Influence of the Al source and synthesis of ordered Al-SBA-15 hexagonal particles with nanostairs and terraces

Impact of heteroatom addition into mesoporous silica for water adsorption in the low partial pressure range

Mesoporous silicas are known to be high-performing water adsorbents in high humidity levels due to their large pore volumes. However, for low humidity conditions, these materials typically present a less expressive performance, which is a drawback for many applications. In the present report, mesoporous silica SBA-15 was functionalized with Al, Ti, Zr and Li in order to improve their performance in this condition. The influence of functionalization in porosity, morphology and acidic sites was investigated. Samples with an increased number of acidic sites and with higher microporosity when compared to pure silica were produced. This was responsible for their enhanced performance for water adsorption in low moisture conditions. Sample functionalized with zirconium in SBA-15 synthesis improved the water adsorption capacity of pure silica by three times, reaching up to 127 g kg⁻¹ at a relative pressure of 0.2 and 570 g kg⁻¹ close to saturation pressure. This sample was found to be a promising material to be applied in processes which require high adsorption capacities in both low and high water partial pressure ranges. Moreover, the understanding of the mechanisms behind the heteroatom functionalization can be applied to any silica material in order to enhance its attractiveness towards any polar molecule.

Acid-Mediated Synthesis of Ordered Mesoporous Aluminosilicates: The Challenge and the Promise

A new intrinsic hydrolysis method was employed, for the first-time, to synthesize well-ordered H-AlSBA-15 with trivalent aluminium exclusively in the tetrahedral framework structure of SBA-15. Unlike other methods, which involve incorporation of aluminium ions in both the framework (Brønsted) and non-framework (Lewis) sites of the silicate matrix, the intrinsic hydrolysis method isomorphously substitutes aluminium ions in the tetrahedral network even at high aluminium content. This unique approach relies mainly on the hydrolysis rates of the inorganic (silicon and aluminium) precursors used for the preparation in such a way that the condensation occurs simultaneously so as to overcome the usually encountered difficulties in stabilizing aluminium ions in the silicate matrix. In this way, we could successfully synthesize high quality Brønsted acidic H-AlSBA-15, hitherto not reported. The synthesized materials were systematically characterized by various analytical, spectroscopic, and imaging techniques, including XRD, Brunauer-Emmett-Teller (BET) surface area measurements, TEM, SEM, ²⁹ Si and ²⁷ Al magic angle spinning NMR spectroscopy, X-ray fluorescence (XRF), and NH₃ temperature-programmed desorption (TPD). The characterization results reveal the presence of a highly porous structure (with narrow pores) and tetrahedrally coordinated trivalent aluminium in the silicate matrix with more medium to strong Brønsted acid sites. The resulting high quality catalysts exhibit excellent activity for tert-butylation of phenol with high selectivity towards para-tert-butyl phenol and 2,4-di-tert-butyl phenol.

Designing ordered mesoporous aluminosilicates under acidic conditions via an intrinsic hydrolysis method

A novel intrinsic hydrolysis method was employed for the synthesis of well-ordered mesoporous aluminosilicates, viz., H-AlSBA-15 and H-AlIITM-56, with trivalent aluminium, exclusively, in a tetrahedral framework structure.

CuO nanoparticles encapsulated inside Al-MCM-41 mesoporous materials via direct synthetic route

Highly ordered aluminum-containing mesoporous silica (Al-MCM-41) was prepared using attapulgite clay mineral as a Si and Al source. Mesoporous complexes embedded with CuO nanoparticles were subsequently prepared using various copper sources and different copper loadings in a direct synthetic route. The resulting CuO/Al-MCM-41 composite possessed p6mm hexagonally symmetry, well-developed mesoporosity, and relatively high BET surface area. In comparison to pure silica, these mesoporous materials embedded with CuO nanoparticles exhibited smaller pore diameter, thicker pore wall, and enhanced thermal stability. Long-range order in the aforementioned samples was observed for copper weight percentages as high as 30%. Furthermore, a significant blue shift of the absorption edge for the samples was observed when compared with that of bulk CuO. H₂-TPR measurements showed that the direct-synthesized CuO/Al-MCM-41 exhibited remarkable redox properties compared to the post-synthesized samples, and most of the CuO nanoparticles were encapsulated within the mesoporous structures. The possible interaction between CuO and Al-MCM-41 was also investigated.

Well-organized zeolite nanocrystal aggregates with interconnected hierarchically micro-meso-macropore systems showing enhanced catalytic performance

Preparation and characterization of well-organized zeolitic nanocrystal aggregates with an interconnected hierarchically micro-meso-macro porous system are described. Amorphous nanoparticles in bimodal aluminosilicates were directly transformed into highly crystalline nanosized zeolites, as well as acting as scaffold template. All pores on three length scales incorporated in one solid body are interconnected with each other. These zeolitic nanocrystal aggregates with hierarchically micro-meso-macroporous structure were thoroughly characterized. TEM images and (29)Si NMR spectra showed that the amorphous phase of the initial material had been completely replaced by nanocrystals to give a micro-meso-macroporous crystalline zeolitic structure. Catalytic testing demonstrated their superiority due to the highly active sites and the presence of interconnected micro-meso-macroporosity in the cracking of bulky 1,3,5-triisopropylbenzene (TIPB) compared to traditional zeolite catalysts. This synthesis strategy was extended to prepare various zeolitic nanocrystal aggregates (ZSM-5, Beta, TS-1, etc.) with well-organized hierarchical micro-meso-macroporous structures.