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Applied Catalysis A, General (v.435-436, #)

Contents (pp. iii-ix).

Editorial Board (pp. co2).

Helical Al- and Ce-MCM-41 materials as novel catalyst for acid and redox processes by Adela I. Carrillo; Elena Serrano; Juan Carlos Serrano-Ruiz; Rafael Luque; Javier Garcia-Martinez (pp. 1-9).

Display Omitted► Synthesis of novel Al- and Ce-containing helicoidal mesoporous materials. ► Low metal containing materials helicoidally structured with catalytic properties. ► Highly active materials in the oxathioacetalisation of aldehydes and ketones and epoxidation of cyclohexene.Helical mesoporous silicas containing aluminium or cerium into their framework have been synthesized via hydrothermal method. The synthesized materials were extensively characterized to understand their physico–chemical properties in view of their future catalytic applications. Low-angle powder XRD patterns of calcined samples showed a hexagonally ordered mesopore structure. NMR spectra of aluminium materials exhibited two signals at 50 and 0ppm assigned to tetracoordinated and octahedrally coordinated Al³⁺. DR-UV–vis and XPS spectrum of cerium content materials show that cerium was incorporated as Ce³⁺ and Ce⁴⁺ into the helical mesoporous material. Materials with molar ratios Si/Al=95 and Si/Ce=500 were found to be catalytically active in acid (oxathioacetalisations and alkylations) or redox (epoxidation of cyclohexene) catalyzed processes, respectively.

Keywords: Helical mesoporous material; Oxathioacetalisation; Oxidation; Hydrothermal; Aluminium; Cerium

Influence of Pt addition to Ni catalysts on the catalytic performance for long term dry reforming of methane by S.R. de Miguel; I.M.J. Vilella; S.P. Maina; D. San José-Alonso; M.C. Román-Martínez; M.J. Illán-Gómez (pp. 10-18).

Display Omitted► Pt was added to a Ni(10%)/Al₂O₃ to test its performance in a long-term dry reforming of methane. ► Pt(0.5%)/Al₂O₃ displayed a pronounced deactivation due to a sintering of the metallic phase. ► Ni(10%)/Al₂O₃ showed high and stable activity. ► Ni(10%)Pt(0.5%)/Al₂O₃ showed higher, stable activity and lower carbon deposition. ► The behaviour of the NiPt catalyst is due to geometric effects.The influence of Pt addition (in very low concentrations) to a Ni/(10%)/Al₂O₃ catalyst in its catalytic performance during long-term experiments of dry reforming of methane was studied.The monometallic Pt(0.5%)/Al₂O₃ catalyst displayed a pronounced deactivation during 6500min reaction time, mainly due to a significant sintering of the metallic phase, whereas the monometallic Ni(10%)/Al₂O₃ catalyst showed a high and stable activity along the reaction time.Compared with the Ni(10%)/Al₂O₃ catalyst, the bimetallic Ni(10%)Pt(0.5%)/Al₂O₃ sample showed a higher, and stable catalytic activity during the 6500min reaction time and a markedly lower carbon deposition. TEM images reveal much less carbon formation and filament grow and this leads to expect a higher stability in long term processes. Characterization techniques indicate that nickel and platinum are in close contact during the simultaneous reduction of the two oxide precursors and that geometric effects (dilution and blocking) are mainly responsible for the excellent catalytic behaviour of the bimetallic NiPt catalyst.

Keywords: Methane dry reforming; PtNi catalysts; Alumina-based catalysts; Catalyst deactivation

Nanosized gold-catalyzed selective oxidation of alkyl-substituted benzenes and n-alkanes by Ankush V. Biradar; Tewodros Asefa (pp. 19-26).

Display Omitted► Supported Au nanoparticles within the pores of mesoporous silica were synthesized. ► Au(III) ions were reduced with hemiaminal groups grafted onto the surface of SBA-15. ► Efficient and selective catalysis for oxidation of various alkanes obtained. ► Oxidative catalytic reaction produced predominantly ketone products. ► Versatile Au/SBA-15 catalyst for oxidation of various substituted and n-alkenes.We report the synthesis of nanoporous silica-supported gold nanoparticle catalysts and their selective and efficient catalytic properties toward oxidation reactions of various substituted alkylbenzenes and linear alkanes. The Au nanoparticles were synthesized by reducing Au(III) ions in situ within the nanopores of hemiaminal-functionalized mesoporous silica by using the supported hemiaminal groups as reducing agents. The resulting mesoporous silica-supported gold nanoparticles efficiently catalyzed the oxidation reactions of different alkyl-substituted benzenes and linear alkanes with t-butyl hydroperoxide (TBHP) as an oxidant. The catalytic reactions gave up to ∼99% reactant conversion and up to ∼100% selectivity toward ketone products in some cases. This high selectivity toward ketone products by the catalysts was unprecedented, especially considering the fact that only mild reaction conditions and no additives were employed during the reactions.

Keywords: Au catalysis; Oxidation; Nanocatalyst; Mesoporous catalyst; Au nanoparticles

Characterization of iron-containing AlPO-5 as a stable catalyst for selective catalytic reduction of N₂O with CH₄ in the presence of steam by Dang-guo Cheng; Fengqiu Chen; Xiaoli Zhan (pp. 27-31).

Display Omitted► FeAlPO-5 shows a low-temperature and stable activity in SCR of N₂O with CH₄ in the presence of steam. ► Fe₂O₃ nanoparticles need high temperature (above 500°C) to activate the reduction of N₂O. ► The site accessibility is an important factor that determines the activity of the zeolites.Iron-containing AlPO-5 prepared by isomorphous substitution and impregnation method for selective catalytic reduction (SCR) of N₂O with methane in the presence of steam was investigated and characterized by nitrogen sorption, XRD, FTIR, H₂-TPR, and EPR. The results indicate that AlPO-5 zeolite has a good capacity to resist steam and FeAlPO-5 has high population of isolated Fe(III) and oligonuclear Fe(III)_xO_y which lead to a better low-temperature and more stable activity than Fe/AlPO-5. Deactivation of Fe/AlPO-5 is ascribed to the agglomeration of Fe₂O₃ particles under steam condition. Combining the activity and characterization results, we deduce that isolated Fe(III) and oligonuclear Fe(III)_xO_y are highly active and responsible for catalytic reduction of N₂O with methane at low temperature (below 500°C). In contrast, Fe₂O₃ nanoparticles need high temperature (above 500°C) to activate both catalytic reduction of N₂O with methane and methane combustion.

