ADSORPTION MECHANISM OF PHOSPHORIC-ACID ON GAMMA-ALUMINA
ADSORPTION MECHANISM OF PHOSPHORIC-ACID ON GAMMA-ALUMINA
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DOI：
10.1016/0021-9517(91)90163-x
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发表时间：
1991-12-01
影响因子：
7.3
通讯作者：
KYDD, RA
中科院分区：
文献类型：
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作者：
LEWIS, JM;KYDD, RA
用红外光谱研究了磷负载量在0-7wt%P范围内的P/Al_2O_3系列催化剂。经70 0℃处理后，γ-Al_2O_3的红外光谱中的OH伸展区有四种羟基被分解。添加磷(作为磷酸)导致除最碱性的羟基外，所有不同的羟基都减少了，在约1wt%P处增加到最大强度，在3676 cm−1处由于POH基团而产生的尖锐带也很容易分辨，并且该带的强度随着磷含量的增加而增加。在此基础上提出了磷酸在氧化铝上的吸附机理，即不同的氧化铝羟基优先与H3PO4反应，这取决于它们的碱度，直到临界表面浓度约为10×1013H3PO4 cm−2。在此浓度以上，H3PO4不仅与AlOH基团反应，而且还与POH基团反应生成聚磷酸盐物种。由于最基本的氧化铝羟基的带强度通过了最大值，因为在低磷负荷下，这些位置可能是由H3PO4与桥联和三桥氧化铝羟基反应产生的，但在较高负荷下不是通过这一过程形成的。
A series of P/Al2O3catalysts with phosphorus loadings in the range 0–7 wt% P has been investigated by infrared spectroscopy. After pretreatment at 700°C, four types of hydroxyls were resolved in the OH stretching region of the IR spectrum for γ-alumina. Addition of phosphorus (as phosphoric acid) resulted in a reduction of all the different hydroxyls with the exception of the most basic, which increased to a maximum intensity at around 1 wt% P. A sharp band at 3676 cm−1due to POH groups was also easily resolved, and this band increased in intensity with increasing phosphorus content. A mechanism for the adsorption of phosphoric acid on alumina is proposed on the basis of these results, whereby the different alumina hydroxyls react with H3PO4preferentially depending on their basicity up to a critical surface concentration of around 10 × 1013 H3PO4cm−2. Above this concentration H3PO4reacts not only with AIOH groups but also with POH groups to form polyphosphate species. The intensity of the band due to the most basic alumina hydroxyls passed through a maximum since, at low phosphorus loadings, these sites may be generated by the reaction of H3PO4with bridging and triply bridging alumina hydroxyls, but are not formed by this process at higher loadings.