Abstract
The modification of Ru/CNTs (CNTs denotes carbon nanotubes) with rare earth, alkali, and alkaline earth compounds were systematically studied. The loading of modifying agents leads to decrease in pore volume and surface area; but improvement in thermal stability of Ru/CNTs. The size and morphology of Ru particles are not affected by the modification. For the catalysts modified by metal nitrates, activities were found in the order of K–Ru>Na–Ru>Li–Ru>Ce–Ru>Ba–Ru>La–Ru>Ca–Ru>Ru, signifying that within the same groups (K, Na and Li; Ba and Ca), the higher the electronegativity of the promoter, the lower is the NH3 conversion. Of all the potassium salts adopted, KNO3, KOH, and KCO3 show similar promotional effect, suggesting that KOH is the active promoter for catalytic activity. The maximum promotional effect was observed at an atomic ratio of K/Ru=2. The electron-withdrawing groups, F−1, Cl−1, Br−1, SO42−, and PO43− are inhibitors of Ru catalysts. The results of N2-TPD investigation revealed that the promotional effects of a modifier is a combined result of: (i) enhancing combinative desorption of nitrogen atoms, and (ii) decreasing of the apparent activation energy of the decomposition reaction.
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