Study of metal oxide catalysts by temperature programmed desorption. 4. Oxygen adsorption on various metal oxides

Abstract

Oxygen adsorption properties of 16 metal oxides were investigated by means of a temperature programmed desorption (TPD) technique. Although oxygen adsorption phenomena were largely different depending on metal oxides, it was possible to classify the oxides as follows: (A) V205, MoOa, Bi203, W03, and 203•2 03 which exhibit no oxygen desorption over the range 10-560 °C; (B) Cr203, Mn02, Fe203, Co304, NiO, and CuO which always give relatively large amounts of oxygen desorption; and (C) Ti02, ZnO, Sn02, A1203, and Si02for which evacuation at high temperature followed by oxygen adsorption at relatively low temperature is required for oxygen desorption to appear over the range 10-400 °C, except the last two oxides. It is noted that group A oxides have layer structures except for Bi2Oa, while group B consists of oxides with cations of d1-d9 electronic structures. Among the oxygen species adsorbed on group C oxides, the 02" ion was directly identified by means of ESR spectroscopy,• and was assigned to specific desorption peaks of respective TPD spectra. The amounts of desorbed oxygen (V^o) for group B and C oxides were only a few percent of the surface coverage, suggesting that the adsorption sites are some sorts of surface defects. There was a fairly good correlation between V560 and the heat of oxide formation per g mol of (-H°), and the amount of adsorbed oxygen tended to decrease with increasing -AH°. These results are discussed in relation to the catalytic properties of the oxides.

Interplay between O2 and SnO2: Oxygen Ionosorption and Spectroscopic Evidence for Adsorbed Oxygen

“…Much effort has been made to correlate the results of the TPD studies on SnO 2 [84,85,[92][93][94][95] with the changes in electrical conductivity, and assign observed TPD peaks to different oxygen species using EPR spectroscopy. In several works, TPD was done in combination with/in parallel to 1) EPR and electrical conductivity, [84] 2) EPR, [93] 3) DC conductance (on thick film samples) and CPD (on films), [95] 4) electrical conductivity.…”

A Linear Free Energy Relationship for Gas‐Solid Interactions: Correlation between Surface Rate Constant and Diffusion Coefficient of Oxygen Tracer Exchange for Electron‐Rich Perovskites

“…The treatment demonstrates the usefulness of linear free energy relationships, which are state of the art for organic solution chemistry, for inorganic solid-state reactions. (10) and (11). The decomposition of DH °i nto contributions from DH°V and DH 0 ox is based on Equation (14).…”

“…[11] Oxygen permeation measurements under surface limited conditions yield a reaction order of [13] ), which indicates that only atomic oxygen species are involved in the rate determining step. The relationship in Equation (2) between the effective activation energies of k * and D* and the mechanism of the diffusion process resulting in Equation (9) imply a significant contribution b DH°V to the effective activation energy E k* of the surface reaction, which stems from the V CC O jump activation enthalpy.…”

Study of cyclohexanol decomposition reaction over the ferrospinels, A1−xCuxFe2O4 (A=Ni or Co and x=0, 0.3, 0.5, 0.7 and 1), prepared by ‘soft’ chemical methods

“…By oxygen-TPD technique, investigation of the oxygen uptake of 16 metal oxides including the first row transition metal oxides has been reported [45,46]. The authors found that the transition metal oxides always gave relatively large amounts of oxygen desorption even at high temperatures.…”