Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.

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.

A series of CrO_x-ZrO₂-SiO₂ (CrZrSi) catalysts was prepared by a “one-pot” template-assisted evaporation-induced self-assembly process. The chromium content varied from 4 to 9 wt.% assuming Cr₂O₃ stoichiometry. The catalysts were characterized by XRD, SEM-EDX, temperature-programmed reduction (TPR-H₂), Raman spectroscopy, and X-ray photoelectron spectroscopy. The catalysts were tested in non-oxidative propane dehydrogenation at 500–600 °C. The evolution of active sites under the reaction conditions was investigated by reductive treatment of the catalysts with H₂. The catalyst with the lowest Cr loading initially contained amorphous Cr³⁺ and dispersed Cr⁶⁺ species. The latter reduced under reaction conditions forming Cr³⁺ oxide species with low activity in propane dehydrogenation. The catalysts with higher Cr loadings initially contained highly dispersed Cr³⁺ species stable under the reaction conditions and responsible for high catalyst activity. Silica acted both as a textural promoter that increased the specific surface area of the catalysts and as a stabilizer that inhibited crystallization of Cr₂O₃ and ZrO₂ and provided the formation of coordinatively unsaturated Zr⁴⁺ centers. The optimal combination of Cr³⁺ species and coordinatively unsaturated Zr⁴⁺ centers was achieved in the catalyst with the highest Cr loading. This catalyst showed the highest efficiency.

The effect of the template nature and modification with MnO _x on the catalytic efficiency of Ce_0.8Zr_0.2O₂ (CZ) in oxidation of CO (2 vol% CO and 1 vol% O₂ in He, pulse feeding) and soot particles (tight contact between soot and catalyst, TGA/DSC) was analyzed. The CZ catalysts were prepared using the CTAB and sawdust (SD) templates and modified with Mn (8 wt%) by wet impregnation followed by calcination at 400 °С. SEM-EDS, XRD, Raman and photoelectron spectroscopy, N₂ adsorption, EPR, TPR-H₂ and catalytic tests results demonstrated better catalytic activity of CZ(SD) in CO oxidation than of CZ(CTAB) because of the biomorphic texture, higher structural defectiveness and improved oxygen mobility of the former catalyst. Low surface reducibility and low concentration of active oxygen species on the CZ(SD) surface deteriorated its catalytic efficiency in the topochemical reaction of soot oxidation. Despite the different structure and degree of interaction between MnO _x and CZ, the Mn-modified catalysts showed the similar catalytic properties: much better than of both unmodified catalysts in CO oxidation and worse than of CZ(CTAB) in soot oxidation. Mn²⁺ ions incorporated better into the surface layer of CZ(SD) than of CZ(CTAB), for which the inhomogeneous distribution of MnO _x and decreased specific surface area were observed.