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Kev tsim cov thev naus laus zis hydrogen yog lub hauv paus ntawm kev lag luam ntsuab. Ua ib qho kev npaj ua ntej rau kev paub txog kev khaws cia hydrogen, cov tshuaj catalysts nquag thiab ruaj khov rau cov tshuaj hydrogenation (de) hydrogenation yog qhov yuav tsum tau ua. Txog tam sim no, thaj chaw no tau raug tswj hwm los ntawm kev siv cov hlau muaj nqis kim. Ntawm no, peb xav kom muaj cov tshuaj catalyst cobalt tshiab uas pheej yig (Co-SAs/NPs@NC) uas cov chaw hlau ib leeg tau faib ua ke nrog cov nanoparticles zoo kom ua tiav cov tshuaj formic acid dehydrogenation zoo. Siv cov khoom siv zoo tshaj plaws ntawm cov khoom CoN2C2 uas tau faib ua atomically thiab cov nanoparticles encapsulated ntawm 7-8 nm loj, siv propylene carbonate ua cov kuab tshuaj, kev tsim cov roj zoo heev ntawm 1403.8 ml g-1 h-1 tau txais, thiab tsis muaj kev poob tom qab 5 lub voj voog. kev ua ub no, uas yog 15 npaug zoo dua li kev lag luam Pd/C. Cov kev sim hauv qhov chaw sim qhia tau tias, piv rau cov hlau ib lub atom thiab nanoparticle catalysts, Co-SAs/NPs@NC ua rau muaj kev nqus thiab ua haujlwm ntawm qhov tseem ceeb monodentate intermediate HCOO*, yog li txhawb nqa CH bond cleavage tom qab. Kev suav theoretical qhia tau tias kev koom ua ke ntawm cobalt nanoparticles txhawb nqa kev hloov pauv ntawm d-band center ntawm ib lub Co atom mus rau hauv qhov chaw nquag, yog li txhim kho kev sib txuas ntawm carbonyl O ntawm HCOO* intermediate thiab Co center, yog li txo qis lub zog thaiv.
Hydrogen raug suav hais tias yog ib qho tseem ceeb rau kev hloov pauv lub zog thoob ntiaj teb tam sim no thiab tuaj yeem yog tus tsav tsheb tseem ceeb ntawm kev ua tiav cov pa roj carbon neutrality1. Vim nws cov khoom siv lub cev xws li kev kub hnyiab thiab qhov ceev qis, kev khaws cia thiab thauj hydrogen kom zoo thiab muaj txiaj ntsig yog cov teeb meem tseem ceeb hauv kev ua tiav kev lag luam hydrogen2,3,4. Cov kua organic hydrogen carriers (LOHCs), uas khaws cia thiab tso tawm hydrogen los ntawm kev tshuaj lom neeg, tau raug pom zoo ua ib qho kev daws teeb meem. Piv rau molecular hydrogen, cov tshuaj no (methanol, toluene, dibenzyltoluene, thiab lwm yam) yooj yim thiab yooj yim rau kev tuav5,6,7. Ntawm ntau yam LOHCs ib txwm muaj, formic acid (FA) muaj kev lom tsawg (LD50: 1.8 g / kg) thiab H2 muaj peev xwm ntawm 53 g / L lossis 4.4 wt%. Qhov tseem ceeb, FA yog tib LOHC uas tuaj yeem khaws cia thiab tso tawm hydrogen hauv qab cov xwm txheej me me hauv qhov muaj cov catalysts tsim nyog, yog li tsis xav tau cov khoom siv hluav taws xob sab nraud loj1,8,9. Qhov tseeb, ntau cov tshuaj catalysts hlau zoo tau tsim los rau kev dehydrogenation ntawm formic acid, piv txwv li, palladium-based catalysts yog 50-200 npaug ntau dua li cov tshuaj catalysts hlau pheej yig 10,11,12. Txawm li cas los xij, yog tias koj coj mus rau hauv tus account tus nqi ntawm cov hlau nquag, piv txwv li, palladium kim dua 1000 npaug.
Cobalt, Kev tshawb nrhiav cov tshuaj catalysts uas ua haujlwm tau zoo thiab ruaj khov heterogeneous tseem niaj hnub nyiam cov kws tshawb fawb ntau hauv kev kawm thiab kev lag luam13,14,15.
Txawm hais tias cov catalysts pheej yig raws li Mo thiab Co, nrog rau cov nanocatalysts ua los ntawm cov hlau zoo / lub hauv paus alloys,14,16 tau tsim rau FA dehydrogenation, lawv cov kev ua haujlwm maj mam thaum lub sijhawm tshuaj tiv thaiv yog qhov tsis zam vim yog kev nyob hauv cov chaw nquag ntawm cov hlau, CO2, thiab H2O los ntawm protons. lossis formate anions (HCOO-), FA kev ua qias tuaj, cov khoom me me sib sau ua ke thiab ua tau CO lom17,18. Peb thiab lwm tus tsis ntev los no tau ua pov thawj tias cov catalysts ib leeg-atom (SACs) nrog cov chaw CoIINx uas tau tawg ua cov chaw nquag txhim kho cov tshuaj tiv thaiv thiab cov kua qaub ntawm formic acid dehydrogenation piv rau nanoparticles17,19,20,21,22,23,24. Hauv cov ntaub ntawv Co-NC no, N atoms ua haujlwm ua cov chaw tseem ceeb los txhawb FA deprotonation thaum txhim kho kev ruaj khov ntawm cov qauv los ntawm kev sib koom tes nrog lub hauv paus Co atom, thaum Co atoms muab H adsorption chaw thiab txhawb CH22 scission, 25,26. Tu siab kawg li, qhov kev ua ub no thiab kev ruaj khov ntawm cov catalysts no tseem tsis tau zoo li cov niaj hnub homogeneous thiab heterogeneous noble metal catalysts (Daim Duab 1) 13.
Lub zog ntau dhau los ntawm cov chaw siv rov ua dua tshiab xws li lub hnub ci lossis cua tuaj yeem tsim tau los ntawm kev siv hluav taws xob ntawm dej. Cov hydrogen uas tsim tawm tuaj yeem khaws cia siv LOHC, cov kua uas hydrogenation thiab dehydrogenation tuaj yeem rov ua dua. Hauv cov kauj ruam dehydrogenation, cov khoom tsuas yog hydrogen, thiab cov kua nqa rov qab mus rau nws lub xeev qub thiab hydrogenated dua. Hydrogen thaum kawg tuaj yeem siv rau hauv chaw nres tsheb roj, roj teeb, cov tsev lag luam, thiab ntau ntxiv.
