Seminars Archive

Electrochemical control of catalytic reactions: a XPS study of propene oxidation

Abstract
An electrochemically Pt catalyst, promoted by Na and supported on a Na
B"-alumina solid electrolyte, was studied by XPS before and after reactions
involving NO, Oxygen and Propene. In the absence of reactants Na can be
reversibly supplied/removed to/from the catalyst in a well controlled
manner by applying a proper bias to the solid electrolyte. Its nature was
found identical to the vacuum deposited Na. In the presence of reactants
the amount and chemical state of Na strongly depends on the electrochemical
bias and gas phase composition. The reactions studied - C3H6 + oxygen and
C3H6 + NO - exhibit marked promotion when a proper amount of Na is supplied
to the catalyst. For both reactions the promotion is followed by poisoning
at high negative bias. In all cases studied the Na amounts present on the
catalyst surface are considerably higher than in the absence of reactants.
This Na occupies part of or all the surface thus leading to the saturation
of the catalyst`s activity or to its complete poisoning. Sodium compounds
responsible for the observed poisoning - carbonates, nitrites or nitrates -
show different thermal and chemical stability but are effectively
decomposed by application of an appropriate electrochemical bias.