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Applied Catalysis B, Environmental (v.59, #3-4)
Preparation and characterization of nanosized anatase TiO2 cuboids for photocatalysis by Hai Wang; Yu Wu; Bo-Qing Xu (pp. 139-146).
Without use of any templates or shape-protectors, uniformly sized anatase TiO2 nanocrystallites with cuboidal morphology were synthesized by changing titanium hydroxide precipitates into their corresponding ethanol-gels (viz. by washing several times with anhydrous ethanol) followed by drying in supercritical ethanol (7.0MPa, 270°C) and calcination at high temperature (AS-preparation). Characterizations with X-ray diffraction (XRD), Raman spectroscopy and nitrogen adsorption suggest that the cuboidal anatase nanocrystallites are highly resistant to thermal sintering. The anatase structure of the cuboidal nanocrystallites was maintained even after calcinations up to temperatures as high as 800°C. Thermogravimetric (TG) measurements in flowing air show that the as-prepared cuboidal TiO2 nanocrystallites were contaminated with some carbonaceous residues, which can be completely removed by calcination at 500°C in air. Application of these cuboidal TiO2 nanocrystallites as photocatalytic materials was evaluated by photocatalytic degradation of methyl orange in water. With increasing the calcination temperature up to 800°C, the photocatalytic activities of anatase TiO2 cuboids increased gradually due to improved crystallization of the material. The sample calcined at 800°C afforded the highest photocatalytic activity, which is comparable to that of the commercial photocatalyst Degussa P-25. Due to the presence of carbonaceous residues after the supercritical drying in the preparation, the samples calcined at temperatures no higher than 400°C showed higher photocatalytic activities than the sample calcined at 500°C. However, further calcination of the sample at 1000°C led to drastic reduction in the photocatalytic activity due to the anatase-to-rutile phase transformation and sintering of the material.
Keywords: Anatase TiO; 2; Cuboidal nanocrystallites; Catalyst preparation; Phase transformation; Photocatalysis; Methyl orange
Phototransformation of metobromuron in the presence of TiO2 by Amina Amine-Khodja; Abdelaziz Boulkamh; Claire Richard (pp. 147-154).
The photocatalytic degradation of the herbicide metobromuron was studied, using TiO2 photocatalysts (Degussa P25 and Millennium PC50, PC100, PC105 and PC500). Intermediate products were identified by means of liquid chromatography–mass spectrometry (LC–MS–MS) using electrospray (ES) interfacing technique. In order of importance, the main reaction pathways were demethoxylation of the urea chain, ring oxidation leading to ortho hydroxylation with respect to the N atom, substitution of Br by OH, ring oxidation with formation of the meta hydroxylated compound. Demethylation of the demethoxylated product occurred as a secondary reaction. Formation of bromide ions was observed too. In the presence of 2-propanol used as a hydroxyl radical scavenger, demethoxylation was drastically inhibited while the other reactions were only partly inhibited. It suggests that demethoxylation was exclusively due to the oxidation by hydroxyl radicals, whereas the other reactions involved positive holes too. The degradation rate of metobromuron varied in the order: PC502 Degussa P25 was therefore the most efficient photocatalyst although its surface area was lower than that of most of Millennium TiO2.
Keywords: Photocatalysis; Photodegradation; TiO; 2; Phenylurea; LC–MS–MS
Decomposition of nonionic surfactant in a labyrinth flow photoreactor with immobilized TiO2 bed by Sylwia Mozia; Maria Tomaszewska; Antoni W. Morawski (pp. 155-160).
The photocatalytic oxidation of nonionic surfactant polyoxyethylene nonyl phenyl ether (Rokafenol N9) in water in the labyrinth flow reactor with immobilized catalyst bed was investigated. Tytanpol A11 titanium dioxide supplied by Chemical Factory “Police� S.A. (Poland) was used as a photocatalyst. The influence of various factors, including reaction mixture flow rate, initial surfactant concentration and time of the process performance on the photodegradation of model compound were examined. It was found that the effect of the initial surfactant concentration on the effectiveness of Rokafenol N9 removal was practically negligible in the range of the investigation, whereas the reaction mixture flow rate has a significant effect on the effectiveness of Rokafenol N9 decomposition. The highest surfactant photodegradation (92%) was obtained at the solution flow rate equal to 11.98dm3/h and the lowest (86%) at 1.64dm3/h. The apparent rate constant k was linearly dependent on the reaction mixture flow rate. Extension of the reaction time from 5 to 60h did not result in a complete mineralization of Rokafenol N9 to CO2 and water.
