Enhanced Catalytic Activity for Methane Combustion
through in Situ Water Sorption
Posted on 2020-07-12 - 19:13
Although
palladium-based materials are efficient catalysts for methane combustion,
H2O-poisoning remains a significant problem at low operating
temperatures (<450 °C). It is a significant research challenge
to find catalysts that can withstand water while delivering rates
comparable to the dry PdO phase. Therefore, an in situ water sorption strategy could be advantageous in maintaining high
rates for the reaction. Here, we investigate water sorbents that are
used to remove the water produced by the reaction, which significantly
enhances the activity of a Pd/CeO2 catalyst for methane
combustion. The results reveal that the addition of zeolites or alumina
to the Pd catalyst can transiently reduce the water concentration
in the reactor and thus lead to increased catalytic rates. However,
due to the limited number of sorption sites, hydroxylation of the
PdO phase takes place rapidly, causing the catalyst to quickly exhibit
the same activity as without the sorbent after a transient state.
However, by using a stronger sorbent such as CaO mixed with the catalyst,
it is possible to obtain higher catalytic activity that is maintained
for longer periods of time. This latter system exhibits a 6-fold improvement
in transient conversion of methane compared to that of the control
catalyst. Meanwhile, long-term stability tests show catalytic activity
higher than that without sorbent for extended periods of time. Mechanistic
analysis demonstrated that the number of adsorptive sites and the
water sorption energy on the sorbents both influenced the water sorption
efficiency. Although the sorbent needs to be regenerated, we envision
this strategy being useful in conditions where regeneration can be
performed without disruption of the catalytic performance. Overall,
this work opens an avenue for promoting the methane combustion activity
of catalysts by in situ water sorption.
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Huang, Weixin; Zhang, Xinrui; Yang, An-Chih; Goodman, Emmett D.; Kao, Kun-Che; Cargnello, Matteo (2020). Enhanced Catalytic Activity for Methane Combustion
through in Situ Water Sorption. ACS Publications. Collection. https://doi.org/10.1021/acscatal.0c02087