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

• Characteristics of the CuZnAl-LDH precursor and ex-LDH materials as active copper catalysts.
• In situ XRD studies of the initial layered structure recovery–memory effect.
• Structural and textural changes of CuZnAl-LDH calcined up to 400 °C reversible to a large extent.
• Above 600 °C the formation of irreversible highly crystalline non-layered oxides.
• Correlation between the heat effect and degree of structure recovery.

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.

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