New catalytic material converts methane to formaldehyde with near-100% selectivity

Researchers from the University College London and two esteemed professors, Zhengxiao Guo from the Department of Chemistry at The University of Hong Kong (HKU) and Junwang Tang from the Department of Chemical Engineering at Tsinghua University, have collaborated to develop a groundbreaking catalytic material. This innovative substance, derived from tungsten trioxide (WO3 catalyst), exhibits exceptional activity and selectivity in converting methane, a potent greenhouse gas, into formaldehyde, a crucial chemical compound. Importantly, this conversion process is waste-free and environmentally friendly.

The unique characteristic of this material lies in its dual active site, consisting of copper and tungsten atomic species. These components work synergistically, ensuring an efficient and selective conversion of methane. Notably, the process achieves nearly 100% selectivity when exposed to visible light, eliminating the production of unwanted byproducts and significantly enhancing overall efficiency. The remarkable findings of this research have been recently published in the esteemed journal Nature Communications.

Change the unchanged: Methane conversion

Methane, the main component of natural gas, is widely utilized as a carbon source for various chemicals. However, its use comes with a downside as it is a potent greenhouse gas, with over 70 times the global warming potential of carbon dioxide. This presents a significant opportunity to address environmental concerns and achieve net-zero energy and chemical supplies by catalytically converting methane into other compounds.

Nevertheless, methane is an exceptionally stable molecule, making it challenging to activate, especially under mild or ambient conditions. The successful activation of the carbon-hydrogen bonds in methane is often considered one of the most difficult goals in catalysis, and chemists worldwide strive to achieve high activity and selectivity in methane conversion.

On the other hand, formaldehyde is a widely used chemical with a market value of USD 8 billion, experiencing a compound annual growth rate (CAGR) of 5.7%. It finds application in various sectors such as households, commercial settings, aviation, medicine, and automotive industry. Formaldehyde is a valuable precursor for the production of melamine, urea-formaldehyde resins, phenolic resins, and more. Additionally, it is safely employed in the manufacture of vaccines, anti-infective drugs, and hard-gel capsules.

Currently, formaldehyde is produced through methanol oxidation-dehydrogenation, which involves silver or metal-oxide catalysts at high reactor temperatures exceeding 500°C–600°C. Unfortunately, this process leads to significant carbon dioxide emissions and energy penalties.

Harnessing sunlight to convert methane

In a recent study, researchers have made a remarkable discovery regarding the conversion of methane gas into formaldehyde using sunlight. By employing a combination of atomically dispersed copper and partially reduced tungsten species over tungsten oxide, they achieved outstanding results in photocatalytic methane conversion to formaldehyde under ambient visible light. The unique synergy between these catalyst components exhibited nearly 100% selectivity and high conversion efficiency, surpassing previously reported photocatalysts in terms of turnover frequency.

The team conducted a thorough mechanistic analysis to understand the underlying processes. They found that copper played a crucial role in facilitating electron movement and creating reactive molecular species, while tungsten aided in methane gas activation. Specifically, copper acted as an electron acceptor, promoting photo-induced electron transfer from the conduction band to dioxygen, which generated highly reactive hydroperoxyl radicals (HOO·). On the other hand, the adjacent tungsten atom with a partial positive charge acted as a hole acceptor. Water molecules preferred adsorption and activation sites on the catalyst, generating hydroxyl radicals and effectively activating methane into methyl radicals. The collaboration between these dual active sites greatly enhanced the overall efficiency and selectivity of the conversion process.

This significant finding opens up new avenues for research and development of novel photocatalysts for various chemical conversions. It holds the potential to drive sustainable and efficient processes in the chemical industry, contributing to both low-carbon and high-value-added chemical syntheses. The study emphasizes the importance of a comprehensive understanding of the conversion mechanism, meticulous catalyst design, and the use of complementary techniques to validate performance. Professor Zhengxiao Guo, one of the corresponding authors, expressed the significance of this research, highlighting the multidisciplinary effort and collaborative dedication involved in achieving such valuable outcomes.

Source: The University of Hong Kong

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