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The demands for high-purity hydrogen required in fuel-cell applications impose new goals and challenges for design of well performing water-gas shift (WGS) catalysts. Gold-based catalysts have exhibited high activity in the WGS reaction at low temperature. Preparation of appropriate and economically viable supports with complex composition by various synthesis procedures is an attractive approach to WGS performance improvement. The effect of two different preparation methods (wet impregnation or mechanical mixing) and ceria content (10, 20 or 30 wt%) on textural, structural, surface and reductive properties and WGS activity of gold catalysts was studied. Additionally, the role of Y 2 O 3 as a promoter of ceria was examined. Long-term stability test was carried out at 260 °C over the most active catalyst. The composition of the best performing sample (composed of about 70 wt% alumina), prepared by mechanical mixing, was considered promising in case of practical applications because of its cost efficiency. The combination of gold nanoparticles and alumina supported Y-doped ceria proved an advantageous approach for developing new catalytic formulations with high effectiveness in clean hydrogen production. Image 1 • Water-gas shift activity of gold catalysts on alumina-supported CeO 2 was studied. • The impact of supports composition (10, 20 and 30 wt% ceria) was investigated. • The effect of support preparation methods was analyzed. • The role of Y-doping of ceria on the WGS activity was examined. • Stability test over the best performing catalyst was carried out. [ABSTRACT FROM AUTHOR]

[Display omitted] • MgSi–Ni–CYO–NR exhibits high TOF (0.18 s−1), X (95%), and low k deactiv. (0.0067 h−1). • Y-doped ceria nanorod is beneficial to oxygen vacancy formation and Ni dispersion. • MgSiO 3 post-coating and CYO–NR enhance the carbon formation resistance and removal. • E vac. and H 2 O splitting barrier of CYO(1 1 0) are lower than CZO(1 1 0) and CYO(1 1 1). Ni-based higher hydrocarbon steam reforming (SR) catalyst usually encounters low water dissociation rate and carbon deposition-induced inactivity and instability. Herein, we report a Ni–Ce 0.9 Y 0.1 O 2 -nanorod (Ni–CYO–NR) with a MgSiO 3 postcoating that exhibits a TOF and conversion of 0.18·s−1 and 95% at 700 ℃ and carbon deposition amount and deactivation rate constant 2 orders of magnitude lower than those of Ni–Ce 0.9 Y 0.1 O 2 -nanoparticle (Ni–CYO–NP). Characterization results suggested that Ni–CYO–NR has a higher oxygen vacancy concentration and Ni dispersion than Ni–Ce 0.9 Zr 0.1 O 2 –NR and Ni–CYO–NP because of its CYO(1 1 0) nature. DFT calculations revealed that CYO(1 1 0) has the lowest formation energy of oxygen vacancies and energy barrier for H 2 O dissociation relative to CZO(1 1 0) and CYO(1 1 1). Additionally, MgSiO 3 postcoating inhibited the deep sintering of Ni, which in turn suppressed carbon formation. This demonstrates that the superior n -dodecane SR performance of MgSi–Ni–CYO–NR can be attributed to the enhanced and stabilized O–H, C–C, and C–H bond dissociation and carbon formation resistance and removal. [ABSTRACT FROM AUTHOR]

Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation method, with sequential deposition–precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd–Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 °C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction.

The preferential CO oxidation in the presence of excess hydrogen (PROX) was studied over gold catalysts on yttrium-modified ceria supports synthesized by impregnation (IM) and co-precipitation (CP) methods. In order to avoid oxygen vacancies ordering by heavily yttrium doping, a low extent Y-modification of ceria (up to 7.5 wt.% Y 2 O 3 , i.e. , 11 at.% Y) was investigated. The samples were characterized by XRD, HRTEM/HAADF, Raman and XP spectroscopy and TPR measurements. At the operating temperature of the fuel cells (80–120 °C) the selectivity of the Y-doped gold catalysts was larger than that of Au/CeO 2 . However, at these temperatures all studied catalysts exhibited quite similar PROX activity and selectivity. This was explained by the similarity in relatively small average size of gold particles (estimated by HRTEM in the 2.1–3.5 nm range) and the reducibility of ceria surface layers. Raman spectroscopy showed a higher extent of bulk defects, O vacancies and interstitials with increasing Y-doping in the supports made by the CP method and-based on sequential spectra obtained under oxidizing and reducing conditions- enabled the assignment of a band at ∼605 cm −1 to a vibrational mode within the anionic (oxygen) sub-lattice that involve mobile (detachable) oxygen atoms that can be delivered by the support under suitable conditions. The absence of correlation between CO conversion and yttrium loading could suggest a preferential role played by the surface modification and surface oxygen mobility in PROX. Although under ideal conditions there was not substantial dependence of the behavior in PROX on the preparation method of doped supports, the IM method was more appropriate than the CP method for PROX with CO 2 and water addition to the gas feed. The improved tolerance to CO 2 could be explained by the lowering of ceria surface basicity due to the nanosized Y 2 O 3 , covering ceria grains. [ABSTRACT FROM AUTHOR]

