Adsorption of hydrogen on a platinum–graphite catalyst. Part 1.—Electron spin resonance measurement in the gas–solid system

Abstract

E.s.r. signals from a platinum–graphite catalyst (Pt–graphite) and pure graphite were observed as functions of hydrogen gas pressure, temperature and the amount of platinum. The signals were inferred to be due to conduction charge carriers. The e.s.r. signal of Pt–graphite exhibits behaviour similar to that of pure graphite with respect to the temperature variation of the g∥ value. The signal from pure graphite was not affected by the presence of hydrogen gas. However, the signal from Pt–graphite at g=g_e(g value of a free electron) decreased with the amount of platinum and increased with the increment in hydrogen gas pressure, obeying the non-dissociative Langmuir isotherm. Detailed analysis indicated that the adsorption of hydrogen on Pt–graphite causes a change in the number of conduction electrons. Adsorbed hydrogen on Pt–graphite is concluded to be positively polarized in molecular form.