Single-phase mixed molybdenum-niobium carbides: Synthesis, characterization and multifunctional catalytic behavior in toluene conversion
Single-phase mixed molybdenum-niobium carbides: Synthesis, characterization and multifunctional catalytic behavior in toluene conversion
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DOI：
10.1016/j.jcat.2017.04.022
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发表时间：
2017-07-01
影响因子：
7.3
通讯作者：
Jentoft, Friederike C.
中科院分区：
文献类型：
--
作者：
Mehdad, Ali;Jentoft, Rolf E.;Jentoft, Friederike C.
合成单相混合的铌-铌碳化物，以建立结构-活性关系。用于渗碳的前体通过水热合成获得，或者为了获得高钼含量（金属分数χ（Mo）= 0.86），通过盐溶液的快速冷冻和随后的冷冻干燥获得。在渗碳过程中的热重和放出气体分析表明，铌前体比单铌更容易还原;随着铌含量的增加，氧的去除转移到更高的温度，从H2O到CO的形成（分别从H-2或CH 4），最终渗碳温度从650 ℃上升到950 ℃。对于chi（Nb）>= 0.38，以立方NbC/MoC（cF 8）结构结晶的碳化物和对于chi（Nb）= 0.38，以六方Mo 2C（hP 3）结构结晶的碳化物比具有较低铌含量的碳化物对酸催化产物的选择性更高，对氢解产物的选择性更低。(C)2017爱思唯尔公司All rights reserved.
Single-phase mixed molybdenum-niobium carbides were synthesized to establish structure-activity relationships. Precursors for carburization were obtained by hydrothermal synthesis or, to achieve high molybdenum content (metal fraction chi(Mo) = 0.86), by flash-freezing of salt solutions and subsequent freeze-drying. Thermogravimetric and evolved gas analysis during carburization showed that bimetallic precursors were more easily reduced than monometallic ones; and as the niobium content increased, the removal of oxygen shifted to higher temperatures and from H2O to CO formation (from H-2 or CH4, respectively), and the final carburization temperature rose from 650 to 950 degrees C. Carbides crystallized in cubic NbC/MoC(cF8) structure for chi(Nb) >= 0.38 and hexagonal Mo2C(hP3) structure for chi(Nb) = 0.38 were more selective toward acid-catalyzed products and less selective toward hydrogenolysis products than carbides with lower niobium content. (C) 2017 Elsevier Inc. All rights reserved.