The architecture of Mg(II) centres in MAPO-36 solid acid catalysts

Abstract

The local structure around Mg2+ ions of a Magnesium substituted aluminophosphate, with the ATS structure (MgAPO-36, Mg/P=0.08), in the as-prepared and calcined state has been investigated by Mg K-edge XAS spectroscopy. High quality XAS data were collected using the solid-state fluorescence detector. Mg2+ is found to replace tetrahedrally co-ordinated Al3+ in the as-prepared state and remained intact even after calcination, thus yielding a highly active, solid acid catalyst.

Coordination of Sr and Mg in calcite and aragonite

“…Despite the short energy range, refinement of first-shell Mg EXAFS is possible (e.g. Sankar et al, 2001). We refined the Mg K-EXAFS of the Mg-carbonates (dolomite, magnesite and hydromagnesite) against their structural models (Table 3) to test the accuracy of EXAFS in calculating MgÀO bond distances.…”

“…Each gives a good fit consistent with their structural model. A typical value for thermal disorder at room temperature around a single Mg site is 0.01À0.02 Å 2 (Sankar et al, 2001). However, as with Sr, refining MgÀO as a single shell in many minerals is a gross simplification and static disorder also contributes to some of the Debye-Waller parameters.…”

Large-Pore FAPO-36: Synthesis and Characterization

“…The incorporation of cobalt, magnesium, manganese, silicon, titanium, vanadium, and zinc in the AlPO 4 -36 has already been reported in the literature, − but there are no literature data concerning the incorporation of iron. To determine the location of metal ions in MeAPO-36 (Me = Co, Mg, Mn, Ti, Zn), different methods have been employed, such as X-ray absorption spectroscopy (XAS), , UV−VIS, , and EPR. , Furthermore, FT-IR spectroscopy has been used to investigate the acidity of these materials using pyridine as a probe molecule. , The acidity measurements of MeAPO-36 (Me = Co, Mg, Mn, Zn) at 473 K have shown the presence of Brønsted and Lewis acid sites. The order of the Brønsted to Lewis acid sites ratio has been as follows: MnAPO-36 < ZnAPO-36 < CoAPO-36 < MgAPO-36 .…”

A New Strategy for Simultaneously Improved Flame Retardancy, Thermal Properties, and Scratch Resistance of Transparent Poly(methyl methacrylate)

“…Additionally, compared to (MMA- co -MSMA)/TMSAP15, the T 0.1 values of all (MMA- co -MSMA)/TMSAP/OLAP nanocomposites are smaller and decrease with increasing OLAP content. The early degradation of the nanocomposites further confirms the catalytic charring effect of OLAP because the OLAP catalyzes charring of polymers through dehydrogenation at relatively low temperature, ultimately improving the thermal stability of residues at high temperature. − , This point can be confirmed by the better thermal stability of the nanocomposites at high temperature: The temperatures at the 80% mass loss rate ( T 0.8 ) are in order of PMMA (336.1 °C) < (MMA- co -MSMA)/TMSAP15 (426.4 °C) < (MMA- co -MSMA)/TMSAP14/OLAP-1 (432.5 °C) < (MMA- co -MSMA)/TMSAP13/OLAP-2 (434.0 °C) < (MMA- co -MSMA)/TMSAP12/OLAP-3 (441.5 °C), indicating the enhanced endurance of the nanocomposites against thermal oxidation at high temperature. Given the characterizations above, the thermal stability enhancement of (MMA- co -MSMA)/TMSAP/OLAP nanocomposites results from the cross-linked network as well as the char formation caused by OLAP and TMSAP.…”

“…Benefiting from the inherent lamellar structure, OLAP shows many attractive characteristics including large surface area and aspect ratio, thermal and chemical stability, high elastic modulus, catalytic activity, and the potential to delaminate within polymers. − These properties of OLAP are similar to those of LDH and clay, suggesting its potential application in improving flame retardancy and thermal stability of PMMA. Moreover, OLAP is a common solid acid catalyst, which could catalyze the dehydrogenation of polymers and promote the charring of polymers. − The catalytic carbonization function is also a favorable factor for the flame retardant system, further making the OLAP a promising candidate for flame-retardant applications in polymeric nanocomposites. , …”