A Highly Effective Catalyst of Sm-MnO_<i>x</i> for the NH₃‑SCR of NO_<i>x</i> at Low Temperature: Promotional Role of Sm and Its Catalytic Performance

Sm-Mn mixed oxide catalysts prepared by the coprecipitation method were developed, and their catalytic activities were tested for the selective catalytic reduction (SCR) of NO with ammonia at low temperature. The results showed that the amount of Sm markedly influenced the activity of the MnO_<i>x</i> catalyst for SCR, that the activity of the Sm-Mn mixed oxide catalyst exhibited a volcano-type tendency with an increase in the Sm content, and that the appropriate mole ratio of Sm to Mn in the catalyst was 0.1. In addition, the presence of Sm in the MnO_<i>x</i> catalyst can obviously enhance both water and sulfur dioxide resistances. The effect of Sm on the physiochemical properties of the Sm-MnO_<i>x</i> catalyst were investigated by XRD, low-temperature N₂ adsorption, XPS, and FE-SEM techniques. The results showed that the presence of Sm in the Sm-MnO_<i>x</i> catalyst can restrain the crystallization of MnO_<i>x</i> and increase its surface area and the relative content of both Mn⁴⁺ and surface oxygen (O_S) on the surface of the Sm-MnO_<i>x</i> catalyst. NH₃-TPD, NO-TPD, and in situ DRIFT techniques were used to investigate the absorption of NH₃ and NO on the Sm-MnO_<i>x</i> catalyst and their surface reactions. The results revealed that the presence of Sm in the Sm_0.1-MnO_<i>x</i> catalyst can increase the absorption amount of NH₃ and NO on the catalyst and does not vary the SCR reaction mechanism over the MnO_<i>x</i> catalyst: that is, the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms (bidentate nitrate is the active intermediate), in which the Eley–Rideal mechanism is predominant

Total Oxidation of Propane over a Ru/CeO₂ Catalyst at Low Temperature

Ruthenium (Ru) nanoparticles (∼3 nm) with mass loading ranging from 1.5 to 3.2 wt % are supported on a reducible substrate, cerium dioxide (CeO₂, the resultant sample is called Ru/CeO₂), for application in the catalytic combustion of propane. Because of the unique electronic configuration of CeO₂, a strong metal–support interaction is generated between the Ru nanoparticles and CeO₂ to stabilize Ru nanoparticles for oxidation reactions well. In addition, the CeO₂ host with high oxygen storage capacity can provide an abundance of active oxygen for redox reactions and thus greatly increases the rates of oxidation reactions or even modifies the redox steps. As a result of such advantages, a remarkably high performance in the total oxidation of propane at low temperature is achieved on Ru/CeO₂. This work exemplifies a promising strategy for developing robust supported catalysts for short-chain volatile organic compound removal

Incorporating Rich Mesoporosity into a Ceria-Based Catalyst via Mechanochemistry

Ceria-based materials possessing mesoporous structures afford higher activity than the corresponding bulk materials in CO oxidation and other catalytic applications, because of the wide pore channel and high surface area. The development of a direct, template-free, and scalable technology for directing porosity inside ceria-based materials is highly welcome. Herein, a family of mesoporous transition-metal-doped ceria catalysts with specific surface areas up to 122 m² g^–1 is constructed by mechanochemical grinding. No templates, additives, or solvents are needed in this process, while the mechanochemistry-mediated restructuring and the decomposing of the organic group led to plentiful mesopores. Interestingly, the copper species are evenly dispersed in the ceria matrix at the atomic scale, as observed in high resolution scanning transmission electron microscopy in high angle annular dark field. The copper-doped ceria materials show good activity in the CO oxidation

Highly Efficient Oxidation of Propane at Low Temperature over a Pt-Based Catalyst by Optimization Support

