Development of highly effective supported nickel catalysts for pre-reforming of liquefied petroleum gas under low steam to carbon molar ratios

The pre-reforming of commercial liquefied petroleum gas (LPG) was investigated over Ni–CeO₂ catalysts at low steam to carbon (S/C) molar ratios less than 1.0. It was found that the catalytic activity and selectivity depended strongly on the nature of the support and the interaction between Ni and CeO₂. The Ni–CeO₂/Al₂O₃ catalysts, which were prepared by impregnating boehmite (AlOOH) with an aqueous solution of cerium and nickel nitrates, exhibited the optimal catalytic activity and remarkable stability for the steam reforming of LPG in the temperature range of 275–375 °C. The effects of CeO₂ loading, reaction temperature and S/C ratio on the catalytic behavior of the Ni–CeO₂/Al₂O₃ catalysts were discussed in detail. The results showed that the catalysts with 10 wt.% CeO₂ had the highest catalytic activity, and higher S/C ratios contributed to LPG reforming and the methanation of carbon oxides and hydrogen. The XRD and H₂-TPR analyses revealed that the strong interaction between Ni and CeO₂ resulted in the formation of CeAlO₃ in the Ni–CeO₂/Al₂O₃ catalysts reduced. The stability tests of 15Ni–10CeO₂/Al₂O₃ catalyst at 350 °C indicated that the catalyst was stable, and the stability could be enhanced by increasing S/C ratio.     

Hydrogen production via chemical looping steam reforming of ethanol by Ni-based oxygen carriers supported on CeO2 and La2O3 promoted Al2O3

This work studies the effects of Ce⁴⁺ and/or La³⁺ on NiO/Al₂O₃ oxygen carrier (OC) on chemical looping steam reforming of ethanol for hydrogen production - alternating between fuel feed step (FFS) and air feed step (AFS). Suitable amount of Ce- and La-doping increases OC carbon tolerance. The solubility limit is found at 50 mol% La in solid solution. At higher La-doping, La₂O₃ disperses on the surface and adsorbs CO₂ forming La₂O₂CO₃ during FFS. From the 1st cycle, 12.5 wt%Ni/7 wt%La₂O₃-3wt%CeO₂–Al₂O₃ (N/7LCA) displays the highest averaged H₂ yield (3.2 mol/mol ethanol) with 87% ethanol conversion. However, after the 5th cycle, 12.5 wt%Ni/3 wt%La₂O₃-7wt%CeO₂–Al₂O₃ (N/3LCA) exhibits more stability and presents the highest ethanol conversion (88%) and H₂ yield (2.7 mol/mol ethanol). Amorphous coke on the OCs decreases with increasing La³⁺ content and can be removed at 500 °C during AFS; nevertheless, fibrous coke and La₂O₂CO₃ cannot be eliminated. Therefore, after multiple redox cycles, highly La-doped OCs exhibits rather low stability.     

Cyclic molecular designed dispersion (CMDD) of Fe2O3 on CeO2 promoted by Au for preferential CO oxidation in hydrogen

A novel cyclic molecular designed dispersion (CMDD) method was employed to uniformly deposit 0.0–6.5 wt% Fe on CeO₂. The gold catalysts (0.0–3.8 wt%) supported on Fe₂O₃-CeO₂ were tested for CO preferential oxidation (PROX). As the CMDD method involved grafting of Fe (acac)₃ onto the surface –OH groups, 2.7 surface –OH/nm² was determined for the CeO₂ by using the Grignard reagent. The performance of CMDD catalysts was compared with the corresponding catalysts prepared by impregnation. The catalysts were characterized by XPS, XRD, TPR, HRTEM-EDX, BET and ICP. The results suggested that Au/Fe₂O₃-CeO₂ was significantly more active and selective than Au/CeO₂. The CMDD-prepared catalysts with 1.4–2.5 wt% iron showed the highest activity and selectivity, especially at temperatures as low as 323 K. The formation of Ce-Fe solid solution for CMDD catalysts promoted the dispersion of both iron and gold. Highly dispersed gold nanoparticles mainly as small as 2.2 nm were observed in HRTEM.     

Performance and life-time behaviour of NiCu–CGO anodes for the direct electro-oxidation of methane in IT-SOFCs

An anodic cermet of NiCu alloy and gadolinia doped ceria has been investigated for CH₄ electro-oxidation in IT-SOFCs. Polarization curves have been recorded in the temperature range from 650 to 800 °C. A maximum power density of 320 mW cm⁻² at 800 °C has been obtained in the presence of dry methane in an electrolyte-supported cell. The electrochemical behaviour during 1300 h operation in dry methane and in the presence of redox-cycles has been investigated at 750 °C; variation of the electrochemical properties during these experiments have been interpreted in terms of anode morphology modifications. The methane cracking process at the anode catalyst has been investigated by analysing the oxidative stripping of deposited carbon species.     

