Pd–Al pillared clays as catalysts for the hydrodechlorination of 4-chlorophenol in aqueous phase

Catalysts based on pillared clays with Pd–Al were synthesized from a commercial bentonite and tested for catalytic hydrodechlorination (HDC) using 4-chlorophenol (4-CPhOH) as target compound and formic acid as hydrogen source. Stable Pd–Al pillared clays, with a strong fixation of the active phase to the solid support were obtained since no Pd was detected in the reaction media. The incorporation of Pd to the pillared clay structure yielded catalysts with high activity in the reaction studied reaching a complete removal of the 4-CPhOH under mild conditions of temperature (50–70 °C). Phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol. The influence of the method of introduction of Pd in the pillared clay (ion-exchange or impregnation) and Pd concentration in the catalytic activity were studied as well as other important operating variables such as reaction temperature, catalyst concentration, 4-CPhOH initial concentration and formic acid to 4-CPhOH molar ratio. The catalysts prepared suffered deactivation after three consecutive runs, probably due to carboneous deposits formation since no appreciable Pd leaching was observed.     

Bimetallic Pd/Al particles for highly efficient hydrodechlorination of 2-chlorobiphenyl in acidic aqueous solution

Pd-based bimetallic materials have been widely studied for the effective hydrodechlorination (HDC) of aqueous chloroorganic compounds. However, the reaction functions of metal substrates and mechanism responsible for changes in reactivity have not been fully elucidated. Here, we synthesized Pd-based bimetals with Mg, Al, Mn, Zn, Fe, Sn, and Cu to explore the influence of metal substrates on HDC reactivity of 2-chlorobiphenyl (2-PCB). Bimetals exhibited disparate reactivity toward 2-PCB in acidic solution. Among these bimetals, Pd/Al particles presented the highest stability and relatively high reactivity to remove 2-PCB. The maintenance and regeneration of Al substrate are attributed to its particular corrosion properties which provide an efficient recycling between Al element and its oxide layer. The fresh and reacted Pd/Al samples were characterized by ICP-OES, SEM, XRD, and BET. The investigation of the pH effect on 2-PCB HDC further revealed the particular behaviour of Al surface. The effect of Pd loading amount on the HDC indicated that the optimal Pd content in terms of catalytic activity was related to the Pd dispersion degree. Finally, a mechanism for 2-PCB HDC on the Pd/Al surface was proposed.     

Dechlorination of chlorophenols using magnesium-palladium bimetallic system

Ninety-four percent removal of 10 mg L(-1) of pentachlorophenol (PCP) was achieved by treatment with 154.5mM Mg(0) and 0.063 mM K(2)PdCl(6) in the presence of 175 mM acetic acid in 1h reaction time. Dechlorination of PCP was found to be sequential and phenol was identified as the end product along with accumulation of trace concentrations of tetra- and trichlorophenols. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) revealed that palladium in its metallic form (Pd(0)) produced by reduction of Pd4+, was spatially separated from magnesium granules when acid was included in the reaction. These colloidal palladium particles generated active reductive species of hydrogen and dechlorinated chlorophenols. In the absence of acid, the efficiency of dechlorination of PCP by Pd/Mg(0) system was very low and chief mechanism of removal of the compound was through sorption onto solid surfaces. Thus, it was important to include acid in the system to: (a) facilitate corrosion of Mg(0) and reduction of Pd4+ to Pd(0), (b) provision of protons to produce H2, (c) retard formation of insoluble oxides and hydroxides that may deposit on the magnesium granules and sorb PCP and its partially dechlorinated products and. Application of 154.5 mM Mg(0)/0.063 mM K(2)PdCl(6) on PCP, 2,4,5-trichlorophenol (TCP) and 2-chlorophenol (MCP) with organic chloride equivalence showed that the rate and extent of removal increased with decrease in number of chlorine atoms on phenol.     

