Phosphotungstate anions supported on spherical beads of carbon as highly efficient catalysts for the dehydration of propan-2-ol to propene

Abstract

There is a continuing need to develop new catalysts for the dehydration of propan-2-ol as opposed to di- iso-propyl ether. The reaction has been extensively studied using zeolites [1] or clays [2] with typical selectivities for propene in the region of 20–40%. The reaction has been used in order to monitor the catalytic behaviour of solids and activity correlates in many cases with the acidity of the solid [3–5]. Phosphotungstates supported on carbons, zirconias or silicas having been previously studied for the dehydration of propan-2-ol [6]. Uniform colloidal particles of salts of tungstophosphoric acids have been prepared by Matijevic and Perez-Maqueda [7], but in all cases, the product is present as a powder. In many cases, the above materials are extremely brittle and deteriorate rapidly when used as catalysts. As a contribution to the preparation of acidic/basic or redox catalysts in a bead form a versatile method has been developed for the support of porous oxides in pyrolysed ion-exchange beads. In previous cases, attempts have been made to remove the carbon matrix but this does not appear to be necessary. A conventional anion-exchange was used in this study, the strongly basic Amberlite IRA-93 (Cl) loaded with tungsten from an aqueous solution of sodium tungstate. After washing with water, converting to either tungstate or phosphotungstate and again washing with water the product, after pyrolysis of the metal-loaded ion-exchange resin, consists of discrete (typically 0.2–0.5 mm diameter) spherical particles of catalyst-loaded carbon, the spherical integrity of the unpyrolysed anion loaded resin being maintained. The tungstate was found to convert up to 80% propan-2-ol to propene and better than 95% conversion if phosphotungstate was used.