of extractinghydrogen from ammonia at low temperatures has not yet beenestablished.2a−c The cracking reaction of NH3 is endothermicwith ΔH298 = 46.1 kJ/mol and is thermodynamically favorableat high temperatures and low pressures.3 However, at theequilibrium cracking fraction of 98% at 400 °C under 1 atm,the cracking reaction does not proceed without catalysts (seethe equilibrium value in Figure 1b). A catalyst mainly works intwo elementary reactions. One is the dissociation of N−Hbonds in the adsorbed NH3 molecule. The other is therecombination of N adatoms generated on the surface of thecatalyst to form N2. The activity of catalysts shows a volcano-type trend as a function of the metal (M)−N interaction in theperiodic table with the apex of Ru. Although Ru exhibitsexcellent properties for this reaction,4a,b there are twodrawbacks, namely, the high and unstable price of Ru and itslow natural abundance, which make it difficult to meet marketdemands. Since the pressure of NH3 during NH3 decom-position is higher than that during NH3 synthesis, the peak forthe volcano plot shifts toward the region of weak M−Ninteraction.5 Thus, Co and Ni, which are relatively inexpensive,are good candidates for Ru alternative catalysts. Although thereare many reports regarding these 3d transition-metalcatalysts,2a,b the process that works even at lower temperatures(below 300 °C) is essential for practical use. Since the supporteffect on NH3 decomposition catalysts is not well-understoodas far as we know, we have explored the use of supports.Recently, we have reported that the Ni/CeO2 catalystsynthesized by the low-temperature thermal oxidation of theCeNi5 intermetallic (IM) shows high activity.6 Its uniquemicrostructure, that is, the large Ni/CeOx interface arisingfrom the interlocking of Ni nanoparticles with the CeO2framework, was attributed to its high catalytic activity. Here,we report the high catalytic activity of Co/LaO1.5 with theunique microstructure. The dispersed Co nanoparticlesattached to the LaO1.5 grain boundary phase enhance thecatalytic reaction. The grain boundary phase suppresses thegrain growth of metallic Co particles at high temperatures.Many Co-based IMs decomposed in the catalytic activitytest under NH3, resulting in the formation of Co particles thatexhibit catalytic activity. The key to designing new catalysts isto induce Co nanoparticle formation via IM decomposition atthe nanoscale level. Among the R−Co systems, we focused onIMs with R = Y, La, or Ce because of their electron donationpower originating from the lower workfunction (WF) of Rions. There exist various IMs in an R−Co binary system. Thepulverization of IMs is often possible because IMs commonlyhave mechanically brittle properties. This feature facilitates thecompositional search for powder catalysts. As an example, thecatalytic activity (conversion in NH3 cracking) for NH3decomposition in the La−Co system is shown in Figure 2.The maximum catalytic activity was observed in La7Co93, thatReceived: November 17, 2024Revised: December 27, 2024Accepted: January 8, 2025Letterpubs.acs.org/JPCL© XXXX The Authors. Published byAmerican Chemical Society796https://doi.org/10.1021/acs.jpclett.4c03309J. Phys. Chem. Lett. 2025, 16, 796−801This article is licensed under CC-BY 4.0Downloaded via NATL INST FOR MATLS SCIENCE (NIMS) on January 14, 2025 at 23:54:03 (UTC).See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hiroshi+Mizoguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Shunqin+Luo"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Masato+Sasase"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Masaaki+Kitano"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hideo+Hosono"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/acs.jpclett.4c03309&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=tgr1&ref=pdfpubs.acs.org/JPCL?