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Applied Catalysis B, Environmental (v.86, #3-4)
Photochemical and enzymatic methanol synthesis from HCO3− by dehydrogenases using water-soluble zinc porphyrin in aqueous media by Yutaka Amao; Tomoe Watanabe (pp. 109-113).
We studied the photochemical and enzymatic synthesis of methanol from HCO3− using formate dehydrogenase (FDH) isolated from Candida boidinii, aldehyde dehydrogenase (AldDH) and alcohol dehydrogenase (ADH) isolated from yeast, and the photoreduction of methyl viologen (MV2+) by the visible-light sensitization using zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) in the presence of triethanolamine (TEOA). When a sample solution containing ZnTPPS, MV2+, FDH, AldDH, ADH, TEOA, and NaHCO3 in potassium phosphate buffer solution (pH 8) was irradiated, the amount of methanol produced increased with the irradiation time. After irradiation for 3h, 4.5μmoldm−3 of methanol was produced from 100μmoldm−3 NaHCO3. The conversion ratio of HCO3− to methanol was approximately 4.5%. This result indicates that a system for the photochemical synthesis of methanol from HCO3− can be developed by using three dehydrogenases (FDH, AldDH, and ADH) and for the photoreduction of MV2+ through the photosensitization of ZnTPPS in aqueous media.
Keywords: CO; 2; fixation; Methanol synthesis; Artificial photosynthesis; Biocatalysis; Photochemical reaction
Selective steam reforming of methanol over silica-supported copper catalyst prepared by sol–gel method by Yasuyuki Matsumura; Hideomi Ishibe (pp. 114-120).
Silica-supported copper prepared by a sol–gel method can selectively catalyze methanol steam reforming to hydrogen and carbon dioxide at 250°C. The catalytic activity increases with the copper content up to 40wt.%. The selectivity to carbon monoxide with the catalysts containing 20–40wt.% of copper is significantly lower than that with a commercial Cu/ZnO/Al2O3 catalyst. Copper particles are highly dispersed in the catalyst whose Cu content is 20wt.% or less. After the reaction at 250°C the particles are present as Cu2O with the mean crystallite size less than 4nm. In the catalyst with the Cu content of 30–50wt.%, the fine Cu2O particles coexist with large metallic Cu particles whose mean crystallite size is 30–40nm after the reaction. The large metallic particles are supposed to contribute to the reaction as well as the fine Cu2O particles although the surface area is estimated to be significantly smaller than that of the latter.
Keywords: Methanol steam reforming; Copper supported on silica; Sol–gel method; CO formation; X-ray diffraction; X-ray photoelectron spectroscopy
Ethanol steam reforming in a membrane reactor with Pt-impregnated Knudsen membranes by Chang-Yeol Yu; Dong-Wook Lee; Sang-Jun Park; Kwan-Young Lee; Kew-Ho Lee (pp. 121-126).
An ethanol reforming membrane reactor (ERMR) with Pt-impregnated Knudsen membranes was investigated to achieve the improvement of ethanol conversion and hydrogen yield. The prepared Pt-impregnated membranes have high permeabilities and reaction activities for the water-gas shift (WGS) reaction. The ethanol reforming-membrane reactor showed ethanol conversion improvement of 7.4–14.4% in comparison with a conventional reactor (CR). Hydrogen yield improvement of 4.2–10.5% was also observed in ERMR with Pt-impregnated SKM in whole reaction temperature range. In addition, CO concentration was considerably reduced via water-gas shift reaction during the permeation.
Keywords: Ethanol steam reforming; Membrane reactor; Composite membranes; Water-gas shift reaction
An investigation of the performance of catalytic aerogel filters by Shengli Cao; King Lun Yeung; Joseph K.C. Kwan; Percy M.T. To; Samuel C.T. Yu (pp. 127-136).
