Abstract
Cerium oxide (CeO2) was prepared using a controlled-precipitation method under microgravity at the International Space Station (ISS). For comparison, ceria was also synthesized under normal-gravity conditions (referred as control). The Brunauer-Emmett-Teller (BET) surface area, pore volume and pore size analysis results indicated that the ceria particles grown in space had lower surface area and pore volume compared to the control samples. Furthermore, the space samples had a broader pore size distribution ranging from 30–600 Å, whereas the control samples consisted of pore sizes from 30–50 Å range. Structural information of the ceria particles were obtained using TEM and XRD. Based on the TEM images, it was confirmed that the space samples were predominantly nano-rods, on the other hand, only nano-polyhedra particles were seen in the control ceria samples. The average particle size was larger for ceria samples synthesized in space. XRD results showed higher crystallinity as well as larger mean crystal size for the space samples. The effect of sodium hydroxide concentration on synthesis of ceria was also examined using 1 M and 3 M solutions. It was found that the control samples, prepared in 1 M and 3 M sodium hydroxide solutions, did not show a significant difference between the two. However, when the ceria samples were prepared in a more basic medium (3 M) under microgravity, a decrease in the particle size of the nano-rods and appearances of nano-polyhedra and spheres were observed.
Highlights
Cerium oxide (CeO2) is a widely used catalyst support due to its high oxygen storage capacity and high oxygen ion conductivity
We report the effect of microgravity on the synthesis of ceria
Regarding the effect of pH on the pore volume and surface area, higher surface areas and pore volumes were observed with increase in basicity of the medium for space samples whereas the opposite trend was exhibited by the control samples
Summary
Cerium oxide (CeO2) is a widely used catalyst support due to its high oxygen storage capacity and high oxygen ion conductivity. A variety of methods to synthesize ceria have been reported until now, including precipitation [20], spray pyrolysis [21,22], thermal hydrolysis [23], micro-emulsion [24], combustion [25], sonochemical [26], hydrothermal [27], solvothermal [28,29], and sol-gel [30] techniques It is a well-established fact that changing the synthesis parameters, such as temperature, pressure, pH, and crystallization time, produces different particle sizes and morphologies, which, in turn, alter the physical and chemical properties of ceria, as well as the catalytic performance of the ceria-supported catalysts. Deshpande et al [32] obtained 17% to 44%
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