Story ID: 
Scientists Devise Cleaner Hydrogen Combustion Engines
By: Hanneke Weitering
Caption: Improved catalytic converters slash harmful nitrogen emissions
Word Count: 416
In the quest for more sustainable aircraft propulsion systems, hydrogen-burning internal combustion engines have garnered interest from OEMs such as Airbus and Rolls-Royce because hydrogen combustion does not produce planet-warming carbon emissions. However, it is not totally emissions-free. Much like their fossil fuel-guzzling counterparts, hydrogen combustion engines produce nitrogen oxides (NOx) that pollute the air and contribute to the formation of ground-level ozone, a major component of smog that damages human health.
To help combat this problem, a team of researchers at the University of California (UC) Riverside have discovered what they say is a low-cost method of reducing NOx pollution from a hydrogen-burning engine by improving the efficiency of its catalytic converter. They accomplished this by infusing a platinum catalyst with a porous material known as “Y zeolites” and detailed the results in a recent paper published in the journal Nature Communications.
Hydrogen engines work by combusting hydrogen and oxygen, which generates energy with only water vapor as a byproduct—at least in principle. In practice, the high temperatures required for combustion trigger chemical reactions in Earth’s atmosphere, turning nitrogen and oxygen into nitric oxide (NO) and nitrogen dioxide (NO2), harmful gases collectively known as NOx.
Catalytic converters help to reduce NOx by breaking it down into harmless nitrogen gas and water vapor. Unfortunately, no catalytic converter is 100% efficient. By infusing platinum catalytic converters with Y zeolites, however, the UC Riverside researchers found that up to five times as much NOx gets converted compared with catalytic converters containing regular platinum catalysts.
Y zeolites are a synthetic type of zeolite, which is a term used to describe a family of compounds mainly consisting of silicon, aluminum, and oxygen. Zeolites are not catalysts, but they can make platinum catalysts more effective by capturing more of the water generated during hydrogen combustion. Creating a more water-rich environment helps to promote the chemical reactions in a catalytic converter, according to the researchers. 
“We don’t need to use complicated chemical or other physical processes,” said Liping Liu, one of the lead authors of the study. “We just mix the two materials—platinum and zeolite—together, run the reaction, and then we see the improvement in activity and selectivity.”
According to a university statement, the zeolite-infused catalytic converter has a pending patent, and the researchers expect the technology to be commercialized by BASF, a German multinational chemical company that provided funding for the research.