New catalyst uses quantum effects to produce fertilizers more efficiently

Synthetic fertilizers, a pivotal advancement in modern agriculture, have played a crucial role in ensuring food security for many nations. Among these, organic ureas (or organoureas) have emerged as significant nitrogen sources for crops. Unlike traditional fertilizers, they don’t readily dissolve in water but are gradually broken down by soil microorganisms, offering a controlled nitrogen supply vital for plant growth.

Yet, the conventional methods of producing organoureas have been detrimental to the environment, involving toxic substances like phosgene. Alternative approaches either rely on costly and scarce noble metals or use non-reusable catalysts.

In a recent endeavor to tackle these issues, a research team led by Honorary Professor Hideo Hosono at the Tokyo Institute of Technology, Japan, harnessed the quantum properties of bismuth selenide (Bi2Se3) to synthesize organoureas. Their groundbreaking work was published in Science Advances.

The researchers exploited the fact that Bi2Se3 is a topological insulator with a remarkably robust surface, boasting unique electronic characteristics that make it an attractive catalyst candidate. To maximize the catalyst’s surface area, they created Bi2Se3 nanoparticles.

Leveraging the robust surface and significant spin–orbit interactions of Bi2Se3, they successfully generated various organic urea derivatives from two amine molecules, carbon monoxide (CO), and oxygen (O2), achieving nearly 100% yield in many cases at room temperature.

To shed light on the reaction mechanism, the team conducted molecular simulations to investigate the surface states of Bi2Se3. A critical step in the synthesis involved removing hydrogen atoms from the amines, allowing them to bond through a –CO group.

The researchers discovered that O2 molecules bind firmly to Bi atoms on the (015) surface of Bi2Se3, altering their spin state from triplet to singlet, which triggers the dissociation of O2. The adsorbed dissociated oxygen groups extract hydrogen from the amines bound to Se, facilitating the CO–amine reaction.

Prof. Hosono explained, “The spin state of the O2 molecule changes from triplet to singlet due to the local magnetic field resulting from the strong spin–orbit interaction of Bi. The singlet O2, with much higher reactivity, pulls hydrogen out of the amine, reducing the energy barrier for the desired reaction.”

This catalytic effect arises from the unique characteristics of topological materials and the strategic choice of Bi and Se for this reaction.

Remarkably, the activity of the Bi2Se3 catalyst surpassed that of other selenium-containing compounds and most existing transition metal-based catalysts. The proposed catalyst nanoparticles also exhibited exceptional stability thanks to their topological features.

Prof. Hosono emphasized, “Catalyst recyclability is vital for practical applications. The Bi2Se3 catalyst can be reused at least 20 times without a significant loss of catalytic activity, in contrast to other selenium-based catalysts which experienced continuous yield decreases.”

This research not only offers a sustainable solution to urea synthesis challenges but also highlights the potential of harnessing specific quantum properties of materials for innovative applications, including sustainable agricultural practices.

Source: Tokyo Institute of Technology

Leave a Comment