Synthesis, Structure, and Acidic Properties of MCM-41 Functionalized with Phosphate and Titanium Phosphate Groups

Abstract

Mesoporous molecular sieves Si-MCM-41 (purely siliceous) and Ti-MCM-41 (partly covered with a surface layer of TiO2) were functionalized with phosphate groups by treatment with POCl3 (denoted -MCM-41(P)and Ti-MCM-41(P), respectively). With the use of TEM, X-ray diffraction, and N2 adsorption, it was shown that the initial hexagonal structure, the high specific surface area, and porosity are retained in the functionalized materials but are not as good as in the starting materials. 1H MAS NMR and 31P MAS NMR revealed that the surface of Si-MCM-41(P) consists of silicon phosphate and pyrophosphate species. That of Ti-MCM-41(P) additionally contains titanium dihydro-, hydro-, and pyrophosphate species, the latter being predominant. TPD of adsorbed ammonia for Si-MCM-41(P) and Ti-MCM-41(P) showed that functionalization leads to the creation of moderate and strong acid sites. A combination of mesoporous structure with acidic properties makes the MCM-41 functionalized with phosphate groups promising for use as solid acid catalysts.

Solid-state synthesis of embedded single-crystal metal oxide and phosphate nanoparticles and in situ crystallization

“…In situ formation of SiP 2 O 7 happens in the presence of SiO 2 and unreacted phosphazenic components, stabilized by P 4 O 7, and is discussed in terms of organometallic decomposition to the pyrophosphate phase. Solid-state reaction of SiO 2 with phosphorus oxides gives rise to SiP 2 O 7 [34][35][36] at the macroscale. Previous routes to the synthesis of metal phosphates, using SiP 2 O 7 as a reagent, showed that the reaction of SiP 2 O 7 with metal oxides yields a solid mixture of silica and metal phosphates; its reaction with metal fluorides yields solid metal phosphates and gaseous mixtures of SiF 4 and POF 3 .…”

Vapor-phase Beckmann rearrangement of cyclohexanone oxime over phosphorus modified Si-MCM-41

“…3 that the intensity at 960 cm -1 increases with increasing P content. This may be a consequence of the replacement of SiO-H by SiO-P [22]. Intensity (a.u.)…”

Chemical modification of TiO2 by H2PO4−/HPO42− anions using the sol-gel route with controlled precipitation and hydrolysis: enhancing thermal stability

“…4e), the 31 P NMR spectrum showed a well-resolved spectrum, characteristic of a well crystalline material. The existence of lines at −38.6, −40.5, −42.9, −44.5, −46.15, −49.48 and −52.35 ppm can be associated with the presence of several crystallographic sites for phosphorus atoms in a 3 × 3 × 3 crystal structure of TiP 2 O 7 [29]. A minor and narrow peak at ∼−27 ppm appeared at 900°C.…”