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Ukuthuthukiswa kobuchwepheshe be-hydrogen kusenhliziyweni yomnotho oluhlaza. Njengemfuneko yokuqala kokugcina i-hydrogen, kudingeka ama-catalyst asebenzayo nazinzile okusabela kwe-hydrogenation (de)hydrogenation. Kuze kube manje, le ndawo ibilokhu ibuswa ukusetshenziswa kwezinsimbi eziyigugu ezibizayo. Lapha, siphakamisa i-catalyst entsha eshibhile esekelwe ku-cobalt (Co-SAs/NPs@NC) lapho izindawo zensimbi eyodwa ezisatshalaliswa kakhulu zihlanganiswa khona ngokubambisana nama-nanoparticles amahle ukuze kufezwe i-formic acid dehydrogenation ephumelelayo. Kusetshenziswa izinto ezinhle kakhulu zamayunithi e-CoN2C2 ahlakazekile nge-athomu kanye nama-nanoparticles ahlanganisiwe anobukhulu obungu-7-8 nm, kusetshenziswa i-propylene carbonate njenge-solvent, kwatholakala ukukhiqizwa kwegesi okuhle kakhulu okungu-1403.8 ml g-1 h-1, futhi akukho ukulahleka ngemva kwemijikelezo emi-5. umsebenzi, ongcono ngokuphindwe ka-15 kune-Pd/C yokuhweba. Ukuhlolwa kokuhlolwa kwendawo kubonisa ukuthi, uma kuqhathaniswa ne-athomu yensimbi eyodwa ehlobene kanye nama-catalyst e-nanoparticle, i-Co-SAs/NPs@NC ithuthukisa ukumuncwa kanye nokusebenza kwe-key monodentate intermediate HCOO*, ngaleyo ndlela ikhuthaze ukuhlukana kwe-CH bond okulandelayo. Izibalo zethiyori zibonisa ukuthi ukuhlanganiswa kwama-cobalt nanoparticles kukhuthaza ukuguqulwa kwesikhungo se-d-band se-athomu ye-Co eyodwa ibe yindawo esebenzayo, ngaleyo ndlela kuthuthukiswe ukuhlangana phakathi kwe-carbonyl O ye-HCOO* intermediate kanye nesikhungo se-Co, ngaleyo ndlela kunciphisa umgoqo wamandla.
I-hydrogen ibhekwa njengomthwali wamandla obalulekile ekushintsheni kwamandla emhlabeni jikelele kwamanje futhi ingaba umshayeli oyinhloko wokufeza ukungathathi hlangothi kwe-carbon1. Ngenxa yezakhiwo zayo ezibonakalayo njengokusha kanye nobuningi obuphansi, ukugcinwa okuphephile nokuphumelelayo kanye nokuthuthwa kwe-hydrogen kuyizinkinga ezibalulekile ekufezeni umnotho we-hydrogen2,3,4. Abathwali be-hydrogen ephilayo ewuketshezi (ama-LOHC), agcina futhi akhiphe i-hydrogen ngokusebenzisa ukusabela kwamakhemikhali, baphakanyiswe njengesixazululo. Uma kuqhathaniswa ne-hydrogen yama-molecule, izinto ezinjalo (i-methanol, i-toluene, i-dibenzyltoluene, njll.) kulula futhi kulula ukuziphatha5,6,7. Phakathi kwama-LOHC endabuko ahlukahlukene, i-formic acid (FA) inobuthi obuphansi (LD50: 1.8 g/kg) kanye nomthamo we-H2 ongu-53 g/L noma u-4.4 wt%. Okuphawulekayo ukuthi i-FA yiyona kuphela i-LOHC engagcina futhi ikhiphe i-hydrogen ngaphansi kwezimo ezithambile lapho kukhona ama-catalyst afanele, ngaleyo ndlela ingadingi ukufakwa kwamandla amakhulu angaphandle1,8,9. Eqinisweni, kuye kwaklanywa ama-catalyst amaningi ensimbi ahloniphekile ukuze kukhishwe i-formic acid, isibonelo, ama-catalyst asekelwe ku-palladium asebenza ngokuphindwe ka-50-200 kune-catalyst ensimbi engabizi kakhulu10,11,12. Kodwa-ke, uma ucabangela izindleko zezinsimbi ezisebenzayo, isibonelo, i-palladium ibiza ngokuphindwe kayi-1000.
I-Cobalt, Ukusesha ama-catalyst ensimbi asebenzayo kakhulu futhi azinzile kuyaqhubeka nokuheha isithakazelo sabacwaningi abaningi kwezemfundo kanye nezimboni13,14,15.
Nakuba ama-catalyst ashibhile asekelwe ku-Mo ne-Co, kanye nama-nanocatalyst enziwe ngama-alloy ensimbi ahloniphekile/ayisisekelo, 14,16 aklanyelwe ukususwa kwe-FA, ukususwa kwawo kancane kancane ngesikhathi sokusabela akunakugwenywa ngenxa yokuhlala kwezindawo ezisebenzayo zezinsimbi, i-CO2, ne-H2O ngama-proton noma ama-anion abumbayo (i-HCOO-), ukungcola kwe-FA, ukuhlanganiswa kwezinhlayiya kanye nobuthi be-CO obungaba khona 17,18. Thina nabanye muva nje sibonise ukuthi ama-catalyst e-athomu eyodwa (ama-SAC) anezindawo ze-CoIINx ezihlakazeke kakhulu njengezindawo ezisebenzayo athuthukisa ukusabela kanye nokumelana ne-asidi kokususwa kwe-asidi ye-formic uma kuqhathaniswa nama-nanoparticles 17,19,20,21,22,23,24. Kulezi zinto ze-Co-NC, ama-athomu e-N asebenza njengezindawo ezinkulu zokukhuthaza ukususwa kwe-FA ngenkathi kuthuthukiswa ukuzinza kwesakhiwo ngokusebenzisana ne-athomu ye-Co ephakathi, kuyilapho ama-athomu e-Co ehlinzeka ngezindawo zokufakwa kwe-H futhi ekhuthaza ukuqhekeka kwe-CH22, 25,26. Ngeshwa, umsebenzi kanye nokuqina kwalezi zikhuthazi kusalokhu kukude kakhulu nezikhuthazi zensimbi ezinhle zesimanje ezifanayo nezingafani (Isithombe 1) 13.
Amandla amaningi avela emithonjeni evuselelekayo njengelanga noma umoya angakhiqizwa yi-electrolysis yamanzi. I-hydrogen ekhiqizwayo ingagcinwa kusetshenziswa i-LOHC, uketshezi oluyi-hydrogenation kanye ne-dehydrogenation yalo okulungisekayo. Esinyathelweni sokukhishwa kwe-hydrogen, umkhiqizo okuwukuphela kwawo yi-hydrogen, bese uketshezi oluthwalayo lubuyiselwa esimweni salo sokuqala bese lufakwa i-hydrogen futhi. I-hydrogen ingasetshenziswa ekugcineni eziteshini zikaphethiloli, emabhethri, ezakhiweni zezimboni, nokuningi.
