Abstract:Lattice oxygen on the transition metal oxides serves as a critical active site in the dehydrogenation of alkanes, whose activity is determined by electronic properties and environmental structures. Hydrogen affinity...
“…As shown in Figure S11, the crossing potential model was employed to investigate the influence of different coordination states of the Co active sites on C 3 H 8 adsorption. 50 The O d −H distances are 2.64 and 3.33 Å for the most stable adsorption of C 3 H 8 on the Na− Co@S-1 and H−Co@S-1 catalysts, respectively. The corresponding adsorption energy of C 3 H 8 on the Na−Co@S-1 catalyst is −0.13 eV, which is weaker than that of the H−Co@ S-1 catalyst (−0.19 eV).…”
Section: Resultsmentioning
confidence: 95%
“…This suggests that the adsorption capacity of C 3 H 8 is enhanced after H + modification, which is consistent with the above TPSR results (Figure d,e). As shown in Figure S11, the crossing potential model was employed to investigate the influence of different coordination states of the Co active sites on C 3 H 8 adsorption . The O d –H distances are 2.64 and 3.33 Å for the most stable adsorption of C 3 H 8 on the Na–Co@S-1 and H–Co@S-1 catalysts, respectively.…”
Section: Resultsmentioning
confidence: 99%
“…For the temperature-programmed surface reaction (TPSR) of PDH, the catalyst samples were first pretreated at 300 °C for 1 h under a N 2 atmosphere. After the mixture was cooled to 50 a reaction gas mixture with a flow rate of 50 mL min −1 was fed into the system using a heating rate of 5 °C min −1 . Mass spectrometer signals were recorded in the range of 50−800 °C.…”
The metals that are embedded in zeolite frameworks exhibit
a specific
catalytic performance in combination with the corresponding microenvironment.
The charge balancing cations that are produced by the valence mismatch
between the doped metal and the Si atoms play a paramount role in
modulating the microenvironment. Based on an ab initio molecular dynamics (AIMD) simulation and X-ray adsorption spectroscopy
(XAS), we disclose for the first time that the local coordination
of the Co active center in the Co@S-1 catalyst reduces from 4 to 3
after the charge balancing cations change from Na+ to H+. Such a dramatic change in the microenvironment greatly affects
the catalytic performance. It was determined that the initial propane
conversion surprisingly increases from 4.1% to 41.3% during propane
dehydrogenation (PDH) due to this change. Further experiments and
calculations verify that the H–Co@S-1 catalyst lowers both
the first and second dehydrogenation energy barriers with its exoteric
Co3c active site and polarized O atoms. These findings
provide novel insight into modulating the microenvironment of the
active center in heterogeneous catalysis.
“…As shown in Figure S11, the crossing potential model was employed to investigate the influence of different coordination states of the Co active sites on C 3 H 8 adsorption. 50 The O d −H distances are 2.64 and 3.33 Å for the most stable adsorption of C 3 H 8 on the Na− Co@S-1 and H−Co@S-1 catalysts, respectively. The corresponding adsorption energy of C 3 H 8 on the Na−Co@S-1 catalyst is −0.13 eV, which is weaker than that of the H−Co@ S-1 catalyst (−0.19 eV).…”
Section: Resultsmentioning
confidence: 95%
“…This suggests that the adsorption capacity of C 3 H 8 is enhanced after H + modification, which is consistent with the above TPSR results (Figure d,e). As shown in Figure S11, the crossing potential model was employed to investigate the influence of different coordination states of the Co active sites on C 3 H 8 adsorption . The O d –H distances are 2.64 and 3.33 Å for the most stable adsorption of C 3 H 8 on the Na–Co@S-1 and H–Co@S-1 catalysts, respectively.…”
Section: Resultsmentioning
confidence: 99%
“…For the temperature-programmed surface reaction (TPSR) of PDH, the catalyst samples were first pretreated at 300 °C for 1 h under a N 2 atmosphere. After the mixture was cooled to 50 a reaction gas mixture with a flow rate of 50 mL min −1 was fed into the system using a heating rate of 5 °C min −1 . Mass spectrometer signals were recorded in the range of 50−800 °C.…”
The metals that are embedded in zeolite frameworks exhibit
a specific
catalytic performance in combination with the corresponding microenvironment.
