Applied Catalysis A, General (v.449, #C)
Editorial Board (CO2).
Green route for the chlorination of nitrobenzene by Marilyne Boltz; Márcio C.S. de Mattos; Pierre M. Esteves; Patrick Pale; Benoit Louis (1-8).
Display Omitted► Novel green chlorination process of nitrobenzene. ► Continuous gas–solid reactor system at mild temperature, 150 °C. ► Use of eco-friendly zeolite catalysts instead of strong liquid acids. ► HUSY zeolite was found as the more promising catalyst, allowing 39% nitrobenzene conversion.A new green chlorination process of deactivated aromatics has been developed, being environmental-friendly and allowing the continuous chlorination of 1.7 kg nitrobenzene/kg catalyst per day.The triple novelty consists of using a non-conventional chlorination agent, the trichloroisocyanuric acid (TCCA, C3N3O3Cl3), along with solid acid catalysts (mainly zeolites) in a continuous flow reactor system. Different zeolites and solid acids have been tested in the chlorination of nitrobenzene, chosen as a model deactivated aromatic substrate.HUSY zeolite was found as the more promising catalyst for performing the chlorination of nitrobenzene, with good conversions (39–64%) at high selectivity toward monochlorinated products (90–99%). Finally, it is worthy to note that HUSY zeolite could be reused for at least five successive runs.
Keywords: Chlorination; Nitrobenzene; Trichloroisocyanuric acid (TCCA); Zeolite; Green chemistry;
A density functional study for adsorption and oxidation of NO on Ir (1 0 0) surface by I.A. Erikat; B.A. Hamad; J.M. Khalifeh (9-14).
Display Omitted► We used DFT to investigate the adsorption of nitrogen oxides on Ir (1 0 0). ► We used constraint minimization method to study oxidation reaction of NO on Ir (1 0 0). ► NO prefers to bond at bridge site on Ir (1 0 0) for all the studied coverages. ► The most stable configuration for NO2 adsorbed on Ir (1 0 0) is μ-N,O-nitrito. ► Oxidation of NO on Ir (1 0 0) surface leads to adsorbed NO2 molecule.Density functional theory (DFT) calculations are used to investigate the adsorption of nitrogen oxides (NO x ) (x = 1, 2) and oxidation reaction on Ir (1 0 0) surface. On clean surface, NO molecule energetically prefers to bond at bridge sites for all studied coverages (Θ = 0.25, 0.50, 0.75 and 1.00) monolayer (ML). An electron donation from the occupied orbitals to the d metal band and a back donation from the substrate to the 2π* orbital occur for adsorbed NO on Ir (1 0 0) surface, which causes an increase in N―O bond. NO2 molecule exhibits a variety of adsorption geometries; the most energetically favorable is the μ-N,O-nitrito configuration with an adsorption energy 1.91 eV. The reaction pathway and the transition state (TS) are determined using constrained minimization method. At the TS, the adsorbed oxygen (Oa) atom and NO molecule diffuse to less stable states (top). Then they react to form chemisorbed NO2 with activation energy about 1.41 eV.
Keywords: DFT; Adsorption; Oxidation; NO; Ir;
The catalytic and physico-chemical properties of Ni/MgF2–MgO catalysts by Michał Zieliński (15-22).
Display Omitted► New non-conventional catalysts for toluene hydrogenation. ► MgF2–MgO, MgF2 and MgO as catalyst support and Ni as an active phase. ► Hydrogenation activity of Ni/MgF2–MgO was higher than that of Ni/Al2O3 or Ni/MgO.The MgF2–MgO system of different quantitative compositions was tested as a potential support for nickel catalysts to be used for hydrogenation of toluene. The catalytic performance of the system was studied as a function of the MgF2/MgO ratio in the support and the reaction conditions. The hydrogenation was performed at temperatures ranging from 75 to 225 °C on the catalysts activated in hydrogen at different temperatures (400–550 °C). The activities of Ni/MgF2–MgO catalysts were compared to those of Ni/MgF2, Ni/MgO and Ni/Al2O3. The highest activities were observed in the case of the catalysts supported on MgF2–MgO (containing 40 mol.% MgO), especially after the activation at 500 °C. The catalytic activity of nickel supported on magnesium oxo-fluoride tested in toluene hydrogenation was much higher than that of Ni supported on the commonly used supports such as Al2O3 or MgO.
Keywords: Nickel catalysts; MgF2; MgO; Magnesium oxo-fluoride; Al2O3; Toluene hydrogenation;
Investigation of the nature of V-species on alumina modified by alkali cations: Development of multi-functional DeSO x catalysts by Rafael Pereira dos Santos; Thiago Crispim da Silva; Maria Luisa Aleixo Gonçalves; Benoît Louis; Evandro Brum Pereira; Marcelo Hawrylak Herbst; Marcelo Maciel Pereira (23-30).
