Roger L. Schneider

Evidence for production of surface formate upon direct reaction of CO with alumina and magnesia

Abstract The observation of adsorbed formate ion produced by the reaction of CO with MgO or γ-Al 2 O 3 surfaces at temperatures between 375 and 575 K is reported. Infrared bands observed near 1590, 1380, 1360, and 1050 are assigned to the fundamentals of adsorbed HCO 2 − ion on the basis of spectra that have been reported for formate ion in solution. The spectral bands and observed isotopic shifts for adsorbed formate produced by reaction of the oxide surface with CO agree with the spectra of formates produced by reaction of methanol or formic acid with the same surfaces. The intensity of IR bands due to formate produced by reaction of the oxide surfaces with CO depends upon the hydroxyl group concentration at the surface. A mechanism for conversion of CO to formate via a surface acylium ion is proposed.

A chemical and physical characterization of alumina-supported Rh6(CO)16

The decarbonylation and carbonylation reactions of the metal cluster carbonyl Rh6(CO)16 supported on Al2O3 were investigated using volumetric gas adsorption measurements, ir spectroscopy, isotopic measurements, transmission electron microscopy, and EPR spectroscopy. Complete decarbonylation by O2 and subsequent recarbonylation to Rh6(CO)16 could be achieved at room temperature provided sufficient physically adsorbed H2O was present. A two-step reaction scheme is presented which accounts for the experimental data; it is suggested that the Rh6 cluster remained intact during these reactions. When heated, in vacuo, above 250 °C, the catalyst lost its ability to undergo the reversible carbonylation/decarbonylation cycle, and the resulting material resembled a highly dispersed conventional Rh catalyst. TEM data showed that no larger crystallites (>10 A) of Rh are formed even when heated in vacuo to 450 °C.

Interactions of cobalt carbonyls with oxide surfaces: I. (CO)9Co3CCH3 on silicas, aluminas, and zeolites

Abstract The adsorption and subsequent reactions of the cobalt cluster compound μ 3 -ethylidine-tris-(tricarbonyl cobalt), I , on silica, alumina, and zeolite supports were investigated. The supports were pretreated, in vacuo , at temperatures between 295 and 700K. On silica, I appears to be physisorbed and reacts only slowly with O 2 to produce decarbonylated products. Adsorption on alumina produces physisorbed I and at least three cobalt carbonyl products of the reactions of I with the support. Aluminas pretreated at lower temperatures are the most reactive toward I , as evidenced by the greater tendency of I to react and form novel cobalt carbonyls on these aluminas. These reaction products are immediatley oxidized by O 2 to produce carbonate, bicarbonate, and oxidized cobalt. Compound I adsorbs at room temperature inside the supercages of a Na Y zeolite; it is subsequently converted, at elevated temperatures (350K), to the carbonyl species which were identified on alumina. Infrared and manometric data show that thermolysis and oxidation of I on zeolite ultimately lead to its total decarbonylation to produce carbonates, bicarbonates, and organic carbonyl fragments.

Model for the vaporization of mixed organometallic compounds in the metalorganic chemical vapor deposition of high temperature superconducting films

A model of the vaporization and mass transport of mixed organometallics from a single source for thin film metalorganic chemical vapor deposition is presented. A stoichiometric gas phase can be obtained from a mixture of the organometallics in the desired mole ratios, in spite of differences in the volatilities of the individual compounds. Proper film composition and growth rates are obtained by controlling the velocity of a carriage containing the organometallics through the heating zone of a vaporizer.

Formation and characterization of YBa2Cu3O7−δ high-Tc thin films by MOCVD with single mixed precursor

Abstract In view of the promising role of the MOCVD technique in the advance of YBCO high- T c superconducting thin films grown for device applications, a simplified chemical vapor deposition system with a single mixed organometallic precursor was built and tested. Single phase YBa 2 Cu 3 O 7-δ films with T c values around 90 K were readily obtained on (100) YSZ and (100) MgO substrates with a normal precursor mass transport. Investigations indicate that, in addition to the gas phase stoichiometry as a major factor, the phase composition and crystallite orientations of the YBCO films were considerably affected by the oxidation agent (partial pressure and concentration) as well as the substrate temperature. The films could be either highly oriented (00 l ) or (100) and / or (110) orientation dominated. A single phase Y 2 Cu 2 O 5 film with (002) orientation was obtained from a Ba deficient gas phase. The variation in superconducting behavior of the YBCO thin films deposited under different conditions was not only related to these phases but also to the growth orientation. The film uniformity and flatness are examined and discussed in terms of the gas flow pattern in the reactor.

Vaporization of a mixed precursor in chemical vapor deposition of YBCO films

Single-phase YBa2Cu3O7−δ thin films withTc values around 90 K are readily obtained by using a single-source chemical vapor deposition technique with normal precursor mass transport. The quality of the films is controlled by adjusting the carrier gas flow rate and the precursor feed rate.