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Applied Catalysis A, General (v.398, #1-2)
Catalytic cracking of hydrocarbons over modified ZSM-5 zeolites to produce light olefins: A review by Nazi Rahimi; Ramin Karimzadeh (pp. 1-17).
Display Omitted► Review of light olefin production via catalytic cracking of various industrial feedstocks over modified ZSM-5 zeolites. ► The influence of various promoters, i.e. alkali and alkaline earth, transition, rare earth elements and phosphorus, on chemical properties of the modified ZSM-5. ► The effect of ZSM-5 modification on the selectivity of products. ► The influence of different factors, such as the ZSM-5 acidity, Si/Al ratio and the temperature, on light olefin production and the reaction scheme. ► The role of incorporated element in the catalytic cracking mechanism.Steam cracking of hydrocarbons has been the major source of light olefins for more than half a century. The recent studies have reported that ethylene and propylene can also be produced through the cracking of hydrocarbons over modified ZSM-5 zeolites in a considerable amount.This paper highlights the important current ideas about acid-catalyzed hydrocarbon cracking that has resulted in high yield of ethylene and propylene. Light olefin production via catalytic cracking of various industrial feedstocks, ranging from heavy hydrocarbons to ethane, over modified ZSM-5 zeolites, has been reviewed in the present paper. Furthermore, the influence of various employed promoters, i.e., alkali and alkaline earth, transition, rare earth elements, and phosphorus, on the chemical properties of the modified ZSM-5 and the performance of resulting catalyst in enhancing the selectivity to light olefins, have been addressed. Moreover, the influences of different factors, including the zeolite acidity, Si/Al ratio and the temperature, on the light olefin production and the reaction scheme have been specified. The role of incorporated element in the catalytic cracking mechanism is also summarized.
Keywords: Light olefins; Catalytic cracking; ZSM-5; Element modification; Lewis/Brønsted acid sites
Kinetics of propane dehydrogenation over Pt–Sn/Al2O3 catalyst by Qing Li; Zhijun Sui; Xinggui Zhou; De Chen (pp. 18-26).
Display Omitted► We modeled kinetics of propane dehydrogenation. ► Model describes kinetics of dehydrogenation, cracking and deactivation. ► First C–H cleavage was identified as the rate determining step. ► Propene was identified as the main precursor for the coke formation. ► Hydrogen suppresses the coke formation.Langmuir–Hinshelwood kinetic models for catalytic propane dehydrogenation on Pt -Sn/Al2O3 are proposed based on the reaction mechanisms that take into account the one step or two-step dehydrogenation and are evaluated by fitting the experiments. When taking into consideration the fitting accuracy, the number of fitting parameters and the rigorousness of the reaction mechanism, the kinetics of propane dehydrogenation based on the assumptions of step-wise dehydrogenation, the first step dehydrogenation as the rate-determining step, and low surface coverage of C3H7 outperforms other kinetic models. The change of catalyst activity with time-on-stream is related to the rate of coke formation that depends on the partial pressures of propene and hydrogen. Finally a complete kinetic model, which includes propane dehydrogenation and cracking and catalyst deactivation because of coking, is developed, which is found to agree well with the changes of propane conversions with time-on-stream under different operating conditions. Direct measurement of coke formation is avoided by the approach employed in this study for the prediction of catalyst deactivation by coke deposition.
Keywords: Propane dehydrogenation; Kinetics; Coke formation; Pt–Sn/Al; 2; O; 3; catalyst
Hydrotreating of coker light gas oil on Ti-HMS supported heteropolytungstic acid catalysts by K. Soni; P.E. Boahene; K. Chandra Mouli; A.K. Dalai; J. Adjaye (pp. 27-36).
Display Omitted► Keggin-type HPAs as starting materials for catalysts preparation has beneficial effect on hydrotreating activity. ► Keggin structure was preserved during impregnation of Ti-HMS and calcination steps. ► NiPW/Ti-HMS catalysts showed better performance in deep HDS and HDN of CLGO.Ti-HMS substrates were synthesized by using dodecylamine as structure-directing agents. A series of HPW/Ti-HMS catalysts with different Si/Ti ratios, promoted by Ni was prepared using Keggin-type heteropolyacids (H3PW12O40) as active phase precursors. These catalysts were compared with corresponding NiW/HMS catalysts prepared from the traditional precursors (ammonium metatungstate). Prepared supports and catalysts were characterized by small- and wide-angle XRD, N2 physisorption, FT-IR, Raman, DRIFT, TEM, and SEM. Catalytic activity was assessed for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of coker light gas oil (CLGO) derived from Athabasca bitumen, in a trickle bed reactor at a temperature, pressure, and LHSV of 370°C, 8.8MPa, and 2.0h−1, respectively. The W catalysts prepared from heteropolyacids showed better performance for hydrotreating than their counterparts prepared from traditionally used W ammonium salts. The incorporation of Ti into HMS afforded catalysts that were more active than the Ti-free counterpart, due to the larger number of coordinately unsaturated sites (CUS) of the metal sulfide on Ti-loaded catalysts. Under steady-state conditions, the NiPW/Ti-HMS (20) catalyst with a Si/Ti ratio of 20 was the most active among the catalysts studied due to more uniform distribution of active species.
