Surface and catalytic properties of MoO{sub 3}/Al{sub 2}O{sub 3} system doped with Co{sub 3}O{sub 4}

Journal Article · Tue Jul 12 00:00:00 EDT 2005 · Materials Research Bulletin

DOI:https://doi.org/10.1016/j.materresbull.2005.04.003· OSTI ID:20889792

Zahran, A A ^[1]; Shaheen, W M ^[2]; El-Shobaky, G A ^[2]

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1. Chemistry Department, Faculty of Science, Ain Shams University, Cairo (Egypt)
2. Department of Physical Chemistry, National Research Center, Cairo (Egypt)

Thermal solid-solid interactions in cobalt treated MoO{sub 3}/Al{sub 2}O{sub 3} system were investigated using X-ray powder diffraction. The solids were prepared by wet impregnation method using Al(OH){sub 3}, ammonium molybdate and cobalt nitrate solutions, drying at 100 deg. C then calcination at 300, 500, 750 and 1000 deg. C. The amount of MoO{sub 3}, was fixed at 16.67 mol% and those of cobalt oxide were varied between 2.04 and 14.29 mol% Co{sub 3}O{sub 4}. Surface and catalytic properties of various solid samples precalcined at 300 and 500 deg. C were studied using nitrogen adsorption at -196 deg. C, conversion of isopropanol at 200-500 deg. C and decomposition of H{sub 2}O{sub 2} at 30-50 deg. C. The results obtained revealed that pure mixed solids precalcined at 300 deg. C consisted of AlOOH and MoO{sub 3} phases. Cobalt oxide-doped samples calcined at the same temperature consisted also of AlOOH, MoO{sub 3} and CoMoO{sub 4} compounds. The rise in calcination temperature to 500 deg. C resulted in complete conversion of AlOOH into very poorly crystalline {gamma}-Al{sub 2}O{sub 3}. The further increase in precalcination temperature to 750 deg. C led to the formation of Al{sub 2}(MoO{sub 4}){sub 3}, {kappa}-Al{sub 2}O{sub 3} besides CoMoO{sub 4} and un-reacted portion of Co{sub 3}O{sub 4} in the samples rich in cobalt oxide. Pure MoO{sub 3}/Al{sub 2}O{sub 3} preheated at 1000 deg. C composed of MoO{sub 3}-{alpha}Al{sub 2}O{sub 3} solid solution (acquired grey colour). The doped samples consisted of the same solid solution together with CoMoO{sub 4} and CoAl{sub 2}O{sub 4} compounds. The increase in calcination temperature of pure and variously doped solids from 300 to 500 deg. C increased their specific surface areas and total pore volume which suffered a drastic decrease upon heating at 750 deg. C. Doping the investigated system with small amounts of cobalt oxide (2.04 and 4 mol%) followed by heating at 300 and 500 deg. C increased its catalytic activity in H{sub 2}O{sub 2} decomposition. This increase, measured at 300 deg. C, attained 25.4- and 12.9-fold for the solids precalcined at 300 and 500 deg. C, respectively. The increase in the amount of dopant added above this limit decreased the catalytic activity which remained bigger than those of un-treated catalysts. On the other hand, the doping process decreased the catalytic activity of treated solids in isopropanol conversion especially the catalysts precalcined at 300 deg. C. This treatment modified the selectivities of treated solids towards dehydration and dehydrogenation of reacted alcohol. The activation energies of H{sub 2}O{sub 2} decomposition were determined for pure and variously doped solids. The results obtained were discussed in light of induced changes in chemical composition and surface properties of the investigated system due to doping with cobalt oxide.

• OSTI ID: 20889792
• Journal Information: Materials Research Bulletin, Vol. 40, Issue 7; Other Information: DOI: 10.1016/j.materresbull.2005.04.003; PII: S0025-5408(05)00114-5; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ADSORPTION
ALUMINIUM HYDROXIDES
ALUMINIUM OXIDES
CALCINATION
CATALYSTS
CHEMICAL COMPOSITION
COBALT
COBALT NITRATES
COBALT OXIDES
DEHYDRATION
DOPED MATERIALS
HYDROGEN PEROXIDE
MOLYBDATES
MOLYBDENUM OXIDES
SOLID SOLUTIONS
SPECIFIC SURFACE AREA
SURFACE PROPERTIES
URANIUM NITRIDES
X-RAY DIFFRACTION