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Applied Catalysis A, General (v.457, #)
Role of alkali metal in a highly active Pd/alkali/Fe2O3 catalyst for water gas shift reaction by Ryo Watanabe; Yuji Sakamoto; Keisuke Yamamuro; Sakurako Tamura; Eiichi Kikuchi; Yasushi Sekine (pp. 1-11).
•Pd/K/Fe2O3 catalyst shows high activity for water gas shift (WGS) reaction.•The K/Pd molar ratio on the catalyst has a remarkable effect on WGS activity.•The addition of alkali metals (Na, K and Cs) drastically enhanced WGS activity.•WGS on Pd/K/Fe2O3 catalyst proceeded via redox using lattice oxygen.•The synergetic effect of Pd and K brought high redox ability and structural stability.Pd/K/Fe2O3 catalyst shows high activity for water gas shift (WGS) reaction. The K/Pd molar ratio on the catalyst has a remarkable effect on WGS activity. The optimum K/Pd molar ratio is about 2. In this study, to clarify the role of alkali metal (potassium), WGS activities of Pd/alkali/Fe2O3 (alkali: Li, Na, K or Cs) catalysts were investigated and the reaction mechanism over the Pd/K/Fe2O3 catalyst was examined with transient response analyses using a concentration jump method with a quadrupole mass spectrometer (Q-Mass). Results showed that the addition of alkali metals such as Na, K and Cs drastically enhanced WGS activity, except for Li-loaded catalyst. WGS reaction over the highly active Pd/K/Fe2O3 catalyst was found to proceed via reduction–oxidation (redox) using lattice oxygen. Thereby, CO was oxidized by lattice oxygen in Fe2O3. The consumed lattice oxygen was regenerated by H2O. The results of CO-TPR revealed that oxidation of CO by lattice oxygen were enhanced by K, Cs or Na addition. H2-TPR results showed that reduction of Fe2O3 was suppressed by an increment of loading amount of potassium, which brought a high stability for the WGS reaction. The result of CO/H2O-TPR showed that steam can promote the regeneration of consumed lattice oxygen. The synergistic effect brought a high release ability of lattice oxygen for CO oxidation and also high regenerating ability of consumed lattice oxygen by H2O to produce hydrogen, to the Pd/K/Fe2O3 catalyst. It enabled high catalytic performance of the Pd/K/Fe2O3 catalyst with K/Pd molar ratio of 2.
Keywords: Water gas shift; Hydrogen production; Alkali metal addition; Redox; Lattice oxygen
One-step hydrothermal synthesis and photocatalytic performance of ZnWO4/Bi2WO6 composite photocatalysts for efficient degradation of acetaldehyde under UV light irradiation by Mirabbos Hojamberdiev; Ken-ichi Katsumata; Koji Morita; Sara Aldabe Bilmes; Nobuhiro Matsushita; Kiyoshi Okada (pp. 12-20).
•ZnWO4/Bi2WO6 photocatalyst can be synthesized by one-step hydrothermal method.•Synthesizing suspension with pH 7 favors the formation of ZnWO4 and Bi2WO6 phases.•Bi2WO6 nanoparticles are separate and/or attached to the surface of ZnWO4 particles.•Composite photocatalyst with 30mol% Bi3+ ion shows higher photocatalytic activity.•The n- n isotype junction and charge separation of each semiconductor have effect.Bi2WO6 with different Bi3+ ion concentrations (0–30mol%) is incorporated with the ZnWO4 photocatalyst to improve the photocatalytic efficiency by forming a ZnWO4/Bi2WO6 composite photocatalyst with hierarchical heterostructure via a one-step hydrothermal method. X-ray diffraction and Raman spectroscopy analyses confirm the presence of ZnWO4 and Bi2WO6 as main phases in the composite photocatalyst. Scanning electron microscopy and transmission electron microscopy observations reveal that the rice- and plate-like Bi2WO6 nanoparticles were either separate or attached to the surface of quasi-spherical ZnWO4 particles. A gradual increase in the Bi2WO6 content of the composite photocatalyst results in a monotonic shift of the absorption edge from ca. 355nm to longer wavelengths up to ca. 450nm. The photocatalytic performance of the ZnWO4/Bi2WO6 composite photocatalyst was evaluated by investigating the degradation of gaseous acetaldehyde (AcH) under UV light irradiation. Only the composite photocatalyst synthesized with 30mol% Bi3+ exhibits higher photocatalytic activity under UV light irradiation compared with both individual ZnWO4 and Bi2WO6, and with a mechanically mixed ZnWO4/Bi2WO6 composite photocatalyst. The enhanced photocatalytic activity is attributed to the n- n isotype junction formed between the two semiconductors and the charge separation of each semiconductor.