Keywords: Ti-HMS; 12-Tungstophosphoric acid; Keggin structure; HDS; HDN; Coker light gas oil
Reaction scheme of o-xylene oxidation on vanadia catalyst by Robert Marx; Hans-Jörg Wölk; Gerhard Mestl; Thomas Turek (pp. 37-43).
Display Omitted► Novel reaction scheme for o-xylene oxidation. ► Identification of several previously unknown intermediates. ► Comparison of pilot plant data to the industrial process. ► Determination of intermediate selectivities.The oxidation of o-xylene (OX) to phthalic anhydride (PA) is one of the important industrial processes based on selective oxidation reactions. However, the fundamental understanding of the by-product formation is still an open task. By using a sample port pilot plant, a detailed investigation was conducted for the first time of the by-product formation at different operation conditions. Several hitherto unknown intermediates could unambiguously be identified. The combination of process conditions and by-product formation enables the discussion of a new improved reaction scheme for the catalytic oxidation of o-xylene.The reaction path from OX to PA is commonly described by a rake mechanism consisting of a number of parallel and serial reactions. Tolualdehyde and phthalide are seen as the main intermediates. The most important by-products are maleic anhydride (MA), CO and CO2. The reaction paths towards these by-products are widely unknown.Several gas phase components, such as toluquinone and 2,3-dimethyl-p-benzoquinone not reported yet in the current literature, were observed for the first time in this study. Most of these previously unknown components are reaction intermediates, which later do not form the desired reaction product, PA.
Keywords: Phthalic anhydride; Vanadia; Partial oxidation; Mechanism; Kinetics
Indications of the reactive species in a heterogeneous Fenton-like reaction using Fe-containing zeolites by R. Gonzalez-Olmos; F. Holzer; F.-D. Kopinke; A. Georgi (pp. 44-53).
Display Omitted► Different KDIE for methanol in heterogeneous and homogeneous Fenton reactions. ► Scavenging experiments revealed that more than one oxidant species is involved. ► Additional oxidant reacts with a higher selectivity and lower reactivity than OH. ► According to the results, this additional oxidant could be a ferryl species.Heterogeneous Fenton-like reactions have potential applications in wastewater treatment. Recently, the use of zeolites containing iron species as catalysts in Fenton-like processes has gained increasing interest. While it has been assumed in the literature that hydroxyl radicals (OH) are the dominant reactive species formed from H2O2 in the presence of Fe-zeolites, no direct evidence for this hypothesis exists so far. This work aims at the elucidation of the type of reactive species involved in the heterogeneous Fenton reaction using the Fe-containing zeolites Fe-ZSM5 and Fe-Beta. Electron paramagnetic resonance (EPR) measurements using dimethyl pyrroline-N-oxide (DMPO) as spin trap were carried out; the formation of the complex DMPO-OH was observed, which is often ascribed to a reaction with OH. However, significant differences were found in the kinetic deuterium isotope effect (KDIE) for methanol oxidation between the heterogeneous Fenton-like reaction and genuine OH reactions initiated by the homogeneous Fenton reaction. The KDIE for methanol oxidation in the heterogeneous reaction increased from 1.33 to 1.41 with increasing concentration of the OH scavenger bicarbonate, whereas the KDIE in the classical Fenton reaction is 1.07 and unaffected by the presence of quenchers. The significantly different values are a clear indication for the participation of additional oxidants beside OH. In addition, Fe-zeolites catalyzed the epoxidation of cyclohexene by H2O2. This type of reaction suggests the participation of a high-valent oxoiron complex (ferryl) in the wet peroxide oxidation of organic compounds catalyzed by Fe-zeolites.
Keywords: Heterogeneous Catalysis; Fenton; Zeolites; Hydroxyl Radical; Ferryl
Deuterium tracer studies on cobalt catalyzed Fischer–Tropsch synthesis: Addition of alcohols by Buchang Shi; Chunfen Jin (pp. 54-58).
Display Omitted► Alcohols cannot initiate the chain growth during Co/SiO2 catalyzed FT reaction. ► Alcohols were incorporated into alkanes when the FT reactions were conducted over Co/SiO2+Al2O3. ► Nearly constant D/molecule (H/molecule) values were obtained. ► The pathways for the formation of ethylidene and propylidene were proposed.Unlike the iron catalyzed Fischer–Tropsch (FT) synthesis, the additions of ethanol-d6 and 2-propanol-d8 during the Co/SiO2 catalyzed FT reactions did not produce detectable amount of deuterated isomer in any alkane. However, when the FT reactions were conducted over a mixture of FT catalyst Co/SiO2 and dehydration catalyst Al2O3, the d1, d2 and d3 isomers of alkanes from C7 to C15 were obtained with a nearly constant D/molecule value of 1.4 when ethanol-d6 was used as the tracer while d1–d6 isotopic isomers of alkanes were observed with a nearly constant D/molecule value of 2.3 when 2-propanol-d8 was used. The similar results were obtained when 1-propanol was used as the tracer. These results lead us to conclude that the C2 or C3 species that initiates the chain growth in the FT reaction resembles ethene or propene. The pathways for the formations of ethylidene and propylidene were proposed.
