Ru-promoted perovskites as effective redox catalysts for CO2 splitting and methane partial oxidation in a cyclic redox scheme

The current study reports A_xA'_1-xB_yB'_1-yO_3-δ perovskite redox catalysts (RCs) for CO₂-splitting and methane partial oxidation (POx) in a cyclic redox scheme. Strontium (Sr) and iron (Fe) were chosen as A and B site elements with A' being lanthanum (La), samarium (Sm) or yttrium (Y), and B' being manganese (Mn) or titanium (Ti) to tailor their equilibrium oxygen partial pressures (P_O2s) for CO₂-splitting and methane partial oxidation. DFT calculations were performed for predictive optimization of the oxide materials whereas experimental investigation confirmed the DFT-predicted redox performance. The redox kinetics of the RCs improved significantly by 1 wt% ruthenium (Ru) impregnation without affecting their redox thermodynamics. Ru-impregnated LaFe_0.375Mn_0.625O₃ (A = 0, A' = La, B = Fe, and B' = Mn) was the most promising RC in terms of its superior redox performance (CH₄/CO₂ conversion >90% and CO selectivity ∼95%) at 800 °C. Long-term redox testing over Ru-impregnated LaFe_0.375Mn_0.625O₃ indicated a stable performance during the first 30 cycles followed by an ∼25% decrease in the activity during the last 70 cycles. Air treatment was effective to reactivate the redox catalyst. Detailed characterizations revealed the underlying mechanism of the redox catalyst deactivation and reactivation. This study not only validated a DFT-guided mixed oxide design strategy for CO₂ utilization but also provides potentially effective approaches to enhance redox kinetics and long-term redox catalyst performance.

Combined Syngas and Hydrogen Production using Gas Switching Technology

This paper focuses on the experimental demonstration of a three-stage GST (gas switching technology) process (fuel, steam/CO₂, and air stages) for syngas production from methane in the fuel stage and H₂/CO production in the steam/CO₂ stage using a lanthanum-based oxygen carrier (La_0.85Sr_0.15Fe_0.95Al_0.05O₃). Experiments were performed at temperatures between 750–950 °C and pressures up to 5 bar. The results show that the oxygen carrier exhibits high selectivity to oxidizing methane to syngas at the fuel stage with improved process performance with increasing temperature although carbon deposition could not be avoided. Co-feeding CO₂ with CH₄ at the fuel stage reduced carbon deposition significantly, thus reducing the syngas H₂/CO molar ratio from 3.75 to 1 (at CO₂/CH₄ ratio of 1 at 950 °C and 1 bar). The reduced carbon deposition has maximized the purity of the H₂ produced in the consecutive steam stage thus increasing the process attractiveness for the combined production of syngas and pure hydrogen. Interestingly, the cofeeding of CO₂ with CH₄ at the fuel stage showed a stable syngas production over 12 hours continuously and maintained the H₂/CO ratio at almost unity, suggesting that the oxygen carrier was exposed to simultaneous partial oxidation of CH₄ with the lattice oxygen which was restored instantly by the incoming CO₂. Furthermore, the addition of steam to the fuel stage could tune up the H₂/CO ratio beyond 3 without carbon deposition at H₂O/CH₄ ratio of 1 at 950 °C and 1 bar; making the syngas from gas switching partial oxidation suitable for different downstream processes, for example, gas-to-liquid processes. The process was also demonstrated at higher pressures with over 70% fuel conversion achieved at 5 bar and 950 °C.

Controlling lattice oxygen activity of oxygen carrier materials by design: a review and perspective

The lattice oxygen activity of oxygen carriers is critical to chemical looping processes and can be effectively controlled with prepared (i) solid solution mixtures, (ii) ternary oxide phases or (iii) core–shell structured oxygen carriers.

A novel low-dimensional heteroatom doped Nd2O3 nanostructure for enhanced electrochemical sensing of carbendazim

Reasonable design and synthesis of high-efficiency nanocatalysts are of great significance for studying the electrocatalytic analysis of fungicides.

Redox oxidative cracking of n-hexane with Fe-substituted barium hexaaluminates as redox catalysts

Promoted hexaaluminate redox catalysts achieved excellent olefin yield while allowing autothermal redox oxidative cracking of naphtha with low CO_x formation.