Facile Controlled Synthesis of Pt/MnO₂ Nanostructured Catalysts and Their Catalytic Performance for Oxidative Decomposition of Formaldehyde

Pt/MnO₂ nanostructured catalysts with cocoon-, urchin-, and nest-like morphologies were synthesized by a facile method. The synthesized MnO₂ nanostructures and Pt/MnO₂ catalysts were characterized by means of X-ray diffraction (XRD), N₂ adsorption–desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). TEM analyses showed that Pt nanoparticles of 1–4 nm were evenly dispersed on the surface of three MnO₂ nanostructures, and no Pt nanoparticle agglomeration occurred in the Pt/MnO₂ catalysts. These Pt/MnO₂ catalysts showed much higher catalytic activities than the corresponding MnO₂ nanostructures for oxidative decomposition of formaldehyde. Comparison of Pt/MnO₂ catalysts with varied Pt loadings and MnO₂ morphologies revealed that 2 wt % is the optimal Pt loading, and 2 wt % Pt/nest-like MnO₂ showed the highest catalytic activity for oxidative decomposition of formaldehyde (temperature for complete decomposition of HCHO is 70 °C). The high dispersion and small size of Pt nanoparticles and the synergistic effect between the Pt nanoparticle and MnO₂ nanostructure are considered to be the main reasons for the observed high catalytic activity of Pt/nest-like MnO₂

Three-Dimensionally Ordered Macroporous Mn_<i>x</i>Ce_1–<i>x</i>O_δ and Pt/Mn_0.5Ce_0.5O_δ Catalysts: Synthesis and Catalytic Performance for Soot Oxidation

Three-dimensionally ordered macroporous (3DOM) Mn_<i>x</i>Ce_1–<i>x</i>O_δ oxides with different ratios of Mn to Ce were successfully synthesized by colloidal crystal template (CCT) method, and 3DOM Pt/Mn_0.5Ce_0.5O_δ with varied Pt loadings were prepared by in situ ethylene glycol (EG) reduction method. 3DOM Mn_<i>x</i>Ce_1–<i>x</i>O_δ supports exhibited well-defined 3DOM nanostructure, and Pt nanoparticles (NPs) with 1–2 nm size were evenly dispersed on the inner walls of uniform macropores. Among 3DOM Mn_<i>x</i>Ce_1–<i>x</i>O_δ catalysts, 3DOM Mn_0.5Ce_0.5O_δ showed excellent catalytic activity for soot combustion; i.e., <i>T</i>₅₀ is 358 °C and <i>S</i>_CO₂^m is 94.2%. 3DOM Pt/Mn_0.5Ce_0.5O_δ catalysts exhibited higher activity than 3DOM Mn_<i>x</i>Ce_1–<i>x</i>O_δ and 3 wt % Pt/Mn_0.5Ce_0.5O_δ showed the highest catalytic activity for soot combustion (<i>T</i>₅₀ is 342 °C and <i>S</i>_CO₂^m is 96.7%). Macropores effect, synergistic effects between Mn and Ce, and synergistic effects between Pt and Mn_0.5Ce_0.5O_δ support are contributed to high catalytic activities of as-prepared catalysts

Simultaneous Removal of Soot and NO<i>_x</i> from Diesel Engines over Three-Dimensionally Ordered Macroporous ZSM-5-Supported MMnO_δ Catalysts

Three-dimensionally ordered macroporous (3DOM) ZSM-5 support was successfully designed and synthesized via a combination of seed- and steam-assisted methods. In addition, MMnOδ/3DOM ZSM-5 (M = Fe, Co, Ce, Pr, and W) catalysts were prepared using ZSM-5 as a carrier and showed good catalytic performance, which may be due to the catalysts’ unique pore structures and interactions between M and Mn. 3DOM ZSM-5-supported PrMnOδ possesses the best reaction performance for soot oxidation, with a lowest peak temperature of 430 °C, and the best low-temperature denitration performance, with a temperature window of 149–336 °C when NO conversion is 80%. This may be due to the catalyst’s better redox performance, abundant active oxygen and acidic sites, and the higher content of Mn4+ and OII/OI ratio compared with the other MMnOδ/3DOM ZSM-5 catalysts. Meanwhile, the high turnover frequency and low Ea over 3DOM ZSM-5-supported PrMnOδ also contributed to its high intrinsic activity. The corresponding reaction mechanisms were proposed according to in situ diffuse reflectance infrared Fourier transform spectroscopy analysis and other characterizations. At low temperature (<300 °C), the selective catalytic reduction reaction follows the Eley–Rideal and Langmuir–Hinshelwood mechanisms. At a high temperature, the mechanisms for soot combustion include active oxygen oxidation and NO2-assisted mechanisms