Cu/Ni‐Loaded CeO2‐ZrO2 Catalyst for the Water‐Gas Shift Reaction: Effects of Loaded Metals and CeO2 Addition

Two different types of metals (Cu and Ni) and the effect of CeO₂ addition to produce a CeO₂‐ZrO₂ co‐supporter were investigated through the water‐gas shift (WGS) reaction. It was found that the WGS activity could be enhanced with CeO₂ addition. At relatively high temperature, Ni‐loaded catalysts exhibited higher CO conversion while Cu‐loaded catalysts demonstrated better performance at low temperatures. The stability and yield of the CO₂ and H₂ products of the Cu catalysts were higher than those of the Ni catalysts. These results may be caused by an irreversible adsorption of CO on Ni and the reverse WGS reaction occurring on the Ni catalysts. In situ diffuse‐reflection infrared Fourier transform spectroscopy data suggests that the WGS mechanism likely proceeded via formate species.     

Synthesis,densification and characterization of Ag doped ceria nanopowders

Nanosized Ag-doped ceria (Ce_1-xAl_xO_2-δ)powders (0.1 ≤ x ≤ 0.04) were obtained by self-propagating room temperature reaction. The solid solubility of Ag into ceria lattice was the highest reported so far. X-ray diffraction analysis and field emission scanning microscopy results showed that the doped samples are single phase solid solutions with fluorite-type structure and all prepared powders were nanometric in size. The average size of Ce1-xAgxO2-▯ particles lies at about 4 nm. Raman spectra revealed an increase in the amount of oxygen vacancies with the increase of Ag concentration, such as is foreseen. The thermal stability of solid solution was followed by XRD. Microstructure development was studied by scanning electron microscopy. By controlling the processing variables, it was possible to obtain high density samples with homogeneous microstructure at low sintering temperature.     

Renewable hydrogen production from steam reforming of glycerol (SRG) over ceria-modified γ-alumina supported Ni catalyst

Excess crude glycerol derived as a by-product from biodiesel industry prompts the need to valorise glycerol to value-added chemicals. In this context, catalytic steam reforming of glycerol (SRG) was proposed as a promising and sustainable alternative for producing renewable hydrogen (H₂). Herein, the development of nickel (Ni) supported on ceria-modified mesoporous γ-alumina (γ-Al₂O₃) catalysts and their applications in catalytic SRG (at 550–750 °C, atmospheric pressure and weight hourly space velocity, WHSV, of 44,122 ml·g⁻¹·h⁻¹ (STP)) is presented. Properties of the developed catalysts were characterised using many techniques. The findings show that ceria modification improved Ni dispersion on γ-Al₂O₃ catalyst support with highly active small Ni particles, which led to a remarkable catalytic performance with the total glycerol conversion (ca. 99%), glycerol conversion into gaseous products (ca. 77%) and H₂ yield (ca. 62%). The formation rate for H₂ production (14.4 × 10⁻⁵ mol·s⁻¹·g⁻¹, TOF (H₂) = 3412 s⁻¹) was significantly improved with the Ni@12Ce-Al₂O₃ catalyst, representing nearly a 2-fold increase compared with that of the conventional Ni@Al₂O₃ catalyst. In addition, the developed catalyst also exhibited comparatively high stability (for 12 h) and coke resistance ability.     

Oxides of copper, ceria promoted copper, manganese and copper manganese on Al2O3 for the combustion of CO, ethyl acetate and ethanol

Combustion of CO, ethyl acetate and ethanol was studied over CuO_x/Al₂O₃, CuO_x–CeO₂/Al₂O₃, CuMn₂O₄/Al₂O₃ and Mn₂O₃/Al₂O₃ catalysts. It was found that modification of the alumina with ceria before subsequent copper oxide deposition increases the activity for combustion of CO substantially, but the effect of ceria was small on the combustion of ethyl acetate and ethanol. The activity increases with the CuO_x loading until crystalline CuO particles are formed, which contribute little to the total active surface. The CuO_x–CeO₂/Al₂O₃ catalyst is more active than the CuMn₂O₄/Al₂O₃ catalyst for the oxidation of CO but the CuMn₂O₄/Al₂O₃ catalyst is more active for the combustion of ethyl acetate and ethanol.