Display Omitted► Vanadium was introduced onto δ-aluminas modified by lithium, sodium or potassium. ► Vanadium species are preferentially located on group I element compared with the alumina surface. ► Vanadium largely improved the rate of SO2 oxidation as well as the rate of sulfate reduction to H2S. ► The reduction of the formed sulfate to H2S was remarkably affected by the V–K proximity. ► Alumina modified by potassium exhibited the best DeSO x performance.The location of vanadium species on δ-aluminas modified by lithium, sodium or potassium has been thoroughly investigated by means of several techniques. XRD, TPR and textural analyses showed that vanadium species are preferentially located on group I element or in its close vicinity when compared with the non-modified alumina.Vanadium species are localized nearby lithium and potassium cations, whilst vanadium species are partially distributed between sodium and alumina support in the sodium-modified alumina. A detailed XPS study was also carried out over potassium-promoted alumina catalysts and confirmed the vanadium distribution nearby potassium.Experiments of SO x capture and sulfate reduction to H2S were performed under realistic Fluid Catalytic Cracking (FCC) conditions with respect to the temperature of the catalyst regeneration (at 725 °C) and during hydrocarbon reactions (around 575 °C).Among different alkali cation modifiers, alumina modified by potassium exhibited the best performance in the DeSO x reaction (in terms of mole of absorbed sulfur per mole of group I cation) according to the following ratios: 0.74, 0.34 and 0.24 observed for K, Li and Na, respectively.Finally, vanadium largely improved the rate of SO2 oxidation as well as the rate of sulfate reduction to H2S.
Keywords: DeSO x ; FCC; Vanadium; Alumina;
Enhanced visible-light photocatalytic activity of V2O5/S-TiO2 nanocomposites by M. Gurulakshmi; M. Selvaraj; A. Selvamani; P. Vijayan; N.R. Sasi Rekha; K. Shanthi (31-46).
Display Omitted► S-TiO2(x) has been synthesized by sol–gel method. ► V2O5/S-TiO2(x) has been synthesized by wet impregnation method. ► The addition of V2O5 to S-TiO2 has enhanced the visible-light absorption. ► The migration of charge carriers in V2O5/S-TiO2 increased the activity. ► The stability of the nanocomposites has been revealed from the fluorescence study.Diverse approaches are being made in search of a visible-light active TiO2 photocatalysts. In this study, S-TiO2(x) nanocatalysts with x = 2, 4 and 6 (x = S/Ti molar ratio) were synthesized by sol–gel method and V2O5/S-TiO2(x) nanocomposites by wet impregnation method using ammonium metavanadate as a source of vanadium. The synthesized catalysts were characterized by diffuse reflectance UV–vis spectroscopy, X-ray diffraction, Raman spectroscopy, N2 adsorption desorption studies, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and high resolution transmission electron microscopy techniques. The photogenerated reactive species •OH radical estimated from photoluminescence spectra was directly correlated to the visible-light absorption of the catalyst. The photocatalytic activities of all the synthesized catalysts were evaluated for the degradation of MB under visible light irradiation. The excellent stability of V2O5/S-TiO2(x) nanocomposites has been revealed from the linear relationship between the fluorescence intensity and the time. The addition of sulfur and V2O5 to TiO2 has significantly enhanced the visible-light photocatalytic activity by modifying the optical and electronic properties of TiO2. The enhanced visible-light photocatalytic activity has been attributed to the efficient visible-light absorption of V2O5/S-TiO2(x) nanocomposites and efficient charge separation due to migration of charge carriers between S-TiO2 and V2O5.
Keywords: Nanotitania; Sulfur; Vanadia; Nanocomposites; Visible-light absorption; Photocatalytic activity;
Ethanol steam reforming over Co/CeO2 catalysts: Investigation of the effect of ceria morphology by I. Ilgaz Soykal; Burcu Bayram; Hyuntae Sohn; Preshit Gawade; Jeffrey T. Miller; Umit S. Ozkan (47-58).
Display Omitted► Co catalysts supported on ceria supports with different morphologies were investigated. ► Two distinct morphologies examined were nano-rods and nano-cubes. ► Catalysts were evaluated for their performance in ethanol steam reforming. ► TEM and XRD showed preferred orientation of different crystal planes in the two morphologies. ► Distinct differences in dispersion, reducibility, pore size distribution and catalytic performance were observed.Co catalysts supported on ceria supports with different morphologies such as nano-rods (NR) and nano-cubes (NC) were investigated in regard to their activity for ethanol steam reforming. Ceria supports were prepared using the hydrothermal method where the particle shape is manipulated by controlling the pH and pressure of the precipitation environment. Structural characterization with TEM and XRD showed the two morphologies to be similar in particle size, but different in the exposure of different crystal planes. The nano-cubes had a higher exposure of the (1 1 0) plane, which is known to have a higher affinity for creating anion vacancies and surface defects. Controlled atmosphere X-ray absorption fine structure analysis, temperature programmed reduction/oxidation, dispersion measurements and steady-state reaction performance tests showed significant differences between the two catalysts. Co catalysts supported on nanocubes showed higher reducibility compared to those supported on nanorods or commercial supports of similar particle size. These catalysts also showed high H2 and CO2 yields in the 400–500 °C range whereas Co/CeO2(NR) had limited carbon cleavage activity and were only active for dehydrogenation and dehydration. The superior performance of Co/CeO2(NC) catalysts is thought to be due to a combination of factors, including improved metal dispersion, increased reducibility and higher oxygen mobility.
Keywords: EXAFS; Cobalt; Morphology; Ceria; Ethanol steam reforming;
Liquid-phase dehydration of propylene glycol using solid-acid catalysts by Timothy D. Courtney; Vladimiros Nikolakis; Giannis Mpourmpakis; Jingguang G. Chen; Dionisios G. Vlachos (59-68).
