Mn Promoter Research Articles

The impact of transition metals (Cr, Mn, and Co) on the performance of the 10%Ni/Al2O3-10%CeO2 catalysts in combined CO2 reforming and partial oxidation of methane

This study explores the efficacy of Cr, Mn, and Co promoters in enhancing the performance of 10%Ni/Al2O3-10%CeO2 catalysts during methane combined reforming process, emphasizing improved metal dispersion and reduced carbon formation. The supports and catalysts were synthesized through mechanochemical and impregnation methods, respectively, and characterized using XRD, BET, TPR, TPO, and FESEM analyses. The synthesized catalysts exhibited a high BET surface area, ranging from 195 to 172 m2 g-1, along with a mesoporous structure characterized by pore sizes between 2 and 12 nm. The introduction of Cr significantly enhanced catalyst performance, resulting in 70.5 % CH4 and 69.1 % CO2 conversions in dry reforming. TPO analysis indicated reduced carbon deposition on promoted catalysts by enhancing Ni dispersion and carbon reactivity. The 10%Ni–3%Cr/Al2O3-10%CeO2 catalyst demonstrated stability over 440 min at 700 °C, achieving 84.9 % CH4 and 68.1 % CO2 conversions in combined reforming. The TPO analysis indicated an absence of carbon deposition on the catalyst surface during combined reforming, which was corroborated by the FESEM analysis. Furthermore, the influence of operating parameters on catalyst efficiency in both dry and combined reforming processes was investigated. As GHSV increased from 8000 to 24,000 ml/h.gcat, CH4 conversion declined in dry reforming and combined reforming, dropping from 77 % to 66 % and from 86 % to 84 %, respectively. Also, in both processes, increasing the oxidizer contents (CH4: CO2 from 2:1 to 1:2, CH4: CO2: O2 from 1:1:0 to 1:1:0.35) led to an increase in CH4 conversion, while CO2 conversion decreased.

Tuning the Size of TiO2-Supported Co Nanoparticle Fischer-Tropsch Catalysts Using Mn Additions.

Modifying traditional Co/TiO2-based Fischer-Tropsch (FT) catalysts with Mn promoters induces a selectivity shift from long-chain paraffins toward commercially desirable alcohols and olefins. In this work, we use in situ gas cell scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) elemental mapping, and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to demonstrate how the elemental dispersion and chemical structure of the as-calcined materials evolve during the H2 activation heat treatment required for industrial CoMn/TiO2 FT catalysts. We find that Mn additions reduce both the mean Co particle diameter and the size distribution but that the Mn remains dispersed on the support after the activation step. Density functional theory calculations show that the slower surface diffusion of Mn is likely due to the lower number of energetically accessible sites for the Mn on the titania support and that favorable Co-Mn interactions likely cause greater dispersion and slower sintering of Co in the Mn-promoted catalyst. These mechanistic insights into how the introduction of Mn tunes the Co nanoparticle size can be applied to inform the design of future-supported nanoparticle catalysts for FT and other heterogeneous catalytic processes.

Stabilized ε-Fe2C catalyst with Mn tuning to suppress C1 byproduct selectivity for high-temperature olefin synthesis

Accurately controlling the product selectivity in syngas conversion, especially increasing the olefin selectivity while minimizing C1 byproducts, remains a significant challenge. Epsilon Fe2C is deemed a promising candidate catalyst due to its inherently low CO2 selectivity, but its use is hindered by its poor high-temperature stability. Herein, we report the successful synthesis of highly stable ε-Fe2C through a N-induced strategy utilizing pyrolysis of Prussian blue analogs (PBAs). This catalyst, with precisely controlled Mn promoter, not only achieved an olefin selectivity of up to 70.2% but also minimized the selectivity of C1 byproducts to 19.0%, including 11.9% CO2 and 7.1% CH4. The superior performance of our ε-Fe2C-xMn catalysts, particularly in minimizing CO2 formation, is largely attributed to the interface of dispersed MnO cluster and ε-Fe2C, which crucially limits CO to CO2 conversion. Here, we enhance the carbon efficiency and economic viability of the olefin production process while maintaining high catalytic activity.

