Synergistic B-Al interaction in SBA-15 affording an enhanced activity for the hydro-isomerization of heptane over Pt-B-Al-SBA-15 catalysts

摘要

Mesoporous M-SBA-15 (M/Si = 1/10) (where M = Al, B or Al-B in a ratio 0.5:0.5) were prepared via a known procedure using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as template. Further deposition of platinum on these supports has been achieved by impregnation with an aqueous solution of H2PtCl6. The prepared supports and catalysts were characterized by the adsorption-desorption isotherms of nitrogen at - 196 degrees C, XRD and TEM measurements, and temperature-programmed desorption of ammonia (TPD-NH3). All these solids were investigated for the hydro-isomerization of heptane. In the investigated range of time (24 h) and temperatures (200-300 degrees C) the supports exhibited no isomerization activity but only a small cracking activity. The addition of platinum to these supports provided activity in this reaction even for a weak acid support as B-SBA-15. However, the presence of both aluminum and boron in a ratio of 0.5 to 0.5 led to a more efficient catalyst. Thus, the Pt-Al-B-SBA-15 catalyst showed a slightly higher conversion than the Pt-Al-SBA-15 one. All the investigated Pt-SBA-15 provided high selectivity for the isomerization to methylhexanes. Dimethylpentanes were also produced but in a different extent, depending on the acidity of the support. Cracking of heptane to C1-C4 molecules accompanied the hydro-isomerization process but in a rather small extent (yields smaller than 5% after 24 h).