Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions

Abstract

O 2 adsorption is a key process for further understanding the mechanism of selective CO oxidation (SCO) on gold catalysts. Rate constants related to the elementary steps of O 2 adsorption, desorption and surface bonding, as well as the respective activation energies, over a nanosized Au/γ-Al 2 O 3 catalyst, were determined by Reversed-Flow Inverse Gas Chromatography (RF-IGC). The present study, carried-out in a wide temperature range (50-300 C), both in excess as well as in the absence of H 2 , resulted in mechanistic insights and kinetic as well as energetic comparisons, on the sorption processes of SCO reactants. In the absence of H 2 , the rate of O 2 binding, over Au/γ-Al 2 O 3 , drastically changes with rising temperature, indicating possible O 2 dissociation at elevated temperatures. H 2 facilitates stronger O 2 bonding at higher temperatures, while low temperature binding remains practically unaffected. The lower energy barriers observed, under H 2 rich conditions, can be correlated to O 2 dissociation after hydrogenation. Although, H 2 enhances both selective CO reactant's desorption, O 2 desorption is more favored than that of CO, in agreement with the well-known mild bonding of SCO reactant's at lower temperatures. The experimentally observed drastic change in the strength of CO and O 2 binding is consistent both with well-known high activity of SCO at ambient temperatures, as well as with the loss of selectivity at higher temperatures.

Kinetics of the catalytic oxidation of morin on γ-Al 2 O 3 supported gold nanoparticles and determination of gold nanoparticles surface area and sizes by quantitative ligand adsorption

“…Well dispersed AuNPs on gamma-alumina (␥-Al 2 O 3 ) support exhibit a high activity in various low-temperature oxidation reactions [4,18,19]. Gamma alumina is of catalytic interest and widely used as a support [3,4,19,20].…”

Determination of Sulfur Dioxide Diffusion Coefficients in Hydrogen, Helium, and Nitrogen by Reversed-Flow Inverse Gas Chromatography

“…Reversed-flow inverse gas chromatography (RF-IGC) is ideal to study slow rate processes, not affected by the mobile phase flow rate, − and carry out physicochemical measurements, thus it is also classified as an inverse GC technique. It has been applied, among the others, for the measurement of gaseous diffusion coefficients, − mass-transfer parameters across the gas–liquid interphase, − collision cross-sectional parameters based on diffusivity measurements, as well as in various studies related to gas–solid interactions. − …”

Reversed-Flow Gas Chromatography as a Tool for Studying the Interaction between Aroma Compounds and Starch

“…RF-GC is a time-honored method which involves the change of the carrier gas flow direction at various time intervals. It has a vast number of applications in a wide scientific field such as the determination of diffusion and mass transfer coefficients, − adsorption isotherms, the kinetic study of alcoholic fermentation, , rate constants for catalytic reactions, − thermodynamic study of polymer solutions, etc.…”