Unraveling the role of support surface hydroxyls and its effect on the selectivity of C2 species over Rh/γ-Al2O3 catalyst in syngas conversion: A theoretical study

Abstract The supported Rh-based catalysts exhibit the excellent catalytic performances for syngas conversion to C 2 species. In this study, all possible elementary steps leading to C 2 species from syngas have been explored to identify the role of support and its surface hydroxyls over Rh/γ-Al 2 O 3 catalyst; Here, the results are obtained using density functional theory (DFT) method. Two models: Rh4 cluster supported on the dry γ-Al 2 O 3 (110) surface, D(Rh4), and on the hydroxylated γ-Al 2 O 3 (110) surface, H(Rh4), have been used to model Rh/γ-Al 2 O 3 catalyst. Our results show that CO prefers to be hydrogenated to CHO, subsequently, starting from CHO species, CH and CH 2 species are the dominate monomers among CH x ( x = 1–3) species rather than CH 3 and CH 3 OH on D(Rh4) and H(Rh4) surfaces, suggesting that γ-Al 2 O 3 -supported Rh catalyst exhibits the high selectivity towards CH x formation compared to the pure Rh catalyst. On the other hand, D(Rh4) is more favorable for C 2 hydrocarbon (C 2 H 2 ) formation, whereas H(Rh4) surface easily produces C 2 hydrocarbon (C 2 H 2 ) and C 2 oxygenates (CHCO,CH 2 CHO), indicating that the surface hydroxyls of support can affect the selectivity of C 2 species over Rh/γ-Al 2 O 3 catalyst in syngas conversion. Moreover, compared to the pure Rh(111) surface, Rh/γ-Al 2 O 3 catalyst can achieve the excellent catalytic performances for syngas conversion to C 2 species.