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Applied Catalysis A, General (v.437-438, #)
Fischer–Tropsch synthesis: Effect of Pd, Pt, Re, and Ru noble metal promoters on the activity and selectivity of a 25%Co/Al2O3 catalyst by Wenping Ma; Gary Jacobs; Robert A. Keogh; Dragomir B. Bukur; Burtron H. Davis (pp. 1-9).
.Display Omitted► Effect of Pd, Pt, Re, and Ru on the performance of 25% Co/Al2O3 was studied. ► Catalysts performance was examined in a 1-L continuously stirred tank reactor (CSTR). ► Noble metal promoters improved initial CO conversion of the Co catalysts. ► Noble metal promoters changed hydrocarbon distribution to some extent.The effect of noble metal promoters (atomic ratio of promoter to Co=1/170) on the activity and selectivity of a 25%Co/Al2O3 catalyst was studied at a similar CO conversion level of 50% at 493K, 2.2MPa and H2/CO=2.1 using a 1-L continuously stirred tank reactor (CSTR). The results show that all promoted catalysts exhibited markedly higher initial CO conversion rates on a per gram catalyst basis than the unpromoted one, which was ascribed to increased Co site density when the promoters were present. This is because the Re, Ru, Pt and unpromoted Co catalysts give essentially the same initial Co TOF values of 0.092–0.105s−1 (based on hydrogen-chemisorption). However, the initial Co TOF value for the Pd-Co catalyst was about 40% lower, which might be caused by Pd atoms segregating on the Co surface and partially blocking Co sites.At 50% CO conversion, Re and Ru promoters decreased CH4 selectivity and increased C5+ selectivity by nearly the same extent, whereas the opposite effect was observed for Pd and Pt promoters. The Re and Ru promoters had less of an impact on C2–C4 olefin selectivity (7.5–60%), but suppressed the secondary reaction of 1-C4 olefin (from 14.3 to 9%) compared to the unpromoted one; however, the addition of Pd and Pt promoters resulted in lower olefin selectivity (4.4–55%) but higher 2-C4 olefin selectivity (14.3 to 27–31%). Pt promotion had a negligible effect on C4 olefin isomerization. The selectivity results were reproducible.Both Pt and Pd promoters slightly increased WGS activity, whereas Re and Ru promoters had a negligible effect. The Pd and Pt promoters were observed to slightly enhance oxygenate formation, while Re and Ru slightly decreased it.
Keywords: Fischer–Tropsch synthesis; Co/Al; 2; O; 3; Co metal; Pd; Pt; Re; Ru; Hydrocarbon selectivity; Hydrogen-chemisorption/pulse reoxidation
Relation between hydrocarbon selectivity and cobalt particle size for alumina supported cobalt Fischer–Tropsch catalysts by Shreyas Rane; Øyvind Borg; Erling Rytter; Anders Holmen (pp. 10-17).
Display Omitted► With increasing particle size, the C5+ selectivity passes through a maximum at 8–9nm. ► δ-Al2O3 as support gives higher C5+ selectivity than θ-Al2O3 for particles ∼<10nm. ► The olefin/paraffin ratio varies in the same way as the C5+ selectivity for all Al2O3 phases. ► With increasing Co size, the influence from the support becomes less important.The relation between hydrocarbon selectivity and cobalt particle size was studied using different alumina supports. Alumina phases, i.e. δ-, θ- and α-Al2O3 were produced from a small and a medium pore γ-Al2O3 by heat treatment. All catalysts were prepared by incipient wetness impregnation resulting in a cobalt loading of 12, 20 and 30wt.% cobalt. The catalysts were tested in a fixed bed reactor at 20bar, 483K and H2/CO=2.1. The relation between methane, olefin and C5+ selectivities was studied for 2–14nm cobalt particles supported on δ- and θ-Al2O3 supports prepared from the two different γ-Al2O3. The C5+ selectivity increases with increasing Co particle size for particles less than 8–9nm where the selectivity goes through a maximum. The C5+ selectivity decreases for larger Co particles and then seems to approach a constant value independent of the alumina phase and pore size. The lowest CH4 selectivity and the highest olefin to paraffin ratio were obtained at maximum C5+ selectivity.
Keywords: Alumina; Cobalt; Particle size; Fischer–Tropsch; C; 5+; selectivity
Preparation of Pd/C designed for chiral modified catalyst: Comparison with Pd/TiO2 in enantioselective hydrogenation of α-phenylcinnamic acid by Takeshi Kubota; Hiroyuki Ogawa; Yasuaki Okamoto; Tomonori Misaki; Takashi Sugimura (pp. 18-23).
Display Omitted► Cinchonidine-modified catalysts were prepared with eggshell and homogeneous Pd/C. ► Optimized loading of Pd on the carbon was only 5%. ► The best prepared Pd/C showed identical performance with the commercial best Pd/C. ► The H2-pretreatment prior to the CD-modification was also effective for the freshly prepared catalyst. ► The properties of Pd/C in enantioselective hydrogenation were different from those of Pd/TiO2.Enantioselective hydrogenation of α-phenylcinnamic acid was investigated on Pd/C catalysts prepared in our laboratory to compare activity and selectivity with those on commercial Pd/C and Pd/TiO2 catalysts. The Pd/C catalysts after the 353 K-H2-pretreatment exhibited satisfactory and comparable performances obtained with commercially available best ever Pd/C by optimizing catalyst preparation. In contrast to Pd/TiO2, a high loading of Pd is not necessary with Pd/C, but only 5% loading on a certain activated carbon was found to result in high e.e. It is suggested that the optimum size or size-distribution of Pd metal particle are different between the two supports, suggesting a support effect of this catalyst system.