Keywords: SCR; N; ₂; O; Methane; AlPO-5; Iron species

Tailoring the properties of hierarchical TS-1 zeolite synthesized from silanized protozeolitic units by D.P. Serrano; R. Sanz; P. Pizarro; I. Moreno (pp. 32-42).

Display Omitted► Hierarchical TS-1 has been synthesized by crystallization of silanized protozeolitic units. ► The influence of both precrystallization time and the silanization agent proportion has been explored. ► Physicochemical and catalytic properties of hierarchical TS-1 can be tailored. ► Enhanced secondary porosity leads to a better epoxidation catalytic activity with TBHP.Hierarchical TS-1 zeolites, characterized by having a secondary porosity within supermicro-mesopore range, have been synthesized by silanization of protozeolitic units, previously generated by means of a precrystallization step. The silanization agent anchors over protozeolitic units surface, acting as crystal growth inhibitor during the hydrothermal crystallization treatment and hindering partially the protozeolitic units growth and aggregation. The secondary porosity arises from the voids existing between these protozeolitics units. Both the duration of the precrystallization step and the proportion of the organosilane compound added to the synthesis gel have a significant influence on the physicochemical and textural properties of the resultant materials. Thus, a precrystallization time comprised between 22 and 24h leads to the highest enhancement of the textural properties. On the other hand, by controlling the organosilane compound proportion added to the synthesis gel, the relative contribution of the secondary porosity can be tailored. The catalytic activity of these materials was evaluated in olefin epoxidation reactions, using tert-butylhydroperoxide (TBHP) as oxidant. The olefin conversion and TOF values reached by hierarchical TS-1 zeolites are remarkably superior to those obtained with the conventional microporous TS-1 zeolite, the best catalytic results being achieved using a 8%mol of silanization agent. Likewise, these zeolites exhibit a high oxidant efficiency and total selectivity to epoxide, parameters which are not affected by the presence of the secondary porosity.

Keywords: TS-1 zeolite; Hierarchical porosity; Silanization; Epoxidation

Liquid phase acetoxylation of α-pinene over Amberlyst-70 ion-exchange resin by M. Golets; S. Ajaikumar; D. Blomberg; H. Grundberg; J. Wärnå; T. Salmi; J.-P. Mikkola (pp. 43-50).

Display Omitted► One-pot process is proposed for α-pinene acetoxylation. ► High temperature improved the conversion and also leaded to products oligomerization. ► Valuable products produced in high yield via both catalytic and non-catalytic modes. ► Kinetic modeling was carried out for the proposed reaction network.Heterogeneously-catalyzed and solvent-catalyzed liquid phase acetoxylation of α-pinene with acetic acid acting as both a solvent and a reagent was studied. Both solvent-catalyzed and catalytic experiments were carried out and various reaction conditions were studied. The influence of temperature, pressure, solvent and gas milieu were taken into account. Bornyl, fenchyl, verbenyl as well as α-terpinyl acetates, limonene, camphene and γ-terpinene were found among reaction products. The addition of the catalyst allowed for maximization of the yield of bornyl acetate. The predominant products obtained were α-terpinyl, verbenyl and bornyl acetates. The reaction pathways were identified and evaluated.The aim of this work was to study the feasibility of batch acetoxylation of α-pinene. The analysis of the complex product distribution is not trivial and, consequently, resolving the reaction network was important. The optimized reaction conditions were searched for aiming at an efficient conversion of α-pinene to a mixture of valuable products.

Keywords: Heterogeneous catalyst; Amberlyst 70; α-Pinene acetoxylation; α-Terpinyl acetate; Biorefinery

Comparison of alumina- and SBA-15-supported molybdenum nitride catalysts for hydrodeoxygenation of guaiacol by I. Tyrone Ghampson; Catherine Sepúlveda; Rafael Garcia; J.L. García Fierro; Nestor Escalona; William J. DeSisto (pp. 51-60).

Display Omitted► Different synthesis method results in different Mo nitride phase on SBA-15 support. ► Activity influenced by the Mo nitride phase. ► Phenol/catechol selectivity influenced by the support. ► Catalysts on SBA-15 favored direct phenol production. ► Nitride catalysts compared favorably with commercial sulfided catalysts.The hydrodeoxygenation of guaiacol (2-methoxyphenol) has been studied in a batch reactor over alumina- and SBA-15 silica-supported molybdenum nitride catalysts at 300°C and 5MPa of hydrogen pressure. The catalysts were prepared by nitriding supported Mo oxide precursors with ammonia gas or nitrogen–hydrogen mixtures via temperature-programmed reaction. The alumina-supported catalysts had a higher activity relative to the SBA-15 silica-supported catalysts which was essentially due to catechol production, an effect of the alumina support. The SBA-15 silica-supported catalysts transformed guaiacol directly to phenol by demethoxylation without noticeable catechol production. On both supports, nitridation by ammonolysis increased the activity by a factor of ∼1.1 relative to nitridation by nitrogen–hydrogen. On SBA-15, ammonolysis preferentially produced the γ-Mo₂N phase while the N₂/H₂ mixture produced the β-Mo₂N_0.78 phase. The incorporation of Co led to a marginal improvement in exposed Mo species but generally had a diminishing effect on HDO activity. The lack of catechol production using the SBA-15 silica support is important in minimizing coking reactions and also opens up possibilities for utilizing silica supports with highly controlled pore sizes to possibly influence product distribution in HDO of more diverse feed streams derived from biomass conversion processes.

Keywords: Hydrodeoxygenation; Alumina; SBA-15; Nitride; Oxynitride; Catalyst

The role of nanobeta zeolite in NiMo hydrotreating catalysts by Songdong Yao; Ying Zheng; Siauw Ng; Lianhui Ding; Hong Yang (pp. 61-67).

