Catalytic ammonia decomposition over CMK-3 supported Ru catalysts: Effects of surface treatments of supports

Abstract

CMK-3 carbon was used as a catalyst support for Ru catalyst for ammonia decomposition. The supports were treated with acid, and the effects of treatment on the properties of CMK-3 supports were studied by N2 adsorption, XRD, XPS and mass titration. The chemical treatment of carbon support cause significant changes in carbon surface chemistry and in turn had significant effects on both catalyst dispersion and catalytic activity. It is found that the as-synthesized CMK-3 carbon is not a good catalyst support for this reaction. However, surface functional groups produced by acid treatments led to larger Ru catalyst particles, while alkali treatments made the Ru catalyst dispersion even worse due to the residue alkali or earth alkali metals. Interestingly, relatively larger Ru catalyst particles but still well dispersed in the channel of the mesoporous structures of the carbon improves NH3 conversion into H2. This is determined by the chemical reaction rate-limiting step of ammonia decomposition. The catalytic activity follows the order: Ru-K/CMK-3 > Ru-Na/CMK-3 > Ru-Ca/CMK-3 > Ru-Cl/CMK-3 > Ru-SO4/CMK-3 > Ru-PO4/CMK-3 > Ru/CMK-3 > Ru-Li/CMK-3. CMK-3 is not a good carbon catalyst support due to its amorphous structure resulting in the poor electron conductivity. © 2006 Elsevier Ltd. All rights reserved.