Keywords: Abbreviations; Pd/C; palladium supported on activated carbon; Pd//TiO; 2; palladium supported on rutile titania; CD; cinchonidine; PCA; phenylcinnamic acid; % e.e.; enantiomer excess of product in percent; r; 0; reaction rate evaluated by the hydrogen uptake at a 25% conversion of PCA (hydrogen consumption in mmol per gram catalyst and per reaction time in hour); G-60; activated carbon supplied by Darco; CGSP; activated carbon supplied by Norit; S-51; activated carbon supplied by Darco; Pd/C-A; powder type activated carbon supplied by Nacalai Tesque; Pd/C-B; granular type activated carbon supplied by Nacalai Tesque; wet dioxane; 2.5% (v/v) water-containing dioxaneEnantioselectivity; Hydrogenation; Chiral modified catalyst; Cinchonidine; Palladium on carbon
Validation of BET specific surface area for heterogeneous Ziegler-Natta catalysts based on αS-plot by Toshiaki Taniike; Patchanee Chammingkwan; Vu Quoc Thang; Toshiki Funako; Minoru Terano (pp. 24-27).
Display Omitted► Validation of the BET surface area of Ziegler-Natta catalysts based on the αS-plot method. ► Non-porous core–shell MgO/MgCl2/TiCl4 catalysts were used as reference. ► Micropore filling heavily overlaps with a multilayer adsorption region for the BET analysis. ► The BET surface area is questionable for typical Ziegler-Natta catalysts.Specific surface area based on the BET method in N2 adsorption has historically posed poor correlation with olefin polymerization activity of heterogeneous Ziegler-Natta (ZN) catalysts. We have investigated the validity of the BET surface area for ZN catalysts based on the αS-plot method, where non-porous core–shell MgO/MgCl2/TiCl4 catalysts were used as a reference material. The αS-plots for typical industrial ZN catalysts clarified the presence of two classes of micropores and resultant difficulty to isolate a multilayer adsorption region for the BET method. The results cast doubt on the application of the BET method to evaluate the surface area of heterogeneous ZN catalysts.
Keywords: Ziegler-Natta polymerization; Polyolefin; Nitrogen adsorption; BET method; α; S; -Plot
Synthesis of TiO2 nanoparticles using novel titanium oxalate complex towards visible light-driven photocatalytic reduction of CO2 to CH3OH by Quang Duc Truong; Thi Hang Le; Jen-Yu Liu; Cheng-Chi Chung; Yong-Chien Ling (pp. 28-35).
Display Omitted► TiO2 NPs with controlled crystalline phase and morphology has been synthesized. ► The synthesized TiO2 is highly active for CO2 reduction under visible light irradiation. ► The junction effect of two crystalline phases is responsible for the high efficiency of brookite–anatase particles.TiO2 nanoparticles (NPs) with controlled crystalline structure and morphology were synthesized by a facile hydrothermal method using a novel titanium oxalate complex. The structure, morphology, and spectral properties of the synthesized TiO2 NPs were characterized by X-ray diffraction, Raman spectroscopy, scanning/transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy. The titania phases of anatase, rutile, or brookite can be easily tuned by tailoring the solution pH during reaction. Highly ordered flower-like rutile could be obtained with oxalic acid additive. The synthesized TiO2 catalysts showed excellent visible light absorption and remarkable photocatalytic activity for CO2 reduction to CH3OH under both UV–vis and visible light irradiation, mainly due to doped carbon and nitrogen. Bicrystalline anatase–brookite composite afforded maximum CH3OH yield, attributed mainly to the unique electrical band structures and efficient charge transfer between the two crystalline phases.
Keywords: TiO; 2; nanoparticles; CO; 2; reduction; CH; 3; OH; Titanium oxalate complex; Visible light response
Thermal decomposition of bulk K-CoMoS x mixed alcohol catalyst precursors and effects on catalyst morphology and performance by Martin J. Menart; Jesse E. Hensley; Kellen E. Costelow (pp. 36-43).
Display Omitted► Lower-temperature thermal treatments of K-CoMoS x mixed alcohol catalyst precursors result in higher specific activity. ► Addition of K to catalyst precursor leads to finished materials with different morphology and performance. ► Cobalt segregates from the catalyst precursor during calcination to form bulk cobalt sulfides. ► Addition of gas phase sulfur during calcination reduces or eliminates segregation of cobalt.Cobalt molybdenum sulfide-type mixed alcohol catalysts were synthesized via calcination of precipitated bulk sulfides and studied with temperature programmed decomposition analysis. Precursors containing aqueous potassium were also considered. Precipitates thermally decomposed in unique events which released ammonia, carbon dioxide, and sulfur. Higher temperature treatments led to more crystalline and less active catalysts in general with ethanol productivity falling from 203 to 97g(kgcat)−1h−1 when the calcination temperature was increased from 375 to 500°C. The addition of potassium to the precursor led to materials with crystalline potassium sulfides and good catalytic performance. In general, less potassium was required to promote alcohol selectivity when added before calcination. At calcination temperatures above 350°C, segregated cobalt sulfides were observed, suggesting that thermally decomposed sulfide precursors may contain a mixture of molybdenum and cobalt sulfides instead of a dispersed CoMoS type of material. When dimethyl disulfide was fed to the precursor during calcination, crystalline cobalt sulfides were not detected, suggesting an important role of free sulfur during decomposition.
