Effects of promoters (Mn, Mg, Co and Ni) on the Fischer-Tropsch activity and selectivity of KCuFe/mesoporous-alumina catalyst

Fischer-Tropsch synthesis (FTS) is one of the promising technologies to produce liquid fuels and fine chemicals from coal, natural gas and biomass. Significant improvements in reactor technology and catalyst development are the focus of research in this area. In this work, the effects of 1.0 wt% promotor such as Mn, Mg, Co and Ni on the FTS activity and selectivity of mesoporous alumina supported KCuFe catalyst were studied. All synthesized promoted catalysts were characterized using BET, XRD, H-2-TPR, XPS, TEM and XANES. The FTS reaction was carried out in a fixed bed reactor at 270 degrees C, 300 psi, 2000 h(-1) and H-2/CO= 1.25. In this work, the Ni-promoted catalyst showed the highest methane selectivity (similar to 29 %). The Co-promoted catalyst showed the least Olefins/Paraffins (O/P) ratio and a similar to 5% increase in methane selectivity. Mg-promoted catalyst performed average but better than Ni and Co-promoted catalysts. However, Mn-supported catalyst outperformed Mg, Ni and Co-promoted catalysts and resulted in higher C-5+ selectivity along with a marginal increase in CO conversion. The similar to 5%, 2%, and 2% decline in CO2, CH4 and C-2-C-4 selectivities were also registered upon the addition of Mn promotor. The improvement in FTS activity and selectivity of Mn-promoted catalyst is related to the increase in iron dispersion and reducibility, as seen during H-2-TPR, XPS and XANES analyses. The presence of Mn+3 and Mn+4, as confirmed by Mn 2p XPS and Mn K-edge XANES, indicates that the interaction at the electronic level between manganese and iron has contributed to improved performance. This study concludes that Mn is the most effective promotor for the synthesized mesoporous alumina supported KCuFe catalyst for the FT synthesis process.

费托合成（FTS）是从煤炭、天然气和生物质生产液体燃料和精细化学品的有前景的技术之一。反应器技术和催化剂开发方面的重大改进是该领域研究的重点。在这项工作中，研究了1.0 wt%的助剂（如锰、镁、钴和镍）对介孔氧化铝负载的KCuFe催化剂的费托合成活性和选择性的影响。所有合成的添加助剂的催化剂都使用BET、XRD、H₂ - TPR、XPS、TEM和XANES进行了表征。费托合成反应在固定床反应器中进行，反应条件为270℃、300 psi、2000 h⁻¹以及H₂/CO = 1.25。在这项工作中，镍添加助剂的催化剂显示出最高的甲烷选择性（约29%）。钴添加助剂的催化剂显示出最低的烯烃/烷烃（O/P）比，并且甲烷选择性增加了约5%。镁添加助剂的催化剂表现中等，但优于镍和钴添加助剂的催化剂。然而，锰负载的催化剂优于镁、镍和钴添加助剂的催化剂，导致更高的C₅⁺选择性以及一氧化碳转化率略有提高。添加锰助剂后，二氧化碳、甲烷和C₂ - C₄选择性分别下降了约5%、2%和2%。锰添加助剂的催化剂在费托合成活性和选择性方面的提高与铁的分散度和还原性的增加有关，这在H₂ - TPR、XPS和XANES分析中可以看到。通过Mn 2p XPS和Mn K - edge XANES证实存在Mn³⁺和Mn⁴⁺，这表明锰和铁在电子层面的相互作用有助于提高性能。这项研究得出结论，对于合成的介孔氧化铝负载的KCuFe催化剂用于费托合成过程，锰是最有效的助剂。