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      Volume 129, Issue 11

      November 2017,   pages  1658a-1794

    • Table of Contents

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    • Preface


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    • Mesoporous silica supported Pd/Ag bimetallic nanoparticles as a plasmonic catalyst for chemoselective hydrogenation of p-nitrostyrene under visible light irradiation


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      Silver-based bimetallic Pd/Ag plasmonic catalysts supported on mesoporous silica catalyze the chemoselective reduction of nitrostyrene (NS) to aminostyrene (AS). Ammonia borane (AB) is used as a mild reducing agent to generate H₂ in situ on the surface of exposed Ag and Pd atoms for −NO₂ reduction at room temperature and atmospheric pressure. Systematic studies on the effect of nanoparticles (NPs) size are performed in dark and under light irradiation conditions. The spherical yellow colored bimetallic Pd/Ag/SBA-15(Y) exhibited maximum AS conversion of 89% at 90 min under visible light irradiation. The catalysts display higher selectivity under visible light irradiation which can be due to the efficient adsorption and transfer ofH⁺ /H⁻ pair to the polar bonds in the nitro group.

    • Preparation, characterization, and post-synthetic modification of layered MCM-22 zeolite precursor


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      Hydrothermal synthesis of MCM-22(P) was carried out with two different silica sources, colloidal silica (28%) and silicic acid with different gel composition. The synthesis was carried out in stirring and static conditions with different crystallization time. MCM-22(P) modified with swelling-sonication method resultedin swollen MCM-22, while alkali treatment yielded desilicated MCM-22. The materials were characterized by X-ray diffraction, low-angle XRD, FE-SEM-EDX, FT-IR, TGA, N₂ adsorption and NH₃-TPD analysis. The results revealed that MCM-22 has a layered sphere, doughnut like morphology and after modification, swollen and broken sphere was observed. Physicochemical analysis revealed that the materials’ mesoporosity increased and acidity also changed. Energy dispersive X-ray analysis revealed the high amount of desilicationin alkali-treated MCM-22(P).

    • Insight into solid-liquid phase transfer catalyzed synthesis of Mecoprop ester using K₂CO₃ as base and development of new kinetic model involving liquid product and two solid co-products


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      2-Methyl-4-chlorophenoxy propionic acid (Mecoprop) is a widely used household herbicide. In the current work, a simple synthetic method is developed for Mecoprop methyl ester using solid-liquid phase transfer catalysis (S-L PTC) with K₂CO₃ as mild base and toluene as solvent. Conversion of 95% was achieved with 100% selectivity for Mecoprop ester at 100 ◦C. Simple isolation process was employed to recover the product from the reaction mixture. A reaction mechanism was proposed and new kinetic model developed involving one liquid and two solid co-products. The activation energy for the reaction was calculated. This is the first example of its kind being reported vis-à-vis kinetics and mechanism.

    • Enhancement of visible light irradiation photocatalytic activity of SrTiO₃ nanoparticles by Pt doping for oxidation of cyclohexane


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      In this research, strontium titanate (SrTiO₃) nanoparticles were synthesised using an ultrasonic method, then were doped with Pt using a photo-assisted deposition method to form Pt/SrTiO₃ nanoparticles.SrTiO₃ and Pt/SrTiO₃ nanoparticles were characterized by XRD, XPS, TEM, BET surface area UV–Vis and PL techniques in order to explore their chemical and physical properties. The visible light irradiation photocatalyticperformances of SrTiO₃ nanoparticles and Pt/SrTiO₃ nanoparticles for photocatalytic oxidation of cyclohexane was investigated, and the results revealed that platinum was doped onto the SrTiO₃ nanoparticles surfaces as metallic platinum, and the weight percent of doped platinum greatly affected the band gap, and the 1.5wt% Pt/SrTiO₃ nanoparticles showed the highest photocatalytic activity due to the low band gap. The stability of thePt/SrTiO₃ nanoparticles for the photocatalytic oxidation of cyclohexane was examined and the results revealed that the Pt/SrTiO₃ nanoparticles could be used five times without losing their efficiency.

    • Morphology-controlled Pd nanocrystals as catalysts in tandem dehydrogenation-hydrogenation reactions


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      A facile synthetic protocol was used to prepare morphology controlled Pd nanocrystals with spherical and cubic shapes of different sizes. Carbon-supported catalysts were prepared from the as-synthesised nanocrystals and their catalytic ability in a tandem dehydrogenation/hydrogenation reaction composed by the dehydrogenation of ammonia borane, serving as a hydrogen source, and the subsequent hydrogenation of 4- nitrophenol (4-NP) to 4-aminophenol (4-AP) was assessed. The catalytic performance was strongly dependent on the nanocrystals morphology and the spherical nanoparticles with an average size of 5.5 nm displayed the best performance among investigated.

