Pt/SO_4^(2-)/ZrO_2-Al_2O_3在正己烷异构化反应中的催化行为

Catalytic Behavior of Pt/SO_4^(2-)/ZrO_2-Al_2O_3 in n-Hexane Isomerization

采用连续流动的固定床微反装置考察了Pt/SO24-/ZrO2-Al2O3(PSZA)在正己烷异构化反应中的催化行为。采用NH3-TPD、H2-TPR及TG表征了催化剂的酸性、还原性能及硫物种含量。结果表明,PSZA的初始异构化催化活性几乎不受反应温度的影响,而稳定性则与反应温度密切相关。低温下反应,催化剂在短时间内迅速失活,而提高反应温度可大大提高PSZA的反应稳定性。PSZA具有良好的再生性能,与新鲜催化剂相比,多次再生后的催化剂异构化催化活性基本没有变化。PSZA在低温下的快速失活与其催化活性中心产生的机理有关,而与其硫损失或硫物种的还原无关。在异构化反应过程中,催化剂通过氢溢流可产生强酸活性中心,并在反应过程中不断被消耗;在高温下通过氢溢流不断产生新的强酸中心,使催化活性保持稳定;而低温下氢溢流难以发生,消耗的强酸活性中心不能及时补充,使催化活性下降。

The catalytic behavior of Pt/SO 2-4/ZrO2-Al2O3（PSZA）in n-hexane isomerization was evaluated in a continuous flow fixed bed micro-reactor. The acidity, reduction properties and sulfur content of PSZA were characterized by NH3-TPD, H2-TPR and TG technology, respectively. The experimental results demonstrated that the initial isomerization catalytic activity of PSZA was independent of the reaction temperature, while the stability of PSZA was closely related to the reaction temperature. The PSZA catalyst was quickly deactivated in short time at low reaction temperature. On the contrary, PSZA exhibited good reaction stability at relatively high temperature. In addition, the spent or deactivated catalyst possessed good regeneration performance. It was inferred that the deactivation of PSZA in short reaction time should be related with the creation mechanism of catalytic active sites and be independent of the sulfur loss or sulfur species reduction. In the process of the isomerization reaction the acid active centers in catalyst produced by hydrogen spillover were continuously consumed. At high reaction temperature, the catalytic active sites in the catalyst may be created in time by the spillover of the dissociated hydrogen atom, so the isomerization catalytic activity of the catalyst was relatively stable. At lower temperature, hydrogen spillover was difficult to occur and the new catalytic active centers of the catalyst could not be produced in time, resulting in the isomerization catalytic activity gradually decreased.