Keywords: Temperature programmed decomposition; Mixed alcohols; Bulk metal sulfide; Potassium promoter
Polymerization of ethylene with (nBuCp)2ZrCl2 supported over mesoporous SBA-15 functionalized with sulfonic acid groups by E. Casas; R. van Grieken; J.M. Escola (pp. 44-52).
Display Omitted► MAO was required to activate the metallocene, despite the sulfonic groups. ► Catalysts impregnated with TMA displayed considerable leaching of the metallocene. ► The activity increased with the content of sulfonic acid group and the acid strength. ► The sulfonic group and the chlorinated MAO might interact activating the metallocene.The polymerization of ethylene in n-heptane with (nBuCp)2ZrCl2 supported over mesoporous SBA-15 catalysts functionalized with propyl or aryl sulfonic acid groups and impregnated with either MAO or TMA was investigated and compared with reference samples. All the supports showed mesoscopic ordering with pore sizes of 7.8–6.6nm, BET surface areas around 700m2g−1, sulfonic acid loadings between 10 and 20 wt% and an acidity of roughly 1–1.7mmol H+g−1. None of the catalysts were capable of polymerizing ethylene in the absence of MAO in spite of using TMA or TIBA as scavengers. The addition of MAO (Al/Zr=800 or 5000) led towards ethylene polymerization, being the activity dependent on Al/Zr molar ratio (higher for Al/Zr=5000). The catalysts treated with TMA during the impregnation exhibited considerable leaching, unlike those treated with MAO wherein the leaching was low (<9 wt%). The presence of the sulfonic acid moiety enhanced the activity of the catalysts. In addition, the activity was also augmented with the increase of the sulfonic acid content from 10 to 20 wt%. Interestingly, the molecular weight of the polyethylene synthesized with the SBA-15 functionalized with sulfonic acid groups were 1.5–2.5 times higher, especially with the propyl moiety which leads towards Mw∼350,000gmol−1 at 1.2barg. The results were explained through an interaction between the sulfonic acid moiety and the chlorinated MAO species, which activates the metallocene.
Keywords: Polyethylene; Sulfonic acid groups; SBA-15; Metallocene
Partial oxidation of methane to syngas on bulk NiAl2O4 catalyst. Comparison with alumina supported nickel, platinum and rhodium catalysts by Rubén López-Fonseca; Cristina Jiménez-González; Beatriz de Rivas; José I. Gutiérrez-Ortiz (pp. 53-62).
Display Omitted► Bulk NiAl2O4 resulted highly active for POM to syngas. ► Its catalytic activity was comparable to that exhibited by a commercial Rh catalyst. ► Reduction of NiAl2O4 favoured the formation of small Ni0 crystallites. ► This catalyst resulted markedly stable during extended time on stream.In this work the catalytic performance of NiAl2O4 catalyst in the partial oxidation of methane (CH4(1)/O2(0.5)/N2(8.5) and 4800mLCH4g−1h−1) was investigated. This bulk catalyst resulted more active (70% conversion at 625°C) than alumina supported nickel catalysts prepared by conventional impregnation (11%Ni/Al2O3-30% conversion at 625°C and 14%Ni/Al2O3-65% conversion at 625°C) and a commercial platinum catalyst (1%Pt/Al2O3-30% conversion at 625°C). Further, the behaviour of NiAl2O4 was comparable to that of a commercial rhodium catalyst (1%Rh/Al2O3-75% conversion at 625°C). Fresh and spent catalysts were characterised by N2-physisorption, H2-TPR, UV-vis-DRS, WDXRF, XRD, TGA-MS, TEM and Raman spectroscopy. After catalyst reduction CH4 conversion over bulk NiAl2O4 was associated with the formation of large amounts of metallic nickel crystallites with a relatively small size. Although significant coking was noticed, conversion and selectivity to H2/CO were not significantly affected after prolonged time on stream.
Keywords: Nickel aluminate; Partial oxidation; Methane; Synthesis gas
Cobalt based hybrid Fischer–Tropsch synthesis catalyst for improved selectivity of hydrocarbons in the JP-8 carbon number range from a synthesis gas obtained from the pyrolysis of the MixAlco process derived sludge by Eliasu A. Teiseh; Sergio Capareda; Yohannes H. Rezenom (pp. 63-71).
