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Applied Catalysis A, General (v.403, #1-2)
n-Butanol to iso-butene in one-step over zeolite catalysts by Dazhi Zhang; Sami A.I. Barri; David Chadwick (pp. 1-11).
.Display Omitted► One step conversion of n-butanol to iso-butene has been demonstrated. ► Medium pore size, unidirectional channel zeolites show high performance. ► The productivity of iso-butene over Theta-1 was greater than 7.0kgkgcalh−1. ► n-Butanol to iso-butene is compared to isomerisation of 1-butene with added water. ► The deactivation of ferrierite is attributed to the effect of product steam from dehydration.The conversion of n-butanol to iso-butene in one-step has been studied over zeolite catalysts (Theta-1, ZSM-2, Ferrierite, ZSM-5, SAPO-11 and Y). The zeolites were characterized by XRF, XRD, BET, and NH3-TPD. Coke formation on the spent catalysts was measured by TGA. The unidirectional channel zeolites Theta-1 and ZSM-23 gave high yields of iso-butene and showed high stability. In contrast, ferrierite, although initially active, deactivated due to the presence of water from dehydration giving progressively lower yields of iso-butene. ZSM-5 showed high activity but low selectivity to iso-butene; SAPO-11 was structurally unstable under the reaction conditions. Ferrierite deactivation was studied in more detail by NH3-TPD,27Al MAS NMR and by a comparison of 1-butene isomerisation with and without the presence of added steam. A similar comparison was made for ZSM-23 and Theta-1 which further emphasised their stability and showed that for these catalysts under the reaction conditions used, the product steam from n-butanol dehydration promoted iso-butene yield by acting as a diluent.
Keywords: n; -Butanol; iso; -Butene; Dehydration; Isomerisation; Zeolite
Effect of barium addition on CO oxidation activity of palladium catalysts by K. Tanikawa; C. Egawa (pp. 12-17).
Display Omitted► CO oxidation over Pd/Ba/Al and Pd/Ba/CZ was investigated by TPR, XPS and DRIFTS. ► The activity of Pd/Al was improved by adding Ba, but it was negative for Pd/CZ. ► The role of barium obviously depends on the properties of supports.CO oxidation over Pd supported on barium fixed alumina (Pd/Ba/Al) and ceria–zirconia mixed oxide (Pd/Ba/CZ) catalysts was investigated by XPS, TPR and in situ DRIFT during light-off using a stoichiometric CO–O2 mixture. The activity of Pd supported on alumina catalyst was improved by increasing barium loading, but the negative effect was observed for Pd on ceria–zirconia mixed oxide. The role of barium in improving the activity of CO oxidation is considered to weaken the adsorption strength of CO on palladium supported on alumina. On the other hand, barium suppresses the interaction of Pd particles with ceria–zirconia mixed oxide support.
Keywords: Palladium; Alumina; Ceria–zirconia; CO oxidation; DRIFTS; XPS
Dispersion measurement of platinum supported on Yttria-Stabilised Zirconia by pulse H2 chemisorption by M. Alves Fortunato; D. Aubert; C. Capdeillayre; C. Daniel; A. Hadjar; A. Princivalle; C. Guizard; P. Vernoux (pp. 18-24).
Display Omitted► A reliable procedure was defined to measure the dispersion of Pt nanoparticles supported on Yttria-Stabilised Zirconia. ► A pre-reduction step in hydrogen at 500°C and a H2 pulse chemisorption at −28°C are required. ► Surface oxygen vacancies on the YSZ support are involved in H2 and CO chemisorption.Platinum nanoparticles were dispersed by wet impregnation on YSZ (8mol% Y2O3) an ionically conducting support. The Pt dispersion of a series of catalysts was determined by using H2 pulse chemisorption. Temperature Programmed Reduction (TPR) experiments were performed to characterize the pre-reduction step before dispersion measurements. Finally, a fast and reliable procedure was defined for the Pt dispersion measurements consisting in a pre-reduction step in hydrogen at 500°C before the H2 pulse chemisorption performed at −28°C. Reproducible Pt dispersion values were obtained in good agreement with those measured by pulse CO chemisorptions and static volumetric titration. In addition, the combination of Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy and TPR has evidenced the role of surface oxygen vacancies on YSZ support for both H2 and CO chemisorptions.
Keywords: Hydrogen pulse chemisorption; Pt dispersion; Yttria-Stabilised Zirconia; Oxygen vacancies; Ionic conductor
Bis(arylimino)pyridine iron(III) complexes as catalyst precursors for the oligomerization and polymerization of ethylene by Christian Görl; Tanja Englmann; Helmut G. Alt (pp. 25-35).
Display Omitted► Synthesis of new bis(arylimino)pyridine iron(III) catalyst precursors. ► The higher oxidation state of the metal center allows interesting modifications of the ligand frameworks. ► Very narrow product distributions were obtained in ethylene oligomerization reactions. ► “Open” ligand structures lead to internal and branched low molecular weight olefins.A series of 26 bis(arylimino)pyridine iron(III) complexes containing either electron withdrawing or electron donating substituents in their ligand frameworks was synthesized and characterized. After activation with methylaluminoxane (MAO), these catalysts oligomerize or polymerize ethylene to give both linear and branched products. In contrast to iron(II) complexes, the presence of at least one ortho-substituent at the iminophenyl rings is not obligative for catalytic activities of the iron(III) complexes. A couple of such iron(III) complexes containing meta- and para-substituted bis(arylimino)pyridine compounds were accessible and their oligomerization behaviour revealed interesting differences to the well known iron(II) analogues since both internal and branched olefins were found in the product mixtures beside the expected linear α-olefins. The widths of the resulting molecular weight distributions and the degrees of isomerization of the resulting oligomers strongly depend on the substitution pattern at the ligand frameworks.
