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) Nitrides 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 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.
The team’s next steps include the synthesis of other bimetallic TMCs, as well as transition metal nitride (TMN) Nitrides Nanoparticles. The team is investigating these materials for other electrocatalytic reactions as well as thermal catalytic reactions, such as hydrodeoxygenation for biomass reforming.
This new method unlocks a broad range of monometallic and heterometallic transition metal carbide and nitride Nitrides Nanoparticles that researchers previously have been unable to synthesize or study,” said Yuriy Rom¨¢n, an assistant professor of chemical engineering who worked on the technology. “While our research focuses mainly on the sustainable replacement of PGMs in thermal and electrocatalytic applications, we also anticipate broader impacts of our new TMC and TMN technologies outside catalysis. Because of their unique chemical, mechanical, and electronic properites, carbides and nitrides have garnered much attention for use in applications as diverse as supercapacitors, medical implants, optoelectronics, coatings, and high-temperature materials for the aerospace and nuclear sectors.”
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These high temperatures cause Nitrides Nanoparticles to sinter into large microparticles with low surface areas
Hongwu International Group Ltd, with HWNANO brand, is a high-tech enterprise focusing on manufacturing, research, development and processing of nanoparticles,nanopowders, micron powders.
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 Nitrides Nanoparticles are relatively easy to synthesize, until now, there have been no known methods to synthesize WC Nitrides 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 Nitrides Nanoparticles to sinter into large microparticles with low surface areas. Methods to date that alleviate this agglomeration instead result in Nitrides 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 Nitrides 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 Nitrides Nanoparticles. This transforms the oxide Nitrides Nanoparticles into transition metal carbide (TMC) Nitrides 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 Nitrides 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 Nitrides 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 Nitrides Nanoparticles made by current state-of-the-art synthesis methods that do not prevent sintering or surface carbon deposition..
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Such “nanotwinned” crystals are much harder than ordinary diamonds, by a factor of two
Hongwu International Group Ltd, with HWNANO brand, is a high-tech enterprise focusing on manufacturing, research, development and processing of nanoparticles,nanopowders, micron powders.
Diamonds are the hardest naturally occurring minerals known to man. Even so, scientists are working to make them even tougher, in order to use the sparkling gems as tools for cutting.
Now, a team of researchers, led by Yongjun Tian and Quan Huang at Yanshan University in China, has created synthetic diamonds that are harder, meaning they are less prone to deformation and breaking, than both natural and other man-made diamonds.
To create these tougher-than-steel diamonds, the researchers used tiny particles of carbon, layered like onions, and subjected them to high temperatures and pressures. The resulting diamonds had a unique structure that makes them more resistant to pressure and allows them to tolerate more heat before they oxidize and turn to either gas (carbon dioxide and monoxide) or ordinary carbon, losing many of their unique diamond properties.
First, a bit about diamonds: Gem-quality diamonds are single crystals, and they are quite hard. But artificial diamonds used on tools are harder still. That’s because they are polycrystalline diamonds, or aggregates of diamond grains called domains, that measure a few micrometers or nanometers across. The grains help to prevent the diamond from breaking, as the boundaries act like small walls that keep chunks of diamond in place. The smaller the domains are, the stronger the diamond.
Tian’s team used the onionlike carbon Nitrides Nanoparticles to make diamonds with domains that are a few nanometers in size and are mirror images of each other. Such “nanotwinned” crystals are much harder than ordinary diamonds, by a factor of two.
The team tested the artificial diamond’s hardness by pressing a pyramid-shaped piece of diamond into the nanotwinned diamond. Tian’s group made a small indentation in their artificial diamond, applying pressures equivalent to nearly 200 gigapascals (GPa) about 1.9 million atmospheres. An ordinary natural diamond would crush under just half that pressure.
The team also tested how hot the nanotwinned diamond could get before oxidizing. In two different tests, they found that the ordinary diamond began to oxidize at about 1,418 and 1,481 degrees Fahrenheit (770 and 805 degrees Celsius), depending on the testing method. The nanotwinned diamonds didn’t oxidize until they reached 1,796 or 1,932 F (980 or 1,056C).
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These high temperatures cause Carbides Nanoparticles to sinter into large microparticles with low surface areas
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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