A statistical approach to control porosity in silica-doped alumina supports

Abstract

A split-plot statistical design was used to identify and systematically study the effects of synthesis variables on the pore properties of silica-doped alumina (SDA) from data obtained for 96 samples. Seven preparation variables (mixing method, time, environment; calcination ramp rate; drying temperature, environment; and alcohol concentration) were found to alter surface area, pore volume, and pore diameter over wide ranges, i.e. factors of 1.8, 1.4, and 3.3, respectively. Large pore diameters (> 40 nm) were obtained by addition of excess alcohol. Large pore volumes (> 2 cm 3 /g) were obtained by drying before calcination at 100C for 24 h. High surface area (> 400 m 2 /g) was obtained when no alcohol was used. The gamma phase of all SDA samples was thermally stable to 1200C. Using split-plot statistical analysis of the experimental data, models were developed which predict quantitatively the relationship between surface properties (surface area, pore volume and pore diameters) and synthesis parameters. Based on these models, optimal conditions to produce SDA samples with large (40-60 nm) or medium (16-19 nm) pore diameters, high surface area (>250 m 2 /g) and large pore volume (>1 cm 3 /g) are quantitatively predicted. Model predictions of optimal conditions were accurately

Relationships between the solution and solid-state properties of solution-cast low-k silica thin films

“…[25][26][27][28][29] The concentration of the SDA and aging time of the casting solution have also been shown to have a notable impact on the size of the pores in silica thin films. [30][31][32][33][34][35][36] Porous silica films can be used as a layer with a lowdielectric constant (low-k) in electronic devices. [37][38][39][40][41][42][43][44][45] By definition, materials with a relative permittivity of less than 4 are referred to as low-k materials.…”

The interplay of polyoxyethylene (40) stearate surfactant concentration and aging time on the Mesoporous γ-alumina synthesis and appraisal of its catalytic activity

“…Furthermore, the PS acts as a structure-directing reagent and prevented single-particle aggregation, favouring the formation of mesostructured AlOOH precursor with more uniform particles [39]. Since the kaolin as a raw material has a very small particle size (< 2 μm), the AlOOH without PS could possed micro-structure due to single particle aggregation, which would have undergone rearrangement through condensation reaction during the drying process to form pores with similar sizes as can be seen from the detectable microporosity in the alumina synthesized without surfactant [18]. This is substantiated by the fact that the factor controlling the final porosity is the nature of the alumina source [41].…”

Controlling cobalt Fischer–Tropsch stability and selectivity through manganese titanate formation

“…Indeed, silica 16 additions are well known to be advantageous and stabilise alumina supports through their incorporation into the vacant tetrahedral spinel sites. 17 Other options include cobalt silicates 18 and cobalt titanates, 19 which have been shown to be inert for FT. Indeed, the addition of manganese in CoTiO 2 FT systems has also been shown to form manganese titanate (MnTi 2 O 4 ), 20 from the manganese MnO analogue (rather than CoO).…”