Synthesis Of Ce2o3 And Characterization Of Hydrogen Insertion Using Neutron Diffraction And Spectroscopic Methods

The catalytic activity of ceria originates from oxygen vacancies. Ce2O3 is the most oxygen-deficient end-member of non-stoichiometric ceria, CeO2-x. A new method of synthesizing air-stable Ce2O3 from the micron- and nano-sized CeO2 powder was developed. The key part of this synthetic process is to reduce the sample in a low-pressure H-2 gas (10 Torr) under vacuum at 1300 degrees C. The percentage of the Ce2O3 phase in the reduced sample ranges from 55% similar to 96 wt.% according to the powder size and reduction time. Hydrogen incorporation in reduced ceria was confirmed by secondary ion mass spectrometry depth profile analysis and vibrational spectroscopic techniques, such as Raman and Fourier transform infrared spectroscopy. The surface region (zero depth) showed the highest H concentration that decreased with increasing profiling depth. The locations of hydrogen incorporated in the Ce2O3 phase in the reduced sample were revealed by calculating the nuclear density distribution. The maximum entropy method-based pattern fitting and Dysnomia program were combined to calculate the nuclear density map using the neutron diffraction data.