Washington, May 22 : In a novel work, researchers have identified the structure of a catalytic material that can turn methane into a safe and easy-to-transport liquid, which lays the foundation for converting excess methane into a variety of useful fuels and chemicals.
"There's a big interest in doing something with this 'stranded' methane other than flaring it off," said chemist Chuck Peden of the Department of Energy's Pacific Northwest National Laboratory. "An important thing researchers have struggled with is determining the structure of the active catalyst," he added.
Now, researchers at PNNL (Pacific Northwest National Laboratory) and the Chinese Academy of Sciences' Dalian Institute of Chemical Physics (DICP), have worked out some of the details that will help researchers zoom in on an efficient catalyst.
To get these results, the chemists, led by Peden at PNNL and Xinhe Bao at DICP, used the world's largest instrument of its kind - a 900-megahertz nuclear magnetic resonance (NMR) spectrometer.
The NMR is armed with one of the strongest magnets constructed and can be outfitted to investigate solid samples, a step above its smaller cousins.
The combination of molybdenum oxide and a zeolite mineral had been shown in 1993 to convert methane, but the catalyst has been difficult to analyse. The technological problem lay in the molybdenum oxide itself.
To study this particular oxide with NMR, the chemists needed to pick up the signal from one variant of molybdenum, 95Mo. The ultra-high field of the NMR, housed at the DOE's (Department of Energy's) Environmental Molecular Sciences Laboratory on the PNNL campus, allowed them to do so.
"The higher magnetic field improves the signal to noise," said Peden. "And its large sample volume allowed us to put enough catalyst into the spectrometer to overcome the poor sensitivity of 95Mo NMR," he added.
The researchers prepared catalysts with increasing concentrations of molybdenum in the zeolite scaffold and focused the 900 MHz NMR on the samples.
The data revealed two different forms of the catalyst, as expected. One form contained the smaller nugget and the other form comprised the much larger clusters. When the concentration of molybdenum rose, more of these large clusters formed.
Then the team added methane and measured how much got converted into benzene by the catalysts.
They found that when more smaller nuggets were present, more benzene was made, indicating the variety of one or two molybdenum oxide molecules was the reactive one.
According to Peden, the challenge is to now design and produce the active form of the catalyst that could be used for large-scale benzene production.