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Ukuthuthukiswa kwethekhnoloji ye-hydrogen kusenhliziyweni yomnotho ohlaza. Njengombandela wokufezekisa ukugcinwa kwe-hydrogen, iinsetjenziswa ezisebenzako nezinzileko zokuphendula kwe-hydrogenation (de)hydrogenation ziyatlhogeka. Bekube nje, indawo le beyibuswa kusetjenziswa kweensimbi ezibizako ezibizako. Lapha, siphakamisa i-catalyst entsha ebiza kancani esekelwe ku-cobalt (i-Co-SAs/NPs@NC) lapho amasayithi we-single-metal asabalaliswe khulu ahlanganiswe ngokubambisana nama-nanoparticles amancani ukufikelela i-formic acid dehydrogenation esebenzako. Ngokusebenzisa izinto ezihle khulu zamayunithi we-CoN2C2 ahlakazwe ngama-athomu kanye nama-nanoparticles ahlanganisiweko we-7-8 nm, kusetjenziswa i-propylene carbonate njenge-solvent, kwatholakala ukukhiqizwa kwegesi okuhle khulu kwe-1403.8 ml g-1 h-1, begodu akukho ukulahlekelwa ngemva kwemijikelezo emi-5. umsebenzi, ongcono ka-15 kune-Pd/C yokuthengisa. Iimhloliso ze-in situ assay zitjengisa bona, nayiqathaniswa ne-athomu yensimbi eyodwa kanye nama-nanoparticle catalysts, i-Co-SAs/NPs@NC ikhulisa ukumuncwa nokusebenza kwe-HCOO* ephakathi kwe-monodentate eqakathekileko, ngaleyindlela ikhuthaze ukuhlukaniswa kwe-CH bond. Iimbalo zethiyori zitjengisa bona ukuhlanganiswa kwama-cobalt nanoparticles kukhuthaza ukutjhugululwa kwesikhungo se-d-band se-athomu eyodwa ye-Co ibe yindawo esebenzako, ngaleyo ndlela kuthuthukise ukuhlanganiswa hlangana ne-carbonyl O ye-HCOO* ephakathi nesikhungo se-Co, ngaleyindlela kwehlisa isithiyo samandla.
I-hydrogen ithathwa njengesithwali samandla esiqakathekileko sokutjhuguluka kwamandla wephasi loke begodu ingaba mtjhayeli omkhulu wokufikelela ukungathathi hlangothi kwekhabhoni1. Ngebanga lezakhiwo zayo ezifana nokuvutha nokuminyana okuphasi, ukugcinwa nokuthuthwa kwe-hydrogen okuphephileko nokuphumelelako ziindaba eziqakathekileko ekufezekiseni umnotho we-hydrogen2,3,4. Iinthwali ze-hydrogen eziphilako (ama-LOHC), ezigcina begodu zikhuphe i-hydrogen ngokusebenzisa ukusabela kwamakhemikhali, ziphakanyiswe njengesisombululo. Nayiqathaniswa ne-molecular hydrogen, izinto ezinjalo (i-methanol, i-toluene, i-dibenzyltoluene, njll.) zilula begodu zilula ukuziphatha5,6,7. Hlangana nama-LOHC ahlukahlukeneko wesintu, i-formic acid (FA) inobuthi obuphasi (LD50: 1.8 g/kg) kanye ne-H2 capacity ye-53 g/L nofana i-4.4 wt%. Ngokuphawulekako, i-FA ngiyo kwaphela i-LOHC engabulunga begodu ikhuphe i-hydrogen ngaphasi kweemeko ezilula lokha nakukhona iintjhukumisi ezifaneleko, lokho kungatlhogi amandla amanengi wangaphandle1,8,9. Kuhlekuhle, iinsetjenziswa ezinengi zensimbi ezihle zithuthukiswe ukwenzela ukukhipha i-hydrogenation ye-formic acid, isibonelo, iintjhukumisi ezisekelwe ku-palladium zisebenza kanengi kanengi ukudlula iintjhukumisi zensimbi ezingabiziko10,11,12. Kodwana, nangabe ucabangela iindleko zeensimbi ezisebenzako, ngokwesibonelo, i-palladium ibiza ngaphezu kweenkhathi eziyi-1000.
I-Cobalt, Ukufunwa kwama-catalysts we-base metal asebenza khulu begodu azinzileko kuragela phambili nokudosa ikareko yabarhubhululi abanengi bezefundo nezebubulo13,14,15.
Nanyana ama-catalysts angabiziko asekelwe ku-Mo no-Co, kanye nama-nanocatalysts enziwe nge-noble/base metal alloys,14,16 athuthukiswe ukukhipha i-FA, ukuvalwa kwawo kancanikancani ngesikhathi sokusabela akunakugwemeka ngebanga lokuhlala eendaweni ezisebenzako zeensimbi, i-CO2, ne-H2O ngamaphrothoni. nofana ama-anions we-formate (HCOO-), ukusilaphazeka kwe-FA, ukuhlanganiswa kweenhlayiya kanye nokutjhejwa kwe-CO okungenzeka17,18. Thina nabanye mhlapha nje sitjengise bona ama-single-atom catalysts (ama-SAC) anamasayithi we-CoIINx asakazeke khulu njengeendawo ezisebenzako athuthukisa ukusabela nokujamelana ne-esidi ye-formic acid dehydrogenation nayiqathaniswa nama-nanoparticles17,19,20,21,22,23,24. Kulezi zinto ze-Co-NC, ama-athomu we-N asebenza njengeendawo ezikulu zokukhuthaza ukususwa kweprothoni ye-FA ngesikhathi kuthuthukisa ukuzinza kwesakhiwo ngokusebenzisana ne-athomu ye-Co ephakathi, ngesikhathi ama-athomu we-Co anikela ngeendawo zokudonsa i-H begodu akhuthaza ukuhlukana kwe-CH22, 25,26. Ngebhadi, ukusebenza nokuzinza kwalezi zikhuthazi kusese kude nama-catalyst wesimanjemanje afanako nahlukileko (Umfanekiso 1) 13 .
Amandla amanengi avela emithonjeni evuselelekako efana nelanga nofana umoya angakhiqizwa ngokusebenzisa igezi yamanzi. I-hydrogen ekhiqizwako ingagcinwa kusetjenziswa i-LOHC, i-liquid ene-hydrogenation nokudehydrogenation kwayo okubuyiselwa emuva. Esigabeni sokukhipha i-hydrogen, umkhiqizo owodwa yi-hydrogen, begodu uketshezi oluthwalako lubuyiselwa ebujameni bayo bokuthoma bese luphinde lufakwe i-hydrogen. I-hydrogen ingagcina isetjenziswe eentetjhini zegesi, emabhetri, ezakhiweni zamabubulo, nokunye.
