Hongwu International Group Ltd, with HWNANO brand, is a high-tech enterprise focusing on manufacturing, research, development and processing of nanoparticles,nanopowders, micron powders.
In a paper published recently in the journal Angewandte Chemie, an MIT team has explained a process of synthesizing catalysts made using modified tungsten carbide (WC) Carbides Nanoparticles as an alternative to platinum.
While platinum-group metals (PGMs) make the most stable and active catalysts, they are unsustainable resources.
In this way, tungsten, with six valence electrons, can be electronically modified to mimic platinum, which has 10 valence electrons, by reacting it with carbon (four valence electrons) to give the ceramic material tungsten carbide. Numerous studies have shown that WC is indeed platinum-like, and able to catalyze important thermo and electrocatalytic reactions that tungsten metal cannot ¡ª such as biomass conversion, hydrogen evolution, oxygen reduction, and alcohol electrooxidation. Importantly, tungsten is more than three orders of magnitude more abundant than platinum in the Earth¡¯s crust, making it a viable material for a global renewable-energy economy.
However, both WC and platinum are heterogeneous catalysts, meaning that they require nanoparticle formulations to create high surface areas and invoke quantum confinement effects to maximize the rates of chemical reactions. While platinum Carbides Nanoparticles are relatively easy to synthesize, until now, there have been no known methods to synthesize WC Carbides Nanoparticles less than 5 nanometers and devoid of surface impurities. Tungsten carbide forms at very high temperatures, typically over 800¡ãC (1500¡ãF). These high temperatures cause Carbides Nanoparticles to sinter into large microparticles with low surface areas. Methods to date that alleviate this agglomeration instead result in Carbides Nanoparticles that are covered with excess surface carbon. These surface impurities greatly reduce, or completely eliminate, the catalytic activity of WC.
To solve this problem, the MIT team developed a ¡°removable ceramic coating method¡± by coating colloidally dispersed transition-metal oxide Carbides Nanoparticles with microporous silica shells. At high temperatures, they show that reactant gases, such as hydrogen and methane, are able to diffuse through these silica shells and intercalate into the encapsulated metal oxide Carbides Nanoparticles. This transforms the oxide Carbides Nanoparticles into transition metal carbide (TMC) Carbides Nanoparticles, while the silica shells prevent both sintering and excess carbon deposition. The silica shells can then be easily removed at room temperature, allowing the dispersal of nonsintered, metal-terminated TMC Carbides Nanoparticles onto any high-surface-area catalyst support. This is the first method capable of this result.
The team has also been successful in synthesizing the first nonsintered, metal-terminated bimetallic TMC Carbides Nanoparticles. Electrocatalytic studies have shown that these materials are able to perform hydrogen evolution and methanol electrooxidation at rates similar to commercial PGM-based catalysts, while maintaining activity over thousands of cycles. The catalytic activities obtained were more than two orders of magnitude better than commercial WC powders and WC Carbides Nanoparticles made by current state-of-the-art synthesis methods that do not prevent sintering or surface carbon deposition..
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