PNNL

Abstract

The activation of C-H and C-C bonds by atomic metal cations remains a profitable area of research to utilize environmentally abundant methane and produce useful hydrocarbon fuel. While methane activation by transition metal cations has been the focus of catalysis research for decades, less is known about the catalytic capabilities of lanthanide cations. Here we employ inductively coupled plasma tandem mass spectrometry to examine the kinetic energy dependences of the reactions of lanthanide cations Ce+, Pr+, Nd+, Sm+, and Eu+ with methane. The resulting energy-dependent reaction cross sections enable a measurement of the associated reaction thermochemistry and provide fundamental insight into the physical characteristics of the Ln+ that enable reactivity. We report values for the Ln+-D bond dissociation energies, D0(Ln+-D) and the first experimentally obtained values for D0(Ln+-CD3) and D0(Ln+-CD). We find that our values for D0(Ln+-D) correlate similarly with the promotion energies from the Ln+ ground state electronic configurations to the 5d6s electronic configurations and indicate that the ability of Ln+ to effectively insert into C-H bonds requires an electron configuration with two valence electrons in non-f orbitals.