Synthesis and characterization of Rh/MnO 2 -CeO 2 /Al 2 O 3 catalysts for CO-PrOx reaction

Mn and Co decorated biomorphic ceria fiber catalysts for soot and benzene total oxidation

Mn or Co supported CeO2 fiber catalysts were synthesized following a biotemplating route and evaluated in soot combustion and benzene total oxidation. The catalysts were characterized by SEM, EDX, N2 physisorption, FTIR-ATR, XRD, RAMAN and XPS. SEM results confirmed that the "twisted ribbon" morphology of the biotemplate was mostly maintained. XRD and Raman showed that Mn and Co cations partially insert into ceria lattice and also segregate at the surface of the fibers. XPS allowed to determine that both set of catalysts exhibit Ce3+ and Ce4+ species, in addition to adsorbed and lattice oxygen. Also, the average oxidation state (AOS) of surface Mn could be calculated. Compared to bare Fib Ce, the performances for both reactions were improved for the supported catalysts, except from the catalyst with lowest Mn content for soot combustion. The catalytic activity was discussed in terms of the physicochemical features of the supported catalysts.

Low-temperature CO preferential oxidation in H2-rich stream over Indium modified Pd-Cu/Al2O3 catalyst

The impact of Indium (In) doping upon the catalytic performance of Pd-Cu/Al2O3 for carbon monoxide preferential oxidation (CO-PROX) in hydrogen (H2) rich atmosphere at low temperature has been studied. A series of catalysts with extremely low palladium (Pd) loading (0.06 wt%) are synthesized by the facile co-impregnation method. When the In/copper (Cu) atomic ratio equals 0.25, Pd-Cu-In0.25/Al2O3 can keep 40% CO conversion and 100% carbon dioxide (CO2) selectivity at least 120 min at 30 °C, which is significantly superior to the catalytic performance of Pd-Cu/Al2O3. The elaborate characterization findings reveal that the added In species to Pd-Cu/Al2O3 causes Indium oxide (In2O3) to generate, which produces the interaction of In2O3 with Pd-Cu/Al2O3, further promoting the dispersion of copper chloride hydroxide (Cu2Cl(OH)3). Moreover, the modification of In facilitates the re-oxidation of Pd0 to Pd+ through reducing the formation of palladium hydride (PdHx) during the CO-PROX reaction. Meanwhile, the addition of In leads to the decrease of Cu+ electron cloud density, making it easier to be oxidized to Cu2+. Collectively, the easy re-oxidation of Pd0 and Cu+ is favorable to fulfill the Wacker cycle between Pd and Cu species, thus improving the catalytic performance for CO-PROX.

High-Performing Au-Ag Bimetallic Catalysts Supported on Macro-Mesoporous CeO2 for Preferential Oxidation of CO in H2-Rich Gases

We report here an investigation on the preferential oxidation of carbon monoxide in an H2-rich stream (CO-PROX reaction) over mono and bimetallic Au-Ag samples supported on macro-mesoporous CeO2. The highly porous structure of ceria and the synergistic effect, which occurs between the bimetallic Au-Ag system and the support, led to promising catalytic performance at low temperature (CO2 yield of 88% and CO2 selectivity of 100% at 60 °C), which is suitable for a possible application in the polymer electrolyte membrane fuel cell (PEMFC). The morphological, structural, textural and surface features of the catalysts were determined by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), N2-adsoprtion-desorption measurements, Temperature Programmed Reduction in hydrogen (H2-TPR), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). Furthermore, the catalytic stability of the best active catalyst, i.e., the AuAg/CeO2 sample, was evaluated also in the presence of water vapor and carbon dioxide in the gas stream. The excellent performances of the bimetallic sample, favored by the peculiar porosity of the macro-mesoporous CeO2, are promising for possible scale-up applications in the H2 purification for PEM fuel cells.

Single and Dual Metal Oxides as Promising Supports for Carbon Monoxide Removal from an Actual Syngas: The Crucial Role of Support on the Selectivity of the Au–Cu System

A catalytic screening was performed to determine the effect of the support on the performance of an Au–Cu based system for the removal of CO from an actual syngas. First, a syngas was obtained from reforming of ethanol. Then, the reformer outlet was connected to a second reactor, where Au–Cu catalysts supported on several single and dual metal oxides (i.e., CeO2, SiO2, ZrO2, Al2O3, La2O3, Fe2O3, CeO2-SiO2, CeO2-ZrO2, and CeO2-Al2O3) were evaluated. AuCu/CeO2 was the most active catalyst due to an elevated oxygen mobility over the surface, promoting CO2 formation from adsorption of C–O* and OH− intermediates on Au0 and CuO species. However, its lower capacity to release the surface oxygen contributes to the generation of stable carbon deposits, which lead to its rapid deactivation. On the other hand, AuCu/CeO2-SiO2 was more stable due to its high surface area and lower formation of formate and carbonate intermediates, mitigating carbon deposits. Therefore, use of dual supports could be a promising strategy to overcome the low stability of AuCu/CeO2. The results of this research are a contribution to integrated production and purification of H2 in a compact system.