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/acs.jpclett.4c03309?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://pubs.acs.org/JPCL?ref=pdfhttps://pubs.acs.org/JPCL?ref=pdfhttps://acsopenscience.org/researchers/open-access/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/is, LaCo13. On the basis of the investigation of an R−Co binarysystem (R = Y or Ce), we also confirmed the high catalyticactivities of CeCo3 and YCo2. Figure 1a shows the temperaturedependence of the catalytic activity. The activity of LaCo13 orCeCo3 fabricated by the process shown in Scheme 1 becamenoticeable at ∼270 °C and reached 91 or 87% at 500 °C,respectively (solid lines in Figure 1a). Note that CeCo3 showsa catalytic activity of 30% at 400 °C. As described later,metallic Co particles are formed in these catalysts, which areresponsible for the observed activity. Figure 1a also shows thedata indicated by dashed lines for the catalysts without anoxidation treatment. The activities of these samples wereincreased by two or three times by oxidation treatment at 350°C. Figure 1b also shows the activities of the Co/ROx catalystswith the same cationic composition prepared by theimpregnation method for comparison. Figure 1c shows thetime course of the catalytic activity. The activity of LaCo13 at500 °C gradually decreased to 78% in 100 h. Figure 1d alsoshows the gas flow rate dependence of the catalytic activity.Table 1 shows the apparent activation energies (Ea = 95−99kJ/mol) of these catalysts, which were calculated from theArrhenius plot. The observed Ea values suggest that thesecatalysts have the same rate-determining step. We comparedthe activities of these catalysts with those of Co-based catalystsreported thus far. Table S1 in Supporting Informationsummarizes representative reports on Co-based catalysts. Weshould compare these data carefully because the activitydepends highly on the reaction temperature or weight hourlyspace velocity (WHSV). The obtained activities (25−30% atFigure 1. Temperature dependence of conversion in NH3 cracking over various Co-based catalysts at a weight hourly space velocity (WHSV) of12000 mLNH3 gcat−1 h−1. Co-based IMs with (solid line) or without (dashed line) oxidation treatment. (b) Reference Co-based catalysts preparedby impregnation method (solid line) and calculated thermodynamically equivalent values (dotted line). (c) Time course of NH3 cracking over Co/LaO1.5 catalyst. (d) WHSV dependence of the conversion in NH3 cracking. As the WHSV increased, the activity decreased because of theshortening of the contact time between the catalyst and the NH3 molecule.Figure 2. Chemical composition dependence in conversion of NH3cracking for La−Co intermetallics.Scheme 1. Flowchart for Preparing Co/ROx CatalystsThe Journal of Physical Chemistry Letters pubs.acs.org/JPCL Letterhttps://doi.org/10.1021/acs.jpclett.4c03309J. Phys. Chem. Lett. 2025, 16, 796−801797https://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=sch1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=sch1&ref=pdfpubs.acs.org/JPCL?ref=pdfhttps://doi.org/10.1021/acs.jpclett.4c03309?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as400 °C) in Figure 1a are comparable to those of Co-basedcatalysts, which show the highest activities as previouslyreported (e.g., Co/Ba-promoted CeO2, Co/La-promotedMgO).78910The catalysts obtained were characterized to elucidate theorigins of their activities. Figure 3a,b, respectively, shows thepowder XRD patterns of LaCo13 and CeCo3 showing highactivities. These IMs were decomposed into c-Co/h-Co/CoO/Co3O4/ROx by oxidation treatment at 350 °C. After the NH3test, Co oxides were converted into c-Co through reductionunder NH3 and/or H2. Hereafter, LaCo13, CeCo3, and YCo2synthesized by the procedure shown in Scheme 1 are indicatedas Co/LaO1.5, Co/CeO2, and