Keywords: Deuterium tracer; Fischer–Tropsch synthesis; Alkylidene mechanism; C–C coupling
Efficiency of ethanol conversion induced by controlled modification of pore structure and acidic properties of alumina catalysts by Leandro Martins; Dilson Cardoso; Peter Hammer; Teresita Garetto; Sandra H. Pulcinelli; Celso V. Santilli (pp. 59-65).
Catalytic results of ethanol dehydration of alumina samples at 300°C, showing that the conversion passes through a minimum that is related to a combination of adequate porosity and acidity of the catalyst.Display Omitted► Bimodal porous alumina catalysts with both continuous macropores and mesopores. ► Evaluation of the effectiveness of macropore insertion. ► Macropores in the catalyst structure enhanced ethanol conversion. ► Emulsifier agent played a negative role in the generation of alumina samples acidity.Bimodal porous alumina catalysts with both continuous macropores and mesopores were prepared using a dual soft template method. The addition of decahydronaphthalene as emulsifier agent successfully contributed to the formation of macropores. The effectiveness of macropore insertion was evaluated in the model reaction of ethanol dehydration at 300°C. Judging from the results obtained by acidity measurements using temperature programmed desorption of ammonia and the performance of these catalysts in the ethanol dehydration, the introduction of macropores in the catalyst structure enhanced the ethanol conversion.
Keywords: Macroporous materials; Mesoporous materials; Alumina; Emulsion; Ethanol dehydration
Dehydrogenation of ethylbenzene over highly active and stable perovskite oxide catalyst – Effect of lattice oxygen on/in perovskite oxide and role of A/B site in perovskite oxide by Ryo Watanabe; Yasushi Sekine; Jungo Kojima; Masahiko Matsukata; Eiichi Kikuchi (pp. 66-72).
Display Omitted► LBFMO catalyst shows high and stable activity for dehydrogenation of ethylbenzene. ► LBFMO catalyst works with redox mechanism using lattice oxygen and steam. ► Rate determining step is regeneration of lattice oxygen. ► Fe substitution suppressed lattice oxygen reduction, promoted its regeneration. ► High catalytic activity and stability is derived from enhanced redox ability of LBFMO.Previously we reported that La0.8Ba0.2Fe0.4Mn0.6O3− δ (LBFMO) perovskite oxide catalyst showed extremely high activity for dehydrogenation of ethylbenzene to produce styrene. The reaction mechanism of dehydrogenation of ethylbenzene over LBFMO catalyst and the role of A/B site cation in the perovskite were investigated using transient response experiments and thermogravimetric analyses in a H2O/H2 atmosphere. Results showed that the dehydrogenation of ethylbenzene over LBFMO perovskite catalyst proceeded via reduction–oxidation (redox) of the perovskite oxide in this temperature range (800–900K). Thereby, oxidative dehydrogenation of ethylbenzene consumed lattice oxygen in the perovskite; the consumed lattice oxygen was regenerated by H2O. We measured the lattice oxygen release rate and regenerating rate over LBFMO perovskite catalyst. The regeneration rate of lattice oxygen was almost equal to the formation rate of styrene in the steady state of the dehydrogenation reaction. Substituting the B site of perovskite with Fe has a stabilizing effect for the lattice oxygen in the perovskite, and enhanced the regeneration rate of lattice vacancy drastically using steam. We concluded that the better stability of LBFMO than that of other catalysts was derived from enhanced lattice oxygen regeneration in the perovskite.
Keywords: Dehydrogenation of ethylbenzene; Redox properties; Perovskite oxides; Lattice oxygen
Alkaline carbons as effective catalysts for the microwave-assisted synthesis of N-substituted-gamma-lactams by V. Calvino-Casilda; R.M. Martín-Aranda; A.J. López-Peinado (pp. 73-81).
Display Omitted► Synthesis of N-substituted-gamma-lactams. ► Substantial enhancing effects in the reaction activated by microwave irradiation. ► Microwave activation and alkaline carbon catalysts offers interesting prospects. ► Excellent yields under mild reaction conditions. ► This process can be also generalized for the production of similar fine chemicals.The selective construction of new CC or Cheteroatom bonds is frequently the fundamental step in the synthesis of derivatives with high added value. In particular, molecules with CN bonds are of great interest due to their widespread use and intrinsic importance. Of the large number of organic compounds with useful biological activity, organic compounds with CN bonds are among the most prominent. For instance, the nitrogenated gamma-lactamic heterocycles are the basic structures of many substances used as intermediates in the synthesis of important compounds with pharmacological properties such as psychotropics and antihypertensives as well as others with biological properties. In the present work, we reported for the first time an efficient and eco-friendly alternative to obtain N-substituted-gamma-lactams by carbon–nitrogen coupling of 2-pyrrolidinone and 1-heptanal assisted by microwave irradiation, over activated alkali-Norit carbon catalysts in solvent-free conditions.
