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Applied Catalysis B, Environmental (v.87, #1-2)
Preparation of black sand-based magnetic photocatalysts for photocatalytic oxidation of aqueous phenol by Mingliang Luo; Derek Bowden; Peter Brimblecombe (pp. 1-8).
A natural magnetic material, black sand, was used as cores to prepare a magnetic photocatalyst, which can be recovered using an external magnetic field. A surfactant-involved scheme was proposed to deposit a rough silica layer on the surface of black sand, which otherwise could not be coated with silica through a conventional scheme involving Stöber process. Titanium dioxide (TiO2) was deposited on the surface of the silica–black sand (Si/BS) through an impregnation process and a direct deposition process. The catalytic property of the resultant photocatalyst (Ti/Si/BS) was evaluated using the oxidation of aqueous phenol and exhibited less reactivity than Degussa P25 TiO2. The phenol removal efficiency showed a pH dependence, which was ascribed to pH effect on (a) the formation of*OH and (b) the electrostatic interaction between the photocatalyst and the substrate. The prepared photocatalyst is reusable despite slight deactivation caused by the mechanical loss of TiO2.
Keywords: Magnetic photocatalyst; Black sand; Titanium dioxide; Phenol; Silica coating
Ageing and SO2 resistance of Pd containing perovskite-type oxides by E. Tzimpilis; N. Moschoudis; M. Stoukides; P. Bekiaroglou (pp. 9-17).
The La0.91Mn0.85Ce0.24Pd0.05O z and La1.034Mn0.966Pd0.05O z perovskite-type oxides were prepared via a combination of the sol–gel and the combustion synthesis methods. They were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray, high resolution transmission electron microscopy and electron energy loss spectroscopy. The effect of ageing and SO2 on the catalytic effectiveness of the Pd/perovskite and of a Pd-based commercial three-way catalyst for stoichiometrically operating natural gas fuelled vehicles were investigated. The La1.034Mn0.966Pd0.05O z catalyst exhibited the highest thermal stability and, in contrast to the La0.91Mn0.85Ce0.24Pd0.05O z and the commercial catalyst, it appeared significantly activated in the presence of 8ppm SO2 in the reactant mixture. The formation of La–Pd mixed oxides or/and La2(Mn–Pd)O6, the enhanced surface Pd2+ composition and the low surface sulfur content were suggested as the possible reasons for the activation under sulfur environment.
Keywords: Pd catalysts; Pd–perovskites; Natural gas vehicles; Ageing; SO; 2; poisoning
Reduction of NO x by H2 on Pt/WO3/ZrO2 catalysts in oxygen-rich exhaust by F.J.P. Schott; P. Balle; J. Adler; S. Kureti (pp. 18-29).
This work addresses the low-temperature NO x abatement under oxygen-rich conditions using H2 as reductant. For this purpose Pt/ZrO2 and Pt/WO3/ZrO2 catalysts are developed and characterised by temperature-programmed desorption of H2 (H2-TPD), N2 physisorption (BET) and powder X-ray diffraction (PXRD). The most active catalyst is a Pt/WO3/ZrO2 pattern with a Pt load of 0.3wt.% and a W content of 11wt.%. This material reveals high deNO x activity below 200°C and high overall N2 selectivity of about 90%. Additionally, the catalyst exhibits outstanding hydrothermal stability as well as resistance against SO x. Furthermore, the transfer from the powder level to real honeycomb systems leads to promising performance as well.Diffuse reflectance Fourier transform infrared spectroscopic studies, kinetic modelling of temperature-programmed desorption of O2 (O2-TPD) and NO x-TPD examinations indicate that the pronounced H2-deNO x performance of the Pt/WO3/ZrO2 catalyst is related to the electronic interaction of WO3 with the precious metal. The tungsten promoter increases the electron density on the Pt thus activating the sample for H2-deNO x and N2 formation, respectively. Contrary, NO x surface species formed on the WO3/ZrO2 support are not supposed to be involved in the H2-deNO x reaction.
Keywords: NO; x; reduction; H; 2; Pt; WO; 3; ZrO; 2; Diesel exhaust; Mechanism; DRIFTS
Photoassisted degradation of endocrine disruptors over CuO x–FeOOH with H2O2 at neutral pH by Yulun Nie; Chun Hu; Jiuhui Qu; Xu Zhao (pp. 30-36).
