Interaction of hydrogen chloride with a molybdena–silica catalyst

Abstract

The interaction of HCl with a molybdena–silica catalyst has been investigated using e.p.r. and infrared spectroscopy. Exposure of reduced catalysts to HCl at room temperature causes a large (up to 20-fold) increase in the amount of Mo^V detected by e.p.r. which is reversed on subsequent outgassing. The accompanying changes in g- and the ⁹⁵Mo hyperfine-tensor components indicate that chloride ions replace oxide ions in the coordination sphere of Mo^V, and the increase in Mo^V spin concentration is attributed to substitution of bridging oxide ligands between magnetically coupled Mo^V ions. Oxidized catalysts are reduced by exposure to HCl. The reaction of HCl with molybdena–silica is compared with that previously reported with molybdena–alumina catalysts.