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. 2020 Dec 30;26(1):141.
doi: 10.3390/molecules26010141.

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support

Ekaterina S Lokteva  1 , Vera V Shishova  1 , Nikolay N Tolkachev  2 , Andrey N Kharlanov  1 , Konstantin I Maslakov  1 , Alexey O Kamaev  1 , Igor Yu Kaplin  1 , Irina N Savina  3 , Elena V Golubina  1
Affiliations

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support

Ekaterina S Lokteva et al. Molecules. .

Abstract

A mesoporous support based on silica and zirconia (ZS) was used to prepare monometallic 1 wt% Pd/ZS, 10 wt% Fe/ZS, and bimetallic FePd/ZS catalysts. The catalysts were characterized by TPR-H2, XRD, SEM-EDS, TEM, AAS, and DRIFT spectroscopy of adsorbed CO after H2 reduction in situ and tested in hydrodechlorination of environmental pollutant 4-chlorophelol in aqueous solution at 30 °C. The bimetallic catalyst demonstrated an excellent activity, selectivity to phenol and stability in 10 consecutive runs. FePd/ZS has exceptional reducibility due to the high dispersion of palladium and strong interaction between FeOx and palladium, confirmed by TPR-H2, DRIFT spectroscopy, XRD, and TEM. Its reduction occurs during short-time treatment with hydrogen in an aqueous solution at RT. The Pd/ZS was more resistant to reduction but can be activated by aqueous phenol solution and H2. The study by DRIFT spectroscopy of CO adsorbed on Pd/ZS reduced in harsh (H2, 330 °C), medium (H2, 200 °C) and mild conditions (H2 + aqueous solution of phenol) helped to identify the reasons of the reducing action of phenol solution. It was found that phenol provided fast transformation of Pd+ to Pd0. Pd/ZS also can serve as an active and stable catalyst for 4-PhCl transformation to phenol after proper reduction.

Keywords: 4-chlorophenol; bimetallic catalyst; hydrodechlorination; iron; mild reduction; palladium; phenol; silica; zirconium oxide.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Nitrogen physisorption isotherms (A) and pore size distributions (B) for unreduced catalysts.
Figure 2
Figure 2
SEM images (A,B) and EDX elemental maps (C–F) for PdFe/ZS after reduction with H2 at 320 °C.
Figure 3
Figure 3
XRD profiles of ZS support and catalysts reduced in H2 flow for 2 h at 320 °C (Pd/ZS and FePd/ZS) or 520 °C (Fe/ZS).
Figure 4
Figure 4
TPR-H2 profiles of the ZS support and unreduced catalysts.
Figure 5
Figure 5
Difference DRIFT spectra of CO adsorbed at room temperature on Pd/ZS(550) before (A) and after H2 treatment at 330 °C (B). CO pressure: 5 Torr—curve 1, 20 Torr—curve 2, 50 Torr—curve 3. F(R)—Kubelka–Munk function (Kubelka–Munk units).
Figure 6
Figure 6
Difference DRIFT spectra of CO adsorbed at room temperature on Fe/ZS(550) before (A) and after H2 treatment (B). CO pressure: 5 Torr—curve 1; 20 Torr—curve 2; 50 Torr—curve 3. F(R)—Kubelka–Munk function (Kubelka–Munk units).
Figure 7
Figure 7
Difference DRIFT spectra of CO adsorbed at room temperature on the FePd/ZS(550) before (A) and after H2 treatment (B). CO pressure: 5 Torr—curve 1; 20 Torr—curve 2; 50 Torr—curve 3. F(R)—Kubelka–Munk function (Kubelka–Munk Units).
Figure 8
Figure 8
4-PhCl content in the reaction mixture vs. reaction time over the catalyst reduced with NaBH4 +H2 (A); conversion of 4-PhCl after 10 min of the reaction (X10) in the first and second runs (B); 4-PhCl conversion after 8 min (X8) in 10 consecutive cycles over FePd/ZS reduced with H2 in water at 30 °C (C). Reaction conditions: T = 30◦C, mcat = 0.1 g, V4-PhCl = 0.015 L, C0 4-PhCl = 75 mg/L (0.8 mmol/L), pH = 7, VH2 = 0.6 L/h.
Figure 9
Figure 9
Difference IR spectra of CO adsorbed at RT on the Pd/ZS before (A), and after treatment with H2 + water solution of phenol (B); spectra of Pd/ZS after mild reduction with H2 at 200 °C (C). CO pressure: 5 Torr—curve 1; 20 Torr—curve 2; 50 Torr—curve 3. F(R)—Kubelka–Munk function (Kubelka–Munk units).
Scheme 1
Scheme 1
A proposed structure of the catalysts and their interaction with H2 and phenol.
See this image and copyright information in PMC

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