Pt-based catalysts have attracted widespread attention in environmental protection applications, especially in the catalytic destruction of light alkane pollutants. However, developing a satisfying platinum catalyst with high activity, excellent water-resistance, and practical suitability for hydrocarbon combustion at low temperature is challenging. In this study, the Pt catalyst supported on the selected Nb2O5 oxide exhibited an efficient catalytic activity in propane oxidation and exceeded that of most catalysts reported in the literature. More importantly, the Pt/Nb2O5 catalyst maintained excellent activity and durability even after high-temperature aging at 700 °C and under harsh working conditions, such as a certain degree of moisture, high space velocity, and composite pollutants. The excellent performance of the Pt/Nb2O5 catalyst was attributed to the abundant metallic Pt species stabilized on the surface of Nb2O5, which prompted the C–H bond dissociation ability as the rate-determining step. Furthermore, propane was initially activated via oxidehydrogenation and followed the acrylate species path as a more efficient propane oxidation path on the Pt/Nb2O5 surface. Overall, Pt/Nb2O5 can be considered a promising catalyst for the catalytic oxidation of alkanes from industrial sources and could provide inspiration for designing superb catalysts for the oxidation of light alkanes

Low-Temperature Methane Combustion over Pd/H-ZSM-5: Active Pd Sites with Specific Electronic Properties Modulated by Acidic Sites of H‑ZSM‑5

Pd/H-ZSM-5 catalysts could completely catalyze CH₄ to CO₂ at as low as 320 °C, while there is no detectable catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the theoretical and experimental results prove that surface acidic sites could facilitate the formation of active metal species as the anchoring sites, which could further modify the electronic and coordination structure of metal species. PdO_<i>x</i> interacting with the surface Brönsted acid sites of H-ZSM-5 could exhibit Lewis acidity and lower oxidation states, as proven by the XPS, XPS valence band, CO-DRIFTS, pyridine FT-IR, and NH₃-TPD data. Density functional theory calculations suggest PdO_<i>x</i> groups to be the active sites for methane combustion, in the form of [AlO₂]­Pd­(OH)-ZSM-5. The stronger Lewis acidity of coordinatively unsaturated Pd and the stronger basicity of oxygen from anchored PdO_<i>x</i> species are two key characteristics of the active sites ([AlO₂]­Pd­(OH)-ZSM-5) for methane combustion. As a result, the PdO_<i>x</i> species anchored by Brønsted acid sites of H-ZSM-5 exhibit high performance for catalytic combustion of CH₄ over Pd/H-ZSM-5 catalysts

Revealing the Size Effect of Ceria Nanocube-Supported Platinum Nanoparticles in Complete Propane Oxidation

The elimination of propane is one of the key tasks in reducing volatile organic compounds (VOCs) and automotive exhaust emissions. The platinum nanoparticle (NP) is a promising catalyst for propane oxidation, while the study of its structural characteristics and functionality remains in its infancy. In this work, we synthesized the nanocubes CeO2 with a well-defined (100) facet supporting Pt NPs with various sizes, from 1.3 to 7 nm, and systematically investigated the effect of the Pt size on complete propane oxidation efficiency. In particular, CeO2(100) supported Pt NPs smaller than 4 nm promote the formation of positively charged Pt sites, which hinder the adsorption and activation of propane and reduce the intrinsic activity for propane oxidation. Consequently, within this size range, the catalytic performance is primarily influenced by the electronic state of the Pt species, with metallic Pt being identified as the active site for the reaction. Conversely, as the particle size exceeds 4 nm, metallic Pt particles become dominant and the geometric structure starts to influence the activity as well. Such entanglement of electronic and geometric factors gives rise to a volcano relationship between reaction rates and Pt particle sizes ranging from 1.3 to 7 nm, while an increased correlation can be observed between the turnover frequencies and the particle sizes in this range. This knowledge can guide the synthesis of highly active catalysts, enabling the efficient oxidation of VOCs with reduced precious metal loadings