Keywords: Titanium dioxide; Surfactant; Polyoxyethylene nonyl phenyl ether; Photodegradation; Photocatalysis; Photocatalyst immobilization; Labyrinth flow reactor
Photoredox processes in the Cr(VI)–Cr(III)–oxalate system and their environmental relevance by Piotr Mytych; Paweł Cieśla; Zofia Stasicka (pp. 161-170).
Irradiation of the [Cr(C2O4)3]3− complex or the chromate(VI)–oxalate mixture, or the ternary system composed of Cr(III), Cr(VI) and oxalate, leads to chromium photoreductions in consequence of the ligand to metal charge transfer (LMCT) excitations induced by artificial solar radiation. In the case of the Cr(III) complex, the photoreduction involves the innersphere electron transfer leading to the formation of the Cr(II) species and the C2O4− radicals. On reacting with molecular oxygen, Cr(II) is oxidised to Cr(III) catalysing thereby the oxalate substitution reaction. Moreover, under specific conditions, Cr(II) can be also oxidised to Cr(VI). Chromate(VI) is not photoreducible, but in the presence of oxalate, or other sacrificial electron donor, the outersphere photoinduced electron transfer (PET) produces Cr(V) species and the C2O4− radicals. This initiates a series of thermal reactions leading to the formation of Cr(III) and oxidized oxalate (CO2). In the system composed of [Cr(C2O4)3]3− and chromate(VI), the acidic medium and anoxic conditions favour the Cr(VI) photoreduction, whereas alkaline oxygenated solutions assist the Cr(VI) photoproduction. When an approximately neutral solution equilibrated with the ambient air is irradiated intermittently, Cr(VI) is consumed and/or produced, accordingly to the time sequence of exposure and dark periods. The oscillations of Cr(VI) concentrations are accompanied by continuous oxidation of oxalate, playing the role of the sacrificial electron donor. The effects of solution pH, molecular oxygen, concentrations of reagents and cations on the reaction rates were investigated. The results of this paper revealed that the Cr(III)/Cr(VI) system under environmental conditions behaves as the photocatalytic one catalysing the oxidation of oxalate or other organic matter by molecular oxygen, contributing thereby to the abatement of pollution.
Keywords: Chromate(VI); Chromium(III); Oxalate; Photoreduction; Photoinduced electron transfer (PET); Oxalate photodegradation
Catalytic effects of activated carbon on hydrolysis reactions of chlorinated organic compounds by Katrin Mackenzie; Juergen Battke; Robert Koehler; Frank-Dieter Kopinke (pp. 171-179).
The hydrolysis reaction of 1,1,2,2-tetrachloroethane (TeCA) is significantly enhanced by sorption on activated carbon. TeCA is quantitatively transformed into trichloroethene (TCE) at moderate pH values. This transformation is exploited as the basic step of a site-adapted groundwater-cleanup technology. The volatility of TCE is a factor of 23 higher than that of TeCA such that the partially dehydrochlorinated product can be easily stripped out of the groundwater flow. The base-mediated and the neutral dehydrochlorination of TeCA were studied as a function of temperature and pH value in batch and column experiments. Surprisingly, it was found that despite high loadings of the sorbent with TeCA and TCE (≥20wt.%) the TeCA remains available for the hydrolysis reaction.
Keywords: Activated carbon; Dehydrochlorination; Hydrolysis; 1,1,2,2-Tetrachloroethane
N2O conversion using manganese binary mixtures supported on activated carbon by Sónia A. Carabineiro; F. Brás Fernandes; Joaquim S. Vital; Ana M. Ramos; Isabel M. Fonseca (pp. 181-186).
Detailed kinetics of N2O conversion and carbon gasification over solids comprised of activated carbon impregnated with Ba, Co, Cu, Fe, Mg, Mn, Ni, Pb and V precursors salts were studied using a GC/MS system. The gasification rates of carbons impregnated with binary mixtures of Mn with other metals were also tested in the temperature range between 300 and 800°C using a microbalance. Synergetic effects were found for all mixtures. The highest rates were obtained for catalysts loaded with Mn+Ba and Mn+Cu. Near complete conversions were obtained around 350°C for the binary Mn mixtures. N2 and CO2 were detected in a stoichiometry of approximately 2:1. Some CO formation was observed at higher temperatures (above 750°C). In situ XRD was carried out to identify the phases present during reactions. The ability of the metal catalysts to melt and spread on the carbon surface and chemisorb the gases going through redox transference of oxygen to the carbon reactive sites seems to explain catalytic reactivity.
