Cobalt rhenium ammonia synthesis catalysts which are highly active at ambient pressure
and 400Β°C under N2/H2 (1:3) have been prepared without an ammonolysis step. For all
highly active cobalt rhenium materials the post-reaction powder XRD patterns reveal there
is a shift of their Re reflections to a slightly higher 2ΞΈ angle. This shift is due to mixing of
cobalt and rhenium within the material and this interaction was confirmed via XAS
analysis. The XRD patterns of cobalt rhenium materials with minimum ammonia synthesis
activity resemble the reference pattern for metallic rhenium and show no signs of
bimetallic mixing. Cobalt rhenium materials have been benchmarked against CsNO3 doped
Ru/Al2O3 materials.
Pre-treatments under N2/H2 (1:3), Ar/H2 (1:3), N2 and Ar gas mixtures have been shown to
influence catalytic performance, with the first resulting in an instantly active material,
whereas, the others lead to a 20 minute induction period prior to the development of
activity upon switching to an ammonia synthesis feedstream. Also, pre-treatment in N2/H2
(1:3) resulted in a material with higher catalytic activity.
CoRe4 was studied via in situ XAS/XRD to elucidate the reducibility and local
environment of the two metals during reaction conditions. The phases present in the CoRe4
catalyst during ammonia production are largely bimetallic Co-Re and also monometallic
Co and Re species formed during both pre-treatments. It was found the presence of
nitrogen during the pre-treatment strongly promotes the mixing of the both Co and Re.
Preliminary tests were also conducted on cobalt rhenium catalysts for ammonia
decomposition and the materials were found to have high activity. To the author's
knowledge this is the first report of low surface area materials being particularly active for
this reaction