Tsis ntev los no, nws tau tshaj tawm tias qhov kev ua haujlwm ntawm cov SAC tshwj xeeb tuaj yeem txhim kho nyob rau hauv qhov muaj cov hlau sib txawv lossis cov chaw hlau ntxiv uas muab los ntawm nanoparticles (NPs) lossis nanoclusters (NCs)27,28. Qhov no qhib qhov ua tau rau kev nqus thiab kev ua haujlwm ntawm lub substrate ntxiv, nrog rau kev hloov kho ntawm geometry thiab cov qauv hluav taws xob ntawm cov chaw monatomic. Hauv txoj kev no, kev nqus / kev ua haujlwm ntawm lub substrate tuaj yeem ua kom zoo dua, muab kev ua haujlwm catalytic zoo dua 29,30. Qhov no muab lub tswv yim rau peb los tsim cov ntaub ntawv catalytic tsim nyog nrog cov chaw ua haujlwm sib xyaw. Txawm hais tias SACs zoo dua tau pom tias muaj peev xwm zoo hauv ntau yam kev siv catalytic 31,32,33,34,35,36, raws li peb paub zoo tshaj plaws, lawv lub luag haujlwm hauv kev khaws cia hydrogen tsis meej. Hauv qhov no, peb tshaj tawm txog kev siv tswv yim ntau yam thiab muaj zog rau kev tsim cov cobalt-based hybrid catalysts (Co-SAs / NPs @ NCs) uas muaj cov nanoparticles txhais thiab cov chaw hlau ib leeg. Cov Co-SAs/NPs@NC uas tau ua kom zoo tshaj plaws qhia tau tias muaj kev ua tau zoo heev ntawm formic acid dehydrogenation, uas zoo dua li cov catalysts uas tsis yog nanostructured (xws li CoNx, cov atoms cobalt ib leeg, cobalt@NC thiab γ-Mo2N) thiab txawm tias cov catalysts hlau zoo. Kev piav qhia hauv qhov chaw thiab kev xam DFT ntawm cov catalysts nquag qhia tau tias cov chaw hlau ib leeg ua haujlwm ua cov chaw nquag, thiab cov nanoparticles ntawm qhov kev tsim kho tshiab no txhim kho qhov chaw d-band ntawm Co atoms, txhawb kev nqus thiab kev ua haujlwm ntawm HCOO *, yog li txo qis qhov kev thaiv zog ntawm cov tshuaj tiv thaiv.
Zeolite imidazolate frameworks (ZIFs) yog cov precursors peb-seem uas tau txhais zoo uas muab cov catalysts rau cov khoom siv carbon-doped nitrogen (hlau-NC catalysts) los txhawb ntau hom hlau 37,38. Yog li ntawd, Co (NO3) 2 thiab Zn (NO3) 2 ua ke nrog 2-methylimidazole hauv methanol los tsim cov hlau sib xws hauv cov kua. Tom qab centrifugation thiab ziab, CoZn-ZIF tau pyrolyzed ntawm qhov kub sib txawv (750–950 ° C) hauv huab cua ntawm 6% H2 thiab 94% Ar. Raws li pom hauv daim duab hauv qab no, cov ntaub ntawv tshwm sim muaj cov yam ntxwv ntawm qhov chaw sib txawv thiab hu ua Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750 (Daim Duab 2a). ). Kev soj ntsuam tshwj xeeb ntawm qee cov kauj ruam tseem ceeb hauv cov txheej txheem synthesis tau piav qhia hauv Daim Duab 1 thiab 2. C1-C3. Kev ntsuas kub hloov pauv X-ray diffraction (VTXRD) tau ua los saib xyuas kev hloov pauv ntawm cov catalyst. Thaum qhov kub pyrolysis ncav cuag 650 ° C, tus qauv XRD hloov pauv ntau vim yog qhov tawg ntawm cov qauv siv lead ua ke ntawm ZIF (Daim duab S4) 39. Thaum qhov kub nce ntxiv, ob lub ncov dav dav tshwm sim hauv cov qauv XRD ntawm Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750 ntawm 20–30 ° thiab 40–50 °, sawv cev rau lub ncov ntawm amorphous carbon (Daim duab C5). 40. Nws yog ib qho tsim nyog sau tseg tias tsuas yog peb lub ncov yam ntxwv tau pom ntawm 44.2 °, 51.5 ° thiab 75.8 °, uas yog rau cov hlau cobalt (JCPDS # 15-0806), thiab 26.2 °, uas yog rau cov hlau graphitic (JCPDS # 41-1487). Cov duab X-ray ntawm Co-SAs/NPs@NC-950 qhia tau tias muaj cov graphite zoo li encapsulated cobalt nanoparticles ntawm cov catalyst41,42,43,44. Cov duab Raman qhia tau tias Co-SAs/NPs@NC-950 zoo li muaj cov D thiab G peaks muaj zog thiab nqaim dua li lwm cov qauv, qhia txog qib siab dua ntawm graphitization (Daim Duab S6). Tsis tas li ntawd, Co-SAs/NPs@NC-950 qhia txog Brunner-Emmett-Taylor (BET) thaj chaw thiab qhov ntim ntawm qhov (1261 m2 g-1 thiab 0.37 cm3 g-1) ntau dua li lwm cov qauv thiab feem ntau ZIFs yog NC derivatives. cov ntaub ntawv (Daim Duab S7 thiab Rooj S1). Kev ntsuas atomic absorption spectroscopy (AAS) qhia tau hais tias cov ntsiab lus cobalt ntawm Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@ yog 2.69 wt.%, 2.74 wt.% thiab 2.73 wt.%. NC-750 feem (Rooj S2). Cov ntsiab lus Zn ntawm Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750 maj mam nce, uas yog vim muaj kev txo qis thiab volatilization ntawm Zn units. Kev nce hauv pyrolysis kub (Zn, boiling point = 907 °C) 45.46. Kev tshuaj xyuas Elemental (EA) qhia tau hais tias feem pua ​​ntawm N txo qis nrog kev nce hauv pyrolysis kub, thiab cov ntsiab lus O2 siab yuav yog vim muaj kev nqus ntawm molecular O2 los ntawm kev raug rau huab cua. (Rooj S3). Ntawm qee cov ntsiab lus cobalt, nanoparticles thiab cov coatoms cais tawm sib koom ua ke, ua rau muaj kev nce ntxiv ntawm cov haujlwm catalyst, raws li tau tham hauv qab no.
Daim duab kos ntawm kev tsim cov Co-SA/NPs@NC-T, qhov twg T yog qhov kub thiab txias pyrolysis (°C). b daim duab TEM. c Daim duab ntawm Co-SAs/NPs@NC-950 AC-HAADF-STEM. Cov Co atoms ib leeg tau cim nrog cov voj voog liab. d EDS spectrum ntawm Co-SA/NPs@NC-950.
Qhov tseem ceeb, kev siv tshuab hluav taws xob kis tau (TEM) tau qhia txog qhov muaj ntau yam cobalt nanoparticles (NPs) nrog qhov nruab nrab loj ntawm 7.5 ± 1.7 nm tsuas yog hauv Co-SAs/NPs@NC-950 (Daim Duab 2 b thiab S8). Cov nanoparticles no tau encapsulated nrog graphite-zoo li carbon doped nrog nitrogen. Lub lattice fringe spacing ntawm 0.361 thiab 0.201 nm sib raug rau graphitic carbon (002) thiab metallic Co (111) particles, feem. Tsis tas li ntawd, high-angle aberration-corrected annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) tau qhia tias Co NPs hauv Co-SAs/NPs@NC-950 tau nyob ib puag ncig los ntawm ntau atomic cobalt (Daim Duab 2c). Txawm li cas los xij, tsuas yog atomically dispersed cobalt atoms tau pom ntawm kev txhawb nqa ntawm ob qho qauv (Daim Duab S9). Daim duab Energy dispersive spectroscopy (EDS) HAADF-STEM qhia txog kev faib tawm ntawm C, N, Co thiab cov Co NPs sib cais hauv Co-SAs/NPs@NC-950 (Daim Duab 2d). Tag nrho cov txiaj ntsig no qhia tau tias cov chaw Co uas tau tawg ua atom thiab cov nanoparticles uas tau encapsulated hauv N-doped graphite-zoo li carbon tau txuas nrog NC substrates hauv Co-SAs/NPs@NC-950, thaum tsuas yog cov chaw hlau cais xwb.
