Chinese Chemists Find the Hidden Atomic Structure That Powers Methane Conversion

Turning methane into syngas — a mixture used to make fuels and chemicals — through a process called partial oxidation of methane has long been thought to rely on tiny particles of metallic nickel as the active catalyst. But researchers led by Profs. Tao Zhang, Aiqin Wang and Xiaoyan Liu of the Dalian Institute of Chemical Physics (DICP) at the Chinese Academy of Sciences, working with colleagues at Xi'an Jiaotong University and Cardiff University, report in Nature Catalysis that the true active structure is something else: a specific atomic arrangement that forms only while the reaction is under way, on the surface of nickel oxide.

The team built a catalyst containing just 0.8% nickel by weight, using a method called microemulsion synthesis. Despite that low nickel content, it converted 92% of the methane fed into it, with carbon monoxide and hydrogen selectivities of 87.0% and a stable hydrogen-to-carbon-monoxide ratio of about 2.0 — performance comparable to a catalyst with ten times as much nickel made by a conventional method. A second catalyst with the same low nickel content, but made by that conventional method, performed far worse and mainly just burned the methane completely instead of converting it.

Almost no metallic nickel could be detected in the well-performing catalyst after the reaction, even though metallic nickel nanoparticles were present at the start and quickly oxidised into nickel oxide. Yet plain nickel oxide alone was not the answer either: a catalyst made of pure nickel oxide showed no useful activity and, like the poorly performing catalyst, only burned the methane. Examining the catalyst while the reaction was happening, the researchers found that the nickel oxide surface reconstructs itself into a specific new atomic unit, which computer calculations showed makes it far easier to break the chemical bonds in methane — the key step in activating the gas.

"Our study highlights the critical role of in situ characterization in identifying dynamic active structures under reaction conditions," said Prof. Wei Liu of DICP. "Dynamic reconstruction enables low-loading catalysts to achieve high performance, offering new opportunities for the rational design of efficient catalysts while reducing reliance on high metal loadings."