Nov 07 2016 11:00 AM
Nov 07 2016 01:00 PM
ABSTRACT: Catalytic reforming of methane with carbon dioxide has gained a lot of interests in recent years because the process converts twogreenhouse gases (CH4 and CO2) into valuable syngas (H2/CO) close to unity. The highly endothermic dry reforming of methane (DRM) proceeds via CH4 decomposition to leave surface carbon species, followed by removal of C with CO2-derived species to give CO. Tuning the reactivity of the active metal towards these reactions during DRM allows in principle the catalyst surface to remain active and clean without carbon deposition for a long-term. The reactivity tuning for stoichiometric CH4/CO2 reactants was attempted by alloying non-noble metal Co and Ni. The bimetallic CoNi catalysts were compared with monometallic Co and Ni catalysts, all of which were prepared by homogeneous deposition precipitation (HDP) method to produce nanoparticles with narrow size distribution. The ZrO2 support was chosen because of its high thermal stability and absence of mixed oxide formation with the active metals (Co, Ni). The catalytic behavior of these catalysts was investigated at high reaction temperatures (750-800 °C) under atmospheric pressure. On monometallic Co catalyst, the kinetic analysis showed first-order in CH4 and negative-order in CO2 on the DRM rate. The Co catalyst deactivated without forming carbon deposits. On contrary, on monometallic Ni catalyst, the DRM rate was proportional to CH4 pressure but insensitive to CO2 pressure. The Ni surface provides comparatively higher rates of CH4 decomposition and the resultant DRM than the Co catalyst but leaves some deposited carbon on the catalyst surface. In contrast, the bimetallic CoNi catalyst showed kinetics resembling the Co catalyst, i.e., the first-order with respect to CH4 pressure and the negative-order with respect to CO2 pressure on the DRM rate. Noticeably, the stability of CoNi catalyst was drastically improved over the monometallic counterparts and no deposited carbon was detected after the DRM reaction. The results suggest that for an appropriate Co/Ni ratio, the bimetallic CoNi/ZrO2 catalyst exhibits intermediate reactivity towards CH4 and CO2 between Co and Ni producing negligible carbon deposition by balancing CH4 and CO2 activation.