Effects of K and Mn promoters over Fe2O3 on Fischer–Tropsch synthesis

Structural and compositional design of core-shell structure is an effective strategy towards enhanced catalysis.Herein,amorphous MnO2 nanosheets and K+-intercalated layered MnO2 nanosheets are controllably assembled over Fe2O3 spindles,in which the MnO2 nanosheets are perpendicularly anchored to the surface of Fe2O3.Such a core shell structure contributes to a high specific surface area and abundant pore channels on the surface of catalysts.In addition,the existence of K+provides large numbers of basic sites and restrains the formation of unpleasant(Fe1-xMnx)3O4.Benefiting from the merits in structure and composition,CO adsorption is enhanced and remaining time of intermediates is prolonged on the surfaces of catalysts during the Fischer–Tropsch synthesis(FTS),facilitating to the formation of active iron carbides and C–C coupling reactions.Resultantly,the Fe2O3@K+-Mn O2 shows both a high CO conversion of 82.3%and a high C5+ selectivity of 73.1%.The present study provides structural and compositional rationales on design high-performance catalysts towards FTS.

Effect of Mn Promoter on Structure and Performance of K-Co-Mo Catalyst for Synthesis of Higher Alcohols from CO Hydrogenation

A series of Mn-doped K-Co-Mo catalysts were prepared by a sol-gel method. The catalyst structure was well characterized by X-ray diffraction, N2 physisorption, NH3 temperature- programmed adsorption, in situ diffuse reflectance infrared Fourier transform spectroscopy, and X-ray absorption fine structure spectroscopy. The catalytic performance for higher alcohol synthesis from syngas was measured. It was found that the Mn-doped catalysts ex- hibited a much higher activity as compared to the unpromoted catalyst, and in particular the C2＋ alcohol selectivity increased significantly. The distribution of alcohol products de- viated from the Anderson-Schulz-Flory law. The portion of methanol in total alcohol was suppressed remarkably and the ethanol became the predominant product. Characterization results indicated that the incorporation of Mn enhanced the interaction of Co and Mo and thus led to the formation of Co-Mo-O species, which was regarded as the active site for the alcohol synthesis. Secondly, the presence of Mn reduced the amount of strong acid sites significantly and meanwhile promoted the formation of weak acid sites, which had a positive effect on the synthesis of alcohol. Furthermore, it was found that the incorporation of Mn can enhance the adsorption of linear- and bridge-type CO significantly, which contributed to the formation of alcohol and growth of carbon chain and thus increased the selectivity to C2＋OH.

CO2 methanation and co-methanation of CO and CO2 over Mn-promoted Ni/Al2O3 catalysts

A series of Mn-promoted 15 wt-% Ni/Al2O3 catalysts were prepared by an incipient wetness impreg- nation method. The effect of the Mn content on the activity of the Ni/Al2O3 catalysts for CO2 methanation and the co- methanation of CO and CO2 in a fixed-bed reactor was investigated. The catalysts were characterized by N2 physisorption, hydrogen temperature-programmed reduc- tion and desorption, carbon dioxide temperature-pro- grammed desorption, X-ray diffraction and high- resolution transmission electron microscopy. The presence of Mn increased the number of CO2 adsorption sites and inhibited Ni particle agglomeration due to improved Ni dispersion and weakened interactions between the nickel species and the support. The Mn-promoted 15 wt-% Ni/ Al2O3 catalysts had improved CO2 methanation activity especially at low temperatures （250 to 400 ℃）. The Mn content was varied from 0.86% to 2.54% and the best CO2 conversion was achieved with the 1.71Mn-Ni/Al2O3 catalyst. The co-methanation tests on the 1.71Mn-Ni/ Al2O3 catalyst indicated that adding Mn markedly enhanced the CO2 methanation activity especially at low temperatures but it had little influence on the CO methanation performance. CO2 methanation was more sensitive to the reaction temperature and the space velocity than the CO methanation in the co-methanation process.

Promotional effect of Mn doping on Ru/layered MCM-49 catalysts for the conversion of Levulinic acid to γ-Valerolactone

Selective hydrogenation of Levulinic acid(LA)toγ-Valerolactone(GVL)is an important reaction to produce high value-added chemicals and fuels but remains a big challenge.Herein we reported a Ru/zeolite catalyst with Mn promotion,which exhibited excellent catalytic performance(yield:98%)towards LA to GVL.The intrinsic activity(TOF)also increased obviously with the Mn addition.The particle size of Ru gradually decreased with the increase of Mn loading and a strong interaction between Ru and support was observed for the Ru-Mn/MCM-49 catalyst.The addition of Mn not only offered a good dispersion of Ru species on MCM-49,but also increased the L/B ratio of the catalyst,thereby contributing to the high GVL selectivity.High dispersed Ru sites were the intrinsic active sites of the catalyst verified by the in-situ experimental studies.The dissociation of the reactants was significantly enhanced,resulting in higher catalytic activity.