Search

A series of NiCe x Al (x = 0.1, 0.3, 0.5, 0.7 and 0.9) mixed metal oxides catalysts was synthesized through decomposing the corresponding layered double hydroxides (LDH) precursors, and then characterized by TG, XRD, N 2 adsorption/desorption, XPS, H 2 -TPR, H 2 -TPD etc. techniques. The results showed that the introduction of Ce could efficiently restrict the agglomeration of Ni species. The generated Ni–Ce–O solid solution could create the oxygen vacancies and enhance the oxygen mobility which further improved the properties of active sites including Ni dispersion and surface area, and suppressed coke deposition. The Ni2+ species was reduced by Ce3+ under the reaction conditions to give the metallic Ni as active sites in catalyzing steam reforming of glycerol for the production of hydrogen. The best catalytic performance was obtained over the sample NiCe 0.7 Al which exhibited the better Ni dispersion and larger surface, and lower quantity of deposited coke by establishing the correlations. The reaction was more selective to hydrogen thanks to the enhancement of water gas shift reaction and suppression of CO methanation reaction. Image 1 • Impurity co-existed in Ce contained NiAl layered double hydroxides precursors. • Ce could stabilize the Ni species but restrict the reduction of Ni2+ by hydrogen. • Ce3+ reduced the Ni2+ into the active metallic Ni under the reaction conditions. • Ce/Al ratio had important influences on Ni properties. • Coke deposition was suppressed by introducing Ce into the catalyst. [ABSTRACT FROM AUTHOR]

ZnO-Al2O3 derived from layered double hydroxides ( ZnAl-LDH) was successfully applied for dispersion of Pd-Ag bimetallic catalysts for the selective hydrogenation of acetylene to ethylene and the Pd-Ag/ ZnO-Al2O3 catalyst showed the best catalytic performance among the prepared samples. It was found that the catalyst carrier of ZnO-Al2O3 metal-oxides derived form ZnAl-LDH could significantly suppress the over-hydrogenation of acetylene to obtain the relatively higher selectivity of ethylene. The introduction of Ag restricted efficiently the formation of coke because of the oligomerization reaction, which was further evidenced by thermal gravimetric analysis. The selectivity towards ethylene was in the order of Pd-Ag/ ZnO-Al2O3>Pd/ ZnO-Al2O3>Pd-Ag/ Al2O3>Pd/ Al2O3 at a high conversion level. As the thermal gravimetric and differential temperature analysis ( TG-DTA) revealed, Pd-Ag intermetallic catalyst on the ZnO-Al2O3 support showed less coke formation. [ABSTRACT FROM AUTHOR]

Abstract: The well-crystallized MZnAl (M=Cu, Co, Ni) layered-double hydroxides (LDHs) were synthesized by combining hydrothermal synthesis with urea homogeneous processes. The LDH precursors were calcined at 450°C to obtain the nanoscale mixed metal oxides. Characterization techniques including XRD, TG–DTG, TPR, N2 adsorption/desorption, HRTEM and SEM were carried out to investigate the LDH precursors, thermal decomposition behavior and reducibility, porosity and morphology of the calcined samples. For the LDHs containing Cu, the thermal decomposition process became more complex because of its Jahn–Teller effect, and the phases of the calcined samples were different as a result of preparation conditions. Hydrothermal synthesis led to easy generation of the spinel phase at lower thermal treatment temperature (450°C). Further, the reducibility and texture properties were influenced. [Copyright &y& Elsevier]

The Co 2 Ni 1 AlO y -MW catalyst exhibited higher catalytic performance and the temperature required to achieve a methane conversion of 90% (T 90) was about 473 °C, this temperature was 40 °C lower than that on the NiO-IWI/Co 3 AlO y sample. The enhanced catalytic activity was correlated with higher surface area, better redox property, higher ratio of surface Co3+/Co2+ species and surface absorbed oxygen and lattice oxygen (O ads /O latt) derived from the synergistic effect over Co 2 Ni 1 AlO y -MW catalysts. • Mesoporous Co x M 3-x AlO y catalysts were prepared by the microwave method. • The nickel salt introduced illustrated the better impact on methane catalytic combustion performance. • There was a higher ratio of surface absorbed oxygen over the lattice oxygen for Co 2 Ni 1 AlO y -MW sample. A series of mesoporous Co x M 3-x AlO y (M Ni, Mn) catalysts have been obtained by calcination of layered double hydroxide (LDH) precursors prepared by the microwave method, the catalysts exhibited high activity for methane catalytic combustion. By changing the preparation method and type of metal salt introduced (Ni and Mn), it is effective for controlling the structure properties and reducibility of catalyst as well as the catalytic performance for the methane catalytic combustion. The Co 2 Ni 1 AlO y catalyst exhibited higher catalytic performance and the temperature required to achieve a methane conversion of 90% (T 90) was about 473 °C, this temperature was 40 °C lower than that on the NiO-IWI/Co 3 AlO y sample. The enhanced catalytic activity was correlated with higher surface area, better redox property, higher ratio of surface Co3+/Co2+ species and surface absorbed oxygen and lattice oxygen (O ads /O latt) derived from the synergistic effect over Co 2 Ni 1 AlO y catalyst. Therefore, the microwave method provided an effective path to develop the efficient combustion catalyst for higher performance. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • High Zr/Al ratio could promote the reduction of free and active Ni2+ species. • The pore structure had an evident transformation as Zr/Al ratio reached 0.5. • NiZr 0.5 Al showed the best abilities in anti-sintering and coke resistance. • NiZr 0.5 Al favored to form gaseous products and suppressed the CO methanation. Abstract The NiZrAl mixed metal oxides catalysts with varied Zr/Al ratio were derived from the layered double hydroxides (LDH) through the thermal decomposition. The different techniques such as TG, XRD, N 2 adsorption/desorption, XPS, TPR, H 2 chemisorption, SEM and TEM etc. were applied to study the thermal decomposition behaviors of the corresponding LDH, crystalline phases changes before and after reaction, the porous structure, chemical state of surface element, reducibility, properties of active phase metallic Ni and the morphology. The results showed that the LDH structure could be kept during the experimental range from 0.1 to 1.0, although high Zr/Al ratio made the structure feature weaken. The porous structure of the calcined catalysts exhibited an significant change when Zr/Al ratio reached 0.5. Both Ni dispersion and surface increased linearly with the increased Zr/Al, however, more amount of surface Ni was reduced and less amount of coke was formed over the sample NiZr 0.5 Al. It consequently gave the best conversion to gaseous products and the highest selectivity of hydrogen by promoting the water gas shift reaction and suppressing the CO methanation reaction. [ABSTRACT FROM AUTHOR]