Beneficial effect of adding γ-AlOOH to the γ-Al2O3 washcoat of a PdO catalyst for methane oxidation

The beneficial effect of adding gamma-AlOOH to the gamma-Al2O3 washcoat of a ceramic cordierite (2MgO center dot 2Al(2)O(3) center dot 5SiO(2)) monolith, used to support a PdO catalyst, is reported for methane oxidation in the presence of water at low temperature (<500 degrees C). The mini-monolith (400 cells per square inch (CPI), 1 cm diameter x 2.54 cm length; similar to 52 cells) was washcoated using a suspension of gamma-Al2O3 plus boehmite (gamma-AlOOH), followed by calcination and then deposition of Pd by wet impregnation. An optimum solid content of 25 wt% in the washcoat suspension was used to obtain a similar to 25 wt% washcoat on the monolith. The presence of gamma-AlOOH enhanced the thermal and mechanical stability of the washcoat, provided that the gamma-AlOOH content was <8 wt%. Temperature-programmed methane oxidation (TPO) showed that the addition of gamma-AlOOH to the gamma-Al2O3 washcoat decreased the catalyst activity. However, when H2O (2 vol% and 5 vol%) was present in the feed gas, the gamma-AlOOH improved the catalyst activity and stability. A gamma-AlOOH content of similar to 5 wt% in the washcoat was determined to provide the highest catalyst activity and stability for CH4 oxidation in the presence of water.