A STUDY OF ANOMALOUS TEMPERATURE-PROGRAMMED REDUCTION PROFILES OF Cu2O, CuO, and CuO-ZnO CATALYSTS

A temperature-programmed reduction (TPR) study of CuO, Cu2O, and CuO-ZnO catalysts, in the atomic range Cu:Zn = 92:8 to 67:33, is reported. In order to promote a correct experimental approach, much attention has been devoted to the choice of the experimental operating variables. Direct evidence is presented that the reduction profiles of the investigated specimens are markedly affected by artefacts when TPR measurements are carried out under conditions of an inadequate combination of initial amount of reducible species, total flow rate, initial hydrogen concentration, and heating rate. It is shown that under correct experimental conditions the reduction profile of each sample is characterized by a single and quite sharp reduction peak. In contrast to this, a dramatic change of shape occurs when an improper combination of the experimental operating variables is imposed: for both CuO and Cu2O an apparent double peak appears, whereas for the CuO-ZnO catalysts the reduction profiles are transformed into broad bands. In all cases, the reliability of the TPR results is completely lost. To explain the complex origin of these artefacts, it is suggested that both a special dynamic situation and activated H2 adsorption- desorption phenomena coinciding with the chemical reduction are responsible for the observed perturbations. A simple kinetic analysis has been developed which enables a qualitative reproduction of the disturbed reduction profiles to be made.