    • Non-oxidative conversion of methane into higher hydrocarbons over Mo/MCM-22 catalyst


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      Molybdenum impregnated zeolite catalyst has been well-known for methane conversion into higher hydrocarbons under non-oxidative condition. HZSM-5 & HMCM-22 zeolites are the effective supports for this purpose. However, the catalytic performance of HMCM-22 supported molybdenum catalyst is consideredsuitable than that for HZSM-5 catalyst with high aromatic selectivity due to unique pore structure and framework of MCM-22 zeolite support. Effect of Mo loading over MCM-22 zeolite has been studied for the activity test and observed that 5 wt% metal content over the support (MCM-22) is optimum for the proper tuning of acidic & metallic sites of the catalyst. Effect of silica/alumina ratio (SAR, molar) of MCM-22 zeolite has also been studied and observed that lower SAR (30) is suitable (C₆H₆ selectivity, 37%) comparatively to higher SAR (55)(C₆H₆ selectivity, 18%). Lower GHSV (720 mL/g.h) is effective for higher hydrocarbon production compared to higher GHSV (1200 mL/g.h) due to low residence time. Mo/MCM-22 catalysts with different Mo loading werecharacterized by BET surface area, XRD, Raman spectroscopy and NH₃-TPD analysis. Unique pore systems [10 & 12 membered ring (MR)] and framework of MCM-22 zeolite support are the key factors for effective methane conversion to value added chemicals when loaded with molybdenum.

    • Esterification of maleic acid and butanol using cationic exchange resin as catalyst


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      Dibutyl maleate is a perfumery ester used as an intermediate in the production of paints, adhesives, and copolymers. Esterification of maleic acid and butanol was studied in presence of acidic cation exchange resin as a catalyst. The objective of this work was to test the suitability and efficacy of heterogeneous catalystssuch as Indion 225H and Amberlyst-15 in the synthesis of dibutyl maleate. Various parameters deciding the conversion of reaction such as mole ratio, catalyst loading, molecular sieves, speed of agitation and effect of temperature were optimized for the maximum rate and conversion. The activation energy was calculated as 71.5 kcal/mol. Diffusivity value DAB (maleic acid in n-butanol) at 80◦C was calculated as 5.08 × 10 ⁻¹⁰ m ²/s and effective diffusivity (De-A) was calculated as 5.08 × 10 ⁻¹¹ m ²/s. Solid–liquid mass transfer coefficient(ksl-A) was calculated as 6.77 × 10 ⁻⁶ m/s for the particle size of Amberlyst-15 as 0.5 mm.

    • Preparation of TiO₂ supported Au–Pd and Cu–Pd by the combined strong electrostatic adsorption and electroless deposition for selective hydrogenation of acetylene


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      TiO₂ supported Au–Pd and Cu–Pd catalysts were prepared by strong electrostatic adsorption (SEA) of Pd followed by electroless deposition (ED) of a second metal with incremental surface coverages of Au or Cu. High dispersion of small Pd particles on the Pd/TiO2 prepared by SEA led to the high amount of second metal deposition on Pd surface. The Cu addition by ED increased the relative ratio of linear CO adsorption mode indicating the presence of higher amount of isolated Pd atoms. The ensemble effect of the Cu–Pd/TiO₂ catalysts resulted in the improved catalytic performances in the selective hydrogenation of acetylene to ethylene. However, as revealed by the blue shift of CO-IR and XPS results, Au addition by ED rather exhibited the electronicmodification. The highest catalytic activity was obtained on the 1.10% Au–Pd/TiO₂ catalyst; however, the Cu addition (0.12% Cu–Pd/TiO₂, θCu = 0.37) showed interesting results as only a small amount of Cu was used to improve the catalyst performances. The bimetallic catalysts were also prepared by conventional impregnation for comparison purposes. These catalysts exhibited several drawbacks such as low Pd dispersion, formation ofsecond metal aggregates, and blockage of isolated Pd atoms.

