A lattice oxygen-free design for efficient and stable photothermal methane dry reforming

Domain: neuroscience
Published: 2026-01-29
Editorial outcome: minor_revision

Abstract
Photothermal dry reforming of methane, a promising approach to producing syngas, typically uses oxide materials and is mediated by lattice oxygen. However, it is limited by the balance of the oxygen-releasing/replenishing loop. Here, we present a methane activation pathway free of lattice oxygen on a N-Ni/NiCo@C catalyst. Direct involvement of reactive oxygen species (O*/OH*) released from CO2 promotes effective CH4 activation and eliminates coke deposition on oxophilic NiCo sites. Control experiments and density functional theory calculations show that forming a C-N-Ni structure is essential for improving catalytic performance. This is achieved by strengthening the electronic interaction between the NiCo nanoparticles and the carbon layer, thereby boosting the elemental steps of CH4 dehydrogenation and CHx oxidation and preventing metal oxidation. The optimal catalyst exhibits a high light-to-chemical energy efficiency of 52%, maintaining stability during 200 hours of continuous operation at a mild temperature of 540 °C. This work demonstrates that highly efficient and stable photothermal dry reforming of methane can be achieved by bypassing lattice oxygen.

Introduction
Methanedryreforming(DRM),whichconvertsthetwomaingreenhousegases(CH4andCO2)intosyngas(COandH2),isapromisingwayofreducingcarbonemissionsandproducingavaluablefeedstockforindustrialprocesses1. However, traditional thermally driven DRMrequireshighoperatingtemperatures(700−1000°C)toovercometheendothermicnatureofthereaction(ΔH298K=247kJmol-1),whichleadstoseverecatalystdeactivationviametalsinteringandcoking,particularlyforNi-andCo-basedcatalysts2,3. Recentadvancementsinlight-drivenDRMofferapromisingwaytoaddresstheseissuesbyusingphotothermaleffectstoreduceoperatingtemperaturesandimproveenergyefficiency4,5. Nevertheless,thisapproachfaceschallengessuchaslowlightutilizationefficiency(typically<10%understandardsolarirradiation) and significant coking at moderate temperatures (400−600°C)6.

Theabundanceandmobilityofactiveoxygenspeciesarecrucialforachievinganti-cokingphotothermalDRM(PDRM).ThisisbecauseallC-HbondsinCH4aretypicallycleavedatoxygensitesbyphotogeneratedholes7–9. Traditionally, metal oxide-based catalysts (e.g., CeO2, β-Ga2O3, WO3) have been employed for the DRM process, enablingcarbonspeciestointeractdirectlywithlatticeoxygen(OL)(C*+OL→CO)10–13. Therefore,theoxygenreleasecapabilityofthesecatalystsplaysakeyroleinmitigatingcoke-induceddeactivation.However,thestrongmetal–oxygeninteractionsinmetaloxidesseverelyrestrict the mobility of lattice oxygen, thereby impeding coke consumptionandreducingDRMefficiency14. Furthermore,theexcessivereleaseofOLduringprolongedDRMoperationresultsinmetalsegregationandacceleratescatalystdeactivation15. Ideally,anapproachshouldbedevelopedthatbypassestheinvolvementoflatticeoxygentoovercomethislimitation.Itiswellestablishedthatsubstantialactiveoxygen species (O*/OH*) are formed during CO2 conversion in the DRM process (CO2→CO+O*, CO2+H*→CO+OH*). Additionally, Ni/Co exhibits a strong binding affinity towards oxygen-containing radicals due to its high oxophilicity16,17. Thus, the adsorbed O*/OH* speciesovertheNi/CositescanbeeffectivelyutilizedforCH4activation,therebysubstitutingtheroleofOL.However,thelimitedelectrontransferefficiencyaroundtheNi/CositesmakesthesemetalssusceptibletooxidationdeactivationbyO*/OH*species6,18. The mainchallenge in addressing this issue lies in constructing an efficient, directional electron transfer channel to enhance electron density aroundthemetalsites.

Recently,metal-organicframework(MOF)-derivedmaterialshaveemergedaspotentialcandidatesforefficient,stable,light-orthermallydrivencatalysis19,20. MOF-templatedsynthesiscanproducemetalcentersthatarehighlydispersedandcoatedwitha carbon layer. This provides broad light absorption, high photothermal efficiency, and especiallyfastelectronconduction20–24. Notably,electrocatalyticstudieshaverevealedthattuningtheN-ligandsduringMOFsynthesiscanfacilitate the formation of metal-N-C structures that exhibit unique capabilitiesinelectronmodulation,intermediateregulation,andmetalanchoring in room-temperature catalysis25,26. This special structural featuremeansthatMOF-derivedcatalystscouldbeusefulfordirectedelectron transfer in PDRM. However, their applications in photothermal catalysis remain unexplored, as high-temperature pyrolysis convertsmetal-N-Cstructuresintometal@NCstructures19,27,28,whichfailtopreservetheintrinsicelectronicandcatalyticpropertiesofthemetal-Ncoordinationsites.

Here, we present the design of an efficient, stable NiCo-MOF-derived N-Ni/NiCo@C catalyst featuring C-N-Ni coordination. This optimized catalyst achieves a light-to-chemical energy efficiency (LTCEE)of52%at2.8Wcm−2oflightirradiation,producingH2andCO at rates of 423.3 and 487.4mmolh−1g−1, respectively. Crucially, it maintains stable H2/CO ratios for 200h at the coke-sensitive temperatureof540°C,outperformingN-freeandsingle-metalsamples,aswellasNiCo/Al2O3,throughsynergisticN-Ni coordination, alloying, and a carbon-coated structure. The C-N-Ni coordination acts as a directional electron transfer pathway that regulates electron distributionwithintheNiCoalloy.ThispromotestheactivationofC-HbondsattheNisitesanddrivestheactivationofCO2attheCosites. Additionally,photoexcitedelectronsaccumulateattheN-Nisitesviathecarboncoating,whicheffectivelypreventstheNiCometalfrombeingdeactivatedbyreactiveoxygenspecies(OH*/O*)duringtheDRMprocess.Notably,abundantoxygenradicalsoxidizeCH*toCHO*andCOundertheinfluenceofphotogeneratedholes,therebyeliminatingcarbondepositionandinhibitingthewater-gasshiftreaction(RWGS). ThepreciseconstructionoftheNi-N-Csitesprovidesafeasiblestrategy for achieving efficient, stable photothermal DRM under mild conditions.

Results
Aseries of MOF-derived NiConanoalloys (denotedN0,N1,and N2) withvaryingnitrogen-dopinglevelswassynthesizedusingaone-stepmicrowave hydrothermal method. Scanning electron microscopy (SEM)and transmission electron microscopy (TEM) images reveala well-defined spherical morphology, with an average diameter of 344nm. These nanospheres are further decorated with uniformly dispersed7.2nmnanoparticles(Fig.1a,bandSupplementaryFig.1a, b). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis (Fig. 1c, d) shows that these nanoparticlesarecoatedingraphiticcarbonandhavealatticefringe spacingof0.206nm,whichisconsistentwiththe(111)crystalplaneof aNiCoalloy22. Elementalmappingandline-scanningprofilesconfirm thehomogeneousspatialdistributionofNiandCoatomsoftheMOF precursorandMOF-derivedcatalyst,aswellasthehighdispersionof thenanoparticles(Fig.1eandSupplementaryFig.2–4).Bycontrast,the referencesamplesN0andN2exhibitinferiornanoparticledispersion andlargeraverageNiCoparticlesizesof11.8and35.8nm,respectively (SupplementaryFig.5and1c,d).

Resultsfrominductivelycoupledplasma-opticalemissionspectroscopy(ICP-OES)showthatasthedosageoftheN-ligandincreasesin N0,N1,andN2,sodoestheNdopingcontent,risingfrom1.5wt.%to 2.4wt.%and3.0wt.%.TheNdetectedinN0islikelytocomefromthe DMF solvent (Fig. 1f and Supplementary Table 1). An increased N doping content was found to lead to a significantly decreased Ni content,rangingfrom28.3wt.%inN0to12.0wt.%inN1and3.1wt.%in N2,whiletheCocontentshowedminimalchange.Consequently,the Co/Nimolarratioincreasedfrom1.2inN0to2.1inN1and8.4inN2. Notably,theCo/Niratioof1.2inN0issimilartotheequalamountsof Ni and Co precursors. Therefore, the sharp decrease in Ni content suggeststhatahigherdosageofN-ligandformsacoordinationbond with Ni, inhibiting the formation of metallic Ni during catalyst synthesis.

