Surface Characterization of Modified Aluminas: III. Surface-Features of PO4-Doped Al2O3
Surface Characterization of Modified Aluminas: III. Surface-Features of PO4-Doped Al2O3
复制标题
DOI：
10.1006/jcat.1995.1093
复制
发表时间：
1995-04
影响因子：
7.3
通讯作者：
C. Morterra;G. Magnacca;P. Maestri
中科院分区：
文献类型：
--
作者：
C. Morterra;G. Magnacca;P. Maestri
摘要用XRD、TEM和FTIR等方法对纯氧化铝和掺PO 4的氧化铝（P2 O 5 ~ 3%）在三种不同温度（773、1273和1473 K）下进行了比较。磷酸盐的加入并不改变低温尖晶石型氧化铝（γ-Al 2 O3）向高温尖晶石型氧化铝（δ，θ-Al 2 O3）的相变，而在一定程度上延缓了尖晶石型氧化铝向α-Al 2 O3的相变。磷酸盐仅对T ≥ 1450 K时获得的刚玉相的表面积和孔隙率有积极影响，其中颗粒形态相对于纯（α-Al 2 O3）发生了改变。PO 4 -的掺杂对表面的碱性和酸性有明显的影响.随着烧成温度的升高，氧化铝的弱碱性逐渐消失。磷酸盐的存在增加了氧化铝的强表面酸性：磷酸盐倾向于优选地聚集在规则晶面的平坦块上，并且这样做减少了规则晶面上存在的刘易斯酸位点（配位不饱和（cus）Al IV离子）的量并增加了其强度。同时，磷酸盐的存在使晶体学和/或配位缺陷构型中存在的强cus Al IV刘易斯酸位点的数量明显增加。当在T ≥ 1400 K处理的体系中发生向α-Al 2 O3的体相转变时，样品保持过渡氧化铝相的表面性质。研究人员认为磷酸盐对氧化铝起相稳定作用的不同观点需要一些修正和补充：磷酸盐在氧化铝载体上的积极作用意味着稳定更高量的强刘易斯酸位点，这在催化应用中最有可能是重要的。
Abstract Pure and PO 4 -doped aluminas (≍ 3% P 2 O 5 ), pretreated at three different temperatures (773, 1273, and 1473 K), have been compared by XRD, TEM, and FTIR spectroscopy. The addition of phosphates does not modify the phase transition of low-temperature spinel aluminas (γ-Al 2 O 3 ) to high-temperature spinel aluminas (δ, θ-Al 2 O 3 ), and delays somewhat the phase transition from spinel alumina to the corundum phase (α-Al 2 O 3 ). Phosphates have a positive effect on surface area and porosity only for the corundum phase obtained at T ≥ 1450 K, in which the particles morphology is modified with respect to pure (α-Al 2 O 3 ). The effect of PO 4 -doping is appreciable on surface basicity and acidity. The weak basicity of alumina is gradually eliminated, with increasing firing temperature. The presence of phosphates increases the strong surface acidity of aluminas: phosphates tend to collect preferably on the flat patches of regular crystal planes, and so doing decrease the amount and increase the strength of the Lewis acid sites (coordinatively unsaturated (cus) Al IV ions) present on the regular crystal planes. Meanwhile, the presence of phosphates produces an appreciable increase of the number of strong cus Al IV Lewis acid sites present in crystallographically and/or coordinatively defective configurations. When the bulk transition to α-Al 2 O 3 has occurred in systems treated at T ≥ 1400 K, the samples retain surface properties reminiscent of those of the transition alumina phases. The diverse opinion of investigators that phosphates act toward alumina as phase stabilizing needs some corrections and additions: the positive role of phosphates on the alumina support implies the stabilization of higher amounts of the strong Lewis acid sites that are most likely to be important in catalytic applications.