    • Reduction of CO₂ to CO in presence of H₂ on strontium doped lanthanum manganite cathode in solid oxide electrolysis cell


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      Electrochemical performance of La₀.₈Sr₀.₂MnO₃−δ (LSM) for CO₂ reduction in solid oxide cell is studied by performing impedance spectroscopy measurement and current-voltage characterizations for varying ratio of CO₂/H₂. Ohmic resistance (RΩ) is observed to be slightly increased from 2.59 to 2.70 Ωcm², however; the cathode polarization resistance (R₂) decreased significantly from 16.20 to 4.70 Ω cm² as the H2 percentage increased from 8 to 82%, respectively. As the H₂ content increased in feed gas, the improved polarization resistance indicated an enhanced activity of LSM for CO₂ reduction reaction. Furthermore, the cathode polarization resistance for CO₂/H₂ of 92/08, is observed to be decreased from 16.20 Ω cm² (OCV 0.89 V) to 1.90 Ω cm² (2.0 V) as the applied potential increased in the electrolysis mode of operation. A maximum conversion of CO₂ of 6.0% with 55% of faradaic efficiency for the production of CO is achieved for CO₂/H₂ ratio of 38/62, which is supported by improved current-voltage polarization, i.e., an increase in reduction current from −0.28 to −0.32 A cm−2 (at 2.5 V) as the CO₂/H₂ ratio decreased from 92/08 to 38/62 respectively. These results demonstrate LSM as an active electrocatalyst to reduce CO₂, which could further be improved by increasing the H₂ concentration in the feed composition to the cathode.

    • BINIVOX catalyst for hydrogen production from ethanol by low temperature steam reforming (LTSR)


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      Nickel doped bismuth vanadate [Bi₄ (V₀. ₉₀Ni₀.₁₀) ₂ O₁₁ ₋ δ;BINIVOX] calcined at 800 ◦C (BINIVOX-800) catalyst is prepared by a solution combustion method. The catalytic activity study is carriedin the temperature range of 250–400 ◦C, and with the molar feed ratios of water: ethanol at 23:1 and 2.5:1. The study reveals an increase in the ethanol conversion and selectivity of carbon dioxide & hydrogen but a decreasein the selectivity of carbon monoxide and methane with an increase in temperature and water: ethanol mole ratio. Fresh and used catalysts are characterized using DTA, TGA, XRD and FTIR. XRD results reveal that thefresh catalyst is phase pure γ-BINIVOX. The phase purity and crystallinity of the catalyst is retained after 30 h of activity study.

    • Efficient utilization of bimetallic catalyst in low H₂/CO environment syngas for liquid fuel production


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      Application of Fischer-Tropsch synthesis (FTS) in the utilization of low H ₂/CO ratio (0.5–1.5) gas obtained from coal and biomass gasification can be done by selecting a catalyst system active for both FTS and WGS reaction. The enhancement of H ₂ content depends on the extent of water gas shift (WGS) reaction and can be quantified by measuring usage ratio define as a mole of H₂ to CO converted. With an attempt to utilize low H ₂/CO ratio syngas bimetallic (Fe/Co/SiO ₂) were prepared and compared with monometallic (Fe/SiO ₂ and Co/SiO ₂) catalysts. The catalysts were tested in fixed bed reactor at industrial relevant FTS conditions(T: 220−260 ◦C, P: 2.0 MPa, GHSV-1.2 SL/gcat-h, H ₂/CO: 1–1.5). The incorporation of Fe-Co bimetallic catalyst facilitates both FT and WGS reaction because of the presence of iron and cobalt phases. Compared to monometallic catalyst there is a significant increase in CO conversion over the bimetallic catalyst. Also, the yield of C ₅+ was significantly higher over bimetallic catalyst compared to iron catalyst, where olefin was the major product. Selected catalyst (Fe/Co/SiO ₂) was tested for their activity toward WGS reaction. Effects of temperature, pressure, and feed composition on WGS reaction over bimetallic catalyst were studied. Lower value usage ratio (1.62 and 1.58) reveals the occurrence WGS reaction Fe-Co bimetallic catalyst at 240 ◦C and 260 ◦C. At 240 ◦C, 72% CO conversion, and 60% C ₅ + selectivity show that the catalyst efficiently utilizes the increased H ₂/CO ratio in the production of liquid hydrocarbon.

    • Solvent free lipase catalyzed synthesis of butyl caprylate


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      The ester, butyl caprylate has wide applications in commercial market and it also possesses characteristic fruity flavor. The work exhibits the effect of various reaction parameters and the optimization study for the synthesis of butyl caprylate in presence of bio-catalyst. To achieve maximum conversion theoptimum parameters thus established include; temperature 60 ◦C, mole ratio of caprylic acid and butanol as 1:2, lipase loading 2% (w/v), 250 rpm speed of agitation and 4g of molecular sieves. The immobilized enzyme wasalso recycled and reused for 7 cycles with only 30% loss from its initial activity. The thermodynamic parametersnat different temperatures were also determined. The esterification was conducted successfully with 92% as maximum conversion in 5 h in a stirred batch reactor under solvent free system and in presence of molecular sieves that was used to adsorb water formed in reaction.