Figure1gshowstheX-raydiffraction(XRD)patternsoftheN0,N1 andN2samples.Thepeakat26°correspondstographiticcarbon(PDF #41-1487), which is consistent with the observations made using HAADF-STEM(Fig.1c).Peaksat44.3°,51.6°and76.0°alignwithcubic metallic nickel (PDF #04-0805) and/or cobalt (PDF #15-0806). The enlarged peak at approximately 44.3° is positioned between the standard peaks of pure Co (111) and Ni (111) (Fig. 1g, inset), which confirmstheformationofaNiCoalloy22,29.Notably,thispeakgradually shifts towards higher angles with increasing N-doping, approaching the Ni (111) position. Meanwhile, the graphitic carbon peakremains unshifted (Supplementary Fig. 6). Typically, the peak shift in NiCo alloystendstoapproachtheincreasedmetal22,whileourICP-OESdata showsignificantNidepletion.ThissuggeststhatN-dopingintroduces latticestrain,causingthelatticespacingtodecrease.Thiscouldsignificantly alter the electronic distribution of Ni-Co nanoalloys and potentiallyenhancetheirphotothermalcatalyticperformance.

ThecatalyticperformanceofcatalystswithvaryinglevelsofN-doping wasevaluatedat600°Cunder2.8Wcm−2lightirradiation(Fig.2a).The H2and CO formationrates exhibited a volcano-type trend as the N contentincreased,peakingat561.8and597.4mmolgcat−1h−1,respec- tively,withanH2/COratioof0.94.Darkconditionsatthesametemperature yielded significantly lower rates and H2/CO ratios (SupplementaryFig.7a).Underfull-spectrumillumination,theoptimal N1 catalyst exhibited higher CH4 and CO2 conversions across 330–600°Ccomparedtothermal-onlyconditions,exceedingthermal equilibrium limits (Fig. 2b). The corresponding H2/CO production ratesandratiosinphoto-enhancedDRMwerealsohigherthanthatin thermalDRM(SupplementaryFig.7b,c),confirmingthephotothermal synergy.

ToclarifytheeffectofchangestotheCo/NiratioonNdoping (Fig.1f),acontrolsample(NiCo@C)withthesamemetalcompositionbutnoexternalNligandwasprepared.ItsH2productionratewas approximately50%lowerthanthatofN1andslightlybelowthatofN0, emphasizingtheimportanceofNdopingratherthanthemetalratioas theprimaryactivityenhancerinthisstudy(SupplementaryFig.7d). The apparent activation energies (Ea) calculated via Arrhenius plots revealedthatthephotothermalEavaluesforH2formationwere93.7, 52.6and188.7kJmol−1forN0,N1andN2,respectively,whicharesignificantlylowerthantheircorrespondingthermalEavaluesof152.3, 160.4 and 222.8kJmol−1 (Fig. 2c and Supplementary Fig. 7e, f). The lowestEaofN1suggeststhatitpossessestheoptimizedactivesitesfor photoelectricactivation.Selectiveanalysisshowsthattheselectivityof CO2 production in photothermal catalysis and thermal catalysis remains almost unchanged (Fig. 2d). However, light irradiation significantly enhances the selectivity of H2 production, indicating that photothermalcatalysisoptimizesthereactionpathwayrelatedtoCH4 activation more effectively. This observation has been further exploredinthemechanismstudy.

TheLTCEEwascalculatedusingthedatainFig.2btoserveasametricforthecatalyst’scapacitytoconvertlightenergyintochemical energy30.AsshowninFig.2e,theLTCEEexhibitedstrongtemperature dependence forN1, peaking at510°C. This suggests that enhanced performance does not solely result from photoelectric activation; rather,suitabletemperaturesenableoptimallightutilization,whichis essential for minimizing energy input in practical applications. Figure2fshowstheLTCEEofallsamplesat510°Cwithdifferentamounts of N doping. The LTCEE values correlate with the catalytic performance of these samples, and N1 exhibits the highest efficiency of 52%, competitive to that of previously reported solar-driven systems7,11–13,18,30–34 (Supplementary Table 2). These results suggest that the appropriate amount of N doping plays a decisive role in enhancingtheLTCEEofthecatalystandtheperformanceofPDRM.

Forpracticalapplications,especiallyinPDRM,thestabilityofthe catalyst is of vital importance, as carbon deposition often leads to rapiddeactivation.Notably,N1exhibitedhighactivityandstabilityfor 200hat540°Cduringcontinuoustesting(Fig.2g).Specifically,theH2/ COratioincreasedslightlyfrom0.8to0.84underlightandfrom0.7to 0.73 in the dark. CH4 conversion declined by only 0.04% per hour underlightversus0.06%inthedark,whileCO2conversiondecreased by0.08%inbothconditions.Thisindicatesthatlightmainlystabilizes active sites for CH4 activation. In contrast, N0 exhibited significant deactivation,withCO2andCH4conversionlossesof1.8%and1.2%per hour,respectively.Furthermore,theconversionrateandH2/COratio ofthereferencesample,NiCo/Al2O3,bothshowedasharpdecline within50h.AdetailedstudyofthespentN1catalystafter200hwas conducted and compared with the fresh sample. As shown in SupplementaryFig.8,nophasechange,lossofactivesites,orincreased amorphouscarbonwasobserved.TheseresultsconfirmthattheN-Ni/ NiCo@Cstructuresignificantlyenhancesthestabilityofhigh-loading NiCocatalystsinDRMbyresistingdeactivationviastructuralprotectionandactivesitestabilization.

To elucidate the influence of N-doping on atomic coordination, we conductedX-rayabsorptionnear-edgestructure(XANES)andextendedX-rayabsorptionfinestructure(EXAFS)studiesontheN1catalyst, alongside the reference samples N0 and N2. The Ni K-edge XANES spectraofthesesamplesshifttowardsNi2+characterwithincreasing N-doping(Fig.3a),thoughthisisdistinctfromthespectrumofNiO. EXAFSanalysisrevealedanincreaseinNi-Nscatteringat1.2ÅfromN0 toN2,togetherwithametallicNi-Ni/Copeakat~2.15Å.Thisconfirms thepresenceofdualcoordinationenvironments(Fig.3b).Consistently,the2.2Åmaximuminwavelettransform(WT)analysisconfirms Ni–Ni/Co coordination, while the gradually emerging peak at approximately1.2ÅdirectlyindicatesincreasedNi–Nbonding(Fig.3d and Supplementary Fig. 9a−c). Regarding the Co K-edge XANES spectra (Supplementary Fig. 9d), all spectra matched the Co foil, indicatingmetallicCostates.CoK-edgeEXAFSshowedprominentca. 2.15ÅCo-CocoordinationpeakswitharightshiftinN2/N1/N0(Fig.3c), suggestingNiConanoalloyformation35,consistentwiththeresultsof XRD and energy-dispersive X-ray spectroscopy (EDS) mapping. The correspondingWTanalysisrevealedaca.2.2ÅCo–Cocoordination feature,withafaintca.1.25ÅsignalinN-dopedsamples(SupplementaryFig.9e–h),implyingN-inducedCoionformation.