Lub xeev valence thiab cov tshuaj lom neeg ntawm cov ntaub ntawv tau txais tau kawm los ntawm X-ray photoelectron spectroscopy (XPS). XPS spectra ntawm peb cov catalysts tau qhia txog qhov muaj cov ntsiab lus Co, N, C thiab O, tab sis Zn tsuas yog muaj nyob hauv Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750 (Daim Duab 2). C10). Thaum qhov kub pyrolysis nce, tag nrho cov ntsiab lus nitrogen txo qis thaum cov hom nitrogen tsis ruaj khov thiab lwj mus rau hauv NH3 thiab NOx gases ntawm qhov kub siab dua (Rooj S4) 47. Yog li, tag nrho cov ntsiab lus carbon maj mam nce los ntawm Co-SAs/NPs@NC-750 mus rau Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-950 (Daim Duab S11 thiab S12). Cov qauv pyrolyzed ntawm qhov kub siab dua muaj qhov sib piv qis dua ntawm cov nitrogen atoms, uas txhais tau tias qhov ntau ntawm NC carriers hauv Co-SAs/NPs@NC-950 yuav tsum tsawg dua li ntawd hauv lwm cov qauv. Qhov no ua rau muaj kev sib xyaw ua ke ntawm cov cobalt me ​​me. Cov O1s spectrum qhia ob lub ncov C = O (531.6 eV) thiab C – O (533.5 eV), feem (Daim Duab S13) 48. Raws li pom hauv Daim Duab 2a, N1s spectrum tuaj yeem daws tau plaub lub ncov ntawm pyridine nitrogen N (398.4 eV), pyrrole N (401.1 eV), graphite N (402.3 eV) thiab Co-N (399.2 eV). Cov ntawv cog lus Co-N muaj nyob rau hauv tag nrho peb qhov qauv, qhia tias qee cov N atoms tau sib koom ua ke rau cov chaw monometallic, tab sis cov yam ntxwv sib txawv heev 49. Kev siv qhov kub siab dua pyrolysis tuaj yeem txo cov ntsiab lus ntawm Co-N hom los ntawm 43.7% hauv Co-SA/NPs@NC-750 txog 27.0% hauv Co-SAs/NPs@NC-850 thiab Co 17.6%@ NC-950. nyob rau hauv -CA/NPs, uas sib raug rau qhov nce ntxiv ntawm cov ntsiab lus C (Daim duab 3a), qhia tias lawv tus lej sib koom ua ke Co-N tuaj yeem hloov pauv thiab hloov pauv ib feem los ntawm C50 atoms. Lub spectrum Zn 2p qhia tau hais tias cov khoom no muaj nyob rau hauv daim ntawv Zn2+. (Daim duab S14) 51. Lub spectrum ntawm Co 2p qhia ob lub ncov tseem ceeb ntawm 780.8 thiab 796.1 eV, uas yog vim Co 2p3/2 thiab Co 2p1/2, feem (Daim duab 3b). Piv nrog Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750, lub ncov Co-N hauv Co-SAs/NPs@NC-950 raug hloov mus rau sab zoo, qhia tias ib qho Co atom rau qhov chaw -SAs/NPs@NC-950 muaj qib siab dua ntawm electron depletion, ua rau lub xeev oxidation siab dua. Nws yog ib qho tsim nyog sau tseg tias tsuas yog Co-SAs/NPs@NC-950 tau qhia txog qhov tsis muaj zog ntawm xoom-valent cobalt (Co0) ntawm 778.5 eV, uas ua pov thawj tias muaj cov nanoparticles los ntawm kev sib sau ua ke ntawm SA cobalt ntawm qhov kub siab.
a N 1s thiab b Co 2p spectra ntawm Co-SA/NPs@NC-T. c XANES thiab d FT-EXAFS spectra ntawm Co-K-edge ntawm Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750. e WT-EXAFS contour plots ntawm Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850, thiab Co-SAs/NPs@NC-750. f FT-EXAFS fitting curve rau Co-SA/NPs@NC-950.
Tom qab ntawd, siv lub sijhawm X-ray absorption spectroscopy (XAS) los tshuaj xyuas cov qauv hluav taws xob thiab qhov chaw sib koom tes ntawm cov Co hauv cov qauv uas tau npaj tseg. Cov xwm txheej Cobalt valence hauv Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750 Cov qauv ntug tau qhia los ntawm kev nqus X-ray ze ntawm Co-K ntug (XANES) spectrum. Raws li pom hauv Daim Duab 3c, qhov nqus ze ntawm ntug ntawm peb cov qauv nyob nruab nrab ntawm Co thiab CoO foils, qhia tias lub xeev valence ntawm Co hom ntau ntawm 0 txog +253. Tsis tas li ntawd, kev hloov pauv mus rau lub zog qis dua tau pom los ntawm Co-SAs/NPs@NC-950 mus rau Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750, qhia tias Co-SAs/NPs@NC-750 muaj lub xeev oxidation qis dua. Kev txiav txim rov qab. Raws li cov txiaj ntsig sib xyaw ua ke, lub xeev Co valence ntawm Co-SAs/NPs@NC-950 kwv yees li +0.642, uas qis dua lub xeev Co valence ntawm Co-SAs/NPs@NC-850 (+1.376). Co-SA/NP @NC-750 (+1.402). Cov txiaj ntsig no qhia tau tias qhov nruab nrab ntawm lub xeev oxidation ntawm cov khoom cobalt hauv Co-SAs/NPs@NC-950 raug txo qis, uas yog sib xws nrog cov txiaj ntsig XRD thiab HADF-STEM thiab tuaj yeem piav qhia los ntawm kev sib koom ua ke ntawm cobalt nanoparticles thiab ib leeg cobalt. Cov Co atoms 41. Fourier transform X-ray absorption fine structure (FT-EXAFS) spectrum ntawm Co K-edge qhia tau hais tias lub ncov tseem ceeb ntawm 1.32 Å yog rau Co-N/Co-C plhaub, thaum txoj kev tawg ntawm cov hlau Co-Co yog ntawm 2.18 tsuas yog hauv Co-SAs Å pom hauv /NPs@NC-950 (Daim duab 3d). Ntxiv mus, qhov wavelet transform (WT) contour plot qhia qhov siab tshaj plaws ntawm 6.7 Å-1 uas tau muab rau Co-N/Co-C, thaum tsuas yog Co-SAs/NPs@NC-950 qhia qhov siab tshaj plaws uas tau muab rau 8.8. Lwm qhov siab tshaj plaws yog ntawm Å−1 rau Co-Co bond (Daim duab 3e). Ntxiv rau, kev tshuaj xyuas EXAFS uas tus neeg xauj tsev ua tau qhia tias ntawm qhov kub pyrolysis ntawm 750, 850 thiab 950 ° C, cov lej sib koom ua ke Co-N yog 3.8, 3.2 thiab 2.3, raws li, thiab cov lej sib koom ua ke Co-C yog 0. 0.9 thiab 1.8 (Daim duab 3f, S15 thiab Rooj S1). Qhia meej dua, cov txiaj ntsig tshiab kawg tuaj yeem raug suav tias yog qhov muaj cov chav CoN2C2 thiab cov nanoparticles uas tau tawg ua atom hauv Co-SAs/NPs@NC-950. Qhov sib piv, hauv Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750, tsuas yog CoN3C thiab CoN4 units xwb. Nws yog qhov tseeb tias nrog rau qhov kub pyrolysis nce ntxiv, N atoms hauv CoN4 unit maj mam hloov los ntawm C atoms, thiab cobalt CA aggregates los tsim cov nanoparticles.
