THE CATALYTIC ACTIVITY OF NATURAL CAVANSITE (CA(VO)SI4O10∙4H2O)

Cavansite is an uncommon, unique phyllosilicate mineral with a vanadyl-silicate framework containing multi-directional pore channels occupied by calcium ions and partially exchangeable water molecules. Cavansite is of particular interest because its vanadium content and porous structure make it a potential candidate for catalytic applications. In this investigation, natural cavansite was evaluated for its ability to act as a volatile organic compound (VOC) catalyst in the oxidation of ethanol (CH₃CH₂OH + 3O₂ --> 2CO₂ + 3H₂O). Ethanol was used because it is a model compound; its oxidation reaction is simple and well-understood. If a material catalyzes ethanol, then it shows potential for more complex VOCs. The oxidation reaction was attempted via the direction of ethanol vapor into a stainless steel tube reactor laden with cavansite and housed in a furnace. The reactor effluent was collected at 150 °C, 200 °C, and 250 °C and analyzed via gas chromatography with flame ionization detection (GC/FID). Scanning electron microscopy (SEM) micrographs and powder X-ray diffraction (XRD) patterns were taken of each sample before and after the reaction to observe if textures, mineral phases, and crystallinity were altered. Preliminary results from one sample of cavansite from Maharashtra, India suggest that the material is not an active catalyst, owing to several potential factors including: (1) poor oxygen mobility in the crystal structure; (2) the nature of the average oxidation states of vanadium; (3) limited ethanol accessibility into the pore spaces of cavansite; (4) the presence of minor amounts of other mineral phases in the bulk; (5) poor thermal stability; and (6) the sequential volatilization of exchangeable water molecules beginning at approximately 200 °C. This result is counter to assertions in the literature that cavansite might be an effective catalyst.