X-ray photoelectron spectroscopy (XPS) analysis reveals significant electronic modulation in NiCo nanoalloys (Fig. 3e and Supplementary Fig. 10). The Ni 2p spectra show that the Ni2+ peak (856.2eV)shiftsby−0.77eVfromN0toN1,withanadditionalshiftof −0.50eVtoN2.Thispositiveshiftincreasestheelectrondensityatthe Nisites,creatingelectron-richNiδ⁺(0<δ<2)speciesthatacceleratethe kineticsofH+reductionforenhancedH2evolution.Thissuggeststhat Ni-Ncoordinationcouldincreasethesurfaceenergyandimprovethe reactivityoftheNisites36.TheCo2pspectrashowadecreaseinCo0 intensity(778.5eV)withN-doping(SupplementaryFig.10);thisaligns with increases in ionic coordination as determined by EXAFS. The distribution of oxygen species further supports catalyst activation, withoxygenvacancies(OA,531.9–532.3eV)dominatingsurfaceoxygen (69.9–75.7%), thereby promoting CO2 adsorption37. N 1s XPS analysisrevealsthatthepredominanceofpyridinic-N(398.8eV)inN1 (62%)exceedsthatinN2(57%)andN0(54%)(Fig.3fandSupplementary Fig. 10). Pyridinic-N has been reported to favor CH4/CO2 activation19,27;thus,theoptimalperformanceofN1islikelyrelatedto theprevalenceofNi-N-Csitesinthismaterial.

TheEXAFSandXPSanalysesabovehaveconfirmedthattheNi-N coordinationsiteincreasestheelectrondensityaroundtheNisites. Densityfunctionaltheory(DFT)calculationswereperformedtofurther explore the effects of N doping on charge transfer in NiCo nanoparticles.ForthepureNiCosurface(Fig.3g),theaveragemetal-metalbondlengthis~2.49Å.N-doping(N-Ni/NiCo)reducesthedistancesbetweenneighboringsitesto2.42Å(Ni-Ni),and2.40Å(Co-Co), indicatinglatticecompressionandconsistentwiththeXRDpeakshifts shown in Fig. 1g. Differential charge analysis revealed electronic transferdynamicsbetweenCoandNi.Ontheundopedsurface,the cobaltmarkedwithacircleactsasanelectronacceptor(1.23e),while nickelreleases1.11e.Conversely,ontheN-Ni/NiCosurface,theelectron transferpathwayhaschanged.TheCoatommarkedwithacircleloses 0.31 e, Ni releases only 0.21 e, and the adjacent N atoms gain approximately1.10e.ThisindicatesthatNsignificantlypromotesthe accumulation of electrons around Ni, which is consistent with the enhancedNielectrondensityobservedintheXPSresults.Thisresult assists in proving the role of Ni-N sites in regulating the electronic environmentofNiCo.

ToinvestigatetheroleofNi-NsitesintheDRMreaction,wefirst examined reactant adsorption and activation via temperature-programmed desorption (TPD)38. In the CH4-TPD experiment (Supplementary Fig. 11a, b), the amount of CO produced increased sequentially from N0 to N2, while CH4 desorption decreased. N2 exhibited the maximum CO yield among them, indicating that CH4 activationisdominatedbytheabundanceofNi-Nsites.Conversely,the amountofCO2desorbedandtheamountofCOderivedfromitprogressivelydiminishedacrosstheseriesduringCO2-TPD(SupplementaryFig.11c,d),whichcorrelateswithreducedmetallicNiCocontent. ThisconfirmsthatCO2activationprimarilyreliesonNiCoalloysites.

Duetothevarietyofactivesites(Ni,Ni-N,andCo)presentinthe investigatedcatalyst,itisdifficulttopreciselydeterminetheirindividualcontributionstotheadsorptionandactivationofCH4andCO2. Therefore,idealizedsurfacemodelsoftheNiCoalloyandtheN-Ni/ NiCocatalystwerecreated,andtheadsorptionenergiesofCH4and CO2 on these active sites were calculated using DFT. As shown in Fig.3h,fourtypesofactivesiteswereconsidered:NiandCoonNiCo, and Ni-N and Co(N) on N-Ni/NiCo. The results show that the CO2 adsorptionenergiesareinthefollowingorder:Ni-N(−2.66eV)>Co(N) (−2.64eV)>Ni(−0.78eV)>Co(−0.60eV).ThissuggeststhatN-doping increasestheCO₂adsorptionenergyontheNiCosurfacebyafactorof 3.4–4.4. Furthermore, N-doping reduces the adsorption energy differencebetweentheNiandCositesfrom0.18eVto0.02eV,favoring CO2 activation at the Co sites. Similarly, for CH4 adsorption, the energies follow the sequence Ni-N (−1.87eV)>Ni (−1.18eV)>Co(N) (−0.89eV)>Co(−0.72eV),indicatingthatN-dopingalsopromotesCH4 activation predominantly mediated by Ni sites rather than Co sites. Therefore,theN-Ni/NiCosurfacepromotesamoreeffectivefunctional differentiation,providingmoreNisitesforCH4activationandmoreCo sitesforCO2activation.Thesefindingsclearlydemonstratethepivotal roleofNdopinginregulatingtheelectronicstructureandcatalytic properties of the active Ni and Co sites. The N-Ni site remarkably enhancesreactantadsorptioncapacityandoptimizesthedistribution ofCH4andCO2adsorptionacrossdifferentsites,whichisconsistent with the TPSR results. This synergistic effect is advantageous for achievinghighcatalyticefficiencyandstability.

InordertoinvestigatethemechanisticeffectsoflightonN1,thesurface intermediates were monitored using in situ diffuse reflectance Fouriertransformspectroscopy(DRIFTS).Underdarkconditionswith aCH4/CO2/Arflowduringtemperaturerampingfrom300to540°C (Fig. 4a), the following characteristicpeaks wereobserved over the N1sample: gas-phaseCH4(3014 and 1302cm−1) and CO2 (2360 and 2340cm−1) vibrations8,18, adsorbed bidentate carbonate (b-CO32−, 1701cm−1) and monodentate carbonate (m-CO32−, 1350cm−1). The intensified O-H stretches (3700and 1600cm−1) indicated the RWGS reaction. Upon illumination, the adsorption of CH4/CO2 intensified markedly,and thecarboxylate peak(1707cm−1) strengthened,while the -CHx species (1460cm−1) emerged8, confirming the enhanced chemisorption of CO2 and CH4. Illumination produced a carboxyl intermediate(-COOH,1538cm-1)39,alongwiththedisappearanceofthe watersignal.ThissuggeststhatH*(fromCH4dissociation)reactswith CO2toform-COOH,whichhasbeenreportedtodecomposereadily into CO and HO* radicals40. This reaction pathway is distinct from conventional CO2 splitting into COand O*39, thus favoring the conversion of CO2. Furthermore, the oxidative HO* could promote the oxidationofhydrocarbonintermediates(-CHx)40,therebyincreasing theH2/COproductratioandimprovingcokingresistance18.

Tofurtherinvestigatetheinfluenceoflightontheactivationof CH4 andCO2,theN1catalystwastestedindividuallyundera10%CH4/ Ar and a 10% CO2/Ar atmosphere, as shown in Fig. 4c and SupplementaryFig.12.Inthedark,astronggaseousCH4peakandweakCO2 signals were observed, suggesting that CH4 was partly oxidized by surfaceoxygenspecies.Uponillumination,theCO2signalintensified, indicating that more surface C* species resulting from CH4 dehydrogenation were oxidized. New bands emerged in the 1500–1600cm−1region,suggestingenhancedCH4activation.Notably, theconversionofCH4toCO2isreportedtomitigatecokingduringthe DRM process8. However, for CO2 activation under a 10% CO2/Ar atmosphere (Supplementary Fig. 12), the adsorption peak showed negligibledifferencesbetweendarkandlightconditions.Thissuggests thatlightprimarilypromotesCH4activationof.Thisisconsistentwith the previousDFTresults,whichhighlightthemainenhancementinCH4 activationovertheN1catalyst.

