Additivity Effects in the Reactivities of Bimetallic Cluster Ions Pt_mAu_n⁺

Abstract

All that glitters…︁The gas‐phase reactions of the bimetallic cluster ions PtmAun+ (m+n≤4) with dioxygen and methane are investigated. The platinum‐rich cluster ions undergo degradation processes and dehydrogenation reactions, which are also known for pure Ptm+ clusters. In contrast, the gold‐rich cluster ions are found to be unreactive, similar to the corresponding Aum+ clusters. This distinct trend in reactivity (see graphic) is correlated with the systems' electronic properties changing as a function of cluster composition.

Coupling of Methane and Ammonia by Dinuclear Bimetallic Platinum–Coinage‐Metal Cations PtM+

“…[12,15] The efficiency of cluster degradation decreases when changing M from Cu to Ag and completely vanishes for Au (Table 1). [7] Presumably, the high ionization energy of gold, IE(Au) = 9.23 eV, strongly disfavors the generation of Au + in comparison to Cu + and Ag + (IE(Cu) = 7.73 and IE(Ag) = 7.58 eV).…”

“…[10] To further elucidate the remarkable role of the second metal in the dinuclear cluster, we have extended our studies to PtCu + and PtAg + . The change from gold to its lighter congeners copper and silver is straightforward in view of their electronic and chemical similarities (note, however, that gold is distinguished from both copper and silver by the operation of much stronger relativistic effects [11] [7,9] …”

“…6 with M = Au (f = 0.03)]. [6,22] ½Pt; M; C; [7] 8.2 [9] (0.59) (0.63) (0.67) (0.85) PtM + + O 2 !M + + PtO 2 0.35 0.04 0 [7] 1.3 [9] (0.064) (0.01) (0.25) PtM + + NH 3 !PtMNH + + H 2 0 0 0 5.4 [9] (0. [10] 9.7 [5] (0.26) (0.24) (0.30) (0.49) For both M = Cu and M = Ag, Equation (6) occurs as well, in the former case with rather high (f = 0.23) and in the latter with low (f % 0.01) efficiency.…”

Methane Activation and Catalytic Ethylene Formation on Free Au2+

“…Whereas small platinum clusters Pt x + were shown to exhibit facile activation and dehydrogenation of even multiple CH 4 molecules, [11] Au x + ions were reported to be completely unreactive towards CH 4 under single-collision gas-phase conditions. [12] Yet, under multiple-collision conditions, reaction products could be stabilized and an uptake of several methane molecules was detected, but there was no indication for the dehydrogenation of CH 4 .…”

Interaction of Cu cluster anions (Cu-n, n = 8–11) with oxygen

“…It was also shown that O 2 mostly chemisorbs molecularly on these metal cluster anions. It turned out that the charge state of a cluster plays a crucial role for the chemical reactivity: positively charged Au clusters are not reactive towards O 2 chemisorption, whereas negatively charged ones may well react with O 2 [20].…”