Fischer-Tropsch to olefin reaction over Fe-based catalysts: Effect of preparation method and synergistic effect of Mn and Zr promoters

BackgroundDirect production of light olefins (basic chemical raw materials in the industrials) from syngas using promoted catalysts demonstrates great potential, because of their upgraded performances. MethodsIn this study, a series of Fe-based catalysts promoted by Mn and Zr were prepared by hydrothermal and microemulsion methods and applied to the Fischer-Tropsch reaction. To optimize the catalysts, response surface methodology combined with the central composite design was applied to three independent parameters of the synthesis method, weight percent of Zr promoter (2th promoter) and reaction temperature. To clarify the relationship between the synthesis methods, the synergistic effect of Zr and Mn promoters, and catalyst performance, in detail, different characterization analyses were studied, including XRD, BET, SEM-EDS, FESEM, TEM, H2-TPR, and CO-TPR. Significant findingsAccording to developed statistical equations, it was revealed that the synthesis method is the most influential parameter on CO% and O/P ratio. The experimental results indicated that Zr and Mn promoters had a negative synergistic effect on the CO% and O/P, but a positive one on the heavy hydrocarbons selectivities. The characterization results demonstrated that hydrothermal prepared FeMn catalyst, due to having uniform particle size distribution, cubic morphology, and better reduction at low temperature had highest CO%.

Fischer-tropsch synthesis of fuels and olefins in 3D printed SS microreactor using iron/graphene oxide catalysts with Mn- and Na-metal promoters

The effects of adding Mn and Na promoter metals to graphene oxide (GO)-supported iron-based catalysts for Ficher-Tropsch Synthesis (FTS) reactions to olefins at 20 bars were investigated in a 3D-printed stainless steel (SS) Microreactor. While promoter metals encourage reduction of iron oxide to iron to form iron carbide, the active metal catalysts in GO allow hydrogenation of CO. These catalysts were synthesized by layer deposition method and characterized by different techniques. The TEM images show the integration of graphene oxide into the catalysts. The XRD and XPS studies confirmed the crystal structure and oxidation states of the metals. The catalytic activity and product selectivity were studied in the temperature range of 200–350°Cwith a 2:1 M ratio of H2: CO. Higher CO conversion with greater selectivity for olefins was observed in the presence of the promoters. FeMnNa@GO showed better stability than both Fe@GO and FeMn@GO catalysts in time-on-stream studies.

CO2 hydrogenation to synthetic natural gas with light hydrocarbons on Mn-promoted mesoporous Co3O4-Al2O3 metal oxides

Direct CO2 conversion into synthetic natural gas (SNG, CH4) with simultaneous small production of light paraffinic C2-C4 hydrocarbons to enhance a heating value of SNG was investigated with ordered mesoporous CoMnAl mixed metal oxides (denoted as m-CoMnAl). CO2 hydrogenation activity to form hydrocarbons with small CO byproduct formed by a reverse water gas shift reaction (RWGS) was strongly affected by the MnO2 promoter content in the ordered Co3O4-Al2O3 mesoporous structures. The m-CoMnAl structures with proper amount of Mn promoter were found to be effective to enhance CO2 conversion to methane with small amount of light hydrocarbons formation, which were mainly attributed to the presence of abundant oxygen vacant sites with a stable preservation of the partially oxidized cobalt nanoparticles in the ordered mesoporous Co3O4-Al2O3 structures even under a reductive hydrogenation condition. Selective methanation of CO2 was found to be more favorable on the highly reduced metallic cobalt nanoparticles formed with smaller amount of Mn promoter (m-CoMnAl(0.05)), however, excessive Mn content such as Mn/Co ratio > 1 (m-CoMnAl(1.0)) revealed less structural stability of ordered mesoporous structures with lower CO2 conversion with relatively higher CO selectivity of 1.4 % with lower olefin selectivity through severe phase segregations of the Co-Mn-Al mixed metal oxides with selective formations of MnCO3 phases.

