Synthesis-property-performance relationships of amorphous silica-alumina catalysts for the production of methylenedianiline and higher homologues

Synthetic and Catalytic Potential of Amorphous Mesoporous Aluminosilicates Prepared by Postsynthetic Aluminations of Silica in Aqueous Media

“…[8,9,28] Compared to the acidities of these commercial materials (ASA-6 and ASA-0.4), the total acidities of % 60 mmol g À1 obtained for the AS1 and AS2 samples are slightly lower.S till, AS1 and AS2-based samples feature considerably higher Si/Al ratios (based on the maximal theoretical amount of incorporateda luminum), and therefore should display substantially highere ffective acidities (Table 2). About 30 %l ower acidities were obtained than with SBA-15( Ta ble 2).…”

“…Amorphous aluminosilicate catalysts have been used industrially on al arge scale for almost ac entury.H owever,t he influence of the pH on the alumination of silica in aqueous solutions has remainedl argely unclear.H erein, room temperature aluminations of different mesoporousa morphous silicas (fumeds ilica, dried silica gel, SBA-15, MCM-41, and COK-12) with aqueous solutionso fv ariousp H (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) are explored. The aqueous solutions are prepared using different aluminums ources( Al(NO 3 ) 3 or NaAlO 2 )and alkaline additives (NaOH or NH 4 OH).…”

“…[2][3][4][5] The advantage of ASA over (purely Lewis acidic) alumina is that Brønsted acid sites are formed if monomeric aluminumi s incorporated in the silica framework with at etrahedral coordination (isomorphous substitution). [8][9][10][11][12][13][14][15][16] Not only the relative quantity of silica and alumina can vary strongly,b ut also their distribution (zoning, gradients, etc. [8][9][10][11][12][13][14][15][16] Not only the relative quantity of silica and alumina can vary strongly,b ut also their distribution (zoning, gradients, etc.…”

“…[8][9][10][11][12][13][14][15][16] One of the most used (and commerciallya ttractive) methods may be the deposition of Al by subjecting silica to Al-containinga queous solutions, taking advantage of the hydrolysis-condensation behavior of Al 3 + ions in water.T he latter is typicallyp erformed by using various Al salts such as Al 2 (SO 4 ) 3 ,A l(NO 3 ) 3 [8][9][10][11][12][13][14][15][16] One of the most used (and commerciallya ttractive) methods may be the deposition of Al by subjecting silica to Al-containinga queous solutions, taking advantage of the hydrolysis-condensation behavior of Al 3 + ions in water.T he latter is typicallyp erformed by using various Al salts such as Al 2 (SO 4 ) 3 ,A l(NO 3 ) 3 …”

“…[6,7] Still, the exact nature of the acidity of ASAsc an be ratherc omplex owing to their large heterogeneity. [8][9][10][11][12][13][14][15][16] Not only the relative quantity of silica and alumina can vary strongly,b ut also their distribution (zoning, gradients, etc. ), their coordination( in the case of Al:t etrahedral/framework versuso ctahedral/extraframework), and accessibility( isolated aluminuma toms within the bulk or accessible on the surface).…”