Abstract:Structured catalysts were prepared, characterized and evaluated in NO 3 removal from drinking water. Different suspensions containing a previously optimized PdCu/5wt% ZrO 2-Al 2 O 3 powder catalyst (hereinafter PdCu/5ZA p) were prepared and deposited on cordierite monoliths by washcoating. The effect of suspension concentration, the particle size, the immersion number, the use of suspension stabilizer agent, and an alumina precoating on the coating adherence and catalytic performance were studied. All the prep… Show more
“…Since the catalytic reduction of nitrate is based on the continuous redox reaction between NO 3 − and the promoter metal, the irreversible oxidation of the latter could limit the progression of the reaction, weakening the reactivity of the bimetallic catalyst and decreasing the NO 3 − removal efficiency [25]. On the other hand, the fouling of the catalyst surface by salt precipitation is the most common deactivation cause in NO 3 − removal treatments in water wherein other compounds are present [13,24,[26][27][28][29][30][31][32]. The loss of metal components is highly dependent on the reaction pH [33] and can be avoided by modifying the catalyst characteristics [34] or operating conditions [33,35].…”
In this work, we study the effect of modifying the metal loading (0.5–1.5 wt.% Pd and 0.1–1 wt.% Sn or In), the impregnation order of noble or promoter metal (Pd–Sn or Sn–Pd), and the type of promoter metal (Sn or In) during the preparation process for a Pd bimetallic catalyst, supported on γ-alumina, used in the catalytic reduction of nitrate. The deposition of the noble metal over the promoter metal, especially with Pd:Sn ratios (wt.) of 1:10 and 1:2, favored the hydrogen spillover rate and increased the H concentration on the catalyst surface, enhancing NH4+ production. On the other hand, Pd–In catalysts showed higher activity than the Sn catalysts, as well as higher NH4+ selectivity. The stability of the Pd–Sn/Al2O3 (1.5–1 wt.%) catalyst was evaluated in long-term experiments for the treatment of synthetic water (100 mg L−1 NO3−) and three different commercial drinking waters. This Pd–Sn/Al2O3 catalyst achieved a stable nitrate conversion for a duration of 50 h in the synthetic water treatment. However, the catalyst showed a significant activity loss in the presence of other ions (different to NO3−) in the reaction medium, increasing slightly the selectivity to NH4+.
“…Since the catalytic reduction of nitrate is based on the continuous redox reaction between NO 3 − and the promoter metal, the irreversible oxidation of the latter could limit the progression of the reaction, weakening the reactivity of the bimetallic catalyst and decreasing the NO 3 − removal efficiency [25]. On the other hand, the fouling of the catalyst surface by salt precipitation is the most common deactivation cause in NO 3 − removal treatments in water wherein other compounds are present [13,24,[26][27][28][29][30][31][32]. The loss of metal components is highly dependent on the reaction pH [33] and can be avoided by modifying the catalyst characteristics [34] or operating conditions [33,35].…”
In this work, we study the effect of modifying the metal loading (0.5–1.5 wt.% Pd and 0.1–1 wt.% Sn or In), the impregnation order of noble or promoter metal (Pd–Sn or Sn–Pd), and the type of promoter metal (Sn or In) during the preparation process for a Pd bimetallic catalyst, supported on γ-alumina, used in the catalytic reduction of nitrate. The deposition of the noble metal over the promoter metal, especially with Pd:Sn ratios (wt.) of 1:10 and 1:2, favored the hydrogen spillover rate and increased the H concentration on the catalyst surface, enhancing NH4+ production. On the other hand, Pd–In catalysts showed higher activity than the Sn catalysts, as well as higher NH4+ selectivity. The stability of the Pd–Sn/Al2O3 (1.5–1 wt.%) catalyst was evaluated in long-term experiments for the treatment of synthetic water (100 mg L−1 NO3−) and three different commercial drinking waters. This Pd–Sn/Al2O3 catalyst achieved a stable nitrate conversion for a duration of 50 h in the synthetic water treatment. However, the catalyst showed a significant activity loss in the presence of other ions (different to NO3−) in the reaction medium, increasing slightly the selectivity to NH4+.
“…Also, monoliths having a macroporous structure with numerous channels allow a better contact between the reactants (H 2 , NO 3 − , NO 2 − , or BrO 3 − ) and the active phase. 18 In addition, clogging, fluidization, and a great loss of pressure, caused by the use of powder catalysts, are avoided.…”
Section: Introductionmentioning
confidence: 99%
“…23 If the structured catalysts are prepared by the washcoating method, different factors influence this adherence, such as the characteristics of the washcoat containing the active phase, the particle size of the solid to be deposited, the nature of dispersive medium, the amount of solid, and the pH. 18 This work focuses on developing different formulations and procedures to reach a good adherence of the active phase on prepared structured supports. Moreover, the development of a fixed-bed reactor containing structured catalysts is addressed in the present work.…”
Section: Introductionmentioning
confidence: 99%
“…One of the ways to avoid the loss of catalytic material is to use pellets, foams, or monoliths to synthesize structured catalysts. , Monolith-based structured catalysts with different chemical compositions are widely used in environmental catalytic applications. , The use of monoliths has the advantage of immobilizing the active phase, thus avoiding contamination of the treated water with metal particles. Also, monoliths having a macroporous structure with numerous channels allow a better contact between the reactants (H 2 , NO 3 – , NO 2 – , or BrO 3 – ) and the active phase . In addition, clogging, fluidization, and a great loss of pressure, caused by the use of powder catalysts, are avoided.…”
Section: Introductionmentioning
confidence: 99%
“…The adherence of the PdCu active phase to the structured support is a critical factor that must be controlled . If the structured catalysts are prepared by the washcoating method, different factors influence this adherence, such as the characteristics of the washcoat containing the active phase, the particle size of the solid to be deposited, the nature of dispersive medium, the amount of solid, and the pH . This work focuses on developing different formulations and procedures to reach a good adherence of the active phase on prepared structured supports.…”
The elimination of hazardous oxyanions NO 3 − , NO 2 − , and BrO 3 − from synthetic and real water samples using novel PdCu/10ZrCe (10 wt % ZrO 2 on CeO 2 ) structured catalysts supported on cordierite monoliths was studied in order to avoid loss of the catalytic material during water treatment. The monoliths were coated with different suspensions of the 10ZrCe support. Particle sizes, suspension concentration of 10ZrCe, and pH effects were evaluated. The structured catalyst was tested in a fixed-bed reactor at different flow rates for the elimination of the selected anions. Good results in terms of activity and selectivity to the products of interest (S N 2 : 0.99 and S Br − :1) were obtained in synthetic water. The structured catalyst was reused three times, maintaining its activity and selectivity. It was evaluated in a real water sample but the activity was lower probably due to competition for active sites by different ions present in the sample. The structured catalyst prepared is promising for the development of a system for water remediation, based on PdCu/ZrO 2 −CeO 2 materials.
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