Keywords: Nitrous oxide (N; 2; O); Conversion; Kinetics; Catalysis; X-ray diffraction
Pt-Ba/alumina NO x storage-reduction catalysts: Effect of Ba-loading on build-up, stability and reactivity of Ba-containing phases by M. Piacentini; M. Maciejewski; A. Baiker (pp. 187-195).
A series of Pt-Ba/Al2O3 catalysts with Ba-loadings in the range 4.5–28wt.% has been prepared by wet impregnation of Pt/Al2O3 with barium acetate (Ba(Ac)2) as Ba precursor. The build-up and thermal stability of the deposited Ba-containing species was followed by means of XRD and thermogravimetry (TG) combined with mass spectroscopy (MS). Samples were characterized before and after thermal treatment (calcination). The study showed that the thermal stability of the Ba-containing phases depends on their interaction with the alumina support and the presence of dispersed platinum. In calcined catalysts, three different Ba-containing species could be distinguished based on their crystallinity and thermal stability. The relative concentration of these species varied with the Ba-loading. The first layer of Ba-containing species, corresponding to saturation of the alumina surface with Ba(Ac)2, contained up to 12.5wt.% of Ba in the form of amorphous BaO. Increasing the Ba-loading further resulted in 5–6wt.% of Ba in the form of amorphous carbonates with relatively low thermal stability (LT-BaCO3). At Ba-loadings higher than about 16wt.%, crystalline barium carbonate became discernible which exhibited remarkably higher thermal stability (HT-BaCO3). NO x storage tests accomplished by exposing the catalysts to pulses of NO in oxygen containing carrier gas at 300°C indicated that from all characterized Ba-containing phases, LT-BaCO3 possesses the highest reactivity for NO x storage, i.e. LT-BaCO3 is transformed most rapidly to Ba(NO3)2.
Keywords: NO; x; storage-reduction; Pt-Ba/Al; 2; O; 3; Effect of Ba-loading; Stability of Ba-containing phases; Thermogravimetry combined with mass spectrometry; Temperature programmed reaction-desorption; Barium oxide; Barium carbonate; Barium nitrate
Bio-recycling of hexanes from laboratory waste mixtures of hexanes and ethyl acetate by ester biotransformation: a green alternative process by Leandro H. Andrade; Patrícia B.Di. Vitta; Roberto S. Utsunomiya; Iracema H. Schoenlein-Crusius; André L.M. Porto; João V. Comasseto (pp. 197-203).
The action of different fungal strains and hydrolytic enzymes on the biotransformation of ethyl acetate constituent of laboratory wastes (mixtures of ethyl acetate–hexanes) was investigated. The studies using Aspergillus terreus SSP 1498 as biocatalyst, showed good results concerning the efficiency of ethyl acetate biotransformation (upto 99%) and quickness of the process (5min). Novozym 435 was found to be the best lipase for the hydrolysis of ethyl acetate from the waste (85% biotransformation).
Keywords: Biodegradation; Ethyl acetate; Hexanes; Biotransformation; Fungus; Enzymes
Nature of nitrogen specie in coke and their role in NO x formation during FCC catalyst regeneration by I.V. Babich; K. Seshan; L. Lefferts (pp. 205-211).
NO x emission during the regeneration of coked fluid catalytic cracking (FCC) catalysts is an environmental problem. In order to follow the route to NO x formation and try to find ways to suppress it, a coked industrial FCC catalyst has been prepared using model N-containing compounds, e.g., pyridine, pyrrole, aniline and hexadecane–pyridine mixture. Nitrogen present in the FCC feed is incorporated as polyaromatic compounds in the coke deposited on the catalyst during cracking. Its functionality has been characterized using XPS. Nitrogen specie of different types, namely, pyridine, pyrrolic or quaternary-nitrogen (Q-N) have been discriminated. Decomposition of the coke during the catalyst regeneration (temperature programmed oxidation (TPO) and isothermal oxidation) has been monitored by GC and MS measurements of the gaseous products formed. The pyrrolic- and pyridinic-type N specie, present more in the outer coke layers, are oxidized under conditions when still large amount of C or CO is available from coke to reduced NO x formed to N2. “Q-N� type species are present in the inner layer, strongly adsorbed on the acid sites on the catalyst. They are combusted last during regeneration. As most of the coke is already combusted at this point, lack of reductants (C, CO, etc.) results in the presence of NO x in the tail gas.