Cov xwm txheej tshuaj tiv thaiv uas tau kawm ua ntej tau siv los kawm txog qhov cuam tshuam ntawm cov xwm txheej npaj rau cov khoom ntawm ntau yam khoom siv (Daim Duab S16)17,49. Raws li pom hauv Daim Duab 4 a, qhov kev ua haujlwm ntawm Co-SAs/NPs@NC-950 yog qhov siab dua li ntawm Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750. Qhov tseem ceeb, tag nrho peb cov qauv Co uas tau npaj tau qhia txog kev ua tau zoo dua piv rau cov txheej txheem ua lag luam hlau muaj nqis (Pd/C thiab Pt/C). Tsis tas li ntawd, cov qauv Zn-ZIF-8 thiab Zn-NC tsis ua haujlwm rau formic acid dehydrogenation, qhia tias cov khoom Zn tsis yog qhov chaw ua haujlwm, tab sis lawv cov nyhuv rau qhov kev ua haujlwm tsis tseem ceeb. Tsis tas li ntawd, qhov kev ua haujlwm ntawm Co-SAs/NPs@NC-850 thiab Co-SAs/NPs@NC-750 tau dhau los ua pyrolysis theem ob ntawm 950 ° C rau 1 teev, tab sis qis dua li ntawm Co-SAs/NPs@NC-750. @NC-950 (Daim Duab S17). Kev piav qhia txog cov qauv ntawm cov ntaub ntawv no qhia tau tias muaj Co nanoparticles nyob rau hauv cov qauv rov ua dua, tab sis qhov chaw tshwj xeeb qis thiab tsis muaj cov pa roj carbon zoo li graphite ua rau muaj kev ua haujlwm qis dua piv rau Co-SAs/NPs@NC-950 (Daim Duab S18–S20). Kev ua haujlwm ntawm cov qauv nrog cov nqi sib txawv ntawm Co precursor kuj tau piv, nrog rau kev ua haujlwm siab tshaj plaws pom ntawm 3.5 mol ntxiv (Rooj S6 thiab Daim Duab S21). Nws yog qhov tseeb tias kev tsim ntawm ntau lub chaw hlau yog cuam tshuam los ntawm cov ntsiab lus hydrogen hauv huab cua pyrolysis thiab lub sijhawm pyrolysis. Yog li ntawd, lwm cov ntaub ntawv Co-SAs/NPs@NC-950 tau soj ntsuam rau kev ua haujlwm formic acid dehydrogenation. Txhua cov ntaub ntawv tau qhia txog kev ua tau zoo nruab nrab mus rau qhov zoo heev; txawm li cas los xij, tsis muaj ib qho ntawm lawv zoo dua li Co-SAs/NPs@NC-950 (Daim Duab S22 thiab S23). Cov yam ntxwv ntawm cov khoom siv qhia tau hais tias nrog lub sijhawm pyrolysis nce ntxiv, cov ntsiab lus ntawm monoatomic Co-N txoj haujlwm maj mam txo qis vim yog kev sib sau ua ke ntawm cov hlau atoms rau hauv nanoparticles, uas piav qhia txog qhov sib txawv ntawm kev ua haujlwm ntawm cov qauv nrog lub sijhawm pyrolysis ntawm 100-2000. qhov sib txawv. 0.5 teev, 1 teev, thiab 2 teev (Cov duab S24-S28 thiab Rooj S7).
Daim duab qhia txog qhov ntim roj piv rau lub sijhawm tau txais thaum lub sijhawm dehydrogenation ntawm cov roj sib dhos siv ntau yam catalysts. Cov xwm txheej tshuaj tiv thaiv: PC (10 mmol, 377 μl), catalyst (30 mg), PC (6 ml), Tback: 110 °C, Tactical: 98 °C, 4 qhov b Co-SAs/NPs@NC-950 (30 mg), ntau yam kuab tshuaj. c Kev sib piv ntawm cov nqi hloov pauv roj ntawm cov catalysts sib txawv hauv cov kuab tshuaj organic ntawm 85–110 °C. d Co-SA/NPs@NC-950 rov ua dua kev sim. Cov xwm txheej tshuaj tiv thaiv: FA (10 mmol, 377 µl), Co-SAs/NPs@NC-950 (30 mg), kuab tshuaj (6 ml), Tset: 110 °C, Tactual: 98 °C, txhua lub voj voog tshuaj tiv thaiv kav ib teev. Cov kab yuam kev sawv cev rau qhov sib txawv ntawm tus qauv suav los ntawm peb qhov kev sim nquag.
Feem ntau, qhov ua tau zoo ntawm FA dehydrogenation catalysts yog nyob ntawm cov xwm txheej ntawm kev ua haujlwm, tshwj xeeb tshaj yog cov kuab tshuaj siv 8,49. Thaum siv dej ua kuab tshuaj, Co-SAs/NPs@NC-950 tau qhia txog qhov pib ua haujlwm siab tshaj plaws, tab sis kev ua haujlwm tsis ua haujlwm tau tshwm sim, tej zaum vim yog protons lossis H2O18 nyob hauv cov chaw nquag. Kev sim cov catalyst hauv cov kuab tshuaj organic xws li 1,4-dioxane (DXA), n-butyl acetate (BAC), toluene (PhMe), triglyme thiab cyclohexanone (CYC) kuj tsis tau qhia txog kev txhim kho, thiab hauv propylene carbonate (PC)) (Daim duab 4b thiab Rooj S8). Ib yam li ntawd, cov khoom ntxiv xws li triethylamine (NEt3) lossis sodium formate (HCCONa) tsis muaj txiaj ntsig zoo rau kev ua haujlwm ntawm catalyst (Daim duab S29). Nyob rau hauv qhov xwm txheej zoo tshaj plaws ntawm kev ua haujlwm, cov pa roj tau txog 1403.8 mL g−1 h−1 (Daim Duab S30), uas yog siab dua li txhua cov tshuaj catalysts Co uas tau tshaj tawm yav dhau los (suav nrog SAC17, 23, 24). Hauv ntau qhov kev sim, tsis suav nrog cov tshuaj tiv thaiv hauv dej thiab nrog cov tshuaj ntxiv, dehydrogenation thiab dehydration selectivities txog li 99.96% tau txais (Rooj S9). Lub zog ua kom muaj zog yog 88.4 kJ / mol, uas yog sib piv rau lub zog ua kom muaj zog ntawm cov hlau zoo catalysts (Daim Duab S31 thiab Rooj S10).
