TL;DR: In this paper, the room-temperature high energy ball-milling technique was used to prepare nanophase Ce1-xZrxO2 (x=0, 0.2, 0., 0.5; 0.8; 1) catalysts and the acid base properties of these catalysts were investigated by means of adsorption microcalorimetry, using NH3 and CO2 as probe molecules.
Abstract: The room-temperature high energy ball-milling technique was used to prepare nanophase Ce1-xZrxO2 (x=0; 0.2; 0.5; 0.8; 1) catalysts. The acid–base properties of these catalysts were investigated by means of adsorption microcalorimetry, using NH3 and CO2 as probe molecules. The catalytic activity for 4-methylpentan-2-ol dehydration was tested at atmospheric pressure in a fixed-bed flow microreactor. The inclusion of increasingly high contents of zirconium into the ceria lattice has a complex influence on the acidity and basicity of the pure parent oxide, in terms of both number and strength of the sites. A maximum in 1-alkene selectivity is observed for the ceria-rich catalyst and a minimum for the zirconia-rich sample. Catalytic results are correlated with the acid–base properties and can be interpreted in the light of the mechanism formerly proposed for zirconia, ceria and lanthania. Surface conditioning of the zirconia-rich catalyst occurs during the run, resulting in a remarkable variation of selectivity.
TL;DR: This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.
Abstract: Ceria has been the subject of thorough investigations, mainly because of its use as an active component of catalytic converters for the treatment of exhaust gases. However, ceria-based catalysts have also been developed for different applications in organic chemistry. The redox and acid-base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow to activate complex organic molecules and to selectively orient their transformation. Pure ceria is used in several organic reactions, such as the dehydration of alcohols, the alkylation of aromatic compounds, ketone formation, and aldolization, and in redox reactions. Ceria-supported metal catalysts allow the hydrogenation of many unsaturated compounds. They can also be used for coupling or ring-opening reactions. Cerium atoms can be added as dopants to catalytic system or impregnated onto zeolites and mesoporous catalyst materials to improve their performances. This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.
TL;DR: In this article, the authors summarized the recent advances in the application of ceria-based catalysts for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) operated at low temperatures.
Abstract: Selective catalytic reduction of NO with NH3 (NH3-SCR) is a powerful technique for the abatement of NOx from stationary sources, and the currently used VOx/TiO2-based catalysts are widely applicable for medium-temperature conditions but not suitable for NH3-SCR operated at low temperatures. Recently, low-temperature NH3-SCR has attracted considerable attention owing to the vast demand in industrial furnaces and its energy-conserving feature. During the past years, a great many studies have demonstrated that ceria-based catalysts are potential candidates as catalysts for low-temperature NH3-SCR. Herein we summarize the recent advances in the application of ceria-based catalysts for low-temperature NH3-SCR. The review begins with a brief introduction of the general guideline for low-temperature NH3-SCR and the interaction between the reactants and CeO2. The different roles of ceria as a pure support/active species, bulk doping component and surface modifier are discussed. As well, the mechanistic investigations (active sites, intermediates, reaction mechanism) and SO2/H2O tolerance are emphasized. Lastly, the perspectives on the opportunities and challenges of ceria-based catalysts for low-temperature NH3-SCR in future research are presented.
TL;DR: The results showed that the spindle-like CeO2 showed the highest DMC yields, followed by nano-rods, nano-cubes and nano-octahedrons, and a synergism among the exposed plane, defect sites, and acid-basic sites was proposed to be crucial to obtaining the high reactivity of DMC formation.
Abstract: This paper describes the synthesis of ceria catalysts with octahedron, nanorod, nanocube and spindle-like morphologies via a template-free hydrothermal method. The surface morphologies, crystal plane and physical-chemical structures were investigated via field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and temperature-programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). The catalytic performance over these ceria catalysts with different exposed planes were tested for dimethyl carbonate (DMC) synthesis from CO2 and methanol. The results showed that the spindle-like CeO2 showed the highest DMC yields, followed by nano-rods, nano-cubes and nano-octahedrons. A synergism among the exposed (111) plane, defect sites, and acid-basic sites was proposed to be crucial to obtaining the high reactivity of DMC formation.
TL;DR: In this article, high specific surface areas (77-244m 2 /g) were obtained for Titania-zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 ¼ ) by the sol-gel method.
Abstract: Titania–zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 wt.%) were prepared by the sol–gel method. High specific surface areas (77–244 m 2 /g) were obtained. Acidity determined by NH 3 -TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 μmol NH 3 /g for TiO 2 to 1226–1456 μmol NH 3 /g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO 2 adsorption, suggesting the formation of mixed oxides with acid–basic properties. XRD spectra identified anatase in the TiO 2 rich region, amorphous material in the mixed oxide 50–50 TiO 2 –ZrO 2 and tetragonal and monoclinic crystalline phases in the ZrO 2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid–basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density.
TL;DR: In this article, a combination of this selective catalyst with an effective H2O removal system can provide a novel process of selective DMC production starting from CO2 with high efficiency.
Abstract: CeO2-ZrO2 solid solution catalysts are very effective in the selective synthesis of dimethyl carbonate (DMC) from methanol and CO2. The methanol conversion is very low because the DMC formation is limited by the reaction equilibrium. For the removal of H2O from the reaction system, the reaction between 2,2-dimethoxy propane (DMP) and H2O can be utilized. The addition of the DMP to the reaction system of DMC synthesis from methanol and CO2 is very effective for the increase of the conversion. However, the addition of larger amounts of DMP is not suitable because of the decrease of DMC formation rate and the by-production of the dimethyl ether (DME). The combination of this selective catalyst with an effective H2O removal system can provide a novel process of selective DMC production starting from CO2 with high efficiency.