Influence of Aluminum Addition in the Framework of MCM-41 Mesoporous Molecular Sieve Synthesized by Non-Hydrothermal Method in an Alkali-Free System

Abstract

Purely siliceous MCM-41 and Al-containing MCM-41 (Al-MCM-41) mesoporous materials were synthesized by non-hydrothermal method in alkali-free ions medium at room temperature and short reaction times. Under these synthesis conditions, it was also investigated the influence of Al incorporation in the crystal structure of MCM-41. The solids were characterized by ICP-OES, AAS, N 2 adsorption at 77 K, XRD, TEM, NH 3 -TPD, 27 Al and 29 Si-MAS-NMR, FT-IR and TGA. The resulting mesoporous materials showed a well-defined hexagonally ordered pore geometry maintaining a uniform and unimodal pore size distribution with high specific surface areas (1000-1400 m 2 g -1 ). The Al +3 ions were introduced successfully in the structure of the purely siliceous MCM-41 expanding the unit cell parameter and forming four-coordinated Al species, and in a less extent, forming six-coordinated Al species. In addition, the surface acidity of the MCM-41 increased with Al loading. Contrary, the presence of Al in the MCM-41 mesoporous structure resulted in a decrease of the crystallinity and specific surface area possibly due to the presence of Al species in highly distorted tetrahedral structures and Al extra-framework or amorphous alumina occluded in the pores. The MCM-41 type mesoporous materials obtained in this work show similar characteristics of those synthesized by conventional hydrothermal methods.

Proton Transport in Aluminum-Substituted Mesoporous Silica Channel-Embedded High-Temperature Anhydrous Proton-Exchange Membrane Fuel Cells

“…The symmetrical and stretching vibration peaks of C − H appeared at 710 and 810 cm −1 , respectively. Notably, the absorption peak for Si−O − Al at 800 cm −1 was observed as a result of the grafting of Al onto mesoporous silica, in accordance with a previous report of Al surface sites grafted onto silica 38,39 . The XRD pattern of Al grafted onto MCM-41 exhibited crystalline peaks corresponding to the (100), (110), (200), and (210) planes (in the narrow-angle profile) ( Fig.…”

Synthesis and characterization of mesoporous materials with SBA and MCM structure types

“…The thermogravimetric analyses showed three mass loss events as a function of temperature increase. From room temperature to 132 °C range, the mass loss was 2% (M6) and 0.7% (M7), and was associated with the desorption of water from the external surface and removal of the occluded water in the mesopores; from 132 to 326 °C, the mass loss was 25% (M6) and 32% (M7), which was related to the oxidative decomposition and removal of the organic species (surfactant and precursors); above 326 °C the mass loss was 7% (M6) and 13% (M7), attributed to the decomposition of the remnants of the organic compounds, as well as related to water loss due to the condensation of adjacent silanol groups (Si-OH) to form siloxane bonds or the elimination of residual ethoxy groups due to hydrolysis of TEOS (in the case of the M7 sample) [29]. The DTG curves of both samples showed similar profiles in relation to the position of the peaks with temperature.…”

MCM-41-supported vanadium catalysts structurally modified with Al or Zr for thiophene hydrodesulfurization

“…It can be also seen a shift of (100)-reflection towards lower 2θ values for the Al-modified supports, indicating an expansion of the structure, confirmed by the increment of pore wall thickness, lattice parameter and interplanar distance, as it can be seen in Table 2. Several authors have reported that the increased wall thickness is a strong evidence of metal incorporation into the MCM-41 framework [17,18,24]. On the contrary, Zr-containing materials showed a different behavior; the (100)-reflection was shifted to higher 2θ values with increasing Zr content.…”