Oxidative dehydrogenation of n-butane to butadiene catalyzed by new mesoporous mixed oxides NiO-(beta-Bi2O3)-Bi2SiO5/SBA-15 system

Designed Nanoarchitectures of a BiOBr/BiOI Nanosheet Heterojunction Anchored on Dendritic Fibrous Nanosilica as Visible-Light Responsive Photocatalysts

Heterojunctions, particularly those involving BiOBr/BiOI, have attracted significant attention in the field of photocatalysis due to their remarkable properties. In this study, a unique architecture of BiOBr/BiOI was designed to facilitate the rapid transfer of electrons and holes, effectively mitigating the recombination of electron-hole pairs. Accordingly, the BiOBr/BiOI nanosheet heterojunction was anchored on dendritic fibrous nanosilica (DFNS) by the immobilization of Bi2O3 nanodots in DFNS and the subsequent reaction with HBr and then HI vapors at room temperature. The 4 nm-Bi2O3 nanodots acted as a sacrificial template to form BiOX nanosheets by reaction with HX vapors (X = Br, I). The BiOBr/BiOI nanosheet heterojunction with the lateral size remained in the range of 90 to 110 nm and a thickness of 15 nm formed on DFNS, where the BiOBr:BiOI ratio in the product was controlled by the exposure time to HX vapors. The reaction sequence (HBr → HI vapors) was a key for the formation of BiOBr/BiOI nanosheet heterojunction with controlled composition. When the reaction of Bi2O3 nanodots with HI vapor was performed in the reverse sequence (HI→ HBr), the substitution of I- with Br- occurred to form BiOBr sheets on DFNS. The BiOBr/BiOI nanosheet heterojunction anchored on DFNS was used as a visible-light-driven photocatalyst for the decomposition of benzene in water under solar light, and its activity was superior to that of single BiOX nanosheets on DFNS.

Structure, Acidity, and Redox Aspects of VOx/ZrO2/SiO2 Catalysts for the n-Butane Oxidative Dehydrogenation

ZrOx/SiO2 and VOx/ZrOx/SiO2 catalysts (5 wt %–25 wt % Zr, 4 wt % V) were prepared by grafting zirconium and vanadium alkoxides on Aerosil 380. All samples were characterized by temperature programmed reduction, N2 physisorption, X-ray diffraction, Raman spectroscopy, and ammonia adsorption microcalorimetry. Tetragonal ZrO2 and zircon (ZrSiO4) were present at 25 wt % Zr, but only amorphous zirconia overlayer existed for lower loadings. At lower Zr loadings (5 wt %–10 wt % Zr), exposed silica surface leads to V2O5 crystallites and isolated VO4 species, although V reducibility behavior changes, from being similar to VOx/SiO2 (5 wt % Zr) to showing VOx/ZrO2 behavior at 10 wt % Zr, and a diminished total amount of reducible V. Highly acidic ZrO2 sites are covered by the vanadium grafting, forming weaker sites (60–100 kJ/mol NH3 adsorption strength). Catalytic conversion and selectivity for the oxidative dehydrogenation of n-butane (673 K, n-C4/O2 = 2.2) over VOx/ZrOx/SiO2 show that 1,3-butadiene is favored over cis-2-butene and trans-2-butene, although there is some selectivity to the 2-butenes when VOx/ZrO2 behavior is evident. At low Zr loadings, butadiene formed during reaction acts as the diene species in a Diels–Alder reaction and gives rise to a cyclic compound that undergoes further dehydrogenation to produce benzaldehyde.