466 research outputs found
Cationic Pyridylamido Adsorbate on Bronsted Acidic Sulfated Zirconia: A Molecular Supported Organohafnium Catalyst for Olefin Homo- and Co-Polymerization
No full textHere we report the combined application of highresolution solid-state 13C−CPMAS-NMR and FT-IR spectroscopy, elemental analysis, kinetic poisoning/active site counting, variable dielectric constant medium, and DFT computation to characterize the surface chemistry of a pyridylamido hafnium complex (Cat1, L1-HfMe2, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) adsorbed on Brønsted acidic sulfated zirconia (ZrS). The spectroscopic and DFT results indicate protonolytic formation of organohafnium cations having a largely electrostatic pyridylamido-Hf-CH3 +···ZrS− interaction with elongated Hf···OZrS distances of ∼2.14 Å. High-molecular-weight polyethylenes and ethylene/1-octene copolymers are obtained with this supported catalyst without an activator/cocatalyst. The DFT calculations reveal that the first ethylene insertion into the Hf-methyl bond has a lower barrier than the corresponding insertion into the Hf-aryl bond of this single-site heterogeneous catalyst
Investigation of the physico-chemical state and aggregation mechanism of surface Cr species on a Phillips CrOx/SiO2 catalyst by XPS and EPMA
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Is the core-peripheral distinction for unaccusative verbs cross-linguistically consistent? Empirical evidence from Mandarin
No full textThis paper presents the results of an empirical investigation into the characteristics of unaccusativity in Mandarin by building on the gradient approach to split intransitivity (Sorace, 2000) and previous analyses of Mandarin within that framework (Liu, 2007). The study explores the acceptability of unaccusative verbs in the verb-subject construction with respect to their core-peripheral features. The results clearly demonstrate support for the gradient approach; however, some important departures from the patterns observed in Western European languages are noted. The analysis of variability between and within semantic categories reveals that verbs in certain peripheral categories exhibit behaviour more characteristic of core unaccusative verbs; conversely, some members of the core category Change of Location display characteristics more typical of peripheral verbs. A refined definition of peripheral verbs (true and pseudo) is proposed which has relevance for the cross-linguistic study of split intransitivity, and the unaccusative gradient for Mandarin is reformulated on the basis of stativity.</jats:p
Electro-responsive 1-D nanomaterial driven broad-band reflection in chiral nematic liquid crystals
No full textA controllable and reversible broad-band reflector can be obtained by virtue of the response of one-dimensional (1-D) nanomaterials in chiral nematic liquid crystalline media to an external electric field. The colour switching originated from the electro-responsive 1-D nanomaterials and the responsive mechanism was discussed based on the relationship between the pitch distribution and the alignment of nanomaterials.Materials Science, MultidisciplinaryPhysics, AppliedSCI(E)EI2ARTICLE2216-219
Peculiarities of Ethylene Polymerization Kinetics with an Imido-Vanadium/Silyl-Chromate Bimetallic Catalyst: Effect of Polymerization Conditions
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