Keywords: Activated carbons; Heterogeneous catalysis; Microwave activation; Green chemistry; 2-pyrrolidinone; N-substituted-gamma-lactams
The role of titania pillar in copper-ion exchanged titania pillared clays for the selective catalytic reduction of NO by propylene by Xinyong Li; Guang Lu; Zhenping Qu; Dongke Zhang; Shaomin Liu (pp. 82-87).
Display Omitted► A series of Cu-Ti-PILC samples with different Ti/clay ratios demonstrated the role of titania pillar in SCR of NO by propylene. ► The titania pillar increased interlay spacing, surface area and Cu2+ content formed in the adjacent layers. ► The titania pillar improved NO adsorption to form the intermediate of nitrate species and its conversion into N2.A series of copper-ion exchanged titania pillared clays (Cu-Ti-PILC) with different Ti/clay rates were used for the selective catalytic reduction (SCR) of NO by propylene to examine the role of titania pillar in these catalysts. Among the catalysts tested, the sample with Ti/clay=10 provided the best performance with 55.4% yield on N2. XRD coupled with N2 adsorption confirmed that the interlay spacing and surface area of the studied catalysts increased with a rise in Ti/clay rate. The TPR study showed that the Cu2+ amount reached a maximum of 0.69μmol/g-cat at Ti/clay=10. The NO+O2-TPD study indicated that the decomposition amount of the adsorbed nitrate species increased remarkably after the introduction of titania into clay as support. Moreover, the largest decomposition amount was obtained for the sample with Ti/clay=10. It is concluded that the titania pillar provides the Cu-Ti-PILC samples with the increased interlay spacing, surface area and Cu2+ amount formed in the adjacent layers. These features make NO adsorbed more easily by copper species to form the intermediate of nitrate species, which enhances the conversion of NO into N2.
Keywords: Cu-Ti-PILC; Ion-exchange; SCR; TPR; TPD
Dioxomolybdenum(VI) complexes containing chiral oxazolines applied in alkenes epoxidation in ionic liquids: A highly diastereoselective catalyst by José A. Brito; Sonia Ladeira; Emmanuelle Teuma; Beatriz Royo; Montserrat Gómez (pp. 88-95).
Display Omitted► Dioxomolybdenum(VI) complexes applied in alkenes epoxidation in ionic liquids. ► Pyrrolidinium-based ionic liquid leads to stable oxazoline-based catalytic systems. ► Diastereospecific bimetallic catalyst in pyrrolidium-based ionic liquids. ►13C and95Mo NMR studies evidence Mo-NHC bond formation in imidazolium IL.New monometallic dioxomolybdenum complexes,2 and3, containing the bis(oxazoline)B and the oxazolinyl-pyridineC respectively, have been prepared and fully characterized both in solution and solid state, including the single-crystal X-ray diffraction analysis for2, which represents the first structure of a Mo(VI) complex coordinated to a bis(oxazoline). These complexes, together with the bimetallic system1, were used as catalytic precursors for alkenes epoxidation (cyclooctene, (R)-limonene, trans-β-methylstyrene) in imidazolium- and pyrrolidinium-based ionic liquids, exhibiting a high chemoselectivity towards the epoxide formation, mainly for cyclooctene and (R)-limonene epoxidation, without formation of the corresponding diols. In [BMP][NTf2] (BMP=butyl methyl pyrrolidinium; NTf2=bis(trifluoromethanesulfonyl)amide), complex1 exclusively gave trans(R)-limonene 1,2-epoxide, while monometallic catalytic systems led to a low diastereoselectivity.95Mo NMR studies helped to understand the catalytic behaviour of1 and2 in ionic liquid medium.
Keywords: Oxomolybdenum(VI) complexes; Oxazoline; Olefin epoxidation; Ionic liquids; Diastereoselectivity
A study on HCHO oxidation characteristics at room temperature using a Pt/TiO2 catalyst by Sung Su Kim; Kwang Hee Park; Sung Chang Hong (pp. 96-103).
Display Omitted► The activity of Pt/TiO2 catalysts was determined by the type of TiO2. ► The reduced Pt sites (metallic Pt, Pt2+) play a key role in the mechanism in HCHO oxidation. ► HCHO conversion rate over optimum Pt/TiO2 catalyst was approximately 100%.The oxidation of HCHO at room temperature was studied on Pt/TiO2 catalysts prepared by wet impregnation. The catalytic activity was dependent on the type of the TiO2 support and HCHO feeding rate. The surface carbon monoxide species were the main intermediate for HCHO oxidation, which was examined using in situ DRIFTS. XPS analysis confirmed that the catalytic performance and valence states of the catalyst were closely related. However, XRD analysis showed that the number of active sites decreased due to Pt agglomeration during reduction treatment at temperatures higher than 873K.
Keywords: HCHO; Pt/TiO; 2; Oxidation; Room temperature; Valence state
Key properties promoting high activity and stability of supported PdSb/TiO2 catalysts in the acetoxylation of toluene to benzyl acetate by S. Gatla; N. Madaan; J. Radnik; V.N. Kalevaru; M.-M. Pohl; B. Lücke; A. Martin; A. Brückner (pp. 104-112).
