Effects of oxide promoters on metal dispersion and metal-support interactions in Ni catalysts supported on activated carbon

Various oxide-promoted Ni catalysts supported on activated carbon were prepared, and the effect of promoters on the surface structure and properties of Ni catalysts was studied. Physical adsorption (Na adsorption), thermogravimetric analysis (TGA), temperature-programmed desorption (TPD), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. It is found that nickel is fairly uniformly distributed in the pores of the carbon support. Addition of promoters produces a more homogeneous distribution of nickel ion in carbon. However, distributions of promoters in the pores are varying. Addition of promoters increases the dispersion of nickel in carbon. Promoters also change the interaction between the carbon and Ni, resulting in significantly different behaviors of catalysts under various environments. CaO and MgO promoters improve the reactivity of nickel catalysts with O-2 but retard the interaction between nickel oxide and carbon. La2O3 shows some inhibiting effect on the interactions between nickel oxide and oxygen as well as carbon.

Relations between coal petrology and gas content in the Upper Newlands Seam, central Queensland, Australia

The Upper Newlands Seam in the northern Bowen Basin, Queensland, Australia consists of six benches (A-F) that have different petrographic assemblages. Benches C and E contain relatively abundant inertodetrinite and mineral matter, as well as anomalously high reflectance values; these characteristics support a largely allochthonous, detrital origin for the C and E benches. Fractures and cleats in the seam show a consistent orientation of northeast- southwest for face cleats, and a wide range of orientations for fractures. Cleat systems are well developed in bright bands, with poor continuity in the dull coal. Both maceral content and cleat character are suggested to influence gas drainage in the Upper Newlands Seam. A pronounced positive correlation between vitrinite abundance and gas desorption data suggests more efficient drainage from benches with abundant vitrinite. Conversely, inertinite-rich benches are suggested to have less efficient drainage, and possibly retain gas within pore spaces, which could increase the outburst potential of the coal. (C) 2001 Elsevier Science BN. All rights reserved.

Unprecedented oxidation of a biologically active aroylhydrazone chelator catalysed by iron(III): serendipitous identification of diacylhydrazine ligands with high iron chelation efficacy

Ligands of the 2-pyridylcarbaldehyde isonicotinoylhydrazone class show high iron (Fe) sequestering efficacy and have potential as agents for the treatment of Fe overload disease. We have investigated the mechanisms responsible for their high activity. X-ray crystallography studies show that the tridentate chelate 2-pyridylcarbaldehyde isonicotinoylhydrazone undergoes an unexpected oxidation to isonicotinoyl(picolinoyl)hydrazine when complexed with Fe-III. In contrast, in the absence of Fel the parent hydrazone is not oxidized in aerobic aqueous solution. To examine whether the diacylhydrazine could be responsible for the biological effects of 2-pyridylcarbaldehyde isonicotinoylhydrazone, their Fe chelation efficacy was compared. In contrast to its parent hydrazone, the diacylhydrazine showed little Fe chelation activity. Potentiometric titrations suggested that this might be because the diacylhydrazine was charged at physiological pH, hindering its access across membranes to intracellular Fe pools. In contrast, the Fe complex of this diacylhydrazine was charge neutral, which may allow facile movement through membranes. These data allow a model of Fe chelation for this compound to be proposed: the parent aroylhydrazone diffuses through cell membranes to bind Fe and is subsequently oxidized to the diacylhydrazine complex which then diffuses from the cell. Other diacylhydrazine analogues that were charge neutral at physiological pH demonstrated high Fe chelation efficacy. Thus, for this class of ligands, the charge of the chelator appears to be an important factor for determining their ability to access intracellular Fe. The results of this study are significant for understanding the biological activity of 2-pyridylcarbaldehyde isonicotinoylhydrazone and for the design of novel diacylhydrazine chelators for clinical use.