Development of Low-Temperature Methane Gas Sensors By Using Cup-Stacked Carbon Nanofilament-Supported Pd Catalyst

Methane gas is found in environment, industrial and domestic areas. On the other hand, methane can cause explosions due to its inflammability. Thus, detection of methane gas in the environment is very important to avoid any accidental explosion. Catalytic combustion-type methane gas sensors can detect methane gas immediately. This type of methane gas sensors utilizes heat from catalytic combustion of methane by Pd-loaded catalysts. To indicate high catalytic activity, it is necessary for catalyst to heat around 250 ~ 600 °C because of thermochemical stability of methane. Consequently, electrical power consumption on the sensors is large. Hence development of efficient methane sensors that could work even at low temperatures is required. In this work, cup-stacked carbon nanofilament (CSCNF) was used for Pd support material. γ-Al2O3 was used for general catalytic combustion-type methane gas sensors. Relatively large amount of Pd is required to indicate catalytic activity in using γ-Al2O3 support. On the other hand, CSCNF has functional groups such as C=O carbonyl-type structures and C-O-C ether-type structures on its edge surface regularly. These functional groups interact with metallic ion in preparing catalysts by impregnating method. Therefore, Pd can be discretely distributed in small particles on the surface of CSCNF. CSCNF supported catalysts are considered to indicated high activity with even small amount of Pd. Therefore, low-temperature combustion of methane is expected. Moreover, sensors can detect heat of methane combustion immediately because CSCNF has good thermal conductivity. Catalytic activity of Pd/CSCNF was evaluated by temperature programmed reaction (TPR). This catalyst combusted 1 % methane in air at relatively low temperature 270 °C. Pd/γ-Al2O3, which was reference, combusted methane at 330 °C. CSCNF support was able to upgrade catalytic activity of Pd nanoparticles. Pd/CSCNF could reduce methane combustion temperature 60 °C lower than that of Pd/γ-Al2O3. It seems that CSCNF supported catalysts are attractive for methane combustion at low temperatures. CSCNF-loaded catalysts are more efficient for catalytic combustion-type methane gas sensors than the conventional sensors.