The Role of Lewis Acid Sites in γ-Al2O3 Oligomerization

Olefin oligomerization by γ-Al₂O₃ has recently been reported, and it was suggested that Lewis acid sites are catalytic. The goal of this study is to determine the number of active sites per gram of alumina to confirm that Lewis acid sites are indeed catalytic. Addition of an inorganic Sr oxide base resulted in a linear decrease in the propylene oligomerization conversion at loadings up to 0.3 wt %; while, there is a >95 % loss in conversion above 1 wt % Sr. Additionally, there was a linear decrease in the intensity of the Lewis acid peaks of absorbed pyridine in the IR spectra with an increase in Sr loading, which correlates with the loss in propylene conversion, suggesting that Lewis acid sites are catalytic. Characterization of the Sr structure by XAS and STEM indicates that single Sr²⁺ ions are bound to the γ-Al₂O₃ surface and poison one catalytic site per Sr ion. The maximum loading needed to poison all catalytic sites, assuming uniform surface coverage, was ∼0.4 wt % Sr, giving an acid site density of ∼0.2 sites per nm² of γ-Al₂O₃, or approximately 3 % of the alumina surface.     

N-Heterocyclic Olefins on a Silicon Surface

The adsorption of N-heterocyclic olefins (NHOs) on silicon is investigated in a combined scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory study. We find that both of the studied NHOs bind covalently, with ylidic character, to the silicon adatoms of the substrate and exhibit good thermal stability. The adsorption geometry strongly depends on the N-substituents: for large N-substituents, an upright adsorption geometry is favored, while a flat-lying geometry is found for the NHO with smaller wingtips. These different geometries strongly influence the quality and properties of the obtained monolayers. The upright geometry leads to the formation of ordered monolayers, whereas the flat-lying NHOs yield a mostly disordered, but denser, monolayer. The obtained monolayers both show large work function reductions, as the higher density of the flat-lying monolayer is found to compensate for the smaller vertical dipole moments. Our findings offer new prospects in the design of tailor-made ligand structures in organic electronics and optoelectronics, catalysis, and material science.     

Dioxygen-Triggered β-Hydroxysulfonylation of Terminal Olefins Controlled by DABCO

A dioxygen-triggered selectively difunctionalization of olefins to achieve β-hydroxysulfones has been developed. Particularly, the mechanism of this reaction can be controlled by DABCO, which act as a single electron transfer reagent, to selectively obtain ketosulfone or hydroxysulfone. The reaction was conducted in a clean, safe, mild, and catalyst-free conditions. Moreover, as a proof-of-concept, two bioactive molecules were synthesized easily using this method.     

Synthesis and Characterization of Star-Branched Nylon 12

Linear and star-branched polyamide 12 were prepared in the presence of mono- and multifunctional acid agents. Molecular masses and molecular mass distributions are discussed according to our model recently presented and are compared with the data obtained by Flory's model. End group titration and SEC data are discussed. Oligomerisation data confirm the general validity of our model.     

SSZ-39分子筛的合成及应用进展

近年来,小孔八元环SSZ-39分子筛因具有特殊的孔道结构和物理化学性质,在小分子择形催化反应中展现出相对优异的催化活性、抗积碳性和水热稳定性.本文概述了SSZ-39分子筛的合成历程,包括不同种类有机模板剂的使用、特定硅源铝源的选择以及凝胶组成的调控等;简要总结了SSZ-39分子筛在甲醇制低碳烯烃、氮氧化物的选择性催化还...