NH3 interaction with chromium-doped WO3 nanocrystalline powders for gas sensing applications

Ammonia interaction with chromium-doped WO3 nanocrystalline powders was investigated. Chromium centres were characterised by EELS, Raman, XPS, EPR and UV-visible spectroscopy. Essentially, these studies revealed that chromium was well distributed on WO3, forming Cr(III) species and chromyl groups [Cr=O](3+). Test of thick-film gas sensors based on chromium-doped WO3 revealed that chromium addition boosted sensor response to NH3. Besides, it also avoided unsatisfactory dynamic behaviour previously found in gas sensors based on pure WO3. DRIFT spectroscopy and TPD were used to investigate the surface chemistry of ammonia over pure and chromium-doped WO3 nanocrystalline powders. It was concluded that chromium favours the combustion of ammonia into molecular nitrogen and nitrous oxide on chromium centres, which contributes to the improvement in the sensing properties of the material.