Loridant S, Feche C, Essayem N, Figueras F
Institut de Recherches sur la Catalyse/CNRS, UPR 5401, 2 avenue A. Einstein, 69626 Villeurbanne, France.
J Phys Chem B. 2005 Mar 31;109(12):5631-7. doi: 10.1021/jp044494o.
W/ZrO(2) catalysts were prepared using anionic exchange of peroxotungstate species with hydroxyl groups of zirconium hydroxide at low pH. The solids were dried and calcined under air at 700 degrees C. Each step of this novel method of preparation was investigated by Raman spectroscopy. A reference sample was also prepared by incipient wetness impregnation of ZrO(2).n(H2O) with an ammonium tungstate solution and characterized throughout its preparation process. Complementary data were collected from X-ray diffraction, chemical analysis, surface area measurements, and thermal analysis. The Raman spectra of the H2WO4-H2O2 precursor solutions evidenced the presence of (W2O3(O2)4(H2O)2)(2-) dimers. These low-nuclearity species were exchanged with zirconium hydroxide at low pH. The Raman spectra of the dried solids did not reveal peroxotungstate species but were typical of tetrahedral (WO4)(2-) species. A slight agglomeration of W species was observed with an increase in the W content. However, for an equivalent W loading, a higher W dispersion was obtained by anionic exchange, compared to the impregnation method. Furthermore, a remarkable homogeneity of the exchanged samples was evidenced by the micro-Raman spectra. The in situ Raman spectra recorded during calcination characterized both crystalline phases and supported tungsten species. Significant modifications were observed during the calcination process. The exchanged and the impregnated samples, with the same W loading, evidenced a similar type of tungsten species with one W=O bond. However, their behavior during calcination up to 700 degrees C was different. This was attributed to different strengths of interaction with the support. Moreover, the spectra recorded after calcination on various points of the exchanged sample with a high W content revealed a better spatial homogeneity than the impregnated one.
采用过氧钨酸盐物种与低pH值下氢氧化锆的羟基进行阴离子交换的方法制备了W/ZrO₂催化剂。将固体在空气中于700℃干燥并煅烧。通过拉曼光谱对这种新颖制备方法的每一步进行了研究。还通过用钨酸铵溶液初湿浸渍ZrO₂·n(H₂O)制备了一个参比样品，并在其整个制备过程中进行了表征。从X射线衍射、化学分析、表面积测量和热分析收集了补充数据。H₂WO₄ - H₂O₂前驱体溶液的拉曼光谱证明了(W₂O₃(O₂)₄(H₂O)₂)²⁻二聚体的存在。这些低核物种在低pH值下与氢氧化锆进行了交换。干燥固体的拉曼光谱未显示过氧钨酸盐物种，而是典型的四面体(WO₄)²⁻物种。随着W含量的增加，观察到W物种有轻微团聚。然而，对于相同的W负载量，与浸渍法相比，通过阴离子交换获得了更高的W分散度。此外，微拉曼光谱证明了交换样品具有显著的均匀性。煅烧过程中记录的原位拉曼光谱表征了晶相和负载的钨物种。在煅烧过程中观察到了显著变化。具有相同W负载量的交换样品和浸渍样品证明了具有一个W = O键的类似类型的钨物种。然而，它们在高达700℃煅烧过程中的行为不同。这归因于与载体相互作用的不同强度。此外，在高W含量的交换样品的不同点上煅烧后记录的光谱显示出比浸渍样品更好的空间均匀性。
