Nickel-Loaded SSZ-13 Zeolite-Based Sensor for the Direct Electrical Readout Detection of NO2

A novel sensor composed of a nickel-loaded SSZ-13 zeolite membrane on interdigitated electrodes (IDES) is demonstrated as a direct electrical NO2 readout sensor. This NO2 adsorbent is made by homogeneously loading SSZ-13 zeolite with nickel(II) through a liquid-phase ion-exchange procedure. Exposure of the zeolite-based sensor to trace NO2 gas elicits an electrical impedance response measured at a single frequency. The sensor shows the same final change in impedance magnitude upon equilibration to different concentrations of trace NO2 in N-2 suggesting that the occupation and eventual saturation of adsorption sites lead to the impedance change. However, the NO2 concentration can be determined through analysis of the rate of impedance change, where lower concentrations of NO2 lead to larger time constants with a logarithmic relationship to the NO2 concentration. Two time constants were observed from the linearized impedance plots, a fast one (tau(1)) and a slow one (tau(2)), where tau(2) showed a larger dependence on the NO2 concentration, increasing faster than tau(1) as the NO2 concentration decreased. Furthermore, the Ni-SSZ-13 sensor response is partially reversible in an inert gas environment, indicating the reversible adsorption of NO2 at nickel surface sites. Under exposure to humid air, differentiation between humid air and dry 5 ppm NO2 is accomplished by examination of the real component of the impedance signal. The resulting NO2 atmosphere shows an increase in the real component (more resistive), whereas the humid air shows a decrease (more capacitive). These results indicate that control of metal-ion loading into SSZ-13 may allow these NO2 selective catalytic reduction catalysts to be further leveraged as low-temperature NO2 sensors.

Automated summary

The novel sensor consists of a nickel-loaded SSZ-13 zeolite membrane on interdigitated electrodes, allowing direct electrical NO2 readout. The sensor shows consistent impedance changes upon exposure to different concentrations of NO2, with lower concentrations resulting in larger time constants. This indicates that metal-ion loading control into SSZ-13 may enhance its use as low-temperature NO2 sensors.