Influence of Mn, Mg, Ce and P promoters on Ni-X/Al2O3 catalysts for dry reforming of methane

In this work, the performance of a series of nickel catalysts supported on alumina containing the promoters Mg, Mn, Ce and P was evaluated against the dry reforming of methane (DRM). Alumina support was obtained quickly and simply through the microwave-assisted combustion method using low levels of urea. The catalysts were characterized by XRD, TPR, FTIR and XRD in situ, proving that successive hydration and heat treatment steps during synthesis can generate modifications in the alumina phases, in addition to the formation of aluminate species that are reduced during the catalytic activation step and modify the level of interaction between active and support phases. The catalytic activity test was performed with GHSV = 100 L g−1 h−1 and the formed carbon was quantified by thermogravimetric analysis. The Mn promoter exhibited the highest methane conversion rate during the initial stages of the reaction, in which the presence of MnO2 favored parallel reactions of methane decomposition. The phosphorus and cerium produced smaller amounts of coke, reducing the carbon generated due to the interaction of promoters with carbon on the surface of the catalytic sites. The Mg increases the interaction of the active phase with the support.

Mn-promoted MoS2 catalysts for CO2 hydrogenation: enhanced methanol selectivity due to MoS2/MnOx interfaces.

Considering the alarming scenario of climate change, CO2 hydrogenation to methanol is considered a key process for phasing out fossil fuels by means of CO2 utilization. In this context, MoS2 catalysts have recently shown to be promising catalysts for this reaction, especially in the presence of abundant basal-plane sulfur vacancies and due to synergistic mechanisms with other phases. In this work, Mn-promoted MoS2 prepared by a hydrothermal method presents considerable selectivity for CO2 hydrogenation to methanol in comparison with pure MoS2 and other promoters such as K and Co. Interestingly, if CO is used as a carbon source for the reaction, methanol production is remarkably lower, which suggests the absence of a CO intermediate during CO2 hydrogenation to methanol. After optimization of synthesis parameters, a methanol selectivity of 64% is achieved at a CO2 conversion of 2.8% under 180 °C. According to material characterization by X-ray Diffraction and X-ray Absorption, the Mn promoter is present mainly in the form of MnO and MnCO3 phases, with the latter undergoing convertion to MnO upon H2 pretreatment. However, following exposure to reaction conditions, X-ray photoelectron spectroscopy suggests that higher oxidation states of Mn may be present at the surface, suggesting that the improved catalytic activity for CO2 hydrogenation to methanol arises from a synergy between MoS2 and MnOx at the catalyst surface.

Exploring the promotion behavior of manganese in Fischer–Tropsch synthesis by changing the interaction patterns between manganese and iron

