Elsevier

Catalysis Communications

Volume 5, Issue 8, August 2004, Pages 441-445
Catalysis Communications

Hydrothermal stability and catalytic activity of mesoporous aluminum-containing SBA-15

https://doi.org/10.1016/j.catcom.2004.05.011Get rights and content

Abstract

Mesoporous silica structure SBA-15 and Al-containing SBA-15 (AlSBA) were synthesized and tested their activity in catalytic cracking of waste fatty acid mixture (palm oil based) in a fixed-bed micro-reactor. The catalytic activity of AlSBA was improved and more selective towards gasoline fraction present in the organic liquid product (OLP) as compared to mesoporous siliceous material SBA-15. Even though the hydrothermal stability of AlSBA was poorer but the sample with Si/Al ratio of 20 was found to be comparable with SBA-15. The hydrothermal stability of AlSBA was higher than AlMCM-41 with similar cracking activity and thus AlSBA is a more potential cracking catalyst.

Introduction

Since the discovery of the mesoporous material, M41S family [1], with a narrow pore size distribution, these materials have attracted attention of the researchers. By using different length of alkyltrimethyl ammonium cations as surfactants, the pore size of these materials can be altered between 2 and 10 nm. Even though this material has a high thermal stability but when expose to high temperature steam and boiling water, it loses its structure [2]. The collapse of the structure has limited the applications of MCM-41 especially in the catalytic reactions involving the aqueous solution. Recently, SBA-15 mesoporous material has been synthesized under acidic condition using triblock copolymer as a surfactant. This novel mesoporous material has shown higher hydrothermal stability as compared to MCM-41 due to its thicker pore walls [3]. They also posses uniform and hexagonal-structured channel similar to MCM-41 with larger pore size which make them more desirable to deal with bulky molecule [4], [5]. However this purely siliceous mesoporous material SBA-15 is lack of acid sites and acidity, therefore incorporation of aluminum AlSBA-15 was investigated in order to create acid sites. With the presence of acid sites, the activity of SBA-15 will be enhanced in the reaction involving acid catalyst.

In the present study, SBA-15 and Al-containing SBA-15 (AlSBA) were synthesized and their hydrothermal stability was investigated. The activity of these mesoporous materials in catalytic cracking of palm oil based waste fatty acid mixture was tested and compared with Al-MCM-41.

Section snippets

Synthesis

SBA-15 and AlSBA were prepared following the procedure reported in the literature [3], [6]. 9.8 g of triblock copolymer poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) (Aldrich, average molecular weight=5800) was dissolved with stirring in 313 ml of deionzed water and 40 ml of hydrochloric acid (37 wt%) for 1 h at 50 °C. Subsequently, 21.7 g of tetraethyl orthosilicate (Merck, TEOS) was added and stirred for another 10 min. The mixture was heated at 60 °C for 24 h and then at

Results and discussion

The isotherm of nitrogen adsorption and desorption in Fig. 1(a) shows the typical result for SBA-15 with a sharp nitrogen uptake at higher relative pressure [3], [6]. Purely siliceous SBA-15 exhibited large hysteresis loop of type E with sloping adsorption branch and steep desorption branch [9]. This hysteresis type was due to the presence of different size of spheroidal cavities with the same entrance pore diameter. In contrast to SBA-15, AlSBA exhibited hysteresis with both the adsorption and

Conclusion

The aluminum-containing SBA-15 (AlSBA) showed a higher hydrothermal stability and cracking activity as compared to purely siliceous SBA-15. Thus AlSBA is more promising catalyst as compared to AlMCM-41 in term of hydrothermal stability, selectivity and activity.

Acknowledgements

The authors would like to acknowledge the Research Grant provided by the Ministry of Science, Technology and Environment, Malaysia under long term IRPA Grant (Project: 02-02-05-2184 EA005), that has resulted in this article.

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