Display Omitted► The catalyst Co-SiO2/Mo-Pd-Pt-HZSM-5 produces fuels with increased selectivity of JP-8 at low pressures. ► At higher pressures, Co-SiO2/Mo-Pd-Pt-HZSM-5 increases further the selectivity of JP-8. ► Production of straight chain hydrocarbons rather than isomers was prevalent for same catalyst.The synthesis gas produced from the pyrolysis of the MixAlco process (which converts wastes into fuels and chemicals) has the composition of ∼45% H2/35% CO together with up to about 20% CH4. Recovery of the methane and application of steam reforming allows the adjustment of the H2:CO ratio to about 1.9 optimum for cobalt performance in an enhanced Fischer–Tropsch synthesis (FTS) process. The performance of a new hybrid catalyst Co-SiO2/Mo-Pd-Pt-HZSM-5 (with a metal–metal–acid functionality) was compared with that of a conventional Co-SiO2 catalyst under the same thermodynamic condition of 10atm and 250°C. The specific surface areas of the two catalysts were characterized using the BET technique. The electron probe microanalyzer (with WDS and EDS capabilities) was then used to confirm the presence of the applied metals Co, Mo, Pd and Pt on the respective supports. The effect of pressure was then examined on the hybrid catalyst at the temperature of 250°C and a higher pressure of 13.6atm. At 10atm and 250°C, the conventional FTS catalyst produced fuels rich in hydrocarbons within the gasoline (C4–C12) carbon number range. Hydrocarbons with carbon numbers within the JP-8 (C8–C17) and to some extent diesel range (C15–C25) were also produced. At the same condition the Co-SiO2-Mo-Pd-Pt/HZSM-5 catalyst increased the selectivity of JP-8 carbon number range hydrocarbons. When the hybrid catalyst Co-SiO2/Mo-Pd-Pt-HZSM-5 was examined at 13.6atm and 250°C, a further increase in the selectivity of JP-8 carbon number range hydrocarbons and to some extent diesel was observed. The relative amounts of olefins and n-paraffins decreased with the distribution shifting towards the production of more isomers. A fixed bed continuous flow catalytic system was used.
Keywords: MixAlco process; Pyrolysis; Sludge; Efficiency; Fischer–Tropsch synthesis; JP-8; Gasoline; Diesel; Selectivity; Co-SiO; 2; /Mo-Pd-Pt-HZSM-5 catalyst
Liquid phase hydrogenation of crotonaldehyde over copper incorporated in MCM-48 by Victoria Gutierrez; Mariana Dennehy; Alejandra Diez; María A. Volpe (pp. 72-78).
Display Omitted► Cu/MCM-48 catalysts are prepared and characterized. ► Copper crystals coexists with highly dispersed copper species. ► The Cu/MCM-48 catalysts are selective toward crotyl alcohol.► The catalytic patterns can be explained on the basis of characterization results.A series of Cu/MCM-48 catalysts is studied for the liquid phase hydrogenation of crotonaldehyde. Copper is incorporated in MCM-48 following a classical hydrothermal synthesis or by wet impregnation of the MCM-48 precursor (before eliminating the directing agent) with Cu(AcAc)2. The copper loading is in the 2–20wt% range. Characterization results from TPR and XRD indicate that copper crystals supported on MCM-48 surface coexist with copper incorporated in the MCM-48 walls. The presence of Cu+ in MCM-48 is concluded from characterization with FTIR of adsorbed CO. This species would be the responsible for the relatively high selectivity of Cu/MCM-48. These catalysts show approximately 50% of selectivity against 7% of Cu/SiO2 (both values measured at 10% of conversion).
Keywords: Copper catalysts; MCM-48; Crotonaldehyde; CO adsorption; Selective hydrogenation
Effects of rehydration of alumina on its structural properties, surface acidity, and HDN activity of quinoline by Guangci Li; Yunqi Liu; Zhe Tang; Chenguang Liu (pp. 79-89).
Display Omitted► γ-Al2O3 can transform completely into boehmite under hydrothermal condition. ► The physicochemical properties of initial γ-Al2O3 were changed remarkably. ► Pore structure and morphology are closely related to crystallite size of γ-Al2O3. ► The change in surface acidity depends on the proportion of γ-Al2O3 crystal planes. ► The hydrogenation activity of catalyst depends on the L acidity strength of alumina.A series of aluminas were obtained through rehydration–dehydration of the initial alumina under different hydrothermal conditions. To investigate the influences of rehydration temperature on the physicochemical properties of the as-obtained aluminas, several techniques were applied, such as X-ray powder diffraction, nitrogen adsorption, scanning/transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, and27Al MAS NMR. The results show that crystal size and morphology of alumina particles changed as the treatment temperature was increased, and alumina crystallites grew mainly along two surface orientations. Consequently, the changes in textural properties of the aluminas took place. In addition, the rehydration process increased not only the weak acid sites but also the strong acid sites, which is closely related to the growth of the (111) and (110) surfaces of γ-Al2O3. The two type acid sites were originated from coordinately unsaturated four-fold aluminum atoms. TPR for a series of Ni(Mo) catalysts were carried out and the results show that rehydration process increased the surface acidity and basicity of alumina simultaneously, which enhanced the interacting force of Ni and Mo species with aluminas respectively. This interaction is closely related to the hydrodenitrogenation (HDN) activity of quinoline over the corresponding NiMo/γ-Al2O3 catalysts.
Keywords: Alumina; Mesoporous materials; Nanostructures; Lewis acidity; HDN
Recyclable biocatalytic composites of lipase-linked magnetic macro-/nano-particles for glycerol carbonate synthesis by Madalina Tudorache; Loredana Protesescu; Alina Negoi; Vasile I. Parvulescu (pp. 90-95).
