FIELD-IONIZATION OF EXCITED ALKALI ATOMS EMITTED FROM CATALYST SURFACES

The emission of excited states of alkali, i.e. Rydberg states, formed at two commercial iron-oxide catalysts (A and B) for styrene production and one commercial vanadium catalyst (C) for sulfuric acid production are studied using field-ionisation techniques. The signals detected for excited-state emission show Arrhenius temperature dependencies with barriers of 1.7 and 0.8 eV for A and B, respectively, and 0.9 eV for C. Emission of excited states occurs at the process temperature range for A and B catalysts and just above the process temperature range for catalyst C. Simulations of the ion trajectories are made with a PC computer program SIMION. The simulations show that field ionisation occurs in a distinct region in the ion source, and that no charged species can move from the catalyst sample under study to the collector. The excited states observed in emission are believed to be formed also under normal operating conditions on the catalyst surfaces.