Keywords: Bismuth tungstate; Composite photocatalyst; Heterostructure; Hydrothermal synthesis; UV light irradiation; Zinc tungstate
Direct synthesis of phenol from benzene catalyzed by multi-V-POMs complex by Hua Yang; Qing Wu; Jun Li; Wen Dai; Hengyun Zhang; Dan Lu; Shuang Gao; Wansheng You (pp. 21-25).
•A POM-based catalyst with multi-isolated vanadium was synthesized.•V atoms were located in both of the cation and anion parts of the catalyst.•Catalytic performance was higher than any parts of the catalyst used alone.•The increased ordered active sites enhanced the activities of the catalyst.•The reused catalyst structure is maintained and its catalytic activity is stable.A novel catalyst, [Mo2V2O9(bpy)6][PMo11VO40], was synthesized by the self-assembling of [PMo11VO40]4− and [Mo2V2O9(bpy)6]4+ unit and characterized by elemental analyses, TG, IR, X-ray powder diffraction and X-ray single crystal diffraction. [Mo2V2O9(bpy)6][PMo11VO40] with multi-isolated active sites showed good catalytic activities for hydroxylation of benzene to phenol. A high yield of phenol (25.5%) with selectivity to phenol of 90.7% was obtained using H2O2 as oxidant. The catalyst can be recycled for 5 times while its structure was unchanged and its catalytic activity was maintained.
Keywords: Heteropolymolybdates; Vanadium-containing cation; Benzene; Phenol; H; 2; O; 2
Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature by Pablo M. Cuesta Zapata; Mónica L. Parentis; Elio E. Gonzo; Norberto A. Bonini (pp. 26-33).
•The sol–gel and hydrothermal treatment let to obtain Cr3+ incorporated to SiO2 support.•The Cr3+ ions are stable and resistant to segregation in air up to 350°C.•These Cr3+ ions produce Lewis acid sites that catalyze the 2-propanol dehydration.•The Cr6+ ions formed after in air calcination (450°C) develops weak Brönsted sites.•2,6-Lutidine adsorption lets to quantify the Lewis and Brönsted sites by FTIR.Cr/SiO2 catalysts (4–8% Cr, w/w), obtained from Cr(III) salts and tetraethylortosilicate (TEOS), were prepared by the sol–gel method. After TEOS hydrolysis in ammoniacal solution (pH: 9.5), the gel was treated under hydrothermal conditions at 120–220°C. The solids were characterized by N2 sorptometry, TG–DTA, DRUV–vis, XRD, and FTIR. In vacuum or N2 atmosphere, Cr3+ ions were stable up to 450°C. However, calcination in air promotes the partial oxidation of Cr3+ to Cr6+ as the temperature increases from 200 to 450°C. The amount of Cr6+ formed depends on the temperature of the hydrothermal treatment. 2,6-Lutidine adsorption allows to determine the evolution, with respect to calcination temperature, of both Lewis and Brönsted acid centers. Cr3+ ions were related to the presence of Lewis sites, and Cr6+ ions to the development of weak Brönsted acid sites. Accordingly, the 2-propanol dehydration reaction rate shows an increase when the catalysts are treated in N2 at 450°C, while catalysts calcined in air develop a lower acidity. The dehydration reaction is attributed to the presence of Lewis acid centers.