Display Omitted► Carbonyl-containing dehydration products showed high conversion to cyclic acetals. ► Zeolite yields broader distribution of dehydration products than Amberlyst. ► Product distribution in each catalyst explained using ab-initio calculations. ► Differences in cyclic acetal conversion relate to the pore sizes of the catalyst. ► Selectivity in the zeolite is governed by stability of chemisorbed intermediates.In this work we combine experiments with Density Functional Theory (DFT) calculations to investigate the heterogeneous dehydration of propylene glycol. The reactions were carried out with pure, liquid propylene glycol over MFI-framework zeolite catalysts or the mesoporous sulfonic-acid resin Amberlyst 36Dry. When Amberlyst 36Dry was used, propylene glycol dehydrated to form propionaldehyde with 77% selectivity. All of the propionaldehyde further reacted with propylene glycol to form a cyclic acetal. The final products consisted of 78% acetal, 13% dipropylene glycol, and the remaining 9% was composed of acetone and a cyclic ketal formed from acetone. The zeolite catalysts demonstrated significantly higher selectivity toward dipropylene glycol compared to Amberlyst 36Dry. Furthermore, the zeolite had a lower conversion to cyclic acetals, improving the selectivity toward C3 products, acetone and propionaldehyde. DFT calculations confirmed that propionaldehyde is the favorable product in both catalysts, since it can be formed either through dehydration of the secondary hydroxyl group or via dehydration of the primary hydroxyl group with a concerted pinacol rearrangement. However, in the case of zeolites, the cyclic acetals experience steric hindrance since their size is comparable to that of the zeolite pores. Thus we argue that the cyclic acetals produced over the zeolite catalyst were formed homogeneously from the C3 products which diffused out of the zeolite pores.
Keywords: Dehydration; Zeolite; Polyol; Dioxolane; Liquid-phase;
Reducibility of alumina-supported cobalt Fischer–Tropsch catalysts: Effects of noble metal type, distribution, retention, chemical state, bonding, and influence on cobalt crystallite size by Kari M. Cook; Samiksha Poudyal; Jeffrey T. Miller; Calvin H. Bartholomew; William C. Hecker (69-80).
.Display Omitted► Co, Pt, and Re spatially uniform; Ru not. ► No loss of Pt, Re; 50% loss of Ru. ► Bonding in reduced catalyst: Co-Pt, Ru-Ru, Re2O7. ► Extent reduced: Pt/Co > Re/Co > Ru/Co > Co.The distribution, retention, chemical state, and bonding of noble metal (NM) promoters (Pt, Re, or Ru), their influence on Co crystallite size, and the resulting Co reducibility and dispersion were investigated in commercially-representative Co Fischer–Tropsch catalysts (nominally 25 wt% Co and 0 to 0.6 wt% NM on a La stabilized alumina support). NM retention during preparation ranged from complete for Pt and Re to < 50% for Ru. Co concentrations were spatially uniform; however, NM concentration varied dramatically from a sharp concentration gradient at the pellet edge in the case of Ru to a homogeneous distribution for Re and Pt. After 360 °C reduction for 1 h, Pt0 bonds directly to Co0, Ru forms separate metal crystallites and Re remains as Re2O7. Despite these differences, all three NMs substantially improved Co reducibility. Pt is the most effective promoter for increasing cobalt reduction rate and gives the highest extent of reduction (EOR). Preliminary activity tests showed no statistical differences in the CO depletion rates of the four catalysts of this study.
Keywords: Cobalt; Fischer–Tropsch; Noble Metal; Reducibility;
Selective gas phase hydrogenation of maleic anhydride over Ni-supported catalysts: Effect of support on the catalytic performance by Silvina A. Regenhardt; Camilo I. Meyer; Teresita F. Garetto; Alberto J. Marchi (81-87).
Display Omitted► Ni supported catalysts are active for selective gas phase hydrogenolysis of succinic anhydride. ► The active metal nickel phase depends on Ni2+–support interaction in oxide precursor. ► Ni–support interaction pattern is: Ni/SiO2 < Ni/SiO2–Al2O3 < Ni/H-BEA. ► The best catalytic performance for GBL production was obtained with Ni/SiO2–Al2O3.The gas phase hydrogenation of maleic anhydride to obtain γ-butyrolactone was studied using Ni supported on SiO2, SiO2–Al2O3 and zeolite H-BEA as catalysts. The samples were prepared by incipient wetness impregnation and characterized by N2 adsorption at −196 °C (Sg), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of NH3 (TPD-NH3) and chemisorption of H2. The reaction was carried out at 170 °C and 220 °C in a fixed bed reactor operating at atmospheric pressure. From the characterization results, it was determined that the degree of Ni2+–support interaction varies according to the following pattern: Ni/HBEA > Ni/SiO2–Al2O3 > Ni/SiO2. All catalysts were very active in the hydrogenation of maleic anhydride to succinic anhydride. However, hydrogenolytic activity and stability of nickel-based catalyst varies with the degree of interaction Ni2+–support. Ni/H-BEA, in which Ni2+–support interaction is the highest, was active in the hydrogenolysis of succinic anhydride to γ-butyrolactone but it was not stable. By contrast, Ni/SiO2–Al2O3 and Ni/SiO2, with medium or low degree of Ni2+–support interaction, were more stable than Ni/H-BEA. In addition, Ni/SiO2–Al2O3, with a medium degree of Ni2+–support interaction, was the most stable and selective to γ-butyrolactone, especially when the reaction was carried out at 220 °C.
