Room-temperature nitrophenol reduction over Ag–CeO2 catalysts: the role of catalyst preparation method

Ag–CeO2 catalysts (20 mol % Ag) were synthesized using different techniques (co-precipitation, impregnation, and impregnation of pre-reduced ceria), characterized by XRD, N2 sorption, TEM, H2-TPR methods, and probed in room-temperature p-nitrophenol reduction into p-aminophenol in aqueous solution at atmospheric pressure. The catalyst preparation method was found to determine the textural characteristics, the oxidation state and distribution of silver and, hence, the catalytic activity in the p-nitrophenol reduction. The impregnation technique was the most favorable for the formation over the ceria surface of highly dispersed silver species that are active in the p-nitrophenol reduction (the first-order rate constant k = 0.656 min−1)

Low-temperature CO oxidation over Ag/SiO2 catalysts: Effect of OH/Ag ratio

Combined application of TPx methods, H2‐O2 titration, UV–vis DRS, TGA‐DSC‐MS, TEM, XRD, N2 adsorption at −196 oC allowed proving the OH/Ag molar ratio as the key parameter defining the catalytic properties of silica-supported silver (Ag/SiO2) in low‐temperature CO oxidation. A new insight into the formation of active species on the catalyst surface is presented. In this study, Ag/SiO2 catalysts with Ag loading of 5 and 8 wt.% were prepared by incipient wetness impregnation method on the basis of commercial silicas preliminary calcined at 500, 700 and 900 °C. Detailed characterization of catalysts by physicochemical methods revealed that molar ratio between the concentration of surface OH groups (normalized to support mass) and silver amount in the prepared catalysts (OH/Ag ratio) affects the silver dispersion, structure of silver nanoparticles (NPs) and their catalytic properties. Only at optimal value of OH/Ag ratio the silver NPs are stated to possess both high dispersion and defective multidomain structure (that consists of several nanodomains) providing the adsorption of weakly bound oxygen species responsible for high catalytic activity in CO oxidation at low‐temperature. Additionally, the co-existence of two types of active sites reacting with CO at room temperature with and without formation of adsorbed carbonate species is discussed. The first type of active sites was catalytically active in low-temperature CO oxidation with CO2 release at room temperature (RT). The second type may retain surface carbonate species up to ∼40–50 °C. The balance between these species shifts towards the first type for the active catalyst

Low-temperature CO oxidation over Ag/SiO2 catalysts: Effect of OH/Ag ratio

Combined application of TPx methods, H2‐O2 titration, UV–vis DRS, TGA‐DSC‐MS, TEM, XRD, N2 adsorption at −196 oC allowed proving the OH/Ag molar ratio as the key parameter defining the catalytic properties of silica-supported silver (Ag/SiO2) in low‐temperature CO oxidation. A new insight into the formation of active species on the catalyst surface is presented. In this study, Ag/SiO2 catalysts with Ag loading of 5 and 8 wt.% were prepared by incipient wetness impregnation method on the basis of commercial silicas preliminary calcined at 500, 700 and 900 °C. Detailed characterization of catalysts by physicochemical methods revealed that molar ratio between the concentration of surface OH groups (normalized to support mass) and silver amount in the prepared catalysts (OH/Ag ratio) affects the silver dispersion, structure of silver nanoparticles (NPs) and their catalytic properties. Only at optimal value of OH/Ag ratio the silver NPs are stated to possess both high dispersion and defective multidomain structure (that consists of several nanodomains) providing the adsorption of weakly bound oxygen species responsible for high catalytic activity in CO oxidation at low‐temperature. Additionally, the co-existence of two types of active sites reacting with CO at room temperature with and without formation of adsorbed carbonate species is discussed. The first type of active sites was catalytically active in low-temperature CO oxidation with CO2 release at room temperature (RT). The second type may retain surface carbonate species up to ∼40–50 °C. The balance between these species shifts towards the first type for the active catalyst

Design of Ni-based catalysts supported over binary La-Ce oxides: Influence of La/Ce ratio on the catalytic performances in DRM

CeO2 and binary La-Ce oxides, with different La/Ce atomic ratios (1:4; 1:1; 4:1), were synthesized using sol-gel method in the presence of citric acid in ammonia solution, at pH~9, and Ni (10wt%) was added by wetness impregnation method. The physical-chemical properties, catalytic activity and long-run stability of the so prepared catalysts were evaluated in DRM reaction. Characterizations of both fresh and spent catalysts were carried out using low-temperature N2 adsorption, XRD, TGA, TPR, Raman and TEM analyses. The DRM gradient catalytic tests performed in the range of 400-800°C revealed higher catalytic conversions for Ni/La2O3-CeO2 catalysts, especially for those with La/Ce ratio 1:4 and 1:1. The stable conversions of CH4 and CO2 (long run at 650 °C for 24h) registered for such Ni/La2O3-CeO2 catalysts were attributed to the presence of small Ni crystallites. During long run tests, Ni-LaCe 1:4 and Ni-LaCe 1:1 formed the same types of carbon, both as filaments and layered carbon with graphene structure, but their catalytic activity was retained. Ni/CeO2 showed the smallest content of carbon, however, exhibited lower CH4 and CO2 conversions in comparison with the Ni-LaCe systems, due to the presence of big Ni particles with sizes of up to 0.5μm

