All gas chromatography measurements were performed in triplicate, unless otherwise stated, and presented as the unweighted mean of the three measurements ± standard deviation (σ). PR Activity was calculated from the molar concentration of H2 present in the headspace gas normalised by time and reactor area or catalyst mass, and reported as 'areal activity' (µmolH 2 m -2 h -1 ) or 'specific activity' (µmolH 2 gCN x -1 h -1 ). Percent activity (%), used for comparisons within recyclability studies, is given by Ai/A0 where Ai is the PR activity of run i and A0 is the activity of the first run. σ was calculated as 𝜎 = √ ∑(𝑥-𝑥̅ ) 𝑛 -1 where 𝑛 is the number of replicates, 𝑥 is the value of a single measurement, and 𝑥̅ is the unweighted mean of the measurements. Standard deviation for bar charts is presented as a black error bar with flat caps, while for line graphs it is represented as a shaded area surrounding the line and data points.