Keywords: Hydrogenation; Hydrogenolysis; Ni-based catalysts; γ-Butyrolactone;
Zinc carboxylic salts used as catalyst in the biodiesel synthesis by esterification and transesterification: Study of the stability in the reaction medium by Deborath M. Reinoso; Daniel E. Damiani; Gabriela M. Tonetto (88-95).
Display Omitted► Transesterification of soybean oil and esterification of oleic acid with methanol. ► Zinc carboxylic salts were used as catalysts. ► The stability of the catalysts in the reaction media was studied. ► Zn laurate, palmitate and stearate were active and stable. ► These solids are soluble in the reaction medium and crystalline at room temperature.Biodiesel is produced by the catalytic transesterification of renewable sources such as vegetable oils and animal fats. It is an attractive alternative to diesel fuel because of its environmental benefits.In this work, the transesterification of soybean oil with methanol using zinc carboxylic salts as Lewis acid catalysts was studied. The esterification of fatty acids was also researched. In both reactions, the stability of the catalyst in the reaction medium was examined.Zinc carboxylic salts of different chain lengths, Zn(C n H2n+1COO)2 with n = 1, 11, 15, and 17, and Zn(C17H33COO)2 (zinc(II) acetate, laurate, palmitate, stearate and oleate, respectively) were prepared and characterized by X-ray diffraction, FTIR spectrometry and thermogravimetric analysis.The Zn salts were tested in the transesterification of soybean oil at 100 °C for 2 h. They presented oil conversions between 88 and 94% with fatty acid methyl ester (FAME) yields between 71 and 74%, and they were stable in three consecutive tests. Zn acetate was not stable. The salts transformed into Zn glycerolate at 140 °C in the reaction medium (zinc laurate, palmitate, and stearate only partially).It was observed that, in the presence of fatty acids, the carboxylates of the salts were gradually exchanged for the acid to be esterified. With oleic acid, this process was completed at 60 °C for all the Zn(C n H2n+1COO)2 salts.Zinc laurate, palmitate and stearate are crystalline solids, but soluble in the reaction medium at 100 °C, and they recrystallize rapidly at room temperature, presenting certain advantages as regards decreasing mass transfer resistance during reaction, and easy separation and recovery from reaction medium.
Keywords: Transesterification; Esterification; Biodiesel; Zinc carboxylic salts; Soybean oil;
Gold supported on ceria nanoparticles and nanotubes by Brenda Acosta; Elena Smolentseva; Sergey Beloshapkin; Ricardo Rangel; Miguel Estrada; Sergio Fuentes; Andrey Simakov (96-104).
Display Omitted► Various CeO2 nanotubes were prepared via hydrothermal treatment of CeO2 particles. ► Au NPs on ceria nanotubes are more active in CO oxidation than those on ceria NPs. ► Redox treatments of ceria nanotubes affect size and activity of Au NPs in CO oxidation. ► Oxidized Au/CeO2-nanotubes samples manifest the highest activity in CO oxidation.The ceria nanotubes with different size have been prepared via a hydrothermal treatment of CeO2 nanoparticles at 120 °C with two different NaOH concentrations (5 or 10 M) for 36 h. The synthesized ceria samples characterized by SEM, TEM, XRD, and UV–visible spectroscopy were used as supports for Au/CeO2 catalysts preparation by DP technique using HAuCl4 as gold precursor and urea as precipitation agent. The formation of gold nanoparticles (Au NPs) has been studied by TEM, in situ UV–visible–mass analysis at temperature programmed reduction and XPS spectroscopy. Three distinguishable steps in the formation of Au NPs accompanied by profound ceria reduction particular for ceria nanotubes have been found. Au NPs stabilized on the ceria nanotubes have been characterized with higher activity in CO oxidation than those supported on ceria nanoparticles. The structure and redox treatment of ceria nanotubes affects size of Au NPs and their catalytic activity in CO oxidation. Pre-oxidized Au/CeO2-nanotubes manifest the highest activity in CO oxidation.
Keywords: Ceria nanotubes; Hydrothermal treatment; Gold nanoparticles; UV–vis in situ; CO oxidation;
Hydrotreatment of sunflower oil using supported molybdenum carbide by L.A. Sousa; J.L. Zotin; V. Teixeira da Silva (105-111).
Display Omitted► The activity of Mo2C/Al2O3 in the hydrotreating of sunflower oil was evaluated. ► Mo2C/Al2O3 promotes deoxygenation of the carboxyl of the free fatty acids. ► The by-product of the reaction is water. ► Little contribution of decarbonylation and decarboxylation was observed. ► Mo2C/Al2O3 is stable in reaction times greater than 150 h.Pure sunflower oil was hydrotreated (T = 633 K, P = 5 MPa) aiming the production of a biofuel in the diesel range using β-Mo2C/Al2O3 as catalyst. The catalyst was synthesized in situ using the temperature-programmed carburization (TPC) methodology with a 20% (v/v) CH4/H2 gas mixture and 923 K/2 h as synthesis temperature. The catalytic evaluation results indicate that for the employed conditions n-C18 was the major product. The association of the results of the experiments without (blank) and with catalyst suggests that the overall triglyceride transformation into linear alkanes proceeds in two steps: (i) thermal cracking of the triglyceride forming free fatty acids and (ii) hydrogenation of the double bonds and of the carboxylic group of the free fatty acid forming n-alkanes. No CO and/or CO2 formation were detected implying that decarbonylation and/or decarboxylation routes do not play an important role when molybdenum carbide is used, contrarily to what is commonly observed when supported Co–Mo or Ni–Mo sulfides are employed as catalysts.