Co/YO1.5, respectively. Theresults indicate that the La−O affinity is stronger than the La−N or La−H affinity, as expected from the thermodynamicstability represented by the Ellingham diagram. We estimatedthe crystallite size (CS) of each phase appearing in thesecatalysts by a fundamental parameter method (Figure S1), andthe estimated CSs are summarized in Table 2. Note that thesizes of ROx phases were ∼10 nm, which were rather smallerthan those of metallic Co particles, showing similarity with aninverse catalyst structure. SEM-EDX measurements indicatedthat the chemical composition of these catalysts agrees withthat of the raw materials. Figure 4 shows the results of STEMobservations of the Co/LaO1.5 catalyst. It also shows that themicrostructure of the samples was uniform and that no largedifference in microstructure was observed for differentlocations. The composition ratio of Co/La was determinedas ∼13 by EDX, which was consistent with that of rawmaterials (LaCo13). Figure 4a,b and Figure 4c,d show theHAADF-STEM and EDX mapping images of the same region,respectively. These images indicate that the catalyst is ananocomposite composed of metallic Co single crystals and aLaO1.5 matrix. Figure 4e shows the nanostructure observed bySTEM. The Co nanoparticles of 10−30 nm size are enclosedby the LaO1.5 phase. The size of the Co particles was consistentwith that estimated by Rietveld refinements. The HAADF-STEM image in Figure 4f shows the interface between a Cosingle crystal and LaO1.5. The LaO1.5 phase, whose latticeimage is derived from the A-type lanthanide sesquioxidestructure (trigonal, space group: P3̅m1), adheres closely to theCo single crystal. We see holes and hollows in the LaO1.5Table 1. Properties of the Co-based catalysts after NH3 testCatalystConversiona.at 500 °C(%)NH3 decomposition ratea(molNH3 gcat−1 h−1)Eab(kJ/mol)Surface area(m2/g)Co surface area(m2/g)WF(eV)Co/LaO1.5 90.5 0.43 99.2 4.8 0.52 4.7Co/CeO2 86.7 0.42 94.8 15.2 1.68 5.2Co/YO1.5 75.6 0.37 98.4 8.5 0.80 -Co - - - - - 5.3aReaction conditions: catalyst, 0.050 g; temperature, 500 °C; NH3 gas, 10 mL min−1, 12000 mLNH3 gcat−1 h−1; pressure, 0.1 MPa. bThermalactivation energy (Ea) was estimated in the temperature region of 310−370 °C.Figure 3. Powder XRD patterns of LaCo13 (a) and CeCo3 (b)catalysts. (1) Before NH3 test. (2) After NH3 test.Table 2. Crystallite sizes estimated by fundamentalparameter methodbCatalysta Phase Volume weighted average diameter (nm)Co/LaO1.5 La2O3 c-Co h-Co7(3) 17.2(2) 13.7(3)Co/CeO2 CeO2 c-Co8.05(5) 12.2(1)aAfter NH3 test bNo predominant strain was found.Figure 4. Nanostructures of Co/LaO1.5 catalyst after NH3 test. (a, b)HAADF images of Co/LaO1.5 nanocomposite. (c, d) The red, green,and blue areas in the EDX mapping images correspond to Co, La, andO, respectively. (e) Schematic of the nanostructure with Co particlesenclosed by LaO1.5 matrix phase. (f) HAADF-STEM image of theCo/LaO1.5 interface. (g) BF image corresponding to (b).The Journal of Physical Chemistry Letters pubs.acs.org/JPCL Letterhttps://doi.org/10.1021/acs.jpclett.4c03309J. Phys. Chem. Lett. 2025, 16, 796−801798https://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?fig=fig4&ref=pdfpubs.acs.org/JPCL?ref=pdfhttps://doi.org/10.1021/acs.jpclett.4c03309?