Gas permeable, photoactive and crack-free titania–silica aerogels of high titanium content (i.e., up to Ti/Si=1) were prepared by two-steps acid–base catalyzed method involving an acid-catalyzed prehydrolysis of silicon alkoxide followed by a base-catalyzed hydrolysis/condensation reactions with a chelated titania precursor. The prepared titania–silica aerogels displayed good mechanical strength (>30kNm−2), large surface area (>550m2/g), mesoporous structure (8–11nm) and good gas permeation. The porous aerogels trap and filter airborne particulates and the titania–silica aerogel have a fair performance for aerosol (65%) and bioaerosol (94%) filtrations. The photoactive anatase nano-TiO2 crystallized within the aerogel displays an order of magnitude higher reaction rate for UVA photooxidation of trichloroethylene compared to commercial Degussa P25 TiO2. The bactericidal activity of the titania–silica aerogel for Bacillus subtilis cells under UVA was also six orders of magnitude better.
Keywords: Titania–silica aerogel; Nano-TiO; 2; Photocatalyst; Antimicrobial; Aerosol
Thin-film CoB catalyst templates for the hydrolysis of NaBH4 solution for hydrogen generation by Palanichamy Krishnan; Suresh G. Advani; Ajay K. Prasad (pp. 137-144).
Thin-film CoB alloy catalysts were prepared on Ni-foam substrates using electroless as well as electroplating techniques. Electroless plating was carried out using cobalt (II) sulfate as the source of Co2+, sodium succinate as the complexing agent, and dimethyamine borane as the source of boron as well as the reducing agent. Electroplating was carried out using cobalt (II) sulfate and cobalt (II) chloride as the sources of cobalt, and boric acid as the source of boron. The thin-film CoB/Ni-foam templates were characterized using ICP, XRD and SEM techniques. The normalized B content was in the range of 1.0–1.30 and 0.20–0.60wt.% for electroless and electroplated templates, respectively. The B content is less than that required for stoichiometric alloy formation, which indicates the simultaneous deposition of the Co metal along with CoB alloy. An optimum condition of 0.100ML−1 each of cobalt (II) sulfate heptahydrate Co(SO4)·7H2O, sodium succinate (Na2C4H4O4) and dimethylamine borane (CH3)2NHBH3, at 60°C with the pH value of 4–5 and a plating time of 1h was identified for the preparation of the catalyst templates by electroless plating. Where as, 0.125ML−1 each of cobalt (II) chloride hexahydrate (CoCl2·6H2O), Co(SO4)·7H2O, 0.125ML−1 of boric acid at the current density range of 160–320mAcm−2 and a temperature of 60°C was identified as the optimum condition for the electroplating method. Maximum H2 generation rates of 1.64 and 0.30Lmin−1g−1 of catalyst were obtained with electroless and electroplated thin-film CoB/Ni-foam templates, respectively. The suitability of the electroless plated CoB/Ni-foam catalyst template for extended duration of hydrogen generation from NaBH4 was studied up to 60h. Activation energies of 44.47 and 54.89kJmol−1 were calculated for electroless and electroplated CoB/Ni-foam catalyst templates, respectively.
Keywords: Cobalt–boron alloy; Thin film; Electroless plating; Electroplating; Sodium borohydride; H; 2; generation
Synthesis of visible light-active nanostructured TiO x ( x<2) photocatalysts in a flame aerosol reactor by Swapnil Y. Dhumal; Tyrone L. Daulton; Jingkun Jiang; Bamin Khomami; Pratim Biswas (pp. 145-151).
Titanium dioxide is a wide band gap (3.2eV) semiconductor which is photo-active when irradiated with UV light. For wider scale use of TiO2 as a photocatalyst, its activity needs to be extended to the visible light region (constituting 45% of total incident solar energy). A diffusion flame aerosol reactor (FLAR) with an oxygen lean environment in the particle formation zone has been used to synthesize oxygen deficient titanium suboxide (TiO x with x<2) nanoparticles. Using a standard-based electron energy loss spectroscopy (EELS) technique, the non-stoichiometry ( x in TiO x) in the flame synthesized particles has been quantified with high accuracy (uncertainty less than 3%). Under an oxygen lean environment in the particle formation zone, the non-stoichiometry in the TiO x particles is a function of the flame temperature. The value of x in the flame synthesized TiO x nanoparticles is in the range of 1.88< x <1.94. Diffuse reflectance spectra confirmed that the oxygen deficient TiO x particles absorbed visible light. Visible light activity of the TiO x particles is demonstrated by photocatalytic degradation of methyl orange solution under visible light illumination.