The role of metal-support interaction in Ag/CeO2 catalysts for CO and soot oxidation

Ajt/CeOi cataljFsts with a sliver loedlnf; Ы I0«t.4 have been prepared Iqr three ditFerent techniques; imprej- luUoo, Ag/CeOi (Imp), Impregnation of prereduced СеОг, Ag/СеОз (red-tinp). and co-deposlttoa preclpltanon, AgOO-j (co-DP). The feaiuces of the prepared composites have heeo studied by km-temperature Nj urplion. TGA, ](RF, TPR-H2. ТЕМ HR. XPS and Raman tpecircecopy. The Raman and )(PS results show that the addition of silver to 00-, slgoificaiuly increases the defectiveness of CeO. particles, and such an effect is a function of the preparntlon method. The Ag-OO^ (co-DPI and Ag/CeOi (red-imp) catalysts show enhanced tnterfacial Ag-CeOi Intemction caused by the epitaxial growth of sliver particles (dm - 2.3S A) on the CeO- surface (d,,, - 3.1 A) as well as high amouni of oxygen vacancies. A motphology-depeodenl Interplay between the oxygen vacancies and the strength of the Ag-CeO^ Interaction has been revealed Strengthening of the metal-supporl Interaction enhances the catalytic activity of the composites in both (Ю oxidation and soot combustion

Design of Ag-CeO2/SiO2 catalyst for oxidative dehydrogenation of ethanol: Control of Ag–CeO2 interfacial interaction

Three Ag-CeO2/SiO2 catalysts were prepared by different methods, namely, sequential impregnation, co-impregnation and impregnation of pre-reduced CeO2/SiO2 and are tested in the oxidative dehydrogenation of ethanol. The order of introduction of silver and ceria precursors is found to influence the catalytic activity that increases in the order of preparation method: sequential impregnation < co-impregnation < impregnation of pre-reduced CeO2/SiO2. Results of TPR-H2, TEM HR, XPS and Raman characterizations show the best interfacial Ag–CeO2 interaction and highest defectiveness of CeO2 nanoparticles in the catalyst prepared by impregnation of pre-reduced CeO2/SiO2. A correlation between Ag–CeO2 interaction and catalytic activity is found in the series of Ag-CeO2/SiO2 catalysts depending on the preparation method. Enhanced Ag–CeO2 interfacial interaction leads to increased activity in oxidative dehydrogenation of ethanol

Design of Anode Materials for IT SOFC:Effect of Complex Oxide Promoters and Pt Group Metals on Activity and Stability in Methane Steam Reforming of Ni/YSZ (ScSZ) Cermets

Ni/YSZ or Ni/ScCeSZ cermets were promoted by up to 10 wt % of fluoritelike (Pr-Ce-Zr- O, La-Ce-Zr-O, and Ce-Zr-O) or perovskitelike (La-Pr-Mn-Cr-O) oxides and small (up to 1.4 wt %) amounts of Pt group metals (Pd, Pt, or Ru). Reactivity of samples, their lattice oxygen mobility, and their ability to activate methane were characterized by temperature-programed reduction by CH4. The catalytic properties of these samples in methane steam reforming were studied at 500-850 degrees C and short contact times (10 ms) in feeds with 8 mol % of CH4 and steam/methane ratio of 1: 3. Oxide promoters ensure stable performance of cermets in stoichiometric feeds at T &gt; 650 degrees C by suppressing carbon deposition. Copromotion with precious metals enhances performance in the intermediate temperature (450-600 degrees C) range due to more efficient activation of methane. Factors determining specificity of these cermet materials' performance (chemical composition, microstructure, oxygen mobility in oxides, interaction between components, and reaction media effect) are considered. The most promising systems for practical application are Pt/Pr-Ce-Zr-O/Ni/YSZ and Ru/La-Pr-Mn-Cr-O/Ni/YSZ cermets demonstrating a high performance in the intermediate temperature range under broad variation in steam/CH4 ratio. [DOI: 10.1115/1.3117255]</p

Design of Anode Materials for IT SOFC: Effect of Complex Oxide Promoters and Pt Group Metals on Activity and Stability in Methane Steam Reforming of Ni/YSZ &quot;ScSZ… Cermets

small (up to 1.4 wt %) amounts of Pt group metal