CuO x-doped α-FeOOH (CuO x–FeOOH) nanorods were synthesized by controlling the reaction between ferrous sulfate, cupric sulfate and sodium borohydride at ambient atmosphere. The resulting materials were characterized by transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. CuO x–FeOOH was mainly composed of α-FeOOH and CuO x (CuO and Cu2O). The catalyst was found to be highly effective for the degradation of endocrine disruptors, including dimethyl phthalate, 2,4-dichlorophenoxyacetic acid, and 2,4-dichlorophenol in the presence of H2O2 and UVA at neutral pH. By the total organic carbon and GC–MS analysis, the degradation process of DMP was shown to proceed with the cleavage of C–O bond in ester linkages and the phenyl ring opening into organic acids and CO2. The studies ofOH formation and cyclic voltammetry revealed that the H2O2 was decomposed intoOH or O2 by the promotion of metal oxide. The obtained results showed that the synergistic effect between CuO x and α-FeOOH markedly enhanced the H2O2 decomposition intoOH in CuO x–FeOOH suspension, causing the higher catalytic reactivity. A possible reaction mechanism was proposed.
Keywords: Endocrine disruptors; CuO; x; FeOOH; Photo-Fenton; H; 2; O; 2; decomposition
MTW zeolites for reducing cold-start emissions of automotive exhaust by Z. Sarshar; M.H. Zahedi-Niaki; Q. Huang; M. Eić; S. Kaliaguine (pp. 37-45).
Increasingly strict environmental legislations have led to the need for better control of vehicle cold-start emissions. In this research work, a series of one-dimensional channel molecular sieves with 12 oxygen ring apertures (12R) having MTW structure (MTW is the designation for ZSM-12 in the IZA nomenclature of zeolite structures), have been synthesized and characterized by different techniques such as: XRD, SEM, BET surface area, elemental analysis by atomic absorption spectroscopy, FTIR of adsorbed pyridine and temperature-programmed desorption (TPD). The synthesized samples were tested as hydrocarbons (HCs) trap adsorbents using toluene and ethylene as heavy (aromatic) and light (olefin) probe molecules present in the exhaust stream at engine cold-start. TPD tests were performed after adsorption under four different mixture conditions: binary (toluene–ethylene), ternary (toluene–ethylene–CO2), ternary (toluene–ethylene–H2O) and quaternary (toluene–ethylene–CO2–H2O). The results demonstrated that a silver exchanged MTW zeolite, Al-ZSM-12 (Ag) exhibited high and stable trapping capacities for both probe molecules in all mixtures investigated in this study, thus showing essentially no sensitivity to CO2 and/or H2O. Moreover, a high desorption temperature, particularly for toluene, was associated with the large amount of strong Lewis and Brönsted acid sites. Isomorphous substitution of Al by Fe in MTW structures did not lead to drastic changes in adsorption capacities and desorption temperatures of the two sorbates.
Keywords: Hydrocarbon trap; ZSM-12; Ion-exchange; Isomorphous substitution; Cold-start emissions; Temperature-programmed desorption; Single-file diffusion; Adsorption
An approach to elucidating photocatalytic reaction mechanisms by monitoring dissolved oxygen: Effect of H2O2 on photocatalysis by Tsutomu Hirakawa; Chifumi Koga; Nobuaki Negishi; Koji Takeuchi; Sadao Matsuzawa (pp. 46-55).
We present a method to analyze the photocatalytic oxidation of ethanol (EtOH) in an aqueous TiO2 suspension by measuring the consumption of dissolved oxygen (DO) as a function of varying EtOH and H2O2 concentrations in the suspension. The consumption of DO was analyzed by means of Langmuir–Hinshelwood (L–H) kinetics. The parameter KD-DO calculated from L–H kinetics, defined as (O2 consumption rate constant)(O2 reproduction rate constant)−1, reflects the adsorption equilibrium of EtOH and the photocatalytic reaction mechanisms. The observed KD-DO values for the photocatalytic oxidation of EtOH reflected to the proposed reaction mechanism measured by HPLC and starch–Iodine methods. By using this DO analysis method, we elucidated the photocatalytic reaction mechanism of EtOH oxidation and discussed the effect of H2O2 as active oxygen species on TiO2 photocatalysis.
Keywords: Photocatalyst; Ethanol; Oxygen; Hydrogen peroxide
Investigation of the photocatalytic degradation of brown water natural organic matter by size exclusion chromatography by Luis A. Tercero Espinoza; Eike ter Haseborg; Matthias Weber; Fritz H. Frimmel (pp. 56-62).