Muva nje, kubikwe ukuthi umsebenzi wangaphakathi wama-SAC athile ungathuthukiswa lapho kukhona ama-athomu ensimbi ahlukene noma izindawo ezengeziwe zensimbi ezinikezwa yizinhlayiya ezincane (NPs) noma ama-nanoclusters (NCs)27,28. Lokhu kuvula amathuba okumuncwa okwengeziwe kanye nokusebenza kwe-substrate, kanye nokuguqulwa kwe-geometry kanye nesakhiwo se-elekthronikhi sezindawo ze-monatomic. Ngakho-ke, ukumuncwa/ukusebenza kwe-substrate kungenziwa ngcono, kuhlinzeke ngokusebenza kahle kwe-catalytic okuphelele29,30. Lokhu kusinika umbono wokudala izinto ezifanele ze-catalytic ezinezindawo ezisebenzayo ze-hybrid. Nakuba ama-SAC athuthukisiwe ebonise amandla amakhulu ezinhlobonhlobo zezicelo ze-catalytic, indima yawo ekugcinweni kwe-hydrogen, ngokwazi kwethu, ayicaci. Kulokhu, sibika isu eliguquguqukayo neliqinile lokuhlanganiswa kwama-catalyst asekelwe ku-cobalt (Co-SAs/NPs@NCs) aqukethe izinhlayiya ezincane ezichaziwe kanye nezikhungo zensimbi ngazinye. Ama-Co-SA/NPs@NC alungiselelwe kahle abonisa ukusebenza okuhle kakhulu kwe-formic acid dehydrogenation, okungcono kune-catalysts ezingezona ezihloniphekile (njenge-CoNx, ama-athomu e-cobalt angawodwa, i-cobalt@NC kanye ne-γ-Mo2N) kanye nama-catalysts ensimbi ahloniphekile. Ukuchaza okungaphakathi kanye nokubalwa kwe-DFT kwama-catalysts asebenzayo kukhombisa ukuthi izindawo zensimbi ngazinye zisebenza njengezindawo ezisebenzayo, kanti ama-nanoparticles alesi sisungulo athuthukisa isikhungo se-d-band sama-athomu e-Co, akhuthaza ukumuncwa nokusebenza kwe-HCOO*, ngaleyo ndlela ehlisa isithiyo samandla sempendulo.
Ama-Zeolite imidazolate frameworks (ama-ZIF) ayizinto ezichazwe kahle ezinezici ezintathu ezinikeza ama-catalyst wezinto ze-carbonaceous ezifakwe i-nitrogen (ama-catalyst ensimbi-NC) ukusekela izinhlobo ezahlukene zezinsimbi37,38. Ngakho-ke, i-Co(NO3)2 kanye ne-Zn(NO3)2 kuhlangana ne-2-methylimidazole ku-methanol ukwakha ama-complex ensimbi ahambisanayo kusisombululo. Ngemva kokufakwa kwe-centrifugation nokomisa, i-CoZn-ZIF yashiswa nge-pyrolyzed emazingeni okushisa ahlukene (750–950 °C) emoyeni ongu-6% H2 kanye no-94% Ar. Njengoba kuboniswe esithombeni esingezansi, izinto ezitholakalayo zinezici ezahlukene zesayithi ezisebenzayo futhi zibizwa ngokuthi i-Co-SAs/NPs@NC-950, i-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 (Isithombe 2a). ). Ukubonwa okuqondile kokuhlolwa kwezinyathelo ezithile ezibalulekile enkambisweni yokwenziwa kuchazwe kabanzi kuZithombe 1 kanye no-2. C1-C3. Kwenziwa i-diffraction ye-X-ray yempuphu yokushisa eguquguqukayo (VTXRD) ukuze kuqashwe ukuvela kwe-catalyst. Ngemva kokuba izinga lokushisa le-pyrolysis lifinyelele ku-650 °C, iphethini ye-XRD ishintsha kakhulu ngenxa yokuwa kwesakhiwo sekristalu esihleliwe se-ZIF (Isithombe S4) 39. Njengoba izinga lokushisa likhula ngokwengeziwe, kuvela iziqongo ezimbili ezibanzi kumaphethini e-XRD e-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 ku-20–30° kanye no-40–50°, okumelela isiqongo sekhabhoni engenasimo (Isithombe C5). 40. Kuyafaneleka ukuqaphela ukuthi iziqongo ezintathu kuphela eziphawulekayo ezibonwe ku-44.2°, 51.5° kanye no-75.8°, okunge-cobalt yensimbi (JCPDS #15-0806), kanye no-26.2°, okunge-graphitic carbon (JCPDS # 41-1487). I-spectrum ye-X-ray ye-Co-SAs/NPs@NC-950 ikhombisa ukuba khona kwama-nanoparticles e-cobalt afakwe njenge-graphite ku-catalyst41,42,43,44. I-spectrum ye-Raman ikhombisa ukuthi ama-Co-SAs/NPs@NC-950 abonakala eneziqongo ze-D ne-G eziqinile futhi ezincane kunezinye izibonelo, okubonisa izinga eliphakeme le-graphitization (Isithombe S6). Ngaphezu kwalokho, ama-Co-SAs/NPs@NC-950 abonisa indawo ephezulu ye-Brunner-Emmett-Taylor (BET) kanye nevolumu ye-pore (1261 m2 g-1 kanye no-0.37 cm3 g-1) kunezinye izibonelo futhi ama-ZIF amaningi ayizinto ze-NC derivatives. (Isithombe S7 kanye neThebula S1). I-atomic absorption spectroscopy (AAS) ikhombisa ukuthi okuqukethwe yi-cobalt kwe-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@ kungu-2.69 wt%, 2.74 % wt. kanye no-2.73% wt. NC-750 ngokulandelana (Ithebula S2). Okuqukethwe yi-Zn kwe-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 kuyanda kancane kancane, okubangelwa ukwehliswa okukhuphukile kanye nokuguquguquka kwamayunithi e-Zn. Ukwanda kwezinga lokushisa le-pyrolysis (Zn, iphuzu lokubila = 907 °C) 45.46. Ukuhlaziywa kwe-elemental (EA) kubonise ukuthi iphesenti le-N liyancipha ngokushisa kwe-pyrolysis okwandayo, futhi okuqukethwe kwe-O2 ephezulu kungase kubangelwe ukumuncwa kwe-molecular O2 kusukela ekuchayweni emoyeni. (Ithebula S3). Ngokuqukethwe okuthile kwe-cobalt, ama-nanoparticles nama-coatom ahlukanisiwe ahlala ndawonye, ​​okuholela ekwandeni okukhulu komsebenzi we-catalyst, njengoba kuxoxwe ngakho ngezansi.
Umdwebo weskimu wokwenziwa kwe-Co-SA/NPs@NC-T, lapho i-T kuyizinga lokushisa le-pyrolysis (°C). b isithombe se-TEM. c Isithombe se-Co-SAs/NPs@NC-950 AC-HAADF-STEM. Ama-athomu e-Co ngamanye amakwe ngezindilinga ezibomvu. d Ithempulethi le-EDS Co-SA/NPs@NC-950.
Okuphawulekayo ukuthi i-transmission electron microscopy (TEM) ibonise ukuba khona kwama-cobalt nanoparticles (NPs) ahlukahlukene anobukhulu obumaphakathi obungu-7.5 ± 1.7 nm kuphela ku-Co-SA/NPs@NC-950 (Izithombe 2 b kanye ne-S8). Lawa ma-nanoparticles ahlanganiswe ne-graphite-like carbon efakwe i-nitrogen. Isikhala se-lattice fringe esingu-0.361 kanye no-0.201 nm sihambisana ne-graphitic carbon (002) kanye ne-metallic Co (111) particles, ngokulandelana. Ngaphezu kwalokho, i-annular averration-corrected annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) iveze ukuthi ama-Co NPs ku-Co-SAs/NPs@NC-950 ayezungezwe yi-atomic cobalt eningi (Isithombe 2c). Kodwa-ke, ama-athomu e-cobalt ahlakazekile nge-atomic kuphela abonwe ekusekelweni kwamanye amasampula amabili (Isithombe S9). Isithombe se-Energy dispersive spectroscopy (EDS) se-HAADF-STEM sibonisa ukusatshalaliswa okufanayo kwe-C, N, Co kanye ne-Co NPs ezihlukanisiwe ku-Co-SAs/NPs@NC-950 (Isithombe 2d). Yonke le miphumela ikhombisa ukuthi izikhungo ze-Co ezihlakazekile nge-athomu kanye nama-nanoparticles ahlanganiswe ku-N-doped graphite-like carbon anamathele ngempumelelo kuma-NC substrates ku-Co-SAs/NPs@NC-950, kuyilapho izikhungo zensimbi ezihlukanisiwe kuphela.