Keywords: Cr/SiO; 2; Sol–gel; DRUV–vis; 2,6-Lutidine; 2-Propanol
A recyclable magnetic nanoparticles supported antimony catalyst for the synthesis of N-substituted pyrroles in water by Fei-Ping Ma; Pei-He Li; Bao-Le Li; Li-Ping Mo; Ning Liu; Hui-Jun Kang; Ya-Nan Liu; Zhan-Hui Zhang (pp. 34-41).
•A novel magnetic nanoparticle catalyst was prepared and characterized.•The synthesized catalyst shows excellent catalytic performance for Clauson-Kaas reaction.•The catalyst can be easily recovered by magnetic separation.•The supported catalyst exhibited high stability and could be reused several times without significant loss of its catalytic activity.A new magnetic nanoparticle-supported antimony catalyst was prepared and evaluated as a recoverable catalyst for Clauson-Kaas reaction. The reaction proceeds efficiently in aqueous medium to give the corresponding N-substituted pyrroles in high yield. The immobilized catalyst could be easily recovered by magnetic separation and recycled for six times without significant loss of its catalytic activity.
Keywords: Magnetic nanoparticle; Immobilization; Ionic liquid; Antimony; Heterogeneous catalyst; Clauson-Kaas reaction; Pyrroles; Water
Effect of surface decoration with LaSrFeO4 on oxygen mobility and catalytic activity of La0.4Sr0.6FeO3− δ in high-temperature N2O decomposition, methane combustion and ammonia oxidation by D.V. Ivanov; L.G. Pinaeva; L.A. Isupova; E.M. Sadovskaya; I.P. Prosvirin; E.Yu. Gerasimov; I.S. Yakovleva (pp. 42-51).
Display Omitted•Surface oxygen mobility influences activity in N2O decomposition and NH3 oxidation.•Influence of bulk oxygen mobility on activity in methane combustion was shown.•High catalytic activity for “LaSrFeO4–La1− xSr xFeO4” composites was demonstrated.•Increased surface18O/16O exchange rate due to formation of interfaces is discussed.This article is an attempt to elucidate the role of lattice oxygen mobility in catalytic activity of Sr-substituted ferrites at high temperatures. For this goal, three catalysts with close element (La, Sr, Fe) content but different phases and surface compositions: LaSrFeO4(surface)–La0.4Sr0.6FeO3 (LSF-N), La0.15Sr0.85FeO3–La0.7Sr0.3FeO3 (LSF-C) and LaSrFeO4 have been studied in high temperature reactions of N2O decomposition, ammonia oxidation and methane combustion. The kinetics of18O/16O oxygen exchange have been analyzed at 800°C and 0.005atm oxygen partial pressure, which is closely corresponding to the reaction conditions, and the rates of surface oxygen exchange and the coefficient of lattice oxygen diffusion have been evaluated. It allowed us to reveal the direct correlation between the surface exchange rate constant and the rate of N2O decomposition. For NH3 oxidation, evidence of the same order of the samples activity both in surface oxygen exchange and ammonia oxidation reaction was shown. In methane oxidation it was found that activity correlates with the rate of exchange for 20 monolayers of oxygen atoms indicating the growing influence of lattice oxygen mobility. The results show that improvement of catalytic properties can be achieved when synthesizing “LaSrFeO4(surface)–La0.4Sr0.6FeO3” composites. Such composites exhibit increased rate of surface oxygen exchange on retention of high lattice oxygen mobility, which can be attributed to formation of heterostructured interfaces.
