Memory effect of the CuZnAl-LDH derived catalyst precursor—In situ XRD studies

Abstract

Thermal decomposition of the CuZnAl-LDH catalyst precursor and the reverse structural transformations of the oxide forms upon addition of water have been investigated. The object of the studies was chosen in such a way that its composition resembled that of the industrial methanol synthesis and low-temperature water gas shift catalysts precursors. The temperature ranges of the corresponding transformations have been assigned and the structural changes have been discussed. The CuZnAl-LDH catalyst precursor shows a distinct “memory effect” up to the temperatures of 400–600°C. The heat effect of the exothermic hydration process of the mixed oxides, (Cu,Zn)AlOx has been estimated and correlated with a degree of recovery of the material layered structure. Above 600°C irreversible structural transformations proceed, leading in consequence to the gradual decline of this effect. The recovery kinetics of the layered ordered structure has been determined based on the in situ XRD measurements and Avrami–Erofeev's model.