Keywords: Oxygen deficient; Titanium dioxide; Flame aerosol reactor; Visible light photocatalytic activity; Nanoparticle
Dechlorination of chlorobenzene compounds on flyash; effects of metals, aqueous/organic solvents and temperatures by Abdul Ghaffar; Masaaki Tabata (pp. 152-158).
Dechlorination of chlorobenzene compounds on flyash by using a solution of calcium hydroxide and sulfur in aqueous/organic solvent at 60–170°C, under oxygen deficient conditions was studied. High percentage of dechlorination was obtained under certain reaction conditions. The results suggested that at 90°C, metals in general and copper and lead in particular enhanced the catalytic potential of flyash for dechlorination by hydrodechlorination and substitution reactions. But at high temperatures (120–170°C), dechlorination process was adversely affected by these metals. The effects of water, organic solvents, temperatures and heating time, were studied and reactions conditions were optimized to get maximum dechlorination.
Keywords: Flyash; Hydrodechlorination; Temperature; Aqueous/organic solvents; Metals
Photocatalytic oxidation of toluene at indoor air levels (ppbv): Towards a better assessment of conversion, reaction intermediates and mineralization by Mohamad Sleiman; Pierre Conchon; Corinne Ferronato; Jean-Marc Chovelon (pp. 159-165).
We report here a new analytical methodology for the investigation of toluene photocatalytic removal at indoor-relevant concentration level (ppbv). Experiments were performed using an annular flow-through reactor with TiO2 as photocatalyst, toluene as a model VOC and under different ranges of relative humidity (RH: 0–70%), inlet concentration (20–400ppbv) and flow rate (70–350mLmin−1). Analysis of reaction intermediates was conducted using an automated thermal desorption technique coupled to GC–MS instrument (ATD–GC–MS) whereas a GC coupled to pulsed discharge helium ionization detector (GC–PDPID) was used for the first time for on-line measurements of CO and CO2 at ppbv level.Under these conditions, toluene conversion was up to 90–100% with a slight influence of inlet concentration and RH, whereas flow rate was found to be a prevalent factor. Mineralization (%) varied from 55 to 95% and has shown to be strongly inhibited by the increase of RH whereas flow rate and inlet concentration exhibited a negligible effect. The reaction intermediates were found to be different according to the RH level: in absence of water vapor, traces of low molecular weight carbonyls (formaldehyde, methyl glyoxal, etc.) were detected and quantified in the gas phase whereas at RH 40%, hydroxylated intermediates such as cresols and benzyl alcohol were observed. On the basis of identification results, a reaction mechanism was proposed involving mainly direct hole oxidation at dry conditions and hydroxylation by OH radicals at high RH level.
Keywords: Photocatalysis; VOC; Toluene; Indoor air; Reaction products
Catalytic combustion of chlorobenzene over MnOx–CeO2 mixed oxide catalysts by Wang Xingyi; Kang Qian; Li Dao (pp. 166-175).
A series of MnOx–CeO2 mixed oxide catalysts with different compositions prepared by sol–gel method were tested for the catalytic combustion of chlorobenzene (CB), as a model of volatile organic compounds of chlorinated aromatics. MnOx–CeO2 catalysts with different ratios of Mn/Ce+Mn were found to possess high catalytic activity in the catalytic combustion of CB, and MnOx(0.86)–CeO2 was identified as the most active catalyst, on which the temperature of complete combustion of CB was 254°C. Effects of systematic variation of reaction conditions, including space velocity and inlet CB concentration on the catalytic combustion of CB were investigated. Additionally, the stability and deactivation of MnOx–CeO2 catalysts were studied by various characterization methods and other assistant experiments. MnOx–CeO2 catalysts with high Mn/Ce+Mn ratios present a stable high activity, which is related to their high ability to remove the adsorbed Cl species and a large amount of active surface oxygen.
