Abstract
Tetraethoxy orthosilicate (TEOS) was used not only as a precursor of silica, but also as an agent which reinforces the skeleton of silica-gel to prepare an aerogel and resultant silica and silica-alumina with large pore size and pore volume. In this gel skeletal reinforcement, the strength of silica aerogel skeleton was enhanced by aging with TEOS/2-propanol mixed solution to prevent the shrink of the pores. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume of calcined silica could be controlled by the amount of TEOS solution and reached 30 nm and 3.1 cm3/g. The results from N2 adsorption measurement indicated that most of pores for this silica consisted of mesopores. Silica-alumina was prepared by the impregnation of an aluminum tri-sec-butoxide/2-butanol solution with obtained silica. Mixed catalysts were prepared by the combination of β-zeolite (26 wt%) and prepared silica-aluminas with large mesopore (58 wt%) and subsequently the effects of their pore sizes on the catalytic activity and the product selectivity were investigated in catalytic cracking of n-dodecane at 500 °C. The mixed catalysts exhibited not only comparable activity to that for single zeolite, but also unique selectivity where larger amounts of branched products were formed.
Highlights
In recent years, excess amounts of heavy oils are coming out and their utilization has been one of the problems
We examined whether only the gel skeletal reinforcement was needed to make silica aerogels with extremely large mesopores, or whether the subcritical condition, using a rigidly sealed container, would be needed simultaneously with the gel skeletal reinforcement
When silica-gel was reinforced by Tetraethoxy orthosilicate (TEOS) solution, silica with large mesopores was prepared
Summary
Excess amounts of heavy oils are coming out and their utilization has been one of the problems. The major treatment process of those heavy oils is catalytic cracking, which produces high octane gasoline with a lower sulfur content. A desulfurization unit is put after the FCC (Fluid Catalytic Cracking) unit, in order to decrease the sulfur content, because sulfur regulation in gasoline is very severe: less than 10 ppm. The development of novel catalysts which have high selectivity for branched products in catalytic cracking has been needed [1,2]. It is well known that catalysts in FCC generally include zeolite as a major component and silica-alumina as a matrix [3]. We have reported that silica-aluminas with about 5 nm of mesopore prepared using malic acid influence the production of branched hydrocarbons in catalytic cracking of n-dodecane [1,2]. Tang et al [10], have reported the matrix effect
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