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This work is focused on the development of Catalytic Membrane Reactors (CMRs) comprising precious metals as active phases for a comparative assessment in continuous-flow catalytic hydrodechlorination (HDC). HDC has proved its remarkable potential for application as polishing step in drinking water treatment plants, but studies operating in continuous mode are scarce. Preliminary experiments were conducted in batch operation using Pd/Al 2 O 3 , Rh/Al 2 O 3 and Pt/Al 2 O 3 powder catalysts to evaluate the influence of the active phase on the removal of prochloraz (PCZ) (100 μg L−1), a pesticide listed on the EU Watch List (2022 /1307), by HDC. PCZ removal was successfully described by a pseudo-first order kinetic equation and reaction pathways were proposed. Among the catalysts tested, Pt-based suffered a significant deactivation, not warranting the elimination of this micropollutant. Pd/Al 2 O 3 exhibited a faster removal of PCZ than Rh/Al 2 O 3 , while this catalyst resulted in further hydrogenation of the non-chlorinated reaction product. Accordingly, different CMRs were developed by decorating cylindrical inert porous alumina membranes with Pd, Rh, and a combination of Pd-Rh as active phases (∼1% wt.). All CMRs showed a remarkable stability along 100 h on stream, being Pd/CMR be the most effective, with a pseudo-first order rate constant value of 0.062 min−1. An assessment of the impact of operating conditions (aqueous flow rate, PCZ initial concentration, temperature and H 2 flow rate) was conducted using the Pd/CMR, which notably remained stable for 450 h on stream. The versatility of the system was finally demonstrated in tap water, achieving a steady-state PCZ conversion close to 95 %. [Display omitted] • HDC is effective for the removal of PCZ using Pd/Al 2 O 3 and Rh/Al 2 O 3 catalysts. • PCZ removal rate was accurately described by a pseudo-first order kinetic equation. • Sequential reaction pathways were proposed depending on the catalytic active phase. • CMRs were highly active and stable, showing the Pd/CMR an outstanding performance. • Pd/CMR feasibility was proved at varying operating conditions, even in tap water. [ABSTRACT FROM AUTHOR]

The activity of monometallic (Pd or Rh) and bimetallic (iron-bearing) catalysts has been tested in the HDC of 4-chlorophenol (4-CP) in aqueous phase. The catalysts were prepared by a simple procedure consisting of incipient wetness impregnation followed by calcination and reduction at different temperatures. This allowed controlling the size, dispersion and oxidation state of the metallic nanoparticles. Increasing the temperature of calcination led to a higher dispersion of the active phase (from 21 to 46% by increasing the calcination temperature from 200 to 400 °C) and a higher ratio of zerovalent to electrodefficient palladium (M 0 /M n + values from 1.15 to 2.17) in the case of the Pd-catalysts. Those calcined in air at 400 °C and reduced with H 2 at 350 °C yielded the highest values of the pseudo-first-order rate constant of 4-CP dechlorination (16.2 L h −1 g cat −1 ). The introduction of iron reduced the metal dispersion of both Pd and Rh but the catalysts maintained their dechlorination activity and showed magnetic properties useful for further separation from the liquid phase. [ABSTRACT FROM AUTHOR]

Abstract Aqueous-phase catalytic hydrodechlorination (HDC) has been scarcely explored in the literature for the removal of chlorinated micropollutants. The aim of this work is to prove the feasibility of this technology for the fast and environmentally-friendly degradation of such kind of compounds. Diclofenac (DCF), a highly consumed anti-inflammatory drug, has been selected as the target pollutant given its toxicity and low biodegradability. The commercial Pd/Al 2 O 3 (1% wt.) catalyst has been used due to its prominent role on this field. Complete degradation of DCF was achieved in a short reaction time (20 min) under ambient conditions (25 °C, 1 atm) at [DCF] 0 = 68 μM; [Pd/Al 2 O 3 ] 0 = 0.5 g L−1 and H 2 flow rate of 50 N mL min−1. Remarkably, the chlorinated intermediate (2-(2-chloroanilino)-phenylacetate (Cl-APA)) generated along reaction was completely removed at the same time, being the chlorine-free compound 2-anilinophenylacetate (APA) the only final product. A reaction scheme based on this consecutive pathway and a pseudo-first-order kinetic model have been proposed. An apparent activation energy of 43 kJ mol−1 was obtained, a comparable value to those previously reported for conventional organochlorinated pollutants. Remarkably, the catalyst exhibited a reasonable stability upon three successive uses, achieving the complete degradation of the drug and obtaining APA as the final product in 30 min. The evolution of ecotoxicity was intimately related to the disappearance of the chlorinated organic compounds and thus, the final HDC effluents were non-toxic. The versatility of the system was finally demonstrated in different environmentally-relevant matrices (wastewater treatment plant effluent and surface water). Graphical abstract Image 1 Highlights • HDC is a fast and environmentally-friendly technology for the removal of diclofenac. • The commercial Pd/Al 2 O 3 catalyst showed a high activity and a reasonable stability. • A kinetic model based on a consecutive reaction pathway fitted the experimental data. • Non-toxic effluents were achieved at the end of reaction. • The versatility of the system was proved in environmentally-relevant water matrices. [ABSTRACT FROM AUTHOR]

