Synthses And Pt Modification Of High-energy Facet Exposed CeO₂ Crystallites Via A Supercritical Water Route

CO has a strong toxic effect on human health, the elimination of which is generally through adsorption or catalytic oxidation processes where the latter has been considered as a promising route. The key to catalytic oxidation technology is the development of efficient catalytic materials.To date, the control syntheses of nano-crystallites with selectively exposing high-energy facets has become a leading edge of the emerging fields in nanotechnology. The exposed high-energy facet could greatly enhance the activity and selectivity of the crystallites during their catalysis applications. In this paper, the face exposure behavior of CeO2 crystallite under supercritical water (sc-H2O) condition has been explored. With the aid of DFT simulation, the mechanism for the high-energy facet exposure of CeO2 was evaluated, coupling with the Pt modification over the CeO2 with an aim to yield highly active catalysts for CO oxidation.(1) Firstly, the paper studied the facet exposure behavior of CeO2 crystallite in supercritical water system (with or without alkali). It was found that either with or without alkali, the CeO2 crystallite had both preferentially exposed (110) high-energy facet surface where the addition of alkali had effectively inhibited the crystal growth of CeO2, reducing the particle size form 100-200 nm to 3-5 nm. Thereafter, a DFT simulation was employed to explore the surface energy of various CeO2 facets in supercritical water system, which showed that the (110) surface had the lowest surface energy, consistent with the experimental result. Accordingly, it could be concluded that the strong oxidation atmosphere of the supercritical water and its high temperature and pressure environment that induced the formation of Ce-OH are the main cause for the high-energy facet exposure of CeO2 crystallite.(2) Secondly, the paper had also investigated the facet exposure behavior of SnO2 and Co3O4 crystallites in supercritical water system. It was found the morphology of SnO2 was in rod bundle flower shape, where its side was exposed (110) facet and its main exposure facet was (221) high-energy facet, growing at the direction of [112]. The Co3O4 crystallite was mainly exposed (110) high energy facet. These results had to some extent demonstrated the universality of supercritical water system in producing metal oxides with high energy facet selective exposure.(3) Finally, the paper explored the CeO2 (110) coupling characteristic with a noble metal Pt. It was found the supercritical water system could effectively result in a Pt and CeO2 (110) coupling. The resulted Pt/CeO2 catalyst was then subjected to CO catalytic oxidation test, which showed an excellent catalytic performance with the CO 100% oxidation at only ca.60℃.