Thermal ageing and water vapour in the feed caused a modest decrease in activity and did not affect the CuO_x–CeO₂/Al₂O₃ and CuMn₂O₄/Al₂O₃ catalysts differently. In addition, no difference in intermediates formed over the two catalysts was observed.

Characterisation with XRD, FT-Raman and TPR indicates that the copper oxide is present as a copper aluminate surface phase on alumina at low loading. At high loading, bulk CuO crystallites are present as well. Modification of the alumina with ceria before the copper oxide deposition gives well dispersed copper oxide species and bulk CuO crystallites associated to the ceria, in addition to the two copper oxide species on the bare alumina. The distribution of copper species depends on the ceria and copper oxide loading. The alumina supported copper manganese oxide and manganese oxide catalysts consist mainly of crystalline CuMn₂O₄ and Mn₂O₃, respectively, on Al₂O₃.     

纳米氧化铈的制备及其在环境保护中的应用

氧化铈具有立方萤石结构,储放氧能力与价电子构型,被广泛应用于催化剂等领域。对不同纳米结构的氧化铈制备研究现状做了较系统的概述,并分析了制备不同形貌氧化铈的影响因素。着重介绍了纳米氧化铈在汽车尾气净化和工业废水处理中应用进展,并展望了今后纳米氧化铈材料的研究方向。     

Low Temperature Water–Gas Shift/Methanol Steam Reforming: Alkali Doping to Facilitate the Scission of Formate and Methoxy C–H Bonds over Pt/ceria Catalyst

Doping Pt/ceria catalysts with the Group 1 alkali metals was found to lead to an important weakening of the C–H bond of formate and methoxy species. This was demonstrated by a shift to lower wavenumbers of the formate and methoxy ν(CH) vibrational modes by DRIFTS spectroscopy. Li and Na-doped Pt/ceria catalysts were tested relative to the undoped catalyst for low temperature water–gas shift and methanol steam reforming using a fixed bed reactor and exhibited higher catalytic activity. Steaming of formate and methoxy species pre-adsorbed on the catalyst surface during in-situ DRIFTS spectroscopy suggested that the species were more reactive for dehydrogenation steps in the catalytic cycle for the Li and Na-doped catalysts relative to undoped Pt/ceria. However, with increasing atomic number over the series of alkali-doped catalysts, the stability of a fraction of the carbonate species was found to increase. This was observed during TPD-MS measurements of the adsorbed CO₂ probe molecule by a systematic increase of a high temperature peak for a fraction of the CO₂ desorbed. This result indicates that alkali-doping is an optimization problem—that is, while improving the dehydrogenation rates of methoxy and formate species, the carbonate intermediate stability increases, making it difficult to liberate the CO₂. Infrared spectroscopy results of CO adsorbed on Pt and ceria suggest that the alkali dopant is located on, and electronically modifies, both the Pt and ceria components. The results not only lend further support to the role that methoxy and formate species play as intermediates in the catalytic mechanisms, but also provide a path forward for improving rates by means other than resorting to higher noble metal loadings.     