Display Omitted► Performance of PdSb/TiO2 catalysts is governed by thermal pretreatment. ► The pretreatment gives best catalyst, Pd with PdO surface and highly dispersed Sb. ► Crystalline PdSb alloys formed in 10%H2/He flow are totally inactive. ► New preparation method makes use of deactivating additives dispensable.The influence of thermal pretreatment in air, helium and 10% H2/He on the catalytic performance of a supported 9% Pd, 12% Sb/TiO2 catalyst in the gas phase acetoxylation of toluene has been studied by integrated evaluation of catalytic tests and catalyst characterization using mainly XRD, TEM and XPS. A pretreatment temperature of 600°C is beneficial for shortening the activation period, while the atmosphere during thermal pretreatment influences the long-term stability. Highest catalytic performance with a good long-term stability was reached with pretreatment in He, which creates Sb-containing Pd particles, on which a mixed Pd0/PdO surface is formed during time on stream. Sb stabilizes oxidized Pd species and leads to more stable catalysts in contrast to air-calcined samples. The catalyst pretreated in H2/He was completely inactive, due to the formation of a stable Pd8Sb3 alloy.
Keywords: Toluene; Benzyl acetate; Acetoxylation; TiO; 2; supported palladium; Deactivation; Thermal pretreatment
Ethylbenzene dehydrogenation over FeO x/(Mg,Zn)(Al)O catalysts derived from hydrotalcites: Role of MgO as basic sites by Rabindran J. Balasamy; Balkrishna B. Tope; Alam Khurshid; Ali A.S. Al-Ali; Luqman A. Atanda; Kunimasa Sagata; Makiko Asamoto; Hidenori Yahiro; Kiyoshi Nomura; Tsuneji Sano; Katsuomi Takehira; Sulaiman S. Al-Khattaf (pp. 113-122).
Display Omitted► Ethylbenzene dehydrogenation. ► Hydrotalcite-derived FeO x/(Mg,Zn)(Al)O catalysts. ► β-H+ abstraction on the Mg2+–O2− basic sites. ► Reduction–oxidation of Fe3+/Fe2+ active sites.A series of Mg3− xZn xFe0.5Al0.5 mixed oxide catalysts derived from hydrotalcites were tested in the ethylbenzene dehydrogenation to styrene in He atmosphere at 550°C. The catalysts were prepared by coprecipitation from the nitrates of metal components followed by calcination to mixed oxides at 550°C. A part of Mg2+ in Mg3Fe0.5Al0.5 mixed oxide was replaced with Zn2+ to test the effect of MgO as the support. The mixed oxides were composed of periclase and spinel-type compounds with a high surface area of100–180 m2gcat−1. Mössbauer and XPS measurements indicated the presence of Fe3+ on the catalysts and H2-TPR measurement suggested that the dehydrogenation reaction is catalyzed by the reduction–oxidation between Fe3+/Fe2+. The activity of Mg3− xZn xFe0.5Al0.5 mixed oxide decreased with increasing x, indicating an important role of MgO on the activity. Both CO2-TPD measurements as well as IR measurements of adsorbed CO2 clearly indicated the presence of basic sites of Mg2+O2− on the catalysts. It seems that the combination of Mg2+O2− and Fe3+ was essential for the catalytic activity. It is concluded that the surface base sites generated on O2− bound Mg2+ near Fe3+ sites are responsible for H+-abstraction; the dehydrogenation of ethylbenzene was initiated by the H+ abstraction on Mg2+O2− basic sites, and accelerated by the reduction–oxidation of Fe3+/Fe2+ active species.
Keywords: Ethylbenzene dehydrogenation; Styrene; FeO; x; /(Mg,Zn)(Al)O catalysts; Mg; 2+; O; 2−; base support; H; +; abstraction
Hydrogen interaction with Pd/Ce0.8Zr0.2O2 nanocomposites prepared by microemulsion, coprecipitation and supercritical CO2 treatment by F.C. Gennari; A. Carbajal Ramos; A. Condó; T. Montini; S. Bengió; A. Cortesi; J.J. Andrade Gamboa; P. Fornasiero (pp. 123-133).
Display Omitted► Low temperature oxygen storage capacity of Pd/Ce0.8Zr0.2O2 depends on the synthesis method. ► Microemulsion is compared to coprecipitation with or without supercritical CO2 drying. ► Supercritical CO2 drying treatment enhances redox properties of Pd/Ce0.8Zr0.2O2.Nanocrystalline Ce0.8Zr0.2O2 solid-solutions (CZ) were synthesized by microemulsion (ME80), co-precipitation (CP80) and co-precipitation followed by supercritical CO2 post-treatment (SC80). Structural, microstructural and textural characterizations of oxides were performed and correlated with their redox properties. The results are consistent with the formation of solid solutions with high surface area ( SBET∼200m2g−1), constituted by nanoparticles (4–6nm) with a fluorite type structure but different mesoporosity.Dynamic oxygen storage capacity (OSC) measurements indicate that the presence of Pd improves the extension of reduction of CZ support, with the higher low-temperature OSC capacity observed for Pd/SC80. Static kinetics measurements, confirm that Pd promotes hydrogen spillover onto CZ favoring both surface and bulk reduction of Ce(IV) to Ce(III) even at 373K. Pd/SC80 presents considerably higher total OSC (691 versus 400–454μmol H2 g−1) with respect to the other samples. Significant Pd sintering was observed over Pd/ME80 only, with the consequent decrease of redox capability for Pd/ME80 catalyst. On the contrary, Pd/CP80 and Pd/SC80 samples presented highly dispersed Pd and good stability after redox cycling. These findings indicate that CP followed by thermal treatment under supercritical conditions is a promising method to synthesize materials with high low temperature OSC and promissory redox properties due to improved Pd/CZ interaction.