Ntxiv rau, peb tau piv rau ntau lwm cov tshuaj catalysts heterogeneous rau formic acid dehydrogenation nyob rau hauv cov xwm txheej zoo sib xws (Daim duab 4c, cov lus S11 thiab S12). Raws li pom hauv Daim Duab 3c, qhov nqi tsim roj ntawm Co-SAs/NPs@NC-950 ntau dua li ntawm cov tshuaj catalysts heterogeneous feem ntau paub thiab yog 15 thiab 15 npaug siab dua li ntawm kev lag luam 5% Pd/C thiab 5% Pd/C, feem, los ntawm 10 ib zaug. % Pt/C catalyst.
Ib qho tseem ceeb ntawm kev siv cov tshuaj catalysts (de) hydrogenation yog lawv qhov ruaj khov. Yog li ntawd, ntau qhov kev sim rov ua dua tshiab siv Co-SAs/NPs@NC-950 tau ua tiav. Raws li pom hauv Daim Duab 4 d, qhov kev ua ub no pib thiab kev xaiv ntawm cov khoom tseem tsis tau hloov pauv dhau tsib qhov kev khiav sib law liag (saib Daim Ntawv S13). Kev sim mus sij hawm ntev tau ua thiab cov roj tsim tau nce linearly dhau 72 teev (Daim Duab S32). Cov ntsiab lus cobalt ntawm Co-SA/NPs@NC-950 siv yog 2.5 wt%, uas ze heev rau qhov ntawm cov tshuaj catalyst tshiab, qhia tias tsis muaj kev leaching ntawm cobalt (Daim Ntawv S14). Tsis muaj kev hloov xim pom tseeb lossis kev sib sau ua ke ntawm cov hlau me me tau pom ua ntej thiab tom qab kev tshuaj tiv thaiv (Daim Duab S33). AC-HAADF-STEM thiab EDS ntawm cov ntaub ntawv siv rau hauv kev sim mus sij hawm ntev tau qhia txog kev khaws cia thiab kev sib cais sib xws ntawm cov chaw sib cais atomic thiab tsis muaj kev hloov pauv tseem ceeb (Daim Duab S34 thiab S35). Cov ncov tshwj xeeb ntawm Co0 thiab Co-N tseem muaj nyob hauv XPS, ua pov thawj qhov kev sib koom ua ke ntawm Co NPs thiab cov chaw hlau ib leeg, uas kuj lees paub qhov ruaj khov ntawm Co-SAs/NPs@NC-950 catalyst (Daim Duab S36).
Txhawm rau txheeb xyuas cov chaw nquag tshaj plaws uas ua rau formic acid dehydrogenation, cov ntaub ntawv xaiv nrog tsuas yog ib lub chaw hlau (CoN2C2) lossis Co NP tau npaj raws li kev tshawb fawb yav dhau los17. Qhov kev txiav txim ntawm formic acid dehydrogenation kev ua ub no pom nyob rau hauv tib qho xwm txheej yog Co-SAs/NPs@NC-950 > Co SA > Co NP (Rooj S15), qhia tias cov chaw CoN2C2 uas tau tawg ua atomically muaj zog dua li NPs. Cov kinetics tshuaj tiv thaiv qhia tau hais tias kev hloov pauv hydrogen ua raws li thawj qhov kev txiav txim tshuaj tiv thaiv kinetics, tab sis cov nqes hav ntawm ntau cov nkhaus ntawm cov ntsiab lus cobalt sib txawv tsis zoo ib yam, qhia tias kinetics tsis yog nyob ntawm formic acid xwb, tab sis kuj nyob ntawm qhov chaw nquag (Daim duab 2). C37). Cov kev tshawb fawb kinetic ntxiv qhia tau hais tias, muab qhov tsis muaj cov hlau cobalt peaks hauv X-ray diffraction tsom xam, qhov kev txiav txim kinetic ntawm cov tshuaj tiv thaiv hauv cov ntsiab lus cobalt tau pom tias yog 1.02 ntawm cov qib qis dua (tsawg dua 2.5%), qhia txog kev faib tawm yuav luag sib xws ntawm cov chaw cobalt monoatomic. lub ntsiab. qhov chaw ua haujlwm (daim duab S38 thiab S39). Thaum cov ntsiab lus ntawm Co cov khoom me me ncav cuag 2.7%, r nce ntxiv tam sim ntawd, qhia tias cov nanoparticles sib cuam tshuam zoo nrog cov atoms ib leeg kom tau txais kev ua haujlwm siab dua. Raws li cov ntsiab lus ntawm Co cov khoom me me nce ntxiv, qhov nkhaus ua nonlinear, uas yog txuam nrog kev nce ntxiv ntawm cov nanoparticles thiab kev txo qis hauv cov haujlwm monatomic. Yog li, qhov kev ua tau zoo LC dehydrogenation ntawm Co-SA/NPs@NC-950 yog los ntawm kev coj cwj pwm koom tes ntawm cov chaw hlau ib leeg thiab nanoparticles.
Ib txoj kev tshawb nrhiav tob tob tau ua tiav los ntawm kev siv qhov kev hloov pauv ntawm qhov chaw sib txawv ntawm Fourier (hauv qhov chaw DRIFT) los txheeb xyuas cov tshuaj tiv thaiv hauv cov txheej txheem. Tom qab ua kom cov qauv kub sib txawv tom qab ntxiv cov kua qaub formic, ob pawg zaus tau pom (Daim Duab 5a). Peb lub ncov tshwj xeeb ntawm HCOOH * tshwm sim ntawm 1089, 1217 thiab 1790 cm-1, uas yog vim qhov tawm ntawm lub dav hlau CH π (CH) ncab kev co, CO ν (CO) ncab kev co thiab C = O ν (C = O) ncab kev co, 54, 55 feem. Lwm pawg ntawm cov ncov ntawm 1363 thiab 1592 cm-1 sib raug rau qhov sib xws OCO kev co νs (OCO) thiab qhov tsis sib xws OCO ncab kev co νas (OCO) 33.56 HCOO *, feem. Thaum cov tshuaj tiv thaiv mus ntxiv, cov ncov sib piv ntawm HCOOH * thiab HCOO * hom maj mam ploj mus. Feem ntau hais lus, qhov kev rhuav tshem ntawm cov kua qaub formic muaj peb kauj ruam tseem ceeb: (I) kev nqus ntawm cov kua qaub formic rau ntawm qhov chaw nquag, (II) kev tshem tawm H los ntawm txoj kev formate lossis carboxylate, thiab (III) kev sib xyaw ua ke ntawm ob lub H adsorbed los tsim hydrogen. HCOO * thiab COOH * yog cov khoom siv tseem ceeb hauv kev txiav txim siab txog txoj kev formate lossis carboxylate, feem 57. Siv peb lub kaw lus catalytic, tsuas yog lub ncov HCOO * tshwm sim, qhia tias kev rhuav tshem cov kua qaub formic tsuas yog tshwm sim los ntawm txoj kev formic acid 58. Cov kev soj ntsuam zoo sib xws tau ua ntawm qhov kub qis dua ntawm 78 ° C thiab 88 ° C (daim duab S40).
Hauv qhov chaw DRIFT spectra ntawm HCOOH dehydrogenation ntawm Co-SAs/NPs@NC-950 thiab b Co SAs. Cov lus dab neeg qhia txog lub sijhawm ua haujlwm ntawm qhov chaw. c Kev hloov pauv ntawm cov roj ntim tsim los ntawm kev siv cov tshuaj reagents sib txawv ntawm isotope labeling dhau sijhawm. d Cov ntaub ntawv Kinetic isotope effect.
