Highly effective bromate reduction by liquid phase catalytic hydrogenation over Pd catalysts supported on core-shell structured magnetites: Impact of shell properties

Pd sub-nanolayer on Au core for enhanced catalytic hydrogenation reduction of oxyanions pollutants: Synergistic effect of Pd and Au

Oxyanion pollutants in industrial wasterwater, such as (Cr(VI)), BrO3- (Br(V)) and SeO32- (Se(IV)) have detrimental or toxic effects on individual health when their concentrations accumulated to a certain level. The conversion of these oxyanions into harmless/industrial-valuable products or removal from wastewater is of significance. Herein, we designed Pd sub-nanolayer on Au core catalysts supported on Al2O3 (sub-Pd-Au/Al2O3) for highly effective catalytic hydrogenation reduction of oxyanions under ambient conditions. The sub-Pd(0.049)-Au(0.927)/Al2O3 catalyst exhibited the highest catalytic activity and TOF value for Cr(VI), Br(V) and Se(IV) reduction, respectively, by optimizing the Pd loading amount. The synergistic effect between Pd sub-nanolayer and Au core enhanced catalytic activity by regulating the Pd dispersion and site property, according to thorough characterizations that included high-angle annular dark-field transmission electron microscopy (HAADF-TEM) image, in-situ CO-IR adsorption, CO chemisorption, and X-ray photoelectron spectroscopy (XPS). This work might provide some new lights on design of highly efficient catalysts for the elimination of oxyanion pollutants.

Accelerating Catalytic Oxyanion Reduction with Inert Metal Hydroxides

Adding CrIII or AlIII salts into the water suspension of platinum group metal (PGM) catalysts accelerated oxyanion pollutant reduction by up to 600%. Our initial attempts of adding K2CrVIO4, K2CrVI2O7, or KCrIII(SO4)2 into Pd/C enhanced BrO3- reduction with 1 atm H2 by 6-fold. Instrument characterizations and kinetic explorations collectively confirmed the immobilization of reduced CrVI as CrIII(OH)3 on the catalyst surface. This process altered the ζ-potentials from negative to positive, thus substantially enhancing the Langmuir-Hinshelwood adsorption equilibrium constant for BrO3- onto Pd/C by 37-fold. Adding AlIII(OH)3 from alum at pH 7 achieved similar enhancements. The Cr-Pd/C and Al-Pd/C showed top-tier efficiency of catalytic performance (normalized with Pd dosage) among all the reported Pd catalysts on conventional and nanostructured support materials. The strategy of adding inert metal hydroxides works for diverse PGMs (palladium and rhodium), substrates (BrO3- and ClO3-), and support materials (carbon, alumina, and silica). This work shows a simple, inexpensive, and effective example of enhancing catalyst activity and saving PGMs for environmental applications.

Efficient Reduction of Selenite to Elemental Selenium by Liquid-Phase Catalytic Hydrogenation Using a Highly Stable Multiwalled Carbon Nanotube-Supported Pt Catalyst Coated by N-Doped Carbon

A stable catalyst, Pt/carbon nanotube (CNT) coated with N-doped carbon (Pt/CNT@CN), was designed to reduce selenite (Se(IV)) in water to elemental selenium by liquid-phase catalytic hydrogenation. Commercial Pt/C, pristine Pt/CNT, and carbon-coated Pt/CNT (Pt/CNT@C) were used for benchmarking. The Pt particles in Pt/CNT@CN were completely embedded beneath the coatings to minimize leaching and were not easily accessible to Se(IV). However, Schottky-Mott-type metal-carbon junctions that activate H2 were formed on the coated catalyst, facilitating effective reduction of Se(IV). The initial activity of Pt/CNT@CN (900.5 mg L-1 gcat-1 h-1) was two times higher than that of commercial Pt/C (448.6 mg L-1 gcat-1 h-1). The commercial Pt/C and uncoated Pt/CNT lost their initial activities during reuse and were almost inactive after 10 cycles due to significant Pt leaching (>90%) during the reaction and acid-washing regeneration processes. Pt/CNT@CN maintained 33% of the initial activity after the first cycle and stabilized over the following 9 cycles due to effective protection of Pt particles by carbon coatings. After 10 cycles, the activity of Pt/CNT@CN was over 20 times higher than that of Pt/C and uncoated Pt/CNT. Overall, catalytic hydrogenation using carbon-coated-supported Pt catalysts is an effective and promising approach to remove Se(IV) in water.

A Review on the Catalytic Hydrogenation of Bromate in Water Phase

The presence of bromate in water sources generates environmental concern due to its toxicity for humans. Diverse technologies, like membranes, ion exchange, chemical reduction, etc., can be employed to treat bromate-polluted water but they produce waste that must be treated. An alternative to these technologies can be the catalytic reduction of bromate to bromide using hydrogen as a reducing agent. In this review, we analyze the research published about this catalytic technology. Specifically, we summarize and discuss about the state of knowledge related to (1) the different metals used as catalysts for the reaction; (2) the influence of the support on the catalytic activity; (3) the characterization of the catalysts; (4) the reaction mechanisms; and (5) the influence of the water composition in the catalytic activity and in the catalyst stability. Based on published papers, we analyze the strength and weaknesses of this technique and the possibilities of using this reaction for the treatment of bromate-polluted water as a sustainable process.