Display Omitted► The role of nanobeta zeolite in NiMo/Al₂O₃ catalysts was investigated in this study. ► Adding nanobeta zeolite can enhance catalyst acidity and induce new Brønsted acid sites. ► Incorporation of nanobeta zeolite can modify the morphology of NiMoS slabs. ► The HDS and HDN activity of NiMo catalyst can be improved with introduction of nanobeta zeolite.Hydrotreating catalyst NiMo/Al₂O₃ was modified by adding nano-sized zeolite beta and by hydrothermal treatments. The catalysts were characterized by BET, XRD, Pyridine-IR,²⁹Si NMR,²⁷Al NMR and TEM. The results showed that the addition of nanobeta could significantly enhance the hydrodesulfurization (HDS), hydrogenation, and hydrocracking abilities of the NiMo catalysts. The catalytic performance decreased in the order NiMo(C)>NiMo(15)>NiMo(D)>NiMo(7.5)≫NiMo/Al₂O₃. The presence of nanobeta could strengthen acid sites which facilitated the abilities of hydrocracking and removal of sulfur-containing compounds, especially those of refractory nature. Introduction of nanobeta could also induce the synergetic effect between NiMoS and the support material with thicker NiMoS slabs. This morphology change might be responsible for the improvement in hydrogenation. It was observed that hydrothermal treatment conditions could affect the acidity and the NiMoS morphology of the catalysts, which in turn alter the catalyst hydrogenation ability.

Keywords: Nanobeta; Hydrothermal treatment; NiMo/Al; ₂; O; ₃; Hydrodesulfurization; Hydrodenitrogenation

On catalyst activation and reaction mechanisms in propane aromatization on Ga/HZSM5 catalysts by Victor de O. Rodrigues; Arnaldo C. Faro Júnior (pp. 68-77).

Display Omitted► Hydridogallium ions cannot be the active sites for alkane aromatization on Ga/HZSM5. ► Hydrogen competes with propane for hydrogenolysis sites on Ga/HZSM5. ► Pre-formed hydridogallium ions on Ga/HZSM5 disappear rapidly under propane flow. ► Hydridogallium ions are formed Ga/HZSM5 upon reduction by hydrogen but not by propane.Ga/HZSM5 catalysts prepared by incipient wetness impregnation of HZSM5 with gallium nitrate solutions and submitted to reductive and oxidative pre-treatments were studied by adsorbed pyridine FTIR, in situ DRIFTS and had their catalytic activity tested in propane aromatization reactions at 703K with different initial hydrogen partial pressures. It is shown that dihydridogallium ions formed under hydrogen at aromatization temperatures, slowly decompose under inert gas flow and rapidly decompose when hydrogen is replaced by propane. During reduction under propane, no dihydridogallium species are observed, only alkylgallium species. Dehydrogenation reactions were inhibited and hydrogenolysis activities went through a maximum with increasing hydrogen partial pressure. The results showed that dihydridogallium ions cannot be the active sites for alkane activation and that, while taking part in hydrogenolysis reactions, hydrogen competes with propane for the active sites. A possible reaction scheme for catalyst activation and the first steps in the aromatization reaction is proposed.

Keywords: Gallium; HZSM5; Alkane aromatization; In situ; DRIFTS; Catalyst activation; Reaction mechanism

Ubiquitous aluminum alkyls and alkoxides as effective catalysts for glucose to HMF conversion in ionic liquids by Dajiang (DJ) Liu; Eugene Y.-X. Chen (pp. 78-85).

Simple, inexpensive aluminum alkyl or alkoxy compounds are effective catalysts for the glucose-to-HMF conversion in [EMIM]Cl, achieving ∼32-fold enhancement in HMF yield over the corresponding halide catalyst.Display Omitted► Glucose conversion into 5-hydroxymethylfurfural (HMF) in ionic liquids. ► Inexpensive aluminum alkyls and alkoxides are as effective as the benchmark catalyst for the conversion. ► Simple aluminum alkyl and alkoxide catalysts are far more effective than aluminum chloride catalysts. ► Catalyst structure in an ionic liquid was characterized by X-ray diffraction.Metal halides (chlorides in particular) are employed almost exclusively as Lewis acid catalysts for the homogeneous conversion of glucose (or cellulose) to HMF (5-hydroxymethylfurfural) in ionic liquids (ILs), with CrCl₂ being arguably the most effective benchmark catalyst. Reported herein is a discovery that ubiquitous aluminum alkyl or alkoxy compounds are very effective Lewis acid catalysts for the glucose-to-HMF conversion in ILs. Under the current reaction conditions (1-ethyl-3-methylimidazolium chloride [EMIM]Cl, 120°C, 6h), simple trialkyl and trialkoxy aluminum species such as AlEt₃ and Al(OⁱPr)₃, which are much cheaper than CrCl₂ (by a factor of 5 for AlEt₃ or 180 for Al(OⁱPr)₃), are at least as effective as CrCl₂ to catalyze this conversion process. The molecular structure of [EMIM]⁺[ClAlMe(BHT)₂]⁻, formed upon mixing the alkylaryloxy aluminum MeAl(BHT)₂ and the IL [EMIM]Cl, has been determined by X-ray diffraction; the structure simulates that of the metallate [EMIM]⁺[CrCl₃]⁻, the proposed active species responsible for the effective glucose to HMF conversion by CrCl₂ in [EMIM]Cl. Another significant finding is that a gradual substitution of the chloride ligand on aluminum by the alkyl ligand brings about a drastic enhancement on the HMF yield, from 1.6% by AlCl₃ to 7.6% by MeAlCl₂ to 17% by Et₂AlCl and to 51% by AlEt₃, thus showing approximately an overall 32-fold HMF yield enhancement going from AlCl₃ to AlEt₃.

Keywords: Biomass; Glucose; Ionic liquids; HMF; Aluminum catalysts

Facile one-pot synthesis of Eu, N-codoped mesoporous titania microspheres with yolk-shell structure and high visible-light induced photocatalytic performance by Jian-Wen Shi; Hao-Jie Cui; Xu Zong; Shaohua Chen; Jinsheng Chen; Bin Xu; Weiya Yang; Lianzhou Wang; Ming-Lai Fu (pp. 86-92).