Keywords: Molybdenum carbide; Vegetable oils; Sunflower oil; Biofuels; HDT; Hydrogenation;
Catalytic carbonization of polypropylene by the combined catalysis of activated carbon with Ni2O3 into carbon nanotubes and its mechanism by Jiang Gong; Jie Liu; Dong Wan; Xuecheng Chen; Xin Wen; Ewa Mijowska; Zhiwei Jiang; Yanhui Wang; Tao Tang (112-120).
Display Omitted► One-pot approach to catalyze conversion of polypropylene into CNTs by combined catalysis of AC and Ni2O3. ► AC affected the degradation products of PP and prompted the growth of CNTs. ► Layer-by-layer assembled mechanism based on benzene rings for the growth of CNTs was proposed.A one-pot approach was established to prepare carbon nanotubes (CNTs) through the carbonization of polypropylene (PP) by the combined catalysts of activated carbon (AC) with Ni2O3. The combination of AC with Ni2O3 showed a synergistic catalysis on the catalytic conversion of PP to form CNTs. The effects of the content of AC and carbonization temperature on the yield of CNTs were studied. The morphology, phase structure and thermal stability of the obtained CNTs were analyzed by means of SEM, TEM, XRD, TGA and Raman. In this synergistic catalysis, the surface functional groups (especially carboxylic groups) of AC were proved to be the key factor. AC not only promoted the cracking of PP fragment radicals into light hydrocarbons and the dehydrogenation and aromatization of the resultant light hydrocarbons into aromatic compounds, but also promoted the formation of the intermediate aromatic compounds or polycyclic aromatic hydrocarbons (PAHs) from the reaction of light hydrocarbon products and aromatic compounds. Additionally, AC assisted in situ Ni catalyst (originated from the reduction of Ni2O3) catalyzing the dehydrogenation and aromatization of intermediate aromatic compounds or PAHs products to form CNTs. At last, a layer-by-layer assembled mechanism based on benzene rings for the growth of CNTs using PP as carbon source and combined AC/Ni2O3 as catalysts was proposed. This mechanism will help to understand the growth mechanism of CNTs using virgin or waste plastics as carbon sources. More importantly, this approach offers a new potential way for large-scale production of CNTs from waste plastics using cheap AC as a cocatalyst.
Keywords: Carbon nanotubes; Polypropylene; Activated carbon; Ni2O3; Catalysis;
Catalytic hydrotreatment of fast pyrolysis oil using bimetallic Ni–Cu catalysts on various supports by A.R. Ardiyanti; S.A. Khromova; R.H. Venderbosch; V.A. Yakovlev; I.V. Melián-Cabrera; H.J. Heeres (121-130).
Display Omitted► Catalytic hydrotreatment of pyrolysis oil was performed with NiCu catalysts. ► Various supports were tested (inorganic and carbon-based). ► Best results were obtained with a NiCu on a TiO2 support. ► Product properties were determined. ► Considerable improvements were observed compared to pyrolysis oil.Bimetallic Ni–Cu catalysts on various supports (CeO2–ZrO2, ZrO2, SiO2, TiO2, rice husk carbon, and Sibunite) with metal contents ranging from 7.5 to 9.0 (Ni) and 3.1–3.6 wt.% (Cu) for the inorganic supports and 17.1–17.8 (Ni) and 7.1–7.8 (Cu) for the carbon supports were synthesised and screened for the catalytic hydrotreatment of fast pyrolysis oil in a batch set-up (350 °C, 200 bar initial pressure). NiCu/TiO2 showed the highest activity (average activity of 576 NLhydrogen kgPO −1 gactive metal −1 for a 4 h batch time) and gave a product oil with the most favourable properties, viz. a H/C ratio of 1.43, a low TG residue (2.7 wt.%) and the highest solubility in a hydrocarbon solvent. The TiO2 based catalyst was characterised as having moderate leaching levels of Ni and Cu metals (Ti remained unchanged), low carbon deposition on the catalyst surface and limited metal sintering.
Keywords: Pyrolysis oil; Nickel–Copper; Catalytic hydrotreatment; HDO; Support effects;
Promoting effect of Fe in preferential oxidation of carbon monoxide reaction (PROX) on Au/CeO2 by Xuemei Liao; Wei Chu; Xiaoyan Dai; Véronique Pitchon (131-138).
Display Omitted► Au/Ce–Fe mixed oxides were prepared by impregnation and co-precipitation method. ► The PROX activity is influenced by the atomic ratio Ce/Fe. ► Au/Ce–Fe mixed oxides catalysts prepared by co-precipitation are the most active. ► The formation of a solid solution between Ce and Fe favors the lability of oxygen. ► Au–Fe/CeO2 catalysts are active and stable in time for PROX reaction.Ce–Fe mixed oxides were prepared by impregnation (IM) method and co-precipitation method (CP). Gold supported on Ce–Fe mixed oxides prepared by direct anionic exchange (DAE) was used as catalyst for preferential oxidation of carbon monoxide (PROX). The influence of the atomic ratio Ce/Fe and of the preparation method (CP or IM) was investigated. It was found that gold supported on modified ceria by iron displayed better catalytic performances. However, the selectivity of Au/CeFe-CP was lower than that of Au/CeO2 catalyst, which could be ascribed to the formation of defects in CeFe support prone to accumulate carbonate species on the surface. The characterization by means of XRD, XPS, H2-TPR and HRTEM indicated that the doping of iron in ceria prepared by CP promoted the formation of a Ce–Fe solid solution, decreased the particle size of ceria and enhanced the dispersion of gold. In the case of the IM catalysts, iron is segregated in the form of Fe2O3, which impedes the activity in PROX. The strong interaction between CeO2 and Fe2O3 supports led to higher oxygen mobility and to the formation of Au3+, which may also contribute to the higher catalytic activity of Au/Ce85Fe15.
