Influence of the preparative route on the properties of WOx-ZrO2 catalysts:: A detailed structural, spectroscopic, and catalytic study
Influence of the preparative route on the properties of WOx-ZrO2 catalysts:: A detailed structural, spectroscopic, and catalytic study
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DOI：
10.1016/j.jcat.2007.03.022
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发表时间：
2007-06-10
影响因子：
7.3
通讯作者：
Sanchez-Royo, Juan F.
中科院分区：
文献类型：
--
作者：
Martinez, Agustin;Prieto, Gonzalo;Sanchez-Royo, Juan F.
采用非常规浸渍法和共沉淀法制备了两个系列的钨锆酸盐（WZ）固体酸，其比表面积在973-1073 K范围内增大（约为70-120 m2/g）。通过N-2物理吸附、XRD、拉曼、XPS、H-2-TPR和DR UV-vis光谱对材料进行了全面表征。评价Pt促进的WZ催化剂（1重量% Pt）对于用作代表费托蜡的模型进料的正十六烷的加氢转化的催化行为。这两个系列的催化剂显示出显着的最大反应速率和最小的选择性支化原料异构体（异-C-16）在中间钨密度（δ（最大））。有趣的是，我们发现，与浸渍催化剂（delta（max，IMP）= 5.2 W at/nm（2））相比，共沉淀催化剂（delta（max，COP）= 6.8 W at/nm（2））的delta（max）向更高的值移动。这已被归因于一个更好的固有能力的共沉淀路线分散钨物种的ZrO 2表面上，推断从建模XPS数据。这就决定了催化活性布朗斯台德酸位点的产生所需的高度互连的无定形WO，域的形成和非活性三维WO 3微晶的生长（通过XRD和拉曼确定）的开始都发生在通过共沉淀产生的WZ固体中比通过浸渍获得的那些中的钨表面密度更高的钨表面密度下。尽管观察到δ（max）的偏移，但每个系列内的两个最具活性的样品显示出几乎相同的每总W原子的固有活性，这表明负载的活性WO 1域的类似性质和尺寸应通过浸渍和共沉淀途径在δ = δ（max）下获得。此外，发现制备方法影响负载的WOx物种的光学和电子性质。因此，共沉淀提供了WZ固体显示较低的价态-传导能隙，以及增强的还原性的聚钨酸盐域由于改进的电子连接与氧化锆支持，在相反的更孤立的字符的WOx集群产生的浸渍。(c)2007爱思唯尔公司所有的战斗保留。
Two series of tungstated zirconia (WZ) solid acids covering a wide range of tungsten surface densities (delta, W at/nm(2)) were prepared by nonconventional impregnation and coprecipitation routes, leading to samples with enhanced surface area (similar to 70-120 m(2)/g) on annealing at 973-1073 K. The materials were thoroughly characterized by N-2 physisorption, XRD, Raman, XPS, H-2-TPR, and DR UV-vis spectroscopy. The catalytic behavior of the Pt-promoted WZ catalysts (1 wt% Pt) was evaluated for the hydroconversion of n-hexadecane used as model feed representative of Fischer-Tropsch waxes. Both series of catalysts displayed a pronounced maximum in the reaction rate and a minimum in the selectivity to branched feed isomers (iso-C-16) at an intermediate tungsten density (delta(max)). Interestingly, we found that delta(max) shifted toward higher values for coprecipitated catalysts (delta(max,COP) = 6.8 W at/nm(2)) compared with the impregnated ones (delta(max,IMP) = 5.2 W at/nm(2)). This has been ascribed to a better inherent capacity of the coprecipitation route for dispersing tungsten species on the ZrO2 surface, as inferred from modeled XPS data. This determines that both the formation of highly interconnected amorphous WO, domains required for the generation of catalytically active Bronsted acid sites and the onset of growth of inactive three-dimensional WO3 crystallites (ascertained by XRD and Raman) occur at higher tungsten surface densities in WZ solids generated by coprecipitation than in those obtained by impregnation. Despite the observed shift in delta(max), the two most active samples within each series displayed nearly the same intrinsic activity per total W atoms, suggesting that a similar nature and size for the supported active WO, domains should be attained by both impregnation and coprecipitation routes at delta = delta(max). Moreover, the method of preparation was found to affect the optical and electronic properties of the supported WOx species. Thus, coprecipitation provides WZ solids displaying a lower valence-conduction energy gap, as well as enhanced reducibility for the polytungstate domains due to an improved electronical linkage with the zirconia support, in opposition to a more isolated character of the WOx clusters generated by impregnation. (c) 2007 Elsevier Inc. All fights reserved.