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 · Tue Jan 01 00:00:00 EST 1991 · 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), Vol. 127:1; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
02 PETROLEUM
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBON MONOXIDE
METHANATION
ETHANE
DEHYDROGENATION
NIOBIUM OXIDES
CALCINATION
CATALYTIC EFFECTS
RHODIUM
VANADIUM OXIDES
AGGLOMERATION
CATALYST SUPPORTS
CATALYSTS
CHEMISORPTION
CONFIGURATION INTERACTION
CRYSTAL STRUCTURE
HEAT TREATMENTS
HYDROGEN
NIOBATES
PROMOTERS
REDUCTION
REGENERATION
RHODIUM COMPOUNDS
SILICON OXIDES
SINTERING
VANADATES
X-RAY DIFFRACTION
ALKANES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
DECOMPOSITION
DIFFRACTION
ELEMENTS
FABRICATION
HYDROCARBONS
METALS
NIOBIUM COMPOUNDS
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
PYROLYSIS
REFRACTORY METAL COMPOUNDS
SCATTERING
SEPARATION PROCESSES
SILICON COMPOUNDS
SORPTION
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
VANADIUM COMPOUNDS
010408* - Coal
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020400 - Petroleum- Processing
400201 - Chemical & Physicochemical Properties