Hydrodechlorination Activity Research Articles

Hydrogenolysis of carbon–halogen and carbon–carbon bonds over Pd/Nb2O5–Al2O3 catalysts

Pd/Nb2O5–Al2O3 catalysts exhibited interesting properties in the hydrodechlorination of dichlorodifluoromethane. Introduction of niobia to alumina increases the selectivity for CH2F2, from ∼40% (for Pd/ Al2O3) up to ∼75%, for similar metal dispersions. High-temperature reduction (773 K, HTR) of Pd/Nb2O5–Al2O3 generates the SMSI state, understood as blocking the Pd surface by (partly) reduced niobia. The extent of SMSI effect is judged from a direct comparison between the performance of differently pretreated Pd/Nb2O5–Al2O3 catalysts tested in n-hexane conversion (hydrogenolysis/isomerisation). After HTR of the niobia-containing Pd catalysts, the hydrodechlorination activity disappeared, however the SMSI state became reversed during hydrodechlorination. It is speculated that CCl2F2 and liberated HCl, interact with NbOx decorants, converting them into volatile niobium oxychloride species.

The hydrodechlorination of chlorobenzene in the vapor phase in the presence of metal-carbon nanocomposites based on nickel, palladium, and iron

Metal-carbon nanocomposites based on nickel, palladium, and iron and bimetallic palladium-nickel-carbon nanocomposites were for the first time used as catalysts of hydrodechlorination of chlorobenzene in the vapor phase in the atmosphere of hydrogen. Nickel and Pd-Ni nanoparticles completely coated by a carbon layer not only were stable to oxidation and agglomeration but also exhibited considerable activity in hydrodechlorination of chlorobenzene at temperatures much lower than those at which dechlorination on carbon carriers occurred. The dependence of catalytic properties (activity, selectivity, and stability) on temperature and nanocomposite composition was studied. Depending on the nature of the metal, the composition of bimetallic particles and temperature the selectivity could be changed, and the reaction could be directed toward the formation of benzene or cyclohexane. Carbon coating was stable under reaction conditions at least up to 350°C and did not hinder hydrodechlorination. Substrate adsorption likely occurred on the outside carbon surface of composite particles. The activity and structure of Ni@C composite remained almost unchanged after triple cycling over the temperature range from 50 to 350°C in a flow system.

Novel one step preparation of silica supported Pd/Sr and Pd/Ba catalysts via an organometallic precursor: Application in hydrodechlorination and hydrogenation

A gas phase hydrodechlorination (HDC) of chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB) has been examined over Pd/SiO 2 (prepared by impregnation with Pd(C 2H 3O 2) 2) and two alkaline earth metal (AEM = Sr and Ba) promoted Pd/SiO 2 catalysts prepared from the organometallic precursor {(DMF) x AEMPd(CN) 4} ∞ (AEM = Sr, Ba; x = 4, 3). While Sr/SiO 2 or Ba/SiO 2 exhibited no measurable HDC activity, the bimetallic catalysts delivered specific HDC rates (per Pd metal surface area) that were up to a factor of 20 times higher than that recorded for Pd/SiO 2. The initial fractional dechlorination recorded for Sr–Pd/SiO 2 and Ba–Pd/SiO 2 was up to two orders of magnitude greater than that for Pd/SiO 2. We associate this promotional effect with a surface Pd/AEM synergy that enhances Pd dispersion with a resultant increase in H 2 chemisorption capacity allied to a more effective C–Cl bond activation for hydrogen scission. Bulk and surface catalyst characteristics, pre-and post-reaction, have been probed by IR, BET, TPR, H 2 chemisorption/TPD, XRD, XPS and TEM-EDX analyses. While 1,2-DCB conversion over Pd/SiO 2 was lower than that observed for CB due to inhibitory inductive and steric effects, CB and DCB reactivity were comparable over AEM-Pd/SiO 2. Each catalyst exhibited a temporal decline in HDC performance that we link to deleterious Cl interactions which impact H 2 uptake/release capacity. Although the bimetallic catalysts were less susceptible to deactivation, the samples post-HDC retain an appreciable Cl content with a redispersion of both AEM and Pd components and a disruption to the surface electronic characteristics that is apparent from the XPS profiles. The presence of AEM had no effect on benzene hydrogenation performance over freshly activated samples but post-HDC, Pd/SiO 2 exhibited depleted hydrogenation activity whereas both bimetallics (notably Sr–Pd/SiO 2) generated a significantly enhanced hydrogenation response that we ascribe to a surface restructuring that is beneficial for aromatic reduction.

