Historically, most work developing catalysts for treatment of nitrate-contaminated water have focused on supported Pd-based catalysts, but high costs of the metal ($712/oz) have limited widespread application of this technology. As part of a general effort to lower the costs of catalysts, we have begun to examine catalysts incorporating much lower cost Ru ($42/oz) as an alternative to Pd. This presentation will describe the first report of aqueous nitrate and nitrite reduction using supported Ru catalysts. A combination of methods was used including kinetics, isotope-labeled experiments for product analysis, catalyst characterization, and theoretical calculations. Ru was found to be highly active for hydrogenation of nitrate with H2(g), leading selectively to ammonium as a sole product. In contrast to Pd bimetallic catalysts, Ru is less active in reducing nitrite than nitrate, and reaction leads to a mixture of NH4+ and N2 products. Although nitrite is less reactive with Ru than nitrate, presence of the former strongly inhibits reaction of the latter, presumably due to strong adsorption of nitrite to the Ru surface reaction sites. Insights from experimental work and density functional theory calculations are combined to propose a tentative mechanism for nitrate and nitrite reduction on Ru surfaces. Challenges to further development of low-cost Ru catalysts for water treatment will also be discussed.

Catalytic hydrogenation of aqueous nitrate with low-cost ruthenium catalysts

251st National Meeting (2016)

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