Lebarbier Vanessa, Clet Guillaume, Houalla Marwan
Laboratoire Catalyse et Spectrochimie, UMR CNRS 6506, ENSICAEN-Université de Caen, 6 Bd. du Maréchal Juin, 14050 Caen Cedex, France.
J Phys Chem B. 2006 Nov 16;110(45):22608-17. doi: 10.1021/jp064202e.
Two series of WO(x)/TiO(2) catalysts, containing W surface densities up to 4.4 W atoms/nm(2), were prepared by pore volume impregnation of two different supports, titanium oxyhydroxide (amorphous) or titanium oxide (crystallized, 100% anatase). The influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performances were examined. The texture and structure of the catalysts were investigated by Brunauer-Emmett-Teller measurements, X-ray diffraction (XRD), and Raman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of titanium oxide, XRD and Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. CO and lutidine adsorption, followed by infrared spectroscopy, showed an increase in the strength and abundance of Brønsted acid sites (measured after lutidine desorption at 573 K) with the W surface density above a threshold of 1.3 W atoms/nm(2). The development of Brønsted acidity correlated with the evolution of the infrared bands attributed to polymerized W species. A direct relationship was observed between the concentration of Brønsted acid sites and the catalytic activity for 2-propanol dehydration. Catalytic activity, for n-hexane isomerization, appears to be associated with the presence of highly condensed W species. The catalysts synthesized by impregnation of titanium oxyhydroxide exhibited a comparable behavior. Hence, for a given W surface density, the W surface structure, concentration of Brønsted acid sites, and catalytic performances were similar. Thus, no significant effect of the initial form of the support (titanium oxyhydroxide versus titanium oxide; 100% anatase) was evidenced.
通过对两种不同载体（氢氧化氧钛（无定形）或氧化钛（结晶，100%锐钛矿））进行孔体积浸渍，制备了两组WO(x)/TiO(2)催化剂，其钨表面密度高达4.4个钨原子/纳米²。研究了钨表面密度和载体性质对表面结构、酸度发展及催化性能的影响。通过布鲁诺尔-埃米特-泰勒测量、X射线衍射（XRD）、拉曼光谱和红外光谱研究了催化剂的织构和结构。对2-丙醇脱水和正己烷异构化反应测试了催化活性。对于通过浸渍氧化钛获得的催化剂，XRD和拉曼结果表明钨以表面相形式存在。红外光谱表明，随着钨表面密度的增加，钨物种的聚合度增加。一氧化碳和2,6-二甲基吡啶吸附后进行红外光谱分析表明，当钨表面密度高于1.3个钨原子/纳米²的阈值时，布朗斯台德酸位点的强度和数量（在573K下2,6-二甲基吡啶脱附后测量）增加。布朗斯台德酸度的发展与归因于聚合钨物种的红外波段的演变相关。观察到布朗斯台德酸位点的浓度与2-丙醇脱水的催化活性之间存在直接关系。对于正己烷异构化反应，催化活性似乎与高度缩合的钨物种的存在有关。通过浸渍氢氧化氧钛合成的催化剂表现出类似的行为。因此，对于给定的钨表面密度，钨的表面结构、布朗斯台德酸位点浓度和催化性能相似。因此，未证明载体的初始形式（氢氧化氧钛与氧化钛；100%锐钛矿）有显著影响。