Herein we report on the photocatalytic degradation of natural organic matter from a bog lake (Lake Hohloh, Black Forest, Germany) as followed by size exclusion chromatography with dissolved organic carbon (DOC) and ultraviolet (λ=254nm) detection (SEC-DOC and SEC-UV). When irradiating this humic-rich water in the presence of 0.5gL−1 titanium dioxide (P25), we found a preferential degradation of the higher molecular weight DOC fraction. This was coupled to growth of the middle and small DOC fractions. Mineralization proceeded in two distinct steps: a first stage without noticeable mineralization, followed by a phase of steady decrease in dissolved organic carbon. Formic, oxalic, succinic and glutaric acids were found in the irradiated samples and contribute significantly to the bioavailable DOC after irradiation, which favors bacterial regrowth.
Keywords: Heterogeneous photocatalysis; Titanium dioxide; Natural organic matter; Size exclusion chromatography; Bioavailability
Electrocatalytic and corrosion behaviour of tungsten carbide in near-neutral pH electrolytes by Falk Harnisch; Uwe Schröder; Marion Quaas; Fritz Scholz (pp. 63-69).
This paper examines the electrochemical and electrocatalytic behavior of tungsten carbide at ambient temperature and at near to neutral pH conditions.▪This paper examines the electrochemical and electrocatalytic behaviour of tungsten carbide at ambient temperature and at near to neutral pH conditions. The electrocatalytic oxidation of hydrogen, formate and lactate is investigated as a function of the composition of the catalyst material, and of the composition and pH of the used electrolyte solutions. It is demonstrated that for the oxidation of hydrogen, different surface and bulk properties are decisive than for the oxidation of formate and lactate. A major problem of tungsten carbide is its stability in aqueous, pH neutral environments, in which noticeable corrosion processes take place. The individual corrosion rates strongly depend on the electrolyte composition and pH, and on the presence of reducing agents.
Keywords: Tungsten carbide; WC; Electrocatalysis; Microbial fuel cell; Corrosion; Biofuel cell
Catalytic hydrodechlorination of 1,2,4-trichlorobenzene over Pd/Mg(Al)O catalysts by B.T. Meshesha; R.J. Chimentão; F. Medina; J.E. Sueiras; Y. Cesteros; P. Salagre; F. Figueras (pp. 70-77).
Catalytic hydrodechlorination (HDC) is an efficient way to remove chloride species from chlorinated hydrocarbons. Hydrodechlorination reaction of 1,2,4-trichlorobenzene was studied over a series of palladium (1wt.%) catalysts supported on calcined Mg/Al hydrotalcite-like materials (HT) prepared with different Mg/Al ratios. The fresh catalysts were characterized using ICP-OES, XRD, N2-physisorption, H2-chemisorption, TPR, and TEM. It has been observed that the activity, stability and selectivity of the catalysts in the hydrodechlorination reaction of 1,2,4-trichlorobenzene were strongly dependent on the Mg/Al molar ratio in the Mg(Al)O support. The sample with Mg/Al ratio of 4 exhibited the highest activity and selectivity towards total hydrodechlorination reaction giving benzene. Rehydration of the calcined hydrotalcite catalyst resulted in an enhancement of the hydrodechlorination performance. The spent samples were characterized by TPO/MS, TGA and ESEM–EDS techniques. Based on our results it was revealed that catalyst deactivation was mainly due to coke formation. The amount of coke decreased with the base character of the support. The amount of coke formed during the reaction can be eliminated by combustion recovering the initial activity.
Keywords: Hydrodechlorination; 1,2,4-Trichlorobenzene; Pd; Pd/MgAlO catalyst; Hydrotalcite; Mixed oxides; Deactivation; Regeneration
Post-plasma catalytic technology for the removal of toluene from indoor air: Effect of humidity by J. Van Durme; J. Dewulf; K. Demeestere; C. Leys; H. Van Langenhove (pp. 78-83).
Hybrid plasma catalyst technology has great potential for indoor air purification. However, humidity is a critical parameter in plasma catalytic processes. In this work, several catalysts were tested downstream of a DC corona discharge and the effect of humidity was investigated on both ozone and toluene removal. Next, sorption measurements onto the catalysts were performed for toluene, trichloroethylene and acetone, using an equilibrium partitioning in closed system procedure to explain the obtained results in a quantitative manner.Catalytic ozone decomposition experiments indicated that catalyst properties have a strong impact on the hybrid plasma catalyst performance. While the effect of humidity on catalytic ozone abatement proved to be negligible, a negative effect was observed on post-plasma catalytic (PPC) toluene removal. Indeed, for an energy density of 10JL−1 using one type of Pd/Al2O3 as PPC, removal efficiencies were >90 and 39% at dry and 74% RH (25°C), respectively. Nevertheless, even at 74% RH and an energy density of 10JL−1, the toluene removal efficiency was still two times higher than in the absence of a catalyst. For the first time, a logarithmic relationship has been established between VOC sorption and plasma catalytic VOC degradation results ( R2=0.982, n=4). Based on the total free energy of adsorption it is suggested that the negative humidity effect on PPC is mostly due to changing Van der Waals interactions.