Isimo se-valence kanye nokwakheka kwamakhemikhali kwezinto ezitholiwe kwafundwa nge-X-ray photoelectron spectroscopy (XPS). Ama-XPS spectra ama-catalyst amathathu abonise ukuba khona kwezinto i-Co, i-N, i-C kanye ne-O, kodwa i-Zn yayikhona kuphela ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 (Umfanekiso 2). ). C10). Njengoba izinga lokushisa le-pyrolysis likhuphuka, okuqukethwe kwe-nitrogen okuphelele kwehla njengoba izinhlobo ze-nitrogen ziba ezingazinzile futhi zibola zibe amagesi e-NH3 kanye ne-NOx emazingeni okushisa aphezulu (Ithebula S4) 47. Ngakho-ke, okuqukethwe kwekhabhoni okuphelele kwanda kancane kancane kusuka ku-Co-SAs/NPs@NC-750 kuya ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-950 (Izithombe S11 kanye ne-S12). Isampula efakwe i-pyrolysis ekushiseni okuphezulu inesilinganiso esiphansi sama-athomu e-nitrogen, okusho ukuthi inani labathwali be-NC ku-Co-SAs/NPs@NC-950 kufanele libe ngaphansi kwalelo kwamanye amasampula. Lokhu kuholela ekushiseni okunamandla kwezinhlayiya ze-cobalt. I-spectrum ye-O1s ikhombisa iziqongo ezimbili ze-C=O (531.6 eV) kanye ne-C–O (533.5 eV), ngokulandelana (Isithombe S13) 48. Njengoba kuboniswe ku-Figure 2a, i-spectrum ye-N1s ingaxazululwa ibe yiziqongo ezine eziphawulekayo ze-pyridine nitrogen N (398.4 eV), i-pyrrole N (401.1 eV), i-graphite N (402.3 eV) kanye ne-Co-N (399.2 eV). Izibopho ze-Co-N zikhona kuzo zonke izibonelo ezintathu, okubonisa ukuthi amanye ama-athomu e-N ahlanganiswe nezindawo ze-monometallic, kodwa izici zihluka kakhulu49. Ukusetshenziswa kokushisa okuphezulu kwe-pyrolysis kunganciphisa kakhulu okuqukethwe kwezinhlobo ze-Co-N kusuka ku-43.7% ku-Co-SA/NPs@NC-750 kuya ku-27.0% ku-Co-SAs/NPs@NC-850 kanye ne-Co 17.6%@ NC-950. ku--CA/NPs, okuhambisana nokwanda kokuqukethwe kwe-C (Isithombe 3a), okubonisa ukuthi inombolo yabo yokuxhumanisa i-Co-N ingashintsha futhi ithathelwe indawo ngokwengxenye ngama-athomu e-C50. I-spectrum ye-Zn 2p ikhombisa ukuthi lesi sakhi sikhona kakhulu ngesimo se-Zn2+. (Isithombe S14) 51. I-spectrum ye-Co 2p ikhombisa iziqongo ezimbili ezivelele ku-780.8 kanye ne-796.1 eV, ezibangelwa yi-Co 2p3/2 kanye ne-Co 2p1/2, ngokulandelana (Isithombe 3b). Uma kuqhathaniswa ne-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750, i-peak ye-Co-N ku-Co-SAs/NPs@NC-950 ishintshelwa ohlangothini oluhle, okubonisa ukuthi i-athomu eyodwa ye-Co ebusweni -SAs/NPs@NC-950 inezinga eliphakeme lokuncipha kwama-electron, okuholela esimweni esiphezulu se-oxidation. Kuyaphawuleka ukuthi yi-Co-SAs/NPs@NC-950 kuphela ebonise ukuphakama okubuthakathaka kwe-zero-valent cobalt (Co0) ku-778.5 eV, okufakazela ukuba khona kwama-nanoparticles avela ekuhlanganisweni kwe-cobalt SA emazingeni okushisa aphezulu.
a N 1s kanye b Co 2p spectra ye-Co-SA/NPs@NC-T. c XANES kanye d FT-EXAFS spectra ye-Co-K-edge ye-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750. e WT-EXAFS contour plots ye-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850, kanye ne-Co-SAs/NPs@NC-750. f FT-EXAFS fitting curve ye-Co-SA/NPs@NC-950.
I-Time-locked X-ray absorption spectroscopy (XAS) yabe isisetshenziswa ukuhlaziya isakhiwo se-elekthronikhi kanye nendawo yokuxhumana kwezinhlobo ze-Co kusampula elungisiwe. Izimo ze-Cobalt valence ku-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 Isakhiwo se-Edge sembulwe ngokumuncwa kwe-X-ray okuseduze nensimu kwe-Co-K edge (XANES) spectrum evamile. Njengoba kuboniswe ku-Figure 3c, ukumuncwa eduze komphetho wamasampula amathathu kutholakala phakathi kwama-foil e-Co kanye ne-CoO, okubonisa ukuthi isimo se-valence sezinhlobo ze-Co sisukela ku-0 kuya ku-+253. Ngaphezu kwalokho, ukushintshela emandleni aphansi kwabonwa kusuka ku-Co-SAs/NPs@NC-950 kuya ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750, okubonisa ukuthi i-Co-SAs/NPs@NC-750 inesimo se-oxidation esiphansi. Ngokusho kwemiphumela yokuhlanganisa okuqondile, isimo se-Co valence se-Co-SAs/NPs@NC-950 silinganiselwa ku-+0.642, esingaphansi kwesimo se-Co valence se-Co-SAs/NPs@NC-850 (+1.376). Co-SA/NP @NC-750 (+1.402). Le miphumela ikhombisa ukuthi isimo se-oxidation esimaphakathi sezinhlayiya ze-cobalt ku-Co-SAs/NPs@NC-950 sincishisiwe kakhulu, okuhambisana nemiphumela ye-XRD kanye ne-HADF-STEM futhi kungachazwa ngokuba khona ndawonye kwezinhlayiya ze-cobalt nanoparticles kanye ne-cobalt eyodwa. Ama-athomu e-Co 41. I-spectrum yesakhiwo esihle sokumuncwa kwe-X-ray esishintshashintshayo (FT-EXAFS) se-Co K-edge ikhombisa ukuthi i-peak eyinhloko ku-1.32 Å ingeyegobolondo le-Co-N/Co-C, kuyilapho indlela yokuhlakazeka kwe-Co-Co yensimbi iku-2.18 kuphela kuma-Co-SA Å atholakala ku-/NPs@NC-950 (Isithombe 3d). Ngaphezu kwalokho, i-contour plot ye-wavelet transform (WT) ikhombisa i-maximum intensity ku-6.7 Å-1 ebangelwa yi-Co-N/Co-C, kuyilapho ama-Co-SA/NPs@NC-950 kuphela ekhombisa i-maximum intensity ku-8.8. Enye i-maximum intensity ku-Å−1 kwi-Co-Co bond (Isithombe 3e). Ngaphezu kwalokho, ukuhlaziywa kwe-EXAFS okwenziwe ngumqashi kubonise ukuthi emazingeni okushisa e-pyrolysis angu-750, 850 kanye no-950 °C, izinombolo zokuxhumanisa ze-Co-N zazingu-3.8, 3.2 kanye no-2.3, ngokulandelana, kanti izinombolo zokuxhumanisa ze-Co-C zazingu-0. 0.9 kanye no-1.8 (Isithombe 3f, S15 kanye neThebula S1). Ngokuqondile, imiphumela yakamuva ingabangelwa ukuba khona kwamayunithi e-CoN2C2 ahlakazekile nge-athomu kanye nama-nanoparticles ku-Co-SAs/NPs@NC-950. Ngokuphambene nalokho, ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750, amayunithi e-CoN3C kanye ne-CoN4 kuphela akhona. Kusobala ukuthi ngokushisa kwe-pyrolysis okwandayo, ama-athomu e-N kuyunithi ye-CoN4 athathelwa indawo kancane kancane ngama-athomu e-C, kanti ama-cobalt CA ahlangana ukuze akhe ama-nanoparticles.