Keywords: Chlorobenzene; MnOx–CeO; 2; CeO; 2; Catalytic combustion
Correlation of the deactivation of CoMo/Al2O3 in hydrodesulfurization with surface carbon species by Jae Hyun Koh; Jung Joon Lee; Heeyeon Kim; Ara Cho; Sang Heup Moon (pp. 176-181).
The deactivation of CoMo/Al2O3 in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was investigated under laboratory conditions that allowed the accelerated deposition of coke on the catalyst. The coke deposition was enhanced at low H2 pressures and when naphthalene was added to the reaction solution. Characterization of deactivated catalysts by elemental analysis (EA) and temperature-programmed oxidation (TPO) identified two types of carbonaceous species deposited on the catalysts, the reactive and the refractory species. The refractory deposit, or hard coke, was a major contributor to the deactivation and, therefore, the amounts of hard coke present on the catalyst determined the overall activity. A correlation was established in this study between the activity and the amounts of deposited hard coke based on the results of accelerated deactivation treatment. A similar relation was also observed between the two parameters when the catalyst was used in an industrial process for long periods. The above findings suggest that the reaction periods of two different scales, i.e., in laboratory and industrial processes, can be correlated with each other based on the amounts of hard coke when coking is the major mechanism of catalyst deactivation.
Keywords: Hydrodesulfurization; CoMo/Al; 2; O; 3; Deactivation; Coke; Dibenzothiophene
Catalytic wet air oxidation of dye pollutants by polyoxomolybdate nanotubes under room condition by Yang Zhang; Dongliu Li; Yang Chen; Xiaohong Wang; Shengtian Wang (pp. 182-189).
In order to develop a catalyst with high activity and stability for catalytic wet air oxidation of pollutant dyes at room condition, a new polyoxometalate Zn1.5PMo12O40 with nanotube structure was prepared using biological template. The structure and morphology were characterized using infrared (IR) spectra, UV–vis diffuse reflectance spectra (DR-UV–vis), elemental analyses, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). And the degradation of Safranin-T (ST), a hazardous textile dye, under air at room temperature and atmospheric pressure was studied as a model experiment to evaluate the catalytic activity of this polyoxomolybdate catalyst. The results show that the catalyst has an excellent catalytic activity in treatment of wastewater containing 10mg/L ST, and 98% of color and 95% of chemical oxygen demand (COD) can be removed within 40min. And the organic pollutant of ST was totally mineralized to simple inorganic species such as HCO3−, Cl− and NO3− during this time (total organic carbon (TOC) decreased 92%). The structure and morphology of the catalyst under different cycling runs show that the catalyst are stable under such operating conditions and the leaching tests show negligible leaching effect owning to the lesser dissolution. So this polyoxomolybdate nanotube is proved to be a heterogeneous catalyst in catalytic wet air oxidation of organic dye.
Keywords: Catalytic wet air oxidation; Safranin-T; Wastewater treatment; Polyoxometalates
Promotional effect of H2 on CO oxidation over Au/TiO2 studied by operando infrared spectroscopy by Laurent Piccolo; Helen Daly; Ana Valcarcel; Frédéric C. Meunier (pp. 190-195).
The oxidation of carbon monoxide in the presence of various concentrations of molecular hydrogen has been studied over a Au/TiO2 reference catalyst by combining diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectrometry. It is shown for the first time that H2 enhances the CO oxidation rate on Au/TiO2 without leading to any major loss of selectivity. Increasing the H2 pressure induces higher CO and H2 oxidation rates. Under H2-free conditions, the surface species detected are Au δ+–CO, Ti4+–CO, carbon dioxide and carbonates. Upon the addition of H2, Au0–CO, water and hydroxyl groups become the main surface species. The occurrence of a preferential CO oxidation mechanism involving H xO y species under the present experimental conditions is proposed.
Keywords: CO oxidation; PrOx; Gold catalysis; DRIFTS; Operando spectroscopy
Influence of reaction products of K-getter fuel additives on commercial vanadia-based SCR catalysts by Francesco Castellino; Anker Degn Jensen; Jan Erik Johnsson; Rasmus Fehrmann (pp. 196-205).