Keywords: Abbreviations; ICDD PDF; International Center for Diffraction Data Powder Diffraction File; DDPA; differential dissolution phase analysis; XRD; X-ray diffraction; XPS; X-ray photoelectron spectroscopy; ASF; atomic sensitivity factorLanthanum–strontium–ferrite mixed oxide; Layer-structured perovskites; Nitrous oxide decomposition; Methane oxidation; Ammonia oxidation; Oxygen mobility
Comparative study of ageing condition effects on Pd/Ce0.5Zr0.5O2 and Pd/Al2O3 catalysts: Catalytic activity, palladium nanoparticle structure and Pd-support interaction by Yidan Cao; Rui Ran; Xiaodong Wu; Baohuai Zhao; Jie Wan; Duan Weng (pp. 52-61).
•Effects of ageing conditions on Pd supported catalysts are studied systematically.•Sintering of Pd species in Pd/Ce0.5Zr0.5O2 is inhibited in air and cyclic ageing.•Sintering of Pd species in Pd/Al2O3 is severe regardless of the ageing condition.•PdOCe bond works with the involvement of oxygen to inhibit the sintering of Pd. PdOCe bond works during cooling down from high temperature.Pd/Ce0.5Zr0.5O2 and Pd/Al2O3 catalysts were prepared by impregnation method and aged in different atmospheres (air, N2, H2 and cyclic (air–H2)) at 1050°C. The CO oxidation activities of the catalysts were evaluated. The states of palladium nanoparticles were characterized by step scanning X-ray diffraction (XRD), CO chemisorption, H2 temperature-programmed reduction (TPR), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (Raman). The Pd/Ce0.5Zr0.5O2 catalysts aged in air and cyclic conditions exhibit much better catalytic activities than those aged in N2 and H2, but the Pd/Al2O3 catalysts aged in different atmospheres show similar activities. Small PdO crystallites are observed in Pd/Ce0.5Zr0.5O2 catalysts after air and cyclic ageing, while larger Pd crystallites are found after N2 and H2 ageing. The sintering of Pd species is inhibited with the presence of oxygen in Pd/Ce0.5Zr0.5O2 catalysts. This is due to the strong interaction between Pd and CZ support in the form of PdOCe bond, which works during the cooling stage (from 1050°C to room temperature). However, the thermal ageing deactivates the Pd/Al2O3 catalysts regardless of the ageing condition. The Pd/PdO particles grow to around 100nm in all the aged Pd/Al2O3 catalysts, leading to the worse activity compared with the Pd/Ce0.5Zr0.5O2 catalysts.
Keywords: Palladium; Ageing condition; Interaction; Pd; O; Ce bond
Hydrogenation of acrylonitrile-butadiene rubber latex using in situ synthesized RhCl(PPh3)3 catalyst by Yin Liu; Zhenli Wei; Qinmin Pan; Garry L. Rempel (pp. 62-68).
Display Omitted► In situ synthesized RhCl(PPh3)3 catalyst from RhCl3 and PPh3 in aqueous system. ► CCs in NBR was selectively hydrogenated. ► High conversion could be achieved (≥95mol.%). ► The diffusion of the catalyst was crucial for high conversion. ► Adding alcohol could improve the in situ synthesis efficiency.Catalytic hydrogenation of acrylonitrile-butadiene rubber (NBR) latex was achieved by using in situ synthesized RhCl(PPh3)3 catalyst. Water-soluble rhodium salt (RhCl3) was used as the catalyst precursor which was reacted in situ with triphenylphosphine (PPh3) to form RhCl(PPh3)3. Compared with using solid RhCl(PPh3)3, hydrogenation of NBR latex using the in situ RhCl(PPh3)3 showed a faster hydrogenation reaction. Based on the retention of catalyst in the polymer, it was revealed that the efficiency of in situ synthesis and the diffusion of the catalyst from the aqueous phase into the polymer particles were crucial in achieving the required high degree of hydrogenation. As a result, it was discovered that by introducing a small amount of alcohol (e.g. RhCl3=0.52mmol/L, PPh3=18mmol/L, ethanol/total NBR latex=1/10 volume ratio) to the feed latex, the in situ synthesized catalyst could be used in the hydrogenation reaction very efficiently.
