Effects of heat treatments of Pt-loaded Al2O3 on catalytic activities of CO oxidation and combustion-type CO sensors

The effects of heat treatment of Pt-loaded theta-Al2O3 catalysts on the CO-oxidation activity and the CO-sensing properties as catalytic combustion-type gas sensors were examined in this study. The CO-oxidation activity of the Pt-loaded theta-Al2O3 heat treated in wet N2 was larger than that in dry air or in dry H-2, and the Ptloaded theta-Al2O3 heat treated in wet N-2 completely oxidized CO to CO2 even at 20 degrees C. We also clarified that the heat treatment of the Pt-loaded theta-Al2O3 heat treated in wet N-2 exhibited the smallest size of Pt particles and the smallest concentration of residual chlorine among the examined catalysts. However, the sensitivity of the sensor using the Pt-loaded theta-Al2O3 heat treated in wet N-2 was smaller than that of the sensor using the Pt-loaded theta-Al2O3 heat treated in dry air, because the heat generated by the CO oxidation over the Pt-loaded theta-Al2O3 heat treated in wet N-2 appeared mainly at the upper part of the catalyst film and it may ineffectively conduct to the negative temperature coefficient (NTC) thermistor. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) revealed that the heat treatment of the Pt-loaded theta Al2O3 in wet N-2 obviously increased the CO adsorption on the Pt surface and enhanced the CO-oxidation activity.

Automated summary

The effects of heat treatment on the Pt-loaded theta-Al2O3 catalysts were investigated in terms of CO-oxidation activity and CO-sensing properties for catalytic combustion-type gas sensors. It was found that the Pt-loaded theta-Al2O3 treated in wet N-2 showed higher CO-oxidation activity and completely converted CO to CO2 even at low temperature. The heat treatment in wet N-2 also resulted in smaller Pt particles and lower residual chlorine concentration in the catalyst. However, the sensor using Pt-loaded theta-Al2O3 treated in wet N-2 had lower sensitivity compared to the sensor using Pt-loaded theta-Al2O3 treated in dry air due to ineffective heat conduction.