Abstract
The low partial pressure of MoO 2(OH) 2 existing over solid MoO 3 in the presence of water vapor was determined at temperatures from 400 ° to 500 °C. It was found that SnO 2, contacted around 450 °C with a gas saturated with MoO 2(OH) 2, sorbs MoO 3 (or a hydrated form) to its surface. The sorbed molybdenum oxide constitutes what may be considered a monolayer. This coverage of the SnO 2 surface with molybdenum oxide is a reversible process. In the oxidation of propylene with molecular oxygen at 370 °C and atmospheric pressure, SnO 2 shows some catalytic activity; half or more of the reacted propylene is completely broken down to CO 2 and CO, while a considerable portion is converted to acrolein. MoO 2 is a much less active oxide. However, SnO 2 covered with a monolayer of molybdenum oxide is 5 to 10 times more active in the oxidation of propylene than SnO 2 alone, and gives a completely different product distribution. The reaction yields mainly acetic acid along with acetone (in varying ratios), while total oxidation to CO and CO 2 is of minor importance. These results can only be obtained in the presence of water vapor (in the experiments with either SnO 2 or MoO 3 alone, water vapor was also used). So, although MoO 3 did not form a bulk compound with SnO 2, it could be bound to the SnO 2 surface, which then exhibited a peculiar catalytic activity.
Published Version
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