Display Omitted► Biocatalyst composite of lipase attached on magnetic particles has been developed. ► Biocatalyst preparation was optimized correlating support morphology with enzyme behavior. ► Lipase-biocatalyst was tested in solvent-free system for glycerol carbonate synthesis. ► Lipase biocomposite had higher catalytic activity than free lipase. ► Lipase biocomposite was more stable and recyclable compared with free lipase.Lipase immobilized biocatalysts were prepared via enzyme binding onto functionalized surface of magnetic micro-/nano-particles. In order to achieve an efficient biocatalytic composite the immobilization parameters ( e.g. lipase concentration, pH of the immobilization phase, activation reagent) were correlated with support morphology and type of the functional group on the support surface. The characterization of the lipase-particle composites was made using FTIR and UV–Vis techniques. The biocatalyst activity was evaluated in the transesterification reaction of glycerol with DMC (dimethyl carbonate). Under solvent-free conditions the conversion of glycerol was of 48.6% with the selectivity in glycerol carbonate (GlyC) of 85%. The biocatalyst composites were easily recycled using the magnetic properties of the support. Compared to free enzyme, recycling experiments demonstrated that the operational stability of the heterogeneous biocatalyst was improved (fifteen cycles for bio-composites vs. four cycles for free enzyme).
Keywords: Biocatalyst; Magnetic nano-/micro-particles; Lipase; Glycerol carbonate
Low temperature conversion of linear C4 olefins using acid ZSM-5 zeolites with aluminum concentration gradient by M. Henry; M. Bulut; W. Vermandel; B. Sels; P. Jacobs; D. Minoux; N. Nesterenko; J.P. Dath (pp. 96-103).
Display Omitted► n-Butenes dimerization at 220°C over ZSM-5 materials with a siliceous rim. ► Sufficiently high amount of aromatic coke to totally fill micropores in aluminous ZSM-5. ► Extra-crystalline catalysis for aluminous ZSM-5, thus low activity. ► Micropores partially blocked by coke for siliceous ZSM-5: intra-crystalline catalysis, thus low changes.Two ZSM-5 materials with high and low overall Si/Al ratio, each with an Al concentration gradient across the crystals (G-samples) have been synthesized, physico-chemically characterized with several techniques (XRD, SEM, N2 adsorption,27Al MAS NMR, NH3-TPD, FT-IR and TOF-SIMS), and catalytically tested in the low-temperature dimerization of n-butenes, paying attention to coke formation. Their acidic properties were found consistent with their framework aluminum content, except for a lower than expected number of Brønsted acid sites as measured by FTIR of adsorbed pyridine. The dimerization – cracking – realkylation mechanism, previously observed for n-butenes dimerization over acid ZSM-5 with homogeneous aluminum distribution, was confirmed over G-type catalysts. The influence of hard coke content, observed in the previous work, on product selectivity and distributions was also found for G-type catalysts. The siliceous G-type catalyst, with low amount of hard coke and micropores partly accessible to reactants, shows shape-selectivity properties consistent with dominating intra-crystalline catalysis. The aluminous G-type catalyst, with high amount of hard coke, and micropores completely filled with aromatic carbonaceous residue, shows thermodynamically equilibrated products selectivity and distributions in agreement with extra-crystalline catalysis.
Keywords: n-Butenes; ZSM-5; Dimerization; Oligomerization; Aluminum gradient; Coke; External surface; Shape-selectivity
Effect of catalyst and solvent on the furan ring rearrangement to cyclopentanone by Milan Hronec; Katarina Fulajtarová; Tibor Liptaj (pp. 104-111).
Display Omitted► Furfural, furfuryl alcohol, but not 2-methylfuran in water affords cyclopentanone. ► In alcohols are hydrogenated furan ring and carbonyl and hydroxymethyl groups. ► Furfural concentration influence the products distribution. ► Mechanism of furan ring rearrangement involve carbocation as reactive intermediate. ► Carbocation is stabilized by strong binding on the catalyst surface.The effect of solvent and Ni, Pt, Pd, Pt–Ru and Ru catalysts on the products distribution has been investigated in the reaction of furfural, furfuryl alcohol and 2-methyl furan under hydrogen pressure of 30–80bar and at the reaction temperatures of 160–175°C. In water as solvent the main reaction pathway is the rearrangement of furfural and furfuryl alcohol to cyclopentanone. In alcohols, the reaction leading to the furan ring rearrangement does not proceed. The distribution of reaction products is influenced by the furfural concentration and acid–base properties of solvent and supported metal catalyst. The important factor influencing the selectivity of the furan ring rearrangement to cyclopentanone is proposed to be stabilization of carbocation by strong binding on the metal surface and by additional interaction with co-adsorbed water and furfural or furfuryl alcohol. In excess of hydrogen this species is created by the scission of the CO bond in the alkoxide or hydroxyalkyl intermediates. A plausible reaction mechanism for the furan ring rearrangement was proposed.
Keywords: Cyclopentanone; Furfural; Furfuryl alcohol; Solvent effect; Hydroxy-cyclopentenone; Ring rearrangement
Catalytic decomposition of 4-phenoxyphenol to aromatics over Pd/ XCs2.5H0.5PW12O40/ACA ( X=10, 20, 30, 40, and 50wt%) catalysts by Hai Woong Park; Ung Gi Hong; Yoon Jae Lee; Jung Ho Choi; In Kyu Song (pp. 112-119).
