Ruthenium-based catalysts for perchlorate reduction and methods of use thereof

Abstract

The invention provides a method for removing perchlorate from an aqueous solution with a catalyst that comprises ruthenium in the presence of a nitrogen source or that comprises ruthenium on a nitrogen-functionalized support material. The invention also provides solutions and reactors that are useful for removing perchlorate from an aqueous solution.

Description

[0001] RUTHENIUM-BASEDCATALYSTS FORPERCHLORATEREDUCTION CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to United States Provisional Application Number 63 / 547,498 that was filed on November 6, 2023. The entire content of the application referenced above is hereby incorporated by reference herein. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under 1932942 awarded by the National Science Foundation. The government has certain rights in the invention. BACKGROUND Perchlorate (ClO4–) is extensively used in energetic materials (Rehwoldt, M. C., et al., J. Phys. Chem. C 2018, 122 (20), 10792-10800.) such as rocket fuels, munitions, and pyrotechnics, resulting in widespread water pollution (Brandhuber, P., et al., J. - Am. Water Works Assoc.2009, 101 (11), 63-73). Excessive exposure to ClO4–can disrupt thyroid hormone production (Greer, M. A, et al., Environ. Health Perspect.2002, 110 (9), 927-937), and the ClO4–toxicity has been previously underestimated (Llorente-Esteban, A., et al., Nat. Struct. Mol. Biol.2020, 27 (6), 533-539). In the United States, the maximum contamination levels for ClO4–in drinking water set by California (www.waterboards.ca.gov / drinking_water / certlic / drinkingwater / -Perchlorate.html (accessed 2023-07-15)) and Massachusetts (www.mass.gov / lists / perchlorate-background- information-and-standards#perchlorate---final-standards- (accessed 2023-07-15)) are 6 and 2 µg L−1, respectively. In 2023, China started nationwide regulation of ClO4–in drinking water at 70 µg L−1(http: / / c.gb688.cn / bzgk / gb / showGb?type=online&hcno=99E9C17-E3547A3C0CE2FD1F FD9F2F7BE (accessed 2023-07-15)). The recent discovery of ClO4–on Mars, Moon, and meteorites implies its widespread distribution in the Solar System (Hecht, M. H., et al., Science 2009, 325 (5936), 64-67; Kim, Y. S., et al., J. Am. Chem. Soc.2013, 135 (13), 4910-4913; Jackson, W. A., et al., Earth. Planet. Sci. Lett.2015, 430, 470-476; and Kounaves, S. P., et al., Icarus 2014, 229, 206-213). Therefore, ClO4–treatment technologies are of great interest for both water purification and human extraterrestrial exploration (Davila, A. F., et al., Int. J. Astrobiol. 2013, 12 (4), 321-325). Early successes of reducing the inert aqueous ClO4–were catalyzed by oxometallates of Mo (Haight Jr, G., et al., J. Am. Chem. Soc.1952, 74 (23), 6056-6059), W (Haight Jr, G., J. Am. Chem. Soc.1954, 76 (18), 4718-4721), Re (Abu-Omar, M. M., et al., Inorg. Chem.1995, 34 (25), 6239-6240), and Os (Crowell, W. R., et al., J. Am. Chem. Soc.1940, 62 (8), 2176-2178) via oxygen atom transfer (OAT) in the presence of concentrated acids and special reductants. Later efforts toward environmental remediation reduced ClO4–using Fe0nanoparticles (Cao, J., et al., J. Nanopart. Res.2005, 7, 499-506) and FeIIsolution (Gu, B., et al., Environ. Sci. Technol.2003, 37 (10), 2291-2295), but harsh conditions and large excess of reductants were still required. Recently, enzyme-inspired Re–Pd / C (Liu, J., et al., ACS Catal.2015, 5 (2), 511-522; and Ren, C.; Liu, J., ACS Catal.2021, 11 (11), 6715-6725) and Mo–Pd / C(Ren, C. J. Am. Chem. Soc.2021, 143 (21), 7891-7896; and Ren, C., et al., ACS ES&T Eng.2022, 2 (2), 181-188) catalysts have realized facile ClO4–reduction under mild and friendly conditions, such as 1 atm H2 as the reductant, pH 3.0 (1 mM H+), and 20 °C: ClO4−+ 4 H2→ Cl−+ 4 H2O (1) These catalysts use ReV–VIIor MoIV–VIredox cycles to enable OAT from ClO4–. In comparison to catalysts prepared from only KReO4(Hurley, K. D., et al., Environ. Sci. Technol.2007, 41 (6), 2044-2049) and Na2MoO4(Ren, C., et al., ACS Catal.2020, 10 (15), 8201-8211) precursors, the coordination with select pyridine (N) (Hurley, K. D., et al., J. Am. Chem. Soc.2009, 131 (40), 14172-14173), oxazoline-phenolate (N–O) (Abu‐Omar, M. M., et al., Angew. Chem.2000, 112 (23), 4480-4483), and bipyridine (N–N) (Ren, C. J. Am. Chem. Soc.2021, 143 (21), 7891-7896) ligands accelerate ClO4–reduction by 12–5,200 fold (Liu, J.; Gao, J., Front. Environ. Sci. Eng. 2022, 17 (2), 26). However, the proton-assisted OAT suffers from significant activity loss at pH>4,( Liu, J., et al., ACS Catal.2015, 5 (2), 511-522; Ren, C. J. Am. Chem. Soc.2021, 143 (21), 7891-7896; Ren, C., et al., ACS Catal.2020, 10 (15), 8201-8211; and Liu, J., et al., Environ. Sci. Technol.2015, 49 (21), 12932-12940) preventing the application at neutral pH. Another major challenge for the reported catalysts is the hydrogenation of aromatic ligands(Ren, C., et al., ACS ES&T Eng.2022, 2 (2), 181-188; and Liu, J., et al., Environ. Sci. Technol.2015, 49 (21), 12932-12940) or decomposition of the ligand-metal complex sites (Ren, C.; Liu, J., ACS Catal. 2021, 11 (11), 6715-6725; and Liu, J., et al., Environ. Sci. Technol.2015, 49 (21), 12932-12940), resulting in irreversible loss of catalyst activity. In contrast, among the common platinum group metal (PGM) nanoparticle catalysts, Ru0has unique reactivity with oxyanions at pH 7 (Chen, X., et al., Chem. Eng. J.2017, 313, 745-752). A bimetallic Ru–Pd / C has exhibited the fastest ClO3–reduction to date (Gao, J., et al., Environ. Sci. Technol.2023) but little activity in ClO4–reduction. A Ru / CeO2 catalyst requires 80 °C to achieve a satisfying rate of ClO4–reduction (Yoshida, D., et al., Appl. Catal. A: Gen.2023, 649, 118982). For environmental applications, heating large volumes of water is a major technical obstacle. Although the catalytic activity of Ru nanoparticles might be further optimized by morphology control or support modification (Axet, M. R., et al., Chem. Rev.2020, 120 (2), 1085-1145), these strategies usually involve extra chemical additives and synthetic procedures. Tuning the surface coordination chemistry of metal nanoparticles with organic ligands is a promising approach to alter the catalytic activity (Liu, P., et al., J. Am. Chem. Soc.2017, 139 (6), 2122-2131). Currently there is a need for catalysts that are useful for water purification applications. There is also a need for facile and commercially feasible methods for preparing such catalysts. In particular, there is a need for catalysts that can be used for removing perchlorate from water at neutral or alkaline pH. SUMMARY Applicant has modified the properties of Ru0nanoparticles with (i) molecular diamine ligands and / or (ii) nitrogen functional groups on the support material, enabling rapid and complete ClO4–reduction at pH 7. Accordingly, in one embodiment, the invention provides a method comprising, treating an aqueous solution that comprises oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) with H2 and a catalyst that comprises: a) ruthenium in the presence of a nitrogen source; or b) ruthenium on a nitrogen-functionalized support material; under conditions where at least some of the oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) is reduced. In one embodiment, at least 50% of the ClO4- is reduced to Cl-. In another embodiment, at least 70% of the ClO4- is reduced to Cl-. In another embodiment, at least 80% of the ClO4- is reduced to Cl-. In another embodiment, at least 90% of the ClO4- is reduced to Cl-. In another embodiment, at least 90% of the ClO4- is reduced to Cl-. In another embodiment, at least 95% of the ClO4- is reduced to Cl-. In another embodiment, at least 99% of the ClO4- is reduced to Cl-. In another aspect the present invention provides a solution that comprises water, oxyanion(s) (e.g., perchlorate, chlorate, or nitrate), a catalyst that comprises ruthenium, and a nitrogen source. Such solutions are useful for preparing aqueous solutions having reduced oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) concentrations. In another aspect the present invention provides a heterogenous catalytic reactor for reducing oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) concentration of an aqueous sample, the reactor comprising a container defining a reaction plenum, with at least one orifice defining an inlet and an outlet, where the aqueous solution to be processed enters through the inlet and exits through the outlet once the oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) concentration has dropped to a desired level, where the reaction plenum encloses a catalyst that comprises ruthenium and a nitrogen source. In another aspect the present invention provides a composition that comprises ruthenium on a nitrogen-functionalized support material Catalyst described herein comprise ruthenium, the most cost-effective platinum group metal, and utilize an inexpensive ligand, to effectively reduce toxic oxyanion(s) (e.g., perchlorate) in water. The catalysts show high activity at neutral pH and room temperature, can be handled in an air environment, and hold a long working life without hydrogenation deactivation. In some embodiments, the oxyanion(s) comprise ClO4−, ClO3−, NO3−and / or BrO3−. In some embodiments, the oxyanion(s) comprise ClO4−, ClO3−, and / or NO3−. In some embodiments, the oxyanion(s) comprise ClO4−, and NO3−. In some embodiments, the oxyanion(s) comprise ClO3−and NO3−. In some embodiments, the oxyanion(s) comprise ClO4−. In some embodiments, the oxyanion(s) comprise ClO3−. In some embodiments, the oxyanion(s) comprise NO3−. