Mechanism on Redistribution Synthesis of Dichlorodimethylsilane by AlCl3/ZSM-5(3T)@γ-Al2O3 Core-shell Catalyst

The redistribution method plays an important role in addressing the issue of organosilicon by-product in the direct synthesis of dichlorodimethylsilane, and the redistribution mechanism is still a topic of debate. The redistribution by ZSM-5(3T)@γ-Al2O3 core-shell catalyst and post-modified AlCl3/ZSM-5(3T)@γ-Al2O3 catalyst was technically performed using the Density Functional Theory (DFT) at the level of B3LYP/6-311++G(3df,2pd). The result shows that No.1 active site of ZSM-5(3T)@γ-Al2O3 core-shell structure has a significant effect on the activity of the catalyst. Indicating that the active center involved in the reaction is H provided by Al-O-H bond, which is an obvious catalytic active center of Bronsted acid. Furthermore, post-modified AlCl3/ZSM-5(3T)@γ-Al2O3 catalyst is in more favor of redistribution reaction comparing with ZSM-5(3T)@γ-Al2O3 core-shell catalyst. It ascribes to the robust Lewis site of aluminum chloride favorable modification.

Dual Lewis site creation for activation of methanol on Fe3O4(111) thin films

Adjacent oxygen adatoms and lattice iron atoms on magnetite surfaces serve as dual Lewis sites that oxidize methanol to formaldehyde.

IR and NMR Studies of the Status of Al and Acid Sites in Desilicated Zeolite Y

The desilication of zeolite Y (of Si/Al = 31) that was previously dealuminated by steaming and acid treatment was studied. Desilication of zeolites of high Si/Al module in alkali solutions extracts both Si and Al from zeolite crystals, but while Si remains in solution, Al is reinserted into the zeolite grain. The main goal of our study was to follow the status of Al reinserted into zeolite during the desilication procedure, and its role in the formation of acid sites of the Brønsted and Lewis types. The properties of Al were followed by 27Al MAS NMR spectroscopy (for parent samples and zeolites treated either with NaOH or NaOH/tetrabutylammonium hydroxide), whereas the acid sites generated in the final stages were studied by IR spectroscopy with NH3 and CO as probe molecules. In non-desilicated zeolite, most of the Al was in a typically zeolitic tetrahedral coordination, while both NMR and quantitative IR studies of NH3 sorption evidenced that Al that was extracted by desilication and was subsequently reinserted had a tetrahedral coordination similar to amorphous aluminosilicates and showed an ion exchange ability. After the exchange of Na+ to NH4+ and decomposition of NH4+ ions, reinserted Al forms generated protonic sites from which some condensed at higher temperatures producing Lewis acid sites (with stoichiometry typical for zeolites i.e., the condensation of two protonic sites produces one Lewis site) but some other kept their character.

Characterization and catalytic properties of a saponite clay modified by acid activation

A natural saponite was acid activated at room temperature or 90°C with different acid/clay ratios and the products were characterized by powder X-ray diffraction, infrared spectroscopy and thermogravimetry. The leaching of Mg from the octahedral sheets is enhanced by an increase in the acid/clay ratio and by an increase in temperature of activation. Textural properties are reported, and it appears that they are strongly correlated to the presence of a noncrystalline silica phase which is formed during the acid activation process. The desorption of cyclohexylamine indicates that for samples activated at 90°C the number of acid sites in the acidactivated saponites decreases following severe acid treatment. Infrared spectroscopy of adsorbed pyridine on samples after calcination at 500°C suggests that acid activation at 90°C produces a single type of Bronsted site but two types of Lewis sites whereas activation at room temperature results in only one type of Lewis site in addition to a Brønsted site. The two Lewis sites are suggested to originate from residual Al in the clay structure and to AI exsolved from the layers during activation. The dehydration of pentan-1-ol has been used as a further probe to measure acidity by monitoring the degree of conversion and selectivity for the different samples.

Early Archaic Settlement in the Southeastern United States: A Case Study from the Savannah River Valley

Surveys and excavations conducted within the Savannah River watershed in recent years have yielded a wealth of information about organization and adaptive strategies of Early Archaic populations, both within the drainage and across the region. Specifically, excavations at Rucker's Bottom (9EB91) and the G. S. Lewis site (38AK228) have yielded large, complementary assemblages indicating watershed-extensive adaptation employing a mixed collector-forager strategy. Comparative analyses with assemblages from the surrounding region document an extensive use of expedient technologies, instead of the more formalized technologies thought to characterize the period. Analyses of local and regional resource structure, theoretical arguments about biocultural needs of hunter-gatherer populations, and evidence from the archaeological record, suggest that large drainage systems served subsistence/resource needs, while biocultural interaction (i.e., information and mating networks) operated both along and across watershed boundaries. A model of Early Archaic settlement is proposed, based on band/macroband mobility and interaction, that is thought to partially account for the variation from this period found on the South Atlantic Slope.