Low-temperature synthesis of MgxCo1-xCo2O4 spinel catalysts for N2O decomposition

Low-temperature synthesis of spinels MgxCo1-xCo2O4 (x = 0.0-0.9) has been investigated with two important synthetic parameters and XRD/FTIR/DSC/BET/ICP/CHN methods. It; is found that with an increase in hydrothermal treatment temperature, precursor compounds change from the hydrotalcite-like to brucite-like and then to cubic spinel phase when the initial metal concentration ratio [Mg2+]:[Co2+] greater than or equal to 1, while from the turbostratic to hydrotalcite-like and then to cubic spinel phase when the [Mg2+]:[Co2+] < 1. The MgxCo1-xCo2O4 (x less than or equal to 1/3) spinels were formed at temperatures as low as 50-100 degrees C. In the postsynthesis thermal treatment, various thermal events have been observed, and in all cases the spinel phase can be prepared at temperatures below 300 degrees C. On the basis of FTIR results, a topotactic mechanism for the formation of the spinel phase has been confirmed. Specific surface area as high as 210 m(2)/g has been attained in 400 degrees C calcined MgxCo1-xCo2O4 with x = 0.9. Causes for the formation of the spinel phase at low temperatures have been addressed. Excellent catalytic activity for N2O decomposition (30.6-38.9 mmol (N2O)/g.h at GHSV = 21200 h(-1) and 380-400 degrees C; N2O = 10 mol % balanced with He) has been observed and discussed for these Mg-Co spinels

Sulfate-functionalized carbon/metal-oxide nanocomposites from hydrotalcite-like compounds

As a new application of hydrotalcite-like compounds, sulfate-functionalized carbon/metal-oxide nanocomposites have been prepared at relatively low temperatures in a single step, in which interlayer sulfonated polymeric anions are catalytically converted to the nanocarbons (secondary phase) while CoAl-containing brucite-like sheets are converted to the metal oxide matrices. The chemical composition and structure of nanocomposites can be controlled via selecting chemical functional groups in the intercalated polymeric anions and varying processing conditions

Synthesis of nanosize supported hydrotalcite-like compounds coAlx(OH)2+2x(CO3)y(no 3)x-2y·nH2o on γ-Al2O3

10.1021/cm000526iChemistry of Materials132297-303CMAT

Insertion direction of hydrogen in protonation of α-MoO3

10.1021/jp010177vJournal of Physical Chemistry B105307178-7181JPCB

Surface and textural properties of network-modified silica as a function of transition metal dopant zirconium

10.1021/jp010828nJournal of Physical Chemistry B105389093-9100JPCB

In-situ generation of maximum trivalent cobalt in synthesis of hydrotalcite-like compounds (MgxCo1-x-yCoyIII)-Co-II(OH)(2)(NO3)(y)center dot nH(2)O

In-situ generation of trivalent cobalt cations has been investigated for the hydrotalcite-like compounds (MgxCo1-x-yCoyIII)-Co-II(OH)(2)(NO3)(y). nH(2)O at 25-40 degrees C under oxygen-containing atmospheres. It is noted that with more involvement of Mg2+ in the compounds, less Co2+ cations are needed to maintain the hydrotalcite-like structure. Because of the presence of the Mg2+, more Co2+ can be oxidized under the current experimental conditions and the highest mole ratios of Co3+ to total cobalt cations (Co3+:Co) observed in this work is 57%. The mole ratio of Co3+ to total metal cations (Co3+:(Mg+Co)) achieved in this work is 31% after 4 days of oxidation reaction, which is close to its upper charge limit to produce a single-phase hydrotalcite-like structure (33%). Two major thermal events are observed when the compounds are heated. The first one at 113-134 degrees C is attributed to the removal of interlayer water molecules while the second at 274-333 degrees C to the dehydroxylation and decomposition of intercalated anions. Higher catalytic activity for nitrous oxide (N2O) decomposition is observed for the Mg-Co oxides with the same cobalt content but lower mole ratios of Co3+:Co in their hydrotalcite-like precursors. The reason for this activity variation has also been addressed