Observing catalysis through the agency of the participating electrons: Surface-chemistry-induced current changes in a tin oxide nanowire decorated with silver

Conductometric measurements were performed on single tin oxide nanowires with and without Ag nanoparticle surface decoration, in flowing oxygen/ethylene mixtures of varying composition. Ag-decorated nanowires showed a significant ethylene effect, which we explain in terms of the modification of the Schottky junction formed between the Ag particles and the tin oxide, resulting from the surface chemical processes involving ethylene and oxygen occurring exclusively on the silver nanoparticles' surface. Assuming the observed temperature dependence of these ethylene-induced current decrements reflect changes in the steady-state concentration of ethylene, oxygen, and a surface intermediate that ultimately leads to ethylene oxide, one calculates the enthalpy for the production of the reaction intermediate to be approximately -4.6 kcal/mol, of the right order of magnitude as the calculated value reported in the literature for the formation of a putative ethylene oxametallacycle intermediate in the ethylene epoxidation reaction. Our results illustrate how fundamental catalytic processes occurring at metal nanoparticle surfaces can significantly influence the electronic properties of oxide nanowires used as metal particle supports.