Display Omitted► Eu, N-codoped TiO₂ with yolk-shell structure was synthesized by one-pot method. ► Synergic effects of two dopants to improve photocatalytic activity were discovered. ► Yolk–shell structure allowed multiple reflections of light within interior cavities. ► The resultant material presented high visible-light induced photocatalytic activity.A new type of Eu, N-codoped mesoporous TiO₂ microspheres with yolk–shell structure (TiO₂@void@TiO₂) was successfully synthesized by a facile one-pot hydrothermal method at low temperature (180°C). The physical and chemical properties of as-synthesized samples, such as morphology, crystal phase, surface elements composition, porous structure, specific surface area and optical response, were characterized in detail. The resultant samples were porous microspheres with a diameter of about 1–3μm, and were composed of a large number of smaller nanoparticles. An interior circular cavity in each microsphere was formed between core and shell to construct a special yolk–shell structure, and a large number of pores were produced in shell and yolk by CO₂ gas bubbles resulting from hydrothermal decomposition of the urea molecules, which tremendously increased the specific surface area and the pore volume of as-obtained samples. The absorption edges of Eu, N-codoped TiO₂ were extended to longer wavelength, which led to notable absorption in the visible-light region. The photocatalytic performances of all samples were evaluated by photocatalytic decoloration of rhodamine B and methyl orange under visible light irradiation ( λ>420nm). Eu, N-codoped TiO₂ with 0.1at.% Eu dopant showed the highest photocatalytic activity, the efficiency of which was 5 times higher than that of Degussa P25. The enhanced photocatalytic performance could be attributed to the synergic effects of many factors, such as high specific surface area, large pore volume and strong absorption to visible light, which were created by the Eu, N-codoping and the unique yolk–shell structure. Based on the above results, the mechanism of enhanced photocatalysis on Eu, N-codoped TiO₂ under visible light was proposed.

Keywords: Titania; Nitrogen; Europium; Co-doping; Photocatalysis; Visible light

Photocatalytic and photoelectrochemical properties of in situ carbon hybridized BiPO₄ films by Bin Lu; Xinguo Ma; Chengsi Pan; Yongfa Zhu (pp. 93-98).

Display Omitted► Carbon hybridized BiPO₄ film was prepared with 30nm of BiPO₄ nanoparticle. ► Photocatalytic activity was enhanced by inhibiting charge carriers recombination. ► The inhibition was ascribed to higher electrons transfer efficiency by carbon.In situ hybridization of carbon with BiPO₄ films were performed through calcination of amorphous complex precursor films on the Ti substrate under various temperatures. The BiPO₄ crystallites were in situ grown into BiPO₄ particles on the surface of the Ti substrate. The formed BiPO₄ particles in situ hybridized with the residual carbon from precursor calcination to form carbon hybridized BiPO₄ films. The extent of hybridization depended on the calcination temperatures. The photocatalytic activities of carbon hybridized BiPO₄ films under different calcination temperatures were estimated through photocatalytic degradation of methylene blue. The results indicated that the film prepared at 400°C presented the highest photocatalytic activity, which was about 1.5 times than that of the film at 550°C. This phenomenon could be attributed to the higher carbon hybridization extent, higher transfer efficiency of photo-induced electrons between carbon and BiPO₄ crystalline nanoparticles in films, and corresponding separation efficiency of photo-induced electrons and holes. The electronic interaction was also systematically investigated by the photoelectrochemical measurements.

Keywords: BiPO; ₄; Carbon; Hybridization; Photo-induced carriers separation

Effect of the support on the catalytic stability of Rh formulations for the water–gas shift reaction by Carolina A. Cornaglia; John F. Múnera; Laura M. Cornaglia; Eduardo A. Lombardo; Patricio Ruiz; Alejandro Karelovic (pp. 99-106).

Display Omitted► Catalysts for high temperature water gas shift reaction in membrane reactors. ► Rhodium over La₂O₃ and La₂O₃·SiO₂ oxides as catalysts. ► Deactivation of the Rh/La₂O₃ solid due to the formation of carbonate/formate species. ► The initial activity is restored after being burnt in air at 673K.The stability of Rh(0.6)/La₂O₃ and Rh(0.6)/La₂O₃(27)·SiO₂ catalysts used in the water–gas shift reaction (WGSR) was studied. In order to understand the different behavior of the two formulations, XRD, Raman spectroscopy and operando-DRIFTS were employed. It was demonstrated that Rh/La₂O₃·SiO₂ showed a constant activity after 50h on stream and that it was made up of La₂Si₂O₇ with very low crystallinity and SiO₂. On the other hand, Rh/La₂O₃ after use evolved to a mixture of oxycarbonates and lanthanum hydroxide evidenced by XRD and confirmed by Raman spectroscopy. This solid suffered a significant deactivation which was assigned to the formation of very small amounts of formate and carbonate residues. These residues disappeared after being burnt in air at 673K and the initial catalytic activity was restored. The results obtained were useful to explain the reasons for the different stability of the two formulations and could have implications for the design of active catalysts used in the WGSR and in the processes in which it is involved.

Keywords: Hydrogen purification; Formate species; Binary support; Deactivation

Functionalized multi-walled carbon nanotubes with stereospecific Ziegler-Natta catalyst species: Towards facile in situ preparation of polypropylene nanocomposites by Ning Wang; Yawei Qin; Yingjuan Huang; Hui Niu; Jin-Yong Dong; Yuexin Wang (pp. 107-114).

