A comparison of niobia- and vanadia-promoted Rh catalysts: The behaviors of RhMO sub 4 (M = Nb, V) on SiO sub 2 during calcination and reduction treatments

Journal Article · Mon Dec 31 23:00:00 EST 1990 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(91)90226-T· OSTI ID:5719684

Hu, Z; Wakasugi, T; Maeda, A; Kunimori, K; Uchijima, T ^[1]

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1. Univ. of Tsukuba (Japan)

The behaviors of Nb{sub 2}O{sub 5} and V{sub 2}O{sub 5} in Rh/SiO{sub 2} catalysts are compared by X-ray diffraction. For vanadia-promoted Rh/SiO{sub 2} catalyst, RhVO{sub 4} compound was formed exclusively by mild calcination at 773 K, and larger crystallites formed by calcination at 973 K. For niobia-promoted Rh/SiO{sub 2} catalysts, RhNbO{sub 4} compound was formed almost exclusively after the high-temperature calcination at 1173 K. The RhVo{sub 4}/SiO{sub 2} and RhNbO{sub 4}/SiO{sub 2} catalysts exhibit significant SMSI behaviors after high-temperature reduction, typically at 773 K; the capacity of H{sub 2} chemisorption diminished almost to zero and the catalytic activity for ethane hydrogenolysis was suppressed by ca. 3.5 orders of magnitude as compared with that after the low-temperature reduction that followed. Redispersion of rhodium was observed during the decomposition of compounds in H{sub 2}. Large RhNbO{sub 4} particles (139 {angstrom}) split to a number of smaller Rh particles (48 {angstrom}) after the H{sub 2} reduction at 773 K, and niovia promoter stabilized such Rh particles which exhibited almost no agglomeration during the thermal treatment in He even at 973 K. Similar redispersion was observed for RhVO{sub 4} compound, and large particles (190 {Angstrom}) split to smaller Th particles with mean size of 40 {angstrom} after the H{sub 2} reduction at 773 K. However, such Rh at much lower temperature than Nb{sub 2}O{sub 5}, with large Th particles being converted to RhVO{sub 4} compound even by the mild calcination at 773 K. This phenomenon may find practical application in the regeneration of sintered Rh catalyst.

• OSTI ID: 5719684
• Journal Information: Journal of Catalysis; (USA), Journal Name: Journal of Catalysis; (USA) Vol. 127:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

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AGGLOMERATION
ALKANES
CALCINATION
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISORPTION
COHERENT SCATTERING
CONFIGURATION INTERACTION
CRYSTAL STRUCTURE
DECOMPOSITION
DEHYDROGENATION
DIFFRACTION
ELEMENTS
ETHANE
FABRICATION
HEAT TREATMENTS
HYDROCARBONS
HYDROGEN
METALS
METHANATION
NIOBATES
NIOBIUM COMPOUNDS
NIOBIUM OXIDES
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
PROMOTERS
PYROLYSIS
REDUCTION
REFRACTORY METAL COMPOUNDS
REGENERATION
RHODIUM
RHODIUM COMPOUNDS
SCATTERING
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SINTERING
SORPTION
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
VANADATES
VANADIUM COMPOUNDS
VANADIUM OXIDES
X-RAY DIFFRACTION