023ChemInform Abstract Titania deposits (TiOx, x 1.9) on a polycrystalline Rh foil are prepared by Ti evaporation under ultrahigh vacuum with subsequent oxidation. The kinetics of CO hydrogenation over these catalysts has been investigated as a function of the TiOx coverage. The methanation rate passes through a maximum at 0.15 monolayers TiOx, corresponding to a threefold increase in activity. This activity enhancement at low coverages is accompanied by a higher selectivity towards olefins (from 10% to 31%), a lower activation energy (from 24.4 to 16.8 kcal mol-1), a higher H2 reaction order (2.6), and a higher CO reaction order (-0.3). The kinetic parameters for olefin production are noticeably different than those for paraffin production. The dependence of the activity on TiOx coverage has been modeled by a Monte Carlo simulation assuming the existence of high activity sites at the oxide-metal interface. This model is consistent with the premise of Ti3+ participation in CO dissociation.

We study experimentally fast flames and their transition to detonation in mixtures of methane, ethane, ethylene, acetylene, and propane mixtures with oxygen. Following the interaction of a detonation wave with a column of cylinders of varying blockage ratio, the experiments demonstrate that the fast flames established are Chapman-Jouguet deflagrations, in excellent agreement with the self-similar model of Radulescu et al. [1]. The experiments indicate that these Chapman-Jouguet deflagrations dynamically restructure and amplify into fewer stronger modes until the eventual transition to detonation. The transition length to a self-sustained detonation was found to correlate very well with the mixtures' sensitivity to temperature fluctuations, reflected by the χ parameter introduced by Radulescu, which is the product of the non-dimensional activation energy E a /RT and the ratio of chemical induction to reaction time t i /t r . Correlation of the measured DDT lengths determined that the relevant characteristic time scale from chemical kinetics controlling DDT is the energy release or excitation time t r . Correlations with the cell size also capture the dependence of the DDT length on χ for fixed blockage ratios.

This study of the water‐contamination reactions of ethylene oxide was conducted by Arthur D. Little, Inc. with funding from, and under the auspices of, the Ethylene Oxide Industry Council, part of the American Chemistry Council. Significant experimental and technical contributions were also made by staff from Shell Chemicals' Westhollow Technology Center in Houston, Texas, and Union Carbide Corporation's Research Center in South Charleston, West Virginia. Unique fourth‐order kinetics for the reactions of ethylene oxide with water, and ethylene oxide with ethylene glycols were derived and validated, as were kinetics for the reactions of neat ethylene oxide and the decomposition of ethylene glycols. The latter data was incorporated into a reaction model useful for the determination of ethylene oxide storage stability and pressure relief system design under water‐contamination scenarios.

No abstract

No abstract