Abstract
X-Ray diffraction (XRD), laser Raman spectroscopy (LRS), and solid-state 51V nuclear magnetic resonance (NMR) have been used to investigate the interaction of vanadium with a sample of sepiolite in the presence of phase impurities. After thermal and hydrothermal treatments, sepiolite decomposes forming enstatite (MgSiO 3). In contrast, in the presence of (⩽ 10%) calcite impurities (as found in naturally occurring samples from Nevada) sepiolite decomposes forming diopside (MgCaSiO 6). When the thermal and hydrothermal treatments are repeated in the presence of 5% V, Mg-containing vanadates are not observed, and Ca 2V 2O 7 is the only heat-stable V compound identified. These results suggest that Ca 2V 2O 7 formation is thennodynamically favored over its Mg analog. Formation of this compound is probably responsible for the preservation of cracking activity observed when cracking V-contaminated gas oil with dual-function cracking catalysts (DFCC) containing sepiolite-calcite granules to passivate V impurities.
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