Catalyzed carbon-NO reaction studied by scanning tunneling microscopy and ab initio molecular orbital calculations

The catalysis of the carbon-NO reaction by alkali (Li, Na, K), alkaline earth (Mg, Ca, Sr, Ba), and transition metal (Fe, Co, Cu) catalysts was studied using scanning tunneling microscopy. An ab initio molecular orbital calculation was performed on model graphite substrates with O- and -O-M groups (where M = metal) bonded to the zigzag face to provide a better understanding of the origin of the catalytic activity for the carbon-NO reaction. The turnover frequencies (TOF) of the catalyzed reactions were calculated based on the channeling rates on the basal plane of graphite with 1% NO at 600°C, and the relative catalytic activities of the catalysts were compared. NO was dissociatively chemisorbed by these catalysts, followed by diffusion of O atoms to the edge carbon sties, where breakage of C-C bonds occurred to free CO. The breakage of C-C bonds was the rate-limiting step for the gasification reaction by NO. The extent of weakening in the C-C bond energy by different metals was in general agreement with the order of catalyst activities measured as TOF. The rank order of TOF by different catalysts was Cu > Ba = K > Sr > Ca > Mg > Na > Co > Fe = Li.