Izimo zokusabela ezifundwe ngaphambilini zazisetshenziselwa ukutadisha umphumela wezimo zokulungiselela ezimpahleni zezinto ezahlukahlukene (Isithombe S16)17,49. Njengoba kuboniswe kuMfanekiso 4 a, umsebenzi we-Co-SAs/NPs@NC-950 uphakeme kakhulu kunowe-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750. Okuphawulekayo ukuthi wonke amasampula amathathu e-Co alungisiwe abonise ukusebenza okuphezulu uma kuqhathaniswa nama-catalyst ajwayelekile ensimbi eyigugu yezentengiselwano (i-Pd/C kanye ne-Pt/C). Ngaphezu kwalokho, amasampula e-Zn-ZIF-8 kanye ne-Zn-NC awazange asebenze ekuqedeni i-formic acid, okubonisa ukuthi izinhlayiya ze-Zn azizona izindawo ezisebenzayo, kodwa umphumela wazo emsebenzini awunamsebenzi. Ngaphezu kwalokho, umsebenzi we-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 wenziwe nge-pyrolysis yesibili ku-950°C ihora eli-1, kodwa wawuphansi kunowe-Co-SAs/NPs@NC-750. @NC-950 (Isithombe S17). Ukucaciswa kwesakhiwo salezi zinto kubonise ukuba khona kwama-nanoparticles e-Co kumasampula aphinde ahlanganiswa, kodwa indawo ephansi yobuso kanye nokungabikho kwe-carbon efana ne-graphite kuholele emsebenzini ophansi uma kuqhathaniswa ne-Co-SAs/NPs@NC-950 (Isithombe S18–S20). Umsebenzi wamasampula anamanani ahlukene we-Co precursor nawo uqhathaniswe, nomsebenzi ophezulu kakhulu oboniswe ekungezeni okungu-3.5 mol (Ithebula S6 kanye nesithombe S21). Kusobala ukuthi ukwakheka kwezikhungo zensimbi ezahlukahlukene kuthonywa okuqukethwe yi-hydrogen emoyeni we-pyrolysis kanye nesikhathi se-pyrolysis. Ngakho-ke, ezinye izinto ze-Co-SAs/NPs@NC-950 zahlolwa ngomsebenzi we-formic acid dehydrogenation. Zonke izinto zibonise ukusebenza okuphakathi kuya kokuhle kakhulu; noma kunjalo, azikho kuzo ezazingcono kune-Co-SAs/NPs@NC-950 (Izithombe S22 kanye ne-S23). Ukucaciswa kwesakhiwo sale nto kubonise ukuthi njengoba isikhathi se-pyrolysis sanda, okuqukethwe kwezikhundla ze-monoatomic Co-N kwehla kancane kancane ngenxa yokuhlanganiswa kwama-athomu ensimbi abe yizinhlayiya ezincane, okuchaza umehluko womsebenzi phakathi kwamasampula anesikhathi se-pyrolysis esingu-100-2000. umehluko. 0.5 h, 1 h, kanye namahora ama-2 (Izibalo S24–S28 kanye neThebula S7).
Igrafu yomthamo wegesi uma kuqhathaniswa nesikhathi esitholwe ngesikhathi sokukhishwa kwe-hydrogen kwezingxenye zikaphethiloli kusetshenziswa ama-catalyst ahlukahlukene. Izimo zokusabela: FA (10 mmol, 377 μl), i-catalyst (30 mg), i-PC (6 ml), i-Tback: 110 °C, i-Tactical: 98 °C, izingxenye ezi-4 b Co-SAs/NPs@NC-950 (30 mg), ama-solvent ahlukahlukene. c Ukuqhathaniswa kwamazinga okuvela kwegesi kwama-catalyst angafani kuma-solvent e-organic ku-85–110 °C. d Co-SA/NPs@NC-950 ukuhlolwa kokuvuselela. Izimo zokusabela: FA (10 mmol, 377 µl), Co-SAs/NPs@NC-950 (30 mg), i-solvent (6 ml), i-Tback: 110 °C, i-Tactical: 98 °C, umjikelezo ngamunye wokusabela uhlala ihora elilodwa. Amabha amaphutha amelela ukuphambuka okujwayelekile okubalwe kusukela ekuhlolweni okusebenzayo okuthathu.
Ngokuvamile, ukusebenza kahle kwama-catalyst e-FA dehydrogenation kuncike kakhulu ezimweni zokusabela, ikakhulukazi i-solvent esetshenziswayo8,49. Lapho kusetshenziswa amanzi njenge-solvent, i-Co-SAs/NPs@NC-950 ibonise izinga eliphezulu kakhulu lokusabela kokuqala, kodwa ukungasebenzi kwenzeke, mhlawumbe ngenxa yama-proton noma i-H2O18 ahlala ezindaweni ezisebenzayo. Ukuhlolwa kwe-catalyst kuma-solvent e-organic njenge-1,4-dioxane (DXA), i-n-butyl acetate (BAC), i-toluene (PhMe), i-triglyme kanye ne-cyclohexanone (CYC) nakho akubonisanga ukuthuthuka, kanye naku-propylene carbonate (PC)) (Isithombe 4b kanye neThebula S8). Ngokufanayo, izithasiselo ezifana ne-triethylamine (NEt3) noma i-sodium formate (HCCONA) azizange zibe nomthelela omuhle ekusebenzeni kwe-catalyst (Isithombe S29). Ngaphansi kwezimo zokusabela ezifanele, isivuno segesi sifinyelele ku-1403.8 mL g−1 h−1 (Isithombe S30), esasiphezulu kakhulu kunawo wonke ama-catalyst e-Co abikwe ngaphambilini (kufaka phakathi i-SAC17, 23, 24). Ezivivinyweni ezahlukahlukene, ngaphandle kokusabela emanzini kanye nezithasiselo ze-formate, ukukhetha kufikela ku-99.96% kokukhishwa kwe-hydrogen kanye nokuphelelwa amanzi emzimbeni kutholakale (Ithebula S9). Amandla okusebenza abaliwe angama-88.4 kJ/mol, okuqhathaniswa namandla okusebenza kwama-catalyst ensimbi ahloniphekile (Isithombe S31 kanye neThebula S10).
