Effects of addition of chromium, manganese, or molybdenum to iron catalysts for carbon dioxide hydrogenation

Catalysts for the Conversion of CO2 to Low Molecular Weight Olefins-A Review

There is a large worldwide demand for light olefins (C₂⁼-C₄⁼), which are needed for the production of high value-added chemicals and plastics. Light olefins can be produced by petroleum processing, direct/indirect conversion of synthesis gas (CO + H₂) and hydrogenation of CO₂. Among these methods, catalytic hydrogenation of CO₂ is the most recently studied because it could contribute to alleviating CO₂ emissions into the atmosphere. However, due to thermodynamic reasons, the design of catalysts for the selective production of light olefins from CO₂ presents different challenges. In this regard, the recent progress in the synthesis of nanomaterials with well-controlled morphologies and active phase dispersion has opened new perspectives for the production of light olefins. In this review, recent advances in catalyst design are presented, with emphasis on catalysts operating through the modified Fischer-Tropsch pathway. The advantages and disadvantages of olefin production from CO₂ via CO or methanol-mediated reaction routes were analyzed, as well as the prospects for the design of a single catalyst for direct olefin production. Conclusions were drawn on the prospect of a new catalyst design for the production of light olefins from CO₂.

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.%.

Study of the Reduction of Fe on Reduced Graphene Oxide as a Catalyst for Carbon Monoxide Reduction

This work aims at optimizing the H2 reduction time of Fe/rGO as a preparatory step for the use of the reduced catalyst in Fisher-Tropsch synthesis (FTS). The catalytic system used was Iron Nanoparticles (NPs) loaded on reduced graphene oxide (rGO) support. The as prepared sample was analyzed by TEM, FTIR and XRD spectroscopy. Samples of the produced Fe/rGO catalyst were used to optimize the reduction conditions in the FBR reactor. The three samples were reduced under 1atm H2 gas flow of 50 sccm at 500°C for 8, 12 and 24 hrs. The samples were collected after reduction and analyzed by XRD, FTIR and TEM imaging. The best condition showing full reduction with minimal sintering was at 12hr.

CO2 hydrogenation using bifunctional catalysts based on K-promoted iron oxide and zeolite: influence of the zeolite structure and crystal size

The influence of the zeolite structure and crystal size on bifunctional tandem catalysts combining K-promoted iron oxide (K/Fe₃O₄) with different zeolites has been studied for the CO₂ hydrogenation reaction at 320 °C and 25 bar.

Selective light driven reduction of CO2 to HCOOH in water using a {MoV9}n (n = 1332-3600) based soft-oxometalate (SOM)

A soft-oxometalate (SOM) based on Mo and V i.e. {MoV₉} in their highest oxidation state reduces CO₂ to HCOOH selectively in water. Catalysis initiates without the use of any photosensitizer and solvent water acts as the sacrificial electron donor which gets oxidized to generate oxygen. Electrons and protons released in this process reduce CO₂ to HCOOH.

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.

Simultaneous activity and stability increase of co-precipitated Ni–Al CO2 methanation catalysts by synergistic effects of Fe and Mn promoters

The activity and stability of co-precipitated NiAlO_x catalysts in the CO₂ methanation reaction is targetedly enhanced by co-doping Fe and Mn.

CO2 hydrogenation to higher hydrocarbons on K/Fe–Al–O spinel catalysts promoted with Si, Ti, Zr, Hf, Mn and Ce

Si and Zr species grafted on Fe–Al–O catalysts act as an inhibitor and promoter, respectively, in CO₂ hydrogenation.