Mn promoter is widely investigated and employed in Fe-based catalysts. However, it remains a substantial challenge to elucidate how the Mn promoter tunes the product selectivity because the Mn promoter can change crystal structure, particle size, phase composition, etc. simultaneously. Hence, three kinds of newly designed catalysts with different interaction patterns between Mn and Fe were developed in this work to explore the promotion mechanism, including Mn-Fe spinel, core–shell Fe3O4@MnO2 and physical mixing of Fe3O4 and MnO2. Texture structure, reduction behavior and phase transformation of the catalysts were carefully investigated. The Mn content and Mn-Fe interaction pattern determine the strength of the Mn-Fe interaction, which affects the Fe species and FTS performance. Strong Mn-Fe interaction in spinel promotes the generation of ε-Fe2C, reducing C5+ selectivity while enhancing C2-C4 selectivity. C2-C4 O/P ratio of Mn-Fe spinel is dramatically elevated while simultaneously rapidly decreasing over time. Although the Mn-Fe interaction patterns are different, the medium content MnO2-coated Fe3O4 catalyst with strong interaction strength exhibits the similar Fe species and FTS performance feature as Mn-Fe spinel. The decrease in the Mn-Fe interaction strength at high MnO2 coating content contributes to the formation of χ-Fe5C2 and displays the alkaline effect of Mn promotion, i.e., a considerable drop in methane selectivity and an increase in C5+ selectivity. The effect on the FTS performance is relatively moderate for physical mixing of Fe3O4 and MnO2 due to the weak Mn-Fe interaction strength. Combining Fe species and product distribution, χ-Fe5C2 is favorable to produce long-chain hydrocarbons while ε-Fe2C is favorable to produce C2=-C4=. Most importantly, our work is expected to open up a new avenue for guiding the design of efficient catalysts.

Effect of metal promoters on catalytic performance of Co/AC for higher alcohols synthesis from syngas

Shifting products of Fischer-Tropsch Synthesis (FTS) from paraffins to value-added higher alcohols receives great attention but remains great challenge. Herein, metal oxides of Mn, Zn, La and Zr are investigated as promoters to tune the activity and product distributions of Co/AC catalyst for syngas conversion. It is found that these promoters show different promotion effect on CO dissociation rate, the formation of Co2C phase and the alcohols selectivity. The formed Co2C/Co0 constitutes the dual active site for higher alcohols synthesis. The strongest CO dissociation rate is observed for Zn-promoted Co/AC catalyst, resulting in the highest activity and space-time yield (STY) of alcohols. The Mn promoter is most conducive to the formation of Co2C, but slightly decreases the activity. The similar CO dissociation rate and CO conversion are obtained over both Zr- and La-promoted Co/AC catalysts, but the Zr-promoted Co/AC catalyst exhibits the highest alcohols selectivity due to the function balance between CO non-dissociative insertion and CO dissociation.

Synthesis of Liquid Hydrocarbon via Direct Hydrogenation of CO2 over FeCu-Based Bifunctional Catalyst Derived from Layered Double Hydroxides.

Here, we report a Na-promoted FeCu-based catalyst with excellent liquid hydrocarbon selectivity and catalytic activity. The physiochemical properties of the catalysts were comprehensively characterized by various characterization techniques. The characterization results indicate that the catalytic performance of the catalysts was closely related to the nature of the metal promoters. The Na-AlFeCu possessed the highest CO2 conversion due to enhanced CO2 adsorption of the catalysts by the introduction of Al species. The introduction of excess Mg promoter led to a strong methanation activity of the catalyst. Mn and Ga promoters exhibited high selectivity for light hydrocarbons due to their inhibition of iron carbides generation, resulting in a lack of chain growth capacity. The Na-ZnFeCu catalyst exhibited the optimal C5+ yield, owing to the fact that the Zn promoter improved the catalytic activity and liquid hydrocarbon selectivity by modulating the surface CO2 adsorption and carbide content. Carbon dioxide (CO2) hydrogenation to liquid fuel is considered a method for the utilization and conversion of CO2, whereas satisfactory activity and selectivity remains a challenge. This method provides a new idea for the catalytic hydrogenation of CO2 and from there the preparation of high-value-added products.

