Consequences of electron-density manipulations on the X-ray photoelectron spectroscopic properties of ferrocenyl-β-diketonato complexes of manganese(III). structure of [Mn(FcCOCHCOCH3)3]

Reaction of [Mn3(OAc)6O·3H2O](+) (1) with ferrocenyl β-diketones of the type FcCOCH2COR with R = CF3 (2a) and CH3 (2b), Ph = C6H5 (2c), and Fc = Fe(II)(η(5)-C5H4)(η(5)-C5H5) (2d) yielded a series of ferrocene-functionalized β-diketonato manganese(III) complexes 3a-3d, respectively, of general formula [Mn(FcCOCHCOR)3]. The mixed-ligand β-diketonato complex [Mn(FcCOCHCOFc)2(FcCOCHCOCH3)] (4) was obtained by reacting mixtures of diketones 2b and 2d with 1. A single-crystal X-ray structure determination of 3b (Z = 2, triclinic, space group P1̅) highlighted a weak axial elongating Jahn-Teller effect and a high degree of bond conjugation. An X-ray photoelectron spectroscopic study, by virtue of linear relationships between group electronegativities of ligand R groups, χR, or ∑χR, and binding energies of both the Fe 2p3/2 and Mn 2p3/2 photoelectron lines, confirmed communication between molecular fragments of 2a-2d as well as 3a-3d. This unprecedented observation allows prediction of binding energies from known β-diketonato side group χR values.J.C.S. acknowledges the NRF (Grant 2054243) and the UFS for financial support. Financial support from Syngaschem BV, The Netherlands, and the UFS is also gratefully acknowledged (B.E.B., E.E., and J.C.S.).http://pubs.rsc.org/en/journals/journalissues/ic2017-03-31hb2016Chemistr

Hydrogen spillover in the Fischer–Tropsch synthesis: an analysis of gold as a promoter for cobalt–alumina catalysts

This study investigated the operation of gold as a potential substitute for the platinum promoter in the Co/Al2O3Fischer–Tropsch catalyst. Au–Co/Al2O3was tested in conjunction with a model Hybrid Au–Co sample (comprised of a mechanical mixture of Au/Al2O3 + Co/Al2O3) to investigate hydrogen spillover which has been demonstrated to play a vital role in the reduction promotion mechanism. TPR, TGA and in situ XRD provided evidence to support the improved reducibility of supported cobalt oxide crystallites in Au–Co/Al2O3. However, no improvement in the reducibility of the Hybrid Au–Co catalyst was observed, in contrast to previous studies on noble metal reduction promoters. It was hypothesized that even though gold-to-cobalt spillover occurred during reduction in Au–Co/Al2O3, the great separation between the gold and cobalt crystallites, combined with gold's much lower affinity for hydrogen activation adversely affected the efficiency of the spillover process in the hybrid sample. Nevertheless, Au–Co/Al2O3had an improved mass-based activity, and a turnover frequency comparable to a platinum promoted sample, which highlighted the potential of gold as a reduction promoter for Co/Al2O3catalysts

Ammonia adsorption and decomposition on Co(0001) in relation to Fischer-Tropsch synthesis

\u3cp\u3eIn order to fundamentally understand cobalt catalyst deactivation in Fischer-Tropsch synthesis (FTS) due to parts per million levels of NH\u3csub\u3e3\u3c/sub\u3e in the synthesis gas, the adsorption and decomposition of NH\u3csub\u3e3\u3c/sub\u3e on Co(0001) are investigated experimentally under ultrahigh vacuum (UHV) conditions and theoretically using density functional theory (DFT) calculations. NH\u3csub\u3e3\u3c/sub\u3e desorbs intact from the surface, between 100 and 270 K. In agreement with this, DFT calculations show that the activation barrier for NH\u3csub\u3e3\u3c/sub\u3e decomposition, 105 kJ/mol, is higher than the adsorption energy of NH\u3csub\u3e3\u3c/sub\u3e, 59 kJ/mol. Neither CO\u3csub\u3ead\u3c/sub\u3e nor H\u3csub\u3ead\u3c/sub\u3e block the adsorption of NH\u3csub\u3e3\u3c/sub\u3e. Instead, CO and NH\u3csub\u3e3\u3c/sub\u3e form a stable coadsorbed layer. Preadsorbed ammonia negatively affects dissociative H\u3csub\u3e2\u3c/sub\u3e adsorption. Electron-induced dissociation produces NH\u3csub\u3ex\u3c/sub\u3e species on the surface at low temperature. The order of stability is NH(+2 H\u3csub\u3ead\u3c/sub\u3e) > N(+3 H\u3csub\u3ead\u3c/sub\u3e) > NH\u3csub\u3e2\u3c/sub\u3e(+ H\u3csub\u3ead\u3c/sub\u3e) > NH\u3csub\u3e3\u3c/sub\u3e. N and NH lower the quantity of CO that can be accommodated on the surface but do not affect the adsorption energy significantly. For FTS, we conclude that (i) NH\u3csub\u3e3\u3c/sub\u3e adsorption on cobalt is not inhibited by the other FTS reactants and thus parts per million levels of NH\u3csub\u3e3\u3c/sub\u3e can already be detrimental, (ii) due to their high stability, NH\u3csub\u3ex\u3c/sub\u3e species are most likely responsible for catalyst deactivation.\u3c/p\u3

Properties of Manganese(III) Ferrocenyl-β-Diketonato Complexes Revealed by Charge Transfer and Multiplet Splitting in the Mn 2p and Fe 2p X-Ray Photoelectron Envelopes

A series of ferrocenyl-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)3] with R = CF3, CH3, Ph (phenyl) and Fc (ferrocenyl) was subjected to a systematic XPS study of the Mn 2p3/2 and Fe 2p3/2 core-level photoelectron lines and their satellite structures. A charge-transfer process from the β-diketonato ligand to the Mn(III) metal center is responsible for the prominent shake-up satellite peaks of the Mn 2p photoelectron lines and the shake-down satellite peaks of the Fe 2p photoelectron lines. Multiplet splitting simulations of the photoelectron lines of the Mn(III) center of [Mn(FcCOCHCOR)3] resemble the calculated Mn 2p3/2 envelope of Mn3+ ions well, indicating the Mn(III) centers are in the high spin state. XPS spectra of complexes with unsymmetrical β-diketonato ligands (i.e., R not Fc) were described with two sets of multiplet splitting peaks representing fac and the more stable mer isomers respectively. Stronger electron-donating ligands stabilize fac more than mer isomers. The sum of group electronegativities, ΣχR, of the β-diketonato pendant side groups influences the binding energies of the multiplet splitting and charge transfer peaks in both Mn and Fe 2p3/2 photoelectron lines, the ratio of satellite to main peak intensities, and the degree of covalence of the Mn–O bond

Energetic Driving Force of H Spillover between Rhodium and Titania Surfaces: A DFT View

Hydrogen spillover from a rhodium particle, over the most stable (111) surface, to a TiO₂ rutile support occurs at low hydrogen coverage because the adsorption energy of H atoms at low hydrogen coverage on rutile is larger than that on rhodium. H diffuses over the support with an activation barrier low enough to allow this. With increased H coverage on the reducible metal oxide support, equilibrium is reached and spillover back to rhodium is feasible