Search Results (39)

Amines and hydroxylamines are essential compounds in the synthesis of pharmaceuticals and other functionalized molecules. However, the synthesis of primary amines and particularly hydroxylamines remains a challenging task. The most common way to obtain amines and hydroxylamines involves the reduction of substances containing C-N bonds, such as nitro compounds, nitriles, and oximes. Among these, oximes are the most readily accessible substrates easily derived from ketones and aldehydes. However, oximes are much harder to reduce compared to nitro compounds and nitriles. The catalytic heterogeneous hydrogenation of oximes often requires harsh conditions and catalysts with high precious metal loadings, while hydroxylamines are hard to be obtained by this method. In this work, we showed that Pt supported on a porous ceria–zirconia solid solution enables the selective and atom-efficient synthesis of both hydroxylamines and amines through the hydrogenation of oximes, achieving yields of up to 99% under ambient reaction conditions in a “green” THF:H₂O solvent system. The high activity of the 1% Pt/CeO₂-ZrO₂ catalyst (TOF > 500 h⁻¹) is due to low-temperature hydrogen activation on Pt nanoparticles with the formation of a hydride, Pt-H. The strong influence of electron-donating and electron-withdrawing groups on the hydrogenation of aromatic oximes implies the nucleophilic attack of hydridic hydrogen from Pt to the electrophilic carbon of protonated oximes. Full article

The oxidation of 1,2-propanediol (1,2-PDO) under alkaline heterogeneous catalysis can be optimized to produce lactic acid, a valuable commodity chemical. In this study, Pd nanoparticles supported on various metal oxides (CeO₂, CuO, ZrO₂, ZnO, SnO₂) were synthesized via a wet-chemistry method. Furthermore, CeO₂-supported Pd nanoparticle catalysts were prepared using different reduction methods. The catalytic performance for the selective oxidation of 1,2-PDO was evaluated using a range of characterization techniques. Under optimal conditions (120 °C, 1.0 MPa O₂ pressure, 2 h reaction time, and a NaOH/1,2-PDO molar ratio of 3.0), a high lactic acid yield of 62.7% was achieved. Single-factor experiments revealed that lactic acid selectivity decreased with prolonged reaction time. Conversely, increasing temperature, NaOH concentration, and O₂ pressure initially enhanced lactic acid selectivity, but further increases resulted in a decline. Physicochemical characterization revealed that different supports and reduction methods affect the basicity of the catalyst, which subsequently influences the selectivity of the target product, lactic acid. Full article

Tailoring the bandgap of a material is necessary for improving its optical properties. Here, the optical bandgap of high-entropy oxide Ce_0.2Gd_0.2Sm_0.2Y_0.2Zr_0.2O_2-δ (HEO) nanoparticles was modified using Pr³⁺. Various concentrations of Pr³⁺ (x = 0, 0.01, 0.02, 0.05, 0.075, 0.1, 0.15) were incorporated into the host high-entropy oxide using a gel combustion synthesis. After the gel combustion step, the powders were heat-treated at various temperatures (650 °C, 800 °C, 950 °C) for 2 h. The obtained Pr³⁺-incorporated HEO powders were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and UV–visible spectroscopy. The results indicate that, when the samples are calcined at 950 °C, a single-phase cubic fluorite structure is obtained without any phase separation or impurity. The optical absorbance red-shifts to higher wavelengths when the concentration of Pr³⁺ is increased. This reduces the bandgap of the material from 3.15 eV to 1.87 eV for Pr³⁺ concentrations of x = 0 (HEO-0) and x = 0.15 (HEO-6), respectively. The obtained HEOs can be suitable candidates for photocatalytic applications due to their absorbance in the visible region. Full article

In recent decades, with the rapid development of the inorganic synthesis and the increasing discharge of pollutants in the process of industrialization, hollow-structured metal oxides (HSMOs) have taken on a striking role in the field of environmental catalysis. This is all due to their unique structural characteristics compared to solid nanoparticles, such as high loading capacity, superior pore permeability, high specific surface area, abundant inner void space, and low density. Although the HSMOs with different morphologies have been reviewed and prospected in the aspect of synthesis strategies and potential applications, there has been no systematic review focusing on the structures and compositions design of HSMOs in the field of environmental catalysis so far. Therefore, this review will mainly focus on the component dependence and controllable structure of HSMOs in the catalytic elimination of different environmental pollutants, including the automobile and stationary source emissions, volatile organic compounds, greenhouse gases, ozone-depleting substances, and other potential pollutants. Moreover, we comprehensively reviewed the applications of the catalysts with hollow structure that are mainly composed of metal oxides such as CeO₂, MnO_x, CuO_x, Co₃O₄, ZrO₂, ZnO, Al₃O₄, In₂O₃, NiO, and Fe₃O₄ in automobile and stationary source emission control, volatile organic compounds emission control, and the conversion of greenhouse gases and ozone-depleting substances. The structure–activity relationship is also briefly discussed. Finally, further challenges and development trends of HSMO catalysts in environmental catalysis are also prospected. Full article