Ngaphezu kwalokho, siqhathanise ezinye izikhuthazi eziningi ezingafani zokukhishwa kwe-formic acid ngaphansi kwezimo ezifanayo (Isithombe 4c, amathebula S11 kanye ne-S12). Njengoba kuboniswe kuMfanekiso 3c, izinga lokukhiqizwa kwegesi le-Co-SAs/NPs@NC-950 lidlula elezikhuthazizi zensimbi eziyisisekelo ezingafani futhi liphakeme ngokuphindwe ka-15 kanye no-15 kunele-5% Pd/C yokuhweba kanye no-5% Pd/C, ngokulandelana. kanye. % Pt/C catalyst.
Isici esibalulekile sanoma yikuphi ukusetshenziswa okusebenzayo kwama-catalyst (de)hydrogenation ukuzinza kwawo. Ngakho-ke, kwenziwa uchungechunge lwezivivinyo zokuphinda usebenzise kabusha ezisebenzisa i-Co-SAs/NPs@NC-950. Njengoba kuboniswe ku-Figure 4 d, umsebenzi wokuqala kanye nokukhetha kwezinto akuzange kushintshe phakathi nokugijima okuhlanu okulandelanayo (bheka futhi iThebula S13). Ukuhlolwa kwesikhathi eside kwenziwa futhi ukukhiqizwa kwegesi kwanda ngokulandelana emahoreni angama-72 (Isithombe S32). Okuqukethwe kwe-cobalt kwe-Co-SA/NPs@NC-950 esetshenzisiwe kwakungu-2.5 wt%, okwakusondele kakhulu kokwe-catalyst entsha, okubonisa ukuthi kwakungekho ukugeleza okusobala kwe-cobalt (Ithebula S14). Akukho shintsho lombala olusobala noma ukuhlanganiswa kwezinhlayiya zensimbi okwabonwa ngaphambi nangemva kokusabela (Isithombe S33). I-AC-HAADF-STEM kanye ne-EDS yezinto ezisetshenziswe kuzivivinyo zesikhathi eside kubonise ukugcinwa kanye nokusabalala okufanayo kwezindawo zokuhlakazeka kwe-athomu futhi akukho zinguquko ezibalulekile zesakhiwo (Izithombe S34 kanye ne-S35). Iziqongo eziphawulekayo ze-Co0 ne-Co-N zisekhona ku-XPS, okufakazela ukuba khona kwe-Co NPs kanye nezindawo zensimbi ngazinye, okuqinisekisa nokuzinza kwe-catalyst ye-Co-SAs/NPs@NC-950 (Isithombe S36).
Ukuze kutholakale izindawo ezisebenzayo kakhulu ezibangela ukukhishwa kwe-formic acid, izinto ezikhethiwe ezinesikhungo sensimbi esisodwa kuphela (i-CoN2C2) noma i-Co NP zalungiswa ngokusekelwe ezifundweni zangaphambilini17. Uhlelo lomsebenzi wokukhishwa kwe-formic acid olubonwe ngaphansi kwezimo ezifanayo yi-Co-SAs/NPs@NC-950 > Co SA > Co NP (Ithebula S15), okubonisa ukuthi izindawo ze-CoN2C2 ezihlakazekile nge-athomu zisebenza kakhulu kune-NPs. I-reaction kinetics ikhombisa ukuthi ukuvela kwe-hydrogen kulandela i-first-order reaction kinetics, kodwa imithambeka yama-curve amaningana kokuqukethwe kwe-cobalt okuhlukile akufani, okubonisa ukuthi i-kinetics ayixhomekile kuphela ku-formic acid, kodwa futhi nasendaweni esebenzayo (Isithombe 2). C37). Izifundo ezengeziwe ze-kinetic zibonise ukuthi, uma kubhekwa ukungabikho kweziqongo zensimbi ye-cobalt ekuhlaziyweni kwe-X-ray diffraction, i-kinetic order yokusabela ngokwezinga le-cobalt itholakale ingu-1.02 emazingeni aphansi (ngaphansi kuka-2.5%), okubonisa ukusatshalaliswa okucishe kufane kwezikhungo ze-cobalt ze-monoatomic. main. indawo esebenzayo (imifanekiso S38 kanye ne-S39). Lapho okuqukethwe kwezinhlayiya ze-Co kufinyelela ku-2.7%, i-r iyanda ngokuzumayo, okubonisa ukuthi izinhlayiya ezincane zisebenzisana kahle nama-athomu ngamanye ukuze zithole umsebenzi ophakeme. Njengoba okuqukethwe kwezinhlayiya ze-Co kukhula ngokwengeziwe, ijika liba yi-nonlinear, elihlotshaniswa nokwanda kwenani lezinhlayiya ezincane kanye nokwehla kwezikhundla ze-monatomic. Ngakho-ke, ukusebenza okuthuthukisiwe kwe-LC dehydrogenation kwe-Co-SA/NPs@NC-950 kubangelwa ukuziphatha kokubambisana kwezindawo zensimbi ngazinye kanye nezinhlayiya ezincane.
Kwenziwa ucwaningo olujulile kusetshenziswa i-in situ diffuse reflectance Fourier transform (in situ DRIFT) ukuhlonza ama-reaction intermediates enkambisweni. Ngemva kokushisa amasampula emazingeni okushisa ahlukene okusabela ngemva kokufaka i-formic acid, kwabonwa amasethi amabili ama-frequency (Isithombe 5a). Iziqongo ezintathu eziphawulekayo ze-HCOOH* zivela ku-1089, 1217 kanye no-1790 cm-1, ezibangelwa ukudlidliza okunwebekayo kwe-CH π (CH) okungaphandle kwendiza, ukudlidliza okunwebekayo kwe-CO ν (CO) kanye nokudlidliza okunwebekayo kwe-C=O ν (C=O) , 54, 55 ngokulandelana . Elinye isethi leziqongo ku-1363 kanye no-1592 cm-1 lihambisana nokudlidliza kwe-OCO okulinganayo νs(OCO) kanye nokudlidliza okunwebekayo kwe-OCO okungavamile νas(OCO)33.56 HCOO*, ngokulandelana. Njengoba ukusabela kuqhubeka, iziqongo ezihlobene ze-HCOOH* kanye ne-HCOO* ziyancipha kancane kancane. Ngokuvamile, ukubola kwe-formic acid kuhilela izinyathelo ezintathu eziyinhloko: (I) ukumuncwa kwe-formic acid ezindaweni ezisebenzayo, (II) ukususwa kwe-H ngendlela ye-formate noma ye-carboxylate, kanye (III) ukuhlanganiswa kwe-H ezimbili ezimuncwe ukuze kukhiqizwe i-hydrogen. I-HCOO* kanye ne-COOH* yizinto ezibalulekile ekunqumeni izindlela ze-formate noma ze-carboxylate, ngokulandelana57. Esimisweni sethu se-catalytic, kuphela i-HCOO* peak ephawulekayo evele, okubonisa ukuthi ukubola kwe-formic acid kwenzeka kuphela ngendlela ye-formic acid58. Ukubonwa okufanayo kwenziwe emazingeni okushisa aphansi angu-78 °C kanye no-88 °C (umfanekiso S40).
I-In situ DRIFT spectra ye-HCOOH dehydrogenation ku-Co-SAs/NPs@NC-950 kanye ne-b Co SAs. Inganekwane ikhombisa izikhathi zokusabela endaweni. c Ukuguquguquka kwevolumu yegesi etholakala kusetshenziswa ama-reagents ahlukene okulebula ama-isotope. d Idatha yomphumela we-Kinetic isotope.