Keywords: NO; x; FCC; Regenerator; XPS
TiO2 coating types influencing the role of water vapor on the photocatalytic oxidation of methyl ethyl ketone in the gas phase by C. Raillard; V. Héquet; P. Le Cloirec; J. Legrand (pp. 213-220).
Four TiO2-based materials, named A, B, C and D, are used to investigate the influence of water vapor on the gas–solid adsorption and heterogeneous photocatalytic oxidation of gaseous methyl ethyl ketone (MEK). Two of the photocatalysts (A and B) are constituted of powdered TiO2 deposited onto two different supports (ordinary glass and non-woven cellulose fibers). The other ones (C and D) are composed of a thin film of TiO2 coated on glass substrates. The effect of water vapor on MEK initial conversion rates is studied for the four photocatalytic materials using the Langmuir–Hinshelwood model at the initial time. On the concentrations range where the model hypotheses are verified, adsorption constants K and kinetics constants k are calculated for experiments under both dry and humid atmosphere. When the relative humidity is increased, the evolution of these constants shows that water vapor acts differently depending on the form of deposited TiO2 (powder and film).
Keywords: Photocatalysis; TiO; 2; Powder; Film; Relative humidity; Methyl ethyl ketone
The selective catalytic oxidation of NH3 over Fe-ZSM-5 by Aaron Akah; Colin Cundy; Arthur Garforth (pp. 221-226).
The abatement of NH3 from waste streams has become an important environmental issue. Selective catalytic oxidation (SCO) of NH3 to N2 has emerged as a potential technology for taking care of NH3 slips and NH3 in waste streams. In this work, we describe the catalytic activity of Fe-zeolite catalysts prepared by incipient wetness technique, ion exchange and hydrothermal synthesis in the SCO of NH3 to N2 using a fixed bed flow reactor. Selective catalytic oxidation was carried out at 573–723K and 105Pa with gas hourly space velocities (GHSV) between 24000 and 240000h−1. Results obtained showed that Fe-ZSM-5 catalysts prepared by incipient wetness technique were active for NH3 conversion (77–100%) and selectivity to N2 (65–100%). Fe-ASA and Fe- Beta showed good catalytic activity and selectivity, but their activity and selectivity were less than that of Fe-ZSM-5. The effects of water vapour, Fe loading, and activation method on the performance of these catalysts was also investigated.
Keywords: Selective catalytic oxidation; Ammonia; ZSM-5; Impregnation
Reactivation of sintered Pt/Al2O3 oxidation catalysts by F. Cabello Galisteo; R. Mariscal; M. López Granados; J.L.G. Fierro; R.A. Daley; J.A. Anderson (pp. 227-233).
The reactivation of thermally sintered Pt/Al2O3 catalysts used in the simultaneous oxidation of CO and propene has been achieved by an oxychlorination treatment. The catalyst can be considered to model the active component of the catalytic converter fitted to diesel driven cars. Platinum crystallites redispersion was verified by XRD, H2 chemisorption, TEM and FTIR. The extent of regeneration reflects the platinum particle redispersion achieved by such a treatment. Oxychlorination also introduced electronic effects in the Pt particle caused by the presence of chlorine at the Pt-Al2O3 interface but no detrimental result of this was observed in the oxidation reactions. The results indicate that the deactivation of the diesel oxidation catalysts (DOCs) can be reverted by this simple treatment resulting in a remarkable recovery of the catalytic activity.
Keywords: Diesel oxidation catalyst; Sintering; Platinum; Reactivation; Oxychlorination
On the mechanism of selective catalytic reduction of NO by propylene over Cu-Al-MCM-41 by Ying Wan; Jianxin Ma; Zheng Wang; Wei Zhou; Serge Kaliaguine (pp. 235-242).
The selective catalytic reduction of NO by propene in the presence of excess oxygen over Cu-Al-MCM-41 catalyst has been studied by a number of catalytic techniques to characterize the structural, chemisorptive and reactive properties. The characterization using XRD and NMR revealed that the structure of Cu-Al-MCM-41 remained unchanged after the reaction. The active sites related to the reduction of NO and the reaction mechanism were explored based on the data of H2 temperature programmed reduction (TPR), NO temperature programmed desorption (TPD), X-ray spectrometry (XPS) and in situ FT-IR. The results showed that a redox of Cu ions in Cu-Al-MCM-41 between monovalent and divalent states happened during the selective catalytic reduction of NO, and the reduction seemed to proceed via the intermediate of organic nitro compounds produced by the reaction of propylene adspecies and NO2. In addition, the presence of oxygen is essential to the formation of NO2 intermediate and to the cycle of active center between Cu2+ and Cu+. However, it also caused the deep oxidation of propylene, leading to the depletion in reducing agent at higher temperature.