Combustion synthesis and characterization of Cu-Sm co-doped CeO2 electrolytes

Nano-sized CSO (Ce_0.80Sm_0.20O_2−δ) and CSCO (Ce_0.79Sm_0.20Cu_0.01O_2−δ) were synthesized by the PVA assisted combustion method, and then characterized by the structure of PVA-cation complexes and nano-powders, as well as mechanical and electrical performance after sintering. The results indicate that the PVA-cation complexes (PVA-(Ce³⁺,Sm³⁺) and PVA-(Ce³⁺,Sm³⁺,Cu²⁺)) were formed by coordinating metal cations to hydroxyl groups, as well as the COO⁻¹ group derived from the oxidation of PVA with NO₃⁻¹. Low temperatures (around 200 °C) caused intense combustion reactions, resulting in the direct crystallization of cubic fluorite nano-CSO (10-20 nm) and nano-CSCO (10-15 nm) crystals with homogeneous element distribution. This slight compositional modification of CSO by co-doping with 1 mol% CuO resulted in a significantly lowered densification temperature, as well as enhanced mechanical and electrical property. The strength improvement can be ascribed to the dense and fine-grained microstructure without normal grain coarsening, resulting in a transgranular-dominant fracture mode during strength testing.     

Chemical composition and corrosion protection of silane films modified with CeO2 nanoparticles

The present work aims at understanding the role of CeO₂ nanoparticles (with and without activation in cerium(III) solutions) used as fillers for hybrid silane coatings applied on galvanized steel substrates.The work reports the improved corrosion protection performance of the modified silane films and discusses the chemistry of the cerium-activated nanoparticles, the mechanisms involved in the formation of the surface coatings and its corrosion inhibition ability.The anti-corrosion performance was investigated using electrochemical impedance spectroscopy (EIS), the scanning vibrating electrode technique (SVET) and d.c. potentiodynamic polarization. The chemical composition of silanised nanoparticles and the chemical changes of the silane solutions due to the presence of additives were studied using X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance spectroscopy (NMR), respectively.The NMR and XPS data revealed that the modified silane solutions and respective coatings have enhanced cross-linking and that silane-cerium bonds are likely to occur.Electrochemical impedance spectroscopy showed that the modified coatings have improved barrier properties and the SVET measurements highlight the corrosion inhibition effect of ceria nanoparticles activated with Ce(III) ions. Potentiodynamic polarization curves demonstrate an enhanced passive domain for zinc, in the presence of nanoparticles, in solutions simulating the cathodic environment.     

Selectivity of high surface area Ce0.68Zr0.32O2 for the new generation of TWC under environments with different redox character

A number of experiments were carried out with fresh and aged high surface area Ce_0.68Zr_0.32O₂ mixed oxide samples with complex feed-streams in order to determine their performance as three way catalyst (TWC). The results confirmed the oxygen storage capacity (OSC) of these samples, which favour NO conversion in cycled versus stationary stoichiometric operation. Several experiments carried out with different feed-streams have shown that a pre-reducing treatment can significantly improve both NO reduction at low-temperature and selectivity to N₂, which can be very useful to reduce the emission of nitrogen oxides immediately after starting the automobile. Although a significant reduction of the specific surface area of the mixed oxide takes place during ageing at 1173 K, it has been shown that the performance of the sample remains similar or even better than when fresh, due to an increased OSC. Thus, the reduction of CO and hydrocarbon emissions during start could be achieved by situating the catalytic converter nearer the exhaust to the engine, where the catalyst will be heated faster.     

Facile hydrothermal synthesis of CeO2 nanosheets with high reactive exposure surface

CeO₂ nanosheets with (1 1 0) dominated surface were synthesized for the first time by a facile one-step hydrothermal method without the assistance of any surfactant or template. The role of NH₃·H₂O on tailoring the morphology of CeO₂ nanocrystals was investigated. It was found the NH₃·H₂O not only serves as the precipitant, but also acts as structural direction agent in the formation of (1 1 0)-dominated CeO₂ nanosheets. Raman and XRD spectra showed that the sample has a cubic fluorite structure. Compared with bulk CeO₂ materials, the prepared CeO₂ nanosheets exhibit an obvious blue-shift in UV absorbance. The increase of the direct band gap energy of the obtained sample exceeds 8%. This method provides an environmentally friendly way for preparing CeO₂ nanostructures and tailoring their morphology. It may also be extended to the synthesis of other nanomaterials.