Ukuhlolwa okufanayo kwe-in situ DRIFT kwenziwe ezintweni ezihlobene i-Co NP kanye ne-Co SA ukuze kufundwe umphumela wokubambisana ku-Co-SA/NPs@NC-950 (Izithombe 5 b kanye ne-S41). Zombili izinto zibonisa izitayela ezifanayo, kodwa iziqongo zezimpawu ze-HCOOH* kanye ne-HCOO* zishintshile kancane, okubonisa ukuthi ukwethulwa kwe-Co NPs kushintsha isakhiwo se-elekthronikhi sesikhungo se-monoatomic. Isiqongo sezimpawu ze-νas(OCO) sivela ku-Co-SAs/NPs@NC-950 kanye ne-Co SA kodwa hhayi ku-Co NPs, okubonisa ukuthi okuphakathi okwakhiwe lapho kungezwa i-formic acid kuyi-monodentate formic acid eqondile ebusweni bosawoti. futhi inamathele ku-SA njengendawo esebenzayo 59. Kubalulekile ukuqaphela ukuthi kwabonakala ukwanda okukhulu kokudlidliza kweziqongo zezimpawu ze-π(CH) kanye ne-ν(C = O), okubonakala sengathi kwaholela ekuphambukeni kwe-HCOOH* futhi kwasiza ukusabela. Ngenxa yalokho, iziqongo eziphawulekayo ze-HCOOH* kanye ne-HCOO* ku-Co-SAs/NPs@NC zacishe zanyamalala ngemva kwemizuzu emi-2 yokusabela, okushesha kakhulu kune-monometallic (imizuzu eyi-6) kanye nama-catalyst asekelwe ku-nanoparticle (imizuzu eyi-12). . Yonke le miphumela iqinisekisa ukuthi i-nanoparticle doping ithuthukisa ukumuncwa kanye nokusebenza kwama-intermediate, ngaleyo ndlela isheshise ukusabela okuphakanyisiwe ngenhla.
Ukuze kuhlaziywe kabanzi indlela yokusabela nokunquma isinyathelo sokunquma izinga (RDS), umphumela we-KIE wenziwa phambi kwe-Co-SAs/NPs@NC-950. Lapha, kusetshenziswa ama-isotope e-formic acid ahlukene njenge-HCOOH, i-HCOOD, i-DCOOH kanye ne-DCOOD ezifundweni ze-KIE. Njengoba kuboniswe kuMfanekiso 5c, izinga lokuphelelwa yi-hydrogenation lehla ngokulandelana okulandelayo: i-HCOOH > i-HCOOD > i-DCOOH > i-DCOOD. Ngaphezu kwalokho, amanani abaliwe e-KHCOOH/KHCOOD, i-KHCOOH/KDCOOH, i-KHCOOD/KDCOOD kanye ne-KDCOOH/KDCOOD ayengu-1.14, 1.71, 2.16 kanye no-1.44, ngokulandelana (Umfanekiso 5d). Ngakho-ke, ukuhlukana kwe-CH bond ku-HCOO* kubonisa amanani e-kH/kD ​​>1.5, okubonisa umphumela omkhulu we-kinetic60,61, futhi kubonakala sengathi kumelela i-RDS ye-HCOOH dehydrogenation ku-Co-SAs/NPs@NC-950.
Ngaphezu kwalokho, kwenziwa izibalo ze-DFT ukuze kuqondwe umphumela wama-nanoparticles afakwe i-doped emsebenzini wangaphakathi we-Co-SA. Amamodeli e-Co-SAs/NPs@NC kanye ne-Co-SA akhiwe ngokusekelwe ekuhlolweni okubonisiwe kanye nemisebenzi yangaphambilini (Izithombe 6a kanye ne-S42)52,62. Ngemva kokulungiswa kwe-geometric, ama-nanoparticles amancane e-Co6 (CoN2C2) ahambisana namayunithi e-monoatomic atholakale, kanti ubude bezibopho ze-Co-C kanye ne-Co-N ku-Co-SA/NPs@NC batholakala ukuthi bungu-1.87 Å kanye no-1.90 Å, ngokulandelana. , okuhambisana nemiphumela ye-XAFS. I-calculated partial density of states (PDOS) ikhombisa ukuthi i-single Co metal atom kanye ne-nanoparticle composite (Co-SAs/NPs@NC) zibonisa i-hybridization ephezulu eduze kwezinga le-Fermi uma kuqhathaniswa ne-CoN2C2, okuholela ku-HCOOH. Ukudluliselwa kwe-electron okubolayo kusebenza kahle kakhulu (Izithombe 6b kanye ne-S43). Izikhungo ze-d-band ezihambisanayo ze-Co-SAs/NPs@NC kanye ne-Co-SA zibalwe njenge--0.67 eV kanye ne--0.80 eV, ngokulandelana, phakathi kwazo ukwanda kwe-Co-SAs/NPs@NC kwaba yi-0.13 eV, okwabangela ukuthi ngemva kokwethulwa kwe-NP, ukumuncwa kwezinhlayiya ze-HCOO* ngesakhiwo se-elekthronikhi esiguquliwe se-CoN2C2 kwenzeka. Umehluko ekubunjweni kweshaja ukhombisa ifu elikhulu le-electron elizungeze ibhulokhi le-CoN2C2 kanye ne-nanoparticle, okubonisa ukusebenzisana okuqinile phakathi kwazo ngenxa yokushintshana kwama-electron. Kuhlanganiswe nokuhlaziywa kweshaja ye-Bader, kutholakale ukuthi i-Co ehlakazekile nge-athomu ilahlekelwe yi-1.064e ku-Co-SA/NPs@NC kanye ne-0.796e ku-Co SA (Isithombe S44). Le miphumela ikhombisa ukuthi ukuhlanganiswa kwezinhlayiya ze-nano kuholela ekunciphiseni ama-electron kwezindawo ze-Co, okuholela ekwandeni kwe-Co valence, okuhambisana nemiphumela ye-XPS (Isithombe 6c). Izici zokusebenzisana kwe-Co-O zokufakwa kwe-HCOO ku-Co-SAs/NPs@NC kanye ne-Co SA zihlaziywe ngokubala iqembu le-Hamiltonian eliyi-crystalline (COHP)63. Njengoba kuboniswe ku-Figure 6 d, amanani angalungile nakahle e--COHP ahambelana nesimo sokuvimbela ukuboshwa kanye nesimo sokubopha, ngokulandelana. Amandla esibopho se-Co-O afakwe yi-HCOO (Co-carbonylOH HCOO*) ahlolwe ngokuhlanganisa amanani e--COHP, ayengu-3.51 no-3.38 e-Co-SAs/NPs@NC kanye ne-Co-SA, ngokulandelana. Ukufakwe kwe-HCOOH nakho kubonise imiphumela efanayo: ukwanda kwenani elihlanganisiwe le--COHP ngemuva kokufakwa kwe-nanoparticle kubonise ukwanda kokuhlanganiswa kwe-Co-O, ngaleyo ndlela kukhuthaze ukusebenza kwe-HCOO kanye ne-HCOOH (Figure S45).
Isakhiwo se-lattice se-Co-SA/NPs@NC-950. b PDOS Co-SA/NP@NC-950 kanye ne-Co SA. c i-isosurface ye-3D yomehluko ekubuneni kwe-charge ye-adsorption ye-HCOOH ku-Co-SA/NPs@NC-950 kanye ne-Co-SA. (d) i-pCOHP yamabhondi e-Co-O afakwe yi-HCOO ku-Co-SA/NPs@NC-950 (kwesobunxele) kanye ne-Co-SA (kwesokudla). e Indlela yokusabela kwe-HCOOH dehydrogenation ku-Co-SA/NPs@NC-950 kanye ne-Co-SA.
