Preparation of magnesia-silica oxides: Effect of Mg/Si ratio and sulfate on acidity

Abstract

Abstract. Mg-Si binary oxides were prepared by the sol-gel method, using magnesium diethoxide and tetraethoxysilane as starting materials. Mg-Si mixed oxides were prepared at pH3 and 9 at nominal concentrations of 1.3, 4.0, and 6.7 mole% MgO. Density and strength of the acid sites were determined by pyridine thermal programmed desorption. Comparable Lewis acidity was found in pH3 and 9 preparations. However, when the samples were sulfated with sulfuric acid, strong Bronsted acidity was developed, reaching a maximum at 6.7 mole% MgO. The strong acidity of sulfated samples was corroborated using the isopropanol decomposition reaction as catalytic test. Similar conversions are obtained at 100~ on sulfated samples, whereas 260~ are required for non-sulfated ones.

Influence of Chemical Conditions on the Nanoporous Structure of Silicate Aerogels

“…In the application of Mg(OEt) 2 , the TEOS precursor must be prehydrolyzed due to the different hydrolysis rate of TEOS and Mg(OEt) 2 . The forsterite gels dried supercritically are characterized by surface areas of ~520 m 2 g -1 [167,168]. In the case of 2 MgO·SiO 2 prepared from alkoxide precursors using various prehydrolysis conditions for TEOS, the aerogels have surface areas between 207 and 340 m 2 g -1 , 0.135 g cm -3 density, and loosely packed agglomerates with primary particle sizes between 10 and 15 nm [169].…”

“…In the synthesisof magnesium silicate (forsterite), magnesium inorganic salt [Mg(NO 3 ) 2 [ 163 , 164 , 165 , 166 ] or alkoxide [Mg(OCH 2 CH 3 ) 2 [ 164 , 167 ] precursors may be used. The aerogels with 5 and 10% MgO provided by Mg nitrate present surface areas of 240 and 200 m 2 g -1 , respectively [ 165 , 166 ].…”