Differential heats of adsorption have been measured for a series of alcohols, a series of nitriles, water, and diethyl ether in H-ZSM-5 and silicalite. Higher differential heats in H-ZSM-5 demonstrated that most of the adsorbates had a significant affinity for the Brønsted sites, and the affinity increased with the gas-phase proton affinity of the adsorbate. For the nitriles and diethyl ether, the differential heats were approximately constant up to a coverage of 1/site, after which values fell to the level on silicalite. The heat of formation of the 1:1, stoichiometric adsorption complexes increased with the proton affinity with a slope of 0.37. Heats of formation of stoichiometric adsorption complexes were difficult to identify for water and the alcohols since the differential heats did not fall at a coverage of 1/site. This is evidence for adsorbate clusters, the result of alcohols being both hydrogen-bond acceptors and donors. The implications of these results for understanding zeolite acidity and acid catalysis are discussed.
The adsorption and reaction of ethanol on the metal-free, pure silicon dioxide surface have been studied as a model system to explore the chemical origin of the defects which are detrimental in the gate oxide exposed to chemical vapors. In addition to molecular adsorption, ethanol decomposed to the extent that a variety of species including ethyl, ethoxy, and hydroxyl were produced even at the surface temperature of 115 K. The silicon dioxide surface was selective for the formation of acetaldehyde through cleavage of the C-H bond. The bare surface, however, was more selective for ethanol conversion to ethylene than the surface covered by fragments and products. Comparison of static secondary ion mass spectra taken from the surface exposed to deuterated and nondeuterated ethanol, respectively, showed that the C-H, Et-OH, and EtO-H bonds were disrupted during the surface decomposition of ethanol. Hydroxyl hydrogen of ethanol readily exchanged with silanol hydrogen of the surface. The formation of Si-H and SiO-H bonds suggests that hydrogen concentration will increase on the metal-free silicon dioxide surface exposed to organic vapors. Its implication to the generations of defects in the silicon dioxide framework and of the stress-induced leakage current will be discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.