Keywords: Bis(arylimino)pyridine iron complexes; Ethylene oligomerization; Isomerization of olefins; Polymerization; Polyethylene
A comparative study of ring opening of naphthalene, tetralin and decalin over Mo2C/HY and Pd/HY catalysts by Shahrzad Jooya Ardakani; Kevin J. Smith (pp. 36-47).
▪.► The conversion of naphthalene, tetralin or decalin at 300°C and 3MPa was higher over Pd/HY than Mo2C/HY catalysts. ► Tetralin was the least reactive among the three model compounds. ► With decalin as reactant, higher selectivity to C10 products was obtained over the Mo2C/HY catalysts than the Pd/HY. ► The catalysts with higher hydrogenation activity (Pd/HY and 1% K–7% Mo2C/HY) had lower deactivation rates.The conversion of naphthalene, tetralin or decalin to ring-opened products over Mo2C/HY, Mg- or K-Mo2C/HY, and a commercial Pd/HY catalyst, is reported. Conversion of all reactants at 300°C and 3MPa was higher over the Pd/HY catalyst than the Mo2C/HY catalysts. Tetralin was the least reactive among the three model compounds over both Pd/HY and Mo2C/HY. With decalin as reactant, higher selectivity to C10 products was obtained over the Mo2C/HY catalysts compared to the Pd/HY. The addition of K or Mg to Mo2C/HY improved the Mo2C dispersion while K also moderated the catalyst Bronsted acidity. The conversion of all three reactants was reduced by the addition of Mg or K to the Mo2C/HY, as was the carbon deposition. For all the studied catalysts, carbon deposition was lowest after reaction with decalin compared to naphthalene or tetralin. These results suggest that the deposited carbon has as its precursor, species that are derived from naphthalene or tetralin, rather than decalin, and the coke species are generated through bimolecular reactions on acid sites. Consequently, the catalysts with higher hydrogenation activity (Pd/HY and 1% K–7% Mo2C/HY) had lower deactivation rates.
Keywords: Ring-opening; Hydrogenation; Bifunctional catalyst; Molybdenum carbide; Palladium; HY zeolite; Naphthalene; Tetralin; Decalin
Highly filled clay polypropylene nanocomposites prepared by in situ polymerization with clay-supported magnesium/titanium catalysts by Marcos L. Dias; Rodrigo M. Fernandes; Rodrigo H. Cunha; Selma Jaconis; Alexandre C. Silvino (pp. 48-57).
Display Omitted► Clay/MgCl2/TiCl4 catalysts generated i-PP nanocomposites by in situ polymerization. ► High crystalline PP was obtained even when the organophylic clay was used as support. ► Highly clay filled PP nanocomposites had about 200°C higher degradation temperatures.Ziegler-Natta catalysts based on TiCl4 supported on clay/MgCl2 were obtained and tested in propylene polymerization. Two types of clay: the sodium clay Gelmax 400 and the organophylic one Cloisite 30B were employed. The catalysts preparation involved the treatment of the clays with an alcohol adduct of MgCl2 followed by treatments with TiCl4 and triethylaluminium (dealcoholation), optionally using ethyl benzoate as internal electron donor. The catalyst performance showed to be markedly influenced by the clay type and synthesis conditions. Dealcoholation was the main factor that affected the catalyst activity. Impregnation of clay/MgCl2 supports with Ti generated catalysts with about 5wt.% of titanium and crystalline structure with different families of lamellar structures, evidenced by low intensity peaks at different (001) plane 2 θ position in the X-ray diffraction curves of the clay-supported catalysts. The catalysts were used in the polymerization of propylene producing polypropylenes with significant isotacticity and crystallinity. Among the catalysts, that prepared using the sodium clay as support without internal donor showed the higher catalytic activity (6433gPP/gTi). Due to different catalyst activity, polypropylenes with different contents of clay were obtained. The residual clay acts as filler, PP nanocomposites, were obtained by this in situ method, some of them highly filled. The degradation behavior of these highly filled nanocomposites was highly improved with increasing of the on set and maximum degradation temperatures in the range of 200°C. The shape of the polymer particles was very similar to those of catalyst particles due to the replica phenomenon, also observed for these catalyst systems.
Keywords: Clay supported catalyst; In situ; polymerization; Nanocomposites; Polypropylene
Isobutane and n-butane cracking on Ni-ZSM-5 catalyst: Effect on light olefin formation by A.J. Maia; B.G. Oliveira; P.M. Esteves; B. Louis; Y.L. Lam; M.M. Pereira (pp. 58-64).