Mhlapha nje, kubikwe bona umsebenzi wangaphakathi wama-SAC athileko ungathuthukiswa ebukhoneni bama-athomu wensimbi ahlukileko nofana amasayithi wensimbi angezelelweko anikelwa ma-nanoparticles (NPs) nofana ama-nanoclusters (NCs)27,28. Lokhu kuvula amathuba wokuragela phambili nokudonswa nokusebenza kwe-substrate, kanye nokuguqulwa kwejometri nesakhiwo se-elekthronikhi samasayithi we-monatomic. Ngalokho-ke, ukumuncwa/ukusebenza kwe-substrate kungenziwa ngcono, kunikele ngokusebenza kuhle okupheleleko kwe-catalytic29,30. Lokhu kusinikela umbono wokwenza izinto ezifaneleko zokukhuthaza ngeendawo ezisebenzako ezihlangeneko. Nanyana ama-SAC athuthukisiweko atjengise amandla amakhulu eensetjenzisweni ezinengi zokukhuthaza, indima yawo ekugcineni i-hydrogen, ngokwazi kwethu, ayikacaci. Mayelana nalokhu, sibika iqhinga elinamandla neliqinileko lokuhlanganiswa kwama-cobalt-based hybrid catalysts (Co-SAs/NPs@NCs) ahlanganisa ama-nanoparticles ahlathululweko kanye namaziko wensimbi ngamunye. I-Co-SAs/NPs@NC ehlelekileko itjengisa ukusebenza okuhle khulu kwe-formic acid dehydrogenation, okungcono khulu kunama-non-noble nanostructured catalysts (njenge-CoNx, ama-athomu we-cobalt eyodwa, i-cobalt@NC kanye ne-γ-Mo2N) ngitjho nama-noble metal catalysts. Ukuhlolwa kwe-in-situ kanye nokubalwa kwe-DFT kwama-catalyst asebenzako kutjengisa bona iindawo zensimbi ngazinye zisebenza njengeendawo ezisebenzako, begodu ama-nanoparticles wokusungulwa kwamanje akhulisa isikhungo se-d-band sama-athomu we-Co, akhuthaza ukumuncwa nokusebenza kwe-HCOO*, ngaleyindlela kwehlisa isithiyo samandla sokusabela. .
Iinhlaka ze-zeolite imidazolate (ama-ZIF) zizinto ezihlathululwe kuhle ezinemikhakha emithathu ezihlinzeka ngama-catalysts wezinto ezine-nitrogen-doped carbonaceous (ama-metal-NC catalysts) ukusekela imihlobo ehlukileko yeensimbi37,38. Ngalokho-ke, i-Co(NO3)2 ne-Zn(NO3)2 zihlangana ne-2-methylimidazole ku-methanol ukwakha iinhlanganisela zensimbi ezihambisanako esixazululweni. Ngemva kokukhipha nokomisa, i-CoZn-ZIF yatjhugululwa emazingeni womtjhiso ahlukileko (750–950 °C) emkhathini we-6% H2 kanye ne-94% Ar. Njengombana kutjengisiwe emfanekisweni ongezansi, izinto eziphumelako zineempawu ezihlukileko zendawo esebenzako begodu zibizwa nge-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 (Umfanekiso 2a). ) . Ukutjheja okuthileko kokuhlola kwezinye iinyathelo eziqakathekileko zenqubo yokuhlanganisa kuvezwe ngokunabileko emifanekisweni 1 no-2. C1-C3. I-X-ray diffraction yepuyere yamazinga womtjhiso atjhugulukako (VTXRD) yenziwa ukutjheja ukutjhuguluka kwe-catalyst. Ngemva kokuthi amazinga womtjhiso we-pyrolysis afinyelele ku-650 °C, iphetheni ye-XRD itjhuguluka khulu ngebanga lokuwohloka kwesakhiwo sekristalu esihlelekileko se-ZIF (Umfanekiso S4) 39 . Njengoba izinga lokutjhisa likhula, kuvela iinqongo ezimbili ezibanzi kumaphetheni we-XRD we-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 ku-20–30° kanye no-40–50°, okujamele isiqongo se-amorphous carbon (Isithombe C5). . I-X-ray spectrum ye-Co-SAs/NPs@NC-950 itjengisa ubukhona be-graphite-like encapsulated cobalt nanoparticles ku-catalyst41,42,43,44. I-Raman spectrum itjengisa bona i-Co-SAs/NPs@NC-950 ibonakala ineenqhema eziqinileko nezincani ze-D ne-G ukudlula amanye amasampula, okutjengisa izinga eliphezulu lokwenza i-graphitization (Umfanekiso S6). Ukungezelela, i-Co-SAs/NPs@NC-950 itjengisa indawo ephezulu ye-Brunner-Emmett-Taylor (BET) kanye nevolumu yama-pore (1261 m2 g-1 kanye ne-0.37 cm3 g-1) ukudlula amanye amasampula begodu ama-ZIF amanengi akhiqizwe yi-NC. izinto (Umfanekiso S7 kanye neThebuli S1). I-Atomic absorption spectroscopy (AAS) itjengisa bona okuqukethwe kwe-cobalt ye-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 kwe-Zn kwe-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 kuyakhula kancanikancani, okubangelwa kukwehla okukhulu nokuvuvuka kwamayunithi we-Zn. Ukunyuka kwamazinga womtjhiso we-pyrolysis (Zn, iphuzu lokubilisa = 907 °C) 45.46. Ukuhlaziywa kwe-elementi (EA) kutjengise bona iphesenteji ye-N yehla ngokukhula kwamazinga womtjhiso we-pyrolysis, begodu okuqukethwe okuphezulu kwe-O kungabangelwa kudonswa kwe-O2 yamamolekhyuli ukusuka ekuvezweni emoyeni. (Ithebula S3). Ekuqukethwe okuthileko kwe-cobalt, ama-nanoparticles nama-coatoms ahlukileko ahlala ndawonye, ​​okurholela ekukhuphukeni okukhulu komsebenzi we-catalyst, njengombana kukhulunywe ngakho ngenzasi.
Umdwebo wesikimu wokuhlanganiswa kwe-Co-SA/NPs@NC-T, lapho i-T ilizinga lokutjhisa le-pyrolysis (°C). b Isithombe se-TEM. c Isithombe se-Co-SAs/NPs@NC-950 AC-HAADF-STEM. Ama-athomu we-Co ngamunye atshwaywe ngemibuthano ebomvu. d I-EDS Template Co-SA/NPs@NC-950.
Ngokuphawulekako, i-transmission electron microscopy (TEM) itjengise ubukhona be-cobalt nanoparticles (NPs) ehlukileko enesayizi ephakathi kwe-7.5 ± 1.7 nm kwaphela ku-Co-SA/NPs@NC-950 (Imifanekiso 2 b kanye ne-S8). Ama-nanoparticles la ahlanganiswe nge-carbon efana ne-graphite ene-nitrogen. I-lattice fringe spacing ye-0.361 ne-0.201 nm ihambisana ne-graphic carbon (002) kanye ne-metallic Co (111) particles, ngokulandelana. Ukungezelela, i-high-angle aberration-corrected annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) yaveza bona ama-Co NPs ku-Co-SAs/NPs@NC-950 begade azungezwe yi-atomic cobalt enengi (Umfanekiso 2c). Kodwana, kwaphela ama-athomu we-cobalt ahlakazeke ngama-athomu abonwa ekusekeleni amanye amasampula amabili (Umfanekiso S9). I-Energy dispersive spectroscopy (EDS) Isithombe se-HAADF-STEM sitjengisa ukusabalala okufanako kwe-C, N, Co kanye nama-Co NPs ahlukanisiweko ku-Co-SAs/NPs@NC-950 (Umfanekiso 2d). Yonke imiphumela le itjengisa bona amasentha we-Co ahlakazeke ngama-athomu kanye nama-nanoparticles ahlanganiswe nge-N-doped graphite-like carbon anamathele kuhle kuma-substrates we-NC ku-Co-SAs/NPs@NC-950, kuthi amasentha wensimbi ahlukaniswe kwaphela.
