Comparison of FeMn, FeMnNa and FeMnK Catalysts for the Preparation of Light Olefins from Syngas

Abstract

The influence of sodium and potassium promoters on the structure and reaction behavior of an FeMn catalyst toward light olefin synthesis from syngas was investigated by N2 adsorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), CO/CO2 temperature-programmed desorption (CO/CO2-TPD), Mössbauer spectroscopy (MES) and CO+H2 reaction. We found that an increase in manganese improves the dispersion of the active Fe component and light olefin selectivity; however, excessive enrichment with the Mn promoter on the catalyst surface suppresses CO conversion. Potassium and sodium inhibit the reduction of the catalyst in H2 and improve the adsorption of CO2 and CO because of the enhanced surface basicity of the catalysts. After reduction with syngas (nH 2 /nCO=20) and reaction with syngas (nH 2 /nCO=3.5), the analysis of the bulk structure was compared with those of the FeMn, FeMnNa, and FeMnK catalysts. The results show that FeCx is found in relatively high levels in the FeMnK 1932 LI Jiang-Bing et al.: Comparison of FeMn, FeMnNa and FeMnK Catalysts for the Preparation of Light Olefins No.10 2 Experimental 2.1 Catalyst preparation The catalysts were prepared by a combination of co-precipitation and impregnation method. A solution containing both Fe(NO3)3 and Mn(NO3)2 (Sinopharm Chemical reagent Co., Ltd, AR) in an appropriate ratio, as well as an individual solution of NH4OH (Sinopharm Chemical reagent Co., Ltd., AR) was prepared and maintained at 80°C in the precipitation reaction. The aqueous salt solution and NH4OH solution were introduced to an agitated vessel at the identical flow rate to hold the pH of a constant of 8.5± 0.1. The mixture solution was stirred for 4 h intensively and kept at 80°C during the precipitation process. After the precipitates were aged for 12 h, the suspension was filtered, washed thoroughly with deionized water, dried overnight at 110°C and then calcined at 500°C for 4 h in air. The calcined precipitates were impregnated with K2CO3 (Na2CO3 or nothing) (Sinopharm Chemical reagent Co., Ltd, AR) and the samples were dried at catalysts because of the stronger alkalinity and adsorbability of CO. However, Fischer-Tropsch synthesis (FTS) results indicate that sodium and potassium improved the selectivity toward light olefins. The best catalytic performance was achieved by the FeMnNa catalyst. Its CO conversion and light olefins selectivity were 96.2% and 30.5% (molar fraction), respectively.

Chemicals and Fuels from Biomass via Fischer–Tropsch Synthesis: A Route to Sustainability

“…These three steps can explain the documented higher olefin selectivity displayed by bulk and supported FeMnK catalysts. 165,166 Similar olefin selectivity was reported on FeK promoted with the reducible metal oxides: V, Nb, Pb, Sn and Bi. [167][168][169][170] Combined (Na, K) and S promotion of Fe-based FT catalysts has also been reported as displaying high selectivity to lower olefins.…”