Enhanced Activity of Ni/Al 2 O 3 Catalysts by CO 2 Treatment for Dry Reforming of Methane

This study investigated dry reforming of methane (DRM) with supported Ni catalysts at 973 K. The α-Al2O3-supported Ni catalyst showed gradual deactivation over time on stream. However, the activity fully recovered to its initial level after air calcination of the catalyst at 973 K. Electron microscopy confirmed carbon deposition on the Ni surfaces, indicating that the deactivation was caused not by the irreversible sintering of Ni particles but by carbon deposition during the reaction. Subsequently, the catalyst was subjected to heat treatment in CO2 atmosphere at temperatures above 923 K; this remarkably increased its catalytic activity by at least 1.5 times, strongly suggesting that CO2 treatment not only removed the deposited carbon but also increased the number of active sites during the DRM reaction. Further, TEM experiments were conducted to further investigate the improvement in DRM activity following CO2 treatment. It was observed that the CO2 treatment led to the re-dispersion of Ni metallic particles, and the mechanism causing this dispersion was also elucidated.