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asphase, as shown in Figure 4a,b. We can also see the presence ofthe amorphous region of LaO1.5 in the interface. Such ananostructure causes distortion and lattice defects in metallicCo, which is softer than LaO1.5. We also observed stackingfaults at the center of the Co single crystal in the BF image,shown in Figure 4g. The theoretical ratio of lattice volumesV(26Co)/V(La2O3) = 77/23 was calculated from the unit cellvolumes. The CS of LaO1.5 is inevitably small in the uniquemicrostructure, and the CS value of ∼10 nm estimated fromRietveld refinements is consistent with the size (10−30 nm) ofthe Co particles and the theoretical ratio of lattice volumes. Inthe microstructure, separation of the matrix into the metallicCo and LaO1.5 phases occurs. Interdiffusion between thesephases is restricted under low-oxygen-partial pressure atmos-phere owing to the large difference in ionic size. That is whythe LaO1.5 phase serves as a barrier for diffusion, preventing thegrain growth of Co nanoparticles at high temperatures. Weobserved two polymorphisms of metallic Co. Phase transitionoccurs at ∼420 °C from the hcp-type crystal structure (low-temperature phase) to the fcc-type structure (cubic, high-temperature phase). The cubic phase is stabilized by surfaceenergy, and nanoparticles tend to adopt the cubic poly-morphism.11 As shown in Figure 3, the reduction of Co oxidesunder an NH3 flow leads to c-Co formation, indicating that theLaO1.5 phase contributes to the formation of the cubic phaseby preventing the grain growth of Co particles. Thermaldesorption spectroscopy (TDS) measurements provide H or Ncontent information (Figure S2 in Supporting Information).Note that the obtained compositions of the Co/LaO1.5 andC o / C e O 2 c a t a l y s t s w e r e C o 1 3 ( L a O 1 . 5 ) -N 0 . 0 2 H 0 . 0 3 ( H 2 O ) 0 . 0 4 ( C O 2 ) 0 . 0 0 8 a n d C o 3 ( C e O 2 ) -N0.16H0.02(NH3)0.02(H2O)0.05(CO2)0.05, respectively. The be-havior of N desorption from the Co/CeO2 catalyst was similarto that of Co2N.12 Table 1 also summarizes BET surface areasand metal surface areas. Metal surface area of Co/LaO1.5 is∼30% of that of Co/CeO2, in spite of the large Co content(Co/La = 13) in Co/LaO1.5. The XPS spectra of the Co/LaO1.5 and Co/CeO2 catalysts were collected in order toobtain information about the surface state. Figure S3a showsthe La 3d spectrum of Co/LaO1.5. The peak at 834.9 eV wasattributed to La 3d5/2 in La3+ state in oxide.13 We can see aweak shoulder at 832.5 eV, indicating reduced La ion(La(3‑x)+). From the peak area, the ratio La(3‑x)+/La3+ wascalculated to be 0.32. In the Ce 3d spectrum of Co/CeO2(Figure S3b), the peak at 882.7 eV was attributed to the Ce4+state. The Ce3+ state shows a peak of 3d5/2 at ∼881 eV,14 whileour catalyst did not. The presence of Ce4+ state was alsoconfirmed by the strong peak at 917.0 eV, which is acharacteristic satellite called u’’’.15 In the Co 2p spectra ofthese catalysts shown in Figure S3c, various valence states ofCo ion were observed. The Co−O related peaks (Cox+)appeared at ∼781.2 and ∼786.5 eV, while the weak peak at∼778.5 eV was ascribed to be a metallic Co state (Co0).16From the peak area, the ratio Co0/Cox+ was calculated to be0.43 for La/O1.5 or 0.18 for Co/CeO2. Table 1 also shows WFsestimated from the Kelvin probe. The WFs of Co/LaO1.5 andCo/CeO2 were 4.7 and 5.2 eV, respectively, which weresmaller than that (5.3 eV) of metallic Co. This result indicatesthe enhanced Co−N interaction in Co/LaO1.5. The decrease inthe WF of Co leads to the weakening of N−H bonds of NH3absorbed on Co surfaces through electron donation17 andcontributes to the cracking of NH3.The Co-rich compositions of Co/ROx catalysts remind usinverse catalysts have a metal-rich composition.18a,b It has beenoften reported that increasing the area of the interface betweenthe catalyst and the support enhances catalytic reaction ininverse catalysts. Here, we discuss the origin of the low WFsobserved in our catalyst, which is expected to be the mainfactor affecting the observed catalytic activities. The low WF ofCo/LaO1.5 indicates electron donation from the LaO1.5 matrixto the Co particles. Stoichiometric LaO1.5 does not commonlywork as a semiconductor, because it is an insulator with abandgap of ∼5 eV. However, the LaO1.5 phase has a smaller CS(∼10 nm), which is derived from the Co-rich composition.LaO1.5 