Gold (3 wt. %) catalysts on Y-doped (1, 2.5, 5 and 7.5 wt. % Y2O3) ceria supports prepared by coprecipitation (CP) or impregnation (IM) were studied in complete benzene oxidation (CBO). A low-extent Y modification was chosen to avoid ordering of oxygen vacancies. The samples were characterized by XRD, TGA, XPS and TPR techniques. A positive role of air pretreatment at 350 °C as compared to 200 °C was established for all Y-containing catalysts and it was explained by cleaning the active sites from carbonates. The oxygen supply cannot be considered as a limiting step for benzene oxidation except for the high 7.5%-doped samples, as suggested by TGA and TPR data. On the basis of XPS results of fresh and used in CBO catalysts, the presence of cationic gold species does not seem important for high CBO activity. The gold catalyst on an IM support with 1% Y-doping exhibited the best performance. A 100% benzene conversion was achieved only over this catalyst and Au/ceria, while it was not reached even at 300 °C over all other studied catalysts. Gold and ceria particle agglomeration or coke formation should be excluded as a possible reason, and the most probable explanation could be associated with the importance of the benzene activation stage. [ABSTRACT FROM AUTHOR]

Cobalt-doped praseodimium nickelates PrNi 1 − x Co x O 3 − δ and Y/(Pr, Y)-doped ceria oxides were synthesized via Pechini route. Nanocomposites were prepared via ultrasonic dispersion of the mixture of perovskite and fluorite nanopowders in isopropanol with addition of polyvinyl butyral followed by drying, pressing and sintering at 1000–1100 °C. The oxygen mobility and reactivity of perovskites, fluorites and powdered composites obtained by crushing and milling of pellets were estimated by oxygen isotope heteroexchange with 18 O 2 and C 18 O 2 using both closed and flow (SSITKA) reactors in the temperature-programmed (TPIE) mode. Co-existence of two routes of oxygen bulk diffusion—the fast one and the slow one in perovskites and composites was revealed. In perovskites, the fast oxygen diffusion is a minor channel related to some defects in their structure. In composites, the fast oxygen diffusion is the main route being related to both phases disordered due to cation redistribution between them, first of all, to fluorite-like domains of Pr,Y-doped ceria and perovskite/fluorite interfaces. [ABSTRACT FROM AUTHOR]

Gold (3 wt. %) catalysts on Y-doped (1, 2.5, 5 and 7.5 wt. % Y2O3) ceria supports prepared by coprecipitation (CP) or impregnation (IM) were studied in complete benzene oxidation (CBO). A low-extent Y modification was chosen to avoid ordering of oxygen vacancies. The samples were characterized by XRD, TGA, XPS and TPR techniques. A positive role of air pretreatment at 350 °C as compared to 200 °C was established for all Y-containing catalysts and it was explained by cleaning the active sites from carbonates. The oxygen supply cannot be considered as a limiting step for benzene oxidation except for the high 7.5%-doped samples, as suggested by TGA and TPR data. On the basis of XPS results of fresh and used in CBO catalysts, the presence of cationic gold species does not seem important for high CBO activity. The gold catalyst on an IM support with 1% Y-doping exhibited the best performance. A 100% benzene conversion was achieved only over this catalyst and Au/ceria, while it was not reached even at 300 °C over all other studied catalysts. Gold and ceria particle agglomeration or coke formation should be excluded as a possible reason, and the most probable explanation could be associated with the importance of the benzene activation stage.

Cobalt-doped praseodymium nickelate PrNi1−xCoxO3−δ (PNCx) and Y-doped ceria Ce0.9Y0.1O2−δ (YDC) oxides were synthesized via Pechini route. PNCx +YDC composites were prepared via ultrasonic dispersion of the mixture of perovskite and fluorite nanopowders in isopropanol with addition of polyvinyl butyral followed by drying, pressing and sintering at 1300°C. The oxygen mobility and reactivity of powdered PNCx and composites obtained by crushing and milling of dense pellets were estimated by O2-TPD and oxygen isotope exchange with 18O2 and C18O2 using both static and flow (SSITKA) reactors in isothermal and temperature-programmed (TPIE) modes. For PNCx samples sintered at 1300°C comprised of (Ni,Co)O and Ruddlesden–Popper type phases (Pr2NiO4, Pr4(Ni,Co)3O10), the oxygen mobility and reactivity tend to decrease with Co content. For composites, the oxygen mobility is much higher due to Pr transfer into YDC thus disordering perovskite-like and fluorite-like phases. TPIE C18O2 SSITKA experiments combined with SIMS analysis of the depth profiles of Pr18O and Ce18O suggest that fast oxygen diffusion in composites is provided by domains of disordered perovskite-like phases as well as Pr,Y-doped ceria. For best composites, the value of the oxygen chemical diffusion coefficient estimated by the weight relaxation technique exceeds that of well known LSFC–GDC composite. [ABSTRACT FROM AUTHOR]

Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation method, with sequential deposition–precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd–Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 °C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction. [ABSTRACT FROM AUTHOR]

To suppress the internal electronic leakage at ceria-based electrolyte, a novel electron-blocking layer consisting of doped BaCe 0.8 Y 0.2 O 3-δ was fabricated in situ at the interface of Ba-containing anode and Y-doped ceria electrolyte. The anode-supported full cell based on Y 0.2 Ce 0.8 O 1.9 (YDC20) electrolyte presents a remarkable peak power density of 814 mW/cm 2 as well as an open-circuit voltage of 1.0 V at 650 °C, which are much higher than those of the cells with Gd 0.1 Ce 0.9 O 1.95 (GDC10) electrolyte (453 mW/cm 2 at 650 °C) and BaCe 0.8 Y 0.2 O 3-δ |Y 0.2 Ce 0.8 O 1.9 (BCY|YDC20) bilayered electrolyte (419 mW/cm 2 at 650 °C). The efficient promotion of the electron-blocking interlayer with high oxygen ionic conductivity is considered as the main reason for the improved performance of YDC20-based solid oxide fuel cell. The composition and the microstructure of the electron-blocking interlayer are further analyzed by scanning electron microscope and transmission electron microscope characterizations.