Influence of gold presence and thermal treatment on recrystallization of copper-manganese ferrite catalysts

Abstract

The present work aims to evaluate the influence of synthesis conditions and gold addition on structural and functional characteristics of copper-manganese ferrites. Object of the investigation is spinel ferrite with composition Cu0.5Mn0.5Fe2O4, thermally treated at different conditions. The influence of gold deposition on structure of ferrites and catalytic properties in water-gas shift reaction (WGSR) is studied on the ferrite sample obtained at 300 ∘C. Structural characteristics of samples are determined by Mossbauer spectroscopy and X-Ray diffraction. The Mossbauer spectra of treated at different temperature ferrite samples consist of sextet and doublet components. A comparative assessment of crystallite size of ferrite phase was accomplished from the calculated value of the hyperfine fields. It was established well expressed tendency of ferrite crystallite growth with increasing of thermal treatment temperature. Increasing of the ferrite crystallite size in presence of gold in the sample is established, too. The analysis of catalytic activity in WGSR shows unexpected result i.e. the activity of gold-modified ferrite sample is lower than that of the sample without gold. Probably this is due to complex factors, including recrystallization of the ferrite phase due to additional thermal treatment at higher temperature, addition of gold, changes of the structural features and phase composition during catalytic test.