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Applied Catalysis A, General (v.295, #2)
Transesterification of triacetin with methanol on solid acid and base catalysts by Dora E. López; James G. Goodwin Jr.; David A. Bruce; Edgar Lotero (pp. 97-105).
Biodiesel is a particularly attractive renewable fuel as it can be used in existing engines, is environmentally friendly, and is readily synthesized from animal fats and vegetable oils. Heterogeneous catalysts offer exciting possibilities for improving the economics of biodiesel synthesis; however, few published investigations have addressed the use of such catalysts to date. The purpose of this research was to investigate the kinetics and selectivities of different solid catalysts for the transesterification of triacetin (a model compound for larger triglycerides as found in vegetable oils and fats) with methanol. Reaction was carried out at 60°C in a batch reactor with a variety of solid and liquid, acid and base catalysts. The homogeneous phase (i.e., liquid) catalysts (NaOH and H2SO4) were studied for comparison. Amberlyst-15, Nafion NR50, sulfated zirconia, and ETS-10 (Na, K) showed reasonable activities, suggesting that they could be suitable alternatives to liquid catalysts. While on a wt.% basis (of reaction mixture) the homogeneous phase catalysts gave higher rates of reaction, on a rate-per-site basis the solid acids were similar to H2SO4. Sulfated zirconia and tungstated zirconia had comparable turnover frequencies as H2SO4. The deactivation characteristics of some of these catalysts were also studied.
Keywords: Biodiesel synthesis; Triacetin; Transesterification; Sulfated zirconia; Tungstated zirconia; Amberlyst-15; Nafion NR50; ETS-10; Supported phosphoric acid; MgO; Hβ zeolite; Sulfuric acid; NaOH
Benzylation of benzene over Fe-modified ZSM-5 zeolites: Correlation between activity and adsorption properties by Eva Díaz; Salvador Ordóñez; Aurelio Vega; Aline Auroux; José Coca (pp. 106-115).
The performance of Fe-ZSM-5 catalysts (prepared by incipient wetness, 0.5–2.5% of Fe) for benzylation of benzene by benzyl chloride was studied in this work and explained in terms of their chemical and adsorption properties. Catalysts were characterised by ICP-MS, XPS, XRD, nitrogen physisorption and calorimetry (in order to determine their surface acidity). Adsorption properties of the catalysts (for the reactants and products) have been studied by inverse gas chromatography (IGC). Enthalpies of adsorption, dispersive energies of adsorption, and specific interaction were selected as parameters to characterise the interaction of benzene, benzyl chloride and diphenylmethane with the studied catalysts.Reaction experiments, carried out in an isothermal batch reactor, showed that increasing amounts of iron lead to more active catalyst, but less selective for the formation of diphenylmethane. Experimental data were modelled considering a serial-parallel scheme.Results reported in this paper, suggest that the reaction is controlled by the adsorption and activation of the benzyl chloride. The addition of iron to the ZSM-5 zeolite largely increases the interaction between this compound and the catalyst surface.
Keywords: Benzylation of benzene; Inverse gas chromatography; Adsorption; Fe-ZSM-5
Isomerization of α-pinene oxide to campholenic aldehyde over Lewis acids supported on silica and titania nanoparticles by G. Neri; G. Rizzo; C. Crisafulli; L. De Luca; A. Donato; M.G. Musolino; R. Pietropaolo (pp. 116-125).
Lewis acids (FeCl3, ZnCl2, H3BO3) supported on SiO2 and TiO2 nanoparticles have been tested in the selective isomerization of α-pinene oxide to campholenic aldehyde. The spherical nanoparticle supports with a narrow particles size distribution have been synthesized by the sol–gel method. The morphological and microstructural characterization of the supports and catalysts was carried out by XRD, SEM–EDX and BET surface area measurements. Acid properties were investigated by DTA and FT-IR after adsorption of triethylamine and pyridine as probe molecules.SiO2 and TiO2 nanoparticles used as supports have shown negligible acidity and consequently low activity in the isomerization of α-pinene oxide. After Lewis acid promoters addition, the activity was markedly enhanced with a high selectivity to campholenic aldehyde.Lewis acids supported on titania have been found more actives than analogous supported silica catalysts due to the higher surface area of the TiO2 support. The selectivity instead was found to be independent on the support used. Among the investigated samples, Zn-doped catalysts resulted the most selective. On the basis of FT-IR of adsorbed pyridine, the selectivity to campholenic aldehyde on these catalysts has been correlated to the strength of the Lewis acid sites. Optimising the preparation of the catalysts and reaction conditions, a maximum yield to campholenic aldehyde of 74% was obtained.
