The adsorption of 1-hexene and 3,3-dimethyl-1-butene on Ru-MCM 41

Williams, Ruth; Singh, U. and Salter, I.D. (2002). The adsorption of 1-hexene and 3,3-dimethyl-1-butene on Ru-MCM 41. In: Rodríguez-Reinoso, F.; McEnaney, B.; Rouquerol, Jean and Unger, K.K. eds. Proceedings of the 6th International Symposium on the Characterization of Porous Solids (COPS-VI), Volume 144. Elsevier, pp. 633–638.




The effect of heat-treatment under reduced pressure (> 10(-5) torr) at 623 K on a sample of MCM 41 prepared using a ruthenium surfactant as a template (Ru-MCM 4 1) has been studied by sorption of nitrogen, 1-hexene, and 3,3-dimethyl-l-butene. Nitrogen sorption (77 K) shows a slight decrease in the BET surface area (330 to 282 m(2)g(-1)) and pore volume (0.19 to 0.16 cm(3)g(-1)) as a result of the heat-treatment. However, adsorption of I-hexene at 303 K shows a doubling of the monolayer uptake of 1-hexene on heat-treatment, which corresponds to an increase in both (1-hexene derived) BET surface area (144 to 295 m(2)g(-1)) and pore volume (0.12 to 0.16 cm(3)g(-1)). For the non heat-treated sample, less than similar to50% of the available surface was accessible to I-hexene, suggesting the I-hexene is sterically hindered compared with nitrogen. However heat-treatment of this sample resulted in improved accessibility of the surface and the pore system to the 1-hexene molecules. This increase in I-hexene uptake without a corresponding change in the nitrogen BET surface area may explain the observed increase in catalytic activity for 1-hexene hydrogenation following heat-treatment of the Ru-MCM 41. The adsorption at 303 K of 3,3-dimethyl-l-butene, which is more bulky isomer of 1-hexene, yielded a (3,3-dimethyl-l-butene derived) BET surface area of 161 m(2)g(-1) on the heat-treated sample, i.e. about half that of the I-hexene derived value (295 m(2)g(-1)). The pore volume determined from this sorptive was also lower (0.13 cm(3)g(-1)) than that for I-hexene (0.16 cm(3)g(-1)) on the heat-treated sample. This suggests that adsorption of 3,3-diinethyl-1-butene, which approximates to a spherical shape, is more sterically hindered compared with that of the long chain 1-hexene.

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