Ukuze kuqondwe kangcono ukusebenza okuphezulu kokukhishwa kwe-hydrogenation kwe-Co-SA/NPs@NC, kwasungulwa indlela yokusabela kanye namandla. Ngokukhethekile, ukukhishwa kwe-FA kuhilela izinyathelo ezinhlanu, okuhlanganisa ukuguqulwa kwe-HCOOH ibe yi-HCOOH*, i-HCOOH* ibe yi-HCOO* + H*, i-HCOO* + H* ibe yi-2H* + CO2*, i-2H* + CO2* ibe yi-2H* + CO2, kanye ne-2H* ku-H2 (Isithombe 6e). Amandla okufakwa kwama-molecule e-formic acid ebusweni be-catalyst ngokusebenzisa i-carbon oxygen aphansi kune-hydroxyl oxygen (Izithombe S46 kanye ne-S47). Ngemva kwalokho, ngenxa yamandla aphansi, i-adsorbate idlula ngokuhlukana kwe-OH bond ukuze yakhe i-HCOO* esikhundleni sokuhlukana kwe-CH bond ukuze yakhe i-COOH*. Ngesikhathi esifanayo, i-HCOO* isebenzisa i-monodentate adsorption, ekhuthaza ukuqhekeka kwezibopho kanye nokwakheka kwe-CO2 kanye ne-H2. Le miphumela ihambisana nokuba khona kwe-νas(OCO) peak in in situ DRIFT, okubonisa ukuthi ukuchithwa kwe-FA kwenzeka ngendlela ye-forme esifundweni sethu. Kubalulekile ukuqaphela ukuthi ngokwezilinganiso ze-KIE, ukuhlukaniswa kwe-CH kunesithiyo samandla okusabela esiphezulu kakhulu kunezinye izinyathelo zokusabela futhi simele i-RDS. Isithiyo samandla sohlelo lwe-catalyst lwe-Co-SAs/NPs@NC olungcono kakhulu lungaphansi ngo-0.86 eV kune-Co-SA (1.2 eV), okuthuthukisa kakhulu ukusebenza kahle kwe-dehydrogenation iyonke. Okuphawulekayo ukuthi ukuba khona kwama-nanoparticles kulawula isakhiwo se-elekthronikhi sezindawo ze-coactive ezihlakazekile nge-athomu, okuthuthukisa kakhulu ukumuncwa nokusebenza kwama-intermediates, ngaleyo ndlela kunciphisa isithiyo sokusabela futhi kukhuthaze ukukhiqizwa kwe-hydrogen.
Ngamafuphi, sibonisa okokuqala ukuthi ukusebenza kwe-catalytic kwama-catalyst okukhiqiza i-hydrogen kungathuthukiswa kakhulu ngokusebenzisa izinto ezinezikhungo ze-monometallic ezisatshalaliswe kakhulu kanye nama-nanoparticles amancane. Lo mqondo uqinisekiswe ngokuhlanganiswa kwama-catalyst ensimbi eyodwa-athomu asekelwe ku-cobalt aguqulwe ngama-nanoparticles (Co-SAs/NPs@NC), kanye nezinto ezihlobene nezikhungo zensimbi eyodwa kuphela (CoN2C2) noma i-Co NPs. Zonke izinto zalungiswa ngendlela elula ye-pyrolysis yesinyathelo esisodwa. Ukuhlaziywa kwesakhiwo kukhombisa ukuthi i-catalyst engcono kakhulu (Co-SAs/NPs@NC-950) iqukethe amayunithi e-CoN2C2 ahlakazekile nge-athomu kanye nama-nanoparticles amancane (7-8 nm) afakwe i-nitrogen kanye ne-graphite-like carbon. Inomkhiqizo omuhle kakhulu wegesi ofinyelela ku-1403.8 ml g-1 h-1 (H2:CO2 = 1.01:1), ukukhetha kwe-H2 kanye ne-CO okungu-99.96% futhi kungagcina umsebenzi oqhubekayo izinsuku eziningana. Umsebenzi walesi sikhuthazi udlula umsebenzi wama-catalyst athile e-Co SA kanye ne-Pd/C ngezikhathi ezi-4 nezingu-15, ngokulandelana. Ukuhlolwa kwe-DRIFT okukhona kukhombisa ukuthi uma kuqhathaniswa ne-Co-SA, i-Co-SAs/NPs@NC-950 ikhombisa ukumuncwa okunamandla kwe-monodentate kwe-HCOO*, okubalulekile endleleni ye-formete, kanye nama-nanoparticles e-dopant angakhuthaza ukusebenza kwe-HCOO* kanye nokusheshisa kwe-C-H. Ukuhlukana kwebhondi kwahlonzwa njenge-RDS. Izibalo zethiyori zibonisa ukuthi ukumuncwa kwe-Co NP kwandisa isikhungo se-d-band sama-athomu e-Co eyodwa ngo-0.13 eV ngokusebenzisana, kuthuthukisa ukumuncwa kwama-intermediate e-HCOOH* kanye ne-HCOO*, ngaleyo ndlela kunciphisa isithiyo sokuphendula kusuka ku-1.20 eV ye-Co SA kuya ku-0 .86 eV. Unesibopho sokusebenza okuvelele.
Ngokubanzi, lolu cwaningo luhlinzeka ngemibono yokuklama ama-catalyst ensimbi amasha e-athomu elilodwa futhi luthuthukisa ukuqonda kokuthi ungathuthukisa kanjani ukusebenza kwe-catalytic ngokusebenzisa umphumela wokubambisana wezikhungo zensimbi ezinobukhulu obuhlukene. Sikholelwa ukuthi le ndlela inganwetshwa kalula kwezinye izinhlelo eziningi ze-catalytic.
I-Co(NO3)2 6H2O (AR, 99%), i-Zn(NO3)2 6H2O (AR, 99%), i-2-methylimidazole (98%), i-methanol (99.5%), i-propylene carbonate (PC, 99%) ethanol (AR, 99.7%) ithengwe eMcLean, eShayina. I-Formic acid (HCOOH, 98%) ithengwe eRhawn, eShayina. Zonke izithasiselo zasetshenziswa ngqo ngaphandle kokuhlanzwa okwengeziwe, futhi amanzi amsulwa kakhulu alungiswa kusetshenziswa uhlelo lokuhlanza oluhlanzekile kakhulu. I-Pt/C (ukulayisha isisindo okungu-5%) kanye ne-Pd/C (ukulayisha isisindo okungu-5%) kuthengwe eSigma-Aldrich.
Ukwenziwa kwama-nanocrystals e-CoZn-ZIF kwenziwa ngokusekelwe ezindleleni zangaphambilini ngezinguquko ezithile23,64. Okokuqala, ama-30 mmol Zn(NO3)2·6H2O (8.925 g) kanye nama-3.5 mmol Co(NO3)2·6H2O (1.014 g) axutshwa futhi ancibilikiswa ku-300 ml ye-methanol. Ngemuva kwalokho, ama-120 mmol e-2-methylimidazole (9.853 g) ancibilikiswa ku-100 ml ye-methanol futhi afakwa esixazululweni esingenhla. Ingxube yavuselelwa ekushiseni kwegumbi amahora angama-24. Ekugcineni, umkhiqizo wahlukaniswa nge-centrifugation ku-6429 g imizuzu eyi-10 futhi wagezwa kahle nge-methanol kathathu. Impushana eyaphuma yomiswa ku-vacuum ku-60°C ubusuku bonke ngaphambi kokusetshenziswa.