Cesium substituted 12-tungstophosphoric (CsxH3−xPW12O40) loaded on ceria-degradation mitigation in polymer electrolyte membranes

A novel multifunctional catalyst Cs_xH_3−xPW₁₂O₄₀/CeO₂ was prepared to mitigate the free radical attack to membranes in fuel cell environment. Cs_xH_3−xPW₁₂O₄₀/CeO₂ nanoparticles synthesized by solution-based hydrothermal method and two-step impregnation method were dispersed uniformly into the Nafion^® resin, and then the composite membrane was prepared using solution-cast method. The particles prepared were characterized by X-ray powder diffraction (XRD), TEM and FT-IR to evaluate the crystallite size, distribution of the nanopaticles and the crystal structure. The membrane degradation was investigated via ex situ Fenton test and in situ open circuit voltage (OCV) accelerated test. In the durability tests, the fluoride emission rate (FER) reduced nearly one order of magnitude by adding Cs_xH_3−xPW₁₂O₄₀/CeO₂ nanoparticles into the Nafion membrane, suggesting that Cs_xH_3−xPW₁₂O₄₀/CeO₂ catalyst has a promising application to greatly improve the proton exchange membrane (PEM) durability.     

Promoting effect of CeO2 in the electrocatalytic activity of rhodium for ethanol electro-oxidation

The promoting effect of ceria in the electrocatalytic activity of rhodium for ethanol electro-oxidation in alkali media has been studied. Rh/C, CeO₂/C and RhCeO₂/C catalysts were synthesized and characterized by TEM, XRD, XPS, TG-MS, H₂-TPR and XAS. The electrocatalytic activity was studied by Cyclic Voltammetry (CV) and chronoamperometry. The onset potential of oxidation on RhCeO₂/C was shifted negatively as compared to that on Rh/C, despite ceria itself does not show any electrocatalytic activity. The promoting effect of ceria has been attributed to the improved rhodium dispersion, and differences in the oxidation state of rhodium between Rh/C and RhCeO₂/C were not found. The carbon support reduces rhodium species to Rh⁰, and also partially reduces ceria, during the samples preparation, and the surface of the carbon support is oxidised.     

Simple fabrication of micro-solid oxide fuel cell supported on metal substrate

A simple method, without using lithography or etching processes, for fabricating a micro-solid oxide fuel cell (micro-SOFC) that utilizes a metal substrate is presented. A porous and thin (<25 μm) metal (Ni) film is fabricated by screen printing a NiO film on a ceramic substrate and subsequently reducing this film. Electrolyte and the cathode layers are sequentially deposited on the Ni-film substrate. Micro-SOFCs with a thin-film Gd-doped ceria electrolyte, supported on the Ni substrate, are successfully tested at 450 °C.     

Solvothermal synthesis of necklace-like carbon nanotube/ceria composites

The necklace-like carbon nanotube (CNT)/ceria composites have been synthesized by a simple solvothermal method. The composites are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the necklace-like nanostructures are a hybrid of face-centered cubic ceria and CNTs, and these beaded ceria particles with a diameter of 80-120 nm are distributed discontinuously along the axis of CNTs. A possible formation mechanism has been suggested to explain the formation of necklace-like CNT/ceria composites, which indicates that this synthesis route is promising and may be extended to fabricate other beaded nanoparticles along CNTs.     

Preparation and characterization of ceria nanospheres by microwave-hydrothermal method

Crystalline ceria (CeO₂) nanoparticles have been successfully synthesized by a simple and fast microwave-hydrothermal method at 130 °C for 20 min. As-synthesized CeO₂ powders were calcinated at 500 °C for 1, 2 and 4 h. The products were characterized by thermogravimetric analysis (TG-DTA), X-ray powder diffraction (XRD), field-emission scanning electron microscopy/STEM mode (FEG/STEM), Fourier Transformed-IR and RAMAN spectroscopies. It is shown that synthesized ceria powders have a spherical shape with particle size below 10 nm, a narrow distribution and exhibit weak agglomeration. The FTIR spectrum of the ceria exhibits strong broad band below 700 cm^− 1 which is due to the δ (Ce-O-C) mode. Raman spectrum is characterized by the presence of a very strong band to 464.5 cm^− 1. The microwave-hydrothermal method enabled cerium compounds to be synthesized at low temperature and shorter time.     

Enhanced Ionic Conductivity in Ce0.8Sm0.2O1.9: Unique Effect of Calcium Co‐doping

In order to identify new oxide ion‐conducting materials in the ceria family of oxides, the unique effect of co‐doping is explored and a novel series of Ce_0.8Sm_0.2–xCa_xO_2–δ compositions is identified that have enhanced properties compared to the single‐doped Ce_0.8Sm_0.2O_1.9 and Ce_0.8Ca_0.2O_1.9 compositions. Moreover, the superior characteristics of the co‐doped Ce_0.8Sm_0.2–xCa_xO_2–δ powders prepared by the mixed‐fuel process aid in obtaining 98 % dense ceramics upon sintering at 1200 °C for 6 h. Though a linear increase in conductivity is observed by replacing Sm with Ca, the composition with the maximum amount of Ca and the minimum amount of Sm exhibits a significant improvement in properties compared to the rest in the series. The composition Ce_0.80Sm_0.05Ca_0.15O_2–δ exhibits a conductivity as high as 1.22 × 10^–1 S cm^–1 at 700 °C with minimum activation energy (0.56 eV) and a superior chemical stability to reduction compared to any of the hitherto known (CaSm) compositions. The absence of Ce^III, confirmed both from X‐ray photoelectron spectroscopy and X‐ray absorption spectroscopy, strongly suggests that the observed increase in conductivity is solely due to the oxide ion conductivity and not due to the partial electronic contribution arising from the presence of Ce^III and Ce^IV. To conclude, the experimental results on the Ce_0.8Sm_0.2–xCa_xO_2–δ series underscore the unique effect of calcium co‐doping in identifying a cost‐effective new composition, with a remarkably high conductivity and enhanced chemical stability to reduction, for technological applications.