Keywords: Ce–Fe mixed oxides; PROX; Impregnation and co-precipitation methods; Gold catalysis;
Photoinduced electron transfer and photodegradation of malonic acid at Au/TiO2 investigated by in situ ATR-IR spectroscopy by Xuefeng Hu; Thomas Bürgi (139-144).
Photoinduced electron transfer and photodegradation of malonic acid at Au/TiO2.Display Omitted► Photodegradation of dicarboxylic acids on TiO2 and Au@TiO2 was studied. ► ATR-IR technique was used to monitor the adsorbed species and shallow trap electrons on the catalyst. ► Electrons are transferred from Au nanoparticles to TiO2 under visible light illumination. ► Electrons are transferred from TiO2 to Au nanoparticles under UV illumination. ► The effect of electron transfer on the catalysis is revealed.TiO2 coated Au nanoparticles were synthesized and characterized by TEM, XPS and XRD. It was found that the Au nanoparticles were coated with TiO2 thus forming a core–shell structure. Electron transfer, adsorption and photodegradation of malonic acid on the catalyst were investigated by in situ attenuated total reflection infrared (ATR-IR) spectroscopy. Malonic acid adsorbed and underwent photodegradation efficiently in air and nitrogen atmosphere under UV light illumination on the prepared catalyst. As intermediate species oxalate was observed on the catalyst surface during the photodegradation of malonic acid. The Au nanoparticles accelerate the degradation of malonic acid by capturing the conduction band electrons of TiO2. The ATR spectra also reveal interface electron transfer from Au nanoparticles to TiO2 under visible light illumination and from TiO2 to Au nanoparticles under UV illumination.
Keywords: Au@TiO2; In situ spectroscopy; Attenuated total reflection; Photocatalysis; Malonic acid;
The concentration effects of reactants and components in the Pd(OAc)2/p-toluenesulphonic acid/trans-2,3-bis(diphenylphosphinomethyl)-norbornane catalytic system on the rate of cyclohexene hydrocarbomethoxylation by I.E. Nifant’ev; N.T. Sevostyanova; V.A. Averyanov; S.A. Batashev; A.A. Vorobiev; S.A. Toloraya; V.V. Bagrov; A.N. Tavtorkin (145-152).
Display Omitted► Novel kinetic study of Pd-catalysed cyclohexene hydrocarbomethoxylation. ► High-performing trans-2,3-bis(diphenylphosphinomethyl)norbornane used as a catalyst. ► Influence of reactants and catalyst component concentrations were revealed.The reactants and components of a catalytic system were studied for their effects on the rate of Pd-catalysed cyclohexene hydrocarbomethoxylation. First-order reaction rate dependences were established for cyclohexene and Pd(OAc)2, while non-monotonic rate dependences were determined for the diphosphine and p-toluenesulphonic acid concentrations and the СО pressure. The reaction was shown to follow first-order kinetics when the methanol concentration was below 0.4 mol/L; however, the reaction rate slowed upon a further increase in the methanol concentration. The obtained results were interpreted by considering a hydride mechanism supplemented with ligand exchange reactions, which decreased the activity of the catalyst, and with hydride complex annihilations by p-toluenesulphonic acid, resulting in complete loss of catalytic activity. Treatment of the proposed mechanism using the quasi-equilibrium concentration method gave a kinetic equation for the reaction that was consistent with the experimental data.
Keywords: Hydrocarboalkoxylation; Catalytic carbonylation; Pd-catalysis; Phosphine-based catalysts; Esters;
Facile open air oxidation of benzylic alcohols in distilled water by in situ made copper(II) complexes by Jahir Uddin Ahmad; Minna T. Räisänen; Marianna Kemell; Mikko J. Heikkilä; Markku Leskelä; Timo Repo (153-162).
Display Omitted► A novel water tolerant catalytic system for alcohol oxidation has been developed. ► Various benzylic alcohols converted to aldehydes with high isolated yields. ► Very low loading of catalyst (0.3 mol%) and TEMPO (3 mol%) is required for efficient oxidation. ► Utilization of distilled water and open air compose a green protocol for the reactions.A highly efficient, selective and green catalytic protocol for open air oxidation of primary benzylic alcohols into aldehydes by in situ made N-isopropyl-3,5-di-tert-butylsalicylaldimine (HL3)–Cu(II) complexes and TEMPO (2,2,6,6-tetramethyl-piperidinyloxyl radical) is introduced herein. Distilled water as a solvent the reaction proceeds at 80 °C temperature without any auxiliarities such as base and/or co-solvent. For example, benzyl alcohol is quantitatively and selectively oxidized to benzaldehyde within a few hours under optimized reaction conditions [80 °C, open air, 0.3 mol% CuBr2, 2 mol% HL3, 3 mol% TEMPO and 5 mL of distilled water]. Under anaerobic conditions, the catalyst decomposes to a free ligand and Cu2O nanoparticles (diameter >50 nm) via anticipated Cu(I)-hydroxo complex. On the basis of these observations and deuteration studies, a plausible reaction mechanism is proposed for the catalytic system.