Complete dehalogenation of bromochloroacetic acid by liquid phase catalytic hydrogenation over Pd/CeO2 catalysts

Bromochloroacetic acid is classified as one of the typical disinfection byproducts (DBPs). In this work, supported palladium catalysts on different supports (CeO_2, Al₂O₃, SiO₂ and activated carbon (AC)) (labelled as Pd/support) were synthesized via the deposition-precipitation method (D-P method) and their activities for the complete dehalogenation of bromochloroacetic acid by liquid phase catalytic hydrogenation were evaluated. Comprehensive characterizations of the catalysts were conducted by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), point of zero charge (PZC), X-ray photoelectron spectroscopy (XPS) and CO chemisorption. Results indicated that the PZCs of the supports varied with each other. The stronger Pd-support interaction and higher Pd dispersion of Pd/CeO₂ and Pd/Al₂O₃ than those of Pd/AC and Pd/SiO₂ were confirmed by X-ray photoelectron spectroscopy and CO chemisorption. Pd/CeO₂ had a higher ratio of positively charged Pd to metallic Pd (Pdⁿ⁺/Pd⁰) than Pd/Al₂O₃ and Pd/AC due to a stronger metal-support interaction. Accordingly, a negligible bromochloroacetic acid conversion was observed on Pd/SiO₂, whereas bromochloroacetic acid was found to be readily decomposed on Pd/CeO₂, Pd/Al₂O₃ and Pd/AC. However, the dechlorination reaction could not further proceed on Pd/Al₂O₃ and Pd/AC catalysts after the bromine functionality was removed from bromochloroacetic acid. A complete dehalogenation of bromochloroacetic acid occurred only on Pd/CeO₂. Furthermore, the dechlorination rate constants of monochloroacetic acid and bromochloroacetic acid over Pd(1.40)/CeO₂ were 0.018 and 0.031 min^-1 respectively, confirming an induced synergistic effect due to the existence of bromine atoms. It was worth noting that a stepwise-concerted pathway was verified during the liquid phase catalytic hydrodehalogenation of bromochloroacetic acid.

Nature and evolution of Pd catalysts supported on activated carbon fibers during the catalytic reduction of bromate in water

Pd/ACF are active catalysts for the bromate reduction and their activity depends on the Pd crystal size with a pseudo-first order kinetic respect to BrO₃⁻ and H₂ partial pressure.

A novel bio-inspired conductive, biocompatible, and adhesive terpolymer based on polyaniline, polydopamine, and polylactide as scaffolding biomaterial for tissue engineering application

A novel electrically conductive nanofibrous scaffold based on polyaniline-co-(polydopamine-grafted-poly(d,l-lactide)) [PANI-co-(PDA-g-PLA)] was fabricated using electrospinning technique and its physicochemical as well as biological characteristics toward bone tissue engineering (TE) were investigated extensively. In detail, PANI-co-PDA was synthesized via a one-step chemical oxidization approach. Then, d,l-lactaide monomer was grafted onto PDA segment using a ring opening polymerization (ROP) to afford PANI-co-(PDA-g-PLA) terpolymer. The successful synthesis of PANI-co-(PDA-g-PLA) terpolymer was confirmed using FTIR spectroscopy as well as TGA analysis. Finally, a solution of the synthesized terpolymer was electrospun to fabricate a conductive nanofibrous scaffold. Some physicochemical features such as mechanical, conductivity, electroactivity, hydrophobicity, and morphology as well as biological characteristics including biocompatibility, biodegradability, as well as enhancing the cells adhesion and proliferation were investigated. According to the above-mentioned experimental results, the fabricated electrospun nanofibers can be considered as a potential scaffold for TE application, mainly due to its proper physicochemical and biological properties.

Core-shell design and well-dispersed Pd particles for three-way catalysis: Effect of halloysite nanotubes functionalized with Schiff base

In this study, we have described the synthesis of core@shell three-way catalyst with well-dispersed Pd nanoparticles which were intercalated into halloysite nanotubes (HNTs) material via ligand assistance. The prepared parameters of Pd@HNTs catalyst included amine source, the molar ratio of amine and aldehyde, and the addition of CeO₂ promoter. As a result, Pd@HNTs performed a good dispersion of Pd particles and high stability, which is attributed to the strong interaction between Pd and HNTs with Schiff base ligands and the high thermal resistance of HNTs as a sintering barrier. Moreover, the results of various characteristic analyses revealed that Pd@HNT-E12 (ethylenediamine: salicylaldehyde in a molar ratio of 1:2) exhibited the highest gases conversion to the others, which has excellent redox ability. Furthermore, the addition of CeO₂, which acted as both a promoter and a protector, could provide more oxygen vacancies for promoting NO reduction and CO and C₃H₈ oxidation at gradually elevated temperatures. Such core-shell catalyst Ce@Pd@HNT-E12 could avoid excess CeO₂ penetrating into the pore volume of halloysite support and facilitate the three-way catalytic reaction.