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A-1D. Time profiles for aqueous ClO4–reduction by Ru catalysts with aromatic ligands added. Fig.1A shows time profiles for reduction by Ru catalysts with phenanthroline ligands. Fig.1B shows time profiles for reduction by Ru catalysts with bipyridine ligands. Fig.1C shows time profiles for reduction by Ru catalysts with aromatic ligands. Fig.1D shows time profiles for reduction by Ru catalysts with amino-substituted o-phenylenediamine. Reaction conditions: 2 g L–1of a commercial 5 wt % Ru / C with 1 mM ligand added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figures 2A-2D.Time profiles for aqueous ClO4–reduction by Ru catalysts with diaminocycloalkanes (or diaminocycloalkene) added. Fig.2A shows time profiles for reduction by Ru catalysts with diaminocycloalkanes. Fig.2B shows time profiles for reduction by Ru catalysts with diaminocycloalkane or diaminocycloalkene. Fig.2C shows time profiles for reduction by Ru catalysts with diaminocycloalkanes. Fig.2D shows time profiles for reduction by Ru catalysts with amino-substituted diaminocycloalkanes. Reaction conditions: 2 g L–1of a commercial 5 wt % Ru / C with 1 mM ligand added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figure 3. Time profiles for aqueous ClO4–reduction by Ru catalysts with linear aliphatic diamines added. Reaction conditions: 2 g L–1of a commercial 5 wt % Ru / C with 1 mM ligand added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C Figures 4A-4D (Fig.4A) Time profiles of ClO4–reduction by Ru catalysts; (Fig.4B) chlorine balance for ClO4–reduction by [cis-DACH]Ru / NC; (Fig.4C) pH effect on [cis-DACH]Ru / NC. For panels a–c: 2.0 g L–1of lab-prepared catalysts (5 wt% Ru), 2 mM cis-DACH added in water. (Fig.4D) Ligand-enhanced ClO4–reduction with Ru colloids (prepared from 1 mM RuCl3, 10 mM NaBH4, and 10 mM cis-DACH) and Ru−Pd / C (2.0 g L–1catalyst; 5 wt% Ru and 5 wt% Pd, 1 mM 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen)). For panels a–d: 1 mM ClO4–, pH 7.0, 1 atm of H2, 20 °C Figure 5.The effect of solution pH on the activity of [cis-DACH]Ru / C (no surface nitrogen functional groups). Reaction conditions: 2 g L–1of the lab-prepared 5 wt % Ru / C, with 2 mM cis-DACH added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figure 6. The effect of solution pH on the activity of a commercial Ru / C (no surface nitrogen functional groups; no cis-DACH added). Reaction conditions: 2 g L–1of 5 wt % Ru / C, 1 mM ClO4–, 1 atm of H2, 20 °C. Figure 7. The effect of cis-DACH concentration. Reaction conditions: 2 g L–1of 5 wt % Ru / NC, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figure 8.The ratio of the immobilized cis-DACH during ClO4–reduction. Reaction conditions: 2 g L–1of 5 wt % Ru / C or Ru / NC with 2 mM cis-DACH added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figure 9. Reduction of 100 mM of ClO4–by [cis-DACH]Ru / NC. Reaction conditions: 2 g L–1of 5 wt % Ru / NC with 2 mM cis-DACH added in the suspension, pH 7, 1 atm of H2, 20 °C. Figure 10. Time profiles of ClO4–reduction in the presence of Cl–and SO42–. Reaction conditions: 2 g L–1of 5 wt % Ru / NC with 2 mM cis-DACH added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figure 11.The reduction of 10 mM ClO4–by the freshly prepared (cycle 1) and reused (cycle 10, already with nine previous spikes of 10 mM ClO4–) [cis-DACH]Ru / NC catalyst. Each ClO4–spike was allowed 24 hours to achieve complete reduction into Cl−, with the 10 spikes taking a total of 10 days to complete. The control dataset involved the freshly prepared catalyst in the presence of 90 mM NaCl, simulating the scenario of complete reduction of nine spikes of 10 mM ClO4–without deactivation. Comparing the time profiles of the control with “cycle 10 at day 10” indicates that the catalyst performance was not affected by either the continuous oxidant addition or the hydrogenating aqueous environment. Reaction conditions: 2 g L–1of 5 wt % Ru / NC with 2 mM cis-DACH added in the suspension, pH 7, 1 atm of H2, 20 °C. Figure 12. The ClO4–reduction by [cis-DACH]Ru / NC before and after air exposure for 1 h. The preparation of [cis-DACH]Ru / NC took 1 h under 1 atm H2. After air exposure, the catalyst suspensions were treated under 1 atm H2for an additional hour before adding ClO4–. Reaction conditions: 2 g L–1of Ru / NC catalyst with 2 mM cis-DACH added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figure 13. The reduction of ClO4–by other carbon-supported platinum group metal catalysts. Reaction conditions: 2 g L–1of commercial catalysts (see Table A1 for details) with 2 mM cis-DACH added in the suspension, 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. Figure 14. XRD patterns of catalyst supports and Ru catalysts Figures 15A-15F. Catalytic reduction of ClO4−in various initial concentrations by the (Figs.15A-15B) [cis-DACH]Ru / NC, (Figs.15C-15D) [cis-DACH]Ru / C, and (Figs.15E-15F) Ru / C. The initial rate of ClO4–reduction at various initial ClO4–concentrations were used for the Langmuir–Hinshelwood (LH) model fits (see Text S1 for details). Reaction conditions: 2 g L–1of 5 wt % Ru / NC or Ru / C with 2 mM cis-DACH added in the suspension, pH 7, 1 atm of H2, 20 °C. Figure 16. Is an example embodiment of reactor for removing perchlorate from an aqueous solution. Such a reactor may be installed locally at a water treatment plant. Figures 17A-17B. Time profiles of ClO4–and NO3−reduction in (Fig.17A) synthetic IX regenerant brine and (Fig.17B) tap water. Default reaction conditions: 2 g L–1of 5 wt% Ru / NC, 2 mM cis-DACH, 1 mM ClO4–,1 atm of H2, 20 °C. DETAILED DESCRIPTION OF THE INVENTION The Ru catalysts can be prepared by impregnating the support material (such as activated carbon, alumina, or silica) with a RuCl3precursor via incipient wetness. The resulting wet paste is dried in an oven (e.g., at 75 °C for 12 hours) and then reduced (e.g., with Ar / H2 (v / v = 95 / 5) at 450 °C for 6 hours) to yield supported Ru catalysts. The sequential addition of Ru catalysts and organic nitrogen ligands into the water to be treated, followed by sparging with H2, enables perchlorate reduction. An even higher performance can be achieved by using the carbon support treated with a reported “soft-nitriding” process (e.g., heating the carbon with some nitrogen-rich organic compound at 300 °C). The ligand-enhanced Ru / NC (Ru supported on “soft-nitriding” carbon) showed high activity of perchlorate reduction at a wide pH range of 3-9. At near neutral pH and ambient conditions, this catalytic system outperforms other abiotic catalysts reported to date in perchlorate reduction and showed similar apparent rate constant to the reaction at 80°C with a previously reported Ru / CeO2 catalyst. The catalysts can be used in batch reactors (with a microfiltration system to separate the catalyst from water) to treat perchlorate for a variety of scenarios, including drinking water, ion-exchange regeneration waste brine, reverse osmosis rejection brine, and soil washing wastewater for environmental remediation. Most of the reported catalysts use pH 3 for the reduction of perchlorate and they completely lose activity at pH 7. The Ru catalyst systems comprising Ru catalyst and ligand described herein show high activity at pH 5-7. Accordingly, they can be used without consumption of acid for pH adjustment. While Ru catalysts have been reported for perchlorate reduction at pH 7 without the addition of ligands, the reaction rate at room temperature is considerably slow. The introduction of nitrogen ligands enables rapid reaction at ambient temperature. The catalysts and methods of the invention avoid the heating process and thus saves energy to a substantial level. The Ru catalyst systems can be prepared conveniently by adding the Ru catalyst and ligand to water. Additionally, they can be handled in an air environment. Additionally, the catalyst cannot be easily hydrogenated, so they have an improved working lifetime. As used herein, the term “drinking water” includes groundwater, surface water, recycled water and stormwater that can be used for human drinking purposes. In certain embodiments, the drinking water is tap water. As used herein, the term “industrial waste” includes wastewater discharged from different manufacturing industries, and saline wastewater (e.g., ion exchange regenerant brine, reverse osmosis concentrate, and oil-gas produced water) generated from different industrial processes. As used herein, the term “hazardous waste” includes aqueous waste containing hazardous levels of substances (e.g., organic contaminants, toxic heavy metals, metalloids, and radionuclides) that have been regulated or will be regulated soon. In certain embodiments, the aqueous solution further comprises sulfate, phosphate, and / or nitrate. In certain embodiments, the aqueous solution further comprises nitrate. In certain embodiments, in addition to the perchlorate being reduced in a method described herein, at least some of the nitrate is reduced by the Ru catalyst described herein, which is resistant to the presence of nitrate and is capable of reducing the nitrate. In one embodiment, at least 50% of the nitrate is reduced. In another embodiment, at least 70% of the nitrate is reduced. In another embodiment, at least 80% of the nitrate is reduced. In another embodiment, at least 90% of the nitrate is reduced. In another embodiment, at least 90% of the nitrate is reduced. In another embodiment, at least 95% of the nitrate is reduced. In another embodiment, at least 99% of the nitrate is reduced. Accordingly, in certain embodiments, the perchlorate reduction methods described herein do not comprise removing or reducing the nitrate from the aqueous solution by another catalyst (e.g., no pretreatment by another catalyst different from the Ru catalyst described herein, such as another metal catalyst). However, in other embodiments, the method may optionally further comprise removing or reducing the nitrate by another catalyst. The solid support can be any material that is suitable for providing a catalyst that can be used to reduce ClO4–to Cl-. For example, in one embodiment, the solid support can comprise porous carbon, alumina, silica, a zeolite, a clay, TiO2, CeO2, ZrO2, Mxene (Nanoscale Horiz., 2020, 5, 235-258), a carbon nanotube, graphene, or biochar. In one embodiment, the solid support comprises carbon. In one embodiment, the solid support is carbon. In one embodiment, the carbon support is prepared using a “soft-nitriding” process (e.g., heating the carbon with some nitrogen-rich organic compound at 300 °C; see Liu, B., et al., J. Am. Chem. Soc.2016, 138 (14), 4718-4721). In one embodiment, the catalyst comprises highly dispersed Ru0. The term highly dispersed Ru0includes dispersions from a single atom to 20 nm. In one embodiment, the term includes dispersions from a single atom to about 5 nm. In one embodiment, the term includes dispersions from a single atom to about 3 nm. In one embodiment, the term includes dispersions from about 3 nm to about 5 nm. Organic Nitrogen Ligands For some catalyst embodiments, the nitrogen source is an organic nitrogen ligand. For some catalyst embodiments, the organic nitrogen ligand comprises the group: wherein each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl. For some catalyst embodiments, the organic nitrogen ligand comprises the group: wherein: A is a monocyclic aryl, a bicyclic aryl, a monocyclic (C3-C8)cycloalkyl, or a polycyclic (C6-C12)cycloalkyl; and each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl. For some catalyst embodiments, the organic nitrogen ligand comprises the group: wherein: A is a (C3-C8)cycloalkyl; and each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl. For some catalyst embodiments, the organic nitrogen ligand is cis-1,2-diaminocyclopentane, cis-1,2-diaminocyclohexane, cis-1,2-diaminocycloheptane, or cis-1,2-diaminocyclooctane. For some catalyst embodiments, the organic nitrogen ligand is selected from the group consisting of:

