Alkali effects on molybdenum oxide catalysts for the oxidative dehydrogenation of propane

被引:112
作者
Chen, KD
Xie, SB
Bell, AT [1 ]
Iglesia, E
机构
[1] Univ Calif Berkeley, EO Lawrence Berkeley Lab, Div Chem Sci, Berkeley, CA 94720 USA
[2] Univ Calif Berkeley, EO Lawrence Berkeley Lab, Div Mat Sci, Berkeley, CA 94720 USA
[3] Univ Calif Berkeley, Dept Chem Engn, Berkeley, CA 94720 USA
关键词
D O I
10.1006/jcat.2000.3025
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
The effects of alkali oxides on the structure and on the catalytic behavior of MoOx/ZrO2 were examined for the oxidative dehydrogenation (ODH) of propane. X-ray diffraction, Raman and X-ray absorption spectroscopy, and estimates of the MoOx surface density are consistent with the predominant presence of two-dimensional polymolybdate domains in samples with similar to4 Mo/nm(2) surface density and (alkali/Mo)(at.) ratios of 0-0.2 treated in air at 773 K. The presence of alkali (Cs, K, Li) did not affect the structure of MoOx domains, but influenced their electronic and catalytic properties. Propane ODH turnover rates decreased monotonically with increasing A:Mo atomic ratio and with increasing basicity of the alkali oxide (Cs > K > Li). These basic oxides inhibit the initial reduction of MoOx in Hz by strengthening Mo-O bonds and increasing reduction activation energies. As a result, rate-determining C-H bond activation steps, which involve the local reduction of Mo6+ centers, and the overall ODH catalytic sequence proceed more slowly when alkali oxides modify the MoOx domains. The ratio of the rate constant for primary propane combustion (k(2)) to that for propane ODH (k(1)) is small (similar to0.1) and it increased slightly with increased alkali content. The ratio of the propene combustion rate constant (k(3)) to the propane ODH rate constant (k(1)) is large (15-25); it decreased with the addition of small amounts of alkali (alkali/Mo similar to 0.05) and then remained constant at higher alkali contents. The stronger inhibition of secondary propene combustion reactions relative to that of primary ODH steps reflects the weaker Lewis acidity of Mo6+ cations modified by the strongly basic alkali oxide species. These effects decrease the binding energy of propene on the sites required for C-H bond activation of both propene and propane. They also account for the lower reaction rates and for the higher selectivity observed at a given propane conversion on alkali-modified MoOx ODH catalysts. (C) 2000 Academic Press.
引用
收藏
页码:244 / 252
页数:9
相关论文
共 32 条
  • [21] OXIDATIVE DEHYDROGENATION OF LOWER ALKANES ON VANADIUM OXIDE-BASED CATALYSTS - THE PRESENT STATE-OF-THE-ART AND OUTLOOKS
    MAMEDOV, EA
    CORBERAN, VC
    [J]. APPLIED CATALYSIS A-GENERAL, 1995, 127 (1-2) : 1 - 40
  • [22] ZIRCONIA AS A SUPPORT FOR CATALYSTS - EVOLUTION OF THE TEXTURE AND STRUCTURE ON CALCINATION IN AIR
    MERCERA, PDL
    VANOMMEN, JG
    DOESBURG, EBM
    BURGGRAAF, AJ
    ROSS, JRH
    [J]. APPLIED CATALYSIS, 1990, 57 (01): : 127 - 148
  • [23] Raman spectroscopy of monolayer-type catalysts: Supported molybdenum oxides
    Mestl, G
    Srinivasan, TKK
    [J]. CATALYSIS REVIEWS-SCIENCE AND ENGINEERING, 1998, 40 (04): : 451 - 570
  • [24] OHNO T, 1987, J CHEM SOC FARADAY T, V83, P1761
  • [25] FORMATION OF THE MO-VI SURFACE PHASE ON MOOX/ZRC2 CATALYSTS
    PRINETTO, F
    CERRATO, G
    GHIOTTI, G
    CHIORINO, A
    CAMPA, MC
    GAZZOLI, D
    INDOVINA, V
    [J]. JOURNAL OF PHYSICAL CHEMISTRY, 1995, 99 (15) : 5556 - 5567
  • [26] A CORRECTED PROCEDURE AND CONSISTENT INTERPRETATION FOR TEMPERATURE-PROGRAMMED REDUCTION OF SUPPORTED MOO3
    REGALBUTO, JR
    HA, JW
    [J]. CATALYSIS LETTERS, 1994, 29 (1-2) : 189 - 207
  • [27] RESSLER T, 1998, WINXAS97
  • [28] LIGAND K-EDGE X-RAY-ABSORPTION SPECTROSCOPY AS A PROBE OF LIGAND-METAL BONDING - CHARGE DONATION AND COVALENCY IN COPPER-CHLORIDE SYSTEMS
    SHADLE, SE
    HEDMAN, B
    HODGSON, KO
    SOLOMON, EI
    [J]. INORGANIC CHEMISTRY, 1994, 33 (19) : 4235 - 4244
  • [29] Sloczynski J, 1997, POL J CHEM, V71, P1585
  • [30] Structures of molybdenum species in silica-supported molybdenum oxide and alkali-ion-modified silica-supported molybdenum oxide
    Takenaka, S
    Tanaka, T
    Funabiki, T
    Yoshida, S
    [J]. JOURNAL OF PHYSICAL CHEMISTRY B, 1998, 102 (16): : 2960 - 2969