Isimo se-valence kanye nokwakheka kwamakhemikhali wezinto ezitholakeleko kwafundwa nge-X-ray photoelectron spectroscopy (XPS). I-XPS spectra yama-catalyst amathathu itjengise ubukhona bama-elementi Co, N, C kanye no-O, kodwana i-Zn beyikhona kwaphela ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 (Umfanekiso 2). ). C10). Njengoba amazinga womtjhiso we-pyrolysis akhuphuka, okuqukethwe kwe-nitrogen kuyehla njengombana imihlobo ye-nitrogen ingazinzi begodu ibola ibe yi-NH3 kanye namagesi we-NOx emazingeni womtjhiso aphezulu (Ithebula S4) 47 . Ngalokho, inani elipheleleko lekhabhoni likhuphuke kancanikancani ukusuka ku-Co-SAs/NPs@NC-750 ukuya ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-950 (Imifanekiso S11 no-S12). Isampula e-pyrolyzed emazingeni womtjhiso aphezulu inezinga eliphasi lama-athomu we-nitrogen, okutjho bona inani lama-NC carriers ku-Co-SAs/NPs@NC-950 kufanele libe ngaphasi kwalawo kwamanye amasampula. Lokhu kurholela ekutheni kube nokutjhiswa okunamandla kweenhlayiya ze-cobalt. I-O 1s spectrum itjengisa iinqongo ezimbili C=O (531.6 eV) kanye ne-C–O (533.5 eV), ngokulandelana (Umfanekiso S13) 48 . Njengombana kutjengiswe kuMfanekiso 2a, i-N 1s spectrum ingararululwa ibe ziinqhema ezine ezihlukileko 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). Amabhondi we-Co-N akhona kiwo woke amasampula amathathu, okutjengisa bona amanye ama-athomu we-N ahlanganiswa namasayithi we-monometallic, kodwana ubujamo bawo buhluke khulu49. Ukusetjenziswa kwezinga lokutjhisa eliphezulu le-pyrolysis kungehlisa khulu okumumethweko kwemihlobo ye-Co-N ukusuka ku-43.7% ku-Co-SA/NPs@NC-750 ukuya ku-27.0% ku-Co-SAs/NPs@NC-850 kanye ne-Co 17.6%@NC-950. ku--CA/NPs, okukhambelana nokwanda kokuqukethwe kwe-C (Umfanekiso 3a), okutjengisa bona inani labo lokuhlanganisa le-Co-N lingatjhuguluka begodu lithathelwe indawo ngama-athomu we-C50. I-Zn 2p spectrum itjengisa bona into le ikhona khulu ngendlela ye-Zn2+. (Umfanekiso S14) 51. I-spectrum ye-Co 2p itjengisa iinqongo ezimbili eziqakathekileko ku-780.8 no-796.1 eV, ezihlobene ne-Co 2p3/2 kanye ne-Co 2p1/2, ngokulandelana (Umfanekiso 3b). Nayiqathaniswa ne-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750, i-Co-N peak ku-Co-SAs/NPs@NC-950 itjhugulukela ehlangothini elihle, okutjengisa bona i-athomu eyodwa ye-Co ukuya ebusweni -SAs/NPs@NC-950 inezinga eliphezulu lokuphelelwa ma-elekthronikhi, okurholela ekubeni ne-oksijini ephezulu. Kuqakathekile ukutjheja bona yi-Co-SAs/NPs@NC-950 kwaphela etjengisa isiqongo esibuthakathaka se-zero-valent cobalt (Co0) ku-778.5 eV, okufakazela ubukhona bama-nanoparticles avela ekuhlanganisweni kwe-cobalt SA emazingeni womtjhiso 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 amaplothi we-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850, kanye ne-Co-SAs/NPs@NC-750. f FT-EXAFS ukulinganisa ijika le-Co-SA/NPs@NC-950.
I-Time-locked X-ray absorption spectroscopy (XAS) yasetjenziswa ukuhlaziya isakhiwo se-elekthronikhi kanye nebhoduluko lokuhlanganiswa kwemihlobo ye-Co esampula elungiselelweko. I-Cobalt valence states ku-Co-SAs/NPs@NC-950, Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 Isakhiwo se-edge sivezwe ngokumuncwa kwe-X-ray eduze kwe-Co-K edge (XANES) spectrum. Njengombana kutjengisiwe emfanekisweni 3c, ukumunywa eduze nomphetho wamasampula amathathu kutholakala hlangana namafoyili we-Co ne-CoO, okutjengisa bona ubujamo be-valence yemihlobo ye-Co busuka ku-0 ukuya ku-+253. Ukungezelela, ukutjhugulukela emandleni aphasi kwabonwa ukusuka ku-Co-SAs/NPs@NC-950 ukuya ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750, okutjengisa bona i-Co-SAs/NPs@NC-750 inesimo esiphasi se-oksijini. ukubuyela emuva. Ngokuya ngemiphumela yokulinganisa okuhlanganisiweko, ubujamo be-Co valence be-Co-SAs/NPs@NC-950 bulinganiselwa ku-+0.642, okuphasi kobujamo be-Co valence be-Co-SAs/NPs@NC-850 (+1.376). I-Co-SA/NP @NC-750 (+1.402). Imiphumela le itjengisa bona ubujamo be-oksijini obuphakathi bama-cobalt particles ku-Co-SAs/NPs@NC-950 bunciphile khulu, okuhambisana nemiphumela ye-XRD ne-HADF-STEM begodu kungachazwa ngokuba ndawonye kwama-cobalt nanoparticles ne-single cobalt. . Ama-athomu we-Co 41. I-Fourier transform X-ray absorption fine structure (FT-EXAFS) spectrum ye-Co K-edge itjengisa bona isiqongo esikhulu ku-1.32 Å ngesegobolondweni le-Co-N/Co-C, kuthi indlela yokusabalala ye-Co-Co yensimbi ise-2.18 kwaphela ku-Co-SA Å @ Å etholakala ku-NC/NCs 3d). Ngaphezu kwalokho, i-wavelet transform (WT) contour plot itjengisa ukuqina okukhulu ku-6.7 Å-1 okuhlobene ne-Co-N/Co-C, ngesikhathi i-Co-SAs/NPs@NC-950 kwaphela etjengisa ukuqina okukhulu okuhlobene no-8.8. Okunye ukuqina okukhulu ku-Å-1 ukuya ku-Co-Co bond (Umfanekiso 3e). Ukungezelela, ukuhlaziywa kwe-EXAFS okwenziwe mthengisi kutjengise bona emazingeni womtjhiso we-pyrolysis angu-750, 850 no-950 °C, amanani wokuhlanganisa we-Co-N bekungu-3.8, 3.2 no-2.3, ngokulandelana, begodu amanani wokuhlanganisa we-Co-C bekuyi-0. 0.9 no-1.8 (Umfanekiso 3. Sf, Ithebula S15). Ngokukhethekileko, imiphumela yakamuva ingabangelwa kukuba khona kwamayunithi we-CoN2C2 asakazeke ngama-athomu kanye nama-nanoparticles ku-Co-SAs/NPs@NC-950. Ngokuphikisako, ku-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750, amayunithi we-CoN3C ne-CoN4 kwaphela akhona. Kusegcekeni bona ngokukhula kwamazinga womtjhiso we-pyrolysis, ama-athomu we-N kuyunithi ye-CoN4 athathelwa indawo kancanikancani ngama-athomu we-C, begodu i-cobalt CA ihlangana ukwakha ama-nanoparticles.