• HDC is an effective technology for the removal of chlorinated micropollutants. • HDC effluents are non-toxic, with only chlorine-free compounds as reaction products. • The Pd/Al 2 O 3 catalyst shows a relatively high stability upon consecutive applications. • The process versatility is proved in relevant aqueous matrices (mineral, surface and tap water). • HDC shows a high potential as polishing step in DWTPs as it also removes THMs. The presence of micropollutants in fresh waters represents an important challenge for drinking water treatment plants (DWTPs). In particular, the chlorinated ones are especially harmful given their high toxicity and strong bioaccumulation potential. The aim of this work is to evaluate the feasibility of catalytic hydrodechlorination (HDC) for the removal of a representative group of chlorinated micropollutants commonly found in the source waters of DWTPs: the antibiotic chloramphenicol (CAP), the anti-inflammatory diclofenac (DCF), the antibacterial agent triclosan (TCL) and the antidepressant sertraline (SRT). The complete degradation of the isolated micropollutants (3 mg L−1) was achieved in 1 h reaction time using a Pd/Al 2 O 3 catalyst load of 0.25 g L−1 and a H 2 flow rate of 50 N mL min−1. The experimental data were properly described by a pseudo-first order kinetic equation, obtaining degradation rate constants in the range of 0.32–1.56 L g cat −1 min−1 and activation energy values within 42–52 kJ mol−1. In all cases, the final reaction products were chlorine-free compounds and thus, HDC effluents were non-toxic (<0.1 TU). Remarkably, the catalyst showed a suitable stability upon five consecutive applications. The versatility of the process was demonstrated in the treatment of the micropollutants mixture in different aqueous matrices (mineral, surface and tap waters). Strikingly, the removal rate was not affected by the presence of co-existing substances, being the micropollutants completely removed in 15 min with 1 g L−1 catalyst concentration. Finally, the potential of HDC for the removal of trihalomethanes, by-products formed along the oxidation step by chlorination in DWTPs, was also demonstrated. [ABSTRACT FROM AUTHOR]

• HDC is an effective technology for the removal of chlorpromazine. • The Pd/Al 2 O 3 catalyst suffered a dramatic loss of activity due to promazine-Pd interaction. • Several thermal and chemical treatments were investigated for catalyst regeneration. • Complete catalyst regeneration was achieved after its treatment with NaOCl solution. The abatement of dissolved organochlorinated pharmaceuticals from water by catalytic hydrodechlorination has been scarcely studied so far, but it represents a promising process for such goal. This work aims to evaluate the feasibility of this system for the removal of chlorpromazine, one of the most used pharmaceuticals for mental disorders treatment, paying special attention to the deactivation and regeneration of the catalyst (commercial Pd/Al 2 O 3 , 1% wt.). Complete conversion of chlorpromazine (3 mg L−1) was achieved in 90 min reaction time at 25 °C and 1 atm, using a catalyst load of 0.25 g L−1 and 50 N mL min−1 H 2 flow rate. Remarkably, the chlorine-free compound promazine was the single reaction product, which allowed to reduce significantly the ecotoxicity of the starting effluent (0.9 TUs) to negligible values. The experimental data were properly described by a pseudo-first order kinetic equation, obtaining a rate constant value of 5.9·10−2 min−1 at 25 °C, and 30 kJ mol−1 as activation energy. Despite the high activity of the catalytic system, it suffered a significant deactivation upon consecutive uses, which was associated to the selective interaction between promazine and Pd active sites. A number of regeneration methods including both thermal (calcination, calcination-reduction) and chemical (NaClO, H 2 O 2 , KMnO 4) treatments were investigated. Remarkably, aqueous-phase NaClO (750 mg L−1) regeneration allowed to recover completely the activity of the initial fresh catalyst. Its suitability was further demonstrated in consecutive HDC-regeneration runs where the catalyst showed a constant activity. This regeneration procedure is particularly promising given its fast mode of action, simplicity and low-cost. [ABSTRACT FROM AUTHOR]

