S.D. Worley

Infrared spectroscopy at high pressure: Interaction of CO with oxidized Rh/Al2O3

Infrared spectroscopy was used to study the interaction of CO with preoxidized Rh/Al{sub 2}O{sub 3} catalyst films in a high-pressure cell reactor. An infrared band near 2,125 cm{sup {minus}1}, which had previously been assigned to a Rh{sup 2+}CO species and to one band component of an asymmetric Rh(CO){sub 3} species by two different laboratories, is now assigned to Rh{sup 2+}CO. This work demonstrates that gas-phase contributions from infrared-active species with high extinction coefficients can be eliminated from surface contributions, even at high pressures of the gas.

A thermal desorption study of methyl formate from W(100) and its relevance to the catalytic production of methane

Abstract Previous work has suggested that methyl formate is a possible intermediate in the catalytic production of methane from formaldehyde on a tungsten (100) single crystal. To test this hypothesis, a study of methyl formate interaction with W (100) has been performed. The major products desorbed upon heating a saturated layer of methyl formate on W(100) were hydrogen and carbon monoxide. However, a significant yield of formaldehyde and small amounts of methane, carbon dioxide, and several organic products believed to be methyl formate, glycolaldehyde, and methyl alcohol were also observed. The thermal desorption products and their desorption kinetics from methyl formate adsorbed on W (100) were very similar to those from formaldehyde on W (100). A sequence of reactions which might account for this similar behavior is suggested.

The electronics structures of small strained rings. An investigation of the interaction between the oxygen and the π orbitals in 3-methyleneoxetane and 3-oxetanone

Abstract The ultraviolet photoelectron spectra of 3-methyleneoxetane (I), 3-oxetanone (II) and β-propiol-octane (III) have been investigated for the purpose of studying the interaction processes between the endocyclic oxygen and the methylene or carbonyl groups of I and II, respectively. Molecular orbital calculations at the MINDO/3, MNDO, and STO-3G/431-G levels have been performed to aid analyses of the data. The interaction process occurs primarily through the pseudo-π-CH 2 orbitals for I and II. Substantial stabilizing inductive effects are noted for the lone-pair and π orbitals for these molecules.

Mode of migration of isocyanate from palladium to silica

The reaction of CO and NH3 over preoxidized PdSiO2 has been studied using infrared spectroscopy to identify surface species. An isocyanate (NCO) surface intermediate on Pd providing an infrared band at 2168 cm−1 was detected after heating to 500 K and subsequent cooling to ambient temperature. No migration of NCO from Pd to the SiO2 support was observed. However, the decomposition of formamide over preoxidized PdSiO2 at ambient temperature did produce an NCO species which migrated to the SiO2 via the formation of HNCO gas. It was concluded that an amide species is not an intermediate in the CONH3 reaction over preoxidized PdSiO2, although it may be for the reaction over preoxidized PdAl2O3.

An AM1 SCF MO study of the reaction of formaldehyde with atomic oxygen

Abstract The decomposition process for formaldehyde in the presence of atomic oxygen has been investigated using AM1 semiempirical SCF MO calculations. It is found that for both singlet and triplet energy surfaces the most facile predicted decomposition pathway involves insertion of atomic oxygen to form formic acid followed by a second insertion to produce carbonic acid which then decomposed to CO 2 and H 2 O. Decomposition through a tetrahedral H 2 CO 2 methylenebis(oxy) species, considered by some previous workers, is predicted to be an unfavorable process.

An infrared study of the hydrogenation of carbon monoxide and carbon dioxide at high pressure over Pd/La2O3

Abstract A newly designed high-pressure infrared cell reactor has been used to study the reactions of CO and CO 2 with H 2 over Pd/La 2 O 3 films. The activation energy for the CO 2 hydrogenation (25.1 kcal mol −1 ) to produce methanol is higher than that reported elsewhere for the analogous CO hydrogenation reaction. It is proposed that the CO 2 reaction proceeds through hydrogenation of adsorbed CO, rather than by direct hydrogenation of CO 2 over Pd/La 2 O 3 .

The nature of the surface site for isocyanate produced in the reaction of ammonia and carbon monoxide over supported catalysts

Abstract The reaction of CO and NH 3 was performed over M/X (M=Rh, Ru, Pd; X=Al 2 O 3 , SiO 2 , TiO 2 ) films. Infrared spectroscopy was used to monitor the formation of surface intermediates. Isocyanate (NCO) was detected for all of the metals when the support was Al 2 O 3 or SiO 2 , but not for TiO 2 . The NCO resided on the Al 2 O 3 support for all M/Al 2 O 3 catalysts, but on the metal when the support was SiO 2 . It was concluded that the formation and location of the NCO was dependent upon the extent of NH 4 + formation on the various supports.

A semi-empirical MO study of a series of amide, imidic acid, and imidate isomers

Semi-empirical SCF MO calculations at the MINDO/3 and MNDO levels have been employed to estimate the relative stabilities of a series of amide, imidic acid, and imidate isomers of general formula C3H7NO. The results obtained here illustrate that sufficient quantities of imidic acids may be present during the photolysis of their more stable amide isomers to provide photochemical access to a low-energy enolic excited state which could after the photochemical behavior of the amides.

The electronic structures of some biological piperazines

Abstract The ultraviolet photoelectron spectra of three piperazine 2,5-diones and their N,Ń-dichloro derivatives have been investigated. The chlorinated derivatives are effective antimicrobial agents. Band assignments have been proposed, and the predominant molecular conformations of the molecules have been predicted based upon the oxygen and nitrogen lone-pair band positions for the six molecules and MINDO/3 SCF MO calculations for the nonchlorinated derivatives.

An infrared study of the oxidation of carbon monoxide over supported rhodium catalysts

Abstract The reaction of carbon monoxide and oxygen over supported rhodium films has been studied using infrared spectroscopy. The focus of the work was the reactivity of the various CO/Rh/X (X = Al2O3, SiO2, TiO2) surface states for supported catalysts having high and low Rh loading. Under the reaction conditions the “linear CO” species was the most stable toward oxidation, but this could have been a result of an oxidized Rh surface. A new CO/Rh surface species has been proposed which exhibits an infrared band at 2000 cm−1 for a 0.5% Rh/TiO2 film. This species is believed to be a bridged carbonyl between Rh1+ and the TiO2 support.