Cov kev sim DRIFT zoo sib xws tau ua tiav rau cov ntaub ntawv cuam tshuam Co NP thiab Co SA los kawm txog cov nyhuv synergistic hauv Co-SA/NPs@NC-950 (Daim Duab 5 b thiab S41). Ob qho khoom siv qhia cov qauv zoo sib xws, tab sis cov peaks tshwj xeeb ntawm HCOOH* thiab HCOO* tau hloov me ntsis, qhia tias kev qhia txog Co NPs hloov cov qauv hluav taws xob ntawm lub chaw monoatomic. Lub peak tshwj xeeb νas(OCO) tshwm sim hauv Co-SAs/NPs@NC-950 thiab Co SA tab sis tsis yog hauv Co NPs, ntxiv qhia tias qhov nruab nrab tsim thaum ntxiv cov kua qaub formic yog monodentate formic acid perpendicular rau lub ntsej muag ntsev. thiab yog adsorbed rau ntawm SA ua qhov chaw nquag 59. Nws yog ib qho tsim nyog sau tseg tias qhov nce ntxiv ntawm kev co ntawm cov peaks tshwj xeeb π(CH) thiab ν(C = O) tau pom, uas pom tseeb ua rau muaj kev cuam tshuam ntawm HCOOH* thiab ua rau muaj kev cuam tshuam. Yog li ntawd, cov yam ntxwv siab tshaj plaws ntawm HCOOH * thiab HCOO * hauv Co-SAs / NPs @ NC yuav luag ploj mus tom qab 2 feeb ntawm kev ua haujlwm, uas yog sai dua li ntawm monometallic (6 feeb) thiab nanoparticle-based catalysts (12 feeb). . Tag nrho cov txiaj ntsig no lees paub tias nanoparticle doping txhim kho kev nqus thiab kev ua haujlwm ntawm intermediates, yog li ua kom cov tshuaj tiv thaiv tau hais los saum toj no.
Txhawm rau txheeb xyuas ntxiv txog txoj kev ua tshuaj tiv thaiv thiab txiav txim siab qhov kev txiav txim siab ntawm tus nqi (RDS), cov nyhuv KIE tau ua tiav nyob rau hauv qhov muaj Co-SAs/NPs@NC-950. Ntawm no, cov isotopes formic acid sib txawv xws li HCOOH, HCOOD, DCOOH thiab DCOOD yog siv rau kev tshawb fawb KIE. Raws li pom hauv Daim Duab 5c, tus nqi dehydrogenation txo qis hauv qhov kev txiav txim hauv qab no: HCOOH > HCOOD > DCOOH > DCOOD. Tsis tas li ntawd, cov nqi ntawm KHCOOH/KHCOOD, KHCOOH/KDCOOH, KHCOOD/KDCOOD thiab KDCOOH/KDCOOD tau suav ua 1.14, 1.71, 2.16 thiab 1.44, feem (Daim Duab 5d). Yog li, CH daim ntawv cog lus cleavage hauv HCOO * qhia txog kH / kD tus nqi ​​> 1.5, qhia txog qhov cuam tshuam loj kinetic 60,61, thiab zoo li sawv cev rau RDS ntawm HCOOH dehydrogenation ntawm Co-SAs / NPs @ NC-950.
Ntxiv rau, DFT kev xam tau ua tiav los nkag siab txog qhov cuam tshuam ntawm cov nanoparticles doped rau qhov kev ua haujlwm intrinsic ntawm Co-SA. Cov qauv Co-SAs/NPs@NC thiab Co-SA tau tsim los ntawm cov kev sim uas tau qhia thiab cov haujlwm yav dhau los (Figs. 6a thiab S42)52,62. Tom qab kev ua kom zoo dua geometric, cov nanoparticles Co6 me me (CoN2C2) sib koom ua ke nrog cov chav monoatomic tau txheeb xyuas, thiab Co-C thiab Co-N bond ntev hauv Co-SA/NPs@NC tau txiav txim siab tias yog 1.87 Å thiab 1.90 Å, feem. , uas yog sib xws nrog cov txiaj ntsig XAFS. Qhov kev xam ib feem ntawm cov xeev (PDOS) qhia tau hais tias ib qho Co hlau atom thiab nanoparticle composite (Co-SAs/NPs@NC) qhia txog kev sib xyaw ua ke siab dua ze ntawm qib Fermi piv rau CoN2C2, ua rau HCOOH. Kev hloov pauv electron decomposed zoo dua (Figs. 6b thiab S43). Cov chaw d-band sib xws ntawm Co-SAs/NPs@NC thiab Co-SA tau suav tias yog -0.67 eV thiab -0.80 eV, feem, ntawm cov uas qhov nce ntawm Co-SAs/NPs@NC yog 0.13 eV, uas tau pab txhawb rau qhov tom qab kev qhia txog NP, qhov kev nqus ntawm HCOO * cov khoom me me los ntawm cov qauv hluav taws xob hloov kho ntawm CoN2C2 tshwm sim. Qhov sib txawv ntawm qhov ceev ntawm qhov them qhia tau hais tias muaj huab cua loj nyob ib puag ncig CoN2C2 thaiv thiab nanoparticle, qhia txog kev sib cuam tshuam muaj zog ntawm lawv vim muaj kev sib pauv hluav taws xob. Ua ke nrog Bader them kev tshuaj xyuas, nws tau pom tias atomically dispersed Co poob 1.064e hauv Co-SA/NPs@NC thiab 0.796e hauv Co SA (Daim Duab S44). Cov txiaj ntsig no qhia tau hais tias kev koom ua ke ntawm nanoparticles ua rau electron depletion ntawm Co qhov chaw, ua rau muaj kev nce hauv Cov valence, uas yog sib xws nrog XPS cov txiaj ntsig (Daim Duab 6c). Cov yam ntxwv ntawm Co-O kev sib cuam tshuam ntawm HCOO adsorption rau ntawm Co-SAs / NPs @ NC thiab Co SA tau raug tshuaj xyuas los ntawm kev xam cov pawg crystalline orbital Hamiltonian (COHP) 63. Raws li pom hauv Daim Duab 6 d, cov nqi tsis zoo thiab zoo ntawm -COHP sib raug rau lub xeev antibonding thiab lub xeev khi, feem. Lub zog sib txuas ntawm Co-O adsorbed los ntawm HCOO (Co-carbonyl O HCOO *) tau raug soj ntsuam los ntawm kev koom ua ke ntawm -COHP cov nqi, uas yog 3.51 thiab 3.38 rau Co-SAs / NPs @ NC thiab Co-SA, feem. HCOOH adsorption kuj tau qhia cov txiaj ntsig zoo sib xws: qhov nce ntawm tus nqi sib xyaw ntawm -COHP tom qab nanoparticle doping qhia txog kev nce hauv Co-O kev sib txuas, yog li txhawb kev ua haujlwm ntawm HCOO thiab HCOOH (Daim Duab S45).
Co-SA/NPs@NC-950 cov qauv lattice. b PDOS Co-SA/NP@NC-950 thiab Co SA. c 3D isosurface ntawm qhov sib txawv ntawm cov nqi densities ntawm HCOOH adsorption ntawm Co-SA/NPs@NC-950 thiab Co-SA. (d) pCOHP ntawm Co-O bonds adsorbed los ntawm HCOO ntawm Co-SA/NPs@NC-950 (sab laug) thiab Co-SA (sab xis). e Txoj kev tshuaj tiv thaiv ntawm HCOOH dehydrogenation ntawm Co-SA/NPs@NC-950 thiab Co-SA.
