Supplementary Material

Nitrate reduction on surface of Pd/Sn catalysts

supported by coal fly ash-derived zeolites

Jaehyeong Parka, Yuhoon Hwangb, and Sungjun Baea,*

aDepartment of Civil and Environmental Engineering, Konkuk University, 120 Neungdong-

ro, Gwangjin-gu, Seoul 05029, Republic of Korea

bDepartment of Environmental Engineering, Seoul National University of Science and

Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Republic of Korea

*Corresponding author: bsj1003@konkuk.ac.kr

phone: +82-42-450-3904

Journal of Hazardous Materials

Chemicals

Supplementary Material

Acetic acid (99.7 %, Dae Jung Chemical, Korea) and NaOH (97.0 %, Dae Jung Chemical,

Korea) were used for the pretreatment of NMFA surface and the alkaline fusion of NMFA,

respectively. Precursor solutions of Pd and Sn were prepared with PdCl2 (99%, Sigma-

Aldrich, USA) and SnCl4 (99%, Sigma-Aldrich, USA). To prepare Pd/Sn catalysts supported

by other support materials, silicon dioxide (~99%, 0.5-10 μm, Sigma-Aldrich, USA) and

aluminum oxide (99.5%, ≤10 μm, Sigma-Aldrich, USA) were used. Sodium borohydride

(98%, Sigma-Aldrich, USA) was used to activate Pd-Sn bimetallic catalysts. Potassium

nitrate (99.0%, Duksan Pure Chemical Co., Korea) and ammonium chloride (98.5%, Duksan

Pure Chemical Co., Korea) were used for stock and standard solutions for ion

chromatography (IC). Sodium bicarbonate (99.7%, Sigma-Aldrich Inc., USA), sodium

carbonate (99.95%, Sigma-Aldrich Inc., USA), sulfuric acid (60%, Dae Jung Chemical,

Korea), and methanesurfonic acid (Sigma-Aldrich Inc., USA) were used to prepare eluent for

IC operation.

Preparation of NMFA

An exact amount of CFA (50.0 g) was washed with 500 mL of DIW under mechanically

stirring at 500 rpm for 1 h. A neodymium magnet was put in the CFA suspension under

vigorous stirring (500 rpm), and black particles attached on the magnet were removed. This

procedure was repeated until the iron-rich FA particles were completely removed from the

suspension. The remaining particles (i.e., NMFA) were washed with DIW three times by

centrifugation (7000 rpm, 3 min) and oven-dried at 105 °C for 24 h. Then, NMFA was

further treated with acetic acid to remove impurities on the surface. An exact amount of

NMFA (20.0 g) was transferred into a beaker containing 200.0 mL of 5 M acetic acid

solution, and then the mixture was magnetically stirred at 700 rpm for 2 h. Then, the mixture

was centrifuged for the solid-liquid separation. The supernatant was removed, and the

Supplementary Material

remaining NMFA particles were washed with DIW three times by centrifugation (7000 rpm,

3 min) and oven-dried at 105 °C for 24 h.

Characterization of CFA-derived zeolites and catalysts

The mineral phases of raw CFA and all FA-derived zeolites were identified by XRD analysis

(Bruker DE/D8 Advance, Germany). The prepared samples were scanned from 0° to 90° 2θ

with a scan speed of 2° min-1. Specific surface areas of the samples (Zeolite-X&A9, Zeolite-

X&A&HS12, Zeolite-X&HS15, Zeolite-X&HS18, and Pd-Sn/Zeolite-X&HS15) were

measured by nitrogen adsorption and desorption at -196 ◦C with BET surface analyzer

(3Flex, Micromeritics, USA) to investigate the effect of crystallization time on the surface

area of zeolites. The morphological characteristic of zeolites and dispersion of Pd-Sn/Zeolite-

X&HS15 was investigated using HR-FESEM (SU8010, Hitachi High Technologies

Corporations) equipped with an energy-dispersive X-ray spectroscopy (EDS). The oxidation

states of Pd and Sn on the zeolite surface was investigated by the XPS analysis using Sigma

Probe system (Thermo Scientific, USA) with Al K X-ray (1486.7 eV) radiation with a

source power of 75 W. The surface charging effects were corrected using the C 1s peak at

285 eV as a reference. The narrow-scan spectra obtained in the ranges 350–330 eV, and 502–

480 eV were used to identify oxidation states of Pd and Sn species on the Pd-Sn/Zeolite-

X&HS15 surface, respectively.