Izimo zokuphendula ezifundwe ngaphambilini zasetjenziselwa ukufunda umphumela wezimo zokulungiselela ezakhiweni zezinto ezihlukahlukeneko (Umfanekiso S16)17,49. Njengombana kutjengisiwe emfanekisweni 4 a, umsebenzi we-Co-SAs/NPs@NC-950 uphezulu khulu kunalowo we-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750. Ngokuphawulekako, woke amasampula amathathu we-Co alungiselelweko atjengisa ukusebenza okungcono khulu nayiqathaniswa nama-catalyst wensimbi eyigugu (i-Pd/C ne-Pt/C). Ukungezelela, amasampula we-Zn-ZIF-8 kanye ne-Zn-NC bekangasebenzi ekukhipheni i-formic acid, okutjengisa bona iinhlayiya ze-Zn azisizindawo ezisebenzako, kodwana umphumela wazo emsebenzini awuqakatheki. Ukungezelela, umsebenzi we-Co-SAs/NPs@NC-850 kanye ne-Co-SAs/NPs@NC-750 wenza i-pyrolysis yesibili ku-950°C i-awa elilodwa, kodwana bewuphasi kunalowo we-Co-SAs/NPs@NC-750. @NC-950 (Umfanekiso S17). Ukuhlukaniswa kwesakhiwo sezinto lezi kutjengise ubukhona bama-Co nanoparticles kumasampula aphinde a-pyrolyze, kodwana indawo ephasi ekhethekileko nokungabi khona kwekhabhoni efana ne-graphite kwabangela umsebenzi ophasi nayiqathaniswa ne-Co-SAs/NPs@NC-950 (Umfanekiso S18–S20). Umsebenzi wamasampula anenani elihlukileko le-Co precursor nawo wamadaniswa, ngomsebenzi ophakemeko otjengiswe ngokungezelelwa kwe-3.5 mol (Ithebula S6 kanye nomfanekiso S21). Kusegcekeni bona ukwakheka kwamaziko wesimbi ahlukahlukeneko kuthonywa mthamo we-hydrogen emkhathini we-pyrolysis kanye nesikhathi se-pyrolysis. Ngalokho-ke, ezinye izinto ze-Co-SAs/NPs@NC-950 zahlolwa ukusebenza kwe-formic acid dehydrogenation. Zoke izinto zitjengise ukusebenza okulinganiselweko ukuya kokuhle khulu; nanyana kunjalo, akukho nanye kizo ebeyingcono kune-Co-SAs/NPs@NC-950 (Iinthombe S22 no-S23). Ukuvezwa kwesakhiwo sezinto kutjengise bona ngokukhula kwesikhathi se-pyrolysis, okuqukethwe kwe-monoatomic Co-N positions kwehla kancanikancani ngebanga lokuhlanganiswa kwama-athomu wensimbi abe ma-nanoparticles, okuhlathulula umehluko wokusebenza hlangana namasampula anesikhathi se-pyrolysis se-100-2000. umahluko. 0.5 h, 1 h, kanye ne-2 h (Imifanekiso S24-S28 kanye neThebula S7).
Igrafu yevolumu yegesi nayiqathaniswa nesikhathi esitholwe ngesikhathi sokukhipha amanzi emhlanganweni wephethiloli kusetjenziswa ama-catalyst ahlukahlukeneko. Ubujamo bokuphendula: i-FA (10 mmol, 377 μl), i-catalyst (30 mg), i-PC (6 ml), i-Tback: 110 °C, i-Tactical: 98 °C, 4 parts b Co-SAs/NPs@NC-950 ( 30 mg), iinsombululo ezihlukahlukeneko. c Ukumadanisa amazinga wokuziphendukela kwegesi wama-catalysts ahlukileko eentweni eziphilako ku-85-110 °C. d Co-SA/NPs@NC-950 ukuhlolwa kabutjha. Ubujamo bokuphendula: FA (10 mmol, 377 μl), Co-SAs/NPs@NC-950 (30 mg), i-solvent (6 ml), Tback: 110 °C, Tactical: 98 °C, umjikelezo ngamunye wokuphendula uthatha i-awa elilodwa. Amabha wephutha ajamele ukuphambuka okujayelekileko okubalwe ukusuka ekuhlolweni okuthathu okusebenzako.
Ngokuvamileko, ukusebenza kuhle kwama-FA dehydrogenation catalysts kuthembele khulu ebujameni bokuphendula, khulukhulu i-solvent esetjenzisiweko8,49. Lokha nakusetjenziswa amanzi njengesisombululo, i-Co-SAs/NPs@NC-950 itjengise izinga eliphezulu lokuphendula lokuthoma, kodwana ukucinywa kwenzeka, mhlamunye ngebanga lamaphrothoni nofana i-H2O18 ehlala eendaweni ezisebenzako. Ukuhlolwa kwe-catalyst eentweni eziphilako ezifana ne-1,4-dioxane (DXA), i-n-butyl acetate (BAC), i-toluene (PhMe), i-triglyme kanye ne-cyclohexanone (CYC) nayo azange itjengise ukuthuthuka, begodu ne-propylene carbonate (PC) ) (Umfanekiso 4b kanye neThebuli S8). Ngokufanako, izengezo ezifana ne-triethylamine (NEt3) nofana i-sodium formate (HCCONa) azange zibe nomthelela omuhle ekusebenzeni kwe-catalyst (Umfanekiso S29). Ngaphasi kweemeko ezihle zokuphendula, ukukhiqizwa kwegesi kwafinyelela ku-1403.8 mL g−1 h−1 (Umfanekiso S30), ebekuphezulu khulu kunawo woke ama-Co catalysts abikwe ngaphambilini (okufaka hlangana i-SAC17, 23, 24). Eemhlolweni ezihlukahlukeneko, ngaphandle kokusabela emanzini kanye nama-additives we-formate, ukukhetha okufika ku-99.96% wokukhipha amanzi nokuphelelwa ngamanzi kwatholakala (Ithebula S9). Amandla wokusebenza abalweko angama-88.4 kJ/mol, okufana namandla wokusebenza wama-catalysts wensimbi ehloniphekileko (Umfanekiso S31 kanye neThebula S10).