The development of direct dimethyl ether (DME) solid oxide fuel cells (SOFCs) has several drawbacks, due to the low catalytic activity and carbon deposition of conventional Ni–zirconia-based anodes. In the present study, the insertion of 2.0 wt.% Ru-Ce_0.7Zr_0.3O_2−δ (ruthenium–zirconium-doped ceria, Ru-CZO) as an anode catalyst layer (ACL) is proposed to be a promising solution. For this purpose, the CZO powder was prepared by the sol–gel synthesis method, and subsequently, nanoparticles of Ru (1.0–2.0 wt.%) were synthesized by the impregnation method and calcination. The catalyst powder was characterized by BET-specific surface area, X-ray diffraction (XRD), field emission scanning electron microscopy with an energy-dispersive spectroscopy detector (FESEM-EDS), and transmission electron microscopy (TEM) techniques. Afterward, the catalytic activity of Ru-CZO catalyst was studied using DME partial oxidation. Finally, button anode-supported SOFCs with Ru-CZO ACL were prepared, depositing Ru-CZO onto the anode support and using an annealing process. The effect of ACL on the electrochemical performance of cells was investigated under a DME and air mixture at 750 °C. The results showed a high dispersion of Ru in the CZO solid solution, which provided a complete DME conversion and high yields of H₂ and CO at 750 °C. As a result, 2.0 wt.% Ru-CZO ACL enhanced the cell performance by more than 20% at 750 °C. The post-test analysis of cells with ACL proved a remarkable resistance of Ru-CZO ACL to carbon deposition compared to the reference cell, evidencing the potential application of Ru-CZO as a catalyst as well as an ACL for direct DME SOFCs. Full article

The use of gold nanoparticles (Au NPs) as catalysts has gained widespread attention in various reactions due to their high activity and selectivity under mild reaction conditions. However, one major challenge in utilizing these catalysts is their tendency to aggregate, leading to catalyst deactivation and hindering their amplification and industrial application. To overcome this issue, herein, we used a method by coating the surface of Au NPs with a thin layer of SiO₂, which resulted in the formation of a superior catalyst denoted as Au@SiO₂/ZA. Characterization studies revealed that the SiO₂ layer is coated on the surface of Au NPs and effectively prevents the aggregation and growth of the gold particles during the reaction process, which makes the catalyst display excellent stability in furfural (FF) oxidative esterification to methyl furoate (MF). Moreover, the stabilization strategy is not limited to SiO₂ alone. It can also be extended to other oxides such as ZrO₂, CeO₂, and TiO₂. We believe this work will provide a good reference for the design and development of an efficient and stable gold catalyst for the oxidative esterification reaction. Full article

The direct synthesis of dimethyl carbonate (DMC) from methanol and CO₂ presents an attractive route to turn abundant CO₂ into value-added chemicals. However, insufficient DMC yields arise due to the inert nature of CO₂ and the limitations of reaction equilibrium. Oxygen vacancies are known to facilitate CO₂ activation and improve catalytic performance. In this work, we have demonstrated that tuning oxygen vacancies in catalysts and implementing in situ water removal can enable highly efficient DMC production from CO₂. Ce_xZr_yO₂ nanorods with abundant oxygen vacancies were synthesized via a hydrothermal method. In liquid-phase DMC synthesis, the Ce₁₀Zr₁O₂ nanorods exhibited a 1.7- and 1.4-times higher DMC yield compared to CeO₂ nanoparticles and undoped CeO₂ nanorods, respectively. Zr doping yielded a CeZr solid solution with increased oxygen vacancies, promoting CO₂ adsorption and activation. In addition, adding 2-cyanopyridine as an organic dehydrating agent achieved an outstanding 87% methanol conversion and >99% DMC selectivity by shifting the reaction equilibrium to the desired product. Moreover, mixing CeO₂ nanoparticles with hydrophobic fumed SiO₂ in gas-phase DMC synthesis led to a doubling of DMC yield. This significant increase was attributed to the faster diffusion of water molecules away from the catalyst surface, facilitated by the hydrophobic SiO₂. This study illustrates an effective dual strategy of enhancing oxygen vacancies and implementing in situ water removal to boost DMC production from CO₂. The strategy can also be applied to other reactions impacted by water accumulation. Full article

Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce_1−xZr_xO₂, where x = 0, 0.1, 0.2, and 0.3) were prepared by combustion synthesis using glycine as the fuel and cerium and zirconium nitrate as oxidants. The obtained powders were characterized using X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, differential thermal and thermogravimetric analysis, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The combustion temperature increases with the increase in zirconium content in the samples, but the XRD patterns exclusively show ceria diffraction peaks. The crystallite sizes are in the range from 25.2 to 11.7 nm, and do not vary substantially after thermal treatment, indicating the good thermal stability of the prepared nanocatalysts. XPS analysis showed that the surface amount of zirconium is lower than the nominal and that the ceria sample with 10 mol. % of zirconium has a higher amount of oxygen vacancies than the 30 mol. % Zr-doped sample. The 10 mol. % Zr-doped sample displays the best catalytic activity in the BTEX (benzene, toluene, ethylbenzene, and o-xylene) oxidation process. Full article

Congo red (CR), a highly pigmented anionic dye, is highly toxic and resistant to degradation. The discharge of CR wastewater into the natural environment can lead to ecological destruction and harm to human health. CeO₂ as an adsorbent possesses the advantages of excellent acid and alkali resistance, biocompatibility, stable physical and chemical properties, and nontoxic by-products. The impact of Zr doping on the adsorption performance of nano-CeO₂ was investigated. XPS and Raman characterisation revealed that Zr doping effectively enhanced the oxygen vacancy ratio at the active sites for CR adsorption on the surface of nano-CeO₂. When the doping amount of Zr was 3%, the nanoparticles with the best adsorption properties were obtained, and the adsorption amount of CR at room temperature was as high as 3642.05 mg/g, which was approximately three times the adsorption amount of undoped CeO₂. This excellent adsorption property shows good prospects for the removal of anionic dyes from wastewater. Full article

Poly(ethylene 2,5-furandicarboxylate) (PEF)-based nanocomposites containing Ce–bioglass, ZnO, and ZrO₂ nanoparticles were synthesized via in situ polymerization, targeting food packaging applications. The nanocomposites were thoroughly characterized, combining a range of techniques. The successful polymerization was confirmed using attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, and the molecular weight values were determined indirectly by applying intrinsic viscosity measurements. The nanocomposites’ structure was investigated by depth profiling using time-of-flight secondary ion mass spectrometry (ToF-SIMS), while color measurements showed a low-to-moderate increase in the color concentration of all the nanocomposites compared to neat PEF. The thermal properties and crystallinity behavior of the synthesized materials were also examined. The neat PEF and PEF-based nanocomposites show a crystalline fraction of 0–5%, and annealed samples of both PEF and PEF-based nanocomposites exhibit a crystallinity above 20%. Furthermore, scanning electron microscopy (SEM) micrographs revealed that active agent nanoparticles are well dispersed in the PEF matrix. Contact angle measurements showed that incorporating nanoparticles into the PEF matrix significantly reduces the wetting angle due to increased roughness and introduction of the polar -OH groups. Antimicrobial studies indicated a significant increase in inhibition of bacterial strains of about 9–22% for Gram-positive bacterial strains and 5–16% for Gram-negative bacterial strains in PEF nanocomposite films, respectively. Finally, nanoindentation tests showed that the ZnO-based nanocomposite exhibits improved hardness and elastic modulus values compared to neat PEF. Full article

Pure Ce_0.5Zr_0.5O₂ and Au (0.1–1.0 wt.%)-deposited Ce_0.5Zr_0.5O₂ nanomaterials were synthesized via hydrothermal and non-aqueous precipitation methods using gold acetate as a chloride-free Au precursor. The synthesized nanostructures exhibited enhanced photocatalytic activity for hydrogen production via aqueous bioethanol photoreforming under visible light. Different characterization tools such as powder XRD, HRTEM, FT-IR, DR UV-vis, XPS and N₂ gas adsorption were used to analyze the physicochemical properties of the synthesized photocatalysts. The band gap value was lowered from 3.25 eV to 2.86 eV after Au nanoparticles were deposited on the surface of Ce_0.5Zr_0.5O₂. The 1.0 wt.% Au-deposited Ce_0.5Zr_0.5O₂ sample exhibited the highest photocatalytic activity for H₂ production (3210 μmol g⁻¹) due to its low band gap, the presence of more oxygen vacancies and its porous character. The EIS results reveal that the deposition of 1.0 wt.% Au nanoparticles is responsible for the highest charge separation efficiency with an increased lifetime of photogenerated e⁻/h⁺ species compared to the other samples. In addition, the presence of plasmonic Au is responsible for the effectiveness of the electron trap in improving the rate of H₂ formation. Full article