Keywords: SiO; 2; TiO; 2; Nanoparticles; α-Pinene oxide; Isomerization reaction
Mechanism of the decomposition of adsorbed methanol over a Pd/α,β-Ga2O3 catalyst by Sebastián E. Collins; Miguel A. Baltanás; Adrian L. Bonivardi (pp. 126-133).
The thermal decomposition of adsorbed methanol on 2wt.% Pd/silica, 2wt.% Pd/gallia and pure gallia, was studied by temperature-programmed surface reaction (TPSR), between 323 and 723K under He flow, using FT-IR spectroscopy. After methanol adsorption on Pd/silica at 323K, the concentration of methoxy species on the silica decreased during the TPRS experiment, but some methoxy groups still remained on this support even at 723K. Simultaneously, methanol decomposed over metallic palladium to yield, stepwise, HCO and CO with the consequent release of H2 (g). On clean gallia, methanol is Lewis-bound adsorbed to the surface, as well as dissociatively adsorbed as methoxy (CH3O), but the position of the infrared bands indicates a stronger interaction of these species on gallium oxide than on silica. Methoxy species on gallia are decomposed to (mono- and bi-dentate) formate groups (m- and b-HCOO, respectively) at T>473K. We suggest that CO and CO2 are further produced by non-stoichiometric transformation of these formates, leading to the release of atomic hydrogen on the surface of the oxide, as detected by the GaH stretching infrared band, and surface anion vacancies. In the presence of Pd on the gallia surface, the dehydrogenation of CH3O species proceeds faster than over the pure oxide, and we propose the following mechanism for methanol decomposition: (i) methanol reacts with OH groups on the gallia surface to produce water and methoxy species, (ii) the dehydrogenation of the latter carbonaceous group leads to H2COO, first, and then to m- and b-HCOO, (iii) the hydrogen atoms released in the previous steps are transferred from gallia to the Pd surface where they recombine and desorb as H2 (g).
Keywords: Methanol decomposition; Gallium oxide; Palladium catalyst; Hydrogen production
Transition metal substituted polyoxotungstates for the oxygen delignification of kraft pulp by J.A.F. Gamelas; A.R. Gaspar; D.V. Evtuguin; C. Pascoal Neto (pp. 134-141).
A series of transition metal substituted polyoxotungstates (TMSP) were tested as catalysts for the oxygen delignification of eucalypt kraft pulp. These include Mn substituted polyoxotungstates of Keggin-type,α-[SiW(12−n)MnnIII(H2O)nO(40−n)](4+n)− ( n=1 (1) or n=2 (2)), sandwich-typeα-B-[(PW9O34)2Mn(4−n)IIMnnIII(H2O)2](10−n)− ( n=1 (3) or n=3 (4)), and the transition metal mono-substituted Keggin-type anions, such as α-[XW11M(H2O)O39] n− (M=CoIII, X=Si (5) and X=B (6); M=RuIV, X=Si (7), and X=P (8)). All TMSP showed a catalytic activity. The experimental results revealed high selectivity of the residual lignin oxidation during oxygen delignification catalysed by1–4, though the final kappa number of delignified pulps varied significantly. This was related to the removal of hexeneuronic acid residues at low pH diminishing the corresponding pulp kappa number counterpart. A comparison of the kappa number decrease and the delignification selectivity in conventional oxygen-alkaline bleaching process and in the TMSP-catalysed oxygen delignification showed significant advantages of the latter process. The best results, concerning both the delignification degree and the selectivity of delignification, were obtained with TMSP α-[SiW11MnIII(H2O)O39]5− (1),α-B-[(PW9O34)2MnIIMn3III(H2O)2]7− (4) and α-[SiW11CoIII(H2O)O39]5− (5). The application of catalysts6–8 was limited by their structural instability under the delignification conditions. The practical aspects of the oxygen delignification catalysed by TMSP are discussed.
