Theoretical study of CO adsorption and activation on h-Fe7C3[formula omitted] for Fischer-Tropsch synthesis

Abstract

The h-Fe7C3 phase of iron carbide catalysts have been gained wide attentions for the impressive intrinsic activity in typical medium-temperature Fischer-Tropsch synthesis (FTS). In this study, the adsorption and activation of CO on h-Fe7C3(11¯1) surface were studied by density functional theory (DFT) calculations to understand the FTS mechanism. Calculated results showed that the B5 site on h-Fe7C3(11¯1) surface demonstrates excellent intrinsic activity for CO adsorption and activation. The route CO+H—HCO—CH+O—CH2+O is identified as a preferred CO activation pathway on the B5 site for h-Fe7C3(11¯1) surface with the effective energy barrier of 1.380 eV. Furthermore, the FTS reaction mechanism with the surface carbon atoms involved was explored preliminarily, which confirms that the surface carbons can undergo hydrogenation reaction to produce the CH species feasibly, and meanwhile, the carbon vacant sites are generated. Subsequently, the influences of carbon vacancy on the CO adsorption and activation on (11¯1) were studied. It was observed that the vacancy surface is more conducive to the elementary reactions of CO adsorbed on the B5 site. In particular, CO can be easily dissociated on the VC2 surface with energy barrier of 0.77 eV.