with a smaller CS tends to be deficient in O at thesurface of the particle. The presence of LaO1.5‑x at the surface isalso consistent with the La 3d XPS spectrum (Figure S3a). Infact, it is reported on the basis of TEM observations and DFTcalculations that CeO2 nanoparticles have Ce3+ ions at theirsurfaces, when the particle size is smaller than ∼10 nm.19Recently, Hayami et al. showed by DFT calculations thatmetallic LaO1.5‑x with O-deficiency has an extremely small WF(∼2 eV), which originates from conduction electrons in the La5d band.20 As shown in Figure 4f, the LaO1.5 phase adheredclosely to the Co single crystal; consequently, a defectiveLaO1.5 region was formed in the interface. The observed lowWF is realized by electron donation from the LaO1.5‑x matrixwith an O deficiency to a Co particle in the interface. Theenhancement of catalytic activity through the anion-deficientsupport in the interface has also been reported recently.17,21We attempted to estimate the fraction of active Co species inthe LaO1.5/(c-Co)13 composition using a rigid band model.When we used the magnetic density of states (DOS) of c-Coreported by Lizarraga et al.,22 the upshift of the Fermi energyof 0.6 eV (=5.3−4.7) is attained approximately throughdonation of 0.48 electrons to down-spin DOS. If we postulate anegatively charged Co0.48− state, LaO1.5 must donate 6.2electrons (=0.48 × 13) to Co13. LaOx cannot have such anumber of conduction electrons, indicating that only a portionof the Co ions among Co13 accept electrons from LaOx andwork as active species. This agrees well with the small metalsurface area of Co/LaO1.5 estimated by the CO pulsechemisorption.In summary, we investigated Co-based catalysts fabricatedby the low-temperature thermal decomposition of R−Co IMs(R = Y, La, or Ce). (1) The Co/CeO2 nanocompositeprepared by the thermal decomposition of CeCo3 exhibited asuperior catalytic activity of ∼30% at 400 °C for NH3 cracking.(2) In the Co/LaO1.5 catalyst derived from LaCo13, the Conanoparticles of 10−30 nm in size are enclosed by the LaOxphase. According to the Co-rich composition (Co/La = 13),the LaO1.5 phase inevitably has a smaller CS (∼10 nm), givingrise to the small crystallite size of LaO1.5. A low WF is realizedfor these catalysts by electron donation from the O-deficientLaO1.5‑x phase to the Co particles in the interface. (3) Theseparation into the metallic Co and LaO1.5 phases occurs. TheLaO1.5 phase serves as a barrier for diffusion, preventing thegrain growth of Co nanoparticles at high temperatures. (4)The thermal decomposition of IMs is a new route to designingunique nanostructures toward the development of catalyticsystems.The Journal of Physical Chemistry Letters pubs.acs.org/JPCL Letterhttps://doi.org/10.1021/acs.jpclett.4c03309J. Phys. Chem. Lett. 2025, 16, 796−801799https://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfpubs.acs.org/JPCL?ref=pdfhttps://doi.org/10.1021/acs.jpclett.4c03309?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309.Powder XRD pattern, TDS spectra, and XPS spectra(PDF)■ AUTHOR INFORMATIONCorresponding AuthorsHiroshi Mizoguchi − Research Center for MaterialsNanoarchitectonics (MANA), National Institute forMaterials Science (NIMS), Tsukuba, Ibaraki 305-0044,Japan; orcid.org/0000-0002-0992-7449;Email: MIZOGUCHI.Hiroshi@nims.go.jpHideo Hosono − Research Center for MaterialsNanoarchitectonics (MANA), National Institute forMaterials Science (NIMS), Tsukuba, Ibaraki 305-0044,Japan; MDX Research Center for Element Strategy, Instituteof Science Tokyo, Midori-ku, Yokohama 226-8503, Japan;orcid.org/0000-0001-9260-6728; Email: hosono@mces.titech.ac.jpAuthorsShunqin Luo − Research Center for MaterialsNanoarchitectonics (MANA), National Institute forMaterials Science (NIMS), Tsukuba, Ibaraki 305-0044,JapanMasato Sasase − MDX Research Center for Element