Abstract--Hydrotalcite-like compounds, described by the formula [Zn, xAlx(OH)2] [(CO3)x/2 9 nHzO], were prepared by coprecipitation methods at 80~ and characterized by bulk chemical analysis, X-ray powder diffraction (XRD), nuclear magnetic resonance (NMR), and scanning-transmission electron microscopy (STEM). An x value of 0.33 was previously assumed to be an upper limit, but recently, Al-rich hydrotalcitelike compounds have been prepared with x as large as 0.44 by hydrothermal synthesis. In the Zn-Al system, #p-rich hydrotalcite was synthesized at normal pressure by coprecipitation. Zn-#P hydrotalcitelike compounds were obtained in the range of x = 0.3 to 0.4. An #P-rich hydrotalcite-like compound with x = 0.44 was formed in mixtures containing large amounts of a poorly crystalline Zn-A1 phase. A continuous contraction of the hydrotalcite-like structure occurred as x increased, both the a and c lattice parameters decreasing for x values as large as 0.44. This study illustrates the advantages of using quantitative analytical electron microscopy with high spatial resolution to complement conventional (and bulk) characterization techniques for correlating structural and compositional characteristics of finely divided materials.

i.e., hydration state of the oxide precursor, composition of the sulfiding mixture H2/H2S or N2/H2S, temperature, and time duration. The important role of these experimental conditions on the detection of transient species during sulfidation has been pointed out. Different intermediates such as oxysulfides, sulfido compounds, and MoS3 appear to be the dominant ones, whose existence depends on the previously mentioned parameters. The crystallite size of the MoS2, a function of the Mo loading and determined by HREM, influences the position and width of the ^385-cnr1 line.

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