Display Omitted► Pd/ XCs2.5H0.5PW12O40/ACA with different Cs2.5H0.5PW12O40 content ( X) was prepared. ► Catalytic decomposition of 4-phenoxyphenol to aromatics was conducted. ► Acidity of the catalysts played an important role in the reaction. ► Total yield for aromatics increased with increasing acidity of the catalysts.Activated carbon aerogel (ACA) was prepared by a chemical activation of carbon aerogel using phosphoric acid (H3PO4). A series of Cs2.5H0.5PW12O40-impregnated activated carbon aerogels ( XCs2.5H0.5PW12O40/ACA) were prepared with a variation of Cs2.5H0.5PW12O40 content ( X) in order to provide acid sites to ACA. Palladium catalysts were then supported on Cs2.5H0.5PW12O40-impregnated activated carbon aerogel (Pd/ XCs2.5H0.5PW12O40/ACA, X=10, 20, 30, 40, and 50wt%) by an incipient wetness impregnation method for use in the decomposition of 4-phenoxyphenol to aromatics. 4-Phenoxyphenol was used as a lignin model compound for representing 4O5 linkage of lignin. Cyclohexanol, benzene, and phenol were mainly produced by the decomposition of 4-phenoxyphenol. Conversion of 4-phenoxyphenol and total yield for main products (cyclohexanol, benzene, and phenol) were closely related to the acidity of Pd/ XCs2.5H0.5PW12O40/ACA. Conversion of 4-phenoxyphenol and total yield for main products increased with increasing acidity of Pd/ XCs2.5H0.5PW12O40/ACA. Among the catalysts tested, Pd/20Cs2.5H0.5PW12O40/ACA with the largest acidity showed the highest conversion of 4-phenoxyphenol and total yield for main products. Conversion of 4-phenoxyphenol and total yield for main products over Pd/20Cs2.5H0.5PW12O40/ACA were much higher than those over palladium catalyst supported on commercial activated carbon (Pd/AC) and palladium catalyst supported on activated carbon aerogel (Pd/ACA).
Keywords: Heteropolyacid-impregnated activated carbon aerogel; Pd catalyst; Lignin; C; O bond; 4-Phenoxyphenol
SAPO-34 and ZSM-5 nanocrystals’ size effects on their catalysis of methanol-to-olefin reactions by Hoi-Gu Jang; Hyung-Ki Min; Jun Kyu Lee; Suk Bong Hong; Gon Seo (pp. 120-130).
Display Omitted► Four catalysts each of 20–5000nm SAPO-34 and ZSM-5 were prepared. ► The smallest (<150nm) catalysts exhibited poor activity in the MTO reaction. ► The largest (>5000nm) catalysts also exhibited poor catalytic activity. ► The catalyst with moderate crystallites (200–500nm) show high catalytic activity. ► Extremely small nanocrystallites (<150nm) significantly hindered catalysis.The catalysis of methanol-to-olefin (MTO) reactions over SAPO-34 and ZSM-5 was strongly shown to depend on the crystallites sizes. Four samples (average size of 50–5000nm) of each catalyst were characterized for shape, size, acidity and diffusion properties. Materials adsorbed and occluded on them during the reaction were directly monitored in situ by IR spectroscopy and analyzed ex situ by GC–MS after extraction. Crystallites of 200–500nm showed the best conversions and lifetimes because of their large external surfaces and short diffusion lengths. SAPO-34 with the smallest crystallites (<150nm) deactivated rapidly due to pore blocking by heavy coke deposits; similarly sized ZSM-5 exhibited low conversion due to the low number of strong Brönsted acid sites in its micropores. The adverse effects of the nanocrystallity of zeolite catalysts are discussed in terms of their framework topology, acidity, and diffusivity.
Keywords: MTO reaction; SAPO-34; ZSM-5; Crystallite size; Deactivation
Vanadium(III) and vanadium(IV) catalysts in a membrane reactor for benzene hydroxylation to phenol and study of membrane material resistance by Raffaele Molinari; Pietro Argurio; Teresa Poerio (pp. 131-138).
Display Omitted► Very low (2.5mmolh−1) oxidant flow rate gave improved phenol production. ► V(III) chloride compared to V(IV) acetyl acetonate gave higher phenol productivity. ► Increased run duration increased phenol extraction/recovery in the organic phase. ► Degradation of polypropylene membrane was evidenced in long time operation.Benzene hydroxylation to phenol by using vanadium based catalysts and product recovery were performed in a two-phase membrane reactor. Benzene permeates, through the hydrophobic polypropylene membrane, in the aqueous phase containing the catalyst while phenol permeates back accumulating in the organic phase. The following fundamental aspects have been studied: dose of hydrogen peroxide, initial oxidation states of vanadium catalysts, duration of catalytic tests and lifetime of the membrane in terms of physical and chemical resistance. It was observed that feeding the oxidant by a micro pump, working in the “bulk tube” mode, phenol yield, final phenol concentration in the organic phase, phenol turnover number and system productivity increased, and no tar was formed. Initial oxidation state of vanadium catalysts influenced system performance: indeed improved results in terms of yield (35.2% vs. 25.1%), conversion of hydrogen peroxide to phenol (36.6% vs. 25.9%), productivity (0.97ggcat−1 h−1 vs.0.78ggcat−1 h−1) were obtained by using vanadium(III) chloride compared to vanadium(IV) acetyl acetonate. Higher phenol extraction/recovery in the organic phase (61.1% vs. 46.3%) and then higher selectivity (97.5% vs. 92.8%) were obtained by increasing test duration from 270 to 510min. A weak membrane resistance was observed after 246h of consecutive catalytic runs on the same membrane piece, showing degradation of the membrane material (polypropylene) caused by the OH radical generated in the reacting mixture.