Strategy,Institute of Science Tokyo, Midori-ku, Yokohama 226-8503,JapanMasaaki Kitano − MDX Research Center for Element Strategy,Institute of Science Tokyo, Midori-ku, Yokohama 226-8503,Japan; orcid.org/0000-0003-4466-7387Complete contact information is available at:https://pubs.acs.org/10.1021/acs.jpclett.4c03309Author Contributions§(H.M. and S.L.) These authors contributed equally to thiswork.NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSWe thank Dr. H. Yasufuku (NIMS) for XPS measurementsand Dr. M. Tsuji for WF measrements. This work wassupported by a Grant-in-Aid for Scientific Research (No.23K23440) from the Japan Society for the Promotion ofScience (JSPS) and Fujikura Foundation (2023). This workwas also supported by ″Advanced Research Infrastructure forMaterials and Nanotechnology in Japan (ARIM)″ of theMinistry of Education, Culture, Sports, Science and Technol-ogy (MEXT) Proposal Number JPMXP1224NM5138.■ REFERENCES(1) (a) Al Ghafri, S. Z. S.; Munro, S.; Cardella, U.; Funke, T.;Notardonato, W.; Trusler, J. P. M.; Leachman, J.; Span, R.; Kamiya,S.; Pearce, G.; Swanger, A.; Rodriguez, E. D.; Bajada, P.; Jiao, F.;Peng, K.; Siahvashi, A.; Johns, M. L.; May, E. F. Hydrogenliquefaction: a review of the fundamental physics, engineering practiceand future opportunities. Energy & Environ. Sci. 2022, 15 (7), 2690−2731. (b) Nazir, G.; Rehman, A.; Hussain, S.; Aftab, S.; Heo, K.;Ikram, M.; Patil, S.; Aizaz Ud Din, M. Recent Advances and ReliableAssessment of Solid-State Materials for Hydrogen Storage: A StepForward toward a Sustainable H2 Economy. Adv. Sustainable Systems2022, 6 (11), No. 2200276.(2) (a) Bell, T. E.; Torrente-Murciano, L. H2 Production viaAmmonia Decomposition Using Non-Noble Metal Catalysts: AReview. Top. Catal. 2016, 59 (15−16), 1438−1457. (b) Lucentini, I.;Garcia, X.; Vendrell, X.; Llorca, J. Review of the Decomposition ofAmmonia to Generate Hydrogen. Ind. Eng. Chem. Res. 2021, 60 (51),18560−18611. (c) Jolaoso, L. A.; Zaman, S. F.; Podila, S.; Driss, H.;Al-Zahrani, A. A.; Daous, M. A.; Petrov, L. Ammonia decompositionover citric acid induced γ-Mo2N and Co3Mo3N catalysts. Int. J.Hydrogen Energy 2018, 43 (10), 4839−4844.(3) Ojelade, O. A.; Zaman, S. F. Ammonia decomposition forhydrogen production: a thermodynamic study. Chem. Papers 2021, 75(1), 57−65.(4) (a) Schüth, F.; Palkovits, R.; Schlögl, R.; Su, D. S. Ammonia as apossible element in an energy infrastructure: catalysts for ammoniadecomposition. Energy & Environ. Sci. 2012, 5 (4), 6278−6289.(b) Kishida, K.; Kitano, M.; Sasase, M.; Sushko, P. V.; Abe, H.; Niwa,Y.; Ogasawara, K.; Yokoyama, T.; Hosono, H. Air-stable calciumcyanamide-supported ruthnium catalyst for ammonia synthesis anddecomposition. ACS Appl. Energy Mater. 2020, 3, 6573−6582.(5) Boisen, A.; Dahl, S.; Norskov, J.; Christensen, C. Why theoptimal ammonia synthesis catalyst is not the optimal ammoniadecomposition catalyst. J. Catal. 2005, 230 (2), 309−312.(6) Mizoguchi, H.; Osawa, Y.; Sasase, M.; Ohashi, N.; Kitano, M.;Hosono, H. Ammonia Cracking Catalyzed by Ni NanoparticlesConfined in the Framework of CeO2 Support. J. Phys. Chem. Lett.2023, 14 (42), 9516−9520.(7) Morlanés, N.; Sayas, S.; Shterk, G.; Katikaneni, S.; Harale, A.;Solami, B.; Gascon, J. Development of a Ba−CoCe catalyst for theefficient and stable decomposition of ammonia. Catal. Sci. Technol.2021, 11 (9), 3014−3024.(8) Hu, X.; Wang, W.; Jin, Z.; Wang, X.; Si, R.; Jia, C. Transitionmetal nanoparticles supported La-promoted MgO as catalysts forhydrogen production via catalytic decomposition of ammonia. J.Energy Chem. 2019, 38, 41−49.(9) Han, X.; Hu, M.; Yu, J.; Xu, X.; Jing, P.; Liu, B.; Gao, R.; Zhang,J. Dual confinement of LaCoOx modified Co nanoparticles forsuperior and stable ammonia decomposition. Appl. Catal., B 2023,328, No. 122534.