Addition of nickel to H-ZSM-5 increases remarkably the selectivity to ethylene and the catalysts activity when compared to the pristine H-ZSM-5. The ethylene is produced through β-scissions processes from oligomeric carbenium ions formed during the process.Display Omitted► Nickel was introduced into H-ZSM-5 by dry impregnation and ionic exchange methods. ► The Ni-ZSM-5 catalysts show high catalytic activity compared to H-ZSM-5. ► Both methods of nickel introduction largely improve the ethylene selectivity. ► Without previous reduction the Ni-ZSM-5 catalysts show a bifunctional behavior.The catalytic activity of Ni-ZSM-5 zeolites was tested in the isobutane and n-butane cracking reaction. Nickel (0.4–6wt%) was introduced into H-ZSM-5 zeolite by dry impregnation and ionic exchange methods. Both methods of nickel introduction led to a drastic improvement both in ethylene selectivity and isobutane cracking activity when compared to pristine H-ZSM-5 zeolite. In particular, the 1% (w/w) Ni-ZSM-5 catalyst increased the catalytic activity by two orders of magnitude with respect to parent H-ZSM-5. The comparison of Ni-ZSM-5 catalyst with mixtures of pure H-ZSM-5 and nickel supported on silica suggests that the dehydrogenation products formed at the nickel sites sequentially reacted on acidic sites. In addition the proximity between nickel and acid sites favors the reaction of the products formed previously on nickel sites onto zeolite acid site. These results support a true bifunctional catalysis behavior even though no reduction was performed before catalytic evaluation.
Keywords: Nickel; ZSM-5; n; -Butane; Isobutane; Ethylene
Modifications of an HY zeolite for n-octane hydroconversion by Regina Claudia R. Santos; Antoninho Valentini; Cleanio L. Lima; Josue M. Filho; Alcineia C. Oliveira (pp. 65-74).
Display Omitted► Pt on CVD-treated HY zeolite. ► More effective than the dealuminated counterparts in the n-octane isomerization. ► Due to the moderate strength of the acidic sites. ► Dispersion of Pt atoms. ► Avoid the formation of coke.Solids based on HY zeolite were modified by either dealuminization (D) followed by chemical vapour deposition of silicon (CVD). Additionally, impregnation of Pt or Ni was performed over selected D and CVD solids. Samples were characterized by XRD,27Al and29Si NMR, acidity measurements, N2 adsorption/desorption isotherms, Raman analysis and evaluated in n-octane hydroconversion at P=1atm and T=300°C. In comparison with the CVD and pure D series of solids, Pt impregnation on dealuminated HY resulted in a high level of isomerization products. Although the conversion upon using Ni-containing dealuminated HY was elevated, cracking products were predominant over this solid. The trends in the activity can be explained by the accessibility of acidic sites and their acidity. The catalytic activity follows the order PtCVD1>NiD>PtD∼D>CVD1. The combined effect of moderate acidity and Pt dispersion resulted in better catalytic performance for the PtCVD1 catalyst, which was active in the hydroisomerization reaction (conversion of 30%) with almost no coking on the sample, whereas cracking products were predominant over other solids. The characterization of spent catalysts showed no loss in activity, with low coke deposition on solid surface over the CVD1 sample in comparison with the D series of solids. Furthermore, mechanistic insights demonstrated that on PtCVD1, the adsorbed carbon species were formed via the cracking and oligomerization of n-octane precursors.
Keywords: Zeolites; Modifications; Coke; Hydroconversion; CVD; Platinum
Essential role of citric acid in preparation of efficient NiW/Al2O3 HDS catalysts by Huifeng Li; Mingfeng Li; Yang Chu; Feng Liu; Hong Nie (pp. 75-82).
Display Omitted► Citric acid does not chelate Ni ions in the Ni–W impregnation solution at pH ≈1.5. ► Citric acid partly changes into the carbonaceous material during sulfidation. ► Citric acid moderates the metal–support interaction by tailoring alumina surface. ► Citric acid decreases the WS2 slab length by its isolating effect. ► The catalyst benefiting from both roles of citric acid, shows high HDS activity.The role of citric acid in preparation of NiW/Al2O3 HDS catalysts was investigated. Four catalysts with the same metal loading were prepared by pore filling method, with different supports (alumina or carbon modified alumina) and the impregnation solutions (adding citric acid or not), followed by drying. The UV–Vis spectra of the aqueous solution of nickel nitrate, ammonium metatungstate and citric acid shows no Ni-complex formation. The N2 physisorption results indicated the addition of citric acid in the impregnation solution has slight effect on the pore structure of the corresponding sulfided catalysts. The TPR profiles of the oxidic catalysts showed metal species supported on carbon modified alumina are easier to be reduced than those on alumina. The results of TPO-MASS indicated there are two types of carbonaceous compounds of different combustive properties in the freshly sulfided samples. HRTEM images showed the addition of citric acid can decrease the average WS2 slab length but increase stacking number. The addition of citric acid can facilitate the formation of Ni–W–S active phases, as determined by XPS. And the HDS tests showed the catalysts prepared by adding citric acid in the impregnation solution, exhibit higher HDS activity for 4, 6-DMDBT.
Keywords: Citric acid; Alumina; Carbon modified alumina; Hydrodesulfurization
The activity of yttrium-modified Mg,Al hydrotalcites in the epoxidation of styrene with hydrogen peroxide by O.D. Pavel; B. Cojocaru; E. Angelescu; V.I. Pârvulescu (pp. 83-90).
