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71.
Susi T Lanzani G Nasibulin AG Ayala P Jiang T Bligaard T Laasonen K Kauppinen EI 《Physical chemistry chemical physics : PCCP》2011,13(23):11303-11307
We have studied the mechanism of the initial stages of nitrogen-doped single-walled carbon nanotube growth illustrated for the case of a floating catalyst chemical vapor deposition system, which uses carbon monoxide (CO) and ammonia (NH(3)) as precursors and iron as a catalyst. We performed first-principles electronic-structure calculations, fully incorporating the effects of spin polarization and magnetic moments, to investigate the bonding and chemistry of CO, NH(3), and their fragments on a model Fe(55) icosahedral cluster. A possible dissociation path for NH(3) to atomic nitrogen and hydrogen was identified, with a reaction barrier consistent with an experimentally determined value we measured by tandem infrared and mass spectrometry. Both C-C and C-N bond formation reactions were found to be barrierless and exothermic, while a parasitic reaction of HCN formation had a barrier of over 1 eV. 相似文献
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73.
Esko Ukkonen 《BIT Numerical Mathematics》1983,23(2):181-192
LetV be a set inR n consisting of finitely many hyperplanes. The linear recognition problem given byV is to determine, using ternary comparisons of the form “f(x):0” wheref:R n →R is a linear function, whether a pointxεR n is inV. We consider lower bounds on the number of comparisons whenV corresponds to some NP-complete problems. A technique is proposed for proving such bounds. If the tests “f(x):0” are restricted so thatf always defines some hyperplane inV, then some NP-complete problems are shown to have exponential lower bounds inn. Examples of larger classes of linear test functions are found such that the exponential lower bounds are still valid. 相似文献
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75.
He M Chernov AI Fedotov PV Obraztsova ED Rikkinen E Zhu Z Sainio J Jiang H Nasibulin AG Kauppinen EI Niemelä M Krause AO 《Chemical communications (Cambridge, England)》2011,47(4):1219-1221
SiO(2) supported cobalt (Co) catalyst could be partially reduced and anchored by unreduced Co ions during a carbon monoxide (CO) chemical vapor deposition (CVD) process. This resulted in the formation of sub-nanometre metallic Co clusters catalyzing the growth of single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution. 相似文献
76.
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78.
Zhu Z Jiang H Susi T Nasibulin AG Kauppinen EI 《Journal of the American Chemical Society》2011,133(5):1224-1227
We demonstrate here a simple and effective (n,m)-selective growth of single-walled carbon nanotubes (SWCNTs) in an aerosol floating catalyst chemical vapor deposition (CVD) process by introducing a certain amount of ammonia (NH(3)). Chiralities of carbon nanotubes produced in the presence of 500 ppm NH(3) at 880 °C are narrowly distributed around the major semiconducting (13,12) nanotube with over 90% of SWCNTs having large chiral angles in the range 20°-30°, and nearly 50% in the range 27°-29°. The developed synthesis process enables chiral-selective growth at high temperature for structurally stable carbon nanotubes with large diameters. 相似文献
79.
Monolayer protected metal clusters are dynamic nanoscale objects. For example, the chiral Au38(2-PET)24 cluster (2-PET: 2-phenylethylthiolate) racemizes at moderate temperature. In addition, ligands and metal atoms can easily exchange between clusters. Such processes are important for applications of monolayer protected metal clusters; however, the mechanistic study of such processes turns out to be challenging. Here we use a configurationally labile, axially chiral ligand, biphenyl-2,2′-dithiol (R/S-BiDi), as a probe to study dynamic cluster processes. It is shown that the ligand exchange of free R/S-BiDi on a chiral Au38(2-PET)24 cluster is diastereospecific. Using chiral chromatography, isolated single diastereomers of the type anticlockwise/clockwise-Au38(2-PET)22(R/S-BiDi)1 could be isolated. Upon heating, the cluster framework racemizes, while the R/S-BiDi ligand does not. These findings demonstrate that during cluster racemization and/or ligand exchange between clusters, the R/S-BiDi ligand is sufficiently confined, thus preventing its racemization, and exclude the possibility that the ligand desorbs from the cluster surface.The ligand exchange between a configurationally labile BiDi ligand and intrinsically chiral Au38 gold nanoclusters is diastereoselective. More importantly, the adsorbed ligand retains its configuration during dynamic cluster processes. 相似文献
80.
Esko Salojrvi Anssi Peuronen Narhari Sapkota Ari Lehtonen 《Molecules (Basel, Switzerland)》2022,27(21)
Molecular molybdenum complexes with sulfur donor ligands are generally studied as soluble model compounds for molybdenum enzymes essential for life. The dioxidomolybdenum(VI) complex with tetradentate aminobisphenolate ligand undergoes a reaction with thionation reagent P2S5 or its organic derivative, Lawesson’s reagent, to yield stable Mo(IV) aminobisphenolate complexes, where pristine oxido ligands have been replaced by bidentate sulfur donors tetrasulfide, S42− or (4-methoxyphenyl)phosphonotrithioate residue derived from Lawesson’s reagent. This is in contrast to the behaviour of analogous dioxidotungsten(VI) complex, which, under similar conditions, yields W(VI) S2 systems. The overall cis,trans,cis geometry of the parent dioxidomolybdenum(VI) aminobisphenolate is retained, namely, the neutral nitrogen donors are in cis positions, phenolate oxygens are trans to each other and sulfur donors are cis. Although formally Mo(IV), thus d2 system, the studied complexes have diamagnetic singlet electron configurations as a result of the axially compressed octahedral structures. 相似文献