The crystal structure of Zr 2 Al 3 C 4 was refined by the Rietveld method from conventional X-ray powder diffraction data. The structure was hexagonal (space group P6 3 mc, Z 5 2) with a 5 0.334680(6) nm, c 5 2.22394(3) nm, and V 5 0.215731(6) nm 3 , being isomorphous with that of U 2 Al 3 C 4 . The final reliability indices were R wp 5 8.57%, R p 5 6.06%, and S 5 1.32. The crystal showed an intergrowth structure with NaCl-type ZrC slabs separated by Al 4 C 3 -type Al 3 C 2 layers.

No abstract

A new series of CuCoZnAl layered double hydroxides (LDHs) with various Cu/Co atomic ratios were synthesized by a coprecipitation method at constant pH#9. The effects of Co on the structural properties and reducibility of both as-synthesized and calcined materials were investigated thoroughly by employing powder X-ray diffraction (XRD), ultraviolet-visible diffuse-reflectance spectroscopy (UV-Vis DRS), thermogravimetrydifferential thermal analysis (TG-DTA), and temperature programmed reduction (TPR) methods. Characterization of as-synthesized materials using these techniques revealed the formation of well-crystallized hydrotalcite (HT)-like LDHs with a general formula [Cu 12(xzyzz) Co x Zn y Al z (OH) 2 ] zz [(CO 3 22 ) z/2 ?mH 2 O] z2 as a major phase. Thermal analyses of materials indicated three stages of endothermic weight loss processes due to the loss of interlayer water and some loosely bound CO 3 22 (100-250 uC), loss of structural water and CO 3 22(250-400 uC) and the loss of some strongly held CO 3 22 anions (above 500 uC). The structural and redox properties of mixed oxides obtained upon thermal activation were investigated by calcining the LDH precursors at 300, 450, 700 and 900 uC. The Cu-rich sample generated a mixture of CuO, ZnO and CuAl 2 O 4 spinel, while Co-based spinel phases were observed at all temperatures in the case of the Co-rich sample. Materials containing both Cu and Co showed a mixture of CuO, Co-based spinel and CuAl 2 O 4 spinel. The interesting observation of the present study was that the reducibility of Cu 2z species of the CuO was enhanced with increasing Co content. On the other hand, the reducibility of Co species decreased with increasing Cu content.

No abstract

No abstract