Keywords: Ceria–zirconia mixed oxide; Oxygen storage capacity (OSC); Palladium based materials; Hydrogen
Synergistic cell-killing by photocatalytic and plasmonic photothermal effects of Ag@TiO2 core–shell composite nanoclusters against human epithelial carcinoma (HeLa) cells by Md. Abdulla-Al-Mamun; Yoshihumi Kusumoto; Tohfatul Zannat; Md. Shariful Islam (pp. 134-142).
Uniform and stable Ag@TiO2 core–shell nanocomposites were prepared and their excellent synergistic effect of photocatalytic and plasmonic cancer cell killing under UV–visible light irradiation was observed.Display Omitted► Uniform core–shell nanostructure of Ag@TiO2 photocatalysts were prepared. ► Resultant core–shell composites were systematically investigated. ► Introducing for enhancing cancer cell (HeLa) killing under UV–visible light irradiation. ► Efficiency depends on the molar ratio of Ag to TiO2, optimum was found to be 1:7. ► Enhanced cancer killing due to plasmon-excited of Ag core and OH radicals was found.The Ag metal core–TiO2 shell (Ag@TiO2) composite nanocluster with uniform size, shape and core–shell structures was successfully synthesized by a new simple citrate reduction method. The core–shell structure of Ag@TiO2 nanocluster was characterized by using TEM, SEM, XPS, EDX, XRD, and photoluminescence spectra analysis. It was found that the Ag core is in metallic form which is covered by TiO2 shell within 3–5nm thickness and the core–shell particles size was about 30nm. The photocatalytic and photothermal cell killing efficiency of colloidal Ag@TiO2 core–shell nanocluster was evaluated against cancer (HeLa) cells under UV–vis irradiation. It was found that the Ag@TiO2 nanocluster with an adequate Ag ratio to TiO2 killed more malignant (HeLa) cells by 80% compared to TiO2 nanoparticles alone. The comparative study of the cell viability using UV only, visible only and UV–visible light revealed that the synergy effect of photocatalytic hydroxyl radical formation and Ag-plasmonic photothermal generation plays a vital role for the cancer cell killing. Based on the obtained results, a plausible mechanism was also proposed.
Keywords: Ag@TiO; 2; Core–shell structure; Fermi level equilibrium; E-redox reaction; Enhancing photocatalytic activity; Synergistic effect of plasmonic and photocatalytic cytotoxicity; Cancer cell (HeLa) killing
Towards an industrial synthesis of diamino diphenyl methane (DADPM) using novel delaminated materials: A breakthrough step in the production of isocyanates for polyurethanes by P. Botella; A. Corma; Robert H. Carr; Christopher J. Mitchell (pp. 143-149).
Display Omitted► ITQ-2, ITQ-6 and ITQ-18 are very efficient catalysts for the synthesis of DADPM. ► Delaminated structure topology imposes precise control of isomer distribution. ► It is possible to achieve DADPM crude under industrial specifications with ITQ-18. ► ITQ-18 is a real chance for replacing HCl in the industrial production of DADPM.Delaminated materials ITQ-2, ITQ-6 and ITQ-18 are very efficient catalysts of zeolitic nature for the synthesis of diamino diphenyl methane (DADPM), the polyamine precursor in the production of MDI for polyurethanes. The exfoliation process results in excellent accessibility of their active sites to reactant molecules as well as fast desorption of products. These catalysts present higher activity and slower rates of deactivation than their corresponding zeolites. Moreover, the topology of the delaminated structure imposes a precise control of the isomer distribution, offering an additional flexibility in the synthesis of DADPM. By optimizing the process conditions it is possible to achieve final DADPM crude under industrial production specifications with ITQ-18. This catalyst represents a real chance for replacing HCl in the industrial production of DADPM.
Keywords: Aniline–formaldehyde condensation; Aminal; Diamino diphenyl methane; Solid acids; Delaminated zeolites
Direct conversion of methane to methanol over nano-[Au/SiO2] in [Bmim]Cl ionic liquid by T. Li; S.J. Wang; C.S. Yu; Y.C. Ma; K.L. Li; L.W. Lin (pp. 150-154).