(10) Gu, Y.; Jin, Z.; Zhang, H.; Xu, R.; Zheng, M.; Guo, Y.; Song,Q.; Jia, C. Transition metal nanoparticles dispersed in an aluminamatrix as active and stable catalysts for COx-free hydrogen productionfrom ammonia. J. Mater. Chem. A 2015, 3 (33), 17172−17180.(11) Amirkhanyan, N. H.; Zakaryan, M. K.; Kharatyan, S. L.;Yeghishyan, A.; Zhukovskyi, M.; Aprahamian, A.; Manukyan, K. V.Stabilization of metastable γ-Co: Combustion synthesis and rapidprocessing. Mater. Chem. Phys. 2024, 319, No. 129368.(12) Ikeda, Y.; Lehmann, T.; Widenmeyer, M.; Coduri, M.;Grabowski, B.; Niewa, R. Crystal structure and phase stability ofCo2N: A combined first-principles and experimental study. J. AlloysComp. 2021, 854, No. 156341.(13) Ni, J.; Chen, L.; Lin, J.; Schreyer, M.; Wang, Z.; Kawi, S. Highperformance of Mg-La mixed oxides supported Ni catalysis for dryreforming of methane,: the effect of crystal structure. Int. J. HydrogenEnergy 2013, 38, 13631−13642.(14) Lin, B.; Liu, Y.; Heng, L.; Ni, J.; Lin, J.; Jiang, L. Effect of ceriamorphology on the catalytic activity of Co/CeO2 catalyst forammonia synthesis. Catal. Commun. 2017, 101, 15−19.(15) Shelef, M.; Haack, L.; Soltis, R.; deVries, J.; Logothetis, E. AnXPS study of interactions in thin films containing a noble metal withvalence-invariant and reducible oxides. J. Catal. 1992, 137, 114−126.(16) Jia, C. J.; Schwickardi, M.; Weidenthaler, C.; Schmidt, W.;Korhonen, S.; Weckhuysen, B. M.; Schuth, F. Co3O4-SiO2 nano-composite: a very active catalyst for CO oxidation with unusualcatalytic behavior. J. Am. Chem. Soc. 2011, 133 (29), 11279−88.(17) Ogasawara, K.; Nakao, T.; Kishida, K.; Ye, T.; Lu, Y.; Abe, H.;Niwa, Y.; Sasase, M.; Kitano, M.; Hosono, H. AmmoniaThe Journal of Physical Chemistry Letters pubs.acs.org/JPCL Letterhttps://doi.org/10.1021/acs.jpclett.4c03309J. Phys. Chem. Lett. 2025, 16, 796−801800https://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?goto=supporting-infohttps://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.4c03309/suppl_file/jz4c03309_si_001.pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hiroshi+Mizoguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-0992-7449mailto:MIZOGUCHI.Hiroshi@nims.go.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hideo+Hosono"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0001-9260-6728https://orcid.org/0000-0001-9260-6728mailto:hosono@mces.titech.ac.jpmailto:hosono@mces.titech.ac.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Shunqin+Luo"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Masato+Sasase"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Masaaki+Kitano"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-4466-7387https://pubs.acs.org/doi/10.1021/acs.jpclett.4c03309?ref=pdfhttps://doi.org/10.1039/D2EE00099Ghttps://doi.org/10.1039/D2EE00099Ghttps://doi.org/10.1039/D2EE00099Ghttps://doi.org/10.1002/adsu.202200276https://doi.org/10.1002/adsu.202200276https://doi.org/10.1002/adsu.202200276https://doi.org/10.1007/s11244-016-0653-4https://doi.org/10.1007/s11244-016-0653-4https://doi.org/10.1007/s11244-016-0653-4https://doi.org/10.1021/acs.iecr.1c00843?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.iecr.1c00843?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/j.ijhydene.2018.01.092https://doi.org/10.1016/j.ijhydene.2018.01.092https://doi.org/10.1007/s11696-020-01278-zhttps://doi.org/10.1007/s11696-020-01278-zhttps://doi.org/10.1039/C2EE02865Dhttps://doi.org/10.1039/C2EE02865Dhttps://doi.org/10.1039/C2EE02865Dhttps://doi.org/10.1021/acsaem.0c00754?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsaem.0c00754?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsaem.0c00754?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/j.jcat.2004.12.013https://doi.org/10.1016/j.jcat.2004.12.013https://doi.org/10.1016/j.jcat.2004.12.013https://doi.org/10.1021/acs.jpclett.3c02446?