Effect of noble metal addition over active Ru/TiO2 catalyst for CO selective methanation from H2 rich-streams

Selective CO methanation from H₂-rich stream has been regarded as a promising route for deep removal of low CO concentration and catalytic hydrogen purification processes. This work is focused on the development of more efficient catalysts applied in practical conditions. For this purpose, we prepared a series of catalysts based on Ru supported over titania and promoted with small amounts of Rh and Pt. Characterization details revealed that Rh and Pt modify the electronic properties of Ru. The results of catalytic activity showed that Pt has a negative effect since it promotes the reverse water gas shift reaction decreasing the selectivity of methanation but Rh increases remarkably the activity and selectivity of CO methanation. The obtained results suggest that RuRh-based catalyst could become important for the treatment of industrial-volume streams.     

Conversion of hydrogen/carbon dioxide into formic acid and methanol over Cu/CuCr2O4 catalyst

Cu/CuCr₂O₄ catalysts were prepared by impregnation method at various calcination temperatures (300, 400, and 500 °C) and then reduced in H₂ stream. The aggregated particles and decreasing surface area/pore volumes of the deactivated catalysts during HCOOH and CH₃OH formations were also observed. Particularly, the EXAFS data showed that first shells of Cu atoms transforms from Cu–O to Cu–Cu after catalytic reactions, their bond distances and coordination numbers are quite different, respectively. It revealed that metallic Cu atoms are one of the important active species over catalyst surface at different reaction temperatures having many unoccupied binding sites for HCOOH and CH₃OH formations. Additionally, the optimal calcination temperature for Cu/CuCr₂O₄ catalysts was demonstrated at 400 °C that attributed to its strongest acidity and basicity. The catalytic reactions in the duration of HCOOH and CH₃OH preparation were proposed that were composed of HCOOH formation, CH₃OH formation, and CH₃OH decomposition happening at CuCr₂O₄, Cu, and CuO active sites, respectively. The highest CO₂ conversion (14.6%), HCOOH selectivity/yield (87.8/12.8%), and TON/TOF values (4.19/0.84) were obtained at 140 °C and 30 bar in 5 h, respectively. Optimal rate constant (2.57 × 10^?2 min^?1) and activation energy (16.24 kJ mol^?1) of HCOOH formation were evaluated by pseudo first-order model and Arrhenius equation, respectively.     

Partial oxidation of methane over CeO2 loaded hydrotalcite (MgNiAl) catalyst for the production of hydrogen rich syngas (H2, CO)

In this work, partial oxidation of methane (POM) was investigated using Mg-Ni-Al (MNA) hydrotalcite promoted CeO₂ catalyst in a fixed bed reactor. MNA hydrotalcite was synthesized using the co-precipitation process, while CeO₂ was incorporated via the wetness impregnation technique. The CeO₂@MNA samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) technique. The catalytic activity of CeO₂ promoted MNA (CeO₂@MNA) for POM reaction was evaluated for various CeO₂ loading kept the feed ratio CH₄/O₂ = 2 at 850 °C. The catalyst containing 10 wt% cerium loading (10%CeO₂@MNA) showed 94% CH₄ conversion with H₂/CO ratio above 2.0, that is more suitable for FT synthesis. The performance of catalyst is attributed to highly crystalline stable CeO₂@MNA with better Ce-MNA interactions withstand for 35 h time on stream. Furthermore, the spent catalyst was examined by TGA, SEM-EDS, and XRD to evaluate the carbon formation and structural changes during the span of reaction time.     

The synthesis and characterization of Ni-M-Tb/Al2O3 (M: Mg,Ca, Sr and Ba) nanocatalysts prepared by different types of doping using the ultrasonic-assisted method to enhance CO2 methanation

In the present study, Ni-M-Tb/Al₂O₃ (M: Mg, Ca, Sr and Ba) nanostructured catalysts with different ratios of the alkali metals were synthesized by the ultrasonic-assisted one-pot method. The catalytic performance was investigated in terms of CO₂ conversion, CH₄ selectivity, and stability via the H₂-TPR analysis. The structural properties were delineated using XRD, SEM, TEM and BET equation. The results showed that the 2Ni-5Mg-5Tb/Al₂O₃ catalyst with a maximum CO₂ conversion of 75.37% and CH₄ selectivity of 100%, at the operating temperature of 400 °C in the molar ratio of H₂:CO₂:3.5 for 100 h, had the best performance. This could benefit from the particular electronic structure of Tb in combination with Mg and Ni, reducing agglomeration, as demonstrated by the SEM and BET results. Based on the current findings, novel catalysts with high conversion efficiency of CO₂ to CH₄ might be achieved by tuning a decent combination of alkaline and rear earth elements as the promoters of Ni-based catalysts.