Influence of particle size and nature of Pd species on the hydrodechlorination of chloroaromatics: Studies on Pd/TiO 2 catalysts in chlorobenzene conversion

TiO 2 supported Pd catalysts were synthesized by two different preparation methods namely conventional impregnation (IMP) and deposition-precipitation methods (DP) using two precursor salts Pd(NO 3) 2 and PdCl 2. The catalysts were characterized by various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature programmed reduction (TPR), CO chemisorption and BET surface area. The catalysts were evaluated for the gas phase hydrodechlorination (HDC) of chlorobenzene (CB) operating at atmospheric pressure. The catalyst prepared by deposition-precipitation using the chloride precursor (DP-Cl) exhibited higher dispersion and different electronic properties compared to the other catalysts. It also exhibited exceptional hydrodechlorination activity and stability. The generation of active electron deficient Pd species (Pd n+ ) on the catalyst surface appears to be the main reason for this behavior.

Hydrodechlorination of Chlorobenzene over Silica-Supported Nickel Phosphide Catalysts

Silica-supported Ni3P, Ni12P5, and Ni2P catalysts were prepared by the temperature-programmed reduction method from nickel phosphate precursors. A Ni/SiO2 catalyst was also prepared as a reference. The effect of the initial Ni/P molar ratio in the precursor on the catalyst structure and hydrodechlorination performance was investigated. The physicochemical properties of the catalysts were characterized by means of N2 adsorption, hydrogen temperature-programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet and visible spectroscopy, hydrogen temperature-programmed desorption, and inductively coupled plasma spectroscopy. The catalyst activities in the hydrodechlorination of chlorobenzene were evaluated in a fixed-bed reactor at atmospheric pressure. The silica-supported nickel phosphides exhibited superior hydrodechlorination activities to that of supported nickel. This can be attributed to the special physicochemical properties of nickel phosphides and a great amount of spillover hydrogen species. In nickel phosphides, there is a small amount of electron transfer from Ni to P, leading to a small positive charge on Ni. This favors a weakening of the interaction between chlorine and nickel sites, as well as between adsorbed hydrogen species and nickel phosphides. The “ensemble effect” of P is also beneficial in decreasing the coverage of chlorine on nickel sites. Because of the reduced interaction between adsorbed hydrogen species and nickel phosphides, the energy barrier of the hydrogen spillover on the silica-supported nickel phosphide catalysts decreases, which accounts for the increased amount of spillover hydrogen species on the catalyst surface. Spillover hydrogen species not only promote the hydrogenolysis of the C−Cl bond, but also favor the removal of chlorine ions from the surface of the catalysts. Hydrodechlorination over the nickel phosphide catalysts is characterized by a reaction induction period that becomes longer with increasing phosphorus content in the catalyst precursor. This is related to the blocking of active sites by excess phosphorus.

Synthesis of a nano-nickel catalyst modified by ruthenium for hydrogenation and hydrodechlorination

Abstract A nano-nickel catalyst was prepared by chemical reduction with N2H4·H2O, and was modified with ruthenium by chemical replacement. The nano-Ni and NiRu catalysts were characterized by X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy. The catalysts were evaluated in the liquid phase hydrogenation of cinnamaldehyde and hydrodechlorination of chlorobenzene. The NiRu catalyst exhibited a much higher selectivity to the hydrocinnamaldehyde and a better hydrodechlorination activity and stability than those of the Ni catalyst.