Keywords: Hydrogenation; In situ catalyst synthesis; Latex; NBR; Alcohol
Ullmann-type coupling reaction using metal-organic framework MOF-199 as an efficient recyclable solid catalyst by Nam T.S. Phan; Tung T. Nguyen; Chi V. Nguyen; Thao T. Nguyen (pp. 69-77).
Display Omitted► MOF-199 was used as catalyst for the Ullmann-type reaction. ► High conversions were achieved using catalytic amounts of the MOF-199. ► The catalyst could be recovered and reused.A highly porous metal-organic framework (MOF-199) was synthesized, and characterized by several methods including XRD, SEM, TEM, TGA, FT-IR, AAS, and nitrogen physisorption measurements. The MOF-199 was used as an efficient recyclable solid catalyst for the Ullmann-type reaction between aryl iodides and phenols to form diaryl ethers. High conversions were achieved for the transformation at the catalyst concentration of 5mol%, in the presence of MeONa as a base. Due to the rare availability and the high cost, Cs2CO3 should only be used for the case of deactivated aryl iodides or deactivated phenols. The MOF-199 catalyst could be facilely separated from the reaction mixture by simple filtration, and could be reused several times without a significant degradation in catalytic activity. The Ullmann-type reaction could only proceed in the presence of the solid MOF-199 catalyst, and the contribution from leached active species in the liquid phase, if any, was negligible.
Keywords: Metal-organic framework; MOF-199; Ullmann-type reaction; Heterogeneous catalyst; Diaryl ethers
Reduced graphene oxide and PbS nanoparticles co-modified TiO2 nanotube arrays as a recyclable and stable photocatalyst for efficient degradation of pentachlorophenol by Xilin Zhang; Yanhong Tang; Yue Li; Yao Wang; Xuanneng Liu; Chengbin Liu; Shenglian Luo (pp. 78-84).
•One-step electrodeposition method to prepare RGO/PbS-TiO2 NTs is simple and green.•A heterogeneous, stable and eco-friendly reusable photocatalyst is utilized.•The ternary photocatalyst enhances photoinduced charges separation.•The photocatalyst displays almost 100% photocatalytic removal of PCP.TiO2 nanotube arrays (TiO2 NTs) were simultaneously modified by reduced graphene oxide (RGO) and PbS nonoparticles (NPs) through a simple one-step electrodeposition process. RGO film is formed on the top surface of TiO2 NTs and PbS NPs showing size less than 20nm are intercalated within the RGO sheets and also dispersed inside/outside walls the TiO2 NTs. Resulting from the synergetic effect of RGO and PbS, the photocatalytic activity of the ternary RGO/PbS-TiO2 NTs photocatalyst far exceeds those of bare TiO2 NTs, the binary RGO-TiO2 NTs and PbS-TiO2 NTs photocatalysts in the degradation of pentachlorophenol (PCP) under simulated solar light. After 120-min irradiation, almost 100% PCP removal is obtained on the RGO/PbS-TiO2 NTs, compared to 61% on bare TiO2 NTs, 76% on RGO-TiO2 NTs, and 86% on PbS-TiO2 NTs. Because the PbS NPs were covered by the RGO sheets, to a certain extent the photocorrosion of PbS was suppressed, and therefore the RGO/PbS-TiO2 NTs photocatalyst shows a good stability relative to the PbS-TiO2 NTs without RGO. This study will inspire better design of advanced photocatalysts with high visible-light photocatalytic activity, easy recovery, and good stability.
Keywords: TiO; 2; nanotube; Reduced graphene oxide; PbS; Photocatalysis; Pentachlorophenol