Nanocarbon catalyst design unlocks new avenue for sustainable fuel additive production

Vehicle exhaust from fossil fuel combustion constitutes a main source of air pollutants like carbon dioxide and carbon monoxide. To mitigate air pollution, researchers are looking into additives to fuels like dimethoxymethane (DMM). But DMM production brings its own environmental hazards.

In their paper published June 21 in Carbon Future, a Chinese research team demonstrated how a series of phosphorous-modified nanocarbon catalysts could advance green DMM production.

Unique fuel properties of this diesel blend fuel include high oxygen content and chemical stability as well as low toxicity. A blend of DMM and conventional diesel fuels has been shown to reduce soot formation by as much as 80%.

Commercially, DMM is produced via an established two step-process of methanol oxidation forming formaldehyde, followed by coupling with methanol. However, this conventional synthetic route is complex and environmentally unfriendly due to the complicated sequenced reactions and the use of hazardous acidic catalysts.

To overcome these drawbacks, researchers have been exploring alternative methods to produce DMM. In one promising route, the use of non-metallic nanocarbon materials as catalyst enables the production of DMM in one step.

Non-metallic nanocarbon-based catalysts have emerged in recent years as sustainable, reliable alternatives to the metal catalysts that have traditionally been used as supports in chemical reactions.

“One-step synthesis of DMM via selective oxidation of methanol under the catalysis of nanocarbon is a green and sustainable but challenging chemical process,” said Wei Qi from the University of Science and Technology of China. “Nanocarbon materials have demonstrated notable activity and stability in various catalytic reactions.”

However, achieving one-step synthesis of DMM via methanol conversion requires striking a delicate balance between redox (oxidation-reduction reaction) and acid sites, and there are still many unanswered questions regarding nano carbon catalysts.

For instance, the performance of nanocarbon materials is significantly influenced by functional groups on the surface—but, so far, nanocarbon materials exhibit uncontrollable surface functional groups, which complicates the identification of active sites for different types of reactions.

Recent studies have shown how modifying nanocarbons with nonmetallic heteroatom can effectively adjust surface characteristics and redox/acidic catalytic activity to achieve highly efficient and selective DMM synthetic routes.

Expanding on this line of research, the Chinese research team prepared a series of phosphorus-modified carbon catalysts for the one-step synthesis of DMM from methanol.

With this approach, the team achieved high methanol conversion and DMM formation rate simultaneously.

Through extensive characterization and corresponding control experiments, their research revealed that the covalent linkage of phosphorus and nanocarbon (namely a bond where a carbon atom and a phosphorus atom share a pair of electrons) is a key factor contributing to high DMM selectivity, which indicates efficiency and precision with which a catalyst converts raw materials into the fuel additive products.

“This work provided not only a novel and sustainable carbon-based catalyst for the one step synthesis of DMM but also deep insights into the rational design of nanocarbon catalyst for related reaction system,” Qi said.

Their publication provided a new idea for the design of novel nanocarbon materials as well as a potential green catalyst for the efficient selective conversion of methanol to DMM.

Other contributors include Xueya Dai, Pengqiang Yan, Yunli Bai and Miao Guo from the Institute of Metal Research at the Chinese Academy of Sciences. Dai and Bai are also associated with the University of Science and Technology of China.