FTMS studies of sputtered metal cluster ions (IV): size-selective effects in the chemistry of Fe+ n with NH3 and Pd+ n with D2 or C2H4

Abstract

Abstract. Fe, + and Pd, + clusters up to n = 19 and n = 25, respectively, are produced in an external ion source by sputtering of the respective metal foils with Xe ÷ primary ions at 20 keV. They are transferred to the ICR cell of a home-built Fourier transform mass spectrometer, where they are thermalized to nearly room temperature and stored for several tens of seconds. During this time, their reactions with a gas leaked in at low level are studied. Thus in the presence of ammonia, most Fe, + clusters react by simply adsorbing intact NH a molecules. Only Fe~ ions show dehydrogenation/adsorption to Fe4(NH)~ + intermediates (m = 1, 2) that in a complex scheme go on adsorbing complete NH3 units. To clarify the reaction scheme, one has to isolate each species in the ion cell, which often requires the ejection of ions very close in mass. This led to the development of a special isolation technique that avoids the use of isotopicatly pure metal sampies. Pd,, + cluster ions (n = 2...9) dehydrogenate C2H4 in general to yield Pd,(C2Hz) +, yet Pd~" appear totally unreactive. Towards D2, Pd~-ions seem inert, whereas Pd~-adsorb up to two molecules.

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

“…Figure b shows the reaction cross sections of Fe n O m + ( n = 3−6, m = 0−3). In the bare iron clusters studied here, Fe 4 + is the most reactive for the NH 3 dehydrogenation, and this result is fairly consistent with the previously published ones, − whereas the reaction cross sections of the simple NH 3 chemisorption for Fe n + are diminished in comparison with those measured by Liyanage et al, probably because of the difference of the temperature of the clusters. The total reaction cross section increases by the introduction of oxygen atoms onto Fe n + , but only Fe 3 O 3 + has an exceptionally small reaction cross section.…”

“…Therefore, the studies on the dehydrogenation of NH 3 can also provide valuable information on catalytic ammonia synthesis. The NH 3 dehydrogenation on metal clusters such as Fe n + , − Ag n + , Pt n ± , − and Au n + has been studied in the gas phase, and Fe 4 + and Pt 2 + exhibited high reactivity. These reaction mechanisms have been confirmed as stepwise dehydrogenation by recent theoretical studies. ,, The effect of the oxygen introduction to Fe 2 + has also been investigated, and it was revealed that the dehydrogenation of NH 3 on Fe 2 O 2 + accompanies the hydrogenation of the atomic oxygen and that a H 2 O molecule is released finally …”

Reactions of cationic iron clusters with ammonia, models of nitrogen hydrogenation and dehydrogenation

“…The only exception is Fe 4 ϩ . In full accordance with a previous report by Irion et al, 45,46 this particular cluster ion reacts with ammonia to give a dehydrogenated product ion:…”

Release of Oxygen from Palladium Oxide Cluster Ions by Heat

“…The unsupported gas-phase clusters provide a unique and ideal environment to prove and quantify the reaction kinetics of a certain cluster in detail. Mass spectrometric studies of gas-phase clusters give good insight into stabilities and reactions at the atomic and molecular levels, because sizes, stoichiometries, and oxidation states, which may determine reactivity, can be controlled at will. , There have been many experimental and theoretical studies on the chemical reactivity of palladium clusters. − Temperature-programmed desorption (TPD) has been applied to the study of gas-phase metal oxide clusters by Lang et al at low temperatures (80–300 K). − Temperature-dependent gas-phase ion trap experiments under multicollision conditions and complementary theoretical calculations elucidated that Pd 3–6 O 4 + complexes have a dissociatively chemisorbed bridging oxygen structure, which impedes further O 2 chemisorption. At cryogenic temperatures, the molecular physisorption of excess O 2 is observed (weak, nonactivated molecular physisorption).…”