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Abstract
AbstractThe influence of chromium compounds on the properties of cobalt molybdenum nitrides was studied. CoMoO4 obtained by precipitation from cobalt and molybdenum salts was modified by the addition of chromium(III) nitrate. A mixture of cobalt-molybdenum nitrides, Co2Mo3N and Co3Mo3N, was formed by ammonolysis of modified CoMoO4. The concentration of Co2Mo3N decreases with increasing chromium content. The specific surface area of cobalt molybdenum nitrides consisting of 2 wt% of Cr atoms increased by 50% in comparison to pure cobalt molybdenum nitrides. The catalytic activity of obtained catalysts in ammonia synthesis process decreases with rising of chromium concentration.
Highlights
Various forms of iron catalysts based on magnetite [1, 2] or wustite [3, 4] are still the most widely used in ammonia plants
The phase analysis of chromium-modified precursors indicates that all materials contain only cobalt molybdate hydrate, which corresponds with the CoMoO4×3/4 H2O structure reported elsewhere [16, 17]
Cobalt molybdate hydrate was transformed into a black product which was identified as a mixture of two crystallographic phases, both being cobalt molybdenum nitrides: Co3Mo3N [18] and Co2Mo3N [19]
Summary
Various forms of iron catalysts based on magnetite [1, 2] or wustite [3, 4] are still the most widely used in ammonia plants. The high energy consumption of the ammonia synthesis based on the iron catalysts is an incentive for the search of novel catalysts which will be effective at lower temperatures or under lower pressure. Theoretical studies have proven that cobalt molybdenum nitride, Co3Mo3N, is potentially the most active catalyst for ammonia synthesis [11]. Experiments have shown that cesium or potassium promoted cobalt molybdenum nitride is more active in the ammonia synthesis process than the industrial iron catalyst [6, 12, 13]. The admixture of alkali metals has a beneficial effect on the activity of the catalyst but at the expense of a less developed porous structure and lower thermal stability [12, 14]
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