Keywords: Benzene oxidation to phenol; Membrane reactor; Vanadium(III) catalyst; Physical membrane resistance
Effect of H2O on catalytic performance of manganese oxides in NO reduction by NH3 by Pingping Hu; Zhiwei Huang; Weiming Hua; Xiao Gu; Xingfu Tang (pp. 139-148).
Display Omitted► The {110} facets of hollandite manganese oxide (HMO) are catalytically active sites in the NH3-SCR reaction. ► NH4+ ions as active species are more favorably adsorbed on the {110} facets of HMO than β-MnO2. ► Brönsted acid sites on the {110} facets of HMO increase in the presence of H2O.The effects of H2O on catalytic performance of hollandite manganese oxide (HMO) and β-MnO2 are comparatively studied in selective catalytic reduction of NO by NH3 (NH3-SCR). The results showed that the HMO possessed higher catalytic activity than β-MnO2 in the presence of H2O, and the NH3-SCR reaction occurring on the HMO predominantly followed an Eley-Rideal mechanism via reacting adsorbed NH4+ with gaseous NO. According to the NH3-TPD analyses, XPS results and the HRTEM observations coupled with the theoretical calculations, the results elucidated that (i) the initial formation of the NH4+(H2O)3OH− double ionic clusters were energetically favorable in the presence of H2O, (ii) the OH− ions from the double ionic clusters reacted with Lewis acid sites of the manganese oxides to transform into Brönsted acid ones, concomitant with release of the NH4+ ions, and (iii) the NH4+ ions both from the double ionic clusters and from reaction of NH3 with Brönsted acid sites can be efficiently adsorbed on the {110} facets of the HMO to complete the NH3-SCR reaction cycles, whereas the NH4+ ions are not stable on the {110} facets of β-MnO2. Therefore, the excellent catalytic performance of the HMO predominantly originates from the special structural {110} facet due to it being suitable for adsorption of NH4+ active species.
Keywords: Manganese oxides; Selective catalytic reduction; NO; Brönsted acid sites; NH; 4; +
Mesoporous solid acid catalysts of sulfated zirconia/SBA-15 derived from a vapor–induced hydrolysis route by Binbin Chang; Jie Fu; Yanlong Tian; Xiaoping Dong (pp. 149-154).
Display Omitted► The solid acid catalyst owns high surface area and connected pore structure. ► without pore blocking even under high loading amount. ► It possesses a high catalytic activity for the esterification of oleic acid.Mesoporous solid acid catalyst, sulfated zirconia loaded mesoporous silica, was reported here by a facile vapor–induced hydrolysis method. The zirconia precursor of Zr(SO4)2 was introduced into the mesopore of SBA-15 by impregnation, and then hydrolyzed under a NH3/H2O vapor ambience to form a thin zirconia layer coated on the pore surface of SBA-15, which was followed by the sulfation of SO42− ions with calcinations. The catalyst was characterized by powder X-ray diffraction, N2 adsorption–desorption, transmission electron microscopy and infrared spectroscopy, and the results indicated that the catalyst retained the ordered mesoporous structure, high BET surface area, connected pore channel without pore blocking and a 0.7nm thin layer of sulfated zirconia coated on the pore surface. This super acid catalyst showed much higher activity compared with those of unloaded sulfated zirconia and sulfated zirconia loaded SBA-15 hydrolyzed by ammonia aqueous solution, for catalyzing the esterification reaction of oleic acid and methanol. The experimental parameters including the molar ratio of reactants and reaction time were optimized, and approximately 70% of acid sites were remained after three cycles.
Keywords: Sulfated zirconia; Mesoporous silica; Vapor–induced hydrolysis; Esterification
Highly dispersed Pt–Ir nanoparticles on titania nanotubes by José A. Toledo-Antonio; Carlos Ángeles-Chávez; Ma. Antonia Cortés-Jácome; I. Cuauhtémoc-López; E. López-Salinas; M. Pérez-Luna; G. Ferrat-Torres (pp. 155-165).
Display Omitted► 1.4nm Pt–Ir nanoparticles homogeneously dispersed on titania nanotubes. ► Ir nanoparticles act as nucleation sites for Pt atoms assembly. ► Pt–Ir nanoparticles were more active for cyclohexene hydrogenation than Pt or Ir nanoparticles.Bimetal ∼1.4nm Pt–Ir nanoparticles were homogeneously dispersed on titania nanotubes by a conventional successive wet impregnation method, by first adding Ir and then, the Pt chloride precursors. Ir precursor interacts strongly with the nanotubular surface yielding highly dispersed ∼1.4nm nanoparticles, and later acts as a nucleation site for the assembly of Pt atoms. The mean sizes of Ir, Pt–Ir were 1.4nm and that of Pt nanoparticles was 3.5nm. Bimetal Pt–Ir nanoparticles were more active in cyclohexene (CHE) disproportionation reaction than the corresponding monometal catalysts. At reaction temperatures <423K, CHE is hydrogenated to cyclohexane (CHA) as the main product, whereas at >473K, CHE is dehydrogenated to produce mainly benzene (BZ). The activity of Pt–Ir nanoparticles increased as the reduction temperature rose from 573 to 673K, suggesting that electronic transfer between reducible NT support and metal nanoparticles favors CHE hydrogenation/dehydrogenation, which is a structure insensitive reaction.
