Thermal transformations of Cu–Mg (Zn)–Al(Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen

Magdalena Jabłońska,Agnieszka Węgrzyn,Lucjan Chmielarz,František Kovanda,Richard I Walton,Stefan Witkowski,Peter W Dunne,Katarzyna Guzik,Zofia Piwowarska

doi:10.1007/s10973-012-2935-9

Abstract

Layered double hydroxides (LDHs) containing Mg2+, Cu2+ or Zn2+ cations in the MeII positions and Al3+ and Fe3+ in the MeIII positions were synthesized by co-precipitation method. Detailed studies of thermal transformation of obtained LDHs into metal oxide systems were performed using high temperature X-ray diffraction in oxidising and reducing atmosphere, thermogravimetry coupled with mass spectrometry and temperature-programmed reduction. The LDH samples calcined at 600 and 900 °C were tested in the role of catalysts for selective oxidation of ammonia into nitrogen and water vapour. It was shown that all copper congaing samples presented high catalytic activity and additionally, for the Cu–Mg–Al and Cu–Mg–Fe hydrotalcite samples calcined at 600 °C relatively high stability and selectivity to dinitrogen was obtained. An increase in calcination temperature to 900 °C resulted in a decrease of their catalytic activity, possibly due to formation of well-crystallised metal oxide phases which are less catalytically active in the process of selective oxidation of ammonia.

Highlights

Hydrotalcite-like compounds belong to a group of layered double general hydroxides formula o(fLDÂHMs)I1IÀxaMndIxIIaðOreHrÞe2pÃxrþes1⁄2AennxtÀ=endÁyHb2yOthxÀe where MII and MIII are divalent and trivalent metal ions andAn- is an interlayer n-valent anion
Surface area of the samples depends on both chemical composition as well as calcination temperature
Calcined Cu–Mg–Al, Cu–Mg–Fe and Cu–Zn–Al hydrotalcites were found to be active catalysts for the selective oxidation of ammonia. The activity of these catalysts depended on their chemical composition as well as calcination temperature

Summary

Introduction

Hydrotalcite-like compounds belong to a group of layered double general hydroxides formula o(fLDÂHMs)I1IÀxaMndIxIIaðOreHrÞe2pÃxrþes1⁄2AennxtÀ=endÁyHb2yOthxÀe where MII and MIII are divalent and trivalent metal ions andAn- is an interlayer n-valent anion. The present work is focussed on the mechanism of thermal decomposition of hydrotalcite-like materials containing magnesium, copper, zinc, iron and aluminium and optimisation of the calcination conditions leading to active and selective catalysts of ammonia oxidation to nitrogen and water vapour.

Results

Conclusion