Keywords: Cu-Al-MCM-41 catalyst; Nitric oxide; Selective catalytic reduction; Mechanism
Synthesis, characterization and catalytic application for wet oxidation of phenol of iron-containing clays by M.N. Timofeeva; S.Ts. Khankhasaeva; S.V. Badmaeva; A.L. Chuvilin; E.B. Burgina; A.B. Ayupov; V.N. Panchenko; A.V. Kulikova (pp. 243-248).
High-surface-area pillared clays (PILC) were prepared from naturally occurring montmorillonites by exchanging interlayer ions to polyoxocations containing (i) aluminum (Al13-PILC), (ii) iron adsorpted onto Al13-PILC, and (iii) iron and aluminum located within the same complex (Fe0.8Al12.2-PILC). The obtained Fe0.8Al12.2-PILCs were characterized by DR–UV–vis and IR spectroscopy, XRD, ESR, scanning electron microscopy and low temperature N2 adsorption measurements. Important factors affecting catalyst activity and phenol removal efficiencies have been studied, i.e. the effect of pH, temperature, catalyst concentration and stability of the catalyst.
Keywords: Catalytic wet oxidation; Iron-containing pillared clay; Hydrogen peroxide; Phenol; Wastewater treatment
Reductive/oxidative treatment with superior performance relative to oxidative treatment during the degradation of 4-chlorophenol by P. Raja; A. Bozzi; W.F. Jardim; G. Mascolo; R. Renganathan; J. Kiwi (pp. 249-257).
This study obtained information on the effectiveness of the photo-assisted Fenton oxidation of 4-chlorophenol (4-CP) combined with zero-valent pretreatment. The kinetic rate parameters of the process as well as the operating conditions were determined. Homogeneous photo-assisted Fenton enhanced processes lead to ∼33% mineralization of 4-chlorophenol (1.25mM) in solutions containing Fe-ions (2–10mg/l) and H2O2 (10mM) within 2h under visible light irradiation. When this solution was pretreated with zero-valent Fe (14g/70ml) in Ar atmosphere, the mineralization attained levels of >80% after the second stage photo-assisted Fenton process. Intermediates that could be effectively degraded by photo-Fenton reactions were not attained in the absence of zero-valent Fe pretreatment. The pretreatment by zero-valent Fe under light lead to about 70% of the stoichiometric amount of chloride contained in 4-CP. Partial recovery of chloride ions indicated the formation of chloro-intermediates. These intermediates were experimentally detected by high-pressure liquid chromatograph (HPLC)–MS and the most important intermediates were identified. Fenton photo-assisted processes were effective employing very low concentrations of Fe2+(2–5mg/l) after the pretreatment stage that do not need to be separated after the 4-CP degradation process. This is important for the practical application of the novel combined heterogeneous–homogeneous process. Evidence for the stable catalytic performance of the coupled process to degrade 4-CP is presented. The effect on the 4-CP degradation of Fe-ion, H2O2, 4-CP concentration and gas atmosphere was systematically investigated. The activation energy ( Ea) of 2.66kJ/mol was found for the abatement of 4-CP.
Keywords: Heterogeneous/homogeneous photo-Fenton processes; Zero-valent Fe; 4-Chlorophenol decomposition; TOC reduction; Activation energy; GC–MS of intermediates; Reductive processes
Electrocatalytic oxidation of p-nitrophenol from aqueous solutions at Pb/PbO2 anodes by M.A. Quiroz; S. Reyna; C.A. Martínez-Huitle; S. Ferro; A. De Battisti (pp. 259-266).
