5 Search Results

Zeolite-confined metal nanoparticles (NPs) have attracted much attention owing to their superior sintering resistance and broad applications for thermal and environmental catalytic reactions. However, the pore size of the conventional zeolites is usually below 2 nm, and reactants are easily blocked to access the active sites. Herein, a facile in situ mesoporogen-free strategy is developed to design and synthesize palladium (Pd) NPs enveloped in a single-crystalline zeolite (silicalite-1, S-1) with intra-mesopores (termed Pd@IM-S-1). Pd@IM-S-1 exhibited remarkable light alkanes deep oxidation performances, and it should be attributed to the confinement and guarding effect of the zeolite shell and the improvement inmore » mass-transfer efficiency and active metal sites accessibility. The Pd–PdO interfaces as a new active site can provide active oxygen species to the first C–H cleavage of light alkanes. This work exemplifies a promising strategy to design other high-performance intra-crystalline mesoporous zeolite-confined metal/metal oxide catalysts for high-temperature industrial thermal catalysis.« less

Carbon dioxide and methane are two main greenhouse gases which are contributed to serious global warming. Fortunately, dry reforming of methane (DRM), a very important reaction developed decades ago, can convert these two major greenhouse gases into value-added syngas or hydrogen. The main problem retarding its industrialization is the seriously coking formation upon the nickel-based catalysts. Herein, a series of confined indium-nickel (In-Ni) intermetallic alloy nanocatalysts (In_xNi@SiO₂) have been prepared and displayed superior coking resistance for DRM reaction. The sample containing 0.5 wt.% of In loading (In_0.5Ni@SiO₂) shows the best balance of carbon deposition resistance and DRM reactivity even aftermore » 430 h long term stability test. The boosted carbon resistance can be ascribed to the confinement of core–shell structure and to the transfer of electrons from Indium to Nickel in In-Ni intermetallic alloys due to the smaller electronegativity of In. Additionally, both the silica shell and the increase of electron cloud density on metallic Ni can weaken the ability of Ni to activate C–H bond and decrease the deep cracking process of methane. The reaction over the confined InNi intermetallic alloy nanocatalyst was conformed to the Langmuir-Hinshelwood (L-H) mechanism revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS). This work provides a guidance to design high performance coking resistance catalysts for methane dry reforming to efficiently utilize these two main greenhouse gases.« less

Mesoporous metal oxides with wide pore size, high surface area, and uniform porous structures have demonstrated excellent advantages in various fields. Yet, the state-of-art synthesis approaches are dominated by wet chemistry, accompanied by use of excessive solvent, and the requirement of time-consuming drying process. Herein, we report a mechanochemical solid-state route to synthesize mesoporous Al₂O₃ (meso-Al₂O₃) via aluminum isopropoxide-copolymers assembly. The obtained meso-Al₂O₃ reflects a record high surface area (~644 m² g^-1) and narrow pore size distribution (centered at ~5 nm). Moreover, a mechanochemical nonhydrolytic sol-gel strategy is introduced to fabricate mesoporous transition metal (Cu, Co, Mn, Fe, Mg, Ni)-aluminummore » binary oxide by using anhydrous metal chlorides and aluminum isopropoxide interplay. More importantly, four or five metals-aluminum oxide complexes with abundant mesopores and single cubic crystalline phase known as high-entropy ceramics are produced. To the best of our knowledge, mesoporous high-entropy metal oxides have not been prepared before, because the high crystallization temperature would make mesopores collapse. Furthermore, this high-entropy property endows (CuNiFeCoMg)O_x-Al₂O₃ with superior SO2-resisting performance (1000 ppm of SO₂ in N₂ at 280 °C) in the catalytic oxidation of CO compared to single CuO-Al₂O₃.« less

Cerium oxide is one of the most important rare earth metal oxides in catalysis, however, the sintering problem of noble metals and CeO₂ at higher temperature (e.g., >700 °C) is still unresolved. Herein, Pt nanoparticles self-assembled on ultra-thin CeO₂ nanowires (NWs) and then confined inside a thermally robust porous silica shell (Pt-CeO2NW@SiO₂) were introduced. The thickness of CeO₂ NWs was just ~2.0 nm. Moreover, Pt-CeO₂ NW@SiO₂ showed significantly enhanced catalytic performances for total oxidation of CO and toluene. The increased catalytic properties are attributed to the strong metal-support interaction effect between Pt and CeO₂ NWs at sub-nanoscale. Most importantly, themore » special core-shell structure also affords excellent sintering resistance retention up to 700 °C for 100 h, due to the guarding effect of porous silica shell. Finally, the formation mechanism of Pt-CeO₂ NW@SiO₂ was investigated in detail. Current strategy should inspire many rational designs of rare-earth metal-based nanocatalysts for real-world catalysts.« less

This work reports a new strategy toward the design of a new class of supported catalysts with intrinsic high-temperature stabilities through entropy maximization.