[0002] . For some catalyst embodiments, the organic nitrogen ligand is cis-1,2-diaminocyclohexane. For some catalyst embodiments, the organic nitrogen ligand can be a compound selected from the following formulae: ; where: X11 can be C-R11 or N, X12 can be C-R12 or N, X13 can be C-R13 or N, X14 can be C-R14 or N; and R11thru R16can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. In some catalysts, the nitrogen donor ligand can be: where R21 thru R25 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. In some catalyst embodiments, R21thru R25can be independently H, hydroxy, chloro, C1-3 alkyl, C1-3 alkoxy, or amino. For some catalysts, the organic nitrogen ligand can be a compound selected from the following formulae: , ; where: A can be an optionally substituted heteroaryl selected from the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, 2-thiazolyl, and 2-imidazolyl, where X31can be either C, O, S or N depending on the heteroaryl, where the hydrogen positions in the heteroaryl can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; Y31 can be either C, O, S or N, where the hydrogen positions in the heteroaryl that contains Y31can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R31thru R33can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R34and R35can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, halogen, amino, cyano, or together with the carbon which they are linked, form a carbon alkyl or alkenyl of 1 to 2 carbon atoms where hydrogen in the link can be independently optionally substituted with H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, halogen, amino, cyano, or O or S for divalent positions, or, when 2 carbon atoms, both carbon positions are optionally substituted with an additional linked alkyl or alkenyl to form an optionally substituted 4-6 carbon heteroaryl from 1 to 2 heteroatoms, where the heteroatom can be N, where the hydrogen positions in the heteroaryl can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. In some catalysts, the organic nitrogen ligand can be: where n is 0 or 1; R41thru R48can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. In some embodiments, R41 thru R48 can be independently H, hydroxy, chloro, C1-3 alkyl, C1-3 alkoxy, or amino. With some catalyst embodiments, the organic nitrogen ligand can be a compound selected from the following formulae: ; where B and C can be independently selected from optionally substituted heteroaryl selected from the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, and 2-imidazolyl, where the hydrogen positions in the heteroaryl can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R51 thru R53 can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R61thru R64can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, cyano, or an optionally substituted aryl, where the aryl can be selected from the group consisting of the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, and 2-imidazolyl, where the hydrogen positions in the heteroaryl can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; and R71thru R76can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. In some embodiments, the organic nitrogen ligand can be: where R81 thru R96 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. In some embodiments, R81thru R96can be independently H, hydroxy, chloro, C1-3alkyl, C1-3alkoxy, or amino. Heterogenous Catalyst Reactor Some embodiments describe a reactor that can be used to remove contaminants from unprocessed fluid. An example embodiment is shown in Figure 16. In some embodiments, the contaminant reduced can comprise oxyanion(s), such as ClO4−, ClO3−, NO3−and / or BrO3−. In some embodiments, the contaminant reduced can comprise halogen oxyanions, such as ClO4−. In some embodiments, the reactor, 300, can comprise a container, 301, defining a reaction plenum, 302, with at least one orifice, 303, defining an inlet and an outlet, where the fluid to be processed enters through the inlet and exits through the outlet once the contaminants have dropped to a desired level. In some reactors, the inlet orifice can become the outlet with external pressure manipulation. In other reactors, there are a plurality of orifices, at least one for the inlet and at least one for the outlet, 304. In some reactors, the reaction plenum can enclose the aforedescribed heterogenous catalyst, 310. In some reactors, the outlet orifice can additionally comprise a membrane, where the orifice is occluded by a membrane such that any fluid being transported through the orifice must pass through the membrane. In some embodiments, the membrane can comprise a microfiltration membrane, where the membrane allows the fluid to pass but retains the catalyst. Embodiments Specific values identified below are for illustration only; they do not exclude other defined values or other values within defined ranges. It is to be understood that two or more specific values may be combined. It is also to be understood that the specific values listed herein below (or subsets thereof) can be excluded from the invention. The following embodiments are specifically contemplated by this disclosure. Embodiment 1. A method comprising, treating an aqueous solution that comprises perchlorate with H2and a catalyst that comprises: a) ruthenium in the presence of a nitrogen source; or b) ruthenium on a nitrogen-functionalized support material; under conditions where at least some of the perchlorate is reduced. Embodiment 2. The method of Embodiment 1 that comprises treating an aqueous solution that comprises perchlorate with H2 and a catalyst that comprises ruthenium in the presence of a nitrogen source under conditions where at least some of the perchlorate is reduced. Embodiment 3. The method of Embodiment 1 that comprises treating an aqueous solution that comprises perchlorate with H2 and a catalyst that comprises ruthenium on a nitrogen-functionalized support material under conditions where at least some of the perchlorate is reduced. Embodiment 4. The method of Embodiment 1 that comprises treating an aqueous solution that comprises perchlorate with H2 and a catalyst that comprises ruthenium on a nitrogen-functionalized support material in the presence of a nitrogen source under conditions where at least some of the perchlorate is reduced. Embodiment 5. The method of any one of Embodiments 1-4, wherein the aqueous solution is drinking water. Embodiment 6. The method of any one of Embodiments 1-4, wherein the aqueous solution is industrial waste. Embodiment 7. The method of any one of Embodiments 1-4, wherein the aqueous solution is hazardous waste. In certain embodiments, the aqueous solution (i.e., water sample) further comprises sulfate, phosphate, and / or nitrate. In certain embodiments, the aqueous solution (i.e., water sample) further comprises chlorate. In certain embodiments, the aqueous solution (i.e., water sample) further comprises bromate. Embodiment 8. The method of any one of Embodiments 1-7, wherein the water sample further comprises sulfate or nitrate. Embodiment 9. The method of any one of Embodiments 1-7, wherein the water sample further comprises nitrate. Embodiment 10. The method of any one of Embodiments 1-9, wherein at least some of the perchlorate is reduced to chloride. Embodiment 11. The method of any one of Embodiments 1-9, wherein at least 90 percent of the perchlorate is reduced to chloride. Embodiment 12. The method of any one of Embodiments 1-11, wherein the catalyst comprises Ru0on a solid support. Embodiment 13. The method of Embodiment 12, wherein the support comprises porous carbon, alumina, silica, a zeolite, a clay, TiO2, CeO2, ZrO2, Mxene, a carbon nanotube, graphene, or biochar. Embodiment 14. The method of Embodiment 13, wherein the support comprises carbon. Embodiment 15. The method of Embodiment 12, wherein the support is carbon. Embodiment 16. The method of any one of Embodiments 1-15, wherein the catalyst comprises highly dispersed Ru0. Embodiment 17. The method of any one of Embodiments 1-2 and 4-16, wherein the nitrogen source comprises an organic nitrogen ligand. Embodiment 18. The method of Embodiment 17, wherein the organic nitrogen ligand comprises the group: wherein each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl. Embodiment 19. The method of Embodiment 17, wherein the organic nitrogen ligand that comprises the group: wherein: A is a monocyclic aryl, a bicyclic aryl, a monocyclic (C3-C8)cycloalkyl, or a polycyclic (C6-C12)cycloalkyl; and each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl. Embodiment 20. The method of Embodiment 17, wherein the organic nitrogen ligand that comprises the group: wherein: A is a (C3-C8)cycloalkyl; and each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl. Embodiment 21. The method of Embodiment 17, wherein the organic nitrogen ligand comprises: cis-1,2-diaminocyclopentane, cis-1,2-diaminocyclohexane, cis-1,2-diaminocycloheptane, or cis-1,2-diaminocyclooctane. Embodiment 22. The method of Embodiment 17, wherein the organic nitrogen ligand is selected from the group consisting of:

[0003] . Embodiment 23. The method of Embodiment 17, wherein the organic nitrogen ligand is cis-1,2-diaminocyclohexane. Embodiment 24. The method of Embodiment 17, wherein the organic nitrogen ligand is selected from the following formulae: ; where: X11is C-R11or N, X12is C-R12or N, X13is C-R13or N, X14is C-R14or N; and R11 thru R16 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. Embodiment 25. The method of Embodiment 17, wherein the organic nitrogen ligand is selected from the following formulae: where R21 thru R25 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. Embodiment 26. The method of Embodiment 25, where R21thru R25are each independently H, hydroxy, chloro, C1-3alkyl, C1-3alkoxy, or amino. Embodiment 27. The method of Embodiment 17, wherein the organic nitrogen ligand is selected from the following formulae: ; where: A is an optionally substituted heteroaryl selected from the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, 2-thiazolyl, and 2-imidazolyl, where X31is either C, O, S or N depending on the heteroaryl, where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkoxy, halogen, amino, or cyano; Y31can be either C, O, S or N, where the hydrogen positions in the heteroaryl that contains Y31 can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R31thru R33are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; n is 0 or 1; and R34and R35are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, halogen, amino, cyano, or together with the carbon which they are linked, form a carbon alkyl or alkenyl of 1 to 2 carbon atoms where hydrogen in the link is independently optionally substituted with H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, halogen, amino, cyano, or O or S for divalent positions, or, when 2 carbon atoms, both carbon positions are optionally substituted with an additional linked alkyl or alkenyl to form an optionally substituted 4-6 carbon heteroaryl from 1 to 2 heteroatoms, where the heteroatom is N, and where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. Embodiment 28. The method of Embodiment 17, wherein the organic nitrogen ligand is: where n is 0 or 1; R41thru R48are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. Embodiment 29. The method of Embodiment 28, where R41 thru R48 is independently H, hydroxy, chloro, C1-3alkyl, C1-3alkoxy, or amino. Embodiment 30. The method of Embodiment 17, wherein the organic nitrogen ligand is a compound selected from the following formulae: , , and where: B and C are independently selected from optionally substituted heteroaryl selected from the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, and 2-imidazolyl, where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R51 thru R53 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R61 thru R64 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, cyano, or an optionally substituted aryl, where the aryl is selected from the group consisting of the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, and 2-imidazolyl, where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; and R71thru R76are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. Embodiment 31. The method of Embodiment 17, wherein the organic nitrogen ligand is: where R81 thru R96 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano. Embodiment 32. The method of Embodiment 31, where R81thru R96are each independently H, hydroxy, chloro, C1-3 alkyl, C1-3 alkoxy, or amino. Embodiment 33. The method of any one of Embodiments 17-32, where the molar ratio of Ru0to organic nitrogen ligand is from 10:1 to 1:10. Embodiment 34. The method of any one of Embodiments 17-32, where the molar ratio of Ru0to organic nitrogen ligand is from 1:1 to 1:4. Embodiment 35. The method any one of Embodiments 1-34, wherein the aqueous solution has a pH of at least about 5. Embodiment 36. The method any one of Embodiments 1-34, wherein the aqueous solution has a pH of at least about 6. Embodiment 37. The method any one of Embodiments 1-34, wherein the aqueous solution has a pH of at least about 7. In certain embodiments, the aqueous solution has a pH of at least about 7.4. In certain embodiments, the aqueous solution has a pH of at least about 8. Embodiment 38. A solution that comprises water, perchlorate, a catalyst that comprises ruthenium, and a nitrogen source. In certain embodiments, the solution further comprises sulfate, phosphate, and / or nitrate. In certain embodiments, the solution further comprises chlorate. In certain embodiments, the solution further comprises bromate. Embodiment 39. The solution of Embodiment 38, that further comprises sulfate or nitrate. Embodiment 40. The solution of Embodiment 38, that further comprises nitrate. Embodiment 41. The solution of Embodiment 38, wherein the catalyst comprises Ru0on a solid support. Embodiment 42. The solution of Embodiment 41, wherein the solid support comprises porous carbon, alumina, silica, a zeolite, a clay, TiO2, CeO2, ZrO2, Mxene, a carbon nanotube, graphene, or biochar. Embodiment 43. The solution of Embodiment 41, wherein the solid support comprises a nitrogen-functionalized support material. Embodiment 44. The solution of Embodiment 41, wherein the solid support comprises carbon. Embodiment 45. The solution of Embodiment 41, wherein the solid support is carbon. Embodiment 46. The solution of Embodiment 41, wherein the solid support is nitrogen-functionalized. Embodiment 47. The solution of any one of Embodiments 38-46, wherein the catalyst comprises highly dispersed Ru0. Embodiment 48. The solution of any one of Embodiments 38-46, wherein the nitrogen source comprises an organic nitrogen ligand. Embodiment 49. The solution of Embodiment 48, wherein the organic nitrogen ligand is a compound as described in any one of Embodiments 18-32. Embodiment 50. The solution of Embodiment 49, where the molar ratio of Ru0to organic nitrogen ligand is from 10:1 to 1:10. Embodiment 51. The solution of Embodiment 49, where the molar ratio of Ru0to organic nitrogen ligand is from 1:1 to 1:4. Embodiment 52. The solution of any one of Embodiments 38-51, wherein the aqueous solution has a pH of at least about 5. Embodiment 53. The solution of any one of Embodiments 38-51, wherein the aqueous solution has a pH of at least about 6. Embodiment 54. The solution of any one of Embodiments 38-51, wherein the aqueous solution has a pH of at least about 7. In certain embodiments, the aqueous solution has a pH of at least about 7.4. In certain embodiments, the aqueous solution has a pH of at least about 8. Embodiment 55. A heterogenous catalytic reactor for reducing perchlorate concentration of an aqueous sample, the reactor comprising a container defining a reaction plenum, with at least one orifice defining an inlet and an outlet, where the aqueous solution to be processed enters through the inlet and exits through the outlet once the perchlorate concentration has dropped to a desired level, where the reaction plenum encloses a catalyst that comprises ruthenium and a nitrogen source. Embodiment 56. A composition that comprises ruthenium on a nitrogen-functionalized support material. Embodiment 57. The composition of Embodiment 56, wherein the support material comprises carbon. Embodiment 58. The composition of Embodiment 56, wherein the solid support is carbon. Embodiment 59. The composition of any one of Embodiments 56-58, wherein the catalyst comprises highly dispersed Ru0. Certain embodiments of the invention provide a catalyst as described herein (e.g., ruthenium on a nitrogen-functionalized support material, or a ligand-coordinated Ru catalyst). In one embodiment, the catalyst is a monometallic catalyst that comprises only one metal element that is ruthenium and does not comprise another metal element. In one embodiment, the metal element comprised within the catalyst consist of ruthenium. In one embodiment, the catalyst does not comprise an oxygen-atom transfer (OAT) transition metal. In one embodiment, the catalyst does not comprise a Group 5, Group 6, or Group 7 metal. In one embodiment, the catalyst does not comprise a Group 5 or Group 6 metal. In one embodiment, the catalyst does not comprise a Group 5 metal. In one embodiment, the catalyst does not comprise vanadium (V), tungsten (W), or molybdenum (Mo). In one embodiment, the catalyst does not comprise tungsten (W), or molybdenum (Mo). In one embodiment, the catalyst does not comprise molybdenum (Mo). The invention will now be illustrated by the following non-limiting Example. EXAMPLE Example 1. Chemicals and materials RuCl3·xH2O (99.98%) and NaClO4 (≥99%) were used as received from Sigma−Aldrich. Detailed information on support materials and commercial catalysts is described in Table A1. The nitrogen ligands were used as received from Oakwood Chemical, Alfa Aesar, Ark Pharm, Combi−Blocks, Sigma−Aldrich, and TCI. All aqueous solutions were prepared with Milli-Q water (resistivity >18.2 MΩ cm). Table A1. Support Materials for Lab-Prepared Catalysts and Commercial PGM Catalysts. material brief description vendor and catalog # carbon powder Norit GSX; steam activated and acid washed; surface Alfa Aesar area of 1300 m2g−1provided by the vendor; used as L11860 received. aluminum oxide 1 / 8" pellets for catalyst support; ground into powders Alfa Aesar before use. 43855 5 wt% Ru / C wet support (dried at 70℃ under air before use). Alfa Aesar 44338 5 wt% Pd / C Degussa type E101 NO / W; wet support (dried at 70℃ Sigma−Aldrich under air before use). 