Display Omitted► The introduction of yttrium in Mg,Al hydrotalcite occurs without its insertion in the Mg or Al octahedral positions. ► The lower electronegativity of yttrium led to an increase of the basicity. ► The memory effect plays an important role in the reconstruction of the LDH structure from the beginning of the reaction. ► Hydration of mixed oxides generates a worm texture and contributes to the decrease of the surface area. ► During reconstruction of the LDH under inert atmosphere part of carbonic anions are replaced by hydroxyl groups.Modification of Mg,Al hydrotalcite with Y3+ prepared following co-precipitation at low suprasaturation led to an improvement of the activity and selectivity for styrene epoxidation with hydrogen peroxide in acetonitrile. The materials were characterized using several techniques such as XRD, DRIFT, TEM, CO2-TPD and adsorption–desorption isotherms of nitrogen at −196°C. It was thus demonstrated that the memory effect of hydrotalcite acts very quickly even in an unfriendly environment like that generated by hydrogen peroxide. A direct correlation between the memory effect and the catalytic behavior in the epoxidation of the styrene has been demonstrated. MgO and Al2O3 were also prepared using the precipitation method. The investigation of MgO, Al2O3 and of a mechanic mixture of them showed that the activity of the catalysts in this reaction correlates very well with their basicity.
Keywords: Hydrotalcite-like materials; Styrene epoxidation; Memory effect
In situ encapsulation of Pt nanoparticles in mesoporous silica: Synthesis, characterisation and effect of particle size on CO oxidation by Atul K. Prashar; S. Mayadevi; P.R. Rajamohanan; R. Nandini Devi (pp. 91-97).
Display Omitted• Employing mesoporous channels as moulds for in situ synthesis of Pt nanoparticles. • Particles of size 4.4nm isolated exclusively in the channels of mesoporous silica. • CO oxidation kinetics studied in catalysts with 1.8, 3.6, 4.4 and 8nm Pt particles. • Particles of size <2nm behave distinguishably different in CO oxidation.Pt nanoparticles of narrow size distribution and average particle size of 4.4nm are isolated exclusively inside SBA-12 mesoporous silica by a novel in situ method. The interaction of Pt precursor with surfactant–polymer composite micelle is followed by NMR and UV studies. The final Pt incorporated silica material is characterised by XRD, TEM and N2 adsorption. The mesoporous nature of the silica is found to be intact after Pt incorporation without any pore blockage. CO oxidation activity of this material is compared with that of mesoporous silica incorporating different sizes of Pt viz., 1.8, 3.6 and 8nm. Activation energies of CO oxidation for all these materials are calculated by a simple differential method based on first principles. A comparison of activation energies and single site yields reveals that these parameters are distinguishably less in catalyst containing 1.8nm Pt nanoparticles but more or less same in catalysts containing 3.6, 4.4 and 8nm Pt nanoparticles.
Keywords: In situ synthesis; Pt nanoparticle; Mesoporous silica; CO oxidation
A process for efficient conversion of fructose into 5-hydroxymethylfurfural in ammonium salts by Quan Cao; Xingcui Guo; Jing Guan; Xindong Mu; Dongke Zhang (pp. 98-103).
Display Omitted► Tetraethyl ammonium chloride achieved 81.3% HMF yield in a 33wt% fructose solution. ► Adding NaHSO4 as co-catalyst achieved 79.2% HMF yield in a 50wt% fructose solution. ► The separation of HMF was successfully achieved in a THF/TEAC biphasic system.Low melting systems consisting of ammonium salts and highly concentrated fructose were used for the conversion of fructose into 5-hydroxymethylfurfural (HMF). Not only acting as solvents, at sufficiently high temperatures, the ammonium salts themselves could also catalyse the dehydration of fructose to HMF. Among those salts, tetraethyl ammonium chloride (TEAC) was found to be the most efficient solvent-catalyst, demonstrated by its ability to achieve 81.3% HMF yield with 33.3wt% fructose concentration at 120°C. 79.2% HMF yield was obtained with 50wt% fructose concentration in the TEAC/fructose system using 5mol% NaHSO4·H2O as a co-catalyst. A semi continuous biphasic system of TEAC/fructose/NaHSO4·H2O melt using tetrahydrofuran (THF) to recover HMF was proposed and demonstrated in a laboratory scale process operating at 120°C. The impurities in the HMF recovered, involving TEAC and NaHSO4·H2O, were determined using1H NMR, elemental analysis and ICP-OES.
Keywords: Ammonium salts; Biphasic system; Dehydration; Fructose; 5-Hydroxymethylfurfural (HMF); Tetraethyl ammonium chloride (TEAC)
Nitrogen-rich copolymeric microsheets supporting copper nanoparticles for catalyzing arylation of N-heterocycles by Zhijun Huang; Fengbo Li; Bingfeng Chen; Fei Xue; Guochang Chen; Guoqing Yuan (pp. 104-111).