Keywords: Key words; Pt–Ir nanoparticles; Titania nanotubes; Cyclohexene hydrogenation; Dehydrogenation
Catalytic performances of ceria and ceria-zirconia materials for the combustion of diesel soot under NO x/O2 and O2. Importance of the cerium precursor salt by Noelia Guillén-Hurtado; Agustín Bueno-López; Avelina García-García (pp. 166-172).
Display Omitted► We report new insights into the role of NO2 and active oxygen in the soot combustion. ► It is possible active-oxygen transfer from a catalyst (submitted to a high temperature calcination) to the soot. ► The degree of contact among soot and catalyst and the presence of NO x are crucial to explain the order of activity.Two different cerium precursors (Ce(NO3)3·6H2O or (NH4)2Ce(NO3)6) and two different calcination temperatures (500°C or 1000°C) were used in the synthesis by coprecipitation method of Ce xZr1− xO2 mixed oxides with three different Ce/Zr ratios (Ce0.8Zr0.2O2, Ce0.5Zr0.5O2 and Ce0.2Zr0.8O2) along with pure cerium and zirconium oxides, obtaining a wide range of oxides with very different textural and structural features. These catalysts were tested for soot combustion in loose-contact mode both under NO x/O2 and O2 atmosphere, pointing out that the choice of the (NH4)2Ce(NO3)6 precursor leads to mixed oxides with better catalytic activity in the two atmospheres proved with regard to the Ce(NO3)3·6H2O precursor. Catalysts with ceria-rich compositions showed better catalytic behaviour than the corresponding zirconia-rich compositions, demonstrating that BET surface area is not the only parameter to be considered for this application, since the catalytic activity of the prepared samples is not proportional to surface area of the solids. Important contribution of the NO2-assisted mechanism exists both to initiate and continue soot combustion under loose-contact mode in NO x/O2, when the ceria-based material produces NO2 at low temperatures (425–450°C), being the capability of the catalyst to produce NO2 the most important feature to explain the soot combustion. However, this role becomes minor when the ceria-based material produces NO2 at higher temperatures. Under O2, in a loose-contact situation, a good Zr-insertion into the lattice affects positively to the soot combustion activity.
Keywords: Catalyst; Ceria-zirconia mixed oxide; Soot combustion; NO; 2; Active oxygen
Effective additives to improve hydrothermal aging of DME reforming catalyst in terms of hydrogen yield and de-NOx performance of RC+LNT combined system by Syungyong Park; Byungchul Choi; Hwanam Kim; Young Jae Lee (pp. 173-183).
Display Omitted► Cerium (Ce) prevented the diffusion of Al to the surface after hydrothermal aging. ► Ce is a more effective additive for DME reforming catalyst. ► NOx conversion of the aged Cat-Ce+LNT system was 4% higher than that of the LNT at 350°C.The purpose of this study is to observe the effects of H2 generation by a reforming catalyst (Cu30/γ-Al2O3) with various additives, so as to improve the durability of the combined system of reforming catalyst (RC)+LNT. Under both fresh and hydrothermal aging conditions, the H2 yields of the Cu29CeO21/γ-Al2O3 catalyst were the highest among the reforming catalysts prepared by the sol–gel method. Even though the H2 yield obtained using the DME reforming reaction of the exhaust gases of DME vehicles has the advantage of using the heat source and water in the exhaust gas, the existence of NO, CO2 and O2 in the exhaust gases is disadvantageous to the DME reforming reaction. The NOx conversion of the combined system of RC (Cu29CeO21/γ-Al2O3)+LNT was higher than that of the LNT alone. This shows that the H2 generated by the reforming reaction using the exhaust gases of the DME engine is a more effective reductant. Therefore, in order to effectively improve the NOx conversion, the combined system of RC+LNT is needed as an after-treatment system for DME vehicles.
Keywords: DME steam reforming; Reforming catalyst; LNT; Additive; Hydrothermal aging
Synthesis of peroxyesters in tri-liquid system using quaternary onium salts and polyethylene glycols as phase-transfer catalysts by Stefan Baj; Agnieszka Siewniak; Katarzyna Bijak (pp. 184-189).
Display Omitted► A mild and efficient method to synthesize organic peroxyesters in tri-liquid system. ► Phase-transfer catalyst forms an insoluble third-liquid phase. ► A method offers the possibility of easy recycling of catalyst. ► Organic peroxyesters were obtained in mild conditions and in good yields.A mild and efficient method for the synthesis of organic peroxyesters from acid chlorides and tertiary alkyl hydroperoxides in the presence of aqueous solution of inorganic base is described. The process was conducted in a tri-liquid system using quaternary onium salts and polyethylene glycols as phase-transfer catalysts. A model reaction of cumyl hydroperoxide (CHP) with butyryl chloride was investigated under a wide range of conditions. Selected peroxyesters were obtained in moderate to high yields (62–93%).
Keywords: Peroxyesters; Phase-transfer catalysis; Tri-liquid system