Temperature-programmed desorption of CO adsorbed on NiO/MgO

The temperature-programmed desorption (TPD) of CO adsorbed on unreduced and reduced NiO/MgO solid solution catalysts was investigated. For the unreduced NiO/MgO, two peaks were observed: one for CO and another one for CO{sub 2}. The CO{sub 2} peak is a result of the reaction between NiO and adsorbed CO. The CO{sub 2} thus generated is adsorbed on the MgO sites, whereas CO is adsorbed in the Ni generated through the reduction of NiO by CO. For the H{sub 2} reduced NiO/MgO, two temperature ranges for CO TPD were identified: (a) A low temperature range (50-200 C), with two overlapped CO peaks whose temperature are independent of the catalyst composition, and no peak for CO{sub 2}. (The two overlapped CO peaks are attributed to CO molecularly adsorbed on Ni.) (b) A high temperature range (400-700 C), with peaks for both CO and CO{sub 2}, whose temperatures depend on the composition of the catalyst. They are attributed to CO species dissociatively adsorbed on Ni. A fraction of these dissociatively adsorbed species of CO are converted to CO{sub 2} via the reaction 2CO {yields} 2C + 2O {yields} CO{sub 2} + C and the reduction of some of the NiO that remained unreducedmore » in H{sub 2}. The CO{sub 2} generated is adsorbed on MgO sites. The other fraction of CO dissociatively adsorbed desorbs as CO. 13 refs., 10 figs., 2 tabs.« less