The charge balancing cations that are produced by the valence mismatch
between the doped metal and the Si atoms play a paramount role in
modulating the microenvironment. Based on an ab initio molecular dynamics (AIMD) simulation and X-ray adsorption spectroscopy
(XAS), we disclose for the first time that the local coordination
of the Co active center in the Co@S-1 catalyst reduces from 4 to 3
after the charge balancing cations change from Na+ to H+. Such a dramatic change in the microenvironment greatly affects
the catalytic performance. It was determined that the initial propane
conversion surprisingly increases from 4.1% to 41.3% during propane
dehydrogenation (PDH) due to this change. Further experiments and
calculations verify that the H–Co@S-1 catalyst lowers both
the first and second dehydrogenation energy barriers with its exoteric
Co3c active site and polarized O atoms. These findings
provide novel insight into modulating the microenvironment of the
active center in heterogeneous catalysis.
“…4 d indicate that oxygen exists in four distinct states, with a binding energy of 530 eV corresponding to O–Co. The binding energies of 531.4 eV, 532.3 eV, and 533.6 eV corresponded to the O–H bond [ 41 ], the O–C bond [ 42 ] and the O–C O bond [ 43 ], respectively. Fig.…”
“…Polyoxometalates (POMs) are a type of metal oxide cluster (typically W 6+ , Mo 6+ , Nb 5+ and V 5+ ) with unique structures and properties, including acidity, basicity, redox and photochemical properties. − POMs have the well-defined structures and distinct sizes; therefore, they represent ideal systems for understanding the role of solid state metal oxides in catalysis. , Especially, lacunary POMs as inorganic multidentate ligands can stabilize effectively Ru single-atom, atomically precise Ag nanoclusters, and Pt, Au nanoparticles, etc., which act as catalysts exhibiting great application potential in catalytic hydrogenation, oxidation and carbon dioxide conversion. − Notably, it has been demonstrated that oxygen vacancies could form as one of the important defects in metal oxide clusters, which played a crucial role in the catalytic reactions, as revealed by both theoretical calculations and experimental observations. − In this scenario, oxygen vacancies in POMs can facilitate oxygen activation and boost the oxidation of various intermediate in oxidation of 5-hydroxymethylfurfural . On the other aspect, the oxygen vacancies in reduced polyoxovanadate-alkoxide can mediate the catalytic deoxygenation of styrene oxide to styrene .…”
In this work, a Keggin-type platinum substituted polyoxometalate (POM) is constructed by the reaction of monolacunary phosphotungstate precursor [PW 11 O 39 ] 7− with chloroplatinic acid. The as-obtained tetrabutylammonium salt (TBA-PWPt) demonstrates that the dimeric Pt 2+ ions are incorporated into POM frameworks and linked by two monolacunary POM anions. Notably, once the Pt-substituted Keggin-type POM anion is reduced by H 2 , the POM anion-stabilizing Pt nanocatalysts are generated, which greatly facilitates forming oxygen vacancies adjacent to Pt 0 species. The Pt nanocatalysts show superior catalytic activity and stability for the selective hydrogenation of quinoline into 1,2,3,4-tetrahydroquinoline in water. Detailed investigations elucidate that the stronger adsorption of quinoline on the Pt surface and the H 2 is activated by the adsorption at the POMs-Pt interface site. Moreover, density functional theory (DFT) calculations show that H 2 O is adsorbed at the interfacial oxygen vacancies and then undergoes homolytic dissociation to produce hydroxyl group (OH − ) and hydride (H − ) species. The H − species are transferred to the N-containing pyridine ring in quinoline hydrogenation, and the OH − species adsorbed on oxygen vacancies help to promote the H 2 heterolytic dissociation to produce H + and H − species. Sequentially, the produced proton and hydroxyl groups generate H 2 O, and the reaction cycle is completed.
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