Ukuze kuhlanganiswe i-Co-SAs/NPs@NC-950, impuphu ye-CoZn-ZIF eyomile yashiswa ku-950 °C ihora eli-1 ekugelezeni kwegesi okungu-6% H2 + 94% Ar, ngesilinganiso sokushisa esingu-5 °C/min. Isampula yabe isipholiswa ekushiseni kwegumbi ukuze kutholakale i-Co-SA/NPs@NC-950. Ku-Co-SAs/NPs@NC-850 noma i-Co-SAs/NPs@NC-750, izinga lokushisa le-pyrolysis lashintshwa laba ngu-850 no-750 °C, ngokulandelana. Amasampula alungiselelwe angasetshenziswa ngaphandle kokucutshungulwa okwengeziwe, njengokuchoboza i-asidi.
Izilinganiso ze-TEM (transmission electron microscopy) zenziwe kuma-microscope e-Thermo Fisher Titan Themis 60-300 “cube” afakwe i-aberration corrector yokuthwebula izithombe kanye nelensi yokubumba i-probe engu-300 kV. Ukuhlolwa kwe-HAADF-STEM kwenziwa kusetshenziswa ama-microscope e-FEI Titan G2 kanye ne-FEI Titan Themis Z afakwe ama-probe kanye nama-photo corrector, kanye nama-detector e-DF4 anezingxenye ezine. Izithombe ze-EDS elemental mapping nazo zitholakale kuma-microscope e-FEI Titan Themis Z. Ukuhlaziywa kwe-XPS kwenziwe kuma-spectrometer e-photoelectron e-X-ray (imodeli ye-Thermo Fisher i-ESCALAB 250Xi). Ama-spectra e-XANES kanye ne-EXAFS e-Co K-edge aqoqwe kusetshenziswa ithebula le-XAFS-500 (i-China Spectral Instruments Co., Ltd.). Okuqukethwe kwe-Co kunqunywe yi-atomic absorption spectroscopy (AAS) (PinAAcle900T). Ama-spectra e-X-ray diffraction (XRD) aqoshwe ku-X-ray diffractometer (Bruker, Bruker D8 Advance, Germany). Ama-isotherm e-nitrogen adsorption atholakale kusetshenziswa idivayisi ye-physical adsorption (Micromeritics, ASAP2020, USA).
Ukusabela kokukhishwa kwamanzi emzimbeni kwenziwa endaweni ye-argon nomoya ususiwe ngokwendlela ejwayelekile ye-Schlenk. Umkhumbi wokusabela wakhishwa futhi wagcwaliswa nge-argon izikhathi ezingu-6. Vula ukunikezwa kwamanzi e-condenser bese ufaka i-catalyst (30 mg) kanye ne-solvent (6 ml). Shisisa isitsha ekushiseni okufunekayo usebenzisa i-thermostat bese usivumela ukuthi silingane imizuzu engama-30. I-Formic acid (10 mmol, 377 μL) yabe isingezwa esitsheni sokusabela ngaphansi kwe-argon. Phendula i-valve ye-burette enezindlela ezintathu ukuze unciphise ukucindezela kwe-reactor, uyivale futhi, bese uqala ukulinganisa umthamo wegesi ekhiqizwa usebenzisa i-burette yesandla (Isithombe S16). Ngemva kwesikhathi esidingekayo ukuze ukusabela kuqedwe, isampula yegesi yaqoqwa ukuze kuhlaziywe i-GC kusetshenziswa i-syringe engangenisi igesi ehlanzwe nge-argon.
Ukuhlolwa kokukhukhuleka endaweni ethile kwenziwa ku-spectrometer ye-Fourier transform infrared (FTIR) (Thermo Fisher Scientific, Nicolet iS50) efakwe i-mercury cadmium telluride (MCT) detector. I-catalyst powder yafakwa kuseli yokusabela (Harrick Scientific Products, Praying Mantis). Ngemva kokwelapha i-catalyst ngomfudlana we-Ar (50 ml/min) ekushiseni kwegumbi, isampula yashiswa yafinyelela ekushiseni okunikeziwe, yabe isifakwa amabhamuza nge-Ar (50 ml/min) kusisombululo se-HCOOH yabe isithululelwa kuseli yokusabela endaweni ethile. ukuze kutholakale ukusabela. Imodeli yezinqubo ze-catalytic ezingafani. Ama-spectra e-infrared aqoshwa ngezikhathi ezisukela kumasekhondi angu-3.0 kuya ehoreni eli-1.
I-HCOOH, i-DCOOH, i-HCOOD kanye ne-DCOOD kusetshenziswa njengezinto ezisetshenziswa ku-propylene carbonate. Izimo ezisele zihambisana nenqubo yokukhipha i-hydrogenation ye-HCOOH.
Izibalo zezimiso zokuqala zenziwe kusetshenziswa uhlaka lwethiyori yokusebenza kobuningi ngaphakathi kwephakheji yokumodela ye-Vienna Ab initio (VASP 5.4.4) 65,66. Iseli le-superunit elinobuso be-graphene (5 × 5) elinobukhulu obuphambene obungaba ngu-12.5 Å lasetshenziswa njenge-substrate ye-CoN2C2 kanye ne-CoN2C2-Co6. Ibanga le-vacuum elingaphezu kuka-15 Å lanezelwa ukuze kugwenywe ukusebenzisana phakathi kwezingqimba ze-substrate eziseduze. Ukusebenzisana phakathi kwama-ion nama-electron kuchazwa ngendlela ye-projected amplified wave (PAW) 65,67. Umsebenzi we-Perdue-Burke-Ernzerhoff (PBE) generalized gradient approximation (GGA) ophakanyiswe yi-Grimm nge-van der Waals correction68,69 wasetshenziswa. Izindlela zokuhlangana zamandla aphelele kanye namandla ziyi-10−6 eV/athomu kanye ne-0.01 eV/Å. Ukunqunywa kwamandla kubekwe ku-600 eV kusetshenziswa igridi ye-Monkhorst-Pack 2 × 2 × 1 K-point. Amandla angabonakali asetshenziswe kulo modeli akhiwe kusukela ekucushweni kwe-elekthronikhi kuya esimweni se-C 2s22p2, isimo se-N 2s22p3, isimo se-Co 3d74s2, isimo se-H 1 s1, kanye nesimo se-O 2s22p4. Amandla okumunca kanye nomehluko wobuningi bama-electron kubalwa ngokususa amandla esigaba segesi kanye nezinhlobo zobuso emandleni esistimu emuncayo ngokuya ngamamodeli okumunca noma esibonakalayo70,71,72,73,74. Ukulungiswa kwamandla amahhala e-Gibbs kusetshenziselwa ukuguqula amandla e-DFT abe amandla amahhala e-Gibbs futhi kucatshangelwa iminikelo yokudlidliza ku-entropy kanye namandla e-zero point75. Indlela ye-ascending image-nudging elastic band (CI-NEB) yasetshenziswa ukusesha isimo sokuguquka kwe-reaction76.
Yonke idatha etholwe futhi yahlaziywa phakathi nalolu cwaningo ifakiwe esihlokweni kanye nezinto ezengeziwe noma iyatholakala kumbhali ohambisanayo uma kucelwa ngokufanele. Idatha yomthombo inikezwe kulesi sihloko.
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