Synthesis and Characterization of Mesoporous Ta−W Oxides as Strong Solid Acid Catalysts

Abstract

Several mesoporous Ta x W10−x mixed oxides prepared from TaCl5 and WCl6 in the presence of poly block copolymer surfactant Pluronic P-123 were examined as potential solid acid catalysts. Amorphous wormhole-type mesopores were observed in samples with x values from 3 to 10, whereas W-rich samples (x = 0−2) formed nonmesoporous structures with crystallized tungsten oxide (WO3). The acid strength increased with addition of W for mesoporous Ta x W10−x oxides, and mesoporous Ta3W7 oxide exhibited the highest acid catalytic activity for the Friedel−Crafts alkylation of anisole and the hydrolysis of disaccharides. The results are compared with those of nonporous Ta2O5−WO3, HTaWO6 nanosheets, which were a solid acid obtained by exfoliation and aggregation of layered HTaWO6 with strong Brønsted acid sites in the interlayer, and a range of conventional solid acid catalysts. Mesoporous Ta−W oxides exhibited a turnover rate higher than that of nonporous Ta2O5−WO3 and HTaWO6 nanosheets, indicating that the mesoporous structure is an advantageous environment for the strong acid sites, because of the high surface area and easy reactant accessibility.

Esterification of fatty acids from waste cooking oil to biodiesel over a sulfonated resin/PVA composite

“…Interestingly, the TOF number of the s-CER/PVA composite (s-CER: PVA=3: 2) was approximately 3.3 and 2.6 times greater than that of s-CER and sulfuric acid, respectively, indicating the higher intrinsic catalytic activity of the s-CER/PVA composite. 44,45 As pointed out earlier, the highly hydrophilic -OH sites in PVA can facilitate the absorption of H 2 O in the reaction mixture by the PVA dominated region and thus liberate the -SO 3 H sites that would otherwise be blocked by H 2 O molecules in s-CER or SO 4 indicates that a greater number of -SO 3 H were utilized in s-CER/PVA for esterification due to water absorption by PVA. The composites with s-CER: PVA mass ratio of 3: 2 had the highest TOF number among all the s-CER/PVA, suggesting that the PVA content had little effect on the intrinsic catalytic activity after -OH content reached a critical value (PVA mass ratio of 40.0 %).…”

Mesoporous Ti–W oxide: synthesis, characterization, and performance in selective hydrogenolysis of glycerol

“…Nevertheless, the sol-gel strategy, directly incorporating tungsten species into metal oxide composites, is supposed to afford a homogenous distribution of tungsten oxide, as well as a high stability for anti-aggregation. [18][19][20][21][22] Mesoporous TiO 2 is widely studied due to the variety of its potential applications. 23 It was reported that the crystallization temperature of TiO 2 was much lower than that of tungsten oxide, 24 and the solid solution of TiO 2 and WO 3 was formed over 700 C.…”

Mechanistic Studies of Solid Acids and Base‐Catalyzed Clean Technologies

“…Mesoporous Nb-W and Ta-W mixed oxides were found to exhibit remarkable acid catalytic activity for Friedel-Crafts alkylation and the hydrolysis of sugars and esterification, surpassing conventional solid acids owing to their high surface area, mesoporous structure, and strong Brønsted acid sites (−12 ≤ H 0 < −6.6) [61,62]. In addition, mesoporous Nb-W and Ta-W oxides have the significant advantages of recyclability and thermal stability.…”

“…Water-tolerant solid acids, such as layered HNbMoO 6 [55,151], HTaMoO 6 [54], mesoporous Nb-W oxides [61], and Ta-W oxides [62], showed high activity for cellobiose hydrolysis, a unit of cellulose. The high performance of layered oxides is attributed to facile intercalation of cellobiose into the interlayer gallery containing strong Brønsted acid sites.…”