A crystalline SbRe2O6 catalyst active for selective ammoxidation of isobutylene and propene

This paper reports the first performance of a crystalline SbRe2O6 catalyst, which is a new family of Re mixed oxide, for the selective ammoxidation reactions of isobutylene to methacrylonitrile and propene to acrylonitrile. The SbRe2O6 with alternate (Re2O6)3– and (SbO)+ layers showed much better performance than two other known Re–Sb–O compounds SbOReO4sdot2H2O and Sb4Re2O13 with tetrahedral (ReO4)– anions and cationic (SbO)+ layers. The SbRe2O6 catalyst was also much more active than a coprecipitated SbRe2Ox catalyst, a supported Re2O7/Sb2O3 catalyst, and Re oxides such as Re2O7, ReO3 and ReO2 for the selective ammoxidation. Rhenium is prerequisite to the ammoxidation catalysis of the Re–Sb mixed oxides. Sb oxides such as Sb2O3 and Sb2O4 were inactive, but Sb in the SbRe2O6 catalyst contributes positively to the methacrylonitrile and acrylonitrile syntheses. Neither change nor modification of the surface composition, crystallinity and morphology of SbRe2O6 occurred under the ammoxidation reaction conditions, where the presence of NH3 stabilized the crystalline SbRe2O6 structure

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

Selective synthesis of methylal from methanol on a new crystalline SbRe2O6 catalyst

A novel SbRe2O6 catalyst was active for the selective methanol oxidation to methylal (CH2(OCH3)(2)). Other known Sb-Re oxides, Sb4Re2O13 and SbOReO4. 2H(2)O produced almost no methylal. The bulk and surface of the SbRe2O6 catalyst was characterized by XRD, Raman, XPS and SEM. The high performance of SbRe2O6 may be attributed to the Re-oxide octahedra connecting with Sb-O chains

Characterization of carbon- and alumina-supported NiW and CoW sulfided catalysts

Sulfided NiW and CoW catalysts supported on activated carbon and alumina were characterized with 57Co Mössbauer emission spectroscopy (MES) and EXAFS at the W–LIII edge. NiW catalysts were studied with MES by probing the Ni atoms with 57Co. MES results demonstrate that the Ni–W–S phase is present in sulfided NiW catalysts. Formation of Co9S8-type phases could be related to the lower thiophene HDS activity of CoW catalysts. W EXAFS showed that addition of Co or Ni to a W/Al2O3 catalyst results in a higher W sulfidation degree. No structural differences were found for carbon- and alumina-supported catalysts, in spite of the two times larger thiophene HDS activity of carbon-supported NiW