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Study of chromia alumia catalysts
Author(s) -
Mathur Indresh,
Bakhshi Narendran N.,
Mathews Joseph F.
Publication year - 1980
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.5450580509
Subject(s) - chromia , catalysis , crystallite , inorganic chemistry , chromium , chemisorption , iodometry , chemistry , specific surface area , materials science , metallurgy , organic chemistry
The purpose of this study was to investigate the effect of increasing chromium concentration on the activity and physical properties of chromia/alumina catalysts. The catalysts were prepared by impregnating η‐alumina support in various concentrations of chromic acid solution and were finally calcined in air. A variety of physical‐chemical properties of the catalysts were studied. These included BET surface area, pore volume, metal concentration, x‐ray diffraction studies, oxidation states using EPR, surface oxidation (excess oxygen) measurement by iodometric titration, metal area measurement and crystallite size determination. Decomposition of hydrogen peroxide was used to determine the activity of various catalysts. A correlation of catalytic activity with crystallite size indicated that both, activity per unit chromia area and activity per g of catalyst were maximum at a crystallite size of 3.7 mm. Also, the activity per unit chromia area is maximum when chromia is deposited 3‐4 layers thick. In contradiction to the view put forth in the literature, this study indicates (on the basis of excess oxygen and chemisorption measurement) that not only is all of the top chromium oxidized to Cr 6 but that the oxidation also takes place in the sub‐surface layer(s).