Effect of thermal and oxidative treatments of activated carbon on its surface structure and suitability as a support for barium-promoted ruthenium in ammonia synthesis catalysts

Abstract

The effect of heat-treating a typical activated carbon at 1600–2500 °C on its structural and textural properties was investigated by gas sorption and X-ray diffraction. Particular attention was paid to the recovery of the surface area and porosity of thermally treated carbons by means of oxidation treatments. It was found that the thermal modification of activated carbon could eliminate carbon impurities, bring about different degrees of graphitization, and improve the resistance of the carbon support to undergo methanation under ammonia synthesis conditions, but the surface area and porosity decreased dramatically. Oxidative treatment partially recovered the surface area and porosity. The higher the thermal treatment temperature, the greater the stability of the carbon support, and the more difficult the recovery of the surface area and porosity becomes. A series of unpromoted ruthenium/carbon catalysts showed that the highly developed texture of the carbon support resulted in a significant increase in Ru dispersion. The ammonia synthesis activity of a Ba-promoted Ru catalyst was greatly improved by using activated carbon C1900ox as a support, which was heated at 1900 °C in an inert atmosphere and then subjected to oxidation treatment.