Effect of surface acid groups associated with amorphous and structured carbon on the catalytic hydrodechlorination of chlorobenzenes

AbstractBACKGROUND: Catalytic hydrodechlorination (HDC) is a progressive approach to treating chlorinated waste streams. While carbon is widely used as a catalyst support, the influence of carbon surface functionality on HDC performance has not been established. This work sets out to assess the impact of surface acid groups associated with activated carbon (AC), graphite and graphitic nanofibers (GNF) on Pd promoted gas phase HDC of chlorobenzene (CB) and 1,3‐dichlorobenzene (DCB).RESULTS: The acid groups were introduced by HNO3 washing and the HDC reaction performed over bulk Pd and Pd physically mixed with each carbon. The carbon was subjected to a thermal treatment to remove the surface acidity. Characterization was by temperature programmed decomposition (TPD), temperature programmed hydrogen treatment (TPH), BET area, acid‐base titration, scanning and transmission electron microscopy. TPD, TPH and titration analyses served to establish the presence of surface oxygen groups after acid washing and facilitated an evaluation of the effectiveness of the thermal treatment to remove these groups.CONCLUSIONS: The surface acid groups inhibited HDC activity, a response most pronounced for Pd + AC, less so for Pd + graphite, while the effect was slight for Pd + GNF. HDC inhibition is attributed to chloroarene interaction with the surface functional (notably carboxylic) groups that impedes HDC. Fractional dechlorination of DCB was equivalent to or lower than CB HDC; there is some evidence of DCB interactions with heat treated graphite and GNF that served to raise HDC activity. Effective HDC over carbon based catalysts requires removal of surface acid groups. Copyright © 2008 Society of Chemical Industry

Influence of Pd Precursor and Method of Preparation on Hydrodechlorination Activity of Alumina Supported Palladium Catalysts

A series of alumina supported Pd catalysts were prepared by the novel deposition-precipitation method adopting the chloride precursor (DP-Cl) of Pd and varying the metal content from 0.25 to 1.0 wt%. The catalytic properties of prepared catalysts were studied by various characterization techniques such as N2 adsorption, CO chemisorption, TPR, XRD, XPS, and TEM techniques. The activity and stability of the catalysts were evaluated for the gas phase hydrodechlorination (HDC) of chlorobenzene operating at atmospheric pressure. At 1 wt% of Pd the catalyst showed higher chlorobenzene conversion with good stability when tested for a period of 25 h, whereas the other catalysts exhibited a loss in activity with time. In order to elucidate the exceptional activity and stability of this catalyst, a few more catalysts with 1 wt% Pd were prepared by impregnation technique and also using a non-chloride precursor, palladium nitrate. The 1 wt% DP-Cl catalyst again was found to be the best among the others. The activity and stability of the DP-Cl catalyst was also found to be superior to two low-dispersed catalysts, each with 10 wt% Pd, prepared by conventional impregnation method using the chloride and nitrate as the precursors. The characterization results reveal that the high activity and stability of the DP-Cl catalyst is related to the formation of electron deficient Pd species and its stabilization in the octahedral vacancies of alumina.

Palladium on ultradisperse diamond and activated carbon: the relation between structure and activity in hydrodechlorination

Ultradisperse diamond was studied as a promising carrier for Pd-containing hydrodechlorination catalysts. Transmission electron microscopy, temperature-programmed reduction, and the adsorption method were used to study catalysts on ultradisperse diamond and activated carbon and a commercial catalyst from Fluca. Catalyst activities in multiphase hydrodechlorination of chlorobenzenes were compared. The activity of Pd-containing catalysts on ultradisperse diamond was found to be several orders of magnitude higher than that of Pd catalysts on activated carbon.