    • Synthesis of quinoxaline derivatives from terminal alkynes and o-phenylenediamines by using copper alumina catalyst


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      An efficient method for the synthesis of quinoxaline derivatives through oxidative coupling of o-phenylenediamines (OPD) with terminal alkynes by using copper-alumina (Cu-Al) catalyst was described. A series of Cu-Al catalysts with different mole ratios of Cu ²⁺ /Al ³⁺, 2:1 (Cu-Al-1), 2.5:1 (Cu-Al-2) and 3:1 (Cu-Al-3) were prepared by co-precipitation method followed by calcination and their activity was checked for the synthesis of quinoxaline derivatives. Cu-Al-2 showed excellent activity at 60 ◦C in presence ofK ₂CO ₃. The catalyst is inexpensive, recyclable and environmentally benign. The fresh and recycled catalysts were characterized by different analytical techniques. Different reaction parameters were optimized; catalyst screening, solvent, base and temperature. The protocol was extended towards different substrates.

    • Green synthetic route for perfumery compound (2-methoxyethyl) benzene using Li/MgO catalyst


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      Ethers are one of the most prominent compounds among perfumery chemicals. (2-Methoxyethyl) benzene commonly known as phenyl ethyl methyl ether (PEME) is widely used in flavour and fragrance industries. Conventionally, synthesis of PEME involves the use of hazardous and polluting chemicals, whichin turn affects the purity of perfumery compound. Thus, developing a green route to synthesise PEME without any hazardous chemicals is desirable. In the current work, a new process is developed for the synthesis of PEME using solid base catalysts including MgO and Li/MgO (with different loadings of lithium) and dimethyl carbonate (DMC) as a methylating agent as well as a solvent. Different kinetic parameters were studied to achieve the optimum yield of the desired product. At optimum reaction conditions i.e., 1000 rpm of speed, 1.33×10−2 g/cm3 of catalyst loading, 1:10.5 mole ratio (2-Phenyl ethanol: DMC), 180 ◦C, 95% conversion of 2-phenyl ethanol with 98% selectivity of PEME was achieved. A detailed kinetic model was also developed andapparent activation energy for the reaction was calculated as 11.93 kcal/mol.

    • Syngas production by CO₂ reforming of methane over Co/Mg1−xNixO catalysts


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      By using catalysts of Co/Mg1−xNixO (x= 0, 0.03, 0.07, 0.15; 1 wt% Co each), we performed the dry reforming of methane. The catalysts were prepared by K ₂ CO ₃ co-precipitation from aqueous nickel nitrate hexahydrate and magnesium nitrate hexahydrate. Impregnation of cobalt(II) acetylacetonate onto MgO-NiO was then conducted. TEM, XRD, FTIR, XRF, XPS, and BET characterizations of the catalysts were carried out. Results showed that the catalysts were reduced at 700 ◦C by H ₂ prior to each reaction. CH ₄ and CO ₂ conversions at 900 ◦C of the catalysts after being tested for 200 h decreased in the arrange Co/Mg0.85Ni0.15O, Co/Mg0.93Ni0.07O, Co/Mg0.97Ni0.03 O, and Co/MgO. The highest H ₂ and CO selectivities were observed at a 1:1 CH ₄ :CO ₂ mole ratio. We further performed a dry reforming in the presence of low-concentration oxygen flow (1.25 Vol %) and found an increased CH ₄ conversion.

    • Syngas production by CO₂ reforming of methane on LaNixAl1−xO₃ perovskite catalysts: influence of method of preparation


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      Two series of LaNixAl1−xO₃ catalysts (0 ≤ x ≤ 1) were prepared by hydrothermal and sol–gel methods and characterized by X-ray diffraction (XRD), BET surface area, Temperature programmed reduction (TPR) and Fourier- transform infrared spectroscopy (FT-IR) techniques. The performance of these catalysts was studied for CO₂ reforming of methane (also called dry reforming of methane, DRM) at atmospheric pressure and in the temperature range of 600−800◦C, maintaining a space velocity of 28,800 h ⁻¹. Catalysts containingtrimetallic perovskite showed higher CH ₄ and CO₂ conversions than the bimetallic perovskite, due to the strong interaction of Ni with the former. Strong interaction increased the reduction temperature of the active speciesand reduced the sintering of metallic particles. At 800◦C, the sol–gel catalysts reached theirmaximum activity in terms of both CH ₄ and CO₂ conversions at x=0.3, whereas the same for hydrothermal catalysts required a Ni ratio x=0.6. The trimetallic perovskite formation was responsible for the catalyst stability. A comparison of the best catalysts from the two series revealed that the hydrothermal catalysts exhibited a slightly better performance during the time on stream analysis. The results are interpreted in terms of changes in the physicochemical properties of the catalysts.

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