Enhancement of Ammonia Dehydrogenation by Introduction of Oxygen onto Cobalt and Iron Cluster Cations

Abstract

Reactions of oxygen-chemisorbed cobalt and iron cluster cations (Co(n)O(m)(+) and Fe(n)O(m)(+); n = 3-6, m = 1-3) with an NH(3) molecule have been investigated in comparison with their bare metal cluster cations at a collision energy of 0.2 eV by use of a guided ion beam tandem mass spectrometer. We have observed three kinds of reaction products, which come from NH(3) chemisorption with and without release of a metal atom from the cluster and dehydrogenation of the chemisorbed NH(3). Reaction cross sections and branching fractions are strongly influenced by the number of oxygen atoms introduced onto the metal clusters. Oxygen-chemisorbed metal clusters with particular compositions such as Co(4)O(+), Co(5)O(2)(+), and Fe(5)O(2)(+) are extremely reactive for NH(3) dehydrogenation, whereas Co(4)O(2)(+) and Fe(4)O(2)(+) exhibit high reactivity for NH(3) chemisorption with metal release. The enhancement of dehydrogenation for specific compositions can be interpreted in terms of competition between O-H and neighboring Co-H (or Fe-H) formation.

Adsorption and dehydrogenation of ammonia on vanadium and niobium nitride cluster cations

“…For example, equiatomic clusters, V 4 N 4 + and V 6 N 6 + , exhibit significantly lower reactivity than the corresponding nitrogen-deficient clusters, V 4 N 3 + and V 6 N 5 + , respectively. V 6 N 5 + has the largest total cross section (85 Å 2 ), which is comparable to the collision cross section estimated by the trajectory method (108 Å 2 ) [31] and the reaction cross section of Co 5 O 2 + measured previously (93 Å 2 ) [32] at E col = 0.2 eV.…”

Catalytic N−H Bond Activation and Breaking by a Well‐Defined CoII1O4 Site of a Heterogeneous Catalyst

“…This requires further investigation. The proposed pathway also demonstrates the crucial role of oxygen sites in affecting the migration of H atoms in NH 3 upon activation of N−H bonds; this was also suggested by previous theoretical calculations on cobalt clusters and oxygen precovered Au(1 1 1) …”

Gas-Phase Reactions of Copper Oxide Cluster Cations with Ammonia: Selective Catalytic Oxidation to Nitrogen and Water Molecules

“…Our previous studies showed that Fe n O m + and Co n O m + (n = 3−6, m = 1−3) clusters mainly exhibit H 2 desorption after the NH 3 adsorption 17. As an elemental step of reaction 1, the formation of M n O m−1 NH + with release of a H 2 O molecule was reported in the reactions of…”