Reduction and Sulfidation Kinetics of Cerium Oxide and Cu-Modified Cerium Oxide

Abstract

The reducibility and H2S absorption capacity of cerium oxide and Cu-containing cerium oxide were examined in this work in the temperature range 623−923 K. The sorbents, prepared in bulk oxide form by the urea coprecipitation/gelation method, were composed of a cerium oxide backbone with a small amount of copper (5−40 atom %). Kinetics testing was conducted in a TGA apparatus. Temperature-programmed-reduction (TPR) experiments and in situ X-ray diffraction analysis were used to determine the reduction temperature and the various metal/oxide crystal phases. CuO in ceria was reduced to Cu metal at temperatures below 453 K. The reducibility of cerium oxide was increased by the presence of copper. A low Cu content (5 atom %) was sufficient to cause surface reduction of ceria at a temperature as low as 423 K. Sulfidation of prereduced samples was performed at 0.1 MPa in H2S−H2−N2 gas mixtures. The contribution of reduced cerium oxide to sulfidation was evident even at the low temperature 623 K. Thus, copper promotes both the reducibility and sulfidation of cerium oxide. The activation energy of the sulfidation reaction was calculated from initial sulfidation reaction rates over the temperature range 623−923 K. A low apparent activation energy of 16 ± 3 kJ/mol was found for the Cu contents 5 and 15 atom % in ceria, while the activation energy is 34 kJ/mol for the 40 atom % Cu−CeO x sorbent. This work has shown that copper-modified cerium oxide can be used as a sulfur sorbent over a wide temperature window.

Transient kinetic model of CO oxidation over a nanostructured Cu0.1Ce0.9O2− catalyst

“…However, as already discussed, the CO oxidation over nanostructured Cu 0.1 Ce 0.9 O 2−y catalyst does not proceed by this type of surface reaction. As shown by other authors, apparent activation energies between 14.2 and 50.1 kJ/mol are typical of various surface reactions over a nanostructured Cu 0.1 Ce 0.9 O 2−y catalyst [43,50,51]. This is in agreement with apparent activation energies between 9.7 and 39.6 kJ/mol measured for surface reactions that were considered in this study.…”

Preparation, characterization and catalytic properties of CuO/CeO2 system

“…3 shows the XRD patterns of CuO/CeO 2 catalysts with various CuO loadings calcined at 500 -C for 3.5 h. Only CeO 2 XRD peaks were observed when CuO loading was lower than 6.30 wt.%. The weak peaks attributed to CuO crystal phase can be observed on 10.08 wt.% CuO/ CeO 2 catalyst, indicating that bulk CuO had already formed on the 10.08 wt.% CuO/CeO 2 catalyst in addition to the dispersed clusters of copper oxide [11]. As expected, the intensity of CuO crystal phase peaks increased with the increase of CuO loading.…”

Determining the Ce2O2S–CeOx phase boundary for conditions relevant to adsorption and catalysis

“…Understanding the interaction of sulfur with ceria is important in a variety of applications where ceria is used as a catalyst, catalyst support, or sorbent [1][2][3][4][5][6]. These applications range from automotive emissions control to sulfur removal from fuels and flue gasses, to solid oxide fuel cells.…”

“…In the case of automotive catalysts it is commonly thought that sulfate formation reduces the ability of the ceria to manage the oxygen partial pressure in the catalytic converter [1]. It is important to note, however, that while sulfates undoubtedly play a role in the deactivation of ceria under oxidizing conditions, different sulfur containing compounds may be formed under reducing conditions [5,6,[15][16][17]. A detailed knowledge of cerium-sulfur chemistry under reducing conditions is therefore needed in order to fully understand sulfur deactivation of ceria.…”