Commercial vanadia-based full-length monoliths have been exposed to aerosols formed by injection of K3PO4 (dissolved in water) in a hot flue gas ( T>850°C) from a natural gas burner. Such aerosols may form when burning fuels with high K- and P-content, or when P-compounds are mixed with biomass as a K-getter additive. The formed aerosols have been characterized by using both a SMPS system and a low pressure cascade impactor, showing a dual-mode volume-based size distribution with a first peak at around 30nm and a second one at diameters >1μm. The different peaks have been associated with different species. In particular, the particles related to the 30nm peak are associated to condensed phosphates, whereas the larger particles are associated to potassium phosphates. Two monoliths have been exposed during addition of 100 and 200mg/Nm3 K3PO4 for 720 and 189h, respectively. Overall, deactivation rates up to 3%/day have been measured. The spent catalysts have been characterized by bulk chemical analysis, Hg-porosimetry and SEM-EDX. NH3-chemisorption tests on the spent elements and activity tests on catalyst powders obtained by crushing the monoliths have also been carried out. The catalyst characterization has shown that poisoning by K is the main deactivation mechanism. The results show that binding K in K–P salts will not reduce the rate of catalyst deactivation.
Keywords: DeNO; x; SCR catalysts; Catalyst deactivation; Vanadia; Biomass; Potassium poisoning; Polyphosphoric acids
Influence of reaction products of K-getter fuel additives on commercial vanadia-based SCR catalysts by Francesco Castellino; Anker Degn Jensen; Jan Erik Johnsson; Rasmus Fehrmann (pp. 206-215).
A commercial V2O5–WO3–TiO2 corrugated-type SCR monolith has been exposed for 1000h in a pilot-scale setup to a flue gas doped with KCl, Ca(OH)2, H3PO4 and H2SO4 by spraying a water solution of the components into the hot flue gas. The mixture composition has been adjusted in order to have P/K and P/Ca ratios equal to 2 and 0.8, respectively. At these conditions, it is suggested that all the K released during biomass combustion gets captured in P–K–Ca particles and the Cl is released in the gas phase as HCl, thus limiting deposition and corrosion problems at the superheater exchangers during biomass combustion. Aerosol measurements carried out by using a SMPS and a low pressure cascade impactor have shown two distinct particle populations with volume-based mean diameters equal to 12 and 300nm, respectively. The small particles have been associated to polyphosphoric acids formed by condensation of H3PO4, whereas the larger particles are due to P–K–Ca salts formed during evaporation of the water solution. No Cl has been found in the collected particles. During the initial 240h of exposure, the catalyst element lost about 20% of its original activity. The deactivation then proceeded at slower rates, and after 1000h the relative activity loss had increased to 25%. Different samples of the spent catalyst have been characterized after 453h and at the end of the experiment by bulk chemical analysis, Hg-porosimetry and SEM-EDX. NH3-chemisorption tests on the spent elements and activity tests on catalyst powders obtained by crushing the monolith have also been carried out. From the characterization, it was found that neither K nor Ca were able to penetrate the catalyst walls, but only accumulated on the outer surface. Poisoning by K has then been limited to the most outer catalyst surface and did not proceed at the fast rates known for KCl. This fact indicates that binding K in P–K–Ca compounds is an effective way to reduce the negative influence of alkali metals on the lifetime of the vanadia-based SCR catalysts. On the other hand, P-deposition was favoured by the formation of the polyphosphoric acids, and up to 1.8wt% P was accumulated in the catalyst walls. Deactivation by polyphosphoric acids proceeded at about 0.2%day−1. About 6–7% of the initial activity was lost due to the accumulation of these species. However, the measured relative activity reached a steady-state level during the last 240h of exposure indicating that the P-concentration in the bulk reached a steady-state level due to the simultaneous hydrolysis of the polyphosphoric acids.
Keywords: SCR; Deactivation; Vanadia; KCl; Polyphosphoric acid; Biomass