Ukungezelela, simadanise inani lezinye iinsetjenziswa ezihlukileko zokukhipha i-formic acid ngaphasi kweemeko ezifanako (Umfanekiso 4c, amathebula S11 no-S12). Njengombana kutjengiswe kuMfanekiso 3c, izinga lokukhiqizwa kwegesi le-Co-SAs/NPs@NC-950 lidlula lelo lama-catalysts we-base metal ahlukileko begodu liphezulu kanengi ka-15 no-15 ukudlula lelo le-5% Pd/C kanye ne-5% Pd/C, ngokulandelana. kanye. % Pt/C isikhuthazi.
Isici esiqakathekileko sanoma ngikuphi ukusetjenziswa okusebenzako kwama-catalysts (de)hydrogenation kukuzinza kwawo. Ngalokho-ke, uchungechunge lwemizamo yokubuyisela kabutjha kusetjenziswa i-Co-SAs/NPs@NC-950 kwenziwa. Njengombana kutjengiswe kuMfanekiso 4 d, umsebenzi wokuthoma nokukhethwa kwezinto kwahlala kungatjhuguluki emidlalweni emihlanu elandelanako (qala neThebuli S13). Iimhloliso zesikhathi eside zenziwa begodu ukukhiqizwa kwegesi kwanda ngokulandelana emahoreni ama-72 (Umfanekiso S32). Okuqukethwe yi-cobalt ye-Co-SA/NPs@NC-950 esetjenzisiweko bekuyi-2.5 wt%, ebegade itjhidelene khulu neye-catalyst etja, okutjengisa bona bekunganakho ukugeleza okusobala kwe-cobalt (Ithebula S14). Akukho ukutjhuguluka kombala okusobala nofana ukuhlanganiswa kweenhlayiya zensimbi okwabonwa ngaphambi nangemva kokusabela (Umfanekiso S33). I-AC-HAADF-STEM kanye ne-EDS yezinto ezisetjenziswe ekuhlolweni kwesikhathi eside zitjengise ukugcinwa nokuhlakazeka okufanako kweendawo zokuhlakazeka kwe-athomu begodu akukho amatjhuguluko aqakathekileko wesakhiwo (Iinthombe S34 kanye ne-S35). Iinqophiso eziqakathekileko ze-Co0 ne-Co-N zisesekhona ku-XPS, okufakazela ukuhlala ndawonye kwe-Co NPs kanye namasayithi wensimbi ngamunye, okuqinisekisa ukuzinza kwe-Co-SAs/NPs@NC-950 catalyst (Umfanekiso S36).
Ukukhomba amasayithi asebenzako khulu anesibopho sokukhipha i-formic acid, izinto ezikhethiweko ezinesikhungo sinye sensimbi (CoN2C2) nofana i-Co NP zalungiswa ngokuya ngeemfundo zangaphambilini17. Ukulandelana kwe-formic acid dehydrogenation activity ebonwe ngaphasi kweemeko ezifanako yi-Co-SAs/NPs@NC-950 > Co SA > Co NP (Ithebula S15), okutjengisa bona amasayithi we-CoN2C2 asakazeke nge-athomu asebenza khulu kune-NPs. I-reaction kinetics itjengisa bona ukutjhuguluka kwe-hydrogen kulandela i-oda lokuthoma lokusabela, kodwana ukutjhinga kwamajika amanengi eendaweni ezihlukileko ze-cobalt azifani, okutjengisa bona i-kinetics ayithembele ku-formic acid kwaphela, kodwana nendawo esebenzako (Umfanekiso 2). C37). Iimfundo ezilandelako ze-kinetic zitjengise bona, nakuqalwa ukungabi khona kweenqhema ze-cobalt metal ekuhlaziyweni kwe-X-ray diffraction, i-oda le-kinetic lokusabela ngokuya kokuqukethwe kwe-cobalt kwatholakala bona lingu-1.02 emazingeni aphasi (ngaphasi kwe-2.5%), okutjengisa ukusabalala okufanako kwamaziko we-cobalt we-monoatomic. okuqakathekileko. isayithi esebenzako (amakhiwane. S38 no-S39). Lokha okuqukethwe ziinhlayiya ze-Co nazifinyelela ku-2.7%, i-r ikhuphuka msinyana, okutjengisa bona iinhlayiya ezincani zisebenzisana kuhle nama-athomu ngamanye ukuthola umsebenzi ophakemeko. Njengoba okuqukethwe ziinhlayiya ze-Co kukhula, ikhefu iba yinto engekho emgqeni, okuhlotjaniswa nokwanda kwenani lama-nanoparticles kanye nokwehla kwezikhundla ze-monatomic. Ngalokho, ukusebenza okuthuthukisiweko kwe-LC dehydrogenation kwe-Co-SA/NPs@NC-950 kubangelwa kuziphatha ngokubambisana kwamasayithi wensimbi ngamunye nama-nanoparticles.
Irhubhululo elijulileko lenziwa kusetjenziswa i-in situ diffuse reflectance Fourier transform (in situ DRIFT) ukukhomba ukusabela okuphakathi kwenqubo. Ngemva kokutjhisa amasampula ukuya emazingeni womtjhiso ahlukileko ngemva kokufaka i-formic acid, kwabonwa amasethi amabili wamafrikhwensi (Umfanekiso 5a). Iinqhema ezintathu eziqakathekileko ze-HCOOH* zivela ku-1089, 1217 kanye ne-1790 cm-1, ezihlobene nokudlidliza okungaphandle kwe-CH π (CH), ukudlidliza kwe-CO ν (CO) kanye nokudlidliza kokunweba kwe-C=O ν (C=O), ngokulandelana. Elinye iqoqo lama-peak ku-1363 no-1592 cm-1 lihambelana nokudlidliza kwe-OCO okulinganako νs(OCO) kanye nokudlidliza okungalinganiko kwe-OCO νas(OCO)33.56 HCOO*, ngokulandelana. Njengoba ukusabela kuragela phambili, iinqophiso ezihlobeneko ze-HCOOH* ne-HCOO* ziya buthakathaka kancanikancani. Ngokuvamileko, ukubola kwe-formic acid kufaka hlangana amagadango amathathu: (I) ukumuncwa kwe-formic acid eendaweni ezisebenzako, (II) ukususwa kwe-H ngendlela ye-formate nofana ye-carboxylate, kanye (III) nokuhlanganiswa kwe-H ezimbili ezidonsiweko ukukhiqiza i-hydrogen. I-HCOO* ne-COOH* zizinto eziphakathi eziqakathekileko ekutholeni iindlela ze-formate nofana ze-carboxylate, ngokulandelana57. Ehlelweni lethu lokuvuselela, kwavela isiqongo se-HCOO* kwaphela, okutjengisa bona ukubola kwe-formic acid kwenzeka kwaphela ngendlela ye-formic acid58. Ukutjheja okufanako kwenziwa emazingeni womtjhiso aphasi angama-78 °C kanye nama-88 °C (umfanekiso S40).
I-situ DRIFT spectra ye-HCOOH dehydrogenation ku-Co-SAs/NPs@NC-950 kanye no-b Co SAs. Inganekwane itjengisa isikhathi sokuphendula endaweni. c Ukuguquguquka kwevolumu yegesi etholwe ngokusebenzisa ama-reagents ahlukileko wokulebula ama-isotope. d Idatha yomthelela we-isotope.