Yuav kom nkag siab zoo dua txog kev ua haujlwm dehydrogenation zoo dua ntawm Co-SA/NPs@NC, txoj kev ua haujlwm thiab lub zog tau txiav txim siab. Tshwj xeeb, FA dehydrogenation muaj tsib kauj ruam, suav nrog kev hloov pauv ntawm HCOOH rau HCOOH*, HCOOH* rau HCOO* + H*, HCOO* + H* rau 2H* + CO2*, 2H* + CO2* rau 2H* + CO2, thiab 2H* hauv H2 (Daim duab 6e). Lub zog adsorption ntawm cov tshuaj formic acid ntawm qhov chaw catalyst los ntawm carboxylic oxygen qis dua li los ntawm hydroxyl oxygen (Daim duab S46 thiab S47). Tom qab ntawd, vim yog lub zog qis dua, cov adsorbate feem ntau dhau los ntawm OH bond cleavage los tsim HCOO* es tsis yog CH bond cleavage los tsim COOH*. Tib lub sijhawm, HCOO* siv monodentate adsorption, uas txhawb nqa kev tawg ntawm cov bonds thiab kev tsim ntawm CO2 thiab H2. Cov txiaj ntsig no yog sib xws nrog qhov muaj νas (OCO) ncov hauv qhov chaw DRIFT, qhia ntxiv tias FA degradation tshwm sim los ntawm txoj kev format hauv peb txoj kev tshawb fawb. Nws yog ib qho tseem ceeb uas yuav tsum nco ntsoov tias raws li KIE ntsuas, CH dissociation muaj qhov cuam tshuam zog ntau dua li lwm cov kauj ruam tiv thaiv thiab sawv cev rau RDS. Qhov cuam tshuam zog ntawm qhov zoo tshaj plaws Co-SAs / NPs @ NC catalyst system yog 0.86 eV qis dua li ntawm Co-SA (1.2 eV), uas txhim kho qhov kev ua haujlwm dehydrogenation tag nrho. Qhov tseem ceeb, qhov muaj cov nanoparticles tswj hwm cov qauv hluav taws xob ntawm cov chaw coactive atomically dispersed, uas ntxiv txhim kho qhov adsorption thiab kev ua haujlwm ntawm intermediates, yog li txo qis qhov cuam tshuam thiab txhawb nqa hydrogen ntau lawm.
Hauv kev xaus lus, peb ua pov thawj thawj zaug tias kev ua haujlwm catalytic ntawm cov catalysts tsim hydrogen tuaj yeem txhim kho tau zoo los ntawm kev siv cov ntaub ntawv nrog cov chaw monometallic faib ntau thiab cov nanoparticles me me. Lub tswv yim no tau raug lees paub los ntawm kev tsim cov cobalt-based ib leeg-hlau catalysts hloov kho nrog nanoparticles (Co-SAs / NPs @ NC), nrog rau cov ntaub ntawv cuam tshuam nrog tsuas yog ib leeg-hlau chaw (CoN2C2) lossis Co NPs. Tag nrho cov ntaub ntawv tau npaj los ntawm ib kauj ruam yooj yim pyrolysis txoj kev. Kev tshuaj xyuas cov qauv qhia tau hais tias cov catalyst zoo tshaj plaws (Co-SAs / NPs @ NC-950) muaj cov chav CoN2C2 atomically dispersed thiab cov nanoparticles me me (7-8 nm) doped nrog nitrogen thiab graphite-zoo li carbon. Nws muaj cov roj tsim tau zoo heev txog li 1403.8 ml g-1 h-1 (H2: CO2 = 1.01: 1), H2 thiab CO selectivity ntawm 99.96% thiab tuaj yeem tswj hwm kev ua haujlwm tas mus li rau ob peb hnub. Qhov kev ua haujlwm ntawm cov catalyst no ntau dua li qhov kev ua haujlwm ntawm qee cov tshuaj Co SA thiab Pd/C los ntawm 4 thiab 15 zaug, raws li. Cov kev sim hauv qhov chaw DRIFT qhia tau tias piv rau Co-SA, Co-SAs/NPs@NC-950 qhia tau tias muaj zog dua monodentate adsorption ntawm HCOO*, uas yog qhov tseem ceeb rau txoj kev formate, thiab cov nanoparticles dopant tuaj yeem txhawb HCOO* kev ua haujlwm thiab C-H acceleration. Qhov kev sib txuas cleavage tau txheeb xyuas tias yog RDS. Kev suav theoretical qhia tau tias Co NP doping nce qhov chaw d-band ntawm ib qho Co atoms los ntawm 0.13 eV los ntawm kev sib cuam tshuam, txhim kho qhov adsorption ntawm HCOOH* thiab HCOO* intermediates, yog li txo qhov kev cuam tshuam ntawm 1.20 eV rau Co SA mus rau 0.86 eV. Nws yog lub luag haujlwm rau kev ua tau zoo heev.
Qhov dav dua, qhov kev tshawb fawb no muab cov tswv yim rau kev tsim cov tshuaj catalysts hlau ib leeg tshiab thiab ua kom nkag siab txog yuav ua li cas txhim kho kev ua haujlwm catalytic los ntawm kev sib koom ua ke ntawm cov chaw hlau ntawm ntau qhov ntau thiab tsawg. Peb ntseeg tias txoj hauv kev no tuaj yeem nthuav dav mus rau ntau lwm cov txheej txheem catalytic.
Co(NO3)2 6H2O (AP, 99%), Zn(NO3)2 6H2O (AP, 99%), 2-methylimidazole (98%), methanol (99.5%), propylene carbonate (PC, 99%) ethanol (AR, 99.7%) tau yuav los ntawm McLean, Suav teb. Formic acid (HCOOH, 98%) tau yuav los ntawm Rhawn, Suav teb. Tag nrho cov reagents tau siv ncaj qha yam tsis muaj kev ntxuav ntxiv, thiab dej ultrapure tau npaj siv lub kaw lus ntxuav ultrapure. Pt/C (5% mass loading) thiab Pd/C (5% mass loading) tau yuav los ntawm Sigma-Aldrich.
Kev tsim cov CoZn-ZIF nanocrystals tau ua tiav raws li cov txheej txheem yav dhau los nrog qee qhov kev hloov kho 23,64. Ua ntej, 30 mmol Zn (NO3) 2 · 6 H2O (8.925 g) thiab 3.5 mmol Co (NO3) 2 · 6 H2O (1.014 g) tau sib xyaw thiab yaj rau hauv 300 ml ntawm methanol. Tom qab ntawd, 120 mmol ntawm 2-methylimidazole (9.853 g) tau yaj rau hauv 100 ml ntawm methanol thiab ntxiv rau cov tshuaj saum toj no. Cov khoom sib xyaw tau do ntawm chav tsev kub rau 24 teev. Thaum kawg, cov khoom tau sib cais los ntawm centrifugation ntawm 6429 g rau 10 feeb thiab ntxuav kom huv si nrog methanol peb zaug. Cov hmoov ua tiav tau qhuav hauv lub tshuab nqus tsev ntawm 60 ° C ib hmos ua ntej siv.