Insitunear-ambientpressureXPS(NAPXPS)studiesofPDRMover theN1catalystreveallight-mediatedstabilizationmechanisms.After 2hofDRMinthedarkat540°C(Fig.4d),theNi0/Ni2+ratiodecreased from 0.8 to 0.4, while the Co0/Co2+ ratio dropped from 1.0 to 0.5. Underillumination,theseratiosincreasedto1.0and1.1,respectively, confirmingthatlightpreservesthemetallicstatesthatarecriticalfor reactant activation. This is because oxidized metal sites promote agglomerationandexhibitpooractivationcapacity41,42.Togetherwith insituDRIFTSresults,metaloxidationappearstoberelatedtotheCO2 conversionprocess,wherebyCO2adsorptiononmetallicsitesoxidizes themetalandgeneratesCO.Incontrast,lightenablesanalternative pathwaybypromotingtheformationofCOOH*intermediates,which decompose into CO and OH* without oxidizing the metal sites (Fig. 4b). The O 1s NAPXPS spectra further support this argument (Fig.4e).TheO1sspectrumofthefreshcatalystexhibitsfourpeaksat 529.0,531.7,533.0and535.0eV,whichareassignedtooxygenvacancies(Ov),surfaceO-C,adsorbedO=CandH2O8,respectively.After2h ofdarkDRMreaction,theintensityoftheOvpeakdroppedsharply whiletheintensityoftheO=Cpeakincreased.ThissuggeststhatCO2- adsorbedspeciesoccupiedmetal-Ovsites,leadingtoelevatedmetal valencestates.TheincreasedH2Opeakcomparedtotheinitialspectrum indicates the occurrence of the RWGS reaction. In contrast, PDRMinducednegligiblechangestotheOvandO=Cpeaks,andthe H2Opeakdisappeared,confirmingthatlightsuppressesbothmetal oxidation and RWGS. Furthermore, the N 1s spectra (Fig. 4f) also changed after a 2-h DRM reaction inthedark.Therewasapositiveshift intheN-metalpeak,asignificantdecreaseintheN-pyridinepeak,and theemergenceofagraphitic Npeak.Importantly,illuminationprevents these degradations. Overall, the light-induced new pathway preserves active sites and suppresses RWGS, thereby endowing N1 withexceptionalPDRMactivity,H2selectivity,andcatalyststability.

Quasi-insituisotopelabelingusing12CH4and13CO2wasfurther employedtotracetheCH4/CO2degradationpathwaysinDRM/PDRM. Gaschromatography(GC)analysisidentifiedthreepeaksat2.5,2.8, and3.6min,withtemperature-dependentshiftsconfirming13Cincorporation (SupplementaryFig. 13a, b).The massspectra (MS) of the threepeaks(P1,P2,P3)at540°Cunderilluminationwereanalyzed.For P1(Fig.5a),thepeaksatm/z=12,16,and28correspondto12COoriginatingfrom12CH4,whilethepeaksatm/z=13,1,6and29correspond to 13CO from 13CO2. Additionally, peaks corresponding to the intermediateproductformaldehyde(H12CHO,m/z=30,31)weredetected. AllthepeaksinP2correspondtotheionfragmentsof12CH4(Fig.5b).In P3(Fig.5c),themainreactant13CO2(m/z=13,16,29,45)wasobserved alongside peaks of 12CO2 (m/z=12, 16, 28, 44). In this system (12CH4+13CO2), 12C-containing substances can only originate from 12CH4 or the graphitic carbon in the MOF material. Thus, a control experiment was carried out in a 13CH4+13CO2 atmosphere, which yieldedno12CO2(Fig.5d).Thisrulesouttheparticipationofcatalyst carbonandconfirmstheconversionprocessfromCH4toCO2.Quantitative analysis of this transformation (Fig. 5d) demonstrated light-enhancedandtemperature-dependentformationof12CO2(m/z=44) from12CH4.Notably,unlikethepreviouslyreportedcarbonexchange mechanism between reactants (i.e., CO2 and CH4) in the PDRM reaction8,thisunidirectionalCH4-to-CO2conversionsuppressescokinginducedbyCH4crackingandreducesH2consumptionbyCO2. Thereactionpathwaycanbefurtherelucidatedbyexaminingthe temperature-dependent evolution of 12CH4 and 13CO2. From 300 to 570°Cunderillumination (Fig.5e),the intensityof13CH4decreased rapidly while the concentrations of 12CO2 and 12CO increased. The H12CHO intermediate first increased and was then completely convertedtoCO/H2/CO243.Inthedarkreaction(Fig.5f),aslowertendency forCH4degradationandproductformationtendencywasobserved, withH12CHOremainingstableathightemperatures.Thisidentifies HCHOasthekeyintermediatespeciesintheconversionofCH4toCO2. Conventional pathways involve stepwise CH4 dehydrogenation followedbyoxidationviacatalystlatticeoxygen44,whichriskscokingif oxidationislacking.Crucially,ourcatalystscontainnolatticeoxygen; thus,thedetectionofHCHOimpliesanalternativeroutewherebyCHx* intermediatesfromCH4crackingareoxidizedbyoxygenradicalsto form HCHO before complete mineralization. Among these reactive oxygenspecies,thereshouldbeO*fromCO2deoxygenationandOH* from*COOHdecomposition.SupplementaryFig.13c,dshowhowthe temperature affects the way13C-labeled substances evolve in PDRM andDRM.ComparedwithDRM,lightsignificantlypromotedtheconversion of 13CO2 to 13CO, which is consistent with the activity test results.Furthermore,noformicacidspeciesweredetectedinthegas phase;however,COOH*wasobservedintheinsituDRIFTS.Thismay beduetothestrongnucleophilicityofCOOH*,causingthemtoadsorb stronglyatthemetalsites.

DFTcalculationswereperformedtoelucidatetheenergeticsofCH4 (Fig.6a)andCO2(Fig.6b,c)dissociationattheNiCoalloyandN-Ni/ NiCointerfaces.Figure6ashowstheCH4dehydrogenationpathwayon bothsurfaces(CH4→CH3*→CH2*→CH*→C*).AttheNiCointerface, theactivationbarriersfortheformationofCH3*,CH2*,andCH*are 0.08,2.13,and1.08eV,respectively.CH3*→CH2*constitutestherate-determining step (RDS). In contrast, the N-Ni/NiCo exhibits lower barriers of −0.27, 0.90, and −1.11eV respectively, indicating that N dopingmarkedlyenhancesCH4activation.ThesubsequentCH*→C* step,whichisresponsibleforcarbonaccumulation,hasanegligible barrier of 0.01eV on NiCo, but rises to 2.09eV on N-Ni/NiCo. This provesthatNincorporationsignificantlysuppressescoking,whichisin agreement with catalyst lifetime tests. Furthermore, the literature reportsthatbothCH*andCH2*canreactwithoxygenradicals(OH* andO*)toyieldCO.CH*+OH*→CHOH*lessfavorablefromakinetic perspectivethanCH2*+OH*→CH2OH*40,45.Inourcalculations,CH2* readily converts to CH* on N-Ni/NiCo with a ΔE of −1.11eV. GC-MS detectionofformaldehydealsosupportstheformationofCOviathe reactionCH*+O*.Therefore,Fig.6ashowsthecalculatedtransition state results for CHO* formation and subsequent dehydrogenation: CH*→CHO*→CO*→CO(g).ThebarriersforthesethreestepsonNiCo are−0.08,2.13,and1.08eVrespectively;allofthesevaluesexceedthe correspondingvaluesonN-Ni/NiCo(−0.10,−2.13and−1.08eV).This demonstrates thatN-Ni/NiCopromotesnotonlyCH*oxidation,but also itssubsequentdehydrogenation toformCO.These calculation results prove that the CH4 →CHO* → CO pathway is energetically favoredforDRMsyngasproductionattheseinterfaces.

In situ DRIFTS under illumination revealed the formation of *COOH on the surface, implying that CO2 reacts with H* to form *COOH. Reportedly, *COOH may either hydrogenate to form the undesired intermediate HCOOH inthe RWGS reaction, or cleave to produce CO and OH*, with the latter facilitating CH4 activation40. SupplementaryFig.14showsthat*COOHhydrogenationtoHCOOH requiresaΔEof−1.25eVonNiCo,butonly0.34eVonN-Ni/NiCo,which highlightsthelatter’ssuperiorabilitytosuppresstheRWGSreaction. Conversely, *COOH cleavage into CO and OH* is highly exergonic (ΔE=−2.61 eV) on N-Ni/NiCo versus −1.43eV on NiCo (Fig. 5b), identifyingCO2→*COOH→CO+OH*asthepreferredCO2activation pathway. Another common CO2 activation pathway is direct deoxygenationtoCO39,whichoccurswithanenergybarrierof−0.49eVon N-Ni/NiCo; this is significantly lower than the −0.13eV required on NiCo(Fig.6c).ThisindicatesthatNdopingcouldenhanceCO2 deoxygenationtoo,whichisconsistentwiththesuperiorDRMperformance ofN-Ni/NiCo.