Keywords: Oxidation; Alcohols; Copper; Open air; Distilled water;
Direct catalytic conversion of glycerol to liquid-fuel classes over Ir–Re supported on W-doped mesostructured silica by Fengbo Li; Fei Xue; Bingfeng Chen; Zhijun Huang; Yin Yuan; Guoqing Yuan (163-171).
Display Omitted► Glycerol in aqueous solution was steadily converted to liquid fuel classes. ► The one-pot process was catalyzed by well-designed mesostructured Ir–Re–W/SiO2 catalysts. ► The tungstate species are active sites over the catalyst surface for acid-catalyzed dehydration. ► Ir species are involved in hydrodeoxygenation and coupling reaction for separate organic phase. ► The oxygen concentration of the oil products is related to the proportion of Re in the catalyst.Glycerol was converted to liquid fuels through a one-pot process catalyzed by mesostructured Ir–Re–W/SiO2. The reaction was performed over 0.4 g of catalyst suspended in an aqueous solution of glycerol (4.72 mmol/ml) at 553 K under a hydrogen pressure of 6.0 MPa for 50 h. A hydrocarbon-enriched organic phase was self-separated from the aqueous solution after the reaction. The total yield of oil products was greater than 40%, and the selectivity toward hydrocarbons was approximately 90%. The conversion proceeds through a complicated mechanism that involves a C―C coupling reaction and hydrodeoxygenation. Doped tungsten oxide species in a silica matrix are active acidic sites for acid-catalyzed dehydration. Supported iridium species are catalytic active sites for hydrodeoxygenation and C―C coupling reactions. The evolution of their chemical states during the catalytic process was detected by X-ray photoelectron spectroscopy. Rhenium species are important co-catalysts for iridium species. These active catalytic species work together to achieve the direct conversion of glycerol in aqueous solution to liquid fuels under a hydrogen atmosphere.
Keywords: Renewables; One-pot conversion; Liquid fuels; Mesostructured silica; Bimetallic catalysts;
Superb efficient and recycle polymer-anchored systems for palladium catalyzed Suzuki cross-coupling reactions in water by Fatma Siga; Hamdi Temel; Murat Aydemir; Yusuf Selim Ocak; Salih Pasa; Akın Baysal (172-182).
Display Omitted► Three new polymer-anchored palladium(II) Schiff base catalysts were synthesized. ► Their catalytic activity was investigated in the Suzuki cross-coupling reaction. ► They provided biphenyls in water with the highest TOF values ever reported.A set of three new polymer-anchored palladium(II) Schiff base catalysts have been synthesized, characterized and their catalytic activity was investigated in the Suzuki cross-coupling reaction between aryl halides and arylboronic acid in the presence of Cs2CO3 as a base. They show excellent catalytic activity in coupling of aryl bromides or aryl iodide with phenylboronic acid under the optimized reaction conditions in water. Polymer–anchored Pd(II) complexes provided turnover frequency of 29,700 or 58,200 h−1 in Suzuki coupling reactions of phenylboronic acid with p-bromoacetophenone or p-iodobenzene, respectively, which are the highest values ever reported for the Suzuki coupling reactions in water as sole solvent. The catalyst 1 could be used for 15 reaction cycles in the Suzuki coupling of p-acetobromobenzene at 100 °C with no loss of catalytic activity.
Keywords: Polymer-anchored Pd(II) complex; Catalysis; Suzuki cross-coupling reaction; Water; Aryl halides;
Silica poisoning in HDT catalysts by light coker naphtha by Patricia Pérez-Romo; Candido Aguilar-Barrera; Juan Navarrete-Bolaños; Luis M. Rodríguez-Otal; Francisco Hernández Beltrán; José Fripiat (183-187).
Silicon content on doped HDT catalyst.Display Omitted► The rate of adsorption is controlled by the transformation of silicon species. ► Silicon species interact with the alumina surface, forming Brønsted acid sites. ► The amount of silicon plays a major role for HDN and hydrogenation reactions.γ-Alumina-based HDT catalysts used as silicon traps adsorb more efficiently silicon compounds from naphtha till saturation, which occurs at a relatively low concentration (5–10 wt%). As the silicon content in the catalyst increases, the surface is progressively deactivated, mainly affecting the hydrodenitrogenation and hydrogenation activity. According to the aforementioned, the deactivation of HDT catalysts was investigated by means of a fraction of naphtha doped with silicone oil with different concentrations, which was used to contaminate the catalysts. The presence of silicon species was detected by 29Si NMR and FTIR spectroscopies. The Si―O―Al formation was evidenced by the B/L ratio measured for the doped HDT catalysts. The results obtained for the deactivation of HDT catalysts exposed to high silicon contents show that this factor plays a major role in the loss of activity.
Keywords: Silica poisoning; HDT alumina catalyst; Silicon compounds; Coker naphtha; Deactivation; FTIR;
Effect of desilication of H-ZSM-5 by alkali treatment on catalytic performance in hexane cracking by Hiroshi Mochizuki; Toshiyuki Yokoi; Hiroyuki Imai; Seitaro Namba; Junko N. Kondo; Takashi Tatsumi (188-197).
