Arrangement Models of Keggin-Al30 and Keggin-Al13 in the Interlayer of Montmorillonite and the Impacts of Pillaring on Surface Acidity: A Comparative Study on Catalytic Oxidation of Toluene

Acid-base reactivity is a key factor for understanding the interfacial geochemistry of clay minerals. Numerous studies showed the significant role of surface acidity of clay minerals in the geological processes and environmentally related applications. In this work, montmorillonite (Mt) was pillared by polycations of Keggin-Al₁₃ and Keggin-Al₃₀. Arrangement models of Keggin-Al₁₃ and Keggin-Al₃₀ in the interlayer region of Mt were put forward based on the chemical composition analysis, the structural formula calculation of Mt, and the results of powder X-ray diffraction. Ammonia temperature-programmed desorption and diffuse reflectance Fourier transform infrared methods were applied to explore the impacts of pillaring by polycations (Keggin-Al₁₃ and Keggin-Al₃₀) on the surface acidic characteristics of Mt. Results demonstrated that one Keggin-Al₃₀ polycation can affect an area of 9.5 unit cells (from two layers, with 4.7-4.8 unit cells in each layer) in Mt, whereas a Keggin-Al₁₃ polycation controls an area of 7.1 unit cells (from two layers, with 3.5-3.6 unit cells in each layer). Pillaring by polycations could lead to a lot of surface acid sites (1.33 mmol NH₃/g) on Mt with the main type of Bronsted acid sites. The increase of surface acid sites on both Keggin-Al₁₃-pillared Mt (Al₁₃-PILM) and Keggin-Al₃₀-pillared Mt (Al₃₀-PILM) is attributed to the high positive charge and high content of aluminum per unit of polycation, which affects the formation of Bronsted acid sites and structural changes of Mt layers. Catalytic oxidation of toluene provided evidence for the high catalytic activity of Al₃₀-PILM under much lower temperature at 78 °C compared with that of Al₁₃-PILM and Mt at 207 and 285 °C, respectively. The basic finding in this study not only reveals the possible sources of abundant micropores and mesopores in the micro/mesoporous materials of Al₁₃-PILM and Al₃₀-PILM but also provides a reasonable mechanism for the formation of abundant Bronsted surface acid sites on these two types of pillared materials. The novel Al₃₀-PILM with an excellent micro/mesoporous structure and extremely high thermal stability also exhibits a potential ability in the application of heterogeneous acid catalysis.

Hydroxyalkylation of phenol to bisphenol F over heteropolyacid catalysts: The effect of catalyst acid strength on isomer distribution and kinetics

Hydroxyalkylation of phenol with formaldehyde to bisphenol F over heteropolyacid impregnated on clay was investigated. These catalysts displayed excellent catalytic performance for this reaction, especially that the effects of acid sites on the isomer distribution are obvious. Various solid catalysts were prepared by impregnating heteropolyacid on different kind of clay matrices, and their chemical compositions, textural properties, and acid strength of the heteropolyacid catalysts were characterized by EDX, BET, NH3-TPD, XRD, and FT-IR. Moreover, the effects of acid sites and reaction temperature on the yield and 4,4'-isomer distribution were launched by comparing the data obtained from the two kinds of catalysts. Furthermore, the kinetics of the hydroxyalkylation of phenol to BPF was established.

Mesoporous Al-incorporated silica-pillared clay interlayer materials for catalytic hydroxyalkylation of phenol to bisphenol F

Mesoporous Al-incorporated silica-pillared clay interlayer materials for catalytic hydroxyalkylation of phenol to bisphenol F.