Display Omitted► Z-N catalyst was for the first time applied in the in situ preparation of PP/CNTs nanocomposites. ► n-BuMgCl and TiCl₄ coupled with a diether electron donor formed the Z-N catalyst. ► PP/CNTs nanocomposites with excellent nano-sized dispersion of CNTs were afforded.Multi-walled carbon nanotubes (MWCNTs) were functionalized with a stereospecific Ziegler-Natta catalyst species for in situ preparation of polypropylene (PP)/MWCNT nanocomposites. The functionalization process involved initially treating MWCNTs containing a few (∼3.0% w/w) surface hydroxyl groups (MWCNT-OH) with an excess amount of Grignard reagent followed by further reaction with TiCl₄. Triethylaluminum (TEA) and dimethoxydiphenylsilane (DDS) were used as co-catalyst and external electron donor, respectively. The resulting MWCNTs (MWCNT/Mg/Ti) only behaved as a fair isospecific Ziegler-Natta catalyst, promoting propylene polymerization at a moderate rate and resulting in PP with moderate isotacticity indices (76.4–91.0%). To improve the catalytic performance, the electron-donating reagent 9,9-bis(methoxymethyl)fluorine (BMMF) was added into the MWCNT functionalization process, incorporating BMMF into the catalytic material and simultaneously reducing the quantity of TiCl₄ immobilization. The BMMF-incorporated functionalized MWCNTs (MWCNT/Mg/BMMF/Ti) produced PP with a high isotacticity index (92.0%) without the use of an external electron donor. PP with an isotacticity index greater than 98% was achieved when DDS was used as external electron donor during the polymerization process.

Keywords: Polypropylene; MWCNTs; Ziegler-Natta catalyst system; In situ; polymerization

Propene epoxidation with oxygen over gold clusters: Role of basic salts and hydroxides of alkalis by Jiahui Huang; Takashi Takei; Hironori Ohashi; Masatake Haruta (pp. 115-122).

Display Omitted► Gold clusters (1.6nm) were deposited on TS-1 free of K by solid grinding. ► Different cations with counter anions were introduced on Au/TS-1 by impregnation. ► Na⁺, K⁺, Rb⁺, or Cs⁺ coordinated with OH⁻, CH₃COO⁻, CO₃²⁻, or PO₄³⁻ promoted propene epoxidation with O₂–H₂O.Titanosilicalite-1 (TS-1) was first treated with aqueous KOH solution to introduce surface defects. Then KOH-treated TS-1 (TS-1K) was further treated with aqueous HNO₃ solution to remove residual potassium. Then, Au was deposited by solid grinding on this support free of K (TS-1KH) as 1.6nm clusters, which could be stabilized by surface detects. Finally, Au/TS-1KH was modified by impregnating potassium salts, alkali hydroxides or alkaline earth metal acetates. XRD and UV–vis spectra indicated that the crystalline MFI structure and 4-fold coordinated Ti⁴⁺ sites of TS-1 were maintained even after different treatments. HAADF-STEM showed that after the modification of Au/TS-1-KH the mean diameter of Au clusters increased only slightly from 1.6nm to 1.8nm. In propene epoxidation with molecular O₂ and H₂O, Au/TS-1KH promoted by basic potassium salts (CH₃COO⁻, CO₃²⁻ and PO₄³⁻) or hydroxides of Na, K, Rb and Cs could produce PO with the selectivity of 12–45%, while Au/TS-1KH combined with neutral potassium salts (KCl, KNO₃ and K₂SO₄), LiOH or alkaline earth metal acetates could not produce PO.

Keywords: Propene epoxidation; O; ₂; –H; ₂; O mixture; Au clusters; TS-1; Alkali metals; Alkaline earth metals

Tartaric acid–Ni supported catalysts obtained from hydrotalcite-like compounds: Effects of catalyst preparation variables on enantioselectivity by Marco-A. López-Martínez; Ian J. Shannon (pp. 123-130).

Display Omitted► Hydrotalcite-like compounds as tartaric acid–nickel supported catalyst precursors. ► Catalysts for the enantioselective hydrogenation of methyl acetoacetate. ► Variables used during chiral modification have no effect on enantioselectivity. ► The nature of the cation comprising the support is central in enantioselectivity.The catalytic properties of tartaric acid–nickel supported catalysts obtained from hydrotalcite-like compounds have been assessed in the enantioselective hydrogenation of methyl acetoacetate. Ni particle size above a minimum threshold of ca. 20nm was found to influence enantioselectivity. For materials with similar Ni crystallite size, e.e. progressively lowers as Mg is incorporated to Ni/Al, whereas incorporation of Zn improves e.e. for all Ni/Zn ratios. In general, activity is higher on Ni/Mg/Al than on Ni/Zn/Al series. Moreover, the synthetic method to obtain hydrotalcite-like compounds affects the catalytic properties of the resultant catalysts. For a series of materials of the same composition, the urea hydrolysis method leads to catalysts with enantiodifferentiation ability, whereas the coprecipitation method does not. Variables of reaction during chiral modification, such as pH and tartaric acid concentration, proved not to have a major effect on enantioselectivity. Furthermore, no direct correlation between the amount of tartaric acid adsorbed onto, or Ni leached from the surface, and the enantiodifferentiation ability of the catalysts was found.

Keywords: Hydrotalcite-like compounds; Tartaric acid–nickel; Enantioselective hydrogenation

Toward the decoration of Pt nanoparticles supported on carbon nanotubes with Fe oxides and its effect on the catalytic reaction by Zhen Guo; Chunmei Zhou; Daming Shi; Yifan Wang; Xinli Jia; Jie Chang; Armando Borgna; Chuan Wang; Yanhui Yang (pp. 131-140).

Display Omitted► Two-step microwave method is effective in making bimetallic catalysts. ► Ultra-fine FeO_x particles can be deposited on preformed Pt nanoparticles. ► Promoted Pt catalysts show excellent activity in hydrogenation of aldehyde. ► The activity was attributed to the unique contact mode between Pt and FeO_x.Deposition of metallic oxides on noble metal catalysts improves their catalytic performance dramatically due to the highly active sites formed at the interface of two metals (nano-contact). In this work, Fe oxides were deposited on preformed Pt nanoparticles by using a novel microwave assisted polyol reduction method. The facile synthesis is performed in liquid phase at 438K, which preserves the growth of large Pt nanoparticles and precludes the formation of Pt–Fe alloy. The Fe promoted Pt catalyst exhibited high activity (6340h⁻¹ in turnover frequency) and selectivity (89.1% for cinnamal alcohol) in the hydrogenation of cinnamaldehyde, which was attributed to the uniform distribution of Fe promoters on Pt surfaces. The characteristics of Fe oxides on Pt nanoparticles were identified by employing electrochemical analysis and X-ray photoelectron spectroscopy.