Display Omitted► The enlargement of the external surface area of ZSM-5 suppressed the pore blocking by coke formation. ► Lewis acid sites are generated by the alkali treatment and removed by the subsequent acid treatment. ► Lewis acid sites accelerated the aromatization and the coke formation in hexane cracking.The effects of external surface and acid properties of desilicated H-type ZSM-5 zeolites (H-ZSM-5) on their catalytic performance in hexane cracking were investigated. H-ZSM-5 with two different crystallite sizes of 100 nm and 1 μm were treated with NaOH solution of different concentrations. The external surface area (S EXT ) was increased with an increase in the NaOH concentration, because of the formation of mesopores inside the H-ZSM-5 crystallites as a result of desilication. The increase in the S EXT of the H-ZSM-5 catalysts contributed to mitigating the catalyst deactivation during the hexane cracking. Although the amount of coke deposited on the alkali-treated H-ZSM-5 was larger than that on the parent H-ZSM-5, the micropore volume of the alkali-treated H-ZSM-5 decreased less due to coke deposition than that of the parent. The deactivation rate and the decrease in the micropore volume of the small-sized H-ZSM-5 catalysts were smaller than those of the large-sized catalysts, because they had shorter average diffusion path lengths. Thus the activity of the alkali-treated H-ZSM-5, especially small-sized one is less sensitive to coke deposition. Lewis acid sites (LASs) were generated by treating with NaOH of high concentrations. The selectivities to benzene, toluene and xylene (BTX) in the hexane cracking were increased with an increase in the LASs amount at high reaction temperatures (≥873 K). The LASs on the alkali-treated H-ZSM-5 were selectively removed by acid treatment. The resultant H-ZSM-5 exhibited a slightly lower hexane conversion and a lower selectivity to BTX but a small amount of coke compared to the parent and alkali-treated H-ZSM-5 catalysts, suggesting that LASs on alkali-treated H-ZSM-5 accelerated the dehydrogenation including hydride transfer and aromatization, forming BTX, which would be precursors of coke.
Keywords: ZSM-5; Alkali treatment; Mesoporous zeolite; Hexane cracking; Lewis acid site;
Influence of formic acid and water on the [Pd(OAc)2(dppp)] catalyzed ethene–carbon monoxide copolymerization carried out in aprotic organic solvents by Andrea Vavasori; Lucio Ronchin; Luigi Toniolo (198-202).
Display Omitted► [Pd(OAc)2(dppp)] as catalyst for the ethene–CO copolymerization. ► Best results in 1,4-dioxane-H2O-HCOOH as reaction medium. ► Productivity and molecular weight higher than in methanol. ► Productivity increases by increasing pressure and temperature. ► Molecular weight increases by increasing pressure.The copolymerization of ethene with carbon monoxide catalyzed by [Pd(OAc)2(dppp)] in an aprotic solvent such as 1,4-dioxane or nitromethane is efficiently promoted both by H2O and HCOOH and yields a perfectly alternating polyketone (PK). The influence of the concentration of the promoters, pressure and temperature on the catalyst productivity and the limiting viscosity number (LVN) has been studied. The productivity increases with the increase of temperature and pressure. The LVN increases upon increasing the pressure and lowering the temperature. At 363 K and 9.0 MPa, in HCOOH/H2O/1-4,dioxane (2.7/1.35/1 molar ratio), the productivity is 37.50 kgPK (gPd h)−1 (LVN 2.77 dL g−1).LVN lowers upon increasing the concentration of the acid, suggesting that it is involved in the protonolysis chain-transfer process.
Keywords: Palladium catalyst; Carbon monoxide; Ethene; Solvent effect; Polyketone;
Preparation of platinum-on-carbon catalysts via hydrolytic deposition: Factors influencing the deposition and catalytic properties by K.M. Kaprielova; O.A. Yakovina; I.I. Ovchinnikov; S.V. Koscheev; A.S. Lisitsyn (203-214).
Display Omitted► Strong promotion of the chloroplatinate hydrolysis by carbons. ► Rapid hydrolytic depositions at neutral pH. ► Small Pt particles, high Pt loadings, uniform distribution over the support. ► Occurrence of pore-size effect. ► Possibility of tuning catalytic properties.The deposition of Pt oxide from aqueous chloroplatinate solutions onto carbon supports (activated carbons, carbon blacks, carbon nanofibers) with the aid of Na2CO3 and without adding the reductants or wetting agents was studied. It has been revealed that carbons accelerate greatly the hydrolysis of chloroplatinate, and the hydrolytic deposition can therefore interfere with the other preparation methods. Neutral pH was found optimum for heterogeneous nucleation and formation of smaller PtO x particles. High temperature (80 °C) allowed depositions of 5–30 wt.% of Pt for a short time (1–3 h) but did not affect Pt dispersions (15–90% at surface concentration of Pt 0.5–30 μmol/m2). The supported particles could be further reduced in the liquid phase with minimal losses of the dispersion (Na-formate as reductant). The heterogeneous nucleation ensured a uniform distribution of Pt particles but provoked particle confinement in narrow pores. The possibility of influencing catalytic properties with the aid of the support, Pt loading and deposition conditions was demonstrated (hydrogenation of cycloalkenes as a model structure-insensitive reaction and oxidation of isopropyl alcohol as structure-sensitive one).
Keywords: Pt catalysts; Carbon supports; Catalyst preparation; Hydrolytic deposition; Pore-size effect;