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Vanadium Effects on Pillared Rectorite Catalysts

Abstract Energy dispersive spectroscopy (EDS), microprobe analysis, X-ray diffraction (XRD), high-resolution electron microscopy (HREM), and 51 V solid-state NMR, together with microactivity test (MAT) measurements, have been used to characterize the effects that V-impurities have on the physiochemical properties of a sample of natural rectorite pillared with alumina clusters. Results indicate that although V initially is preferentially located in the pillared clay micropares, after calcination or steaming it migrates, generating clay platelets with a V-enriched surface. During thermal treatment in the presence of 0.5-l.0% V, minor changes in the clay-pillared structure are observed by XRD or HREM. However, at hydrothermal conditions, 1% V causes pillar decomposition and a collapse of the clay microporous structure that result in a loss of surface area, basal spacing, and catalytic activity for gas-oil cracking. HREM data show that steaming in the presence of 1% V generates wavy and misoriented planes; however, in contrast to montmorillonites, the collapsed rectorite partially retains its face-to-face stacking of silicate layers. These processes are conveniently monitored by 51 V solid-state NMR, which is capable of distinguishing the various coordination environments in which V can be found after thermal and hydrothermal treatments.