[Display omitted] • HDC is an effective technology for the removal of chlorinated azole pesticides. • HDC effluents are non-toxic, with only chlorine-free compounds as reaction products. • Intermediates were identified and the reaction mechanism was proposed. • The Pd/Al 2 O 3 catalyst shows a relatively high stability upon consecutive applications. • The process versatility was proved in relevant aqueous matrices (DWTP and tap water). Catalytic hydrodechlorination (HDC) is regarded as a promising purifying technology for drinking water treatment. So far, it has proved to be highly effective for the removal of different groups of chlorinated micropollutants including pharmaceuticals, neonicotinoid pesticides, personal care products or chloroacetic acids. The azole pesticides, recently included in the EU Watch Lists (Decisions 2020/1161 and 2022/1307), are a group of micropollutants of particular concern for drinking water given their high toxicity, persistence, and bioaccumulation potential. In this work, the feasibility of HDC for the removal of a representative group of chlorinated azole pesticides tebuconazole (TEB), tetraconazole (TET), prochloraz (PCZ), penconazole (PEN), metconazole (MET) and imazalil (IMZ)) is demonstrated, and their reactivity is compared with that observed for other halogenated micropollutant groups. Notably, all the pesticides investigated in this work (100 μg L−1) were completely dechlorinated within 30 min under ambient conditions using a 1 wt% Pd/Al 2 O 3 catalyst concentration of 0.25 g L−1 and a H 2 feeding of 50 mL N min−1. The experimental data were accurately described by a pseudo-first order kinetic equation and rate constant values in the range from 1.08 to 2.60 L g cat −1 min−1 were obtained. These values are quite close to those achieved for the most reactive neonicotinoid pesticides and significantly higher than the obtained for chloroacetic acids and most pharmaceuticals (e.g. diclofenac, sertraline or chlorpromazine). From the identification of the generated reaction intermediates and the final non-chlorinated products, sequential reaction pathways were proposed for each pollutant. Remarkably, despite the high toxicity exhibited by the azole pesticides tested, with LC 50 values within the 0.4–7.0 mg L−1 range using A. salina , HDC effluents were non-toxic in all cases. Furthermore, the catalyst showed a remarkable stability upon three consecutive runs. Finally, the versatility of the process was demonstrated in the treatment of real aqueous matrices such as DWTP and tap water, where no significant differences were found either in terms of activity or stability. [ABSTRACT FROM AUTHOR]

In this work, polymer-based spherical activated carbon (PBSAC) (dp = 500 μm) has been used as support to synthesize several Pd/PBSAC (1% wt.) catalysts. These catalysts have been tested in the hydrodechlorination (HDC) of 4‐chlorophenol (4-CP) in aqueous phase under ambient-like conditions (30 °C, 1 atm) at [4-CP] 0 = 3.9 mmol L −1 ; [catalyst] 0 = 1 g L −1 and 50 N mL H 2 min −1 . A sequential calcination (200 °C, air atmosphere) − reduction (80 °C, H 2 atmosphere) treatment was required to obtain active HDC catalysts with a convenient proportion of zero-valent and electrodefficient Pd species. This catalyst allowed to achieve complete conversion of 4-CP in 90 min reaction time, giving rise to phenol as main reaction product. An expanded kinetic model accounting for both consecutive reaction and sorption processes was used to successfully fit the experimental data. The values obtained for the effective rate constant of 4-CP disappearance (3.26–10.88 × 10 −4 s −1 ) and apparent activation energy (31.6 kJ mol −1 ) were close to the previously reported for powdered supported Pd catalysts. Remarkably, the catalyst showed a high stability in long-term continuous application (100 h on stream). [ABSTRACT FROM AUTHOR]

[Display omitted] • A Pd-based catalytic membrane reactor with controlled feeding of H 2 was developed. • The Pd/CMR was tested in continuous flow HDC under ambient conditions. • The Pd/CMR showed an outstanding activity and stability for up to 200 h. • The activity of the catalytic system was not affected by the initial DCF concentration. • The versatility of the system was successfully demonstrated in a tap water matrix. This work is focused on the development of a Pd-based catalytic membrane reactor (Pd/CMR) for its application in continuous flow hydrodechlorination (HDC) of chlorinated micropollutants. A cylindrical inert porous alumina membrane was decorated on the outer with well-dispersed Pd nanoparticles (0.2 % wt.). The Pd/CMR was fully characterized by different techniques. The catalytic system was applied for the degradation of the persistent anti-inflammatory drug diclofenac (DCF) under ambient conditions. A remarkable stability was observed upon long-term HDC reaction, with a reasonable DCF conversion (60 %). Notably, as the process could be described by pseudo-first order kinetic, the initial concentration did not affect the final conversion achieved. Finally, the versatility of the system was successfully demonstrated using a real aqueous matrix (tap water). All in all, Pd/CMR exhibited a remarkable feasibility for the implementation of the HDC technology on a larger scale, showing an extraordinary catalytic performance for up to 200 h. [ABSTRACT FROM AUTHOR]