The Research On MEMS Methane Catalytic Combustion Sensor Based On Pd/Pt Catalyst

With the rapid development of micro-electro-mechanical systems (MEMS), many micro-machining ways were well developed and used, which made the micromation, low power consumption and intelligence of sensors possible. During the development of MEMS methane catalytic combustion sensor, it was found that the signal was very low companied with the small signal noise ratio when traditional matrix and catalyst were used. This can be attributed to the very limited heating area of the catalytic element (the heating area of a micro-heater is only about0.01mm2), which is only about one percent of that of traditional catalytic combustion sensor. The straightforward and effective way to improve the sensitivity of the MEMS sensor is to enlarge the valid contact area between catalyst and target gases. Mesoporous material has high surface area and well defined pore structure. In the thesis mesostructure were intruduced into MEMS catalytic combustion sensor, the loaded catalyst amount and contacted area between methane and the catalyst were greatly enhanced compared with that using traditional catalyst structure, and much higher sensitivity can be obtained.Firstly, mesoporous alumina and noble metal catalyst/alumina composite were prepared using sol-gel method in the thesis. Through spin-coating and electricallly heating approach, the meso-structure materials were successfully introducted on the surface of MEMS micro-heater. After assembed as MEMS methane catalytic combustion sensor, it showed a fast response and decay toward the methane exposure and insulation at all methane concentrations. The signal output increased linearly with increasing the methane concentration and the T90response time was less than17s. The power consumption was only1/5of that of traditional LEL sensor.At the same time, the same structure materials were also prepared using revised micro-emulsion method. The resulting materials showed higher surface area compared with that using sol-gel method. The surface area of alumina could be320m2/g and catalyst/alumina could be119m2/g. The MEMS methane catalytic combustion sensor assembled by these materials showed much higher output signal. The T90response time was22s, longer than that of sol-gel method. The power consumption of the sensor was also only1/5of that of traditional LEL sensor.For methane catalytic combustion sensor, it is important to match the resistance precisely between the reference element and catalytic element. However, it was found in the experiment, the resistances of two elements were usually difficult to match well due to the technique reason and different resistance-temperature coefficient. In order to resolve this problem, an adjustable resistance was introduced paralleled connection to the reference element. The resistance of reference element and catalytic element can be match well through adjusting this parallel resistance. At50%LEL methane concentration, for the only one layer catalyst coated MEMS sensor the signal output can be reached3mV for sol-gel method and8mV for reversed micro-emulsion method.