title: Experimental and theoretical studies of ammonia generation: Reactions of H2 with neutral cobalt nitride clusters.
abstract: Ammonia generation through reaction of H(2) with neutral cobalt nitride clusters in a fast flow reactor is investigated both experimentally and theoretically. Single photon ionization at 193 nm is used to detect neutral cluster distributions through time-of-flight mass spectrometry. Co(m)N(n) clusters are generated through laser ablation of Co foil into N(2)/He expansion gas. Mass peaks Co(m)NH(2) (m = 6, 10) and Co(m)NH(3) (m = 7, 8, 9) are observed for reactions of H(2) with the Co(m)N(n) clusters. Observation of these products indicates that clusters Co(m)N (m = 7, 8, 9) have high reactivity with H(2) for ammonia generation. Density functional theory (DFT) calculations are performed to explore the potential energy surface for the reaction Co(7)N + 3∕2H(2) → Co(7)NH(3), and a barrierless, thermodynamically favorable pathway is obtained. An odd number of hydrogen atoms in Co(m)NH(3) (m = 7, 8, 9) probably come from the hydrogen molecule dissociation on two active cobalt nitride clusters based on the DFT calculations. Both experimental observations and theoretical calculations suggest that hydrogen dissociation on two active cobalt nitride clusters is the key step to form NH(3) in a gas phase reaction. A catalytic cycle for ammonia generation from N(2) and H(2) on a cobalt metal catalyst surface is proposed based on our experimental and theoretical investigations.
authors.affiliation: Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA.
authors.forename: Shi
authors.initials: S
authors.lastname: Yin
authors.forename: Yan
authors.initials: Y
authors.lastname: Xie
authors.forename: Elliot R
authors.initials: ER
authors.lastname: Bernstein
mesh_terms: D000641:Ammonia / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D017672:Nitrogen Compounds / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D017672:Nitrogen Compounds; D003035:Cobalt; D000641:Ammonia; D006859:Hydrogen; D009584:Nitrogen