Basedontheaboveresearchresults,Fig.6dshowsaschematic diagramofthePDRMmechanism.IntheNiCoalloy,Niisthemainsite foractivatingCH4andCO2.ThehigherelectronegativityofColeadsto electronstransferringfromNitoCo.ThisformsNisiteswithelectron deficiency,whichreducesNi’sabilitytoactivateC-Hbonds.Thismakes thedehydrogenationofCH4therate-limitingstepoftheDRMreaction. In contrast, the N-Nisites adjust the electron transfer path underthe influence of lattice strain and the electron-withdrawing effect. This inhibits charge transfer from Ni to Co and makes Co sites more effectiveatactivatingCO2,whileNisitesmainlyactivateCH4.When illuminated,photogeneratedelectronsinthecarbonlayertransferto theN-NiandadjacentNi-Cosites.ThisenhancestheactivationofCH4 onN-NiandinhibitstheoxidationofNi-CobyCO2.Thisprocessgeneratesalargenumberofsurfaceoxygenspecies(O*/OH*),whichreact withCH*withtheassistanceofphotogeneratedholestoformthekey intermediate*CHOandultimatelyconverttoCO/CO2.Thisnewreaction pathway, combined with efficient directional charge transfer, gives the N-Ni/NiCo@C catalyst anextremely high LTCEE,excellent photothermal catalytic performance, an improved H2/CO ratio, and superior durability. This highlights the role of engineering the electron structure in optimizing the photothermal catalytic pathway.

Methods
The NiCo-MOF was synthesized using the microwave hydrothermal method.Specifically,0.362gNi(NO3)2·6H2O(AR,SinopharmChemical Reagent Co., LTD), 0.3662g Co (NO3)2·6H2O (99.99%, Aladdin), 0.262g1,3,5-benzenetricarboxylicacid(Beijing BailingweiTechnology Co., LTD), 3.275g polyvinylpyrrolidone (Aladdin) and variable 1,10-phenanthroline (98.0%, Macklin) were dissolved in 75mL N, N-dimethylformamide(DMF),andstirredwithamagneticstirrerfor 30min,afterwhichtheyweretransferredtoa250mLautoclave.After sealing, the autoclave was installed in a microwave hydrothermal reactor, and the temperature was raised to 150 °C for 1.5 h. Upon completion,theautoclavewasnaturallycooledtoroomtemperature before being taken out. The resulting product was centrifuged and filtered,washedthreetimeswithDMF,anddriedat60°Cinanovenfor 8htoobtainNiCo-MOFpowder.Theas-preparedNiCo-MOFpowder was calcined at 700°C for 2h feed with 200mL/min Ar to yield N-dopedcarbon-coatedcatalyst(N-Ni/NiCo@C).Theadditionamount of1,10-phenanthrolinewascontrolledat0,0.203,0.406,0.609,and 0.816g.TheobtainedsamplesweresequentiallylabeledasN0,N0.5, N1,N1.5,andN2.

DRM performance measurements were carried out under ambient pressureinafixed-bedcontinuousflowquartzreactorwithaquartz windowatthemiddleofthefurnaceforlightirradiation.Foreachtest, 20mgofcatalystwasloadedandheldinplacebyquartzwool.The reactiongas(10%CH4/10%CO2/80%Ar)wascontinuouslyintroduced intothereactorwithaflowrateof50mLmin−1,givingaweighthour spacevelocity(WHSV)of150,000mL/(gh).A300Wxenonlamp(PLS- SXE300E,PerfectLight)wasemployedasthelightsourcetodrivethe DRM reaction. The products were evaluated by an online gaschromatograph(GC-2014ATFSPL,Arcarrier,Shimadzu)equippedwithtwo flameionizationdetectors(FIDs)andathermalconductivitydetector (TCD). The bulk temperature of the catalyst powder was detected usingathermocouple.

Quantificationofreactionrates:
CH4 conversion= nCH4(in) - nCH4(out) / nCH4(in) ×100%
CO2 conversion= nCO2(in) - nCO2(out) / nCO2(in) ×100%
rCO= nCO(out) / m
rH2= nH2(out) / m
H2 selectivity= nH2(out) / 2[nCH4(in) - nCH4(out)] ×100%
CO selectivity= nCO(out) / [nCH4(in) - nCH4(out) + nCO2(in) - nCO2(out)] ×100%
ni(in)= F×Xi(in) / 24×60
ni(out)= F×Xi(out) / 24×60
wherenirepresentmolarflowrateofgas(molh−1),Xirepresentsthe gasvolumefractiondetectedbyTCD,rCOandrH2aretheproduction ratesofCOandH2(molgh−1),Fistheoriginalflowrateofthegas(L/ min),andmistheweightofcatalyst(g).

AccordingtoArrheniusformula,thelogarithmoftheH2reaction rate(InrH2)wasplottedagainstthereciprocaloftemperature(1/T), andtheactivationenergy(Ea)wasobtainedfromthefollowingslope:
InrH2 = -Ea/R × 1/T +InA
Risthemolargasconstant(8.314Jmo1−1K−1),Aisthepre-factor, and T is the thermodynamic temperature (K) of each temperature gradient.

LTCEE calculation: Δr(H2)=r(H2)PDRM - r(H2)DRM, Δr(CO)= r(CO)PDRM - r(CO)DRM, Δr(H2)=2α-βandΔr(CO)=2α+βwerewritten, where α and β represent the reaction rates of DRM and RWGS, respectively.
α= Δr(H2) + Δr(CO) / 3
β= Δr(CO) - Δr(H2) / 2
LTCEE is defined as:
LTCEE= αΔH(DRM) + βΔH(RWGS) / P ×100%
whereΔH(DRM)(247KJmol−1)andΔH(RWGS)(41KJmol−1)arethestandard reaction enthalpy of DRM and RWGS reaction, respectively, and P referstothepowerofirradiation.

Catalystcharacterizations
XRDpatternswererecordedonaRigaku-Smartlab9KWfromJapan with Cu-Kα radiation (λ=1.54178Å). Morphology and EDS element mappingwererecordedbySEM,HRTEMandHAADF-STEM.XPSwas performedonaThermoScientificESCALAB250Xispectrometerwith AlKαastheX-raysource.XAFSspectroscopywiththeCoK-edgeand NiK-edgewastestedontheTableXAFS-500Ausinga1.6kWX-raylight source. The elemental content data are collected using ICP-OES by UTLIMA-2 (JY, France) and ONH836TOC (LECO). Raman spectra (PicRamanM3,timegate)areusedtoanalyzethecokingofthesamples.TGAanalysiswascarriedontheNETZSCHTG209F1LibraTGAto determinetheamountofcarbondeposited.

CH4-TPD measurements. CH4-TPD measurements were carried out onAutoChem2920(Micromeritics).Typically,100mgofcatalystwas placedinaquartztubereactorandtreatedunderH2flowat300°Cfor 60mintoremoveimpurities.Aftercoolingto40°C,thecatalystwas exposedto10%CH4/90%Ar.Then,thecatalystbedtemperaturewas increasedfrom40to700°C(rampingrate,10°Cmin−1)underHe flow. The desorption products were detected by the mass spectrometry. CO2-TPD experiments were performed in a similar process except usingCO2flow.

InsituDRIFTSmeasurements.TheinsituDRIFTSmeasurementswere performedusingaThermoScientificIS50Fourier-transformspectrometerequippedwithaHarrickdiffusereflectanceaccessory.Inthetest ofCO2andCH4adsorptionandactivation,thefreshcatalystwasfirst purged with Ar flow for 30min at room temperature to remove impurities.Thenthefreshcatalystwasexposedto10%CH4/10%CO2/ 80%ArflowtocollecttheDRIFTSspectraforCO2andCH4adsorption. Afteradsorptionsaturation,thesystemwasexposedtolightirradiation (PLS-SXE300E, Perfect light), and the temperature data were recorded continuously. The DRIFTS for respective CO2 and CH4 adsorptionandactivationwereperformedinasimilarprocessexcept using10%CO2/90%Arflowand10%CH4/90%Ar,respectively.

