Enhanced Catalytic Activity for Methane Combustion through in Situ Water Sorption

Abstract

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.

Zr-Doped NiO Nanoparticles for Low-Temperature Methane Combustion

“…In Figure 1D,E was carried out at a lower temperature in wet conditions as it has been uncovered that the water inhibition effect would be more prominent in the low-temperature regime. 37 It is worth noting that Ni 0.89 Zr 0.11 O 2−δ provided a stable performance (47−50% methane conversion) without deactivation for 50 h in the presence of steam at 360 °C. This phenomenon verified that the incorporation of Zr was beneficial to enhancing the low-temperature activity of NiO-based nanocatalysts regardless of the presence of water vapors.…”

“…Despite the conversion rate over both catalysts being lowered due to the introduction of steam, a relatively high conversion (82–86%) could be well maintained over Ni 0.89 Zr 0.11 O 2−δ . To further confirm the great water resistance of Ni 0.89 Zr 0.11 O 2−δ , the on-stream test was carried out at a lower temperature in wet conditions as it has been uncovered that the water inhibition effect would be more prominent in the low-temperature regime . It is worth noting that Ni 0.89 Zr 0.11 O 2−δ provided a stable performance (47–50% methane conversion) without deactivation for 50 h in the presence of steam at 360 °C.…”

Promoting the Methane Oxidation on Pd/CeO2 Catalyst by Increasing the Surface Oxygen Mobility via Defect Engineering

“…In addition, as Cargnello et al. recently suggested, physically mixing H 2 O sorbent with Pd/CeO 2 catalysts would improve its resistivity toward H 2 O in the methane oxidation reaction [5f] . This study highlights that the catalytic activity in methane oxidation reaction could be promoted by inducing the active participation of support oxygen in the reaction via the simple defect engineering.…”

“…Although surface oxygen of ceria could not participate in the reaction with H 2 O, our present approach could be effective in the area where the H 2 O concentration in the reactant feed is low. For example, only 41 ppm of H 2 O is present in the gas system according to the data from natural gas industry [5f,18] . In addition, as Cargnello et al.…”

Supported RuxIr1‐xO2 Mixed Oxides Catalysts for Propane Combustion: Resistance Against Water Poisoning

“…In the alkane combustion process, water in the reaction feed or produced by the reaction is known to hamper the catalytic combustion reaction, [41][42] a problem that has already been studied extensively for the methane combustion [4,[43][44][45][46] but to lesser extent for the catalytic propane combustion, employing Pd and Pt-based catalysts. [47][48][49][50] For example, Murata et al 51 found that hydrophobic carrier (α-Al 2 O 3 ) reduces water poisoning in the methane combustion reaction over supported PdO, while Huang et al 52 used water sorbent that was physically mixed with Pd/CeO 2 catalyst to enhance the activity of methane combustion. Since water possibly impedes the catalytic combustion by blocking the active sites, one would expect that water poisoning is equally important in the catalytic propane combustion over Ru x Ir 1-x O 2 -based catalysts and this poisoning effect may depend critically on the composition x of Ru x Ir 1-x O 2 and on the specific carrier material.…”