Selective methanol conversion to methylal on Re-Sb-O crystalline catalysts: catalytic properties and structural behavior

Abstract

Three crystalline compounds, SbOReO4·2H2O, Sb4Re2O13 and SbRe2O6, and several supported Re catalysts were employed as catalysts for the selective oxidation of methanol to methylal (3CH3OH+1/2O2 → CH2(OCH3)2+2H2O). A high selectivity of 92.5% to methylal at a conversion of 6.5% under conditions of GHSV = 10000 mL h-1g-1-cat and 573 K was obtained on the new SbRe2O6 catalyst, while no significant formation of methylal was observed with the other two catalysts. No structural change in the bulk and surface of SbRe2O6 and Sb4Re2O13 occurred after methanol oxidation below 593 K, but SbOReO4·2H2O was transformed to Sb4Re2O13, as characterized by XRD, Raman spectroscopy, XPS and SEM. The high performance of SbRe2O6 for the selective methylal synthesis was ascribed to Re oxide species stabilized by a specific connection with Sb oxides at the crystal surface.