Palladium catalysts sensor applications

As can be seen in Table 11.1, noble metals Pt, Pd, and Rh are the most usable catalysts in calorimetric gas sensors designed. It was established that of all the catalysts known they have the highest activity with respect to oxidation of combustible gases (see Fig. 11.2) and provide acceptable operation temperatures. Morooka and coworkers (Morooka and Ozaki 1966 Morooka et al. 1967) showed that activity for a model reaction, propylene oxidation, correlates with the strength of the metal-oxygen (M-0) bond. Because an LEL sensor must oxidize all ambient hydrocarbon species, the highest activity catalysts hold the most promise for the application. Therefore, the choice of palladium and platinum and sometimes rhodium for application in combustion gas sensors is natural (Miller 2001). This explains why the automobile exhaust system is treated with platinum or palladium compounds and is called a catalytic converter. 

Palladium (Pd) is among the most widely used transition metals in industrial applications. Catalysis has been by far the most common use for palladium, with carbon-carbon coupling reactions such as the StiUe reaction, Suzuki reaction, Heck reaction and hydrogenahon reactions being amongst the most prominent More recently, palladium has also been found to play a fundamental role in several processes related to the life sciences. These applications have included its use as a catalyst to manufacture pharmaceuticals and agricultural herbicides [1], in the degradation of harmful environmental pollutants [2, 3], and as a sensor [4] for the detection of various analytes. While the uses of palladium are extensive, there remain several additional applications yet to be uncovered as the metal is reduced to the nanoscale. 

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