Silica- and titania-supported Ni–Au: Application in catalytic hydrodechlorination

The catalytic gas-phase (473 K) hydrodechlorination (HDC) of 2,4-dichlorophenol has been investigated over Ni/SiO 2, Ni/TiO 2, Ni–Au/SiO 2, and Ni/Au–TiO 2 (Ni loading ca. 5 wt%; bulk Ni/Au atomic ratio = 10). The samples were prepared by either (co-)impregnation or (co-)deposition–precipitation. The catalyst samples were characterized in terms of BET surface area, TPR, H 2 chemisorption, and TEM-EDX measurements. The impregnated Ni/SiO 2 and Ni/TiO 2 samples had a similar narrow Ni particle size distribution (1–6 nm). The addition of Au to both Ni/support samples lowered the temperature requirements for Ni II reduction and suppressed H 2 chemisorption. The impregnated Ni–Au/SiO 2 (10–150 nm) and Ni–Au/TiO 2 (2–95 nm) were characterized by a wider range of particle sizes than the monometallic nickel catalysts and a variable surface Ni/Au atomic ratio (<1–40). In comparison, Ni–Au/TiO 2 prepared by deposition–precipitation exhibited a narrower particle size range (2–60 nm) and a more uniform Ni and Au surface distribution (Ni/Au atomic ratio of <1–15). The titania-supported catalysts delivered significantly higher specific HDC rates and distinct HDC selectivities than the silica systems, with catalytic responses discussed in terms of metal–support and reactant–surface interactions. The incorporation of Au, regardless of the support or method of preparation, resulted in higher HDC activity, an effect attributed to a surface Ni–Au synergism. Hydrogen thermal treatment of the bimetallic catalysts after reaction resulted in appreciable surface reconstruction, notably a more homogeneous combination of Ni and Au in smaller particles, which enhanced HDC performance.

A characterization of Ln-Pd/SiO 2 (Ln=La, Ce, Sm, Eu, Gd and Yb): Correlation of surface chemistry with hydrogenolysis activity

The gas phase hydrodechlorination (HDC) of chlorobenzene (CB), 1,2-dichlorobenzene (1,2-DCB) and 1,3-dichlorobenzene (1,3-DCB) has been investigated over Pd/SiO 2 and a series of Ln-Pd/SiO 2 prepared from the organometallic precursor{(DMF) 10Ln 2[Pd(CN) 4] 3} ∞ where Ln = La, Ce, Sm, Eu, Gd and Yb; Pd loading = 5%, w/w. Under identical reaction conditions, the following overall sequence of increasing initial fractional dechlorination has been established: Pd/SiO 2 < Yb-Pd/SiO 2 ≈ Sm-Pd/SiO 2 < Gd-Pd/SiO 2 < La-Pd/SiO 2 ≈ Ce-Pd/SiO 2 < Eu-Pd/SiO 2; reaction over Ln/SiO 2 resulted in a negligible conversion. HDC activity declined with time-on-stream but the Ln-Pd/SiO 2 catalysts maintained a significantly higher fractional HDC than Pd/SiO 2; loss of activity is attributed to deleterious HCl/surface interactions. The pre- and post- reaction catalyst samples have been characterized in terms of BET area, TPR, TEM, H 2 chemisorption/TPD, XRD and XPS analyses. When compared with Pd/SiO 2, Pd is present in the Ln-Pd/SiO 2 samples as much smaller particles, while the lanthanide component is finely dispersed over the surface, i.e. Ln is in intimate contact with Pd. The promotional effect of Ln in Ln-Pd/SiO 2 is attributed to a surface Pd/Ln synergism resulting in an enhancement of surface reactive hydrogen and a more effective C Cl bond activation for hydrogenolytic attack. HDC performance is discussed in terms of surface composition, Pd particle size, Ln electronic structure and H 2 uptake/release dynamics.