Display Omitted► Nitrogen-rich copolymeric microsheets were synthesized through controlled condensation of nitrogen-rich precursors. ► Monodispersed filigree copper nanoparticles over such nitrogen-rich substrate were obtained. ► The supported nanoparticles show high activity for catalyzing arylation for N-heterocycles. ► The catalyst retains considerable activity after a five-run recycling test.Nitrogen-rich copolymeric microsheets were synthesized through incomplete condensation of melamine and cyanuric chloride. The materials can be well-dispersed in polar solvent and perform excellently as supports or stabilizing agents for metal nanoparticles. The presence of nitrogen in the lattice improves their interaction with the copper nanoparticle precursor (Cu(II) ions). Monodispersed copper nanoparticles over these supports were obtained after reducing the absorbed precursors. The materials were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The catalytic C–N coupling reaction was selected as the model reaction to evaluate the catalytic performance of the supported nanoparticles. The catalysts show above 90% yield of coupling products and retain activity after a five-run recycling test. Surface chemistry and morphology transforming during the catalytic process was further investigated. Nitrogen-rich copolymeric microsheets were proven to be excellent supports and stabilizing agents for metal nanoparticles.
Keywords: Heterogeneous catalysis; Nanomaterials; Surface chemistry; Copper; Arylation
Effects of amorphous-zinc-silicate-catalyzed ozonation on the degradation of p-chloronitrobenzene in drinking water by Yue Liu; Jimin Shen; Zhonglin Chen; Lei Yang; Yu Liu; Ying Han (pp. 112-118).
Display Omitted► Amorphous zinc silicate was synthesized. ► High activity and stability for catalytic ozonation. ► The catalyst is easily recycled.This paper describes a single-step method for synthesizing amorphous zinc silicate (AZS) using Zn(NO3)2 and Na2SiO3 as precursors and the first use of AZS as an ozonation catalyst. This compound showed significant activity in the decomposition of p-chloronitrobenzene ( pCNB) in aqueous solution. AZS was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformation infrared (FTIR) analysis. The results showed that the as-synthesized sample was mainly composed of amorphous silica (AS), ZnO, and Zn–O–Si composites. The effectiveness of the removal of p-chloronitrobenzene ( pCNB) by catalytic ozonation was investigated under various physicochemical conditions. The results showed that the presence of AZS in the ozonation further enhanced pCNB decomposition by 38% and TOC removal by 24%. The results of a hydroxyl radical scavenger experiment using spin-trapping/EPR technology to identify hydroxyl radicals (OH) confirmed thatOH was the main active species involved in the removal of pCNB during the AZS-catalyzed ozonation process. The composition of ZnO and the Zn–O–Si composite had a positive impact on the oxidation affinity of pCNB. Our results showed that the catalytic activity of AZS decreased from 99% to 94% after six successive reuse cycles. The formation of Zn–O–Si composites inside AZS strengthened the frameworks of the AZS matrixes.
Keywords: Abbreviations; AZS; amorphous zinc silicate; p; CNB; p; -chloronitrobenzene; ZS; zinc silicate; AS; amorphous silica; [O; 3; ]; 0; dissolved ozone concentration (mg/L); [AZS]; AZS dose (mg/L); [; p; CNB]; 0; p; CNB dose (μg/L); [Zn; 2+; ]; Zn; 2+; dose (mg/L); [Catalyst]; catalyst dose (mg/L)Amorphous zinc silicate; Catalytic ozonation; p; -chloronitrobenzene; Recyclability; Water purification; p; -chloronitrobenzene
Immobilized molybdenum acetylacetonate complex on montmorillonite K-10 as catalyst for epoxidation of vegetable oils by Maritana Farias; Márcia Martinelli; Guilherme Koszeniewski Rolim (pp. 119-127).
.Display Omitted► In this work, molybdenum (VI) complex was immobilized onto montmorillonite clay. ► The catalyst was tested for the epoxidation of both soybean and castor oils. ► The catalyst showed high performance for epoxidation reactions of vegetable oils. ► After the first use, the catalyst showed an enhanced activity in recycling experiments. ► The best results for epoxidation reactions were obtained for castor oil.Heterogeneous catalyst was obtained by the direct immobilization of molybdenum compound on montmorillonite K10 clay. The resultant solid was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffractometry (XRD), scanning electron microscopy coupled in a energy dispersive X-ray spectrometer (SEM-EDS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller and Barret–Joyner–Halenda isotherms (BET/BJH), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis-DRS) and Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR). The catalyst was tested for the epoxidation of both soybean and castor oils, using tert-butyl hydroperoxide (TBHP) as oxidizing agent. After the first use, the immobilized catalyst showed an enhanced activity and also catalytic stability in recycling experiments. The best results for epoxidation reactions concerning castor oil were observed under conditions of 80°C for 24h (100% conversion and 75% selectivity) and catalytic reuse.
Keywords: Molybdenum (VI) acetylacetonate complex; Montmorillonite K10; Epoxidation; Heterogeneous catalysis; Soybean oil; Castor oil
New insight into the preparation of copper/zirconia catalysts by sol–gel method by Serena Esposito; Maria Turco; Giovanni Bagnasco; Claudia Cammarano; Pasquale Pernice (pp. 128-135).