Suzuki–Miyaura reaction and solventfree oxidation of benzyl alcohol by Pd/nitrogen-doped CNTs catalyst

Suzuki–Miyaura C–C coupling reactions were investigated with Pd/nitrogen-doped carbon nanotubes (Pd/N-CNTs) as a catalyst. Also, the same catalyst was examined for the solventfree oxidation of benzyl alcohol to benzaldehyde. Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized from 1-ferrocenylmethyl(2-methylimidazole) and benzophenone via a chemical vapour deposition technique. Acetonitrile was used as a solvent and source of both carbon and nitrogen constituents of N-CNTs. Pd nanoparticles (Pd NPs) were successfully dispersed on N-CNTs via a metal organic chemical vapour deposition method. SEM, TEM, XRD, elemental analysis and ICP-OES measurements were used to characterize the nanomaterials. From the TEM analysis, it was observed that Pd NPs were spherical and with particle sizes ranging from 3 to 8 nm. For Suzuki C–C coupling reactions, phenylboronic acid, aryl halide, Pd/N-CNTs catalyst and a base (NaOAc, K₂PO₄, K₂CO₃, NaOH, Et₃N and Na₂CO₃) were used. The optimized experiments indicate that K₂CO₃, as the base, and ethanol/water (1:1 v/v, 10 mL) mixture, as a solvent, are the best reaction conditions. The solventfree oxidation reactions of benzyl alcohol were also done with Pd/N-CNTs catalyst and benzyl alcohol as a substrate. In both sets of reactions, C–C coupling and oxidation, the increase in pyrrolic nitrogen species was found to be responsible for higher catalytic activities of Pd/N-CNT catalysts, and this was attributed to the ease of Pd NP dispersion on N-CNTs, relative to pristine CNTs. Also, the higher catalytic activity of Pd/N-CNTs could be ascribed not only to the smaller Pd NP size or surface area, but to also the surface properties and the nature of the support when compared with the undoped counterpart, Pd/CNTs.     

Enhancing both selectivity and coking-resistance of a single-atom Pd<Subscript>1</Subscript>/C<Subscript>3</Subscript>N<Subscript>4</Subscript> catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading,where Pd-based catalysts are widely used because of their high hydrogenation activities.However,poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns.In this work,atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation.During selective hydrogenation of acetylene in excess ethylene,the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/A12O3 and Pd/SiO2 catalysts.In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement.More impressively,the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance.Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.     

新型MgCl_2/SiO_2复合载体催化剂的乙烯聚合研究Ⅰ.乙烯淤浆聚合

由格氏试剂制备的新型ＪＭ复合载体催化剂对乙烯聚合具有很高的活性。着重考察了复合载体催化剂对乙烯聚合的催化活性及聚合产物堆密度的影响。     

Plasma assisted degradation of phenol solutions

Solutions of 2-chlorophenol, 4-chlorophenol and 2,6-dichlorophenol in bidistilled and water from the river Danube were treated in plasma reactor. In this reactor, based on coaxial dielectric barrier discharge at atmospheric pressure, plasma is formed over a thin layer of treated water. After one pass through the reactor, starting chlorophenols concentration of 20 mg/l was diminished up to 95%. Kinetics of the chlorophenols degradation was monitored by High Pressure Liquid Chromatography method (HPLC).     

Comparison treatment of various chlorophenols by electro-Fenton method: relationship between chlorine content and degradation

This study describes a comparative degradation of various chlorophenols by electro-Fenton method. Chloride released and reaction intermediate products were determined by ionic chromatography (IC) and gas chromatography/mass spectrometry (GC/MS). Using pentachlorophenol (PCP) as the model compound, we investigated the effects of cell voltage, electrolyte concentration and pH to optimize the degradation conditions. It was noted that the addition of small quantities of Fe3+ or Fe2+ significantly accelerated the degradation rate. Under the optimal conditions, electro-Fenton method was used to treat various chlorophenols including PCP, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and their mixture aqueous solutions. Their pseudo first-order degradation rate constants at the first stages were calculated and compared, which gave the following sequence: 2,4-DCP>2,4,6-TCP>PCP>4-CP. The relationship between the chlorine content and degradation rate was discussed and compared with other advanced oxidation processes. Finally, we proposed the degradation pathways of different chlorophenols.     

Photocatalytic decomposition of 4-chlorophenol over oxide catalysts.

4-Chlorophenol in the presence of catalysts was decomposed in aqueous solution by a 125 W medium pressure mercury lamp in a thermostated quartz batch photoreactor, and the organic bound chlorine was catalytically converted into the environmentally less harmful inorganic chloride. Differences in the concentration of 4-chlorophenol and of the intermediates, such as hydroquinone and quinone, are followed by HPLC. The best catalyst among a homolog series for the photo-decomposition of 4-chlorophenol was selected as finely dispersed platinum oxide on a TiO2 semiconductor support, and kinetic parameters of the Langmuir-Hinshelwood type decomposition reaction were reported for the selected catalyst. A simple mechanism of substrate degradation in accord with the chosen kinetic model was postulated. The developed process may serve photooxidative removal of chlorophenols in wastewater without using costly oxidants.     

