Antimony Oxide-Modified Vanadia-Based CatalystsPhysical Characterization and Catalytic Properties

Abstract

Antimony-modified vanadia-on-titania catalysts were prepared for the selective oxidation of o-xylene to phthalic anhydride by ball milling of powder mixtures followed by calcination. A binary Sb 2 O 3 -V 2 O 5 system was also prepared for comparison purposes. The resulting materials were physically characterized by surface area measurements, X-ray diffraction analysis (XRD), laser Raman spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, electron spin resonance (ESR), magnetic susceptibility determination, and 15 V solidstate NMR. The catalytic performance of the TiO 2 -supported materials was tested for o-xylene oxidation. After calcination of the Sb 2 O 3 -V 2 O 5 binary mixture at 673 K, Sb 3+ is almost quantitatively oxidized to Sb 5+ , while both V 3+ and V 4+ are detected. V 3+ and some V 4+ are most likely located in a nonstoichiometric VSbO 4 -like structure, while the majority of V 4+ preferentially concentrates within shear domains in oxygendeficient V 2 O 5-x particles. In the titania-supported catalyst system, both Sb 2 O 3 and V 2 O 5 spread on the anatase surface. Sb 3+ is oxidized to Sb 5+ , and V 3+ , V 4+ , and V 5+ are detected. VSbO 4 -like structures are not observed. The presence of antimony leads to the formation of presumably V 3+ -O-V 5+ redox couples. The paramagnetic centerssin contrast to the binary mixturesare largely isolated. Antimony preferentially migrates to the surface and appears to exhibit a dual function catalytically. It is inferred from the experimental data that the addition of antimony leads to site isolation and to a reduction of surface acidity. We suggest that V-O-V-O-V domains or clusters are interrupted by incorporation of Sb to form V-O-Sb-O-V species. As a consequence of this site isolation and a reduction of surface acidity, overoxidation of o-xylene is reduced. These two effects are therefore most probably responsible for the improved selectivity of the ternary catalyst system over the binary one toward phthalic anhydride.

Hydrothermal synthesis of antimony oxychloride and oxide nanocrystals: Sb4O5Cl2, Sb8O11Cl2, and Sb2O3

“…4a, in which the lattice space of 0.31 nm corresponds to that of the (002) plane. In the case of Sb 8 O 11 Cl 2 obtained at pH [4][5]its TEM images (Figs. 4c and d) show that the sample consists of nanobelts (major) and nanowires (minor) with the lengths up to several micrometers.…”

“…Senarmontite has long been used as an additive to enhance the flame retardancy of polymer resins, whereas valentinite has not due to its undesirable oxidization when exposed to air or sunlight [4]. Senarmontite was shown to act as a catalyst in combination with vanadium for the selective oxidation of o-xylene [5]. Valentinite is a major component of the Sb 2 O 3 -B 2 O 3 binary glasses possessing nonlinear optical properties [6].…”

Redox Isotherms for Vanadia Supported on Zirconia

“…Vanadia-based catalysts are used for a number of partial oxidation reactions including the oxidation of methanol to formaldehyde [1][2][3][4], the oxidation of o-xylene to phthalic anhydride [5,6], and the oxidative dehydrogenation (ODH) of propane [7][8][9] and butane [10,11] to produce alkenes. An important aspect of these catalysts is that the active form generally consists of highly dispersed vanadia supported on a second high-surface-area oxide such as TiO 2 , ZrO 2 , or Al 2 O 3 [12].…”

Propane Oxidative Dehydrogenation on V–Sb/ZrO2 Catalysts

“…It is well known that tetrahedral V is the active species but its environment remains controversial. The relevance of site isolation to make the system selective is apparently a key element [17,18]. Alkene selectivity would be linked to isolated VO 4 tetrahedra [6,7,[19][20][21] but others point to pyrovanadate structures [11,22].…”