Formulated Mn-promoted SAPO-34/kaolin/alumina sol micro-size catalyst with a superior performance for methanol to light olefins conversion in a fluidized bed reactor

Formulation of zeolite molecular sieves powder is necessary to prepare an excellent micro-size catalyst for methanol conversion to light olefins (MTO) in a fluidized bed reactor. In this work, new fluidizable micro-meso pore catalysts were successfully fabricated by spray drying a slurry containing Mn(x)SAPO-34 powder, kaolin filler, alumina sol binder, and HCl additive. A mixed template of TEAOH/morpholine with different amounts of Mn ion was used in primary gel during hydrothermally synthesis of the crystals. The catalytic samples were characterized utilizing different methods. A moderate acidity reached by catalyst formulation using kaolin and alumina sol as well as through Mn incorporation into the chabazite cages was helpful for MTO performance of the final shape-selective catalyst in terms of selectivity to light olefins and lifetime. The enhancement effect of Mn promoter on ethylene production was much more than propylene because of entering Mn to the micro-pores and imposing restriction on heavier hydrocarbons diffusion. The uniformity and crystalinity were also appeared to be enhanced once Mn(0.05) was introduced into the gel composition. The suggested spray dried catalyst was SD-Mn(0.05)SAPO-34 (70–120 µm) in which provided a superior selectivity up to 88.4% to light olefins and catalytic lifetime of 330 min in a fluidized bed reactor at 450℃, WHSV = 4 h−1, and XMeOH = 0.75 in the feed.

Unraveling the regulation of Mn in Cu-ZnOx formation during methanol synthesis from syngas over Cu/ZnO/Al2O3-Mn catalysts

This study unravels the regulation of Mn promoter in catalytic activity and surface identities of Cu/ZnO/Al2O3 catalysts by reaction kinetics, TPR/TPD, N2O titration experiments and in situ spectra techniques. The methanol formation EA of Cu/ZnO/Al2O3 catalyst almost remained unchanged with the addition of Mn, confirming the methanol synthesis pathways were not affected. With an increase in the content of Mn, the sizes of Cu and ZnO decreased whereas the reduction degree of ZnO to Zn0 on the catalyst surface increased, forming more Cu-ZnOx active sites in CAZ-2%Mn. TPSR confirmed that the amount of the surface CO and H species were highest in CAZ-2%Mn. Therefore, more Cu-ZnOx active site and surface species in CAZ-2%Mn accounts for the higher methanol formation activity. A detailed understanding of the regulation of Mn in the Cu-ZnOx sites formation is expected for the precise design of the CuZnAl catalysts for methanol synthesis.

Pressure dependence and mechanism of Mn promotion of silica-supported Co catalyst in the Fischer-Tropsch reaction

The mechanism of Mn promotion of a silica-supported Co catalyst in the Fischer-Tropsch reaction has been studied at varying pressures up to 20 bar. IR spectroscopy in combination with DFT calculations suggest adsorbed CO is activated by reaction with an oxygen vacancy in the MnO, which covers the Co surface. This leads to a higher activity, higher CHx coverage and thus higher C5+ and lower CH4 selectivity. Increasing the pressure magnifies the selectivity differences. However, above around 4 bar, the effect of Mn on the selectivities is reversed and the C5+ selectivity is decreased by Mn addition. This is tentatively attributed to Mn promoting the C-O bond dissociation but not the chain growth. Formed monomers have to migrate to stepped sites for chain growth on the Co surface. Whilst this is migration is not impeded by co-adsorbates at low pressure, migration could be hindered by especially the high CO coverage at high pressure.

Effect of interaction degree between Mn and Ce of MnOX-CeO2 formulation on NO reduction and o-DCB oxidation performed simultaneously

MnOX-CeO2 catalysts were prepared by different methods in order to assess the influence of Mn and Ce interaction on the catalytic activity of NO reduction and 1,2-dichlorobencene (o-DCB) oxidation carried out simultaneously. Changes on catalytic properties were evaluated by XRD, Raman, N2-physisorption, H2-TPR and NH3-TPD. The samples prepared by co-precipitation and sol-gel exhibited the best catalytic activity over the whole temperature range. These preparation methods provide high interaction between Mn and Ce at surface and bulk, which was evidenced by the formation of mixed oxide phase. According to characterisation, the enhancement of catalytic activity with Mn and Ce interaction is associated to the promotion of structural defects, which improve redox and acid properties. Oxidative capability is also improved as a consequence of the oxygen vacancies generated by the presence of those structural defects. On the other hand, the promotion of Mn and Ce interaction favours the production of N2O in NO reduction at a lower temperature, and also leads to o-DCB total oxidation by decreasing CO production.