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpclett.3c02446?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1039/D0CY02336Ahttps://doi.org/10.1039/D0CY02336Ahttps://doi.org/10.1016/j.jechem.2018.12.024https://doi.org/10.1016/j.jechem.2018.12.024https://doi.org/10.1016/j.jechem.2018.12.024https://doi.org/10.1016/j.apcatb.2023.122534https://doi.org/10.1016/j.apcatb.2023.122534https://doi.org/10.1039/C5TA04179Ahttps://doi.org/10.1039/C5TA04179Ahttps://doi.org/10.1039/C5TA04179Ahttps://doi.org/10.1016/j.matchemphys.2024.129368https://doi.org/10.1016/j.matchemphys.2024.129368https://doi.org/10.1016/j.jallcom.2020.156341https://doi.org/10.1016/j.jallcom.2020.156341https://doi.org/10.1016/j.ijhydene.2013.08.041https://doi.org/10.1016/j.ijhydene.2013.08.041https://doi.org/10.1016/j.ijhydene.2013.08.041https://doi.org/10.1016/j.catcom.2017.07.015https://doi.org/10.1016/j.catcom.2017.07.015https://doi.org/10.1016/j.catcom.2017.07.015https://doi.org/10.1016/0021-9517(92)90143-6https://doi.org/10.1016/0021-9517(92)90143-6https://doi.org/10.1016/0021-9517(92)90143-6https://doi.org/10.1021/ja2028926?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/ja2028926?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/ja2028926?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acscatal.1c01934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-aspubs.acs.org/JPCL?ref=pdfhttps://doi.org/10.1021/acs.jpclett.4c03309?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asDecomposition over CaNH-Supported Ni Catalysts via an NH2‑-Vacancy-Mediated Mars-van Krevelen Mechanism. ACS Catal. 2021,11, 11005−11015.(18) (a) Yan, H.; Yang, C.; Shao, W. P.; Cai, L. H.; Wang, W. W.;Jin, Z.; Jia, C. J. Construction of stabilized bulk-nano interfaces forhighly promoted inverse CeO2/Cu catalyst. Nat. Commun. 2019, 10(1), 3470. (b) Zeng, S.; Wang, Y.; Ding, S.; Sattler, J.; Borodina, E.;Zhang, L.; Weckhuysen, B.; Su, H. Active sites over CuO/CeO2 andinverse CeO2/CuO catalysts for preferential CO oxidation. J. PowerSources 2014, 256, 301−311.(19) Hao, X.; Yoko, A.; Chen, C.; Inoue, K.; Saito, M.; Seong, G.;Takami, S.; Adschiri, T.; Ikuhara, Y. Atomic-Scale Valence StateDistribution inside Ultrafine CeO2 Nanocubes and Its Size Depend-ence. Small 2018, 14 (42), No. e1802915.(20) Hayami, W.; Tang, S.; Tang, J.; Qin, L. C. Effects of low work-function lanthanum oxides on stable electron field emissions fromnanoscale emitters. Nanoscale Adv. 2022, 4 (21), 4669−4676.(21) Xu, K.; Liu, J. C.; Wang, W. W.; Zhou, L. L.; Ma, C.; Guan, X.;Wang, F. R.; Li, J.; Jia, C. J.; Yan, C. H. Catalytic properties oftrivalent rare-earth oxides with intrinsic surface oxygen vacancy. Nat.Commun. 2024, 15 (1), 5751.(22) Lizarraga, R.; Pan, F.; Bergqvist, L.; Holmstrom, E.; Gercsi, Z.;Vitos, L. First Principles Theory of the hcp-fcc Phase Transition inCobalt. Sci. Rep. 2017, 7 (1), 3778.The Journal of Physical Chemistry Letters pubs.acs.org/JPCL Letterhttps://doi.org/10.1021/acs.jpclett.4c03309J. Phys. Chem. Lett. 2025, 16, 796−801801https://doi.org/10.1021/acscatal.1c01934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acscatal.1c01934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1038/s41467-019-11407-2https://doi.org/10.1038/s41467-019-11407-2https://doi.org/10.1016/j.jpowsour.2014.01.098https://doi.org/10.1016/j.jpowsour.2014.01.098https://doi.org/10.1002/smll.201870195https://doi.org/10.1002/smll.201870195https://doi.org/10.1002/smll.201870195https://doi.org/10.1039/D2NA00536Khttps://doi.org/10.1039/D2NA00536Khttps://doi.org/10.1039/D2NA00536Khttps://doi.org/10.1038/s41467-024-49981-9https://doi.org/10.1038/s41467-024-49981-9https://doi.org/10.1038/s41598-017-03877-5https://doi.org/10.1038/s41598-017-03877-5pubs.acs.org/JPCL?ref=pdfhttps://doi.org/10.1021/acs.jpclett.4c03309?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as