Display Omitted► Design of two different sol–gel procedures to prepare Cu–ZrO2 catalysts. ► Cu2+ ions incorporation shifts the crystallization of ZrO2 to higher temperature. ► Textural and redox properties of Cu–ZrO2 are related to the preparation route. ► Methanol conversion and yield to H2 are influenced by the Cu precursor.Cu/ZrO2 catalysts prepared by the sol–gel method were characterized by XRD, N2 adsorption, DTA/TG, TPR and N2O dispersion measurements and tested as catalysts for the oxidative steam reforming of methanol (OSRM). Two synthesis procedures, based on the Cu precursors Cu(CH3COO)2·H2O (A-ZrCu samples) and Cu(NO3)2·2.5H2O (N-ZrCu samples) respectively, were compared to investigate the consequence of synthesis parameters on the physical and chemical properties of the prepared materials. The adopted procedures resulted in remarkable differences in thermal behaviour: the crystallization of tetragonal ZrO2 was shifted to higher temperature inN-ZrCu samples in comparison with pure ZrO2, while this effect was not observed inA-ZrCu. XRD data indicated that Cu2+ ions were incorporated into the ZrO2 lattice inN-ZrCu samples.Though both synthesis lead to very high surface areas, the textural properties of the reduced samples suggested the existence of different interactions between Cu ions and the ZrO2 matrix inA-ZrCu and inN-ZrCu.The Cu/ZrO2 systems showed noticeable catalytic activity for the oxidative steam reforming of methanol, even without the pre-reduction treatment, but the catalytic response is drastically affected by the preparation procedure and the pre-treatments.N-ZrCu samples gave higher methanol conversion and yield to H2. Moreover, the distribution of secondary products was completely different:N-ZrCu produced a lot of CO, whileA-ZrCu gave large amounts of CH2O and (CH3)2O.
Keywords: Sol–gel synthesis; Copper precursors; Cu–ZrO; 2; catalysts; Oxidative steam reforming of methanol
Catalytic performances of Mn–Ni mixed hydroxide catalysts in liquid-phase benzyl alcohol oxidation using molecular oxygen by Qinghu Tang; Chengming Wu; Ran Qiao; Yuanting Chen; Yanhui Yang (pp. 136-141).
Display Omitted► Mn–Ni mixed hydroxide catalyst is prepared by facile co-precipitation. ► A Mn-in-Ni(OH)2 solid solution is formed and shows low reduction onset. ► The prepared catalyst is active in benzyl alcohol aerobic oxidation. ► Excess Mn results in segregated Mn3O4 phase with poor activity. ► The synergistic interactions exsit between Mn(III) and Ni(II) cations.Mn–Ni mixed hydroxide was synthesized by a facile co-precipitation method and the catalytic performance in the aerobic oxidation of benzyl alcohol using molecular oxygen was examined. The Mn/Ni molar ratio played an important role and the sample with Mn/Ni molar ratio of 6:4 showed the best catalytic activity. High specific activity of 8.9mmol/(gh) along with the benzaldehyde selectivity of 99% was achieved at 100°C within 1h. Characterizations of X-ray diffraction, X-ray absorption and hydrogen temperature-programmed reduction suggested that co-precipitation method afforded the formation of Mn-in-Ni(OH)2 solid solution without phase segregation. Excess amounts of Mn resulted in segregated Mn3O4 crystalline phase, which showed low surface area and poor catalytic activity. The synergistic interactions between Mn(III) and Ni(II) cations through oxygen bonding were suggested to enhance the activity of Mn–Ni mixed hydroxide catalysts for benzyl alcohol oxidation.
Keywords: Mn–Ni mixed hydroxide catalyst; Benzyl alcohol; Oxidation; Molecular oxygen
Rh, Ni, and Ca substituted pyrochlore catalysts for dry reforming of methane by Sarthak Gaur; Daniel J. Haynes; James J. Spivey (pp. 142-151).
Display Omitted► Rh-, Ni-, and Ca-substituted La2Zr2O7 pyrochlore catalysts were synthesized. ► High catalytic activity of Rh, and Ca-substituted pyrochlores with time-on-stream was observed. ► Rapid and continuous deactivation of Ni-substituted catalyst was observed. ► Partial substitution of a metal in the lattice creates Oxygen vacancies.Dry reforming of methane (DRM) has been widely investigated, with most studies showing rapid deactivation due to carbon deposition. This suggests a need to develop catalysts that limit carbon formation while avoiding structural changes at the elevated temperatures typical of this reaction. Here, we report CO2 reforming of methane on four pyrochlore catalysts. First, rhodium was partially substituted for Zr in lanthanum zirconate (La2Zr2O7) to give La2Zr2− xRh xO7− δ (LRZ, x=0.112, 2wt% Rh) pyrochlore. A second pyrochlore catalyst was synthesized in which Ca was further substituted into the La-site to give La1.95Ca0.05Zr2− xRh xO7− δ (LCRZ, x=0.055, 1wt% Rh). This was done to compare the effect of Ca substitution on the La site along with Rh substitution on Zr site. A third catalyst was synthesized where Ni was substituted in the Zr-site to give La2Zr2− xNi xO7− δ (LNZ, x=0.112, 1wt% Ni). A fourth catalyst, containing no catalytically active metal, La1.97Sr0.03Zr2O7− δ (LSZ), was synthesized to provide a direct comparison to the substituted pyrochlores. Effects of substitution and kinetic measurements were examined for dry reforming of methane in a fixed-bed reactor. XRD results prior to reaction showed that all the pyrochlore catalysts had a cubic unit-cell lattice. Results from XPS suggested that there were two oxidic phases (RhO2 and Rh2O3) in Rh-substituted LRZ and LCRZ and two phases (NiO and Ni2O3) present in Ni substituted LNZ. TPR of the catalysts confirmed the presence of two reducible Rh species in LCRZ and LRZ, and four reducible Ni species in LNZ. Textural measurements revealed that among the active catalysts, LCRZ had the highest BET surface area (10.0m2/g) and pore volume (0.10cm3/g). Temperature programmed surface reaction (TPSR) tests indicated different light-off curves for different catalysts, with LCRZ being the most active by this measure. Steady state tests at 750°C using an equimolar reactant feed for 450min showed that the Ni-based pyrochlore (LNZ) deactivated rapidly. LCRZ and LRZ showed similar activity, however, LCRZ showed lower carbon built-up. XRD of the spent catalysts showed that the pyrochlore structure was unchanged during reaction for all catalysts. Carbon deposited on catalyst surface during reaction was characterized by TPO. The Ni-based pyrochlore showed higher carbon deposition (1.4g/gcat.) than either LCRZ (0.26g/gcat.) or LRZ (0.44g/gcat.). These results suggested that Rh substituted into the pyrochlore was more active and selective for synthesis gas compared to a directly comparable atomic loading of Ni. In addition, the replacement of Ca2+ for La3+ may provide improved oxygen mobility of the catalyst (through the introduction of lattice oxygen defects) resulting in the oxidation of carbonaceous species deposited on the active sites on the catalyst during the reaction. Substitution of metals into the crystal lattice might have also lowered the bond energy of La–O and Zr–O lattice bonds resulting in the release of oxygen from the lattice, which probably oxidized surface carbon thus slowing down carbon accumulation.