InsituNAP-XPSmeasurements.InsituNAP-XPSmeasurementswere performedonThermoScientificESCALAB250XispectrometerwithAl KαastheX-raysource.Thefreshcatalystwasfirsttreatedatultrahigh vacuum (up to 10−9mbar). After that, the system was purged with 0.5mbarCO2and0.5mbarCH4for2hat540°Ctocollectthedata. The in-situ NAP-XPS for PDRM was performed in a similar process, exceptadding300WXelampirradiation.

Quasiin-situ13C-labeledisotopelabellingexperiments.Quasiin-situ 13C-labeledisotopelabellingexperimentswereperformedinthesame reactor with activity test by using two different reactant systems as feeding gas, including equivalent amounts of 12CH4+13CO2 (I), 13CH4+13CO2 (II).Inatypicaltest,10mgoffreshcatalystwasused.After sealing, the systems (i.e., SystemsIorSystemsII)wereintroducedwiththetemperatureincreasingfrom300to600°Catarateof10°C/minindarkorunder300WXe lamp irradiation, the products were analyzed using a GC-MS (8860- 5977C,Hecarrier,Agilent)andthedatacollectedcontinuously.

DFTcalculations
Basedondensityfunctionaltheory(DFT),aseriesoftheoreticalcalculationmethodswereemployedinthisstudy46,includingtheVienna ab initio simulation package (VASP), the Perdew–Burke–Ernzerhof (PBE)functionalwithinthegeneralizedgradientapproximation(GGA) framework, the projector-augmented wave (PAW) method, the Monkhorst–Packk-pointgrid,andtheDFT+Ucorrectionmethod.The energyconvergencethresholdforself-consistentiterationwas10−6eV, and the residual force for ionic relaxation needed to be below 0.02eVÅ−1.ItshouldbenotedthatthePBE-GGA-basedDFTapproach possesses inherent limitations, including the neglecting nuclear quantumeffects,inadequatecharacterizationofvanderWaalsinteractions,andrestrictiontoground-statepropertiesintheabsenceof supplementaryextensions.

Thecatalystmodelwasconstructedusinga3×3supercellforthe (111)facetofCoNialloy(N0)2,witha15Åvacuumlayerinsertedtopreventinteractionsbetweenadjacentperiodicimages.TosimulateNatom incorporation,foursurfacemetalatomsontheCoNi(111)surfacewere substitutedwithNatoms,formingtheN-Ni/CoNi(111)structure(N1). The adsorption energy (ΔEads) of surface species on N1 or N0surfaceswascalculatedusingthefollowingequation:
ΔEads=Etotal - (Eadsorbate + Esurface)
where ΔEads, Etotal, Eadsorbate, and Esurface denote the total energy of the adsorbedsurfacespecies,theenergyoftheadsorbateinthegasphase, andtheenergyofthecleanN1/N0surfaces,respectively.

The Gibbs free energy (ΔG) for gas molecules (CH₄, CO₂) and adsorbateswascalculatedusingthefollowingequation:
ΔG=ΔE+ΔZPE - TΔS
whereEisthetotalstructuralenergyfromDFTcalculations,ZPEisthe zero-pointenergy,andSisthevibrationalentropy.