For surface analysis of Pd-Sn/Zeolite-X&HS15, the catalyst after activation with NaBH4

was transferred to an anaerobic chamber (Coylab) and washed with deaerated deionized

water (DDIW), DDIW + deaerated ethanol (v:v=1:1), and deaerated ethanol sequentially. We

also analyzed Pd-Sn/Zeolite-X&HS15 after the NO3− reduction (90 min-reaction) to

investigate the stability of catalyst in this study. After finishing the reaction, the suspension

was purged with Ar and then the catalyst was collected through vacuum filtering using a

Supplementary Material

membrane filter (0.2 μm, Advantech, Japan) in anaerobic chamber to minimize the surface

oxidation by O2 in air. The collected catalyst was washed with DDIW, DDIW + deaerated

ethanol (v:v=1:1), and deaerated ethanol sequentially.

Analytical methods

To measure the concentrations of NO3−, nitrite (NO2

−), and ammonium (NH4+), 3 mL of

sample was taken from the reactor using a 5 mL syringe (Korea Vaccine Corp., Korea) at

each sampling time. The sample was immediately filtered using 2 μm PVDF syringe filter

(Whatman) and the concentration of NO3− and NO2

− in the filtrate was determined using ion

chromatography (IC) (Metrohm, 883 Basic IC plus) equipped with a compact autosampler

(Metrohm, 863 Compact IC) and anion column (Shodex IC Anion Sep No.82504A). Mixture

of Na2CO3 (3.5 mM) and NaHCO3 (3.5 mM) was prepared for IC eluent. The concentration

of NH4+ was measured using IC (DIONEX, ICS-2000) equipped with an autosampler

(DIONEX, AS40 automated sampler) and cation column (DIONEX, No.046073).

Table S1. Nitrate removal, kinetics and N2 selectivities of bimetallic catalysts for nitrate reduction

Catalyst NO3− removal (%)

N2 selectivity (%)

K (min-1) K’ (min−1

gcat−1)

K’’ (L min-1

gPd−1)

Pd/Sn/zeolite-X&A9

99.23± 0.23 87.34±0.07 0.032±0.001 0.130±0.002 1.728±0.028

Pd/Sn/zeolite- 100 87.29±0.00 0.041±0.001 0.164±0.005 2.181±0.069

Supplementary Material

X&A&HS12Pd/Sn/zeolite-

X&HS15100 88.06±0.19 0.055±0.005 0.219±0.021 2.922±0.276

Pd/Sn/zeolite-X&HS18

100 86.88±0.17 0.050±0.003 0.201±0.013 2.673±0.169

Table S2. Surface area, pore volume, and pore size of each synthesized zeolite samples. Synthesized zeolites BET surface area

(m2 g-1)Pore volumea (cm3 g-1)

Zeolite-X&A9 62.95 0.089

Zeolite-X&A&HS12 97.00 0.101

Zeolite-X&HS15 94.82 0.112

Zeolite-X&HS18 70.15 0.091

aBJH Adsorption cumulative volume of pores between 1.000 Å and 3000.000 Å diameter.

Supplementary Material

Figure S1. XRD patterns of of (a) CFA, Zeolite-X&A9, -X&A&HS12, -X&HS15, and -

X&HS18. XRD peaks of (b-d) hydroxy sodalite (2θ = 14.0°, 24.4°, and 34.8°) and (e-g) Na-

X (2θ = 15.4, 23.3 and 26.7°).

Supplementary Material

Figure S2. HR-FESEM images of Zeolite-X&A9 (a, a1), -X&A&HS12 (b, b1), -X&HS15 (c,

c1), and -X&HS18 (d, d1).

Supplementary Material

Figure S3. EDS analysis of Zeolite-X&A9 (a), -X&A&HS12 (b), -X&HS15 (c), and -

X&HS18 (d); EDS electron mapping of O (a1, b1, c1, d1), Al (a2, b2, c2, d2), and Si (a3, b3,

c3, d3).

Supplementary Material

Figure S4. The concentrations of NO3−, NO2

− and NH4+ as a function of reaction time during

the catalytic reduction of NO3− on Pd-Sn/Zeolite-X&HS15 catalysts (1.25 g/L, Pd=1.5 wt.%,

Sn=1.5 wt%) with only H2 , only CO2, and both H2 and CO2; H2 flow rate = 30 cc/min, CO2

flow rate = 40 cc/min. Reaction time was 90 min.