Keywords: FeO; _x; decorated Pt catalyst; Electrochemical measurement; Microwave assisted polyol reduction; Selective hydrogenation; Cinnamaldehyde

Effect of the tungsten precursor on the high activity of the WO₃/ZrO₂ catalyst in the oxidative lactonization of 1,2-benzenedimethanol by Quanjing Zhu; Xiaofeng Chu; Zhaoyan Zhang; Wei-Lin Dai; Kangnian Fan (pp. 141-147).

Display Omitted► Highly active commercial zirconia-supported tungsten oxide catalysts. ► Using tungstic acid–oxalic acid complex as the tungsten precursors. ► Excellent activity for oxidative lactonization of 1,2-benzenedimethanol. ► Polymeric WO₆ units on the catalyst played an important role.A series of tungsten oxide supported on commercial ZrO₂ was synthesized via a traditional impregnation method using ammonium tungstate, phosphotungstic acid hydrate and tungstic acid–oxalic acid complex as the tungsten precursors. The supported catalysts were characterized by XRD, UV–vis DRS, Raman and XPS. It was found that the tungsten precursor and the calcination temperature were crucial to the dispersion and the nature of the tungsten species on ZrO₂. The catalytic performances of the catalysts were investigated in the oxidative lactonization of 1,2-benzenedimethanol to phthalide with H₂O₂. The excellent catalytic performance of the catalyst prepared by calcination at 823K after using tungstic acid-oxalic acid complex as the tungsten precursor was attributed to the presence of polymeric WO₆ units.

Keywords: WO; ₃; /ZrO; ₂; catalysts; Tungsten precursor; Oxidative lactionzation; H; ₂; O; ₂

Transition metal coordination polymers: Synthesis and catalytic study for hydroxylation of phenol and benzene by Hanna S. Abbo; Salam J.J. Titinchi (pp. 148-155).

Display Omitted► New Ni(II) and Cu(II) coordination polymers were synthesized and characterized. ► The coordinated polymers is assessed for hydroxylation of phenol and benzene by H₂O₂. ► The catalysts show high activity and selectivity to catechol for phenol hydroxylation. ► The catalysts can be recovered and reused without significant loss of activity.New coordination polymers of Ni(II) and Cu(II) of the polymeric salen-type Schiff base ligand derived from the condensation of 5,5′-methylene bis-(salicyaldehyde) with 1,2-diaminopropane yielded N, N′-1,2-propylenebis(5-methylenesalicylidenamine) abbreviated [CH₂(H₂sal-1,2-pn)]_n have been synthesized. Both coordinated polymers with the general formula of [CH₂(ML·XDMF)]_n, where X=0, M=Cu; N, N′-1,2-propylenebis(5-methylenesalicylidenaminato)copper(II) and X=2, M=Ni; N, N′-1,2-propylenebis(5-methylenesalicylidenaminato)nickel(II) have been characterized by elemental analysis, magnetic susceptibility measurements, IR, electronic spectra and thermogravimetric studies. The ligand behaves as a bis-bidentate molecule coordinating through the phenolic oxygen and azomethine nitrogen atoms.These coordinated polymers have been assessed as catalysts for liquid phase hydroxylation of phenol and benzene using H₂O₂ as an oxidant. The results show a high activity and selectivity of both catalysts toward the formation of diphenols from phenol, and a low activity in the oxidation of benzene. The Cu-based catalyst exhibited higher activity than Ni-based catalyst for hydroxylation of phenol and benzene. The activity and efficiency of H₂O₂ depends on the reaction parameters viz., temperature, molar ratio of the reactants and the solvent. Concentration of the oxidant and other reaction parameters has been optimised for the maximum oxidation of these substrates. These catalysts can be recovered and reused without notable loss of activity.

Keywords: Coordination polymer; Phenol hydroxylation; Hydroxylation of benzene; Heterogeneous catalysts

Promotional effect of F-doped V₂O₅–WO₃/TiO₂ catalyst for NH₃-SCR of NO at low-temperature by Shule Zhang; Hongyu Li; Qin Zhong (pp. 156-162).

Display Omitted► The catalytic activity of VWTi was promoted by F doping. ► Improve the interaction of WO₃ with TiO₂ by F doping. ► Improve the activity of a catalyst with low WO₃ loading. ► Investigating the reduced W⁶⁺ could improve the NO conversion.A F-doped V₂O₅–WO₃/TiO₂ has been developed for low-temperature selective catalytic reduction (SCR) of NO with NH₃. The aim of this novel design was to improve the activity of a catalyst with low WO₃ loading. Analysis by PL spectra, XRD, XPS and EPR showed that F doping improved the interaction of WO₃ with TiO₂ by oxygen vacancies to facilitate the formation of W⁵⁺ that was important to improve the formation of superoxide ions. The experimental results showed that NO conversion could be improved by F doping and V₁W₃TiF_1.35 showed the highest NO removal efficiency in SCR reaction at low temperatures.

Keywords: F-doped V; ₂; O; ₅; –WO; ₃; /TiO; ₂; SCR; Oxygen vacancies; W; ⁵⁺; Superoxide ions

Effect of macroreticular acidic ion-exchange resins on 2-methyl-1-butene and 2-methyl-2-butene mixture oligomerization by M. Granollers; J.F. Izquierdo; F. Cunill (pp. 163-171).

Display Omitted► On the external catalyst surface mainly takes place the dimerization. ► Trimerization and cracking-copolimerization take place mainly inside the gel-phase. ► Conversion, yields and reactivity are related to superficial acid density of resins. ► A kinetic Eley-Rideal model shows a better fit than a pseudo-homogeneous model.A screening of macroreticular ion exchange resins has been carried out in order to select the most suitable catalysts for liquid-phase oligomerization of an isoamylene mixture. The reaction was performed at mild temperature (343K) to promote the dimerization and trimerization, and at higher temperature (383K) to evaluate side reactions like cracking and copolymerization. No compounds higher than trimers were significantly detected at studied conditions. By plotting product yields versus conversion at 343K, it was showed no significant differences between all catalysts tested. However, at 383K, the ion exchange resins which mainly work in the external zone were more selective to dimerization and less to cracking and trimerization products, which suggests that trimerization and cracking mainly took place inside the gel-phase of the macroreticular resins.The most active catalysts were the oversulfonated resins with high cross-linking degree and high acid capacity. A heterogeneous Eley-Rideal kinetic model showed better fitting of dimerization rates than two pseudo-homogeneous models.

