介孔磷酸盐分子筛上钒物种的引入方式及其对丙烷氧化脱氢催化性能的影响

Methods of introduction of vanadium species on phosphate mesoporous sieves and their influence on the catalytic performance for oxidative dehydrogenation of propane

以溶剂挥发诱导自组装法(evaporation–induced self–assembly,EISA)合成的有序磷酸盐介孔分子筛Na_(0.1)Zr_(0.9)PO为载体,分别采用掺杂和浸渍两种方式引入过渡金属钒作为活性物种,制备了一系列不同钒含量的催化剂样品。通过小角X射线衍射、N_2吸附-脱附和透射电镜表征了所制备样品的孔道结构,采用Raman光谱着重研究了不同方式引入的钒物种在Na_(0.1)Zr_(0.9)PO上的存在状态,并将催化剂上钒物种的存在状态与其在丙烷氧化脱氢反应中的催化性能相关联,探讨在介孔磷酸盐分子筛上构筑丙烷氧化脱氢活性位的合适方法。研究结果表明:掺杂方式引入的钒物种不仅可以同时以孤立态和聚集态存在,并且当钒含量高于8%时仍能保持高度分散状态,不容易出现导致催化性能下降的结晶态V_2O_5,与浸渍负载相比,本文采用掺杂方式制备的钒基催化剂样品普遍显示出更好的丙烷氧化脱氢活性和更高的丙烯选择性。此外,以碱金属Na掺杂的介孔磷酸盐分子筛Na_(0.1)Zr_(0.9)PO作为钒基催化剂的载体,虽然丙烷氧化脱氢反应的活性受到一定程度的抑制,但却可以使丙烯的选择性有所提升。

A series of catalyst samples were prepared by incorporating or impregnating of different amounts of active vanadium species on the phosphate mesoporous sieves Na0.1Zr0.9PO which was synthesized in advance by evaporation–induced self–assembly. The pore structure of the prepared samples was characterized by N2 adsorption-desorption and small angle X-ray diffraction as well as transmission electron microscope. Meanwhile, the state of vanadium species on the Na0.1Zr0.9PO was explored by Raman spectrum, which was used to interpret their catalytic performance with an eye toward properly building the catalytic active sites on the phosphate mesoporous sieves. The experimental results showed that the vanadium species introduced by incorporating exist in both isolation and aggregation states. Furthermore,the vanadium species are highly dispersed without the formation of crystalline V2O5 even with more than8% of vanadium loading. In summary, the catalyst samples prepared by incorporating vanadium species into the phosphate mesoporous sieves showed better catalytic activity and selectivity for oxidative dehydrogenation of propane to propylene than the samples obtained by impregnating. Furthermore, the activity of oxidative dehydrogenation of propane to propylene declined over the vanadium catalysts supported on phosphate mesoporous sieves doped with Na, but the selectivity was increased.