Effects of Tin on Product Distribution and Catalyst Stability in Hydrodechlorination of CCl4 over Pt-Sn/γ-Al2O3

The Pt−Sn/γ-Al2O3 catalyst with a moderate amount of tin showed an enhanced catalytic stability and selectivity to CHCl3 in hydrodechlorination of CCl4 compared to monometallic platinum catalyst. The tin added in consecutive order to 1.0wt%Pt/γ-Al2O3 acted as a diluting component of platinum ensemble sites and resulted in reducing the formation of C2 compounds and carbon deposition. Furthermore, tin addition modifies the electronic state of supported platinum particles by the electron transfer from tin to platinum, results in the reduction of the binding energy of intermediate species, and suppresses the complete hydrodechlorination activity of surface intermediates. Thus on Pt−Sn/γ-Al2O3 catalysts, adsorbed CCl4 is readily desorbed as CHCl3 instead of residing too long on the surface until it is completely dechlorinated to form CH4.

Catalytic hydrodechlorination on palladium-containing catalysts

The catalytic liquid-phase hydrodechlorination of chlorobenzene on supported palladium-containing catalysts has been investigated. The following processes capable of deactivating the catalyst occur during the liquid-phase hydrodechlorination: the coarsening of supported metal particles, the washoff of the active component with the reaction medium, and potassium chloride deposition on the catalyst surface. The effects of the active component composition and of the preparation method on the hydrodechlorination activity and deactivation stability of the catalysts have been studied. The catalysts have been characterized by several physical methods.

Aqueous-Phase Hydrodechlorination of 2,4-Dichlorophenol over Pd/Al2O3: Reaction under Controlled pH

The aqueous-phase hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP) over a Pd/Al2O3 catalyst has been studied with adjustment of the bulk solution pH either by base (NaOH and NH4OH) addition prereaction or with a continual supply of base during HDC. With a starting pH in the range 7−11.6, the solution pH can be controlled to within ±0.1 with an external supply of NaOH during HDC. A preliminary kinetic analysis suggests that 2,4-DCP HDC is predominately stepwise, yielding 2-chlorophenol (2-CP) as the partially dechlorinated product, which is further converted to phenol and ultimately to cyclohexanone. Pd/Al2O3, operating under controlled pH, delivered maximum HDC activity in the pH range 7−8, where the selectivity with respect to 2-CP was lower than that associated with pH = 11.6. In the absence of mass transport constraints, initial HDC rate as a function of 2,4-DCP concentration exhibits Langmuir−Hinshelwood mechanistic behavior involving competitive adsorption of H2 and 2,4-DCP with the surface ...

Methods for the preparation of bimetallic xerogel catalysts designed for chlorinated wastes processing

The aim of this work is to simplify and generalize the synthesis procedure of bimetallic supported catalysts by sol–gel process. For Pd–Ag/SiO2 co-gelled xerogels catalysts a number of synthesis procedures were compared: use of one or two specific alkoxides able to form a chelate with palladium and/or silver cations, reagent mixing in one or two steps, use of industrial grade chemicals instead of laboratory grade chemicals. The catalysts obtained are quite similar: same metal dispersion, same tailored morphology, same localization and accessibility of Pd–Ag alloy nanoparticles inside microporous silica, same activity and selectivity for hydrodechlorination of 1,2-dichloroethane into ethylene. For catalyst production at large scale the synthesis can be achieved in one step with 3-(2-aminoethyl)aminopropyltrimethoxysilane of industrial grade as chelating alkoxide, tetraethylorthosilicate (TEOS) of industrial grade and ethanol denatured with diethyl phthalate.

