Performance and characterization of a new crystalline SbRe2O6 catalyst for selective oxidation of methanol to methylal

Three well-defined compounds, SbRe2O6, Sb4Re2O13, and SbOReO4 . 2H(2)O, and several supported Re catalysts were employed as catalysts for the selective oxidation of methanol to methylal (3CH(3)OH + 1/2O(2) --> CH2(OCH3)(2) + 2H(2)O). High selectivity of 92.5% to methylal was obtained on the new crystalline catalyst SbRe2O6 at 573 K, while no methylal formation or negligible activity was observed with the other catalysts. No structural change in the bulk and surface of the SbRe2O6 catalyst occurred after the methanol oxidation below 600 K as characterized by XRD, Raman, XPS, and SEM. The reaction rate increased with increasing methanol partial pressure, while the selectivity to methylal was independent of methanol partial pressure as well as O-2 partial pressure (<10 mol%). There existed two types of active lattice oxygen species in TPD experiments on SbRe2O6, both being responsible for the methylal formation. The high performance of SbRe2O6 for the selective synthesis of methylal from methanol may be ascribed to the Re-oxide species stabilized by the specific connection with Sb oxides at the crystal surface. (C) 2000 Academic Press.