Development of high-performance solid catalysts for selective oxidative dehydrogenation of ethane by structural fine tuning with in-situ XRD

用Rietveld分析了SrBi_3O_4Cl_3催化剂的结构。在X1 X2结构中，金属-氧片层被单氯层和双氯层交替分隔。SrBi_3O_4Cl_3晶体属14/mmm空间群，晶格常数a=3.9370（1），c=27.0177（7）nm。结构表明，在Bi（1）和Bi（2）两个晶位之间，前者是金属氧片中Bi的晶位面对单氯片，后者面对双氯片，Sr离子只占据Bi（2）晶位，而不占据Bi（1）晶位。基于这种结构材料，开发了许多高选择性和高活性的催化剂。在KSr_2Bi_3O_4Cl_6组成的催化剂上，640℃乙烷氧化脱氢，乙烯收率达74%。在SrBi_3O_4Cl_3催化剂的阳离子-氧层中引入镧离子 ...更多信息 s时，SrBi_<3-n>La_nO_4Cl_3（n ≤ 0.75）催化剂仍保持X1 X2结构，乙烷氧化脱氢活性显著提高。对SrBi_ La_ O_4Cl_3催化剂XRD图谱的Rietveld分析<2.25><0.75>表明，面对双氯片的金属离子的配位数从8增加到9，导致双氯片的厚度减小。金属氧化物片层与氯片层之间的相互作用增强，这是由SrBi_ La_ O_4Cl_3中氯的结合能降低所支持<2.25><0.75>的。La ~（2+）的取代促进了结构氯活化成自由基形式，从而提高了乙烷的氧化活性，用Rietveld法对Bi_2SmO_4Cl催化剂进行了结构细化。空间群为P4/mmm，a=3.8938（1）&lt;$，c=8.9691（3）&lt;$。可以看到[Bi_2SmO_4]层的存在，它可以被认为是一个“三”而不是“双”萤石单元。该阳离子层由最简单的阴离子层Cl^-平衡，因此该结构沿晶体学c轴具有-Cl-[Bi_2SmO_4]- Cl-等沿着的层序。La离子仅与氧化物层配位，Bi离子与氧化物层和氯化物层配位。Bi_2LaO_4Cl催化剂对乙烷氧化表现出较高的活性，但乙烯选择性较低，这归因于La-氧-La片层的促进氧化能力。少

The structure of the SrBi_3O_4Cl_3 catalyst was analyzed by a Rietveld analysis. In the X1X2 structure, metal-oxygen sheets were separated by single chlorine layers and double chlorine layers alternately. SrBi_3O_4Cl_3 crystallized in space group 14/mmm with lattice parameters of a=3.9370(1), c=27.0177(7)Å. The structure showed that between two Bi(1) and Bi(2) sites, the former being of Bi in the metal-oxygen sheet faced the single chlorine sheet and the later faced the double chlorine sheet, strontium ions occupied the Bi(2) site only, and did not occupy the Bi(1) site. Based on this structural materials, much highly selective and active catalysts were developed. 74% yield of ethene has been attained in the oxidative dehydrogenation of ethane at 640℃ over the catalyst having a composition of KSr_2Bi_3O_4Cl_6.The lanthanum-substituted complex metal chloride oxide catalysts were also investigated. With the replacement of lanthanum ion in the cation-oxygen sheet of SrBi_3O_4Cl_3 catalyst … More s, the SrBi_<3-n>La_nO_4Cl_3 (n【less than or equal】0.75) catalyst remained the X1X2 structure, the activity for the oxidative dehydrogenation of ethane were promoted prominently. The Rietveld analysis of the XRD patterns of SrBi_<2.25>La_<0.75>O_4Cl_3 catalyst revealed that the increased coordination number of the metal ion facing the double chlorine sheet from 8 to 9 resulted in a decrease of the thickness of the double chlorine sheet. The interaction between the metal-oxide sheet and the chlorine sheet became stronger, which is supported by a reduced binding energy of chlorine in SrBi_<2.25>La_<0.75>O_4Cl_3. It is suggested that the activation of structural chlorine into a radical form is promoted by the replacement with lanthanum ion, which turns out to be the increase of the oxidation activity of ethane.The structure of the Bi_2SmO_4Cl catalyst was refined by Rietveld method. The space group is P4/mmm, a=3.8938(1)Å, c=8.9691(3)Å. It can be seen that the [Bi_2SmO_4] layer is present, which may be regarded as a'triple' rather than'double' fluorite unit. This cationic layer is balanced by the simplest possible anionic layer, Cl^-, hence the structure has the layer sequence -Cl-[Bi_2SmO_4]- Cl- etc. along the crystallographic c axis. La ion is coordinated only by oxide layers and Bi by both oxide and chloride layers. The Bi_2LaO_4Cl catalysts showed a high activity for the oxidation of ethane, but the selectivity to ethene were low, which can be attributed to the promoted oxidation ability of La-oxygen-La sheets. Less