Sawdust as an effective biotemplate for the synthesis of Ce0.8Zr0.2O2 and CuO–Ce0.8Zr0.2O2 catalysts for total CO oxidation

Abstract

Wood sawdust (SD) was successfully used as a biotemplate to prepare precursors of Ce_0.8Zr_0.2O₂ (CZ) and CuO–Ce_0.8Zr_0.2O₂ (Cu–CZ, about 25% of CuO) catalysts, which were tested in total CO oxidation at 100–400 °C after calcination at 500 or 600 °C, and compared with analogous systems prepared using cetyltrimethylammonium bromide (CTAB). The improved specific surface area and oxygen mobility of the catalysts calcined at 500 °C resulted in an increased efficiency in CO oxidation. CZ (SD-500) demonstrated much higher catalytic efficiency than the CZ (CTAB-500) sample despite having a two times less S_BET due to the promoting action of Ca and K inherited from sawdust and improved concentration of superoxide surface centers. Both facilitation of CO adsorption on peroxide and superoxide centers and increased oxygen mobility provide improvement in the high-temperature efficiency of biomorphic CZ in CO oxidation. The XRD, XPS and TPR data testify that Cu in modified systems partially exists as a separate CuO phase, in small amounts as Cu⁺, and partially is incorporated in the surface Cu_yCe_xZr_1−x−yO_2−z and/or Cu_yCe_1−yO_2−x phases. Modification with Cu enhances the low-temperature efficiency of CZ systems, prepared using both templates and calcined at 500 °C. Cu–CZ (SD-500) was a bit less active than Cu–CZ (CTAB-500) only at 100–150 °C, primarily due to the decreased CuO content, and the difference in CuO interaction with CZ support, found by TPR. Presumably CuO provides low-temperature CO oxidation through the Langmuir–Hinshelwood mechanism; the Cu⁺/Cu²⁺ pair can also participate as an additional redox pair in high-temperature CO oxidation by the Mars–van-Krevelen mechanism.