Yuav kom ua tau Co-SAs/NPs@NC-950, cov hmoov CoZn-ZIF qhuav tau pyrolyzed ntawm 950 °C rau 1 teev hauv cov pa roj ntawm 6% H2 + 94% Ar, nrog rau qhov kub ntawm 5 °C/min. Tom qab ntawd cov qauv tau txias rau qhov kub hauv chav kom tau txais Co-SA/NPs@NC-950. Rau Co-SAs/NPs@NC-850 lossis Co-SAs/NPs@NC-750, qhov kub pyrolysis tau hloov pauv mus rau 850 thiab 750 °C, raws li. Cov qauv npaj tau siv tau yam tsis tas ua ntxiv, xws li acid etching.
Kev ntsuas TEM (transmission electron microscopy) tau ua tiav rau ntawm lub tshuab Thermo Fisher Titan Themis 60-300 "cube" microscope uas muaj lub tshuab kho duab thiab lub lens shaping 300 kV probe. Kev sim HAADF-STEM tau ua tiav los ntawm kev siv FEI Titan G2 thiab FEI Titan Themis Z microscopes uas muaj cov probes thiab cov tshuab kho duab, thiab DF4 plaub-segment detectors. Cov duab EDS elemental mapping kuj tau txais los ntawm lub tshuab FEI Titan Themis Z microscope. Kev tshuaj xyuas XPS tau ua tiav rau ntawm lub tshuab X-ray photoelectron spectrometer (Thermo Fisher qauv ESCALAB 250Xi). XANES thiab EXAFS Co K-edge spectra tau sau los ntawm kev siv lub rooj XAFS-500 (China Spectral Instruments Co., Ltd.). Cov ntsiab lus Co tau txiav txim siab los ntawm atomic absorption spectroscopy (AAS) (PinAAcle900T). Cov duab xoo hluav taws xob X-ray diffraction (XRD) tau raug kaw rau ntawm lub tshuab X-ray diffractometer (Bruker, Bruker D8 Advance, Lub Tebchaws Yelemees). Cov isotherms adsorption nitrogen tau txais los ntawm kev siv lub tshuab adsorption lub cev (Micromeritics, ASAP2020, Tebchaws USA).
Qhov kev tshuaj tiv thaiv dehydrogenation tau ua tiav hauv huab cua argon nrog cua raug tshem tawm raws li tus qauv Schlenk. Lub thawv tshuaj tiv thaiv tau raug tshem tawm thiab rov ua kom tiav nrog argon 6 zaug. Tig rau qhov dej condenser thiab ntxiv catalyst (30 mg) thiab cov kuab tshuaj (6 ml). Ua kom sov lub thawv rau qhov kub xav tau siv lub thermostat thiab cia nws sib npaug rau 30 feeb. Formic acid (10 mmol, 377 μL) tom qab ntawd tau ntxiv rau hauv lub thawv tshuaj tiv thaiv hauv qab argon. Tig lub qhov valve peb-txoj kev burette kom txo qhov siab ntawm lub reactor, kaw nws dua, thiab pib ntsuas qhov ntim ntawm cov roj tsim tawm siv lub burette phau ntawv (Daim Duab S16). Tom qab lub sijhawm xav tau rau qhov kev tshuaj tiv thaiv kom tiav, cov qauv roj tau sau rau GC kev tshuaj ntsuam siv lub koob txhaj tshuaj roj-tight purged nrog argon.
Cov kev sim DRIFT hauv qhov chaw tau ua tiav rau ntawm lub tshuab ntsuas Fourier transform infrared (FTIR) (Thermo Fisher Scientific, Nicolet iS50) uas muaj lub tshuab ntsuas mercury cadmium telluride (MCT). Cov hmoov catalyst tau muab tso rau hauv lub cell tshuaj tiv thaiv (Harrick Scientific Products, Praying Mantis). Tom qab kho cov catalyst nrog cov dej ntws ntawm Ar (50 ml/min) ntawm qhov kub thiab txias hauv chav, cov qauv tau raug cua sov rau qhov kub thiab txias, tom qab ntawd muab Ar (50 ml/min) npuas hauv cov kua HCOOH thiab nchuav rau hauv lub cell tshuaj tiv thaiv hauv qhov chaw. rau kev tiv thaiv. Qauv cov txheej txheem catalytic heterogeneous. Cov spectra infrared tau raug kaw ntawm lub sijhawm sib txawv ntawm 3.0 vib nas this mus rau 1 teev.
HCOOH, DCOOH, HCOOD thiab DCOOD yog siv ua cov substrates hauv propylene carbonate. Cov xwm txheej seem sib xws rau cov txheej txheem HCOOH dehydrogenation.
Cov kev suav thawj zaug tau ua tiav los ntawm kev siv lub hauv paus ntsiab lus ntawm kev ua haujlwm ceev hauv Vienna Ab initio modeling package (VASP 5.4.4) 65,66. Lub cell superunit nrog lub ntsej muag graphene (5 × 5) nrog qhov ntev transverse ntawm kwv yees li 12.5 Å tau siv ua lub substrate rau CoN2C2 thiab CoN2C2-Co6. Qhov nrug ntawm ntau dua 15 Å tau ntxiv kom tsis txhob muaj kev sib cuam tshuam ntawm cov khaubncaws sab nraud povtseg uas nyob ib sab. Kev sib cuam tshuam ntawm ions thiab electrons tau piav qhia los ntawm txoj kev projected amplified wave (PAW) method65,67. Lub Perdue-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) function nrog van der Waals correction uas Grimm68,69 tau siv. Cov qauv sib sau ua ke rau tag nrho lub zog thiab lub zog yog 10−6 eV/atom thiab 0.01 eV/Å. Lub zog txiav tawm tau teeb tsa ntawm 600 eV siv Monkhorst-Pack 2 × 2 × 1 K-point grid. Lub pseudopotential siv hauv tus qauv no yog tsim los ntawm kev teeb tsa hluav taws xob mus rau hauv C 2s22p2 xeev, N 2s22p3 xeev, Co 3d74s2 xeev, H 1 s1 xeev, thiab O 2s22p4 xeev. Lub zog adsorption thiab qhov sib txawv ntawm electron density yog xam los ntawm kev rho tawm lub zog ntawm cov roj theem thiab cov hom nto los ntawm lub zog ntawm lub kaw lus adsorbed raws li adsorption lossis interface qauv 70,71,72,73,74. Kev kho Gibbs dawb zog yog siv los hloov DFT zog mus rau hauv Gibbs dawb zog thiab coj mus rau hauv tus account vibrational contributions rau entropy thiab xoom point zog 75. Txoj kev ascending image-nudging elastic band (CI-NEB) tau siv los tshawb nrhiav lub xeev hloov pauv ntawm cov tshuaj tiv thaiv 76.
Tag nrho cov ntaub ntawv tau txais thiab tshuaj xyuas thaum lub sijhawm kawm no suav nrog hauv tsab xov xwm thiab cov ntaub ntawv ntxiv lossis muaj los ntawm tus sau ntawv sib xws thaum thov. Cov ntaub ntawv qhov chaw tau muab rau tsab xov xwm no.
Tag nrho cov code siv hauv kev ua qauv qhia nrog tsab xov xwm no muaj los ntawm cov kws sau ntawv sib xws thaum thov.
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