Display Omitted► The process of methane conversion was a green chemical process. ► SiO2-supported nano-gold, dispersed in an ionic liquid, were used as the catalyst. ► The catalysis system (Au/IL) can be recycled and utilized. ► The main product is methanol. ► The methane conversion is 24.9%. The selectivity is 71.5%. The yield is 17.8%.This article describes a green chemical process employing nano-particle gold as the catalyst and ionic liquids (IL) as solvent for the methane oxidation. The catalytic reaction was carried out in a 100ml autoclave filled with 2MPa of CH4 gas, together with nano-particle gold supported on SiO2 as the catalyst, [Bmim]Cl as the solvent, trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAA) as the acidic reagents, and K2S2O8 as the oxidant. The influence of the amounts of Au/SiO2 and the ionic liquid on the conversion of methane was investigated at reaction temperature of 90°C. The main product is methanol, which exists as the methyl group of the methyl trifluoroacetate. In presence of 0.01g Au/SiO2 and 1g IL, the methane conversion is 24.9%, the selectivity of product is up to 71.5% and the yield is 17.8%. The selectivity of carbon dioxide is 1.6% and the yield is 0.6%. The selectivity of hydrogen is 0.4% and the yield is 0.1%. In the reaction system, the gold particles and IL can be recycled, which recovery is about 96.9%. The conversion of methane in the recycled system remains as high as 21.75%. The mechanism of methane to methano conversion, as well as the catalytic action of the nano-gold, was also discussed.
Keywords: Oxidation of methane to methanol; Ionic liquid; Nano-gold catalyst; Green chemistry
Dissociation of CO and H2O during water–gas shift reaction on carburized Mo/Al2O3 catalyst by Tatsuro Namiki; Shinpei Yamashita; Hiroyuki Tominaga; Masatoshi Nagai (pp. 155-160).
Display Omitted► The dissociation of CO and H2O and the mechanism for the water–gas shift reaction. ►13C16O and H218O were dissociated to form13C18O,13C18O16O,13C18O2 and H216O. ► The formate was formed through the carbonate species from the formed CO2 hydrogenation. ► The reaction on the carburized Mo/Al2O3 followed mainly the redox route.The dissociation of CO and H2O during the water–gas shift reaction (WGSR) on the 973 K-carburized 4.8 and 8.5wt% Mo/Al2O3 catalysts at 423K was studied by in situ mass and infrared spectroscopies. It was found that both CO and H2O were dissociated on the basis of the formation of H2,13C18O,13C18O2 and13C18O16O after the injection of H218O into the13C16O stream. Regarding the12C- and16O-labeled atoms,12C16O2,12C16O18O and12C18O2 were not formed, but H216O,12C16O,12C18O and13C16O2 were formed. The H216O,12C16O and13C16O2 were formed by the reaction of the dissociated16O of13C16O with the surface carbon or the lattice carbon atom of the Mo oxycarbide. The infrared spectroscopy results for the injection of H2O into the C18O flow showed that C18O had no effect on forming the formate group. The formate and carbonate which were probably formed during the CO2 hydrogenation were observed when using the 973 K-carburized Mo/Al2O3 catalyst and alumina in a stream of CO. The WGSR on the Mo oxycarbide of the carburized Mo/Al2O3 catalyst followed the redox route together with the dissociation-association mechanism.
Keywords: Water–gas shift reaction; Molybdenum oxycarbide; 13; CO- and H; 2; 18; O-isotopes; Mass spectroscopy; Infrared spectroscopy
Catalytic activity improvement of Ni3Al foils for methanol decomposition by oxidation–reduction pretreatment by Jun Hyuk Jang; Ya Xu; Masahiko Demura; Dang Moon Wee; Toshiyuki Hirano (pp. 161-167).
Display Omitted► The Ni/Al2O3 layer formed over the Ni3Al foil reduced after oxidation at 973K. ► The Ni/NiAl2O4/Al2O3 layer formed over the Ni3Al foil reduced after oxidation at 1173K. ► Both pretreated foils exhibited considerably improved catalytic activity for methanol decomposition. ► High activity was attributed to the formation of the outmost Ni layer.A two-step pretreatment, oxidation in air followed by reduction in hydrogen, was performed on Ni3Al foils to improve the catalytic activity for methanol decomposition. A two-layer structure, Ni/Al2O3, was formed over the foil surface which was oxidized at 973K and reduced, whereas a three-layer structure, Ni/NiAl2O4/Al2O3, was formed over the foil surface that was oxidized at 1173K and reduced. In both cases the outmost Ni layer consisted of polycrystals and continuously covered the underlying oxides. Both pretreated foils exhibited lower onset temperature and enhanced catalytic activity for methanol decomposition into H2 and CO, compared to the untreated foil, and the difference between them was very small. In addition, they exhibited a good stability in catalytic performance at 673K. The results demonstrate that the oxidation–reduction pretreatment effectively improves the catalytic performance of Ni3Al foil by the formation of an outmost Ni layer on the foil surface.
Keywords: Ni; 3; Al foil; Ni catalysts; Oxidation–reduction; Pretreatment; Methanol decomposition
Application of liquid phase deposition method for preparation of Co/ZrO x/SiO2 catalyst with enhanced Fischer–Tropsch synthesis activity: Importance of Co–Zr interaction by Naoto Koizumi; Hiroyuki Seki; Yasuhiko Hayasaka; Yasufumi Oda; Takayoshi Shindo; Muneyoshi Yamada (pp. 168-178).