Keywords: Transition metal substituted polyoxometalates; Oxygen bleaching; Oxygen delignification; Kraft pulp; Catalysis
Preparation and characterization of CuO/CeO2 catalysts and their applications in low-temperature CO oxidation by Xiucheng Zheng; Xiaoli Zhang; Xiangyu Wang; Shurong Wang; Shihua Wu (pp. 142-149).
CeO2 nanoparticles were prepared by thermal decomposition of cerous nitrate and then used as supports for CuO/CeO2 catalysts prepared via the impregnation method. The samples were characterized by HRTEM, XRD, H2-TPR, and XPS. The catalytic properties of the prepared catalysts for low-temperature CO oxidation were studied by using a microreactor–GC system. The results showed that the thermal decomposition temperature affected the physical properties of the prepared CeO2 particles, such as particle size and morphology. The loading of CuO in non-crystalline forms on CeO2 supports was different in the CuO/CeO2 catalysts. The loading of non-crystalline CuO was higher on the CeO2 prepared via thermal decomposition at 500°C than those on the CeO2 prepared via thermal decomposition at 400, 600 and 700°C. One part of the non-crystalline CuO in CuO/CeO2 catalysts entered the CeO2 lattice and the other part dispersed over the CeO2 surface. Calcination temperature had little effect on the catalytic activity when it was lower than 600°C. However, heating the catalysts to higher temperatures (i.e. 800°C) had a significant impact on the catalytic activity because the crystallite size rapidly grows and more CuO and CeO2 phase-separation occurs.
Keywords: Thermal decomposition; Ceria; CuO/CeO; 2; catalysts; Low-temperature CO oxidation
Catalytic glucose and fructose conversions with TiO2 and ZrO2 in water at 473K: Relationship between reactivity and acid–base property determined by TPD measurement by Masaru Watanabe; Yuichi Aizawa; Toru Iida; Ryo Nishimura; Hiroshi Inomata (pp. 150-156).
The effects of TiO2 (anatase TiO2 or rutile TiO2) and ZrO2 (monoclinic/tetragonal mixture ZrO2) on glucose and fructose reactions were examined in hot-compressed water at 473K with a batch type reactor. Rutile TiO2 (r-TiO2) is inactive during glucose reactions. A monoclinic/tetragonal mixture of ZrO2 (m/c-ZrO2) was the basic catalyst for the reaction at this temperature. Anatase TiO2 (a-TiO2) showed both acidity and basicity during the reactions. In order to understand the catalytic activity of a-TiO2, r-TiO2, and m/c-ZrO2, we measured the acidity and basicity by means of NH3- and CO2-TPD, respectively. The TPD analysis showed us that the amount of acid (670μmol/g) and base (550μmol/g) sites on m/c-ZrO2 were the highest among these three catalysts, while the density of acid site (17μmol/m2) and that of basic site (9μmol/m2) of the a-TiO2 were the highest. Such the acidity and basicity analyses suggested that the amount of basicity was the key factor for the isomerization while the density of acidity and basicity was important for the HMF formation from glucose.
Keywords: Glucose; TiO; 2; ZrO; 2; Acidity; Basicity; TPD; BET
Catalytic properties in n-heptane reforming of Pt–Sn and Pt–Ir–Sn/Al2O3 catalysts prepared by surface redox reaction by Florence Epron; Christelle Carnevillier; Patrice Marécot (pp. 157-169).
