Quantum dots keep atoms apart for increased catalysis

Engineers at Rice University have led the development of processes that use functionalized graphene quantum dots to trap transition metals and achieve single-atom catalysis with higher metal loads. Credit: Wang Group / Rice University

Wait a minute, graphene. Seriously, your grip may help make a better catalyst.

Rice University engineers may assemble and transform what they say Chemical catalysis By significantly increasing the number of transition metal single atoms that can be placed on carbon carriers.

This technique uses graphene quantum dots (GQD), which are 3-5 nanometer particles of ultra-strong 2D carbon material, as a fixation support. They promote high density transition metal single atoms with ample space between atoms to avoid agglomeration.

An international team led by Haotian Wang, a chemistry and biomolecule engineer at Brown Institute of Technology in Rice, and Yongfeng Hu, a Canadian Light Source at the University of Saskatchewan, Canada, Nature Chemistry.

They proved the value of general synthesis of high metal loads. Single atom catalyst By creating a GQD-enhanced nickel catalyst, the electrochemical reduction of carbon dioxide was significantly improved in reaction tests compared to catalysts with low nickel content.

Wang said expensive precious metals such as platinum and iridium have been extensively studied by the single-atom catalyst community with the aim of reducing the mass required for catalytic reactions. However, metals are difficult to handle and usually make up a small portion of up to 5-10% by weight of the total catalyst, including the carrier material.

In contrast, Wang Labs achieved transition metal loading with a single atom of iridium. catalyst Single metal atoms up to 40% by weight, or 3-4 spaced for every 100 carbon substrate atoms. (This is because iridium is much heavier than carbon.)

“This work focuses on the basic but very interesting questions we always ask ourselves. How many more single atoms can be loaded on the carbon support and will not eventually aggregate? ? ”Said Wang, whose lab is focusing on the energy-efficient catalysis of precious chemicals.

“Reducing the size of bulk materials to nanomaterials increases surface area and catalysis,” he said. “In recent years, people have begun to work on shrinking catalysts into single atoms to show better activity and better selectivity. The higher the load reached, the better the performance that can be achieved.”

“Single atoms exhibit the maximum surface area for catalysis, and their physical and electronic properties are very different compared to bulk or nanoscale systems,” he said. “In this study, we wanted to push the limits of the number of atoms that could be loaded onto a carbon substrate.”

He said the synthesis of single-atom catalysts must now be a “top-down” or “bottom-up” process. The first one, carbon Sheets or nanotubes for metal atoms, but the pores are often too large or non-uniform, so the metal can still agglomerate. The second is to anneal and “carbonize” metals and other organic precursors, but metals still tend to cluster.

The new process takes an intermediate approach by synthesizing GQDs functionalized with amine linkers and then pyrolyzing them with metals. atom..Amine metal It diffuses ions and maximizes their availability to catalyze the reaction.

“Using this approach, the maximum seems to be about 3-4 atomic percent,” Wang said. “Future challenges include ways to further increase the density. Single atomIt ensures high stability of real-world applications and scales up their synthesis process. ”

Mobilize bacteria to build catalysts atom by atom

For more information:
Chuan Xia et al, General Synthesis of High Metal Loaded Single Atomic Catalysts Using Graphene Quantum Dots, Nature Chemistry (2021). DOI: 10.1038 / s41557-021-00734-x

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Rice University

Quote: Quantum dots are catalytically obtained from on June 25, 2021 (2021, June 25). ) Keep atomic spacing to boost

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Quantum dots keep atoms apart for increased catalysis

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