Iimhloliso ezifanako ze-in situ DRIFT zenziwa eentweni ezihlobeneko i-Co NP ne-Co SA ukufunda umphumela wokusebenzisana ku-Co-SA/NPs@NC-950 (Iinthombe 5 b kanye ne-S41). Zombili izinto zitjengisa imikghwa efanako, kodwana iinqophiso ze-HCOOH* ne-HCOO* zitjhugulukile kancani, okutjengisa bona ukungeniswa kwama-Co NPs kutjhugulula isakhiwo se-elekthronikhi sesikhungo se-monoatomic. Isiqongo se-νas(OCO) esibonakalako sivela ku-Co-SAs/NPs@NC-950 kanye ne-Co SA kodwana ingasi ku-Co NPs, okutjengisa bona okuphakathi okwakhiwa lokha nakungezelelwa i-formic acid yi-monodentate formic acid eqondileko ebusweni be-plane salt. begodu idonswa ku-SA njengendawo esebenzako 59 . Kuqakathekile ukutjheja bona ukwanda okukhulu kokudlidliza kweenqhema eziqakathekileko π(CH) kanye no-ν(C = O) kwabonwa, okukhanyako kwaholela ekuhlanekezelweni kwe-HCOOH* begodu kwasiza ukusabela. Njengomphumela, iinqophiso eziqakathekileko ze-HCOOH* ne-HCOO* ku-Co-SAs/NPs@NC zipheze zanyamalala ngemva kwemizuzu emi-2 yokuphendula, okurhaba ukudlula leyo ye-monometallic (imizuzu eyi-6) kanye nama-catalysts asekelwe ku-nanoparticle (imizuzu eli-12). . Yonke imiphumela le iqinisekisa bona ukufakwa kwe-nanoparticle kukhuphula ukumuncwa nokusebenza kwezinto eziphakathi, ngaleyindlela kukhawuleze ukusabela okuphakanyiswe ngehla.
Ukuragela phambili nokuhlaziya indlela yokuphendula nokuthola igadango lokunquma izinga (RDS), umphumela we-KIE wenziwa phambi kwe-Co-SAs/NPs@NC-950. Lapha, ama-isotopes we-formic acid ahlukileko afana ne-HCOOH, HCOOD, DCOOH kanye ne-DCOOD asetjenziselwa iimfundo ze-KIE. Njengombana kutjengiswe kuMfanekiso 5c, izinga lokukhipha amanzi lehla ngokulandelana okulandelako: HCOOH > HCOOD > DCOOH > DCOOD. Ukungezelela, amanani abalweko we-KHCOOH/KHCOOD, KHCOOH/KDCOOH, KHCOOD/KDCOOD kanye ne-KDCOOH/KDCOOD bekuyi-1.14, 1.71, 2.16 kanye ne-1.44, ngokulandelana (Umfanekiso 5d). Ngalokho, ukuhlukaniswa kwe-CH bond ku-HCOO* kutjengisa amanani we-kH/kD >1.5, okutjengisa umphumela omkhulu we-kinetic60,61, begodu kubonakala ngasuthi kumele i-RDS ye-HCOOH dehydrogenation ku-Co-SAs/NPs@NC-950.
Ukungezelela, ukubalwa kwe-DFT kwenziwa ukuzwisisa umphumela wama-nanoparticles ahlanganisiweko emsebenzini wangaphakathi we-Co-SA. Amamodeli we-Co-SAs/NPs@NC kanye ne-Co-SA akhiwe ngokuya ngokuhlolwa okutjengisiweko nemisebenzi edlulileko (Imifanekiso 6a kanye ne-S42)52,62. Ngemva kokwenza ngcono i-geometric, ama-Co6 nanoparticles amancani (CoN2C2) ahlala ndawonye namayunithi we-monoatomic akhonjwa, begodu ubude be-Co-C ne-Co-N bond ku-Co-SA/NPs@NC kwatholwa bona bube yi-1.87 Å kanye ne-1.90 Å, ngokulandelana. , okuhambisana nemiphumela ye-XAFS. I-partial density of states (PDOS) ebalweko itjengisa bona i-Co metal atom eyodwa kanye ne-nanoparticle composite (Co-SAs/NPs@NC) zitjengisa ukuhlanganiswa okuphezulu eduze nezinga le-Fermi nayiqathaniswa ne-CoN2C2, okurholela ku-HCOOH. Ukudluliselwa kwe-elekthronikhi ebolileko kusebenza kuhle khulu (Iinthombe 6b no-S43). Amaziko we-d-band ahambelanako we-Co-SAs/NPs@NC kanye ne-Co-SA abalwa bona abe yi--0.67 eV kanye ne-0.80 eV, ngokulandelana, hlangana nalokho ukwanda kwe-Co-SAs/NPs@NC bekungu-0.13 eV, okwenza bona ngemva kokungeniswa kwe-NP, ukumuncwa kwama-HCOO* weenhlayiya ze-elekthronikhi ze-Co-NC 22. Umehluko wokuminyana kwetjhaji utjengisa ifu elikhulu lama-elekthronikhi elizungeze ibhlogo le-CoN2C2 kanye ne-nanoparticle, okutjengisa ukusebenzisana okuqinileko hlangana nazo ngebanga lokutjhinisana kwama-elekthronikhi. Kuhlanganiswe nokuhlaziywa kwe-Bader charge, kwatholakala bona i-Co ehlakazwe ngama-athomu ilahlekelwe yi-1.064e ku-Co-SA/NPs@NC kanye ne-0.796e ku-Co SA (Umfanekiso S44). Imiphumela le itjengisa bona ukuhlanganiswa kwama-nanoparticles kurholela ekupheleni kwe-elekthronikhi yamasayithi we-Co, okurholela ekukhuphukeni kwe-Co valence, okuhambisana nemiphumela ye-XPS (Umfanekiso 6c). Iimpawu zokusebenzisana kwe-Co-O zokudonswa kwe-HCOO ku-Co-SAs/NPs@NC kanye ne-Co SA zahlaziywa ngokubala i-crystalline orbital Hamiltonian group (COHP)63. Njengombana kutjengiswe kuMfanekiso 6 d, amanani angakalungi namahle we--COHP ahambelana nobujamo bokulwa nobujamo bokubopha, ngokulandelana. Amandla wokubopha we-Co-O edonswe yi-HCOO (Co-carbonyl O HCOO*) ahlolwa ngokuhlanganisa amanani we-COHP, ebegade angu-3.51 no-3.38 we-Co-SAs/NPs@NC kanye ne-Co-SA, ngokulandelana. Ukumuncwa kwe-HCOOH nakho kutjengise imiphumela efanako: ukwanda kwenani elihlangeneko le--COHP ngemva kokufakwa kwe-nanoparticle kutjengise ukwanda kokubopha kwe-Co-O, ngaleyindlela kwakhuthaza ukusebenza kwe-HCOO ne-HCOOH (Umfanekiso S45).
Isakhiwo se-Lattice se-Co-SA/NPs@NC-950. b PDOS Co-SA/NP@NC-950 kanye ne-Co SA. c 3D isosurface yomehluko we-charge densities ye-HCOOH adsorption ku-Co-SA/NPs@NC-950 kanye ne-Co-SA. (d) i-pCOHP yamabhondi we-Co-O afakwe yi-HCOO ku-Co-SA/NPs@NC-950 (kwesokunxele) kanye ne-Co-SA (kwesokudla). e Indlela yokuphendula ye-HCOOH dehydrogenation ku-Co-SA/NPs@NC-950 kanye ne-Co-SA.
