Effect of Sulfate Modification on Structure Properties, Surface Acidity, and Transesterification Catalytic Performance of Titanium-Submitted Mesoporous Molecular Sieve

Abstract

A series of sulfated titanium-submitted mesoporous molecular sieves denoted as S/Ti-MCM-41 were prepared by wet impregnation method with H 2 SO 4 solution as promoter. The results of XRD, N 2 adsorption−desorption, NH 3 -TPD, FTIR of pyridine adsorption, and XPS analysis indicated that S/Ti-MCM-41 samples possess well-ordered hexagonal mesostructure, although the pore diameter and specific surface area shrunk with the increasing coverage of sulfur species. As a result of the electron inductive effect from the SO bond of SO 4 2− , Lewis acidity is intensified significantly and new Bronsted acid sites are generated from the activated hydroxyl groups. Bronsted acid sites are medium strength, while part of the Lewis acid sites are of weak strength and part of them are medium. The S/Ti-MCM-41 catalysts exhibited desirable activity for transesterification of dimethyl oxalate and phenol. INTRODUCTIONThe M41S family of mesoporous molecular sieves has attracted extensive attention of many researchers since their discovery in 1990s. 1,2 On behalf of these materials, MCM-41 is an important class of a hexagonally arranged cylindrical pores with a large surface area, regular pore diameters, and high thermal stability. Thus, these properties make MCM-41 material suitable for many catalytic applications, such as isomerization, 3,4 selective oxidation, 5−7 photocatalysis, 8−10 and so forth. As reported, the incorporation of heteroatoms in MCM-41 could generate new acidity wherein Lewis and Bronsted acid sites are involved. 11−14 The heteroatom-submitted MCM-41 has opened opportunities to obtain new acid sites for catalytic applications. Concerning the improvement of acidity, on the other hand, the sulfurcontaining catalysts are of interest because the modification of sulfate species has been reported to enhance both strength and amount of acidity on the surface of molecular sieves and metal oxide catalysts. 15−17 Many of studies were carried out for the synthesis of Ti-MCM-41 catalysts. 5,15−21 To the best of our knowledge, however, there are no reports on sulfated Ti-MCM-41 preparation. In this work, titanium containing MCM-41 material was prepared with the microwave irradiation method and modified by H 2 SO 4 aqueous solutions to further improve the acidity. The structure and acid properties of the materials were characterized with XRD, N 2 adsorption−desorption, NH 3 -TPD and FT-IR of pyridine adsorption, and XPS analysis. Transesterification of dimethyl oxalate (DMO) with phenol, as an acid catalyzed reaction, was employed as a probe reaction to test the effects of sulfate modification on acid catalytic properties. In this route, DPO is synthesized via two steps; namely, the transesterification of DMO with phenol into methyl phenyl oxalate (MPO) (eq 1) followed the disproportionation reaction of MPO to DPO (eq 2), while a major byproduct during the above process was anisole (AN),

Controllable Acid/Base Propriety of Sulfate Modified Mixed Metal Oxide Derived from Hydrotalcite for Synthesis of Propylene Carbonate

“…One possible explanation is due to the inductive effects of acid-base sites improved by the addition of sulfur species. The reaction accelerating effect through sulfur species have been reported in previous reports [47][48][49], and all the metal nodes on the Mg-Al dioxides are improved and supplied as an excellent Lewis acid sites in reactions. Meanwhile, the original oxygen adjacent to the metal nodes could act as Lewis base sites because of the free outmost electrons on the oxygen orbital.…”

Mesoporous titania–silica–polyoxometalate nanocomposite materials for catalytic oxidation desulfurization of fuel oil

“…In the NH 3 -TPD curves, peaks are generally distributed into two regions : below and above 400 1C, referred to as low-temperature (LT) and high-temperature (HT) regions, respectively. 39 The peaks in the HT region can be attributed to the desorption of NH 3 from strong Bro ¨nsted and Lewis type acid sites, and the peak in the LT region is assigned as the desorption of NH 3 from some relatively weak acid sites. 40 FT-IR measure of adsorbed pyridine has been performed as further determination for the nature of acidity on the surface of HPW-TiO 2 -SiO 2 samples.…”

Hollow and mesoporous M@aluminosilicate (M = Rh, Pd and Pt) bifunctional catalytic nanoreactors for the hydrodeoxygenation of lignin-derived phenols

“…According to the NH 3 -TPD profiles, the peaks below 250 °C were ascribed to the weak sites; peaks at 250–500 °C were assigned to the middle acid sites; the peaks above 500 °C were ascribed to the strong acid sites. 39,40 The intensity of weak and medium desorption peaks significantly increased with increasing Al contents, indicating that the amount of the weak and medium acid sites gradually increased (Fig. 6).…”