Chargedensitydifferenceswereusedtoanalyzeelectrondensity and electron cloud distribution changes for the substituted metal atomsonN1andN0surfaces.Thechargedensitydifferencewascalculatedusingthefollowingequation:
Δρ=ρtotal - ρsurface - ρM
where ρtotal, ρsurface, and ρM represent the charge densities of the substituted surface, clean surface, and substituted metal atom, respectively.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this study, the authors report a N-Ni/NiCo@C catalyst for highly efficient and stable photo-thermal methane dry reforming, which is distinct from the conventional metal oxide-supported catalysts. The structure-activity relationship investigation reveals the synergistic effect among the precise catalyst structure, involved carbon layer encapsulation, C-N-Ni electron transfer channels, and highly dispersed nano Ni/Co alloy particles, achieving high light utilization efficiency, performance, and stability. Furthermore, in situ characterization reveals a CH4 activation pathway that is free of lattice oxygen. The substantial O* released from CO2 is adsorbed on oxophilic NiCo alloy, and then effectively oxidizes the carbon species (CH*) into CHO*, with the assistance of photo-generated holes. The findings in this work are interesting, offering a novel strategy for producing long-term stable NiCo-based catalysts for photo-thermal methane dry reforming. Minor revision is recommended, and the following comments and suggestions should be addressed.\n1. H2 atmosphere is a typical atmosphere for preparing metallic state catalysts. Why does this paper use the inert gas Ar? Does the gas composition affect the metal dispersion?\n2. Given that the performance evaluation conditions for the photo-thermal DRM reaction vary in different literature and the data on light utilization efficiency is often missing, how can the comparability of the data in this work (LTCEE) and those in the literature be ensured?\n3. Using XRD, Raman, and XPS to observe the carbon deposits may not be precise enough. Employing TGA or TG-MS for carbon deposit quantification is strongly recommended.\n4. Ni/Co catalysts supported on common metal oxides tend to agglomerate easily during DRM reactions. Imaging technology is recommended to calculate the particle size of spent catalysts for further verification of sintering resistance.\n5. How was the existence of C-N-Ni sites determined? Is it possible that the NiN phase was formed and contributed to the DRM reaction?\n6. The catalytic performance was measured at 600 °C in this manuscript, and it was proved that the carbon in the material would not be oxidized to CO. However, traditional dry reforming of methane requires a temperature of 700-800 °C. What is the maximum temperature at which this type of C-coated catalyst can be used?", "reviewer_2": "This study reports a metal-organic framework (MOF)-derived N-doped NiCo nanoalloy catalyst (N-Ni/NiCo@C) for photothermal methane dry reforming. The core innovation resides in circumventing the traditional lattice oxygen-dependent reaction pathway in catalysis; instead, efficient methane activation and exceptional anti-coking stability are achieved through the deliberate construction of a C-N-Ni coordination structure. The authors have conducted systematic and in-depth investigations encompassing experimental design, advanced characterization techniques, and theoretical calculations, with conclusions well-supported by sufficient data and rigorous reasoning. As a result, I recommend the acceptance of this manuscript for publication after addressing the following issues.\n1.How did the authors ensure the successful preparation of the NiCo bimetallic MOF? Characterization of the MOF precursor should also be provided.\n2.The authors mention in the Supplementary Information that the reactant conversion rates and product production rates are calculated based on the outlet flow stream. It is requested to clarify how the outlet flow rate is obtained: whether it is directly measured using mass flow meters or derived from N2 balance calculations.\n3.For Fig. 2b, the authors mention that it presents comparative results of photothermal and pure thermal conversion rates measured at the same temperature. It is noteworthy that the authors need to specify whether this temperature refers to the bulk temperature of the catalyst powder (measured by a thermocouple) or the set temperature of the electric heating component in the reactor. This clarification directly impacts the validity of the definition for light-to-chemical energy efficiency.\n4.In the mechanism study, the authors state that light irradiation generates carboxyl intermediates (-COOH) at 1538 cm-1. However, according to the in situ DRIFTS spectra under both dark and light conditions, the peak at 1538 cm-1 can be observed in both cases. If the authors consider the positive and negative peaks at 1538 cm-1 as corresponding to different species, how to interpret the negative peak in PDRM at 300℃? It is recommended that the authors re-analyze the in situ DRIFTS spectra.", "reviewer_3": "In this manuscript, a photothermal DRM reaction on a nitrogen-doped carbon-coated N-Ni/NiCo@C catalyst was reported. Different from the traditional oxygen involved semiconductor-based catalyst, this material structure for solar DRM would be new and the performance is good. Mechanism investigation and explanation would also interest a wide readship compared to the conventional ‘lattice oxygen’ involving Mars-van Krevelen pathway. In addition, the experiments were systematically and well conducted in most parts. A Minor Revision would be recommended and following comments and suggestions should be properly addressed and corrected.\n(1) The manuscript attributes the remarkable 200-h stability primarily to the electronic effect of the C–N–Ni site, which is proposed to suppress oxidation. This interpretation overlooks a more obvious factor: the physical confinement and encapsulation provided by the graphitic carbon layer. Although the authors report a drastic stability difference between N-Ni/NiCo@C and the NiCo/Al2O3 reference, these systems differ in at least two major respects: (i) the presence of the proposed C–N–Ni site and (ii) the carbon surface itself. Hence, the enhanced durability cannot be unambiguously assigned to the C–N–Ni site without decoupling these effects.\n(2) ICP–OES indicates severe Ni loss upon increasing N-doping (28.3 to 3.1 wt%). The authors should clarify the origin of this depletion and reconcile it with the proposed stabilization mechanism.\n(3) The mapping shows clear O signals (Figure 1e), which conflicts with the “lattice-oxygen-free” claim as presently phrased. Please (i) define the scope of “lattice-oxygen-free” (bulk vs. surface) and (ii) pinpoint the oxygen’s location—carbon-support functionalities vs. an alloy oxide overlayer—to avoid a potentially misleading title.\n(4) The authors state that “the Ni 2p spectra show the Ni2+ peak (856.2 eV) shifts by +0.77 eV from N0 to N1.” However, the plotted positions indicate a −0.77 eV shift (i.e., to lower binding energy) from N0 to N1. Please double check the sign and report the absolute peak positions for both samples.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "We really appreciate your high evaluation and constructive suggestions to our manuscript. Following your advice and suggestions, we have modified the manuscript by taking care of your comments to further improve the quality of this manuscript.\n1. H atmosphere is a typical atmosphere for preparing metallic state catalysts. Why does this paper use the inert gas Ar? Does the gas composition affect the metal dispersion?\nAuthor reply: Thank you very much for your positive comments on our manuscript. We optimized the preparation conditions of the catalyst and found that the performance of the catalyst obtained via H pyrolysis was significantly lower than that of the sample prepared under an Ar atmosphere, as displayed in the following Fig. 1a. Therefore, Ar was selected as the optimal pyrolysis atmosphere. SEM and TEM observations (Fig. 1b-d) revealed that the sample pyrolyzed in H featured a thicker carbon layer coating and blurry lattice. In contrast, the sample prepared via Ar pyrolysis exhibited more uniformly dispersed metal particles (Manuscript-Fig.1a-c), which is more conducive to the contact between metal active sites and reactants in gas-solid catalytic reactions.\nFig. 1 a, H production on catalysts prepared with different pyrolysis atmosphere. b-d, morphology of catalysts obtained from H pyrolysis.\n2. Given that the performance evaluation conditions for the photo-thermal DRM reaction vary in different literature and the data on light utilization efficiency is often missing, how can the comparability of the data in this work (LTCEE) and those in the literature be ensured?\nAuthor reply: We sincerely appreciate your consideration. Given the inconsistencies in temperature and light intensity used for performance evaluation in the literature, we recalculated the LTCEE values from all collected relevant studies to enhance comparability. In the calculation process, the thermal catalytic reaction rate was deducted to compare the light efficiency, and the ratio of LTCEE to light intensity (LTCEE/Light intensity) was adopted to evaluate the light utilization efficiency per unit light intensity.\n3. Using XRD, Raman, and XPS to observe the carbon deposits may not be precise enough. Employing TGA or TG-MS for carbon deposit quantification is strongly recommended.\nAuthor reply: Following your valuable advice, we have supplemented the TGA results of the fresh sample and 200 h-used sample in Supplementary Figure 8d. The relative experiment method and discussion were also provided in the Supplementary Information, which is also presented as follows.\nThe NETZSCH TG 209 F1 Libra TGA was utilized to determine the amount of carbon deposited on the DRM spent catalyst samples via temperature programmed oxidation. The spent catalyst was heated at a temperature between 25 ℃ and 800 ℃ at a heating rate of 10 ℃/min with an air flow of 50 mL/min. The rate of weight change with temperature helped provide information on the amount of carbon deposited.\nSupplementary Figure 8. Structural characterization comparison of fresh and 200-h used N1 samples: (a) XRD patterns, (b) Raman spectra, (c) Ni 2p XPS spectra and (d) TGA results of fresh and 200-h used N1 samples. (e) HRTEM image of 200 h-used N1 catalyst and (f) its particle distribution.\nThe carbon deposition on the 200-h used catalyst from the stability test was determined using the TGA temperature-programmed oxidation, as shown in Supplementary Fig. 8d. It was observed that the first weight loss occurred for both spent catalysts at 345 and 374 ℃, which was respectively 12.8 and 10.4% for fresh and used samples. Besides, at the second weight loss occurring around 450 ℃, the fresh catalyst displayed a weight loss of 30% while the spent catalyst had a weight loss of 27.5%. It can be deduced from this result that there was the possibility of a reduction in the amount of crystalline carbon nanoparticles present after 200 h. Therefore, it can be concluded that the stability of the catalyst is not affected by carbon deposition during DRM reaction, thus contributing to the prolonged lifetime on stream.\n4. Ni/Co catalysts supported on common metal oxides tend to agglomerate easily during DRM reactions. Imaging technology is recommended to calculate the particle size of spent catalysts for further verification of sintering resistance.\nAuthor reply: In line with your suggestion, we have supplemented the particle distribution of spent catalyst from the HRTEM images in Supplementary Figure 8e-f, which is also displayed as follows:\nSupplementary Figure 8. Structural characterization comparison of fresh and 200-h used N1 samples: (a) XRD patterns, (b) Raman spectra, (c) Ni 2p XPS spectra and (d) TGA results of fresh and 200-h used N1 samples. (e) HRTEM image of 200 h-used N1 catalyst and (f) its particle distribution.