Cobalt rhenium catalysts for ammonia synthesis

摘要

Cobalt rhenium ammonia synthesis catalysts which are highly active at ambient pressureudand 400°C under N2/H2 (1:3) have been prepared without an ammonolysis step. For alludhighly active cobalt rhenium materials the post-reaction powder XRD patterns reveal thereudis a shift of their Re reflections to a slightly higher 2θ angle. This shift is due to mixing ofudcobalt and rhenium within the material and this interaction was confirmed via XASudanalysis. The XRD patterns of cobalt rhenium materials with minimum ammonia synthesisudactivity resemble the reference pattern for metallic rhenium and show no signs ofudbimetallic mixing. Cobalt rhenium materials have been benchmarked against CsNO3 dopedudRu/Al2O3 materials.udPre-treatments under N2/H2 (1:3), Ar/H2 (1:3), N2 and Ar gas mixtures have been shown toudinfluence catalytic performance, with the first resulting in an instantly active material,udwhereas, the others lead to a 20 minute induction period prior to the development ofudactivity upon switching to an ammonia synthesis feedstream. Also, pre-treatment in N2/H2ud(1:3) resulted in a material with higher catalytic activity.udCoRe4 was studied via in situ XAS/XRD to elucidate the reducibility and localudenvironment of the two metals during reaction conditions. The phases present in the CoRe4udcatalyst during ammonia production are largely bimetallic Co-Re and also monometallicudCo and Re species formed during both pre-treatments. It was found the presence ofudnitrogen during the pre-treatment strongly promotes the mixing of the both Co and Re.udPreliminary tests were also conducted on cobalt rhenium catalysts for ammoniauddecomposition and the materials were found to have high activity. To the author'sudknowledge this is the first report of low surface area materials being particularly active forudthis reaction.