Structural Characteristics and Catalytic Properties of Highly Dispersed ZrO₂/SiO₂ and V₂O₅/ZrO₂/SiO₂ Catalysts

Abstract

Highly dispersed ZrO2/SiO2 and V2O5/ZrO2/SiO2 catalysts were successfully synthesized by the incipient wetness impregnation method. The surface structures of these catalysts in hydrated and dehydrated states were characterized by in situ Raman and UV−vis−near-infrared diffuse reflectance spectroscopies. Temperature-programmed reduction and methanol oxidation were employed as chemical probe reactions to examine the reducibility and reactivity/selectivity properties of these catalysts. These characterization techniques demonstrate that both zirconium oxide and vanadium oxide species are highly dispersed as two-dimensional metal oxide overlayers on the silica support. The spectroscopic results revealed that the surface vanadium oxide species on the highly dispersed ZrO2/SiO2 supports are predominantly isolated VO4 units [OV(O−support)3] in the dehydrated state and become polymerized vanadium oxide species upon hydration. The surface vanadium oxide species preferentially interact with the zirconium oxide species on the silica surface. The substitution of SiIV−O- by ZrIV−O- ligands significantly affects the chemical properties of the isolated VO4 units: the reducibility of the surface vanadium oxide species increases, and the methanol oxidation turnover frequency (TOF) increases by 1−2 orders of magnitude relative to V2O5/SiO2. The present study demonstrates that the support effect, variation in the reactivity of supported metal oxide catalysts due to different oxide supports, essentially originates from the difference in oxygenated ligands around the active metal cations.

n-Butane Isomerization Catalyzed by Sulfated Zirconia Nanocrystals Supported on Silica or γ-Alumina

“…The broad absorption cannot be attributed to a shift of the band gap as an effect of zirconia particle size, because these spectra are very similar to the spectra of the uncalcined samples (not shown), which do not contain zirconia. Spectra of finely dispersed zirconia on silica [25,32] do not exhibit contributions at wavelengths higher than 250-300 nm, suggesting that the sulfate in our samples may be part of the species causing the absorption towards longer wavelengths. On the other hand, a broad shoulder extending towards 360 nm in the spectrum of ZrO 2 has been explained by defects and non-stoichiometry [28].…”

“…Zirconia can be dispersed on or interspersed with silica by sol-gel methods using binary solutions [47,54] or it can be dispersed on the extremely large surface area of MCM-41 [50,67,69] by liquid deposition. It may be well dispersed on silica when an alkoxide is used as precursor [30,32] but poorly dispersed when nitrate is used [30]. For both supports, silica and alumina, the dispersion may even be dependent on the solvent used during deposition [26].…”

“…The literature reports on zirconia-alumina [19,20] and zirconia-silica [21][22][23][24][25] mixed oxides in various compositions, and zirconia has been dispersed on alumina [26][27][28][29] and on silica [26,27,[30][31][32][33]. Zirconium has been embedded in the walls of MCM-41 [34][35][36][37] and SBA-15 [38].…”

Design, Synthesis, and Mechanistic Evaluation of Iron-Based Catalysis for Synthesis Gas Conversion to Fuels and Chemicals

“…Also the intensities of silanol groups decreased with increasing Zr density on ZrO 2 /SiO 2 surfaces (Table 1). Figure 4.2 shows that the Raman spectra of ZrO 2 /SiO 2 samples contains a sharp band at 477 cm -1 , attributed to three-dimensional amorphous zirconia [37][38][39][40]. These results show that these impregnation methods can terminate some of the hydroxyl groups on the SiO 2 surface and that they give a high dispersion of ZrO 2 for samples up to 20 wt.% ZrO 2 loading, for which ZrO 2 crystallites are not detected in their Raman spectra.…”

On the applicability of SiO2/Al2O3/Nb2O5and SiO2/Al2O3/TiO2as a biocompatible platform for chloroperoxidase

“…By means of EDFRX, the initial amounts of the precursors used in the synthetic routes should yield materials with 20 SiAlTi. These values are similar to those reported in literature for mixed oxides obtained using sol-gel processes.…”