SILICA-ALUMINA-SUPPORTED MO OXIDE CATALYSTS - GENESIS AND DEMISE OF BRONSTED-LEWIS ACIDITY

被引:122
作者
RAJAGOPAL, S [1 ]
MARZARI, JA [1 ]
MIRANDA, R [1 ]
机构
[1] UNIV LOUISVILLE,DEPT CHEM ENGN,LOUISVILLE,KY 40292
关键词
D O I
10.1006/jcat.1995.1021
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
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.
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页码:192 / 203
页数:12
相关论文
共 59 条
[1]  
BAIRD MC, 1968, PROGR INORGANIC CHEM, V9, P28
[2]   NATURE OF ACIDIC SITES ON SILICA-ALUMINA . A REVALUATION OF RELATIVE ABSORPTION COEFFICIENTS OF CHEMISORBED PYRIDINE [J].
BASILA, MR ;
KANTNER, TR .
JOURNAL OF PHYSICAL CHEMISTRY, 1966, 70 (05) :1681-&
[3]   NATURE OF ACIDIC SITES ON SILICA-ALUMINA . CHARACTERIZATION BY INFRARED SPECTROSCOPIC STUDIES OF TRIMETHYLAMINE + PYRIDINE CHEMISORPTION [J].
BASILA, MR ;
RHEE, KH ;
KANTNER, TR .
JOURNAL OF PHYSICAL CHEMISTRY, 1964, 68 (11) :3197-&
[4]   INFRARED STUDY OF THE SURFACE-PROPERTIES OF METAL-OXIDES .2. INTERACTION OF AMMONIA WITH THE SURFACE OF FE2O3, ZNO, MOO3, AND V2O5 [J].
BELOKOPYTOV, YV ;
KHOLYAVENKO, KM ;
GEREI, SV .
JOURNAL OF CATALYSIS, 1979, 60 (01) :1-7
[5]  
BENESI HA, 1978, ADV CATAL, V27, P97
[6]   BRONSTED ACID SITES IN TRANSITION-METAL OXIDE CATALYSTS - MODELING OF STRUCTURE, ACID STRENGTHS, AND SUPPORT EFFECTS [J].
BERNHOLC, J ;
HORSLEY, JA ;
MURRELL, LL ;
SHERMAN, LG ;
SOLED, S .
JOURNAL OF PHYSICAL CHEMISTRY, 1987, 91 (06) :1526-1530
[7]   STRUCTURE AND CATALYTIC ACTIVITY OF MOO3.SIO2 SYSTEMS .1. SOLID-STATE PROPERTIES [J].
CASTELLAN, A ;
BART, JCJ ;
VAGHI, A ;
GIORDANO, N .
JOURNAL OF CATALYSIS, 1976, 42 (01) :162-172
[8]   STATE OF MOLYBDENUM IN SILICA-MOLYBDENUM OXIDE CATALYSTS [J].
CHUMACHENKO, NN ;
YURIEVA, TM ;
TARASOVA, DV ;
ALESHINA, GI .
REACTION KINETICS AND CATALYSIS LETTERS, 1980, 14 (01) :87-91
[9]   ACIDIC PROPERTIES OF BINARY OXIDE CATALYSTS .2. MOSSBAUER-SPECTROSCOPY AND PYRIDINE ADSORPTION FOR IRON SUPPORTED ON MAGNESIA, ALUMINA, AND TITANIA [J].
CONNELL, G ;
DUMESIC, JA .
JOURNAL OF CATALYSIS, 1986, 102 (01) :216-233
[10]  
DUNKEN H, 1965, Z CHEM, V5, P432