Keywords: Abbreviations; DC; direct current; EPICS; equilibrium partitioning in closed system; FID; flame ionisation detector; GC; gas chromatograph; HA; hydrogen acceptor; HD; hydrogen donor; IPC; in-plasma catalysis; K; equilibrium partitioning coefficient; LOD; limit of detection (ppb; v; ); ppb; v; parts per billion (=μL; m; −3; ); PPC; post-plasma catalysis; ppm; v; parts per million (=mL; m; −3; ); RH; relative humidity; SSA; specific surface area (m; 2; g; −1; ); VdW; Van der Waals interaction; VOC; volatile organic compoundsNon-thermal plasma; Catalysis; Humidity; Volatile organic compound; Ozone; Advanced oxidation; Sorption
Study of Pt–CeO2 interaction and the effect in the selective hydrodechlorination of trichloroethylene by N. Barrabés; K. Föttinger; A. Dafinov; F. Medina; G. Rupprechter; J. Llorca; J.E. Sueiras (pp. 84-91).
The feasibility of a catalytic technology to remediate waste streams of halogenated compounds has been improved in order to increase the selectivity towards valuable compounds. Two series of Pt/CeO2 catalysts prepared by different synthesis protocol, co-combustion and impregnation, have been tested in hydrodechlorination of trichloroethylene in gas phase at mild reaction conditions (temperature between 100 and 300°C, and 1bar of pressure). The catalytic behaviour of Pt–Al2O3 catalysts was also studied for comparison. Several techniques (BET, XRD, FTIR, HRTEM, etc.) were performed for catalysts characterization. Using the combustion method, the platinum is introduced into ceria matrix, whereas by the impregnation one, the platinum particles are deposited on the surface. In both cases a strong interaction between the support and the platinum particles is observed. Smaller platinum particles sizes are obtained using the impregnation method when compared with the combustion one. When the main product for Pt–Al2O3 catalysts was ethane, the use of CeO2 as support increased the ethylene selectivity. Platinum catalysts obtained by combustion method showed the highest selectivity to ethylene. These results indicate that both the presence of CeO2 as support and the interaction between ceria and platinum play an important role in the selectivity to ethylene.
Keywords: Dechlorination; Trichloroethylene; Pt/CeO; 2; Ethylene
One-step synthesis of nanostructured Pd-doped mixed oxides MO x-CeO2 (M=Mn, Fe, Co, Ni, Cu) for efficient CO and C3H8 total oxidation by Jin-Yong Luo; Ming Meng; Jin-Song Yao; Xin-Gang Li; Yu-Qing Zha; Xitao Wang; Tian-Yong Zhang (pp. 92-103).
A series of nanostructured Pd-doped mixed oxides MO x-CeO2 (M=Mn, Fe, Co, Ni, Cu), with uniform mesoporous structure and large surface area exceeding 115m2g−1, were synthesized in one step by a surfactant-assisted co-precipitation. Their catalytic performance was investigated using total oxidation of CO and C3H8 as the model reactions. The results show that, a synergism exists between even trace amounts of exposed Pd and 3d-transition metal oxides for CO oxidation, whereas such an effect is absent for C3H8 oxidation. In situ diffuse reflectance infrared spectroscopy (DRIFTS) study reveals that the synergistic essential for CO oxidation should be the interaction-assisted generation of active oxygen species between Pd and MO x, which react readily with CO, forming bidentate carbonate (1587 and 1285cm−1) as intermediates. Moreover, structural characterization results indicate that a solid solution is formed between CeO2 and Mn2O3 or Fe2O3, resulting in the very strong interaction between Pd and MO x, as well as the greatly improved CO oxidation. The light-off temperatures for Pd-doped Mn and Fe-containing catalysts, as compared with the Pd-free catalysts, are decreased by more than 70 and 100°C, respectively. In particular, a CO conversion as high as 80% can be achieved even at room temperature on Pd-doped Mn-containing catalyst. While for C3H8 oxidation, the C–H bond activation, but not the oxygen activation, plays a crucial role. The C–H bond activation ability of the catalysts is largely determined by the d-electron configurations of the M cations. A ‘double-peak’ phenomenon can be derived with the increase of d-electron number.
Keywords: Palladium; Ceria; CO oxidation; Propane oxidation; Synergism; Mechanism