A team of researchers from University of California Riverside, BASF, Virginia Tech and Brookhaven National Laboratory have mixed platinum (Pt) catalyst with zeolites to improve significantly catalytic performance in the selective catalytic reduction of nitrogen oxides (NO_x) with H2 (H2-SCR), a process aiming at NO_x removal from internal combustion engines fueled by carbon-free hydrogen (H2-ICE).

In an open-access paper in the journal Nature Communications, the team reported that the physical mixing of Pt/TiO₂ with Y zeolite (Pt/TiO₂ + Y) resulted in a “remarkable” enhancement of NO_x reduction activity and N₂ selectivity. The incorporation of Y zeolite effectively captured the in-situ generated water, fostering a water-rich environment surrounding the Pt active sites.

Effect of physical mixing Pt/TiO₂ with Y zeolite on the H2-SCR performance. (a) NO_x conversion, and (b) N₂ selectivity in H2-SCR reaction; (c) NO selective conversion (i.e., NO reacting with H₂ or O₂) in H2-SCR reaction over Pt/TiO₂ and Pt/TiO₂ + Y catalysts; (d) Correlation between N₂ selectivity and NO_x conversion in H2-SCR reaction over Pt/TiO₂, Pt/TiO₂ + TiO₂, and Pt/TiO₂ + Y catalysts. Reaction conditions: 26 mg of Pt/TiO₂ catalyst, or a physical mixture containing 26 mg of Pt/TiO₂ and 26 mg of Y or TiO₂; steady-state testing; 500 ppm NO, 1% H2, 10% O₂, 5% CO₂, and 5% H₂O; weight hourly space velocity (WHSV) = 461,540 mL·gPt/TiO₂^–1·h^–1. Xie et al.

This environment weakened the NO adsorption while concurrently promoting the H₂ activation, leading to the strikingly elevated H2-SCR activity and N₂ selectivity on Pt/TiO₂ + Y catalyst.

Compared to a catalytic converter without zeolites, the amount of NO_x reduced increased by four to five times at an engine temperature of 250 degrees Celsius, the study found. The system was particularly effective at lower temperatures, which is crucial for reducing pollution when engines first start up and are still relatively cool.

The technology can also reduce pollution from diesel engines equipped with hydrogen injection systems, explained Fudong Liu, the corresponding author and associate professor of chemical and environmental engineering at UCR’s Bourns College of Engineering. The hydrogen injection would be similar to the injection systems used in selective catalytic reduction systems for big-rig diesel trucks.

Zeolites are low-cost materials with a well-defined crystalline structure composed primarily of silicon, aluminum, and oxygen atoms. Their large surface area and three-dimensional, cage-like framework of uniform pores and channels allow for more efficient breakdown of pollutants.

By physically mixing platinum with Y zeolite—a synthetic type from the broader family of zeolite compounds—the researchers created a system that effectively captures water generated during the hydrogen combustion process. This water-rich environment promotes hydrogen activation, which is key to improving nitrogen reduction efficiency.

Shaohua Xie, a research scientist at UCR and lead author of the study, explained that the zeolite itself is not a catalyst. Instead, it enhances the effectiveness of the platinum catalyst by creating a water-rich environment. Liping Liu, a Ph.d. student, and Hongliang Xin, an associate professor at Virginia Tech, further validated this concept through theoretical modeling of the new catalyst system.

This concept can also apply to other types of zeolites. It’s a universal strategy.

—Shaohua Xie

Liu and Xie expect BASF, which funded the study, to commercialize the technology, which is the subject of a pending patent.

Resources

• Xie, S., Liu, L., Li, Y. et al. Zeolite-promoted platinum catalyst for efficient reduction of nitrogen oxides with hydrogen. Nat Commun 15, 7988 (2024). doi: 10.1038/s41467-024-52382-7