Ukuze sizwisise ngcono ukusebenza okuphezulu kokukhipha amanzi kwe-Co-SA/NPs@NC, indlela yokusabela namandla kwasungulwa. Ngokukhethekileko, ukukhipha i-FA kufaka hlangana amagadango amahlanu, kufaka hlangana ukutjhugululwa 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 (Umfanekiso 6e). Amandla wokudonsa wamamolekhyuli we-formic acid ebusweni be-catalyst nge-carboxylic oxygen aphasi kunalawo nge-hydroxyl oxygen (Imifanekiso S46 no-S47). Ngemva kwalokho, ngebanga lamandla aphasi, i-adsorbate yenza i-OH bond cleavage ukwakha i-HCOO* kunokobana i-CH bond cleavage ukwakha i-COOH*. Ngesikhathi esifanako, i-HCOO* isebenzisa ukumuncwa kwe-monodentate, okukhuthaza ukuphuka kwamabhondi nokwakheka kwe-CO2 ne-H2. Imiphumela le iyahambisana nokuba khona kwe-νas(OCO) peak ku-in situ DRIFT, okutjengisa godu bona ukuwohloka kwe-FA kwenzeka ngendlela ye-formate esifundweni sethu. Kuqakathekile ukutjheja bona ngokuya ngokulinganisa kwe-KIE, ukuhlukaniswa kwe-CH kunesithiyo esiphezulu khulu samandla wokuphendula kunamanye amagadango wokuphendula begodu kumele i-RDS. Isithiyo samandla se-Co-SAs/NPs@NC catalyst system esihle khulu siphasi nge-0.86 eV kunaleyo ye-Co-SA (1.2 eV), okwenza ngcono khulu ukusebenza kuhle kokukhipha amanzi. Ngokuphawulekako, ubukhona bama-nanoparticles bulawula isakhiwo se-elekthronikhi samasayithi we-coactive ahlakazekile ngama-athomu, okuthuthukisa ukumuncwa nokusebenza kwezinto eziphakathi, ngaleyindlela kwehlisa isithiyo sokuphendula begodu kukhuthaze ukukhiqizwa kwe-hydrogen.
Ngokufingqa, sitjengisa kokuthoma bona ukusebenza kwe-catalytic yama-catalysts wokukhiqiza i-hydrogen kungathuthukiswa khulu ngokusebenzisa izinto ezinamaziko we-monometallic asabalaliswe khulu nama-nanoparticles amancani. Umqondo lo uqinisekiswe ngokuhlanganiswa kwe-cobalt-based single-atom metal catalysts etjhugululwe ngama-nanoparticles (Co-SAs/NPs@NC), kanye nezinto ezihlobeneko ezine-single-metal centers (CoN2C2) nofana i-Co NPs. Zoke izinto zalungiswa ngendlela elula ye-pyrolysis enegadango elilodwa. Ukuhlaziywa kwesakhiwo kutjengisa bona isikhuthazi esihle khulu (i-Co-SAs/NPs@NC-950) siqukethe amayunithi we-CoN2C2 ahlakazeke ngama-athomu kanye nama-nanoparticles amancani (7-8 nm) ahlanganiswe ne-nitrogen ne-graphite-like carbon. Inomkhiqizo omuhle khulu wegesi ukuya ku-1403.8 ml g-1 h-1 (H2:CO2 = 1.01:1), i-H2 ne-CO selectivity ye-99.96% begodu ingagcina isebenza njalo amalanga ambalwa. Umsebenzi we-catalyst le udlula umsebenzi we-Co SA kanye ne-Pd/C catalyst ngeenkhathi ezi-4 nezi-15, ngokulandelana. Iimhloliso ze-DRIFT ze-in situ zitjengisa bona nayiqathaniswa ne-Co-SA, i-Co-SAs/NPs@NC-950 itjengisa ukumuncwa okunamandla kwe-HCOO*, okuqakathekileko endleleni ye-formate, begodu ama-nanoparticle we-dopant angakhuthaza ukusebenza kwe-HCOO* nokurhaba kwe-C–H. Ukuhlukaniswa kwesibopho kwahlonzwa njenge-RDS. Iimbalo zethiyori zitjengisa bona ukufakwa kwe-Co NP kukhuphula isikhungo se-d-band sama-athomu we-Co ngama-0.13 eV ngokusebenzisana, kukhulisa ukumuncwa kwe-HCOOH* kanye ne-HCOO* okuphakathi, ngaleyindlela kwehlisa isithiyo sokusabela ukusuka ku-1.20 eV ye-Co SA ukuya ku-0 .86 eV. Unomthwalo wokusebenza kuhle khulu.
Ngokubanzi, irhubhululo leli linikela ngemibono yokuklama ama-catalyst wesimbi we-athomu yinye begodu lithuthukisa ukuzwisisa kokuthi kungathuthukiswa njani ukusebenza kwe-catalytic ngokusebenzisa umphumela wokusebenzisana wamasentha wesimbi wamasayizi ahlukileko. Sikholelwa bona indlela le inganwetshwa lula kwezinye iinhlelo ezinengi zokukhuthaza.
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%) i-ethanol (AR, 99.7%) yathengwa e-McLean, e-China. I-formic acid (HCOOH, 98%) yathengwa e-Rhawn, e-China. Zoke ii-reagents zasetjenziswa ngqo ngaphandle kokuhlanzwa okungezelelweko, begodu amanzi ahlwengileko khulu alungiselelwe kusetjenziswa ihlelo lokuhlanza khulu. I-Pt/C (5% yokulayisha ubukhulu) kanye ne-Pd/C (5% yokulayisha ubukhulu) zathengwa ku-Sigma-Aldrich.
Ukuhlanganiswa kwama-nanocrystals we-CoZn-ZIF kwenziwa ngokuya ngeendlela zangaphambilini ngokutjhugulula okuthileko23,64. Kokuthoma, i-30 mmol Zn(NO3)2·6H2O (8.925 g) kanye ne-3.5 mmol Co(NO3)2·6H2O (1.014 g) yahlanganiswa begodu yancibilikiswa ku-300 ml ye-methanol. Bese, i-120 mmol ye-2-methylimidazole (9.853 g) yancibilikiswa ku-100 ml ye-methanol bese yengezwa esixazululweni esingenhla. Umxube lo bewuvuselelwa emazingeni womtjhiso wegumbi ama-awa ama-24. Ekugcineni, umkhiqizo wahlukaniswa ngokutjhuguluka ku-6429 g imizuzu eli-10 begodu wahlanzwa kuhle nge-methanol kathathu. Ipuyere ephumelako yomiswa ngaphakathi kwe-vacuum ku-60°C ubusuku boke ngaphambi kokusetjenziswa.
