英语翻译This is obtained mostly by preventing sidereactions from

英语翻译
This is obtained mostly by preventing side
reactions from occurring through a limitation of the contact
between the catalyst and the reacting mixture.Figure 6 clearly
shows that a short enough contact time is required to achieve a
good selectivity,but excessively short will compromise the
production rate.On the other side,a longer contact time,which
maximizes the production rate,results in a detrimental effect
on selectivity.
Consideration of the residence time can be reformulated in
terms of reaction mechanism progress along the catalyst bed.
The above evidence allows speculation that only reactions of
H2O2 direct synthesis and water formation occur in the first part
of the catalytic bed,due to the low concentration of H2O2.It is
reported19,28,31,32 that completely oxidized Pd2+ (likely in the
form of PdO) preferentially supports water formation instead
of H2O2 synthesis in the absence of promoters (as we operate).
Since oxygen is fed largely exceeding H2,we speculate that a
significant fraction of the irregular palladium clusters could be
indeed Pd2+,notwithstanding the initial reduction pretreatment,
thus favoring water formation.