Display Omitted► ZrO x modification of SiO2 by LPD method enhanced FTS activity of Co/ZrO x/SiO2. ► Activity enhancement reached 4.4-fold, which was larger than those of literatures. ► ZrO x modification enhanced both dispersion and turnover frequency of Co0 particles. ► Co species was interacted with both Si–OH and Zr–OH in the calcined Co/ZrO x/SiO2.Liquid phase deposition (LPD) method using (NH4)2ZrO(CO3)2 was applied to modifying chemical nature of SiO2 surface with ZrO x species. ZrO x-modified SiO2 was then impregnated with Co nitrate solution for preparation of Co/ZrO x/SiO2 catalysts with 5 and 20mass% Co loadings. Modification of SiO2 surface with ZrO x using the LPD method enhanced FTS activity of the Co/ZrO x/SiO2 catalysts under the reaction conditions of 503K and 1.1MPa. The LPD method was superior to other method reported previously such as impregnation and sol–gel methods in terms of surface modification of SiO2 with ZrO x. H2-TPR, XRD and hydrogen chemisorption measurements revealed that modification of SiO2 surface with ZrO x using the LPD method enhanced dispersion of Co0 without loss of high reducibility of Co. However, degree of Co0 dispersion was less than that expected from enhancement of activity for the catalysts induced by ZrO x modification, indicating that turnover frequency (TOF) increased in the presence of ZrO x. This effect was particularly important for the catalyst with the low Co loading. Furthermore, in situ DRIFT measurement provided evidence for the formation of specific interaction of Co species with Si–OH and Zr–OH species in the Co/ZrO x/SiO2 catalysts. It was suggested that the formation of such specific interaction was responsible for not only enhancement of Co0 dispersion but also increase in TOF of the ZrO x modified catalysts.
Keywords: Fischer–Tropsch synthesis; Co/ZrO; x; /SiO; 2; Liquid phase deposition method
Photocatalytic properties of WO3 nanoparticles obtained by precipitation in presence of urea as complexing agent by D. Sánchez Martínez; A. Martínez-de la Cruz; E. López Cuéllar (pp. 179-186).
. The degradation of organic dyes by the action of WO3 can take place by two ways, by (a) true photocatalysis and by (b) photosensitization process.Display Omitted► WO3 nanoparticles were able to the partial mineralization of rhB and IC. ► Participation ofOH radicals in the degradation of dyes over WO3 was confirmed. ► WO3 can be considered as a photocatalyst active under visible-light irradiation.WO3 nanoparticles were synthesized by a precipitation method in presence of urea at different calcination temperatures. The characterization of the WO3 samples was carried out by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), adsorption–desorption N2 isotherms (BET), and diffuse reflectance spectroscopy (DRS). During the precipitation process, the presence of urea led to the formation of WO3 nanoparticles with rectangular and ovoid shapes as a function of calcination temperature. The photocatalytic activity of WO3 samples was evaluated in the degradation of rhodamine B (rhB), indigo carmine (IC) and congo red (CR) molecules in aqueous solution under UV and visible-light radiation. The best results were obtained with the sample synthesized at 500°C due to a contribution of factors such as morphology, surface area and the degree of aggregation of their particles. The photocatalytic activity for the degradation of organic dyes followed the sequence IC>rhB>CR. When the best photocatalyst was tested, the reached mineralization degrees after 96h of irradiation were 29% for rhB and 86% for IC.
Keywords: WO; 3; Heterogeneous photocatalysis; Photosensitization; Organic dyes
NiO reduction with hydrogen and light hydrocarbons: Contrast between SiO2-supported and unsupported NiO nanoparticles by Syed Shatir A. Syed-Hassan; Chun-Zhu Li (pp. 187-194).
Display Omitted► Reduction of NiO nanoparticles differs from that of SiO2-supported NiO. ► Kinetics of NiO reduction depends on the fates of radicals formed on the surface. ► Desorption of radicals slows down the reduction of unsupported NiO nanoparticles.The reduction of solid metal oxide by hydrogen or hydrocarbon gases represents a class of reactions that are important to various technological applications. This study investigates the reduction of unsupported NiO nanoparticles and silica-supported NiO with different reducing gases (hydrogen, methane and ethane) in the temperature range of 500–600°C. It was found that, in addition to the reaction and mass transfer of molecular species, the fates and activities of surface-formed radical species have to be considered in explaining the kinetics of nickel oxide reduction. It is believed that the desorption of hydrocarbon radicals from the particle surface has significantly slowed down the reduction of unsupported NiO nanoparticles. The ease with which a radical migrates from its generation site on a metallic island to the Ni–NiO surface boundary, on the other hand, is an important rate-determining factor in the reduction of silica-supported NiO.
Keywords: Surface-generated radicals; Nickel oxide reduction; Light hydrocarbons; Hydrogen
Corrigendum to “Coking behavior of a submicron MFI catalyst during ethanol dehydration to ethylene in a pilot-scale fixed-bed reactor” [Appl. Catal. A: Gen. 393 (2011) 161–170]
by Fei Wang; Man Luo; Wende Xiao; Xiaowei Cheng; Yingcai Long (pp. 195-195).