James J. Carberry

Some unique aspects of CO oxidation on supported Pt

Abstract Supported Pt catalyzed oxidation of CO was studied as a function of sintering severity. Specific rate data (moles CO oxidized/time · area of Pt) indicate the reaction to be demanding at low CO concentration and facile at higher CO concentrations. Further, sustained isothermal oscillations were observed. Overall kinetic behavior and the oscillations can be rationalized by viewing the oxidation process as one consisting of (a) an Eley-Rideal mechanism involving gaseous CO reacting with adsorbed O 2 at low CO concentrations, and (b) chemisorption of O 2 upon a surface partially covered with CO at higher CO concentrations. Global sintering kinetics in air are found to be second order in surface area with an activation energy of about 60 kcal.

Spurious limit cycles and related phenomena during CO oxidation on supported platinum

A study of CO oxidation on Ptα-Al2O3 catalyst was carried out in the temperature range 370 to 420 °K, in oxygen. Attention was devoted specifically to isothermal limit-cycle phenomena in this reaction. Spurious limit-cycle phenomena resulting from trace impurities in the oxygen stream were observed. Some characteristics of these, and the conditions under which they occur were elucidated. Further, changes in catalytic behavior proceeding from modifying treatments in oxidizing and reducing environments were noted and related to similar phenomena reported by other authors.

Surface characterization and catalytic properties of perovskite type solid oxide solutions, La0.8Sr0.2BO3 (B = Cr, Mn, Fe, Co or Y)

The surface compositions of La0.8Sr0.2BO3 (B = Cr, Mn, Fe, Co or Y) were investigated by X-ray photoelectron spectroscopy (XPS). Among the five solid oxide solutions, the yttrium showed the highest concentration in the surface atomic ratio [B-ion(La + Sr)]. Furthermore, the O1s spectra characteristics of yttrium perovskite are found to be different from those of the other solid solutions with the peak shifted to higher binding energy value. The electrical conductivity of La0.8Sr0.2CrO3 and La0.8Sr0.2YO3 were also measured as a function of temperature in air. The Eσ values for conduction were found to be 0.12 and 0.72 eV respectively. The conductivity data correlated well with the catalytic activity of these solid solutions for the oxidation of methane.

Mass diffusion and isothermal catalytic selectivity

An elementary analysis provides a general expression for isothermal selectivity in the first-order reaction sequence A → B → C as catalysed by porous pellets consisting of micropores branched from macropores. Selectivity (yield of B) is concisely related to the intrinsic rate constants, the micro- and macropore effectiveness factors and the fluid phase transport coefficients for the pertinent species. Conditions corresponding to zero and negative selectivity are specified in terms of effective rate coefficient and intraparticle diffusivity ratios for a given intrinsic (surface) selectivity.

On the merits of partially impregnated catalysts

Abstract A digital computer simulation of adiabatic SO2 oxidation over supported platinum was carried out in which performance of partially impregnated catalysts (Pt deposited solely to within a fractional distance of total support radii) is compared to that of a totally impregnated support. In this diffusion-affected reaction, definite advantages in space-time-yield are shown for the partially impregnated support.

Design and optimization of a tube-wall reactor

Abstract Optimization of a tube-wall reactor and comparison with an optimized conventional fixed-bed reactor shows the wall reactor to have several significant advantages. Among these are higher productivity and yield, smaller reactor volume, less catalyst, lower pressure drop, and improved sensitivity and control. It is also shown that the Hooke-Jeeves pattern search optimization algorithm is rather severely hampered by the imposition of a length constraint.

Surface characterization and catalytic properties of La1−xAxMO3 perovskite type oxides. Part I. Studies on La0.95Ba0.05MO3 (M = Mn, Fe or Co) oxides.

Abstract Perovskite type La 0.95 Ba 0.05 MO 3 ( M = Mn , Fe or Co ) oxides were prepared by a liquid precursor method and characterized by X-ray diffraction, oxygen desorption, and X-ray photoelectron spectroscopic studies. XPS analysis revealed the characteristic changes of the O1s peak (∼530 eV) resulting from the substitution of Ba in LaMO 3 . The methane deep oxidation reaction was carried out in a plug flow reactor with 2% CH 4 in air in the temperature range of 200 to 700°C. Among the three compounds, the Mn perovskite showed the lowest temperature for the methane conversion with a maximum at 700°C. Temperature programmed desorption (TPD) experiments also indicated the maximum oxygen desorption for Mn perovskite in this temperature range. The results for oxygen chemisorption and surface area of these samples were found to be consistent with the observed variation in the catalytic oxidation of methane.

On the influence of γ-Irradiation upon catalytic selectivity: I. Oxidation of ethylene over supported silver

Abstract The yield of ethylene oxide in the oxidation of ethylene over a commercial (Engelhard) supported catalyst is significantly enhanced by preirradiation of said catalyst in a 60Co γ-source. The effect is reversible in that reduction in H2 and reoxidation restores normal behavior and reirradiation in air restores the enhancement. Electron spectroscopy chemical analysis studies reveal that irradiation prompts the appearance of Ca upon the surface which rediffuses into the bulk upon reduction and reappears upon reirradiation. The observed yield of ethylene oxide enhancement is attributed to chemisorbed superoxide (of Ca) formation upon the surface, a postulate in accord with the speculation that ethylene oxide is generated via surface O2− sites.

Effect of surface area on CO oxidation by the perovskite catalysts La1−xSr x MO3-δ (M = Co, Cr)

The catalytic oxidation of carbon monoxide by two compounds in the system La0.8 Sr0.2MO3-δ (M = Co, Cr) was measured at different BET surface areas of the oxide materials. The light-off temperature was found to decrease with increasing surface area up to a certain level beyond which it remained constant for the cobalt-containing compound. This limiting value could not be attained for the chromium-containing compound because of equilibration problems in the preparation. As the active catalytic area as distinct from the total (BET) catalyst area was not clarified, these preliminary results show the need for further inquiry.

CO oxidation activity and XPS studies of PtCuγ-Al2O3 bimetallic catalysts

Abstract The kinetics and activity for CO oxidation of sintered and unsintered PtCu γ Al 2 O 3 catalysts were studied. Hydrogen chemisorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were employed to characterize the catalysts and interpret differences in catalytic activity. The results suggest that both separate and combined PtCu entities coexisted in these catalysts. Preferential Cu enrichment was also observed in the combined entities. The activity of the sintered bimetallic catalysts increased slightly whereas the activity of the sintered Pt catalyst decreased significantly.