330116 5 wt% Rh / C wet support (dried at 70℃ under air before use). Alfa Aesar 11761 5 wt% Pt / C wet support (dried at 70℃ under air before use). Alfa Aesar 46306 1 wt% Ir / C wet support (dried at 70℃ under air before use). Alfa Aesar 38330 Catalyst preparation Nitrogen-functionalized carbon (NC): NC was prepared following a previously reported “soft nitriding” method (Liu, B., et al., J. Am. Chem. Soc.2016, 138 (14), 4718-4721). One gram of activated carbon and 1.5 g of urea were mixed and ground in a crucible. The mixture was annealed at 150 °C for 2 hours and then 300 °C for another 2 hours. The resulting powder was first washed with ethanol and Milli-Q water to remove the unreacted urea and then dried in a 75 ℃ oven. Supported Ru catalysts: The RuIIICl3 precursor was impregnated into the support material (C, NC, or Al2O3) by incipient wetness. The resulting wet paste was first dried in an oven at 75 ℃ for 12 hours and then reduced with Ar / H2(v / v = 95 / 5) at 450 ℃ for 6 h to yield Ru0 / C, Ru0 / NC, and Ru0 / Al2O3 (Lin, B., et al., ChemCatChem 2013, 5 (7), 1941-1947; and Lin, B., et al., ACS Catal.2019, 9 (3), 1635-1644). Ligand-modified Ru catalysts: A 50 mL flask was sequentially loaded with 100 mg of Ru catalysts, 50 mL of DI water, and desired amount of nitrogen ligand. Since the protonation of nitrogen ligands increased the solution pH, H2SO4 was used to adjust pH to 7 (or other designated pH values). After being sealed with a rubber stopper, the flask was sonicated for 1 minute to disperse the catalyst particles. The suspension was stirred at 360 rpm and sparged with H2 (1 atm) at room temperature (around 20℃) for 1 hour to afford the ligand-modified Ru catalyst suspension (e.g., [cis-DACH]Ru / NC) and allow the reduction of surface oxide on Ru nanoparticles. The H2 gas supply was achieved by two 16-gauge stainless steel needles (introduced through the stopper), which served as gas inlet and outlet, respectively. Perchlorate reduction and aqueous sample analysis The reaction was initiated by adding the NaClO4 stock solution into the catalyst suspension at 20 °C. Aliquots were collected through the H2 outlet needle with a 3-mL plastic syringe and immediately filtered through a 0.22-μm cellulose acetate membrane. ClO4–concentration was measured by ion chromatography (Dionex ICS–5000) equipped with a conductivity detector and an IonPac AS16 column. The column was used at 30 °C, with 65 mM KOH eluent at 1 mL min−1. The concentration of cis-DACH in aqueous samples was determined by total nitrogen analysis of the solution using a Shimadzu TOC-LCSH system equipped with a total nitrogen measurement unit (TNM-L). The control experiment confirmed that nitrogen leaching from the NC material is negligible. TON and TOF calculation The calculation assumed that the Ru sites reacted with all ClOx–(x = 4, 3, 2, and 1) substrates. The turnover number (TON) was calculated as TON = 4 × [ClO4–]0× Mw / (Lcat.× Cmetal× Dmetal) where [ClO4–]0 is the initial concentration of perchlorate (mol L−1), Mw is the atomic mass of Ru (g mol−1), Lcat.is the loading of catalyst powder (g L−1), Cmetalis the metal content, and Dmetalis the metal dispersion. The initial turnover frequency (TOF0, in h−1) was calculated as TOF0 = 4 × ([ClO4–]0 – [ClO4–]t) × Mw / (Lcat. × Cmetal × Dmetal × t) where [ClO4–]tis the concentration at the first sampling point of reaction time t (h). Catalyst collection and characterization The freshly prepared catalyst suspension was immediately transferred into an anaerobic glove bag (98% N2, 2% H2; Coy Laboratories) to avoid artifacts from air oxidation and then filtered under vacuum. The filter paper coated by the catalyst was transferred into a 20 ml scintillation vial and dried in a 110 °C sand bath for 8 hours. The dried catalyst powder was stored in the glove bag before further characterization. X-ray photoelectron spectroscopy (XPS): The dried catalyst powder was loaded onto a copper conductive tape inside the glove bag and transported with an anaerobic tube to the XPS instrument (AXIS Supra Kratos Analytical, equipped with monochromatized Al Kα source) at the UC Irvine Materials Research Institute. The sp2C 1s peak (284.5 eV) of the carbon support was used as the reference for binding energy calibration. CasaXPS software (version 2.3.19) was used for the fit of XPS spectra in the resolution of 0.1 eV. Diffuse reflectance FT-IR spectroscopy (DRIFTS): In situ DRIFTS experiments of CO adsorption-desorption on Ru / Al2O3and [cis-DACH]Ru / Al2O3were performed on a Nicolet iS50 FTIR spectrometer with a liquid nitrogen-cooling MCT detector. The backgrounds and spectra taken had a resolution of 4 Each spectrum was the average of 100 scans, with the background subtracted automatically. Before the measurement, 30 mg of the powder sample was loaded into a high-temperature IR cell (PIKE DiffusIR cell with ZnSe windows) and pretreated in an Ar flow of 30 mL min–1at 200 °C for 1 hour. Subsequently, the sample was controlled at 25 °C and purged by Ar (50 mL min–1) for 30 minutes before collecting the background spectrum. For CO adsorption at 25 °C, the feed stream of 1% CO balanced with Ar was introduced into the cell with a flow rate of 50 mL min–1for 30 minutes to achieve the saturated CO adsorption. The CO flow was then discontinued, while Ar (50 mL min–1) was kept flowing for 15 minutes to remove the gaseous and weakly adsorbed CO. Scanning transmission electron microscope (STEM): Before being characterized by STEM (FEI Titan Themis 300 equipped with an energy dispersive X-ray spectrometer (EDX) system), the catalyst powder was resuspended and sonicated in distilled water to further reduce the size. The STEM images were acquired with a high-angle annular dark-field (HAADF) detector. Nano Measurer software package was used for the statistical analysis of average particle size in the STEM images. Supplemental analyses: Elemental analyses of Ru and N were conducted by the Microanalysis Laboratory, University of Illinois at Urbana-Champaign. After microwave digestion, the Ru content in the catalyst powder was measured by inductively coupled plasma–optical emission spectrometry (ICP–OES, PerkinElmer Optima 8300). The N content was determined by an elemental analyzer (Exeter Analytical, Inc., Model CE440). The specific surface area of Ru particles in the catalysts were measured by CO pulse titration experiments on a Quantachrome Autosorb-iQ physisorption-chemisorption instrument with the surface Ru:CO stoichiometry of 12:7.4X-ray diffraction (XRD) characterization was performed with a Panalytical Empyrean instrument (45 kV / 40 mA) equipped with a Cu Kα source. Various nitrogen ligands were added to a water suspension of a commercial Ru / C and substantially enhanced ClO4–reduction was achieved at 20 °C. The saturated cis-1,2-diaminocyclohexane (cis-DACH) provided the highest activity enhancement (Table 1 and Figures 1–3). Compared to the original Ru / C, the initial turnover frequency (TOF0) was accelerated by 81-fold. The activity enhancement by cis-DACH was over twice as high as its trans- isomer (Table 1, entry 1 versus 2). The six-member ring backbone also provided a higher activity than other cis-1,2-diamino analogs with five- and seven-member rings (Table 1, entry 1 versus 7 and 8). The cis-DACH was also superior to the unsaturated, aromatic, and linear aliphatic diamine ligands (Table 1, entries 5, 6, and 9–11), and to all pyridine-containing ligands (Table 1, entries 12–22). In general, ligands with steric hindrance resulted in lower activity (Table 1, entry 2 versus 3 and 4; entry 9 versus 10 and 11; entry 13 versus 16 and 17), indicating the interaction between Ru and N atoms. The bipyridine (bpy) and phenanthroline (phen) ligand families also showed higher reaction rates from increased electron-donating character (Table 1, entries 12–15 and 18–20). Therefore, the nitrogen ligands appeared to enhance the catalytic performance by altering the electronic properties on the Ru0nanoparticle surface (characterized in the later section). Table 1. Perchlorate Reduction Activity of Ru / C Enhanced by Various Ligandsaentry ligand TOF0 (h-1)bentry ligand TOF0 (h-1)b