Spectroscopic study of the structure of chromium(VI), molybdenum(VI) and tungsten(VI) oxospecies anchored on aluminium oxide

Abstract

Diffuse reflectance in the ultraviolet-visible and Raman spectra indicate that CrV1 anchored to the A1,0, surface by 'pulse-' and ' step-' addition methods is in a monomeric form both before and after activation. Monomeric MoV1 and Wvl oxospecies are also the most probable products on both freshly exchanged and activated dilute samples. On more concentrated samples spectral modifications occur which can be understood without invoking polymerization effects.

Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

“…In the case of Cr/ SiO 2 , methyl formate formation could be suppressed by reducing the surface concentration of hydroxyls via high-temperature calcination since these sites were required for the adsorption of methanol and its subsequent reaction with Cr-generated formaldehyde to form methylformate. 60 A formaldehyde selectivity of approximately 90% could be obtained with Cr/SiO 2 catalysts that had been precalcined at 700°C. 61 Calcined chromium aluminophosphate molecular sieves (CrAPO-5) are active in the selective oxidation of various secondary alcohols (cyclohexanol, ethylbenzyl alcohol, methylbenzyl alcohol, tetralol, and indanol), using either molecular oxygen or tert-butyl hydroperoxide as oxidant.…”

In SituRaman Spectroscopy of Supported Chromium Oxide Catalysts: 18O2−16O2Isotopic Labeling Studies

“…1 In previous RS studies, supported chromium oxide catalysts were extensively studied under hydrated and dehydrated conditions as a function of the support type. [2][3][4][5][6][7] The characterization studies revealed that under hydrated conditions the molecular structure of the surface chromium oxide species is determined by the iso-electric point of the oxide support. Thus, the monochromate/polychromate ratio increases with the iso-electric point of the support and with decreasing Cr oxide loading.…”

Effect of Phosphorous Additive on the Surface Chromium Oxide Species on Alumina for Propane Oxidation to Propylene

“…( [38] and references within). It is known that the nature of the Cr species that are formed when Cr oxide is deposited on a support depend on various factors such as the nature of the support, the Cr oxide loading, the extent of hydration of the catalyst [36,[41][42][43][44][45][46][47]. In the present study, it is observed that the presence of an additive such as P can also affect the structure and distribution of the Cr species that are present in the supported catalyst…”

“…2e) and 1 T 2 / 1 A 1 (1t 1 ? 2e), respectively [36][37][38][39][40]. The bands at 460 and 580 nm have been assigned to 4 T 2g and 4 T 1g / 4 A 2g transitions, typical of Cr 3?…”