2025 AIChE Annual Meeting

(53c) Drifts Investigation of the Effects of Hydrogen-Natural Gas Blends on Selective Catalytic Reduction of NOx for Stationary Power Applications

Authors

Varun Viswamithra, University of California Irvine
Jarod Vaquilar, University of California Irvine
Kyle Horiuchi, University of California, Irvine
Bihter Padak, University of California, Irvine
Introducing hydrogen (H2) as a carbon-free fuel can reduce fossil fuel consumption and greenhouse gas emissions. Authors have recently studied effects of hydrogen blending with natural gas on ammonia selective catalytic reduction (NH3-SCR) units. Results show that hydrogen blending (0–100%) has little impact on NOx conversion in NH3-SCR units, suggesting minimal changes are needed for commercial implementation. Interestingly, 100% hydrogen content shows improved resistance in SCR activity to high SO2 concentrations of 500 ppm. While these are promising results, the underlying mechanisms involving the effect of hydrogen are still not fully understood. The objective of this study is to elucidate the effect of hydrogen on NH3-SCR through a series of in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments.

In-situ DRFITS experiments were performed with a simulated flue gas environment in an SCR unit created via blending NH3 (800 ppm), NO (800 ppm), O2 (0-10%), and/or H2O (0-34%), with balance N2. Both fresh and used catalysts, previously tested in an SCR environment with SO2 present, were exposed to the simulated flue gas in the DRIFTS cell. The test matrix included flue gas mixtures from various H2/CH4 blends at equivalence ratios of 0.5 and 0.98 to probe operando behavior and in-situ component binding on the catalyst. Results indicate that NH₃ adsorption occurs on Brønsted and Lewis acid sites, forming protonated (NH4⁺) and coordinated (NH3) species, respectively. Under SCR conditions, NH3 adsorption dominates due to its stronger affinity for acidic sites. However, SO₂ exposure modifies catalyst acidity, enhancing NH4⁺ formation, but also promoting NH3 oxidation in the presence of O2. Increasing water content was found to modulate NH3 adsorption, reducing NH3 coordination and altering surface acid site interactions which must be considered in hydrogen-rich fuel environments.