Synthesis and characterization of novel silica-supported Pd/Yb bimetallic catalysts: Application in gas-phase hydrodechlorination and hydrogenation

The gas-phase hydrodechlorination (HDC) of chlorobenzene (CB), 1,2-dichlorobenzene (1,2-DCB), and 1,3-dichlorobenzene (1,3-DCB) was investigated over a 5% w/w Pd/SiO 2 and a series of SiO 2-supported Yb–Pd (5% w/w Pd and Yb / Pd = 2 / 3 mol / mol ) catalysts. The Pd/SiO 2 catalyst was prepared by Pd(C 2H 3O 2) 2 impregnation, supported Yb synthesized by contacting SiO 2 with Yb powder in liquid NH 3 and the bimetallic catalysts prepared by two stepwise routes: Pd(C 2H 3O 2) 2 impregnation of Yb/SiO 2 (Pd–Yb/SiO 2-step) or Pd impregnation preceding Yb introduction (Yb–Pd/SiO 2-step) and a single-step simultaneous introduction of Pd and Yb from a {(DMF) 10Yb 2[Pd(CN) 4] 3} ∞ precursor (Yb/Pd/SiO 2-sim). Under identical reaction conditions, the following specific initial CB HDC rate sequence was established: Pd–Yb/SiO 2-step (0.21 mol Cl h −1 m −2) ≈ Pd/SiO 2 (0.24 mol Cl h −1 m −2) < Yb/Pd/SiO 2-sim (0.41 mol Cl h −1 m −2) ≈ Yb–Pd/SiO 2-step (0.46 mol Cl h −1 m −2); reaction over Yb/SiO 2 resulted in a negligible conversion. Yb acts as a CB HDC promoter through a surface synergism with Pd; the extent of this promotion depends on the nature of the catalyst precursor and the sequence of metal(s) introduction to the support. The promotional effect of Yb extends to DCB HDC, where Yb–Pd/SiO 2-step outperforms Yb/Pd/SiO 2-sim (with a specific HDC rate 25 times greater than that delivered by Pd/SiO 2) and to catalytic hydrogenation (benzene → cyclohexane). The prereaction and postreaction catalyst samples were characterized in terms of BET area, TPR, TEM-EDX, H 2 chemisorption/TPD, XRD, and XPS measurements. The role of Yb as a promoter is discussed in terms of electron donation and impact on Pd dispersion but is attributed to the action of YbH 2, which serves as an additional source of surface reactive hydrogen; Yb activation of the C Cl bond(s) for hydrogenolytic attack is also considered. HDC activity decreased with time-on-stream, an effect that we link to deleterious HCl/catalyst interactions that modify surface composition, leading to a disruption in H 2 uptake/release; XPS and TEM-EDX were used to characterize the residual surface Cl post-HDC.

Use of unsupported and silica supported molybdenum carbide to treat chloroarene gas streams

The gas phase catalytic hydrodechlorination (HDC) of mono- and di-chlorobenzenes (423K≤T≤593K) over unsupported and silica supported Mo carbide (Mo2C) is presented as a viable means of detoxifying Cl-containing gas streams for the recovery/reuse of valuable chemical feedstock. The action of Mo2C/SiO2 is compared with MoO3/SiO2 and Ni/SiO2 (an established HDC catalyst). The pre- and post-HDC catalyst samples have been characterized in terms of BET area, TG-MS, TPR, TEM, SEM, H2 chemisorption/TPD and XRD analysis. Molybdenum carbide was prepared via a two step temperature programmed synthesis where MoO3 was first subjected to a nitridation in NH3 followed by carbidization in a CH4/H2 mixture to yield a face-centred cubic (α-Mo2C) structure characterized by a platelet morphology. Pseudo-first order kinetic analysis was used to obtain chlorobenzene HDC rate constants and the associated temperature dependences yielded apparent activation energies that decreased in the order MoO3/SiO2 (80±5kJmol−1)≈MoO3 (78±8kJmol−1)>Ni/SiO2 (62±3kJmol−1)≈α-Mo2C (56±6kJmol−1)≈α-Mo2C/SiO2 (53±3kJmol−1). HDC activity was lower for the dechlorination of the dichlorobenzene reactants where steric hindrance influenced chloro-isomer reactivity. Supporting α-Mo2C on silica served to elevate HDC performance, but under identical reaction conditions, Ni/SiO2 consistently delivered a higher initial HDC activity. Nevertheless, the decline in HDC performance with time-on-stream for Ni/SiO2 was such that activity converged with that of α-Mo2C/SiO2 after three reaction cycles. A temporal loss of HDC activity (less extreme for the carbides) was observed for each catalyst that was studied and is linked to a disruption to supply of surface active hydrogen as a result of prolonged Cl/catalyst interaction.

