Development and Validation of an Ammonia-Resistant Thermal-Conductivity Analyzer for In Situ Monitoring of NH3-Cracking-Processes.

Ammonia is increasingly considered a promising hydrogen carrier due to its high hydrogen density and well-established infrastructure. Monitoring ammonia cracking efficiency requires robust, continuous gas analysis across a wide concentration range, with resistance to corrosive gases. Conventional methods such as gas chromatography or mass spectrometry meet these requirements, but are costly and operationally complex. To address this gap, a Thermal Conductivity Analyzer (TCA) was developed based on an OEM module and validated for continuous in situ monitoring of ammonia cracking. The system includes a pump-driven bypass extraction line and a three-stage calibration procedure: zero-point correction, look-up table generation, and span calibration. Measurement stability was assessed using binary H2/N2 mixtures and a quasi-binary surrogate of the ammonia cracking product gas, mixed via mass flow controllers (MFCs). The analyzer was then applied to characterize a monolithic ammonia cracking catalyst from 200-650 °C. With daily zero-point and span calibration, all measured H2 concentrations fell within the mixing uncertainty of the MFCs across 0-100 vol.%. For the synthetic cracking gas, maximum conversion ratio deviations of +0.317 and -0.224 percentage points were achieved. These results demonstrate that the TCA offers a simple, ammonia-resistant alternative for monitoring NH3 cracking processes, with uncertainties competitive with MFC repeatability.