Ukuze kwenziwe i-Co-SAs/NPs@NC-950, ipuyere eyomileko ye-CoZn-ZIF yayi-pyrolyzed ku-950 °C isikhathi esingange-awa ekugelezeni kwegesi okungu-6% H2 + 94% Ar, ngezinga lokufuthumala elingu-5 °C/min. Isampula yapholiswa yaba sezingeni lokushisa legumbi ukuthola i-Co-SA/NPs@NC-950. Ku-Co-SAs/NPs@NC-850 nofana i-Co-SAs/NPs@NC-750, izinga lokutjhisa le-pyrolysis latjhugululwa laya ku-850 no-750 °C, ngokulandelana. Amasampula alungiselelweko angasetjenziswa ngaphandle kokusetjenziswa okungeziweko, njengokutlolwa nge-asidi.
Iinlinganiso ze-TEM (i-transmission electron microscopy) zenziwa ku-Thermo Fisher Titan Themis 60-300 “cube” microscope ene-aberration corrector yokuthatha iinthombe kanye ne-300 kV probe shaping lens. Iimhloliso ze-HAADF-STEM zenziwa kusetjenziswa ama-microscope we-FEI Titan G2 kanye ne-FEI Titan Themis Z afakwe ama-probes nama-image correctors, kanye nama-DF4 ane-segment detectors. Iinthombe ze-EDS ze-elemental mapping nazo zatholwa ku-FEI Titan Themis Z microscope. Ukuhlaziywa kwe-XPS kwenziwa nge-X-ray photoelectron spectrometer (Thermo Fisher model ESCALAB 250Xi). I-XANES kanye ne-EXAFS ye-Co K-edge yabuthelelwa kusetjenziswa itafula le-XAFS-500 (i-China Spectral Instruments Co., Ltd.). Okuqukethwe kwe-Co kwatholakala nge-atomic absorption spectroscopy (AAS) (PinAAcle900T). I-X-ray diffraction (XRD) spectra yarekhodwa ku-X-ray diffractometer (Bruker, Bruker D8 Advance, Germany). Ama-isotherm wokudonswa kwe-nitrogen atholakala kusetjenziswa isisetjenziswa sokudonsa esibonakalako (Micromeritics, ASAP2020, USA).
Ukusabela kokukhipha amanzi kwenziwa emmoyeni we-argon lapho umoya ususwe ngokuya ngendlela ejayelekileko ye-Schlenk. Umkhumbi wokuphendula wasuswa begodu wagcwaliswa nge-argon amahlandla asithandathu. Vulela amanzi we-condenser bese ufaka i-catalyst (30 mg) kanye ne-solvent (6 ml). Futhumeza isitja sibe sezingeni lokutjhisa elifunekako ngokusebenzisa i-thermostat bese usivumela bona silinganise imizuzu ema-30. I-formic acid (10 mmol, 377 μL) yafakwa emkhunjini wokusabela ngaphasi kwe-argon. Jikisa ivalvu ye-burette eneendlela ezintathu ukunciphisa umfutho we-reactor, uyivale godu, bese uthoma ukulinganisa ivolumu yegesi ekhiqizwako ngokusebenzisa i-burette yesandla (Umfanekiso S16). Ngemva kwesikhathi esitlhogekako kobana ukusabela kuphele, isampula yegesi yabuthelelwa ukuhlaziywa kwe-GC kusetjenziswa isirinji esingangeni igesi esihlanjululwe nge-argon.
Ukuhlolwa kwe-in situ drift kwenziwa ku-Fourier transform infrared (FTIR) spectrometer (Thermo Fisher Scientific, Nicolet iS50) ene-mercury cadmium telluride (MCT) detector. I-catalyst powder yafakwa eselini lokusabela (i-Harrick Scientific Products, Praying Mantis). Ngemva kokuphatha i-catalyst ngomfudlana we-Ar (50 ml/min) emazingeni womtjhiso wegumbi, isampula yafuthunyelwa ukuya emazingeni womtjhiso anikelweko, bese yabubble nge-Ar (50 ml/min) esixazululweni se-HCOOH bese ithululelwa ngaphakathi kweseli lokuphendula. ukuphendula. Imodeli yeenkambo ezihlukahlukeneko zokukhuthaza. I-infrared spectra yarekhodwa ngeenkhathi ezisukela emizuzwaneni emi-3.0 ukuya kwe-awa eli-1.
I-HCOOH, i-DCOOH, i-HCOOD kanye ne-DCOOD zisetjenziswa njengezisekelo ku-propylene carbonate. Ubujamo obuseleko buhambisana nekambiso yokukhipha amanzi e-HCOOH.
Iimbalo zokuthoma zenziwa kusetjenziswa ihlaka lethiyori yokusebenza kwe-density ngaphakathi kwephakheji yokumodela ye-Vienna Ab initio (VASP 5.4.4) 65,66. Iseli ye-superunit enendawo ye-graphene (5 × 5) enobukhulu obuphambeneko obulinganiselwa ku-12.5 Å yasetjenziswa njengesisekelo se-CoN2C2 ne-CoN2C2-Co6. Ibanga le-vacuum elingaphezu kwe-15 Å lafakwa ukubalekela ukusebenzisana hlangana namalarha we-substrate aseduze. Ukusebenzisana hlangana nama-ayoni nama-elektroni kuchazwa yindlela ye-projected amplified wave (PAW)65,67. I-Perdue-Burke-Ernzerhoff (PBE) generalized gradient approximation (GGA) umsebenzi ophakanyiswe ngu-Grimm ngokulungiswa kuka-van der Waals68,69 kwasetjenziswa. Indlela yokuhlangana yamandla woke namandla yi-10-6 eV/athomu kanye ne-0.01 eV/Å. Ukuvalwa kwamandla kwabekwa ku-600 eV kusetjenziswa igridi ye-Monkhorst-Pack 2 × 2 × 1 K-point. I-pseudopotential esetjenziswe kile modeli yakhiwe ukusuka ehlelweni le-elekthronikhi ibe sebujameni be-C 2s22p2, ubujamo be-N 2s22p3, ubujamo be-Co 3d74s2, ubujamo be-H 1 s1, kanye nebujamo be-O 2s22p4. Amandla wokudonsa kanye nomehluko wokuminyana kwe-elekthronikhi kubalwa ngokususa amandla wesigaba segesi kanye nemihlobo yephasi ukusuka emandleni wehlelo elidonsiweko ngokuya ngamamodeli wokudonsa nofana wokuhlangana70,71,72,73,74. Ukulungiswa kwamandla wamahhala we-Gibbs kusetjenziselwa ukutjhugulula amandla we-DFT abe ngamandla wamahhala we-Gibbs begodu kuqakathekisa igalelo lokudlidliza ku-entropy kanye namandla we-zero point75. Indlela ye-ascending image-nudging elastic band (CI-NEB) yasetjenziselwa ukufuna ubujamo bokutjhuguluka kwe-reaction76.
Yonke idatha etholwe begodu yahlaziywa ngesikhathi sesifundo lesi ifakwe esihlokweni kanye nezinto ezingezelelweko nofana iyatholakala kumtloli ohambelana naye ngesibawo esizwakalako. Idatha yomthombo inikelwe esihlokweni lesi.
Yonke ikhodi esetjenziswe ekulingisani okukhambisana ne-atikili le iyatholakala ebatlolini abahambelana nayo lokha nayibawa.
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