Keywords: Pyrochlores; CO; 2; reforming of methane; Ni catalyst; Rh catalyst
Combustion synthesized materials as catalysts for liquid-phase oxidation by Benjamin Jäger; Achim Stolle; Peter Scholz; Matthias Müller; Bernd Ondruschka (pp. 152-160).
Display Omitted► Combustion synthesis leads to a variety of catalytic active oxides. ► The synthesized materials exhibit significantly improved activity. ► With combustion synthesis one can obtain smaller crystallites and higher strains. ► Combustion synthesis realizes a quenching process in the catalyst synthesis. ► Crystallite size and strains have influence on both conversion and selectivity.With combustion synthesis it is possible to achieve catalytic active binary oxides of chromium, iron, cobalt, nickel and copper within a few seconds. The catalytic activity of combustion synthesized oxides was compared with commercially available spinel oxides and materials obtained by thermal nitrate decomposition in the selective liquid-phase oxidation of benzyl alcohol to benzaldehyde with a stoichiometric amount of tert-butyl hydroperoxide as the oxidant. The combustion synthesized materials revealed both higher reactivity and higher stability compared to those oxides available from high temperature ceramic processes or thermal nitrate decomposition. Crystallite sizes, microstrains, and phase compositions have been analyzed by X-ray powder diffractometry as important parameters for the catalytic activity. By applying combustion synthesis, it is possible to obtain several different low density oxides with smaller crystallites and higher values for microstrains compared to other methods of preparation. Thus, providing an explanation for the improved catalytic performance of those materials.
Keywords: Combustion synthesis; Crystallite size; Liquid-phase catalysis; Microstrain; Spinels
12-Tungstophosphoric acid anchored to SBA-15: An efficient, environmentally benign reusable catalysts for biodiesel production by esterification of free fatty acids by Varsha Brahmkhatri; Anjali Patel (pp. 161-172).
Display Omitted► Synthesis and characterization of 12-tungstophosphoric acid anchored to SBA-15. ► Catalytic activity for biodiesel production by esterification of free fatty acid. ► Excellent activity in terms of high conversion of oleic acid, high TOF, 9.3min−1. ► Catalyst can be reused up to four cycles without any significant loss in activity. ► Environmentally benign reusable catalyst for biodiesel production.12-Tungstophosphoric acid anchored to SBA-15 was synthesized and characterized by various physico-chemical techniques such as TGA, FT-IR, DRS, XRD, N2 adsorption–desorption, solid state NMR (31P and29Si), SEM and TEM. The use of synthesized catalyst was explored for biodiesel production by esterification of free fatty acid, oleic acid with methanol. Influence of various reaction parameters (such as catalyst concentration, acid/alcohol molar ratio and reaction temperature) on catalytic performance was studied. The catalyst shows high activity in terms of conversion of oleic acid as well as high turnover frequency of 9.3min−1. It also shows potential of being used as recyclable catalyst material after simple regeneration. Kinetic investigation reveals that the esterification reaction of oleic acid with methanol follows a first order dependency on the concentration of the oleic acid and the catalyst. The influence of temperature on rate constant was also studied and the activation energy was found to be 44.6kJmol−1. As an application, preliminary study was carried out for biodiesel production from waste cooking oil, as feedstock without any pre-treatment, with methanol. Studies show that the catalyst can be used for biodiesel production from waste cooking oil under mild conditions.
Keywords: 12-Tungstophosphoric acid; SBA-15; Oleic acid; Waste cooking oil; Biodiesel
Hydrogenolysis of glycerol on bimetallic Pd-Cu/solid-base catalysts prepared via layered double hydroxides precursors by Shuixin Xia; Zhenle Yuan; Lina Wang; Ping Chen; Zhaoyin Hou (pp. 173-182).
