Dry reforming of methane (DRM), in which carbon dioxide and methane are combined to form synthesis gas (H2 and CO), is an attractive route to making syngas because it does not require consumption of water and does not produce CO2 like the conventional route, steam-methane reforming. Nickel-based zeolite catalysts can facilitate DRM, but they are subject to rapid deactivation via sintering and coke formation at the temperatures that would be ideal for the conversion at industrial scale.
To alleviate the problem of catalyst deactivation, researchers at the Oak Ridge National Laboratory (ORNL; Oak Ridge, Tenn.; www.ornl.gov) studied the bonding between the nickel active sites and the catalyst support, as well as how the synthesis method affects the catalyst deactivation. The information they gathered allowed them to devise a synthetic process for the catalyst that led to stronger interactions between the metal active sites and the zeolite support material. These strengthened interactions suppressed coke formation and sintering during the DMR reaction.
“The underlying chemistry of Ni-Si interaction in zeolites for the creation of stable catalytic sites is poorly understood, and thus, catalyst optimization defaults to inefficient trial-and-error,” writes the ORNL team, led by Felipe Polo-Garzon and Junyan Zhang. “In this study, we establish a fundamental understanding regarding the impact of catalyst synthesis mechanisms on catalyst properties, and ultimately on catalyst performance for DRM.”
An example of a zeolite structure
The synthesis method involves anchoring highly dispersed Ni sites onto de-aluminated zeolite supports. The ORNL researchers found that “dispersion and Ni-zeolite interaction can be precisely controlled by adjusting the airflow during calcination, allowing for tunable metal dispersion ranging from [Ni] nanoparticles to isolated sites within the framework.” The high airflow enhanced the removal of decomposition byproducts, which strengthened the Ni-support interaction, the ORNL team hypothesized.
Using a combination of infrared spectroscopy, X-ray absorption spectroscopy and microscopy allowed the scientists to characterize the dispersion of the synthesized Ni species and their interaction with the support. “Structure-performance correlations demonstrated that the finely tuned synthesis method leads to catalysts with significantly enhanced stability during DRM,” the researchers write in a paper recently published in Nature Communications.
This fundamental understanding of the precision synthesis of active sites and their intrinsic activity opens new avenues to rational catalyst design, the researchers say.