Effect of biogenic substrate concentration on the performance of sequencing batch reactor treating 4-CP and 2,4-DCP mixtures

Effect of a biogenic substrate (peptone) concentration on the performance of sequencing batch reactor (SBR) treating 220 mg/l 4-chlorophenol (4-CP) and 110 mg/l 2,4-dichlorophenol (2,4-DCP) mixtures was investigated. In this context, peptone concentration was gradually decreased from 300 mg/l to null in which chlorophenols were fed to the reactor as sole carbon and energy sources. By this way, the effect of peptone concentration on observed yield coefficient (Y), biomass concentration, chlorophenols and COD removal performances were investigated. Decreasing peptone concentration accompanied with lower biomass concentration led to increase in peak chlorophenol and COD concentrations within the reactor during each SBR cycle. This, in turn, caused noteworthy declines in the removal rates as chlorophenol degradations followed Haldane substrate inhibition model. Also, increased peak chlorophenol concentrations led to the accumulation of 5-chloro-2-hydroxymuconic semialdehyde (CHMS), which is -meta cleavage product of 4-CP. Despite the decreased removal rates, complete chlorophenols and CHMS degradation, in addition to high COD removal efficiencies (>90%), were observed for all studied conditions, even chlorophenols were added as sole carbon and energy sources. Another significant point is that 2,4-DCP at slightly elevated concentrations (>20 mg/l) within the reactor caused a strong competitive inhibition on 4-CP degradation. In SBR, feeding the influent to the reactor within a certain period (i.e. filling period) provided dilution of coming wastewater, which decreased the chlorophenols concentrations to which microorganisms were exposed. Therefore, use of SBR may help to avoid both self and competitive inhibitions in the treatment of 4-CP and 2,4-DCP mixture especially in the presence high biogenic substrate concentrations. In addition, isolation and identification studies have indicated that Pseudomonas sp. and Pseudomonas stutzeri were dominant species in the acclimated mixed culture.     

Nano-scale Au supported on Fe3O4: characterization and application in the catalytic treatment of 2,4-dichlorophenol

Catalytic hydrodechlorination (HDC) is an effective means of detoxifying chlorinated waste. Gold nanoparticles supported on Fe(3)O(4) have been tested in the gas phase (1 atm, 423 K) HDC of 2,4-dichlorophenol. Two 1% w/w supported gold catalysts have been prepared by: (i) stepwise deposition of Au on α-Fe(2)O(3) with subsequent temperature-programmed reduction at 673 K (Au/Fe(3)O(4)-step); (ii) direct deposition of Au on Fe(3)O(4) (Au/Fe(3)O(4)-dir). TEM analysis has established the presence of Au at the nano-scale with a greater mean diameter (7.6 nm) on Au/Fe(3)O(4)-dir relative to Au/Fe(3)O(4)-step (4.5 nm). We account for this difference in terms of stronger (electrostatic) precursor/support interactions in the latter that can be associated with the lower pH point of zero charge (with respect to the final deposition pH) for Fe(2)O(3). Both catalysts promoted the preferential removal of the ortho-Cl substituent in 2,4-dichlorophenol, generating 4-chlorophenol and phenol as products of partial and total HDC, respectively, where Au/Fe(3)O(4)-step delivered a two-fold higher rate (2 × 10(-4) mol(Cl) h(-1) m(Au)(-2)) when compared with Au/Fe(3)O(4)-dir. This unprecedented selectivity response is attributed to activation of the ortho-C-Cl bond via interaction with electron-deficient Au nanoparticles. The results demonstrate the feasibility of a controlled recovery/recycling of chlorophenol waste using nano-structured Au catalysts.     

具有三维网状结构的石墨相氮化碳/还原氧化石墨烯/钯复合材料的合成及可见光催化性能

石墨相氮化碳(g-C_3N_4)已经被认为是一种高效的非金属半导体光催化剂。为进一步优化其光催化性能,通过热解-水热两步法制备了三维网状结构的g-C_3N_4/还原氧化石墨烯(rGO)/钯纳米颗粒(Pd NPs)复合材料。该复合材料由大量超薄片组成,而且薄片上有大量直径约为10nm的Pd NPs。g-C_3N_4/rGO/Pd NPs复合材料展现了一个宽的可见光吸收(边~460nm),其在460~800nm波长范围内还有一个随波长增加的光吸收。经可见光(λ400nm)照射140 min后,g-C_3N_4/rGO/Pd NPs复合材料可降解90%罗丹明B(RhB)。此外,循环实验表明g-C_3N_4/rGO/Pd NPs复合材料具有良好的稳定性。因此,g-C_3N_4/rGO/Pd NPs复合材料有望成为一种高效稳定的光催化剂,在水污染处理领域具有潜在的应用价值。     

