The researchers, led by Rice University’s Michael S. Wong, originally set out to find catalysts that were cheaper than palladium catalysts. In their search, however, they discovered that rhodium, while not cheaper than palladium, actually performs?better under certain circumstances and can?also be used to create additional compounds.
For example, the researchers discovered that at higher pH values, palladium created mostly dinitrogen, while rhodium created significant quantities of ammonium.?In addition to working better?at higher pH levels, the rhodium catalyst?also created?hydrazine. This?discovery opens new doors for creating additional useful chemicals from nitrite wastewater.
The researchers speculate that catalytic converter technology based on the new rhodium catalyst could be most useful as a filter installed at sites prone to runoff, such as farms.
“Agricultural fertiliser runoff is contaminating ground and surface water, which causes ecological effects such as algae blooms as well as significant adverse effects for humans, including cancer, hypertension and developmental issues in babies,” said Wong, professor and chair of the Department of Chemical and Biomolecular Engineering in Rice’s Brown School of Engineering. “I’ve been very curious about nitrogen chemistry, especially if I can design materials that clean water of nitrogen compounds like nitrites and nitrates.”
The creation of ammonia from nitrite waste is especially exciting to Wong’s team. Ammonia-based fertilisers are critical for global food supplies, and ammonia has also been discussed as a carbon-free liquid fuel that could address climate change. But ammonia producers still rely heavily on the energy-intensive Haber-Bosch process, and making ammonia from nitrite waste could provide a green alternative, Wong said.
“I’m excited about removing nitrite, forming ammonia and hydrazine, as well as the chemistry that we figured out about how all this happens,” Wong said. “The most important takeaway is that we learned how to clean water in a simpler way and created chemicals that are more valuable than the waste stream.”
Additional co-authors include C. Prakash Reddy, Hao Xu, Kimberly Heck and Guohua Luo, all of Rice. The research was partially supported by the National Science Foundation’s Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment (NEWT).