aReaction conditions: 2.0 g L–1of 5 wt% Ru / C (Alfa Aesar #44338) with 1 mM ligand added in the water suspension, 1 mM ClO4–, pH 7.0, 1 atm of H2, 20 °C. bThe calculation assumed that each surface Ru atom reacted with all ClOx–(x = 4, 3, 2, and 1) substrates. Details are described in SI. Having confirmed the positive effect of molecular ligands added from the aqueous solution, the effect of nitrogen functional groups from the support material was examined. Amine- and amide-functionalized carbon supports (NC) were prepared following a “soft nitriding” method using urea at 300 °C (Liu, B., et al., J. Am. Chem. Soc.2016, 138 (14), 4718-4721). Then Ru / C and Ru / NC were prepared by incipient wetness impregnation of RuCl3 and heated H2reduction. Elemental analyses found nitrogen contents in Ru / C and Ru / NC as 0.75 and 3.32%, respectively. Compared with Ru / C, the nitrogen groups in Ru / NC increased the ClO4–reduction activity by 460% (Figure 4A). Adding cis-DACH to the two catalysts further increased the total nitrogen contents in [cis-DACH]Ru / C and [cis-DACH]Ru / NC to 1.70 and 3.93%, respectively. In the presence of cis-DACH, the nitrogen groups in Ru / NC still increased the ClO4–reduction activity by 37% (Figure 4A). At pH 7, the dually enhanced [cis-DACH]Ru / NC catalyst outperformed all reported abiotic catalytic systems in ClO4–reduction (Table S1). Table S1. Detailed Performance Data for ClO4−Reduction by Various Catalysts. 2 [cis-DACH]Ru / C 2 7.0 20 ℃ 1 mM 53.9 40.0 11.3 this work 3 Ru / CeO2 1 7.0 25 ℃ 1 mM N.A.bN.A.b254 Ru / CeO2 1 7.0 80 ℃ 1 mM 30.6 15.3 2355 Re(O)(hoz)2−Pd / C 0.5 6.0 25 ℃ 1 mM N.A.cN.A.b0.36catalysts used at acidic pH 6 [cis-DACH]Ru / NC 2 3.0 20 ℃ 1 mM 43.5 17.2 5.4 this work 7 [cis-DACH]Ru / C 2 3.0 20 ℃ 1 mM 53.9 19.9 5.2 this workaNormalized to the mass of metal for cross-comparison of catalysts with variable metal contents; bThe ClO4−concentration−time profiles were unavailable; cThe reaction was very slow and did not complete; dNormalized to the mass of Pd because Mo is a relatively abundant and inexpensive metal. The reaction rate at 20 °C was similar to the previously reported Ru / CeO2 used at 80 ℃ (Yoshida, D., et al., Appl. Catal. A: Gen.2023, 649, 118982). A good mass balance was observed between ClO4–and Cl−(Figure 4B), indicating the complete reduction of ClO4–to Cl−without accumulating ClOx–intermediates. The [cis-DACH]Ru / NC and [cis-DACH]Ru / C showed similar responses to solution pH (Figure 4C and Figure 5), with the highest activity at pH 5−7. Because the original Ru / C preferred acidic pH (Figure 6), the lowered activity at acidic pH was attributed to the protonation of −NH2, which impeded the coordination with Ru0nanoparticles. The optimized cis-DACH dose was 2 mM (Figure 7), with 59 % immobilized on Ru / NC (41 % in aqueous solution, determined by total nitrogen analysis). Lowering the cis-DACH dose reduced the dissolved portion (Table S2) at the cost of catalytic activity (Figure 7). Table S2. Percentage of cis-DACH Ligand Immobilized on Ru / NC and Ru / C.acis-DACH Immobilized on Immobilized on 0.5 75.4 77.9 1 73.9 69.5 2 59.4 55.1 aConcentration of cis-DACH in aqueous samples was measured based on the total nitrogen in the solution using a Shimadzu TOC-LCSH system equipped with a total nitrogen measurement unit (TNM-L). The immobilized percentage = After filtration, the redispersion of the collected [cis-DACH]Ru / NC solid in water still released 10% of the initial cis-DACH into the aqueous phase. Thus, cis-DACH was distributed in an equilibrium between the catalyst surface and water. However, the dissolved cis-DACH maintained the same concentration throughout ClO4–reduction (Figure 8). The robustness of [cis-DACH]Ru / NC catalyst was further demonstrated under harsh conditions. The reduction of highly concentrated 100 mM ClO4–achieved >99.9% completion within 50 h (Figure 9, turnover number TON=4,350). In the presence of concentrated salts such as 0.1 M NaCl, 2 M NaCl, and 1 M Na2SO4, the activity decreased by 54, 93, and 75%, respectively (Figure 10). After ten successive spikes of 10 mM ClO4–(one spike per day) into the [cis-DACH]Ru / NC suspension, the activity loss observed at day 10 was merely due to the accumulated Cl−from ClO4–reduction (Figure 11). Furthermore, cis-DACH did not have the concern about ligand hydrogenation, which was a major challenge to the previously reported Mo−Pd / C catalyst. The latter used 4,4’-diamino-2,2’-bipyridine as the best ligand and deactivated by 60% under continuous exposure to 1 atm H2 for a week (Ren, C., et al., ACS ES&T Eng.2022, 2 (2), 181-188). Moreover, the catalyst prepared from simple mixing of cis-DACH and Ru nanoparticles did not deactivate upon exposure to air. Upon resuming the H2supply, the ClO4–reduction activity was fully restored (Figure 12). The H2 atmosphere preserved Ru as metallic nanoparticles, resulting in no detected Ru in the aqueous phase (Gao, J., et al., Environ. Sci. Technol.2023).30Hence, the catalyst showed a high promise of treating concentrated ClO4–in brines from ion-exchange resin regeneration (Gu, B., et al., Environ. Sci. Technol.2007, 41 (17), 6277-6282), particularly for the easy preparation, mild reaction condition, robustness, longevity, and easy handling. The adaptability of the [cis-DACH]Ru / NC design to other metals and systems was further evaluated. However, cis-DACH resulted in very limited ClO4–reduction for Rh / C and Ir / C and no activity for Pd / C and Pt / C (Figure 13), indicating the critical role of the Ru element. Ru0rather than RuIIor RuIIIwas also confirmed as the active site for ClO4–reduction. First, mixing RuCl3 and cis-DACH in water under 1 atm H2 provided no activity. The direct reduction of aqueous RuIIIby H2under ambient temperature and pressure was sluggish (Gao, J., et al., Environ. Sci. Technol. 2023). Instead, NaBH4 effectively reduced RuIIIinto Ru0colloids (Yu, W., et al., J. Colloid Interface Sci.1998, 208 (2), 439-444) and the presence of cis-DACH enabled ClO4–reduction (Figure 4D). Second, adding pre-synthesized [RuII(phen)3]2+, [RuII(bpy)3]2+, RuII(bpy)2Cl2, and [RuII(NH3)6]2+complexes (Table S3) into Pd / C under H2did not reduce ClO4–. Table S3. Commercial RuIIComplexes Tested for ClO4–Reduction with Pd / C and H2.a# Tris(2,2’-bipyridyl)dichlororuthenium(II) 50525-27-4 [Ru(bpy) ]Cl ·6H O 99.95% hexahydrate 3 2 2 aReaction conditions: 2 g L–1of 5 wt % Pd / C catalyst with 1 mM RuIIcomplexes (equivalent to ~5 wt % as Ru if immobilized), 1 mM ClO4–, pH 7, 1 atm of H2, 20 °C. None of these RuIIcomplexes showed activity in ClO4–reduction. In contrast, mixing RuCl3, free phen or bpy ligands, and Pd / C under H2 enabled ClO4–reduction (Figure 4D). The discrepancy between the two strategies can be attributed to the rapid formation of Ru0nanoparticles from RuCl3, which can be substantially accelerated by Pd / C (Gao, J., et al., Environ. Sci. Technol.2023). The results suggest the active site as ligand-coordinated Ru0 nanoparticles rather than single-atom Ru0(ligand)x complexes. However, the performance of [phen]Ru−Pd / C and [bpy]Ru−Pd / C were very similar to the initially screened [phen]Ru / C and [bpy]Ru / C (Figures 1A and 1C). Hence, the incorporation of Pd, which only accelerated the formation of Ru0but not the reduction of ClO4–was not further pursued. After finalizing the catalyst preparation strategy and procedure, an investigation of how cis-DACH and the nitrogen groups on NC interacted with Ru and enhanced ClO4–reduction was made. First, the nitrogen ligands did not change the morphology of Ru nanoparticles. Scanning transmission electron microscopy (STEM) characterization observed good dispersion of Ru particles and very similar size distribution (1.6 ± 0.3 nm for Ru / C and 1.5 ± 0.3 nm for Ru / NC). The small particle size led to no sharp Ru0crystal peaks under X-ray diffraction (XRD) characterization (Figure 14). CO chemisorption observed very similar Ru dispersion in Ru / C (10.2%) and Ru / NC (12.6%). Therefore, nitrogen groups on the NC support did not lead to a significantly better dispersion of Ru. Because cis-DACH was added to the Ru catalysts at room temperature, it did not alter the metal dispersion as expected. Kinetic analysis with Langmuir-Hinshelwood (LH) model (Eq.2) differentiated the contributions of cis-DACH and the nitrogen groups on NC: where r is the apparent rate of ClO4−reduction in the bulk aqueous phase (mmol gcat−1h−1), ^^1is the equilibrium constant for ClO4−adsorption (L mmol−1), ^^3is the rate constant for the reduction of surface-adsorbed ClO4−(mmol gcat−1 h−1), and [ ] is the ClO4−concentration in the bulk aqueous phase (mmol L−1). The LH kinetic model assumes that the surface reaction is the rate-limiting step of the overall reaction. This implies that the transfer of ClO4−from the bulk solution to