Unique Performance and Characterization of a Crystalline SbRe₂O₆Catalyst for Selective Ammoxidation of Isobutane

Abstract

The catalytic performances of a new family of crystalline Re-Sb-O compounds SbRe 2 O 6 , SbOReO 4 ‚2H 2 O and Sb 4 Re 2 O 13 in selective ammoxidation of isobutane (i-C 4 H 10 ) to methacrylonitrile (MAN) have been studied and compared with those of a mechanical mixture of Sb 2 O 3 + Re 2 O 7 , coprecipitated SbRe 2 O x , Sb 2 O 3 -supported Re 2 O 7 , bulk Re oxides, and Sb oxides. SbRe 2 O 6 efficiently catalyzed the i-C 4 H 10 ammoxidation to MAN at 673 K with the good selectivity to MAN (44.9%) and to the sum of MAN + i-C 4 H 8 (84.3%) at a steady-state conversion of 4.4%, while significantly no MAN activity was observed on the other catalysts. No structural change in the bulk and surface of SbRe 2 O 6 after the i-C 4 H 10 ammoxidation was observed by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and in situ confocal laser Raman microscopic spectroscopy (LRM). The good performance of SbRe 2 O 6 may be ascribed to its specific crystal structure composed of alternate octahedral (Re 2 O 6 ) 3and (SbO) + layers. It was found that the presence of NH 3 was prerequisite to the C-H bond breaking of i-C 4 H 10 , and the oxidation/ dehydrogenation of i-C 4 H 10 never proceeded in the absence of NH 3 . The presence of NH 3 was also prerequisite to maintain the crystal structure of SbRe 2 O 6 under the reaction conditions. Fourier transformed infrared (FT-IR) spectra showed that NH x species irreversibly adsorbed on the SbRe 2 O 6 catalyst. The i-C 4 H 10 ammoxidation proceeded on SbRe 2 O 6 by a redox mechanism, in which the oxidative dehydrogenation of i-C 4 H 10 to i-C 4 H 8 was the rate-determining step. Increasing reaction temperature and decreasing GHSV did not give rise to increase in the formation of byproducts CO 2 and acetonitrile. Thus the crystalline SbRe 2 O 6 compound may be regarded to be a new promising catalyst for the ammoxidation of light alkanes.

Studies on the SbOx species of SbOx/SiO2 catalysts for methane-selective oxidation to formaldehyde

“…Antimony has been widely used as a key component in many selective oxidation catalysts, including V-Sb-O [1][2][3][4][5], MoSb-O [6,7], Fe-Sb-O [8,9], Sn-Sb-O [10,11], V-Sb-Ni-O [12], Re-Sb-O [13]. Excess antimony of antimony-containing mixed oxide catalysts has been found to be a clue to high selectivity to partially oxidized products [14].…”

Reversible Structure Transformation of Antimony Oxides on SiO2Relevant to Selective Catalytic Oxidation of Ethanol

“…Antimony is widely used as a key element in mixed oxide catalysts for selective oxidation of hydrocarbons, such as Fe−Sb−O, − Sn−Sb−O, − V−Sb−O, ,− Mo−Sb−O, − and Re−Sb−O. − Many studies on the mixed oxides except for Re−Sb−O have demonstrated that excess antimony at surfaces is a clue to high selectivity to partially oxidized products. Allen and Bowker investigated propene oxidation on FeSbO 4 catalysts and reported that the catalyst surfaces were covered by antimony rich thin layers under the selective oxidation conditions .…”

High‐pressure Raman investigation of the semiconductor antimony oxide

“…1 Introduction Antimony trioxide (Sb 2 O 3 ) is a transparent material with an indirect band gap of 3.3 eV and has been widely used in fields of catalysis, fire retardants, glasses, sensors, as anode material for the Li-ion batteries, and retardants for rubber, ceramics, enamels, fabrics, and fiber products [1][2][3][4][5][6][7]. Moreover, the Sb 2 O 3 thin film behaves as an n-type semiconductor [8], which invites its photovoltaic applications.…”