Preparation and characterisation of some nano-structured catalytic materials for low-temperature oxidation of carbon monoxide

Abstract

This project is focused on the synthesis, modification and characterization of rhodium based catalysts supported on MCM-41 mesoporous silica to produce well-defined active sites for catalysis of CO oxidation at low-temperature. The Rh catalysts were prepared by incipient wetness impregnation (IWI) then modified by the inclusion of different transition metal oxides (ca. CeOx, ZrOx, CrOx, Ce0.5Zr0.5Ox and Ce0.5Cr0.5Ox) via two different routes. The first was achieved by pre-modification of MCM-41 support during its synthesis using the inorganic precursors of the promoter oxides followed by the addition of the specified Rh precursor (0.5 - 2.5 wt%), i.e. post-synthesis of Rh catalysts. The second route was performed by the post addition of the promoters using their non-inorganic sources [ca. Ce(acac)3, Zr(acac)4 and bis(benzene)chromium] by the controlled surface modification (CSM) method. The catalysts were characterized by using TGA, FT-IR, N2 physisorption analysis, PXD, SEM-EDX, TEM, DR UV/Vis spectroscopy and XPS. Furthermore, the structure-performance relationship and the dependence of the preparation method towards CO oxidation were also investigated by in situ QEXAFS-MS spectroscopy in the temperature range of 300 - 573 K. The combination of soft and hard X-ray absorption edges was applied to in situ structural studies. In addition to the Rh K-edge, the Ce L3, Zr K or Cr K-edges were used as probes of the catalysts as a function of temperature (300 - 573 K) under of different ambient gases (He, 10% H2/He, 10% O2/He and 10% CO/O2/He) during activation and reaction conditions. As a result, the fractions of Rh active species, coordination numbers and atom-to-atom distances were extracted from analysis of XANES and EXAFS results. In addition, the turnover frequency (TOF) values and CO conversion% over these catalysts were also calculated. The results revealed that Rh species and/or the promoter oxides prepared by both two methods were well confined into the mesoporous framework of silica support in amorphous nano-sized scale. However, the distribution of the Rh atoms and/or the promoter oxides depends mainly on the preparation method with much more homogeneity and local vicinity in those prepared by the CSM method. Furthermore, the preparation method played a crucial rule not only in the local structure, but also in the catalysts performance towards CO oxidation with high activity for catalysts prepared by CSM.

More information

Identifiers

ORCID for John Evans: orcid.org/0000-0003-3290-7785

Catalogue record

Export record