【摘要】 考察了300℃和500℃温度下还原的Pt/Al₂O₃和含有不同Ti量的Pt-Ti/Al₂O₃催化剂的环己烷脱氢反应性能。300℃还原时,Pt/Al₂O₃的环己烷脱氢活性随着Ti量的增加而增加,这可能是因为300℃还原时,Ti⁴⁺不能被H₂还原,它具有吸引Pt的外层电子的能力。因此使Pt的脱氢活性增强。500℃还原时,Ti⁴⁺被部分还原成Ti^<4+或Ti⁰,它们都具有给电子的能力,邻近的Pt原子接受此电子后使其缺电子的程度减弱,从而使其活性变低,但因为Ti⁴⁺部分地抵消了Ti^<4+和Ti⁰减弱Pt活性的作用,所以Pt-Ti/Al₂O₃中含Ti量即使多达5.0％（重）。其环己烷脱氢活性仍比单组分Pt/Al₂O₃的高。更多还原

【Abstract】 The dehydrogenation of cyclohexane has been carried out on Pt/Al2O3 and Pt-Ti/Al2O3 reduced at 300 and 500℃ respectively. It is found that the dehydrogenation activity of catalyst with 0.50 wt% of Ti reduced at 500℃ exhibits a maximum value, the activity of Pt-Ti/Al2O3 will be still higher than that of Pt/Al2O3 even if the content of Ti amounts to 5.0 wt%; whereas the dehydrogenation activity of catalysts reduced at 300℃ increases successively with the increase of the amount of Ti (see Fig. 2).Interesting phenomena are observed from a comparison of the activation energies of both catalysts reduced at 300 and 500℃ respectively (Table 2). For Pt/Al2O3, the activation energy of catalyst reduced at 300℃(E300) is equal to that of catalyst reduced at 500℃ (E500). For Pt-Ti/Al2O3, if the amount of Ti is 0.25 wt%,E300 is also equal to E500;however, when the amount of Ti is larger than 0.5 wt%,E500 is higher than E300. It is supposed that the Ti4+ ions of the catalysts which contain small amount of Ti, performing the function of core for the dispersion of Pt, are difficultly reduced by hydrogen, so that the Ti4+ ions exist as the main ions on the catalyst surface whether the catalysts are reduced at 300℃ or 500℃, and therefore E300= E500. On the contrary, in the cases of Ti>0.5wt%, when the catalysts are reduced at 500℃, a part of Ti4+may be reduced by hydrogen to Ti<4+ or Ti0, which does not perform the function of core for dispersion of Pt, therefore E500 is higher than E300.The facts given above indicate indirectly that small amount of additive Ti (i. e. Ti<1.0wt%) in Pt-Ti/Al2O3 is present mainly as Ti4+,which possesses the action to strengthen the activity of Pt, while the content of Ti increases to 1.0-5.0 wt%,the amount of Ti<4+ or Ti0 is also increased, the strong interaction between Pt and Ti<4+ or Ti0 may cause the reduction of the activity of catalysts. But for the dehydrogenation of cyclohexane, the effect of Ti4+ on Pt is stronger than that of Ti<4+ or Ti0, therefore the dehydro-genation activity of Pt-Ti/Al2O5 (Ti<5.0wt%) is always higher than that of Pt/Al2O3.更多还原