the liquid-solid interface occurs rapidly compared to the chemical reactions at the surface. It is thus necessary to evaluate internal and external mass transfer to confirm this assumption. Internal Mass Transfer Weisz-Prater (WP) criterion were used to evaluate the impact of pore diffusion resistance on measured reaction rates (Shuai, D., et al., Environ. Sci. Technol.2012, 46 (5), 2847-2855; and Weisz, P.; Prater, C., J Adv. Catal 1954, 6 (143), 60390-9). In general, the WP criterion and WP parameter (^^^^^^) are described as follows: internal mass transfer limitation is negligible; If , the internal mass transfer limitation is significant. where ^^^^^^^^ is the observed pseudo-first-order rate constant of heterogeneous reaction (^^^^^^−1), ^^ is the tortuosity factor of the catalyst particle, ^^ is the radius of the catalyst particle (^^), ^^ is the diffusion coefficient of reactant in bulk solution (^^2^^−1), and ^^ is the porosity of the catalyst particle. To evaluate ^^^^^^ conservatively, the highest reaction rate (i.e., 3.175 h−1) measured in this study was used. The typical range for parameters ^^ and ^^ are 2−10 and 0.2−0.7, respectively. For the conservative calculation, 10 and 0.2 were used as the estimated values for ^^ and ^^, respectively (Davie, M. G., et al., Environ. Sci. Technol.2006, 40 (23), 7329-7335; and Satterfield, C. N. Mass Transport in Heterogeneous Catalysis; MIT Press: Cambridge, MA, 1970). The catalyst particle diameter is 25 μm (provided by the vendor of carbon support). The diffusion coefficient of ClO4−in bulk solution is 1.79×10−9^^2^^−1.14Hence, ^^^^^^ was calculated as: Therefore, the internal mass transfer limitation is negligible. External Mass Transfer To estimate the mass transfer coefficient (^^^^^^ / ^^) of ClO4−between the catalyst surface and the aqueous solution, the Sherwood number (^^ℎ) was first calculated (Sänger, P.; Deckwer, W. D., Chem. Eng. J 1981, 22 (3), 179-186; and Sano, Y., et al., J. Chem. Eng. Japan 1974, 7 (4), 255-261). In Eq.2, ^^ is the rate of flow energy supply per unit mass of liquid (^^2^^−3), ^^^^ is the diameter of the catalyst particle (^^), ^^ is the kinematic viscosity of water (1.003 × 10−6^^2^^−1at 20℃), ^^^^ is Schmidt number, and ^^^^ is Carman’s surface factor (assume the catalyst particle is spherical, ^^^^ = 1). ^^^^ and ^^ were evaluated using the following equations: (3) (4) where ^^^^ is the power number (normally ^^^^ ≈ 5.0)17, ^^ is the length of the stir bar (^^ ≈ 3 ^^^^), ^^ is the rotating speed of the stir bar (^^ = 360 ^^^^^^^^^^ ^^^^^^−1= 6 ^^^^^^^^^^ ^^−1), and ^^ is the volume of the reactor (^^ = 50 ^^^^3). The Sherwood number was then calculated using the calculated values of ^^^^ and ^^: And ^^^^^^ / ^^ was calculated by Eq.6: (6) The geometric surface area of the catalyst per volume of solution (^^)1is calculated by using Eq.7: (7) where ^^^^^^ is the geometric surface area of one catalyst particle (^^2), ^^ is the mass of catalyst inthe reduction test (0.1 ^^), is the density of the catalyst ( ), ^^^^ is the volume of one catalystparticle (^^3), and ^^^^ is the volume of the reactor (50 ^^^^). For the mass transfer rate calculation, the geometric surface area of the catalyst per volume of the solution was multiplied by the mass transfer coefficient. (8) Based on the estimated values, the external mass transfer rate is significantly higher than the observed rate constant ^^^^^^^^ = 3.175 h−1for ClO4−reduction. As a result, the impact of external mass transfer on the reaction rates can be considered negligible. Langmuir-Hinshelwood Model The Langmuir-Hinshelwood (LH) model was used to analyze the kinetic data of Ru / C, [cis-DACH]Ru / C, and [cis-DACH]Ru / NC catalysts. The catalytic reduction of ClO4−involves multiple steps, including reversible adsorption of ClO4−onto the unoccupied active sites, reduction of ClO4−on active sites, and desorption of products. Assuming that (i) the surface reaction is the rate-limiting step, (ii) ClO4−and H2are adsorbed on the catalyst surface non-competitively, (iii) there is no activity loss of the Ru sites, and (iv) the adsorption of ClO4−on activated carbon is minimal, the surface reaction rate (^^) can be simplified to a single site model, and the global reaction rate can be defined as: ^^ = ^^2[^^^^] = ^^2^^[^^] (9) where ^^2 is the surface reaction rate constant, [^^^^] and [^^] denote the surface concentration of occupied sites (ClO4−associated with metal active sites) and total active sites (occupied plus unoccupied sites), respectively. ^^ is the surface coverage, which is defined as ^^ = [^^^^] / [^^]. Since the adsorption and desorption of ClO4−are assumed to be fast, the steady-state approximation can be applied to ^^^^: where and are the adsorption rate constant and desorption rate constant of ClO4−, respectively, and [^^] denotes the aqueous ClO4−concentration. Hence, ^^ is solved as: Since the surface reaction is assumed to be the rate-limiting step (i.e., ^^2 ≪ ^^1[^^] and ^^2 ≪ ^^−1), ^^ can be simplified to: From Eq.12 and Eq.9, ^^ can be expressed in terms of [^^]: where ^^1 = ^^1 / ^^−1 is the adsorption equilibrium constant, ^^3= ^^2[S] is affected by the total amount of the Ru active sites. Perchlorate reduction experiments were carried out at pH 7 using varying initial concentrations of ClO4−(Figure 15). The initial rates of ClO4−reduction ^^ (mmol gcat–1h–1) were fit to Eq.13. The adsorption equilibrium constant ^^1 (L mmol–1) and rate constant ^^3 (mmol gcat–1h–1) for Ru / C, [cis-DACH]Ru / C, and [cis-DACH]Ru / NC catalysts are shown below. Example 2. We further tested the performance of [cis-DACH]Ru / NC in additional practical application scenarios, including ClO4–treatment in (i) waste brines resulting from ion-exchange (IX) resin regeneration and (ii) drinking water containing ClO4–as disinfection byproduct or from source water. We prepared a synthetic waste brine with all anions found in a prior brine study (Table 2). Notably, due to the low selectivity of early IX resins for ClO4–, the waste brines produced during resin regeneration often contained significantly higher concentrations of nitrate (NO3–), sulfate, and even phosphate than ClO4–. In this scenario, the Re and Mo-based catalysts require a two-stage treatment for ClO4–reduction, as NO3–can deactivate them and needs to be removed first with another catalyst (e.g., In–Pd / Al2O3). Ru catalysts are highly effective in reducing NO3–, obviating the need for pretreatment with another catalyst. [cis-DACH]Ru / NC reduced more than 99% of the 38 mM of NO3–within 10 h (Figure 17A). Although the complex water matrix components substantially slowed the reaction rate (Figure 17A), over 99.99% of ClO4–was reduced within 84 h. We also tested the performance of [cis-DACH]Ru / NC in tap water matrix. The tap water had a pH of 8 and contained 0.4 mM NO3–, as well as various other anions (Table 2). [cis-DACH]Ru / NC reduced over 99.99% of NO3–and 99.7% of the spiked 1 mM ClO4–within 4 and 10 h, respectively (Figure 17B). These positive practical test results further affirm the potential application of [cis-DACH]Ru / NC in real wastewater treatment. Table 2. Composition of Synthetic IX Regenerant Brine and Tap Water concentration in component concentration in tap waterfsynthetic IX regenerant brineachloride 0.9 M0.92 mMperchlorate 1 mMb 1 mMgnitrate 38 mM0.4 sulfate 48 mM0.66 mMphosphate 0.22 mM0.5 μMfluoride NAc 0.025 mMalkalinity 7 g / L as CaCO3d0.17 g / L as CaCO3pH 7.4e 8eaNa+was the sole cation introduced alongside the anionic species, as K+, Ca2+, and Mg2+, while present in the brine in small quantities, had negligible effects on reaction kinetics.bThe ClO4−concentration in the real brine was at 0.02 mM (~2 mg L−1). To ensure accurate ClO4−quantitation within the concentrated salt matrix and to compare with the majority of experiments using 1 mM ClO4−as the probe, we increased the concentration to 1 mM. The catalyst can effectively reduce >99% of the 0.02 mM ClO4−.cData was not available in the prior brine study.d0.14 M sodium bicarbonate was added.eWhile the reduction of ClO4−does not consume H+, the reduction of NO3–consumes H+and raises the pH. The experiment used a 50 mL double-neck flask with rubber stoppers on both necks. One stopper held two needles for H2 inlet and outlet / sampling port, while the other accommodated a pH electrode to monitor pH changes. H2SO4 (0.1 M) was introduced via the sampling needle when the pH exceeded the initial value (i.e., 7.4 or 8).fThe tap water was sourced from Southern California, with information on the concentrations of other components available in the local water quality report.gThe ClO4−concentration in the tap water was below the detection limit of ion chromatography (0.1 µM). We raised it to 1 mM for the accuracy of quantitation and convenient comparison.

