Article,
Raman studies of nanocomposites catalysts: temperature and pressure effects of CeAl, CeMn and NiAl oxides
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, (2018)
DOI: 10.1016/j.saa.2018.02.064
Abstract
High temperature and pressure effects on the physicochemical properties
of binary oxides catalysts were investigated. The nanocomposites
catalysts comprising of CeAI, CeMn and NiAl were characterized through
various physicochemical techniques. A study of the temperature and
pressure induced phenomena monitored by Raman spectroscopy was proposed
and discussed. Spectral modifications of the Raman modes belonging to
the CeMn suggest structural changes in the solid due to the MnO2 phase
oxidation with increasing temperature. The thermal expansion and lattice
anharmonicity effects were observed on CeMn due to lack of stability of
the lattice vacancies. The CeAI and NiAl composites presented
crystallographic stability at low temperatures however, undertake a
phase transformation of NiO/Al2O3 into NiAl2O4, mostly without any
deformation in its structure with increasing the temperature. It was
also inferred that the binary oxides are more stables in comparison with
monoxides. Detailed pressure-dependent Raman measurements of the T-2g
phonon mode of CeMn and NiAl revealed that the pressure contributes to
modify bonds length and reduces the particles sizes of the solids. On
the contrary, high pressure on CeAI sample improved the stability with
addition of Al2O3 in the CeO2 lattice. The results then suggest a good
stability of CeAl and NiAl composite catalysts at high pressure and low
temperature and show how to prospect of tuning the catalysis for surface
reactions entirely through in situ spectroscopic investigations means.
(C) 2018 Elsevier B.V. All rights reserved.