Keywords: Oligomerization; Ion exchange resins; Isoamylene

Aqueous phase reforming of xylitol and sorbitol: Comparison and influence of substrate structure by Alexey V. Kirilin; Anton V. Tokarev; Leonid M. Kustov; Tapio Salmi; J.-P. Mikkola; Dmitry Yu. Murzin (pp. 172-180).

Display Omitted► Aqueous phase reforming of xylitol was studied over Pt/Al₂O₃ catalyst. ► Stable catalyst performance over 160h time-on-stream. ► Higher selectivity to H₂ compared to sorbitol. ► Advanced reaction network based on the substrate structure was proposed.The behavior of abundant polyol stemming from hemicelluloses, xylitol, was investigated in the aqueous phase reforming (APR) over supported Pt/Al₂O₃. The data obtained in the case of xylitol was compared to aqueous phase reforming of sorbitol under the same operating conditions. The effect of weight hour space velocity on the performance of a catalytic system as well as on selectivity toward hydrogen and alkanes was studied. The catalyst showed stable performance with insignificant deactivation over 160h time-on-stream. The selectivity toward H₂ diminished from 86 to 70% within 120h. The regeneration of the catalytic system in a H₂ flow allowed to recover the catalyst activity and to improve selectivity toward H₂ to 75%. It was found that both polyols demonstrated similar behavior in the APR in the whole range of space velocities studied. The selectivity toward H₂ went through a maximum in the case of xylitol and sorbitol when changing a space velocity. This behavior was attributed to a number of side reactions which involved hydrogen thus leading to its consumption. Additionally, the yields of target APR product, hydrogen, were higher in the case of xylitol compared to sorbitol due to the longer carbon chain in the latter substrate. The plausible reaction network based on the hypothesis that APR process proceeds through the terminal position of polyol was proposed to explain similarity in the gas and liquid product composition in the APR of xylitol and sorbitol. The reaction scheme describing formation of the main gas and liquid products via various pathways was proposed and discussed. The results obtained and explanations provided are in perfect agreement with the results obtained for other feedstocks in the literature.

Keywords: Catalysis; Biomass conversion; Xylitol; Pt/Al; ₂; O; ₃; Aqueous reforming; Hydrogen

Effect of the sequence of impregnation on the activity and sulfur resistance of Pt–Ni/γ-Al₂O₃ bimetallic catalysts for the selective hydrogenation of styrene by Carolina Betti; Juan Badano; M. Juliana Maccarrone; Vanina Mazzieri; Carlos Vera; Mónica Quiroga (pp. 181-186).

Styrene total conversion as a function of time in the absence of poison. (▪) Pt, (▪) NiClPt, (▪) NiNPt, (▪) PtNiCl and (▪) PtNiN.Display Omitted► Low-loaded Pt and Ni bimetallic catalysts were prepared. ► Elenctron-rich species of Pt δ⁻ were found by XPS on the bimetallic catalysts. ► Due to an electronic effect, PtNi and NiPt were more active than monometallic Pt. ► NiPt catalysts were more sulfur resistant because of steric and electronic effects. ► Species of Ni⁰ and Pt δ⁻ on PtNiCl are responsible of poisoning.The influence of the preparation of bimetallic Pt–Ni catalysts on their activity and sulfur resistance during styrene semi-hydrogenation was studied. The preparation variables assessed were the sequence of impregnation and the kind of nickel precursor used. The catalysts were tested with the styrene hydrogenation reaction and further characterized by ICP, TPR, XPS and pyridine TPD.All catalysts showed high selectivities to ethylbenzene (>98%). The bimetallic catalysts were more active than monometallic Pt and the following activity order was found: Pt≅NiClPt≤NiNPt

Keywords: Key words; Selective hydrogenation; Bimetallic catalysts; Sulfur resistance; Platinum; Nickel

Influence of the Brönsted and Lewis acid sites on the catalytic activity and selectivity of Fe/MCM-41 system by N.A. Fellenz; J.F. Bengoa; S.G. Marchetti; A. Gervasini (pp. 187-196).

.Display Omitted► Lewis acid sites were produced using iron oxide in Fe/MCM-41 system. ► Brönsted acid sites were neutralized by silylation treatment. ► Brönsted acidity is not enough to modify the selectivity in POX isomerization. ► Different calcination atmospheres lead to different types of acid Lewis sites of Fe³⁺.The system Fe₂O₃/MCM-41, with high iron dispersion, was synthesized in order to introduce Lewis acid sites into the MCM-41 structure. Two calcination atmospheres (inert and oxidant) were used to produce iron nanoclusters with different structural properties. Besides, a silylation treatment was realized on both solids with the aim of neutralizing the Brönsted acidity associated with the MCM-41 silanol groups. The samples were characterized by atomic absorption spectroscopy, X-ray diffraction at low angles, N₂ adsorption, temperature-programmed reduction, Fourier transform infrared spectroscopy, nuclear magnetic resonance of²⁹Si, and Mössbauer spectroscopy. The influence of the structural changes of the nanoclusters and the effect of the simultaneous presence of Lewis and Brönsted acid sites were evaluated studying the product distribution from the α-pinene oxide isomerization reaction. It was determined that the Brönsted acidity of the Fe/MCM-41 system has not the sufficient acid strength to modify the product distribution which is mainly governed by the Lewis sites.

Keywords: POX isomerization; Lewis acid sites; MCM-41; Mössbauer spectroscopy

Biopolymer templated porous TiO₂: An efficient catalyst for the conversion of unutilized sugars derived from hemicellulose by Sudipta De; Saikat Dutta; Astam K. Patra; Bharat S. Rana; Anil K. Sinha; Basudeb Saha; Asim Bhaumik (pp. 197-203).

