Microkinetic study of oxygenate and hydrocarbon formation from syngas on rhodium and cobalt surfaces: Effect of site structure on catalytic cycles

Rh and Co-based catalysts are known to selectively convert syngas into oxygenates and hydrocarbons under high temperature and pressure conditions. Insights into the mechanistic cycle, structure-reactivity and structureselectivity correlations required for catalyst design are however, lacking. Herein, we validate reaction networks on Rh and Co surfaces with theoretical and experimental efforts and investigate active site requirements. Microkinetic models are used to investigate competitive routes for forming oxygenates and hydrocarbons on both flat and stepped Rh and Co surfaces. Direct CO dissociation is promoted on defect sites and an alternative hydroxyl methylene based route is kinetically favored for CO activation on flat surfaces for both Rh and Co. Methylene addition to R-CH2 and CO is deduced to be the precursor for long chain hydrocarbon and C2-oxygenate formation respectively. Our results indicate that catalytic routes are preferred on step sites irrespective of the reaction considered.