Durable, inexpensive catalyst reduces carbon footprint of ammonia production

Credit: Tokyo Tech

The Haber-Bosch process, commonly used to synthesize ammonia (NH.)3)—the basis for synthetic nitrogen fertilizers—by combining hydrogen (H2) and nitrogen (N2) about catalysts at high pressures and temperatures, is one of the most important scientific discoveries that has helped improve crop yields and increase food production worldwide.

However, the process requires a high input of fossil fuels due to the high temperatures and pressures. The hydrogen used for this process is produced from natural gas (mainly methane). This hydrogen production process consumes energy and is accompanied by enormous emissions of carbon dioxide.

To overcome these problems, several catalysts have been developed to allow the reaction to proceed under milder conditions, using hydrogen produced by water electrolysis via renewable energy. Among them are nitride-based catalysts containing active metal nanoparticles such as nickel and cobalt (Ni, Co) loaded on lanthanum nitride (LaN) supports.

In these catalysts, both the support and the active metal are involved in the production of NH3. The active metal splits the H2 while the LaN carrier contains nitrogen vacancies and nitrogen atoms in its crystal structure that adsorb and activate nitrogen (N2

). While these catalysts are inexpensive (because they avoid the use of ruthenium, which is costly), their catalytic performance is reduced in the presence of moisture, with the LaN support changing to lanthanum hydroxide (La(OH)3).

Now, in a new study published in Angewandte Chemistry, researchers from China and Japan, led by Professor Hideo Hosono of the Tokyo Institute of Technology (Tokyo Tech), Japan, have developed a chemically stable catalyst that is stable in the presence of moisture. Inspired by stable rare earth compounds containing chemical bonds between a rare earth metal (in this case La) and a metal, they incorporated aluminum atoms into the LaN structure and synthesized a chemically stable La3AlN support with La-Al bonds that prevent lanthanum atoms from reacting with moisture.

The La-Al-N support together with the active metals, such as nickel and cobalt (Ni, Co), could produce NH3 at rates comparable to those achieved with conventional metal nitride catalysts, and could maintain stable production when fed with nitrogen gaseous moisture. “The Ni- or Co-loaded La-Al-N catalysts showed no apparent degradation after exposure to 3.5% moisture,” says Prof. Hosono.

While the Al atoms stabilized the support, the lattice nitrogen and nitrogen defects present in the doped support enabled the synthesis of ammonia in a manner comparable to the conventional active metal/rare earth nitride catalysts. “Both lattice nitrogen and nitrogen vacancy in La-Al-N play a key role in N2 adsorption, where the La-Al-N support and the active metal Ni are responsible for N2 and H2 absorption and activation respectively,” explains Prof. Hosono.

Related Post

The Haber-Bosch process is an energy-intensive chemical reaction, accounting for approximately 1% of global annual CO2 emissions. While alternative eco-friendly approaches for NH3

production, the introduction of low-cost catalysts can provide immediate benefits by operating the process under milder conditions.

Filling the Void in Ammonia Synthesis: The Role of Nitrogen Vacancies in Catalysts

More information:
Yangfan Lu et al, Approach to chemically sustainable nickel and cobaltlanthane nitride-based catalysts for ammonia synthesis, Angewandte Chemie International Edition (2022). DOI: 10.1002/anie.202211759

Provided by Tokyo Institute of Technology

Quote: Sustainable, low-cost catalyst reduces carbon footprint from ammonia production (2022, October 19) Retrieved October 19, 2022 from https://phys.org/news/2022-10-durable-inexpensive-catalyst-carbon-footprint.html

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