High surface-area, mesoporous CeO₂, ZrO_2, and Ce-Zr composite nanoparticles were developed using the hydrothermal template-assisted synthesis method. Samples were characterized using XRD, N₂ physisorption, TEM, XPS, and FT-IR spectroscopic methods. The CO₂ adsorption ability of the obtained materials was tested under dynamic and equilibrium conditions. A high CO₂ adsorption capacity in CO₂/N₂ flow or CO₂/N₂/H₂O was determined for all studied adsorbents depending on their composition flow. A higher CO₂ adsorption was registered for Ce-Zr composite nanomaterials due to the presence of strong O²⁻ base sites and enriched surface oxygen species. The role of the Ce/Zr ratio is the process of the formation of highly active and selective adsorption sites is discussed. The calculated heat of adsorption revealed the processes of chemisorption and physisorption. Experimental data could be appropriately described by the Yoon–Nelson kinetic model. The composites reused in five adsorption/desorption cycles showed a high stability with a slight decrease in CO₂ adsorption capacities in dry flow and in the presence of water vapor. Full article

Non-stoichiometric CeO_2−y, especially in the form of nanocrystal aggregates, exhibits exceptional catalytic activity in redox reactions. It significantly improves the activity of transition metals and their oxides dispersed on/or in it, also acting as an oxygen buffer. Particularly, active oxygen species (O₂ⁿ⁻, O⁻) are generated at the M/CeO_2−y nanoparticle interface, as well as in the surface layer of their solid-state solutions M_xCe_1−xO_2−y. The crystal structure of CeO₂, ZrO₂ and (Ce, Zr)O₂ and its defects are discussed in connection with the resulting specific catalytic activity. All the methods (simple precipitation and co-precipitation from mother liquors, sol–gel methods, precipitation from nanoemulsions, hydrothermal and solvothermal techniques, combustion and flame spray pyrolysis, precipitation using molecular and solid-state matrices, 3D printing and mechanochemical methods) used for the synthesis of these nanomaterials are comprehensively reviewed, describing the rules of individual procedures and preparation details. Methods of deposition of metal catalysts and their oxides on CeO₂ nanoparticles, such as impregnation, washcoating and precipitation deposition, were also discussed. This review contains more than 160 references to representative papers wherein the reader can find further details on individual syntheses of effective ceria-based catalysts for redox reactions. Full article

The effect of support on the performance of Pd₁Ag₁₀/Al₂O₃ and Pd₁Ag₁₀/CeO₂–ZrO₂ catalysts in the selective hydrogenation of diphenylacetylene (DPA) was studied. Characterization of the catalyst by DRIFTS-CO and HRTEM revealed the formation of a PdAg single-atom alloy (SAA) structure on the surface of PdAg nanoparticles, with Pd₁ sites isolated by Ag atoms. It was found that the use of CeO₂–ZrO₂ as a carrier makes it possible to increase the activity of the Pd₁Ag₁₀ catalyst by a factor of three without loss of selectivity compared to the reference Pd₁Ag₁₀/Al₂O₃. According to the HRTEM data, this catalytic behavior can be explained by an increase in the dispersion of Pd₁Ag₁₀/CeO₂–ZrO₂ compared to its Pd₁Ag₁₀/Al₂O₃ counterpart. As evidenced by DRIFTS-CO data, the high selectivity of the Pd₁Ag₁₀/CeO₂–ZrO₂ sample presumably stems from the stability of the structure of isolated Pd₁ sites on the surface of SAA Pd₁Ag₁₀/CeO₂–ZrO₂. Full article

The paper considers the relationship between the structure and properties of nanostructured conductometric sensors based on binary mixtures of semiconductor oxides designed to detect reducing gases in the environment. The sensor effect in such systems is determined by the chemisorption of molecules on the surface of catalytically active particles and the transfer of chemisorbed products to electron-rich nanoparticles, where these products react with the analyzed gas. In this regard, the role is evaluated of the method of synthesizing the composites, the catalytic activity of metal oxides (CeO₂, SnO₂, ZnO), and the type of conductivity of metal oxides (Co₃O₄, ZrO₂) in the sensor process. The effect of oxygen vacancies present in the composites on the performance characteristics is also considered. Particular attention is paid to the influence of the synthesis procedure for preparing sensitive layers based on CeO₂–In₂O₃ on the structure of the resulting composites, as well as their conductive and sensor properties. Full article