Efficient methanol steam reforming over ZnCeZrOx: the unique role of cerium

Zn1Ce1Zr9Ox is a ternary solid solution with Zn and Ce doped into the lattice of ZrO2, which is more active and stable than the counterpart without cerium doping in steam reforming of methanol.

New Insights on the Nickel State Deposited by Hydrazine Wet-Chemical Synthesis Route in the Ni/BCY15 Proton-Conducting SOFC Anode

Yttrium-doped barium cerate (BCY15) was used as an anode ceramic matrix for synthesis of the Ni-based cermet anode with application in proton-conducting solid oxide fuel cells (pSOFC). The hydrazine wet-chemical synthesis was developed as an alternative low-cost energy-efficient route that promotes ‘in situ’ introduction of metallic Ni particles in the BCY15 matrix. The focus of this study is a detailed comparative characterization of the nickel state in the Ni/BCY15 cermets obtained in two types of medium, aqueous and anhydrous ethylene glycol environment, performed by a combination of XRD, N₂ physisorption, SEM, EPR, XPS, and electrochemical impedance spectroscopy. Obtained results on the effect of the working medium show that ethylene glycol ensures active Ni cermet preparation with well-dispersed nanoscale metal Ni particles and provides a strong interaction between hydrazine-originating metallic Ni and cerium from the BCY15 matrix. The metallic Ni phase in the pSOFC anode is more stable during reoxidation compared to the Ni cermet prepared by the commercial mechanical mixing procedure. These factors contribute toward improvement of the anode’s electrochemical performance in pSOFC, enhanced stability, and a lower degradation rate during operation.

Heterostructured CeO2-M (M = Co, Cu, Mn, Fe, Ni) Oxide Nanocatalysts for the Visible-Light Photooxidation of Pinene to Aroma Oxygenates

Herein, we report the enhanced photocatalytic activity of heterostructured CeO₂ nanocatalysts interfaced with Cu, Co, Ni, Mn, and Fe metal oxides. The CeO₂ catalysts exhibited an enhanced red shift in the visible-light response compared to CeO₂. This improved absorption range effectively suppressed electron (e^-)/hole (⁺h) recombination by forming localized energy bands associated with defect oxygen vacancies (V _o) induced by the Mⁿ⁺ ions incorporated in CeO₂. Under visible-light irradiation, CeO₂ catalysts are active for α-pinene oxidation to the aroma oxygenates, pinene oxide, verbenol, and verbenone. Both Fe₂O₃-CeO₂ and NiO-CeO₂ gave the highest pinene conversions of 71.3 and 53.1%, respectively, with corresponding pinene oxide selectivities of 57.3 and 58.2%. The enhanced photocatalytic performance of the heterostructured CeO₂ catalysts compared to CeO₂ is attributed to their enhanced visible-light absorption range and efficient suppression of e^-/⁺h recombination. The Fe₂O₃-CeO₂ catalyst was highly recyclable and did not show any significant loss of its photoactivity.

A detailed insight into the catalytic reduction of NO operated by Cr-Cu nanostructures embedded in a CeO2 surface

Replacing rare and expensive elements, such as Pt, Pd, and Rh, commonly used in catalytic devices with more abundant and less expensive ones is mandatory to realize efficient, sustainable and economically appealing three-way catalysts. In this context, the surface of a Cr-Cu/CeO2 system represents a versatile catalyst for the conversion of toxic NO into harmless N2. Yet, a clear picture of the underlying mechanism is still missing. We provide here a detailed insight into such a reaction mechanism by means of a combined experimental and theoretical study. Fourier-transform infrared spectroscopy is used to detect all the products resulting from catalytic reactions of NO and CO on the surface of a Cr-Cu/CeO2 nanocatalyst. CO pulsing experiments unveil that reactions of CO with O atoms at the Cr-Cu/CeO2 surface are the major factors responsible for the formation of surface vacancies. On these grounds, a comprehensive picture of the NO reduction and the role of both Cu and Cr dopants and vacancies is rationalized by first-principles modeling. Our findings provide a general route for the realization of ceria-based cost-effective catalysts.

Comparative study of Cu-based bimetallic oxides for Fenton-like degradation of organic pollutants

In order to provide useful information for the rational design of effective Fenton-like catalyst, a series of Cu-based bimetallic oxides were synthesized and their Fenton-like performances for the degradation of Orange II and ciprofloxacin were compared. The structure, chemical oxidation state, surface charge property and redox ability of the catalysts were also investigated by different characterization techniques. Among them, NiCu exhibited the highest adsorption capacity towards Orange II and the highest activity for the production of OH from H₂O₂ decomposition, which could be attributed to its high surface area and highly positively charged surface. However, FeCu exhibited the highest activity for the degradation of Orange II. The reason might be that FeCu has more unpaired electrons and higher redox ability, thus promoting the activation of adsorbed Orange II through the electron transfer process. By contrast, NiCu exhibited the highest activity for the removal of ciprofloxacin because ciprofloxacin was mainly degraded by OH. Finally, the main degradation intermediates of Orange II and ciprofloxacin were determined by liquid chromatography-mass spectrometry.

Insight into the H2S selective catalytic oxidation performance on well-mixed Ce-containing rare earth catalysts derived from MgAlCe layered double hydroxides

A series of well-mixed Ce-containing MgAlCe rare earth catalysts derived from layered double hydroxides were synthesized and tested for H₂S selective catalytic oxidation. Particularly, no chemisorption O-vacancies but intrinsic defect sites were present on catalyst surface. Significantly, the catalysts exhibited excellent catalytic activity, reasonable durability, and outstanding sulfur selectivity (100%) at relatively low temperatures. Furthermore, the catalyst followed a step-wise mechanism, and the catalyst deactivation was due mainly to the slower oxidation rate of Ce³⁺ to Ce⁴⁺ by O₂ as compared to the reduction rate of Ce⁴⁺ to Ce³⁺ by H₂S. Particularly, the added water, a Lewis base, can compete with inefficient S₈ catalyst for the occupation of Lewis acid sites and active sites. Meanwhile, it can change the characteristics of catalyst surface, resulting in sulfur existing form transforming from inefficient S₈ catalyst to inactive S₃. Thus, lead to a decrease of deposited inefficient S₈ catalyst content. Consequently, decrease the catalytic activity.