Temperature-programmed reduction of mixed iron—manganese oxide catalysts in hydrogen and carbon monoxide

Preparation of VOC low-temperature oxidation catalysts with copper and iron binary metal oxides via hydrotalcite-like precursors

Design diagram for the removal toluene by Cu–Fe catalyst prepared from precursor hydrotalcite.

Improved Thermochemical Energy Storage Behavior of Manganese Oxide by Molybdenum Doping

To improve the thermochemical energy storage (TCS) behavior of Mn₂O₃, several Mn-Mo oxides with varying amounts of MoO₃ (0-30 wt%) were prepared by a precipitation method. The physico-chemical properties of the solids were studied by N₂ adsorption-desorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and H₂-temperature-programmed reduction (TPR), while their TCS behavior was determined by thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC). Apart from Mn₂O₃ and MoO₃ phases, XRD revealed a mixed MnMoO₄ phase for MoO₃ loadings equal or higher than 1.5 wt%. All samples showed a well-formed coral-like surface morphology, particularly those solids with low MoO₃ contents. This coral morphology was progressively decorated with compact and Mo-enriched MnMoO₄ particles as the MoO₃ content increased. TPR revealed that the redox behavior of Mn₂O₃ was significantly altered upon addition of Mo. The TCS behavior of Mn₂O₃ (mostly oxidation kinetics and redox cyclability) was enhanced by addition of low amounts of Mo (0.6 and 1.5% MoO₃) without significantly increasing the reduction temperature of the solids. The coral morphology (which facilitated oxygen diffusion) and a smoother transition from the reduced to oxidized phase were suggested to be responsible for this improved TCS behavior. The samples containing 0.6 and 1.5 wt% of MoO₃ showed outstanding cyclability after 45 consecutive reduction-oxidation cycles at high temperatures (600-1000 °C). These materials could potentially reach absorption efficiencies higher than 90% at concentration capacity values typical of concentrated solar power plants.

Waste plastics recycling for producing high-value carbon nanotubes: Investigation of the influence of Manganese content in Fe-based catalysts

Thermo-chemical conversion is a promising technology for the recycle of waste plastics, as it can produce high-value products such as carbon nanotubes (CNTs) and hydrogen. However, the low yield of CNTs is one of the challenges. In this work, the addition of Mn (0 wt.%, 1 wt.%, 5 wt.%, and 10 wt.%) to Fe-based catalyst to improve the production of CNTs has been investigated. Results show that the increase of Mn content from 0 wt.% to 10 wt.% significantly promotes CNTs yield formed on the catalyst from 23.4 wt.% to 32.9 wt.%. The results show that Fe-particles in the fresh catalysts are between 10-25 nm. And the addition of Mn in the Fe-based catalyst enhanced the metal-support interactions and the dispersion of metal particles, thus leading to the improved catalytic performance in relation to filamentous carbon growth. In addition, the graphitization of CNTs is promoted with the increase of Mn content. Overall, in terms of the quantity and quality of the produced CNTs, 5 wt.% of Mn in Fe-based catalyst shows the best catalytic performance, due to the further increase of Mn content from 5 wt.% to 10 wt.% led to a dramatic decrease of purity by 10 wt.%.

Effects of Sm on Fe-Mn catalysts for Fischer-Tropsch synthesis

Sm-promoted FeMn catalysts were prepared by the co-precipitation method and characterized by N2 adsorption, XRD, CO-TPD, H2-TPD, CO2-TPD, H2-TPR, XPS and MES. It was found that compared with the un-promoted catalyst, when Sm was added at a proper content, the catalyst showed a larger BET surface area and promoted the formation of iron particles with a smaller size. The presence of Sm could increase the surface charge density of iron, which enhanced the Fe-C bond and promoted the stability and amount of CO dissociated adsorption, as confirmed by XPS and CO-TPD. Furthermore, according to MES, Sm could promote the formation of Fe5C2, which was the active phase of FTS. In addition, Sm could also enhance the basicity of the catalysts and suppress the H2 adsorption capacity, which inhibited the hydrogenation reaction and the conversion of olefins to paraffins, as verified by the results of CO2-TPD and H2-TPD. According to the FTS performance results, compared with the observations for the un-promoted catalysts, when the molar ratio of Sm to Fe was 1%, the CO conversion increased from 63.4% to 70.4%, the sum of light olefins in the product distribution increased from 26.6% to 32.6, and the ratio of olefins to paraffins increased to 4.18 from 4.09.

Supported Fe/MnOx catalyst with Ag doping for remarkably enhanced catalytic activity in Fischer–Tropsch synthesis

The role of Ag in the promotion of the FTS performance and the evolutions of structure and phase over the Fe/MnO_x catalyst has been clearly elucidated.

Mn–Fe nanoparticles on a reduced graphene oxide catalyst for enhanced olefin production from syngas in a slurry reactor

Fe nanoparticles (NPs) supported on reduced graphene oxide (rGO) nano-sheets were promoted with Mn and used for the production of light olefins in Fischer–Tropsch reactions carried out in a slurry bed reactor (SBR). The prepared catalysts were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), transmission electron microscope (TEM), Raman spectroscopy, N₂ physisorption, temperature programmed reduction (TPR) and X-ray photoelectron spectroscopic (XPS) methods. Mn was shown to preferentially migrate to the Fe NP surface, forming a Mn-rich shell encapsulating a core rich in Fe. The Mn shell regulated the diffusion of molecules to and from the catalyst core, and preserved the metallic Fe phase by lowering magnetite formation and carburization, so decreasing water gas shift reaction (WGSR) activity and CO conversion, respectively. Furthermore, the Mn shell reduced H₂ adsorption and increased CO dissociative adsorption which enhanced olefin selectivity by limiting hydrogenation reactions. Modification of the Mn shell thickness regulated the catalytic activity and olefin selectivity. Simultaneously the weak metal–support interaction further increased the migration ability owing to the utilization of a graphene-based support. Space velocities, pressures and operating temperatures were also tested in the reactor to further enhance light olefin production. A balanced Mn shell thickness produced with a Mn concentration of 16 mol Mn/100 mol Fe was found to give a good olefin yield of 19% with an olefin/paraffin (O/P) ratio of 0.77. Higher Mn concentrations shielded the active sites and reduced the conversion dramatically, causing a fall in olefin production. The optimum operating conditions were found to be 300 °C, 2 MPa and 4.2 L g⁻¹ h⁻¹ of 1 : 1 H₂ : CO syngas flow; these gave the olefin yield of 19%.

Mn acted as a promoter by forming a Mn-rich layer around a core rich in Fe. The outer layer hindered the formation of magnetite, and impeded H₂ adsorption whilst encouraging CO dissociative adsorption, which gave the perfect conditions for olefin production.

Use of stability diagrams to predict catalyst speciation during Fischer Tropsch reduction stage: a mini-review

An alternative way of predicting phase evolution of iron-based Fischer Tropsch synthesis catalysts during activation.

Response surface methodology as an efficient tool for optimizing the Fischer–Tropsch process over a novel Fe–Mn nano catalyst

A novel Fe–Mn–resol/SiO₂ nano-catalyst with improved surface area and porosity was prepared and used in the Fischer–Tropsch process.

CH4 Deep Oxidation on Ag Promoted Manganese Oxide Catalysts

Manganese oxide modified by various amounts of Ag was prepared and used for CH