Highly Efficient Synthesis of High‐Value Olefins from Syngas over Layered Fe‐Mn/Magadiite Catalyst

AbstractThe simultaneous realization of high olefin/paraffin (O/P) ratio and low CH4 selectivity has always been a bottleneck for the conversion of syngas to high‐value olefins (HVOs). Magadiite (MAG) is a layered silicate material with active SiOH, which increases the interlayer charge density and ion‐exchange ability. Herein, a MAG‐supported, Mn‐modified Fe3O4 microsphere catalyst exhibits excellent CO conversion of 76.5 % and HVO selectivity, with a high O/P ratio of 5.02 and low CH4 selectivity of 16.1 % for conversion of syngas to HVOs. The layered structure of the MAG support promotes dispersion of the active centers and the Mn promoter improves the basic properties of the catalyst. Moreover, the Mn promoter and MAG support have a synergistic effect, which promotes CO dissociation and suppresses H2 adsorption, thereby resulting in high HVO selectivity and low CH4 selectivity.

Unraveling the Mn-promoted coke elimination mechanism by CO2 over NaFeMn/ZSM-5 catalyst during CO2 hydrogenation

Coke deposition and catalyst deactivation are widely viewed as a crucial issue for CO2 hydrogenation performance, however, effective strategy for coke attenuation and the corresponding underlying mechanism are still rarely explored. In this research, we discovered that the reactant CO2 can also play a vital role in diminishing coke deposits during CO2 conversion, and carbon on zeolite can just be eliminated with the assistance of activated iron catalysts. Moreover, Mn promoter can restrict Na migration to zeolite, sustaining zeolite acidity for aromatization. Significantly, the migrating Mn on zeolite from NaFeMn can promote the formation of CO2-oxidizable coke, thus accelerating coke oxidation by CO2. These findings are beneficial for the improvement of catalyst stability and optimization of reaction system.

Investigation of Mn and Ca promoter effects in iron-based catalysts: CO hydrogenation reaction

Cu–Fe catalysts incorporated with different amounts of Ca and Mn promoters were prepared using a wet-impregnation method and applied in the Fischer–Tropsch synthesis reaction.

Controlling cobalt Fischer–Tropsch stability and selectivity through manganese titanate formation

Mn promotion in FT can direct products between oxygenates and paraffins. A simple in situ treatment forms MnTiO3 while an ex situ support is demonstrated with the benefits of Mn inclusion while controlling activity and inhibiting alcohol selectivity.

Enhancing selectivity of aromatics in direct conversion of syngas over K/FeMn and HZSM-5 bifunctional catalysts

Mixed Fischer-Tropsch synthesis (FTS) catalysts and HZSM-5 (HZ5) have received attention as bifunctional catalysts that directly convert syngas into value-added aromatic monomers. However, both low selectivity of aromatics and severe deactivation remain challenges. Here we report a simple method for obtaining selective aromatics from syngas by tuning the distribution of hydrocarbon (HC) intermediates on K/FeMn. We prepared K/FeMn catalysts with a varying Mn/(Fe+Mn) wt% to demonstrate the effect of the HC distribution as intermediates of aromatization on HZ5. The C6-C10 distribution was increased by addition of up to 60 wt% of Mn promoter due to the improved dispersion of Fe7C3 and alkyl insertion of MnO. At 340 °C under 20 bar, 97.2% CO conversion and 39.8% aromatics selectivity were achieved by using a physically mixed catalyst of K/FeMn with Mn/(Fe+Mn) 60 wt% and HZ5 with an optimization of the FTS-derived C6-C10 olefin yield as efficient intermediates in Syngas to Aromatics (STA).