Origin of Ammonia Selective Oxidation Activity of SmMn2O5 Mullite: A First-Principles-Based Microkinetic Study

Based on first-principles calculations and microkinetic analysis, the reaction routes and origin of the activity of SmMn₂O₅ mullite for the selective catalytic oxidation of ammonia (NH₃-SCO) are systematically investigated on three low-index surfaces under experimentally operating conditions. Key influencing factors and contributions of different iconic intermediate species (NH*, N₂H₄*, and HNO*) to the overall reaction process have been identified. In detail, Mn⁴⁺ serves as the primary active site for NH₃ adsorption, while lattice oxygen participates in the dehydrogenation of NH₃ on (010)⁴⁺ and (001)⁴⁺ surfaces. Furthermore, the (010)⁴⁺ surface shows both the best activity and the highest N₂ selectivity at low temperatures via the synergy effect of exposed Mn-Mn dimers and the most labile O² atoms. We further evaluate the potential catalytic performances of six A-site doped (010)⁴⁺ facets, among which La, Pr, and Nd dopings are predicted to possess better catalytic performances. Our study provides deep insights into the microscope reaction mechanisms and provides the specific optimization strategy for NH₃-SCO on mullite oxides.

Porous Mn-based oxides for complete ethanol and toluene catalytic oxidation: the relationship between structure and performance

SmMn₂O₅ exhibited a higher catalytic activity for catalytic oxidation of ethanol and toluene than SmMnO₃, Mn₃O₄ and Mn₂O₃. Mn³⁺–Mn³⁺ dimers facilitate C–C bond cleavage.

Superior low-temperature NO catalytic performance of PrMn2O5 over SmMn2O5 mullite-type catalysts

PrMn₂O₅ is demonstrated as a superior catalyst compared to SmMn₂O₅ for low temperature NO oxidation, both experimentally and theoretically.

Improved durability of Co3O4 particles supported on SmMn2O5 for methane combustion

To eliminate the aggregation of Co₃O₄ in the methane combustion process at high temperature, a thermally stable mullite structure, SmMn₂O₅ (SMO), was utilized as a support to improve the catalytic durability of Co₃O₄ particles.

Highly dispersed Pd on macroporous SmMn2O5 mullite for low temperature oxidation of CO and C3H8

The catalytic behavior of a palladium catalyst supported on macroporous SmMn₂O₅ mullite (Pd/SMO-EG&M) for CO and C₃H₈ oxidation was measured under lean-burn conditions. Different analytical techniques including XRD, Raman, BET, CO chemisorption, SEM, FTEM, XPS, TPD, TPR and CO + O₂ pulse were undertaken to evaluate its physical and chemical properties. It was concluded that the crystal structure, morphology and specific surface area (SSA) of SmMn₂O₅ remained unchanged after Pd addition. The Pd/SMO-EG&M exhibited a low complete transformation temperature for CO (105 °C) and C₃H₈ (350 °C) oxidation. Such remarkable oxidation activity was attributed to high Pd dispersion (38.4%), which improved the reducibility and mobility of oxygen species, as revealed by TPR and TPD measurements. The high activity of oxygen species for Pd/SMO-EG&M above 250 °C accelerated the oxidation capacity as well. In a word, our study indicates that the macroporous Pd–mullite catalyst has potential applications in exhaust purification for gasoline vehicle.

Pd-modified SMO mullite catalysts were synthesized and found to have excellent catalytic activity for CO and C₃H₈ oxidation. The remarkable oxidation activity was attributed to the high Pd dispersion.

CO oxidation over MOx (M = Mn, Fe, Co, Ni, Cu) supported on SmMn2O5 composite catalysts

The ability to oxidize CO at relatively low temperature is barely satisfactory for pure SmMn₂O₅ (SMO) catalysts.

Macroporous SmMn2O5 mullite for NOx-assisted soot combustion

A series of mullite SmMn₂O₅ oxides were prepared by citric acid (CA), hydrothermal (HT) and co-precipitation (CP) and combustion of ethylene glycol and methanol solutions (EG&M) methods, and tested for NO_x-assisted soot combustion.