Sn助剂对Pt-Sn/γ-Al_2O_3催化剂上C_(12)正构烷烃脱氢反应的影响

以正十二烷烃临氢脱氢反应为探针,并结合氮气物理吸附-脱附、压汞、CO脉冲化学吸附、原位X射线光电子能谱及热重等催化剂物化表征手段,研究了Sn助剂对于Pt-Sn/γ-Al2O3长链烷烃脱氢催化剂反应性能的影响。结果表明,当Pt-Sn/γ-Al2O3催化剂中Sn∶Pt原子比为3时,催化剂表现出最佳的反应初活性。继续增加Sn的含量,由于更多的零价锡生成,并与Pt形成合金反而使催化剂活性下降。此外,在催化剂中引入Sn组分后,催化剂的稳定性有所改善,并且随着Sn含量的增加,脱氢反应产物选择性明显提高。     

Effect of thermal deformation on giant magnetoresistance of flexible spin valves grown on polyvinylidene fluoride membranes

We fabricated flexible spin valves on polyvinylidene fluoride(PVDF) membranes and investigated the influence of thermal deformation of substrates on the giant magnetoresistance(GMR) behaviors. The large magnetostrictive Fe_(81)Ga_(19)(Fe Ga) alloy and the low magnetostrictive Fe_(19)Ni_(81)(Fe Ni) alloy were selected as the free and pinned ferromagnetic layers.In addition, the exchange bias(EB) of the pinned layer was set along the different thermal deformation axes α_(31) or α_(32) of PVDF. The GMR ratio of the reference spin valves grown on Si intrinsically increases with lowering temperature due to an enhancement of spontaneous magnetization. For flexible spin valves, when decreasing temperature, the anisotropic thermal deformation of PVDF produces a uniaxial anisotropy along the α_(32) direction, which changes the distribution of magnetic domains. As a result, the GMR ratio at low temperature for spin valves with EB α_(32)becomes close to that on Si, but for spin valves with EB α_(31)is far away from that on Si. This thermal effect on GMR behaviors is more significant when using magnetostrictive Fe Ga as the free layer.     

铝硼复合氧化物负载Pt-Sn催化剂的丙烷脱氢性能研究

采用蒸发自组装法制备铝硼复合氧化物((AlB_x)_2O_3),真空配合浸渍法制备PtSn双金属催化剂,并应用于丙烷脱氢制丙烯.采用N_2物理吸附、 SEM、 TEM、 XRD、 H_2-TPR、 NH_3-TPD、 TG和ICP-OES对催化剂进行表征.掺入B可大幅增加载体的总酸量和酸中心密度,降低酸强度.当B掺入量为Al的10%时, Cat-AB_(0.1)的总酸量是Cat-AB_0总酸量的2.45倍,且只有弱酸中心.当B掺入量为Al的50%时, Cat-AB_(0.5)的酸中心密度是Cat-AB_0的4.3倍.以铝硼复合氧化物负载的催化剂均优于纯氧化铝负载的催化剂,催化剂的脱氢活性和稳定性与载体的硼铝摩尔比之间存在如下规律:AB_(0.1)AB_(0.3)AB_(0.5)AB_0.     

K助剂对Pt-Sn-K/γ-Al2O3催化剂上C16正构烷烃脱氢反应的影响

 以络合真空浸渍法制备了 Pt-Sn-K/γ-Al2O3 催化剂. 采用吡啶吸附红外光谱、CO脉冲吸附、程序升温还原、热重及程序升温氧化等手段对催化剂进行了表征, 研究了 K 助剂对 Pt-Sn-K/γ-Al2O3 催化剂结构及其催化 C16 正烷烃临氢脱氢反应性能的影响. 结果表明, K 的引入减弱了 SnOx 和 Al2O3 间的相互作用, 促进了 Pt 对 SnOx 的还原, 并导致催化剂的脱氢反应活性降低. K 的加入还减少了强酸中心数目, 一方面减少了催化剂酸性位上的副反应, 提高了产物选择性; 另一方面提高了催化剂的抗积炭能力, 催化剂稳定性有所改善. 但过量的 K 助剂减弱了催化剂的金属位-酸性位的协同作用, 使得催化剂活性和稳定性均有所降低.