Display Omitted► Pd-Cu bimetallic catalyst exhibited synergistic effect for glycerol hydrogenolysis. ► This synergistic effect was attributed to hydrogen spillover from Pd to Cu. ► Glycerol hydrogenolysis performed sufficiently in ethanol solution. ► Solid base can suppress the cleavage of C–C bond in glycerol. ► Cu leaching in the polar medium would bring deactivation.A series of bimetallic Pd-Cu/solid-base catalysts were prepared via thermal decomposition of Pd xCu0.4Mg5.6− xAl2(OH)16CO3 layered double hydroxides precursors and used in hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO). X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2O oxidation and followed H2 titration characterizations confirmed that well structured layered double hydroxides Pd xCu0.4Mg5.6− xAl2(OH)16CO3 crystals could be prepared when the amount of added Pd was less than x<0.04. Pd and Cu dispersed highly in reduced Pd xCu0.4/Mg5.6− xAl2O8.6− x and Pd improved the reduction of Cu. Hydrogenolysis of glycerol proceeded easily on bimetallic Pd-Cu/solid-base catalysts than separated Pd and Cu. On Pd0.04Cu0.4/Mg5.56Al2O8.56, the conversion of glycerol and selectivity of 1,2-PDO reached 88.0 and 99.6%, respectively, at 2.0MPa H2, 180°C, 10h in ethanol solution. And this catalyst is stable in five recycles. It was concluded that H2-spillover from Pd to Cu increased the activity of Pd xCu0.4/Mg5.6− xAl2O8.6− x in hydrogenolysis of glycerol.
Keywords: Glycerol; Hydrogenolysis; Bimetallic Pd-Cu; Solid base; 1,2-Propanediol
Selective synthesis for light olefins from acetone over ZSM-5 zeolites with nano- and macro-crystal sizes by Teruoki Tago; Hiroki Konno; Mariko Sakamoto; Yuta Nakasaka; Takao Masuda (pp. 183-191).
Display Omitted► C2–C4 light olefins synthesis from acetone over ZSM-5 zeolites. ► The nano-sized zeolite shows longer catalyst lifetime than macro-sized zeolite. ► Selective deactivation of acid sites near the external surface. ► Improvement of olefins yield by the selective deactivation of acid sites.Production of light olefins such as ethylene, propylene and isobutylene from acetone was examined over ZSM-5 zeolites. These light olefins are produced from acetone over the acid sites of the zeolite via a series of consecutive reactions where olefins such as ethylene and propylene are obtained by cracking of isobutylene produced from aldol condensation products of acetone. Macro- and nano-sized ZSM-5 zeolites were prepared by conventional hydrothermal and emulsion methods, respectively, and the ZSM-5 zeolites with nearly the same acidity and BET surface area were obtained regardless of the crystal sizes. From SEM observations, the crystal sizes of the zeolites were approximately 2000nm and 30–40nm. These zeolites with different crystal sizes were applied to light olefins synthesis from acetone, and the effect of crystal size on catalytic activity and stability was investigated. As compared with the macro-seized zeolite, the nano-sized zeolite exhibited a high activity over a long lifetime. However, because the nano-sized zeolite possesses a large external surface area, undesirable reactions to form aromatics from the produced light olefins occurred on the acid sites located near the external surface. To inhibit aromatics formation, selective deactivation of the acid sites located near the outer surface of the zeolite was achieved via the catalytic cracking of silane (CCS) method using diphenyl silane (DP-silane). The CCS method was effective in deactivating the acid sites located near the external surface of the ZSM-5 zeolite. Moreover, the nano-size zeolite after the CCS treatment using DP-silane exhibited high olefins and low aromatics yields under high acetone conversion conditions.
Keywords: ZSM-5 zeolite; Crystal size; Light olefins
Use of ethanol in the catalytic abatement of NO x by Fabrício Thiengo Vieira; Maria A.S. Baldanza; José Carlos Pinto; Martin Schmal (pp. 192-198).
Display Omitted► Pd–Ba/ZrO2 catalysts were investigated for the nitric oxide reduction by ethanol. ► Catalytic results showed effect of barium contents producing very high N2 yields. ► DRIFTS analyses suggested the presence of two types of Ba sites. ► Surface ionic nitrate and nitrites indicate multiple sites capable to capture NO. ► Evidence of reaction of NO x with Ba(OH)2 species.Oxygenated molecules have attracted increasing interest for the reduction of NO. In this work Pd–Ba x/ZrO2 catalysts were investigated for the NO x reduction by ethanol. Catalysts were prepared for different Ba contents by incipient wetness impregnation and subsequently with Pd nitrate and characterized by several techniques. Temperature programmed NO desorption analyses revealed the existence of combined palladium and barium effects, suggesting involvement of multiple sites for the N2 formation. DRIFTS analyses strongly suggest the presence of two types of Ba sites, depending on the proximity of Ba and Pd atoms. Catalytic results of NO reduction by ethanol showed positive effect of barium towards N2 yield and high conversion of NO and ethanol. Particularly, the sample 1.5Pd23Ba exhibited very high N2 yields, which is related to the nitrite/nitrate formation and Pd–Ba interaction.
Keywords: NO; x; reduction; Ethanol; Effect of barium; Pd catalyst; DRIFTS