In this work, the elimination of p-nitrophenol ( p-NPh) from aqueous solutions by electrochemical oxidation at Pb/PbO2 anodes was investigated. The process was studied under galvanostatic polarization mode in acidic and alkaline media, as a function of the temperature (20, 40 and 60°C) and of the anodic current density ( J=10, 20 and 30mAcm−2). In acidic media (0.5M H2SO4), the oxidation process allowed a 94% p-NPh conversion in 7h, at 20°C and with J=20mAcm−2, with a wide distribution of degradation products (in particular: 39% p-benzoquinone and 26% hydroquinone, as given by a mass balance at the above electrolysis time). Under these conditions, the current efficiency for the substrate oxidation was 15.4% ([AhL−1]exp=7 versus [AhL−1]theo=1.08AhL−1). In alkaline media (0.1M NaOH, pH 8.5), the most effective p-NPh elimination (97%) was obtained at 60°C, 20mAcm−2 and 420min of electrolysis time, again with the production of p-benzoquinone and hydroquinone (52.7 and 15.1%, respectively). Under the latter conditions, an almost complete chemical oxygen demand (COD) abatement was attained, with a high level of p-NPh mineralization (>80%), a yield of p-NPh conversion greater than 95% and a scarce formation of aliphatic acids (most probably maleic acid). From the degradation curves ([ p-NPh] versus t), in both acidic and alkaline media, the UV analyses and/or COD measurements, a complete oxidation of aliphatic acids to form CO2 could be predicted for electrolysis time >420min, according to a suggested oxidation pathway.
Keywords: Electrooxidation; Electrocatalytic degradation; p; -Nitrophenol; Pb/PbO; 2; anodes
Degradation of polycyclic aromatic hydrocarbons by hydrogen peroxide catalyzed by heterogeneous polymeric metal chelates by Petr Baldrian; Tomáš Cajthaml; Věra Merhautová; Jiřà Gabriel; František Nerud; Pavel Stopka; Martin Hrubý; Milan J. Beneš (pp. 267-274).
Chelating sorbents with 8-hydroxyquinoline (IVa), 8-hydroxyquinoline-5-sulfonic acid (IVb), and tris(2-aminoethyl)amine (VI) ligands immobilized on macroporous methacrylate matrix were prepared and saturated with Co(II), Cu(II), and Fe(II). All these chelates catalyze cleavage of H2O2 yielding highly reactive hydroxyl radicals. All were able to degrade by this mechanism polycyclic aromatic hydrocarbons (anthracene, benzo[ a]pyrene and benzo[ k]fluoranthene). The most effective catalystsIVa-Fe,IVb-Fe, andVI-Cu (25mg with 100μmol H2O2) performed complete decomposition of 33μg anthracene and benzo[ a]pyrene during one 7-day catalytic cycle at 25°C. The fastest decomposition proceeded during the 1st day of incubation; 75% of anthracene and 74% of benzo[ a]pyrene were decomposed byIVb-Co within the first 24h. More than 25% decomposition within the 1st day was also achieved withIVb-Fe,VI-Cu,IVa-Cu, andVI-Co for anthracene and more than 30% benzo[ a]pyrene was decomposed byIVb-Fe,VI-Cu,IVa-Cu, andIVb-Cu during the same period. 1,4-Anthracenedione was the main product of anthracene oxidation by all catalysts. The catalysts were stable at pH 2–11 depending on their structure and able to perform sequential catalytic cycles without regeneration.
Keywords: Degradation; Polycyclic aromatic hydrocarbon; Hydrogen peroxide; Heterogeneous catalysis; Metal chelate
Hydrodechlorination of 3-chloropyridine and chlorobenzene in methanol solution over alkali-modified zirconia-supported palladium catalysts by José M. Moreno; Maria A. Aramendía; Alberto Marinas; José M. Marinas; Francisco J. Urbano (pp. 275-283).
The liquid-phase hydrodechlorination of 3-chloropyridine and chlorobenzene has been studied over alkali-modified zirconia-supported palladium catalysts. The modification of the ZrO2 with alkali metal carbonates improves the catalytic activity of the final palladium catalyst. Therefore, the larger the ionic radii (Li+++), the greater the catalytic activity (TOF) of the palladium catalyst. For 3-chloropyridine, hydrodechlorination proceeds without catalyst deactivation. This is explained as the result of the interaction of reaction products (pyridine and HCl) forming pyridinium chloride, thus avoiding the detrimental effect of HCl on the palladium particles. Catalytic hydrodechlorination of chlorobenzene over Pd catalysts exhibits an initial catalytic activity (TOF) much lower than that of 3-chloropyridine and the Pd catalysts deactivate as the reaction proceeds. Finally, chlorobenzene hydrodehalogenation has also been carried out in the presence of an equimolecular amount of pyridine resulting in a decrease in the initial reaction rate on the one hand, but also in an increase in final conversion on the other.
Keywords: Alkali-modified zirconia; Palladium catalysts; Hydrodechlorination; Hydrodehalogenation; Catalyst deactivation