\nAfter 200 hours of continuous testing, the sample retained a morphology of carbon-coated and highly dispersed metal particles, demonstrating the superior structural stability of the catalyst (Supplementary Figure 8e-f).\n5. How was the existence of C-N-Ni sites determined? Is it possible that the NiN phase was formed and contributed to the DRM reaction?\nAuthor reply: The formation of C-N-Ni sites was confirmed by two lines of evidence. First, a characteristic peak of the N-C bond was observed in the N 1s XPS spectrum, and the signal of the N-Ni bond was detected via XAS measurements (Fig. 3 in the manuscript). Its N coordination environment was highly consistent with that of the nickel phthalocyanine standard sample, indicating that the sites possess a C-N-Ni structure. Second, supplementary confirmation was obtained through a control experiment. When only N-containing ligands (without oxygen-containing ligands) were added during catalyst preparation, no precipitation of metal crystals was observed. This indicates the absence of a simple N-Ni coordination structure in the system, which indirectly verifies the specific formation of the C-N-Ni coordination structure.\n6. The catalytic performance was measured at 600 °C in this manuscript, and it was proved that the carbon in the material would not be oxidized to CO. However, traditional dry reforming of methane requires a temperature of 700-800 °C. What is the maximum temperature at which this type of C-coated catalyst can be used?\nAuthor reply: Thank you for your comprehensive considerations. Theoretically, the activation temperature for the oxidation of carbon by CO₂ is 800 °C. Following your suggestion, we tested the catalytic DRM performance at 700 °C and 800 °C (as shown in Fig. 2 below). The results demonstrate that the catalyst with a carbon support is not suitable for high-temperature thermal catalytic DRM, but is more compatible with medium-to-low temperature photothermal catalytic reactions.\nFig. 2 DRM reaction over N1 catalysts at high temperature.\nWe thank for your positive evaluation and suggestions to our manuscript. Following your advice and suggestions, we have modified the manuscript to improve the quality of this work.\n1. How did the authors ensure the successful preparation of the NiCo bimetallic MOF? Characterization of the MOF precursor should also be provided.\nAuthor reply: We sincerely appreciate your positive feedback on our manuscript. Following your advice, we have supplemented the HRTEM image and mapping of the MOF precursor before pyrolysis in Supplementary Information Fig. 4, and revised the manuscript in Line 104-107, which is also presented as follows.\nSupplementary Figure 4. HRTEM and mapping of the MOF precursor.\nLine 104-107\nElemental mapping and line-scanning profiles confirm the homogeneous spatial distribution of Ni and Co atoms of the MOF precursor and MOF-derived catalyst, as well as the high dispersion of the nanoparticles (Fig. 1e, Supplementary Fig. 2–4).\n2. The authors mention in the Supplementary Information that the reactant conversion rates and product production rates are calculated based on the outlet flow stream. It is requested to clarify how the outlet flow rate is obtained: whether it is directly measured using mass flow meters or derived from N balance calculations.\nAuthor reply: Thank you for your comprehensive considerations. In practice, we used Ar as the internal standard to calculate the outlet flow stream. To clarify this point further, we have refined the calculation formula in Supplementary Information, which is shown below:\nQuantification of reaction rates:\nnCH4 (in)−nCH4 (out)\nCH4 conversion = ×100%\nnCH4 (in)\nnCO2(in)−nCO2 (out)\nCO2 conversion = ×100%\nnCO2(in)\nnCO(out)\nrCO = \nm\nnH2\n(out)\nrH2\n= \nm\nnH2\n(out)\nH2 selectivity = ×100%\n2[nCH4 (in)−nCH4 (out)]\nnCO(out)\nCO selectivity = ×100%\nnCH4 (in)−nCH4 (out)+nCO2 (in)−nCO2 (out)\nF×Xi(in)×60\nni(in) = \n22.4\nF×Xi(out)×XAr(in)×60\nwhere n represent monla i r( ofulot)w= ra te of gas (mol h-1), X represents the gas volume\ni XAr(out)×22.4i\nfraction detected by TCD, r\nCO\nand r\nH2\nare the prod⋅uction rates of CO and H\n2\n(mol g h-\n1), F is the original flow rate of the gas (L/min), and m is the weight of catalyst (g)⋅. ⋅\n3. For Fig. 2b, the authors mention that it presents comparative results of photothermal and pure thermal conversion rates measured at the same temperature. It is noteworthy that the authors need to specify whether this temperature refers to the bulk temperature of the catalyst powder (measured by a thermocouple) or the set temperature of the electric heating component in the reactor. This clarification directly impacts the validity of the definition for light-to-chemical energy efficiency.\nAuthor reply: Following your valuable advice, we have clarified in the \"DRM Performance Measurements\" section of the Supporting Information: The bulk temperature of the catalyst powder was detected using a thermocouple.\nSpecifically, to ensure temperature consistency between photothermal and thermal DRM reactions, we start heating slowly at a rate of 2 °C/min under stable illumination conditions from room temperature. This ensures that the set temperature aligns with the ambient temperature of the catalyst measured by the thermocouple.\n4. In the mechanism study, the authors state that light irradiation generates carboxyl intermediates (-COOH) at 1538 cm-1. However, according to the in-situ DRIFTS spectra under both dark and light conditions, the peak at 1538 cm-1 can be observed in both cases. If the authors consider the positive and negative peaks at 1538 cm-1 as corresponding to different species, how to interpret the negative peak in PDRM at 300℃? It is recommended that the authors re-analyze the in-situ DRIFTS spectra.\nAuthor reply: In-situ DRIFTS spectra show that under illumination, a distinct signal at 1538 cm-1 can be observed, while in the absence of illumination, there is no positive peak (absorption spectrum) signal. To highlight this, we selected 540°C for comparison as shown in Figure 3 below. The negative peak in the experiment may be due to the desorption of surface substances on the catalyst during the heating process, so we only analyze the changes of the surface absorption peak. At 300°C, the DRM reaction hardly occurs, so it is only used as a reference spectrum of the reaction process. Due to the weak signal during the initial adsorption at this temperature, some small negative peaks are seen after subtracting the baseline, but it does not affect the subsequent observation and analysis of the absorption peaks.\nFigure 3. In-situ DRIFTS spectra under dark and light conditions at 540 ℃.\nWe really appreciate your high evaluation and constructive suggestions to our manuscript. Following your advice and suggestions, we have modified the manuscript by taking care of your comments to further improve the quality of this manuscript.\n1. The manuscript attributes the remarkable 200-h stability primarily to the electronic effect of the C–N–Ni site, which is proposed to suppress oxidation. This interpretation overlooks a more obvious factor: the physical confinement and encapsulation provided by the graphitic carbon layer. Although the authors report a drastic stability difference between N-Ni/NiCo@C and the NiCo/Al O reference, these systems differ in at least two major respects: (i) the presence of the proposed C–N–Ni site and (ii) the carbon surface itself. Hence, the enhanced durability cannot be unambiguously assigned to the C–N–Ni site without decoupling these effects.\nAuthor reply: We sincerely appreciate your positive feedback on our manuscript. To further confirm the effect of the C-N-Ni coordination structure on catalytic performance, we additionally tested the stability of the NiCo@C catalyst with carbon layer coating but without C-N-Ni coordination (denoted as N0), except for the NiCo/Al O catalyst,\n2 3\nas shown in Figure 2g in manuscript. Relevant analyses indicate that although N0 exhibits excellent stability due to the carbon layer coating, its CH conversion loss rate\n4\nis still 45 times faster than that of N1 (Line 194-201). This confirms that the stability of N1 stems not only from the carbon layer coating but also from the C-N-Ni coordination structure.\n2. ICP–OES indicates severe Ni loss upon increasing N-doping (28.3 to 3.1 wt%). The authors should clarify the origin of this depletion and reconcile it with the proposed stabilization mechanism.\nAuthor reply: We appreciate your attention. To investigate the reason of Ni loss in the catalyst, we conducted control experiments, and the results confirmed that O ligands are a necessary condition for the formation of MOF precursors. The increase in N ligand dosage leads to a decrease in Ni content, primarily due to the following mechanism that N ligands preferentially coordinate with Ni2+ to form O-Ni-N type coordination precipitates. However, excess N ligands will form soluble Ni-N coordination species, which cannot be retained during subsequent separation processes and ultimately result in a reduction in the Ni loading of the catalyst. Benefiting from the strong selective coordination of rigid phenanthroline with Ni2+, the as-prepared N-doped NiCo bimetallic catalyst exhibits excellent pyrolysis resistance.\n3. The mapping shows clear O signals (Figure 1e), which conflicts with the “lattice-oxygen-free” claim as presently phrased. Please (i) define the scope of “lattice-oxygen-free” (bulk vs. surface) and (ii) pinpoint the oxygen’s location—carbon-support functionalities vs. an alloy oxide overlayer—to avoid a potentially misleading title.\nAuthor reply: Thank you for your consideration. (i) The lattice oxygen referred to in this manuscript denotes the oxygen coordination species adjacent to metals (Metal-O²⁻), including both surface and bulk lattice oxygen, which is uncontroversial. (ii) Notably, the O signal detected by elemental mapping primarily originates from surface-adsorbed oxygen species (O , O ⁻), which was analyzed in detail in the O 1s of the XPS analysis\n2 2\n(Supplementary Figure 10b). XAS results confirm that Ni and Co in the catalyst exist in the metallic state (Fig.3 in the manuscript); thus, there is no lattice oxygen or oxidation of metal surface.\n4. The authors state that “the Ni 2p spectra show the Ni2+ peak (856.2 eV) shifts by +0.77 eV from N0 to N1.” However, the plotted positions indicate a −0.77 eV shift (i.e., to lower binding energy) from N0 to N1. Please double check the sign and report the absolute peak positions for both samples.\nAuthor reply: Thank you for pointing out the error. We have corrected the relevant content in Lines 230-232 of the manuscript as follows: The Ni 2p spectra show that the Ni2+ peak (856.2 eV) shifts by -0.77 eV from N0 to N1, with an additional shift of -0.50 eV to N2.\nWe believe that these changes adequately address the reviewers' comments. We appreciate the reviewers' valuable feedback and their recognition of the quality of our work. Thank you for your consideration and assistance with this manuscript. Please do not hesitate to contact us if any additional information is required. We look forward to hearing from you regarding this submission. Finally, on behalf of all authors, we would like to thank the Editor and Reviewers again for your precious time and helpful suggestions for improving the quality of this manuscript and keeping the high standard of the Nature Communications."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have satisfactorily addressed my comments, resulting in a notable improvement in the quality of the work. I recommend the revised manuscript for publication in the journal.", "reviewer_2": "All the requested revisions are adequately addressed, so I recommend this work can be published without any more revision.", "reviewer_3": "This manuscript has been carefully revised according to reviewers' comments. It should be accepted.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": ""}]

Decision letter