Selective catalytic hydrogenation of CH from plasma-driven CH coupling without extra heat: mechanistic insights from micro-kinetic modelling and reactor performance.

We study the selective catalytic hydrogenation of CH, the main product from non-oxidative CH coupling in gas-phase plasmas, to CH, a cornerstone of the global chemical industry, by experiments and temperature-dependent micro-kinetic modelling. The model is validated against new experimental data from a nanosecond pulsed plasma reactor integrated with a downstream catalytic bed consisting of Pd/AlO. We explore the effects of varying Pd loadings (0.1, 0.5, and 1 wt%) on the catalyst activity and the CH/CH product distribution. Consistent with the experimental data, our surface micro-kinetic model shows that while higher Pd loadings lower the catalyst activation temperature for CH conversion, they also induce over-hydrogenation to CH at lower temperatures and increase oligomerisation in the experiments, which are detrimental to the CH yield. The model also elucidates reaction mechanisms and pathways across different temperature regimes, expanding our understanding of the hydrogenation process beyond the experimental range. Besides highlighting the importance of optimising the metal loading to balance CH and CH selectivity, our findings demonstrate the effective implementation of post-plasma catalysis using a simple catalyst bed heated by hot gas from the plasma region. This study opens possibilities for testing different plasma sources, catalysts, gas flow magnitude and patterns, and catalyst bed-to-plasma distances.