MnO_x promotional effects on olefins synthesis directly from syngas over bimetallic Fe‐MnO_x/SiO₂ catalysts

Abstract

The direct synthesis of lower olefins via the Fischer‐Tropsch reaction (FTO) has been performed over a series of Fe‐MnOx/SiO2 catalysts. The addition of MnOx could improve the dispersion of iron species, and promote the reduction of iron oxide during the activation and subsequent carburization. Moreover, the results of characterization demonstrated that MnOx could enhance the surface basicity of the catalysts due to electronic effects and promote the formation of iron carbides. For the first time, the intrinsic power‐law kinetics for FTO was obtained for both Fe20/SiO2 and Fe20‐Mn1/SiO2 catalysts. Kinetic parameters and structure characterizations indicated that MnOx could facilitate the CO dissociation on the catalyst surface, thus enhancing the adsorption strength and capacity of surface carbonaceous intermediates. The weak hydrogenation of carbonaceous species would boost the selectivities toward lower olefins. Finally, a plausible mechanism for FTO, involving the promotional effects of MnOx on Fe, has been proposed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4451–4464, 2017

Cobalt‐Iron‐Manganese Catalysts for the Conversion of End‐of‐Life‐Tire‐Derived Syngas into Light Terminal Olefins

“…However, for these Co‐Mn/TiO 2 FTS catalysts, it was already found that the role is complex as MnO x was considered to be both a structural and electronic promotor, resulting in higher metal dispersions and lower hydrogenation activity. These findings are in line with a recent paper of Han and co‐workers who found that the addition of MnO x to a Fe/SiO 2 FTS catalyst increased the reaction rate (by for example, enhancing the dissociation adsorption of CO) and the olefin selectivity . Furthermore, these authors observed that MnO x improved the dispersion of supported FeO x , facilitating its reduction and enhanching the carburization of FeO x .…”

“…[55,56,64,65] However, for these Co-Mn/TiO 2 FTS catalysts, it was already found that the role is complex as MnO x was considered to be both a structurala nd electronic promotor,r esulting in higher metal dispersions and lower hydrogenation activity.T hese findings are in line with ar ecent paper of Han and co-workersw ho found that the addition of MnO x to aF e/SiO 2 FTS catalyst increasedt he reactionrate (by for example, enhancing the dissociation adsorption of CO) and the olefin selectivity. [66] Furthermore, these authors observed that MnO x improved the dispersion of supported FeO x ,f acilitating its reduction and enhanching the carburizationo fF eO x .I nterestingly,X iaohaoa nd coworkers have recently investigated the addition of MnO x to a Co/SiO 2 FTS catalyst. [67] These authors found that MnO x affects the formation of Co 2 C, ap hase which has been recently shown to have ah igh selectivity towards lower olefins.…”

Hydrogenation of CO2 to Olefins over Iron-Based Catalysts: A Review

“…Even a small amount of MnO x can improve the dispersion of FeO x and the carburization of Fe [88,101]. Kinetic studies further demonstrated the effect of MnO x on promoting CO dissociation and monomer formation, reducing the effective sites of H 2 dissociation, olefin reabsorption and secondary hydrogenation [102], which promoted the generation of low-carbon olefins. Unlike CO hydrogenation, Kuei et al [103] concluded that manganese showed little promotion effect on the selectivity of olefinic hydrocarbons in CO 2 hydrogenation.…”

Unravelling the metal–support interactions in χ-Fe5C2/MgO catalysts for olefin synthesis directly from syngas

“…Our previous work has demonstrated that H 2 could adsorb on the surface competitively with CO and other species. 63 Therefore, the adsorption of H 2 on the surface is expected to be weakened, given that CO adsorption is promoted on χ-Fe 5 C 2 /MgO. Li et al 64 found that H 2 adsorption on surface Fe sites could be suppressed with the addition of MgO and became stronger with the increase of the MgO amount.…”