Catalytic hydrodechlorination of 2,4-dichlorophenol on Pd/Rh/C catalysts

Catalytic hydrodechlorination of 2,4-dichlorophenol was studied over 0.97% Pd/C, 0.98% Rh/C and 0.8% Pd–0.19% Rh/C catalysts. The catalysts were prepared by incipient wetness impregnation of support and characterized by BET surface area, temperature programmed reduction (TPR) and X-ray diffraction (XRD). The 0.97% Pd/C catalyst, which had the largest crystallite size, was the most active and selective towards the formation of 2- and 4-chlorophenols among three catalysts in liquid phase. Hydrodechlorination activity of carbon-supported catalysts were in the order of Pd/C > Pd/Rh/C > Rh/C. The kinetic equation explained experimental data well and kinetic parameters of three catalysts were provided and discussed.

Catalytic hydrodechlorination over Pd supported on amorphous and structured carbon

The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene has been studied ( T = 423 K ) over Pd ( 8 ± 1 wt% ) supported on activated carbon (Pd/AC), graphite (Pd/graphite), and graphitic carbon nanofiber (Pd/GNF). The activated carbon (875 m 2 g −1) and graphite (11 m 2 g −1) substrates were obtained from a commercial source, but the carbon nanofibers (74 m 2 g −1) were synthesized by ethylene decomposition over unsupported Ni to yield a mean fiber diameter of 225 nm. Under identical reaction conditions, the following initial HDC activity sequence was established: Pd/GNF ≈ Pd/AC > Pd/graphite. HDC activity declined with time-on-stream (four reaction cycles were considered), where Pd/GNF maintained a significantly higher fractional HDC and Pd/AC activity decreased continually to converge with Pd/graphite at a common residual conversion. The prereaction and postreaction catalyst samples were characterized by BET area/pore size analysis, temperature-programmed reduction, transmission electron microscopy, scanning electron microscopy, H 2 chemisorption/temperature-programmed desorption (TPD), X-ray diffraction (XRD), and acid/base titration. Pd size distribution is given in each case where surface area-weighted Pd diameter increased in the order: Pd/graphite < Pd/GNF < Pd/AC. The spent catalysts exhibited lower H 2 uptake with a disruption to the TPD profiles. Pd on each support adopted (on the basis of XRD analysis) an exclusive cubic geometry, but whereas the particles on AC were globular in nature, faceted Pd particles predominated on the graphite and (to a lesser extent) GNF supports. HDC activity and temporal behavior is rationalized on the basis of metal–support interactions, Pd particle size, and H 2 uptake/release characteristics.

Rapid dechlorination of chlorinated organic compounds by nickel/iron bimetallic system in water

Detoxification of chlorinated organic compounds via reaction with nickel/iron powder was implemented in aqueous solution. Compared to iron, nickel/iron bimetallic powder had higher hydrodechlorination activities for both atrazine (ATR) andp-chlorophenol (pCP); nickel/iron (2.96%, w/w) was shown to have the largest specific surface area and the optimum proportion for the dechlorination of both ATR andpCP. Electrochemical measurements showed that the adsorbed hydrogen atom on the nickel must have been the dominant reductive agent for the dechlorination of both ATR andpCP in this system.