SILICA-ALUMINA-SUPPORTED MO OXIDE CATALYSTS - GENESIS AND DEMISE OF BRONSTED-LEWIS ACIDITY
SILICA-ALUMINA-SUPPORTED MO OXIDE CATALYSTS - GENESIS AND DEMISE OF BRONSTED-LEWIS ACIDITY
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DOI：
10.1006/jcat.1995.1021
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发表时间：
1995-01-01
影响因子：
7.3
通讯作者：
MIRANDA, R
中科院分区：
文献类型：
--
作者：
RAJAGOPAL, S;MARZARI, JA;MIRANDA, R
利用化学吸附吡啶的漫反射FTIR光谱研究了催化剂组成和处理对Bronsted和Lewis酸含量的影响。该研究包括含有2、4、8和12 wt% MoO3的氧化和还原性Mo氧化物催化剂。载体为7种二氧化硅-氧化铝，SiO2含量在0 ~ 100%之间。在200℃氦气流下采集红外光谱，1545和1450 cm（-1）吸光度带下的面积分别与Bronsted和Lewis酸位的浓度有关。结果表明：随着载体中SiO2含量的增加，Bronsted / Lewis酸浓度的比值（B/L）增大，SiO2:Al2O3 = 75:25 wt%时达到最大值；对于Al2O3和富铝载体，随着MoO3的增加，B/L不断增加，这是由于新的Bronsted酸位点的生成和Lewis酸位点的减少。对于富含二氧化硅的支架，B/L在2 wt% MoO3时达到最大值，然后随着MoO3负载的增加而略有下降。MoO3负载高达12 wt%的SiO2载体在无水环境中不含任何Bronsted酸性。负载型催化剂在500℃的氢气中还原后，无论SiO2含量和MoO3的含量如何，B/L比都有所下降。一个包含氧化钼四面体表面种类的结构模型解释了结果。(C) 1995学术出版社，Inc。
Diffuse reflectance FTIR spectroscopy of chemisorbed pyridine was used to investigate the influence of catalyst composition and treatment on the content of Bronsted and Lewis acidity. This investigation included oxidic and reduced Mo oxide catalysts containing 2, 4, 8, and 12 wt% MoO3. The supports were seven silica-aluminas of composition between 0 and 100 wt% SiO2. The IR spectra were collected at 200 degrees C under helium flow, and the areas under the 1545 and 1450 cm(-1) absorbance bands were related to the concentration of Bronsted and Lewis acid sites, respectively. The results indicate that the ratio of Bronsted to Lewis acid concentration (B/L) increases with SiO2 content in the support and reaches a maximum for SiO2:Al2O3 = 75:25 wt%. For Al2O3 and alumina-rich supports B/L increases continuously with MoO3 loading because of the generation of new Bronsted acid sites and decrease of Lewis acid sites. For silica-rich supports, the B/L has a maximum at 2 wt% MoO3 and then decreases slightly as MoO3 loading is increased. The SiO2 support with MoO3 loading up to 12 wt% does not contain any Bronsted acidity in water-free environment. Upon reduction of the supported catalysts at 500 degrees C in hydrogen, the B/L ratio decreases irrespective of SiO2 content and MoO3 loading. A structural model that includes tetrahedral surface species of Mo oxide explains the results. (C) 1995 Academic Press, Inc.