Claims

CLAIMS What Is Claimed Is:

1. A method comprising, treating an aqueous solution that comprises oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) with H2and a catalyst that comprises: a) ruthenium in the presence of a nitrogen source; or b) ruthenium on a nitrogen-functionalized support material; under conditions where at least some of the oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) is reduced.

2. The method of claim 1 that comprises treating an aqueous solution that comprises perchlorate with H2and a catalyst that comprises ruthenium in the presence of a nitrogen source under conditions where at least some of the perchlorate is reduced.

3. The method of claim 1 that comprises treating an aqueous solution that comprises perchlorate with H2 and a catalyst that comprises ruthenium on a nitrogen-functionalized support material under conditions where at least some of the perchlorate is reduced.

4. The method of claim 1 that comprises treating an aqueous solution that comprises perchlorate with H2 and a catalyst that comprises ruthenium on a nitrogen-functionalized support material in the presence of a nitrogen source under conditions where at least some of the perchlorate is reduced.

5. The method of any one of claims 1-4, wherein the aqueous solution is drinking water.

6. The method of any one of claims 1-4, wherein the aqueous solution is industrial waste.

7. The method of any one of claims 1-4, wherein the aqueous solution is hazardous waste.

8. The method of any one of claims 1-7, wherein the water sample further comprises sulfate or nitrate.

9. The method of any one of claims 1-7, wherein the water sample further comprises nitrate.

10. The method of any one of claims 1-9, wherein at least some of the perchlorate is reduced to chloride.

11. The method of any one of claims 1-9, wherein at least 90 percent of the perchlorate is reduced to chloride.

12. The method of any one of claims 1-11, wherein the catalyst comprises Ru0on a solid support.

13. The method of claim 12, wherein the support comprises porous carbon, alumina, silica, a zeolite, a clay, TiO2, CeO2, ZrO2, Mxene, a carbon nanotube, graphene, or biochar.

14. The method of claim 13, wherein the support comprises carbon.

15. The method of claim 12, wherein the support is carbon.

16. The method of any one of claims 1-15, wherein the catalyst comprises highly dispersed Ru0.

17. The method of any one of claims 1-2 and 4-16, wherein the nitrogen source comprises an organic nitrogen ligand.

18. The method of claim 17, wherein the organic nitrogen ligand comprises the group:wherein each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl.

19. The method of claim 17, wherein the organic nitrogen ligand that comprises the group:wherein: A is a monocyclic aryl, a bicyclic aryl, a monocyclic (C3-C8)cycloalkyl, or a polycyclic (C6-C12)cycloalkyl; and each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl.

20. The method of claim 17, wherein the organic nitrogen ligand that comprises the group:wherein: A is a (C3-C8)cycloalkyl; and each of Rw, Rx, Ry, and Rzis independently selected from the group consisting of H and (C1-C6)alkyl.

21. The method of claim 17, wherein the organic nitrogen ligand comprises: cis-1,2-diaminocyclopentane, cis-1,2-diaminocyclohexane, cis-1,2-diaminocycloheptane, or cis-1,2-diaminocyclooctane.

22. The method of claim 17, wherein the organic nitrogen ligand is selected from the group consisting of:.

23. The method of claim 17, wherein the organic nitrogen ligand is cis-1,2-diaminocyclohexane.

24. The method of claim 17, wherein the organic nitrogen ligand is selected from the following formulae:; where: X11 is C-R11 or N, X12 is C-R12 or N, X13 is C-R13 or N, X14 is C-R14 or N; and R11 thru R16 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano.

25. The method of claim 17, wherein the organic nitrogen ligand is selected from the following formulae:where R21thru R25are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano.

26. The method of claim 25, where R21thru R25are each independently H, hydroxy, chloro, C1-3alkyl, C1-3alkoxy, or amino.

27. The method of claim 17, wherein the organic nitrogen ligand is selected from the following formulae:; where: A is an optionally substituted heteroaryl selected from the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, 2-thiazolyl, and 2-imidazolyl, where X31 is either C, O, S or N depending on the heteroaryl, where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkoxy, halogen, amino, or cyano; Y31 can be either C, O, S or N, where the hydrogen positions in the heteroaryl that contains Y31 can be independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R31 thru R33 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; n is 0 or 1; and R34and R35are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, halogen, amino, cyano, or together with the carbon which they are linked, form a carbon alkyl or alkenyl of 1 to 2 carbon atoms where hydrogen in the link is independently optionally substituted with H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, halogen, amino, cyano, or O or S for divalent positions, or, when 2 carbon atoms, both carbon positions are optionally substituted with an additional linked alkyl or alkenyl to form an optionally substituted 4-6 carbon heteroaryl from 1 to 2 heteroatoms, where the heteroatom is N, and where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano.

28. The method of claim 17, wherein the organic nitrogen ligand is:where n is 0 or 1; R41thru R48are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano.

29. The method of claim 28, where R41thru R48is independently H, hydroxy, chloro, C1-3alkyl, C1-3 alkoxy, or amino.

30. The method of claim 17, wherein the organic nitrogen ligand is a compound selected from the following formulae:, , where: B and C are independently selected from optionally substituted heteroaryl selected from the groupconsisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, and 2-imidazolyl, where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R51 thru R53 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; R61thru R64are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, cyano, or an optionally substituted aryl, where the aryl is selected from the group consisting of the group consisting of 2-pyridinyl, 2-pyrimidinyl, 2-benzimidazolyl, 4,5-dihydrooxazolyl, 2-oxazolyl, and 2-imidazolyl, where the hydrogen positions in the heteroaryl are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano; and R71thru R76are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano.

31. The method of claim 17, wherein the organic nitrogen ligand is:where R81 thru R96 are independently H, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, halogen, amino, or cyano.

32. The method of claim 31, where R81 thru R96 are each independently H, hydroxy, chloro, C1-3alkyl, C1-3alkoxy, or amino.

33. The method of any one of claims 17-32, where the molar ratio of Ru0to organic nitrogen ligand is from 10:1 to 1:

10.

34. The method of any one of claims 17-32, where the molar ratio of Ru0to organic nitrogen ligand is from 1:1 to 1:

4.

35. The method any one of claims 1-34, wherein the aqueous solution has a pH of at least about 5.

36. The method any one of claims 1-34, wherein the aqueous solution has a pH of at least about 6.

37. The method any one of claims 1-34, wherein the aqueous solution has a pH of at least about 7.

38. A solution that comprises water, oxyanion(s) (e.g., perchlorate, chlorate, or nitrate), a catalyst that comprises ruthenium, and a nitrogen source.

39. The solution of claim 38, that further comprises sulfate or nitrate.

40. The solution of claim 38, that further comprises nitrate.

41. The solution of claim 38, wherein the catalyst comprises Ru0on a solid support.

42. The solution of claim 41, wherein the solid support comprises porous carbon, alumina, silica, a zeolite, a clay, TiO2, CeO2, ZrO2, Mxene, a carbon nanotube, graphene, or biochar.

43. The solution of claim 41, wherein the solid support comprises a nitrogen-functionalized support material.

44. The solution of claim 41, wherein the solid support comprises carbon.

45. The solution of claim 41, wherein the solid support is carbon.

46. The solution of claim 41, wherein the solid support is nitrogen-functionalized.

47. The solution of any one of claims 38-46, wherein the catalyst comprises highly dispersed Ru0.

48. The solution of any one of claims 38-46, wherein the nitrogen source comprises an organic nitrogen ligand.

49. The solution of claim 48, wherein the organic nitrogen ligand is a compound as described in any one of claims 18-32.

50. The solution of claim 49, where the molar ratio of Ru0to organic nitrogen ligand is from 10:1 to 1:

10.

51. The solution of claim 49, where the molar ratio of Ru0to organic nitrogen ligand is from 1:1 to 1:

4.

52. The solution of any one of claims 38-51, wherein the aqueous solution has a pH of at least about 5.

53. The solution of any one of claims 38-51, wherein the aqueous solution has a pH of at least about 6.

54. The solution of any one of claims 38-51, wherein the aqueous solution has a pH of at least about 7.

55. A heterogenous catalytic reactor for reducing oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) concentration of an aqueous sample, the reactor comprising a container defining a reaction plenum, with at least one orifice defining an inlet and an outlet, where the aqueous solution to be processed enters through the inlet and exits through the outlet once the oxyanion(s) (e.g., perchlorate, chlorate, or nitrate) concentration has dropped to a desired level, where the reaction plenum encloses a catalyst that comprises ruthenium and a nitrogen source.

56. A composition that comprises ruthenium on a nitrogen-functionalized support material.

57. The composition of claim 56, wherein the support material comprises carbon.

58. The composition of claim 56, wherein the solid support is carbon.

59. The composition of any one of claims 56-58, wherein the catalyst comprises highly dispersed Ru0.

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