Display Omitted► Biopolymer templating for high surface area TiO₂ with mesoscopic void space. ► Lewis acidity in biopolymer templated porous TiO₂. ► Utilization of epimers of glucose: mannose, galactose, and lactose as feedstocks. ► Microwave assisted HMF synthesis via nanocatalysis. ► Sustainable chemistry for the synthesis of fine chemicals from biorenewables.An efficient procedure for the conversion of unutilized abundant sugar derivatives, such asd-mannose,d-galactose and lactose, into platform molecule 5-hydroxymethylfurfural in aqueous and organic medium is reported. This process involves biopolymer sodium alginate templated porous TiO₂ nanocatalysts containing strong Lewis acidic sites as determined by pyridine-IR and temperature programmed desorption (TPD) of ammonia studies. Porous TiO₂ materials were characterized by XRD, SEM, HR-TEM and N₂ sorption techniques. Biopolymer templating pathway provided effective synthetic route for the TiO₂ nanomaterials, which contain considerable mesoscopic void space as revealed from the HR-TEM and N₂ sorption studies. Using this TiO₂ catalyst, improved HMF yields were obtained without using expensive ionic liquids as solvents. Hydrothermally obtained TiO₂ nanocatalysts showed maximum activity ind-mannose conversion to HMF, whereas nonporous TiO₂ is inactive in this reaction. Porosity (surface area), small particle size and strong acidic sites generated through biopolymer templating pathway are crucial for high catalytic activity.

Keywords: Biopolymer templating; Mesoporosity; Nanostructure; Biomass; Platform chemical; Mannose

Comparison of heterogeneous B(OⁱPr)₃-MCM-41 and homogeneous B(OⁱPr)₃, B(OEt)₃ catalysts for chemoselective MPV reductions of unsaturated aldehydes and ketones by Burcu Uysal; Birsen S. Oksal (pp. 204-216).

Display Omitted► Boron alkoxide-containing ordered mesoporous silica material (B(OⁱPr)₃-MCM-41) was prepared. ► B(OⁱPr)₃-MCM-41was successfully applied in the MPV reduction of unsaturated carbonyl compounds. ► High selectivity for the unsaturated alcohols was obtained with “B(OⁱPr)₃-MCM-41” catalyst. ► B(OⁱPr)₃-MCM-41 was compared with the homogeneous B(OⁱPr)₃ and B(OEt)₃ catalysts. ► In comparison with homogeneous catalysts, B(OⁱPr)-MCM-41 showed higher activity and better selectivity.Boron tri-isopropoxide, B(OⁱPr)₃, was immobilized on mesoporous material, MCM-41, and denoted as “B(OⁱPr)₃-MCM-41”. The prepared new heterogeneous catalyst, B(OⁱPr)₃-MCM-41, was characterized in details by using PXRD, FT-IR-,¹¹B NMR-,²⁹Si NMR-,¹³C NMR-, TEM, EDX, N₂ adsorption and ICP-OES. The results demonstrated the successful homogenous distribution of the B(OⁱPr)₃ on the MCM-41 support. Heterogeneous B(OⁱPr)₃-MCM-41 catalyst in comparison with the homogeneous B(OⁱPr)₃ and B(OEt)₃ catalysts, display similiar catalytic activity in the Meerwein–Ponndorf–Verley (MPV) reduction of unsaturated aldehydes and ketones with alcohols as reductants. Reduced reaction times, higher rate constants and very high selectivities for the unsaturated alcohols were obtained with the heterogenous catalyst than the homogeneous catalysts. In most cases, there were no side products other than the desired alcohol. The B(OⁱPr)₃-MCM-41 catalyst was found to be encouraging as the catalyst is recyclable up to six cycles without any significant loss in its catalytic activity. This work enriches the family of heterogeneous MPV catalysts for chemoselective reductions of unsaturated aldehydes and ketones.

Keywords: Mesoporous MCM-41; Boron tri-isopropoxide; Chemoselectivity; Unsaturated aldehydes and ketones; MPV reduction

Studies on surface impregnation combustion method to prepare supported Co/SiO₂ catalysts and its application for Fischer–Tropsch synthesis by Lei Shi; Yuzhou Jin; Chuang Xing; Chunyang Zeng; Tokimasa Kawabata; Kouji Imai; Kenji Matsuda; Yisheng Tan; Noritatsu Tsubaki (pp. 217-224).

Display Omitted► Highly dispersed Co/SiO₂ catalysts were prepared by surface impregnation combustion method. ► Co₃O₄ crystalline sizes of the as-prepared catalysts were only about 10nm. ► The activity of the as-prepared catalysts for FTS was higher.A series of supported Co/SiO₂ catalysts were prepared by surface impregnation combustion method using cobalt nitrates and citric acid, and the precursors were burnt in different atmospheres. The effects of different calcination atmospheres on the properties of the supported Co/SiO₂ catalysts were systemically studied by TG-DTA, XRD, Raman spectrum, TPR, in situ FTIR, TEM, BET and H₂-chemisorption techniques. The burnt catalyst C_{argon-air-reduction} which was first burnt in argon and then oxidized in air had about 10nm Co₃O₄ crystalline size, much smaller than that which was directly burnt in air (Co₃O₄ size: about 15nm) and that prepared by conventional impregnation method (Co₃O₄ size: about 32nm) using cobalt nitrate as impregnating solution. Characterizations and FTS results of two other references using different organic cobalt salt aqueous (cobalt acetate and cobalt citrate) as impregnating solution were also added in the supporting information. Comparing with our previously reported C_argon catalyst directly burnt in the argon atmosphere without further reduction, the influence from surface amorphous carbon and carbonic residues was completely eliminated. The activity of the burnt catalyst C_{argon-air-reduction} prepared by surface impregnation method was threefold higher than that of the reference C_N-reduction prepared by conventional incipient-wetness impregnation method. The surface impregnation combustion method described herein was promising to prepare highly dispersed supported metallic catalysts with smaller particle sizes.

Keywords: Surface impregnation combustion; Metallic catalysts; Co/SiO; ₂; Fischer–Tropsch synthesis

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Applied Catalysis A, General (v.435-436, #)