Pd负载型介孔ZrO2-TiO2复合材料的设计合成及其CO催化氧化性能研究

以介孔结构的复合ZrO₂-TiO₂为载体负载活性组分, 制备了具有高CO催化氧化活性的Pd/ZrO₂-TiO₂与PdCu/ZrO₂-TiO₂负载型催化剂。XRD、TEM研究结果表明: 活性组分Pd、Cu物种可均匀分散于介孔载体中。系统考察了不同的催化剂载体、制备方法和助催化剂等对该介孔复合材料CO催化氧化性能的影响, 结果表明: 以ZrO₂-TiO₂为载体的催化剂其CO催化氧化活性明显优于以介孔Al₂O₃或介孔SBA-15为载体的催化剂; 一步法制备的介孔Pd/ZrO₂-TiO₂催化剂其CO催化氧化的低温活性较浸渍法制备的Pd/ZrO₂-TiO₂有很大提高; 并且Pd和Cu物种共负载的介孔ZrO₂-TiO₂复合催化剂具有最优的CO催化氧化活性, 其CO的完全催化氧化温度可降至170℃, O₂-TPD分析说明Pd和Cu之间的相互作用使得PdCu/ZT催化剂在更低温度具有氧化还原活性。     

β-SiC的快速合成及其作为载体制备的Pd/SiC催化剂性能

以蔗糖为碳源,硅酸钠为硅源,盐酸为酸度调节剂,硫酸为催化剂,通过简单的溶胶-凝胶过程和碳热还原法,快速合成出比表面积为159m2/g的碳化硅(SiC)。并以其作为载体,制备负载型Pd/SiC催化剂,研究其在CO和C3H6氧化反应中的催化活性。结果表明当Pd负载量为0.45%(质量分数)时,所制备的催化剂具有较高的活性,其中CO的最低完全转化温度为230℃,C3H6的最低完全转化温度为235℃。     

Mesoporous Nitrogen‐Doped Carbon‐Nanosphere‐Supported Isolated Single‐Atom Pd Catalyst for Highly Efficient Semihydrogenation of Acetylene

Semihydrogenation of acetylene in the ethylene feed is a vital step for the industrial production of polyethylene. Despite their favorable reaction activity and ethylene selectivity, the Pd‐based intermetallic compound and single‐atom alloy catalysts still suffer from the limitation of atomic utilization derived from the partial exposure of active Pd atoms. Herein, a hard‐template Lewis acid doping strategy is reported that can overcome the inefficient utilization of Pd atoms. In this strategy, N‐coordinated isolated single‐atomic Pd sites are fully embedded on the inner walls of mesoporous nitrogen‐doped carbon foam nanospheres (ISA‐Pd/MPNC). This synthetic strategy has been proved to be applicable to prepare other ISA‐M/MPNC (M = Pt and Cu) materials. This ISA‐Pd/MPNC catalyst with both high specific surface area (633.8 m² g^?1) and remarkably thin pore wall (1–2 nm) exhibits higher activity than that of its nonmesoporous counterpart (ISA‐Pd/non‐MPNC) catalyst by a factor of 4. This work presents an efficient way to tailor and optimize the catalytic activity and selectivity by atomic‐scale design and structural control.     

Hydrodechlorination of DDT and chloroalkanes over carbon-supported Ni-Mo catalyst

Catalytic hydrodechlorination (HDC) is an efficient method for the elimination of chlorinated compounds from organic wastes. HDC allows for the recovery of parent hydrocarbons. Herein, we studied the dechlorination of chlorododecane (CDD), dichlorocyclohexane (DCH) and dichlorodiphenyltrichloroethane (DDT) over a sulfided Ni-Mo/C catalyst in a flow reactor. The Ni-Mo/C catalyst was prepared by the incipient wetness method using a granular activated carbon support. In contrast to alumina, which is a commonly used support for commercial catalysts, the carbon support is resistant to decomposition by HCl formed during the HDC reaction. The composition of the tested catalyst was 5 wt.% NiO and 15 wt.% MoO(3), and it was characterized by well developed both the micro- and mesoporosity (V(mic)=0.559 cm(3)g(-1), V(mes)=0.430 cm(3)g(-1)). The level of conversion of CDD, DCH, and DDT was directly related to reaction temperatures in the HDC process; the total chlorine removal was achieved at 200 degrees C. The tested catalyst was determined to have good thermal stability in the HDC process at 170 degrees C for 100 h. This corresponded to conversions of 85-72% for CDD and 81-79% for DCH. For CDD the hydrogen pressure affected the ratio of dodecane to dodecene in the reaction products.     

