UBC Faculty Research and Publications

The Impact of CeO₂ Loading on the Activity and Stability of PdO/γ-AlOOH/γ-Al₂O₃ Monolith Catalysts for CH₄ Oxidation AlMohamadi, Hamad; Smith, Kevin J.

Abstract

This study reports on the activity and stability of PdO/γ-AlOOH/γ-Al₂O₃ monolith catalysts, promoted with varying amounts of CeO₂, for CH₄ oxidation. Although the beneficial effects of CeO₂ have been reported for powdered catalysts, this study used a cordierite (2MgO.2Al₂O₃.5SiO₂) mini-monolith (400 cells per square inch, 1 cm diameter × 2.5 cm length; ~52 cells), washcoated with a suspension of γ-Al₂O₃ combined with boehmite (γ-AlOOH), followed by sequential deposition of Ce and Pd (0.5 wt.%) by wetness impregnation. The monolith catalysts’ CH₄ oxidation activity and stability were assessed in the presence of CO, CO₂, H₂O and SO₂ at low temperature (≤550 °C), relevant to emission control from lean-burn natural gas vehicles (NGVs). The CeO₂ loading (0 to 4 wt.%) did not significantly impact the adhesion and thermal stability of the washcoat, but CeO₂ reduced the inhibition of CH₄ oxidation by H₂O and SO₂. The catalyst activity, measured by temperature-programmed methane oxidation (TPO) in a dry feed gas with 0.07 vol.% CH₄, showed that adding CeO₂ to the γ-AlOOH/γ-Al₂O₃ washcoat suppressed the activity of the catalysts; whereas, CeO₂ improved the catalyst activity when H₂O (2 and 5 vol.%) was present in the feed gas. Moreover, adding CeO₂ decreased catalyst deactivation that occurred in the presence of 10 vol.% H₂O and 5 ppmv SO₂ at 500 °C, measured over a 25 h time-on-stream (TOS) period. The highest catalyst activity and stability for CH₄ oxidation in the presence of H₂O was obtained by adding 2 wt.% CeO₂ to the washcoat.

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