Collagen fiber with surface-grafted polyphenol as a novel support for Pd(0) nanoparticles: Synthesis,characterization and catalytic application

The aim of this study is to use collagen fiber (CF) as a natural polymeric support to synthesize a novel palladium (Pd) nanoparticle catalyst. To achieve a stable immobilization of Pd on CF support, epigallocatechin-3-gallate (EGCG), a typical plant polyphenol, was grafted onto CF surface, acting both as dispersing and stabilizing agent for Pd nanoparticles. Scanning electron microscopy showed that this catalyst was in ordered fibrous state with high flexibility. The presence of EGCG grafted on CF and the interaction mechanism of Pd ions with support was investigated by X-ray photoelectron spectroscopy. X-ray diffraction and transmission electron microscopy offered evidence that the well-dispersed Pd nanoparticles were generated on the outer surface of CF. By using the hydrogenation of allyl alcohol as a model reaction, the synthesized catalyst presented remarkably improved activity, selectivity and reusability as compared with the Pd catalyst supported by CF without grafting of EGCG.     

Catalytic stepwise nitrate hydrogenation in batch-recycle fixed-bed reactors

Pd (1.0 wt.%)-Cu (0.3 wt.%) bimetallic and Pd (1.0 wt.%) monometallic catalysts were synthesized by means of incipient-wetness impregnation technique and deposited on alumina spheres (dp=1.7 mm). The prepared catalysts were tested at T=298 K and p(H2)=1.0 bar in the integrated process of catalytic liquid-phase hydrogenation of aqueous nitrate solutions, in which the denitration step was carried out consecutively in separate, single-flow fixed-bed reactor units operating in a batch-recycle mode. In the first reactor packed with a Pd-Cu bimetallic catalyst, nitrate ions were transformed to nitrites at pH 12.5 with a selectivity as high as 93%; the rest was found in the form of ammonium ions. Liquid-phase nitrite hydrogenation to nitrogen in the second reactor unit packed with a Pd monometallic catalyst was conducted at low pH values of 3.7 and 4.5, respectively. Although these values are well below the pHpzc of examined catalyst (6.1), which assured that the nitrite reduction was carried out over a positively charged catalyst surface, up to 15% (23% in the presence of 5.0 g/l NaCl in the solution) of initial nitrite content was converted to undesired ammonium ions. Since a negligible amount of these species (below 0.5mg/l) was produced at identical operating conditions over a powdered Pd/gamma-Al2O3 catalyst, it is believed that the enhanced production of ammonium ions observed in the second fixed-bed reactor is due to the build-up of pH gradients in liquid-filled pores of spherical catalyst particles. Both Pd-Cu bimetallic and Pd monometallic catalysts were chemically resistant in the investigated range of pH values.     

Pd Single‐Atom Catalysts on Nitrogen‐Doped Graphene for the Highly Selective Photothermal Hydrogenation of Acetylene to Ethylene

The selective hydrogenation of acetylene to ethylene in an ethylene‐rich gas stream is an important process in the chemical industry. Pd‐based catalysts are widely used in this reaction due to their excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single‐atom catalysts on nitrogen‐doped graphene (Pd₁/N‐graphene) by a freeze‐drying‐assisted method is reported. The Pd₁/N‐graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C₂H₂ with H₂ in the presence of excess C₂H₄ under photothermal heating (UV and visible‐light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C₂H₄ hydrogenation. Importantly, the Pd₁/N‐graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar‐driven photothermal catalyst systems based on single‐atom active sites for selective hydrogenation reactions.     

纳米纤维素限域钯纳米颗粒的室温催化活性及化学选择性

本文利用水合低共熔溶剂结合超声法制备了羧基化纤维素纳米纤丝(CNF),并利用其表面的羧基官能团为反应活性位点原位合成了具有均匀分散性和高负载量(9.6 wt%)的CNF-Pd复合催化剂.研究结果表明:CNF-Pd具有显著的限域特性,包括在CNF表面羧基官能团上原位固定生长Pd纳米颗粒的化学限域和CNF冷冻干燥过程中自组...