Multimetallic Pt–Ir–Sn/Al2O3 catalysts, prepared by surface redox reaction, were tested in the conversion of n-heptane, used as model reaction of paraffin dehydrocyclization, under industrial-type conditions. Their catalytic performances were measured after 5 and 65h of reaction in order to evaluate the stability of the catalysts, and compared to those of a well-known Pt–Sn bimetallic catalyst as a function of the preparation medium, of the tin and iridium contents, of the chorine content and of the resulting acidity, and of the amount of coke deposited. The addition of tin to the monometallic Pt and to the bimetallic Pt–Ir increases the stability of the catalysts and also the selectivity toward toluene. The same toluene yield is obtained with bimetallic and trimetallic catalysts after 65h of reaction, but less tin is needed in the case of the trimetallic catalyst. Similar evolutions between the toluene yield and the amount of Lewis acid sites were observed: the highest amount of Lewis sites, the highest toluene yield. There is no simple relationship between the amount of coke deposited after 65h of reaction and the activity in n-heptane conversion. The coke deposition affects the strong Lewis and Brønsted acid sites. Whereas catalysts are strongly deactivated after 65h of reaction for cyclohexane dehydrogenation at atmospheric pressure, they are still active for the n-heptane transformation at higher pressures that means that only few metallic sites take part in this reaction. It was demonstrated that the addition of an inactive promoter on a bimetallic Pt–Ir catalyst can replace the sulfiding step that is necessary to decrease the hydrogenolysis activity of this type of catalyst. However, the deposition of tin modifies not only the metal function but also the acidity of the catalyst.
Keywords: n; -Heptane reforming; Trimetallic catalysts; Pt–Ir–Sn; Redox reactions
MCM-41-supported metal bis[(perfluoroalkyl)sulfonyl]imides as heterogeneous catalysts for aromatic nitration by Yubin Yuan; Jin Nie; Zhengbo Zhang; Shuojin Wang (pp. 170-176).
MCM-41-supported metal bis[(perfluoroalkyl)sulfonyl]imides were synthesized and characterized by FTIR, pyridine-FTIR, XRD, SEM, TG-DTA and N2-adsorption techniques. The heterogeneous catalysts were employed for nitration of aromatic compounds with 1eq. of 65wt% nitric acid in the liquid phase. The results showed that MCM-41-supported metal bis[(perfluoroalkyl)sulfonyl]imides were highly effective and could be recycled at least five times without substantial loss of catalytic activity.
Keywords: MCM-41; Metal bis[(perfluoroalkyl)sulfonyl]imide; Supported Lewis acid; Catalysis; Nitration
Insight into copper oxidation catalysts: Kinetics, catalytic active species and their deactivation by Petro Lahtinen; Elina Lankinen; Markku Leskelä; Timo Repo (pp. 177-184).
The catalytic properties of in situ formed copper(II) complexes of N, N, N′, N′-tetramethylethylenediamine (TMEDA), rac-1,2-diaminocyclohexane (DACH) and 9,10-diaminophenantrene (DAPHEN) were investigated under optimized reaction conditions in the oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) with molecular oxygen in alkaline aqueous solutions. The kinetics of the reaction, catalytic species and their deactivation were studied, in order to clarify the reasons for low conversions in Cu(TMEDA) and Cu(DACH) catalyzed reactions. The most active catalyst was the scarcely soluble Cu(DAPHEN) with turn over number 5700 in the oxidation of veratryl alcohol. The catalytic precursors in Cu(TMEDA) catalyzed reactions is binuclear hydroxyl bridged complex (LCu-μ-(OH)2-CuL)2+. The main reason for the deactivation of these catalysts according to our results is the reactivity of the ligands under reaction conditions.
Keywords: Copper; Diamine; Catalytic; Oxidation; Benzylic alcohol; Dioxygen; Water solution
H3PW12O40 supported on MCM-41 molecular sieves: An effective catalyst for acetal formation by B. Rabindran Jermy; A. Pandurangan (pp. 185-192).
Mesoporous Si-MCM-41 and Al-MCM-41 molecular sieves in four Si/Al ratios: 25, 50, 75 and 100, were synthesized under hydrothermal conditions. Ten weight percent, 15wt.% and 20wt.% H3PW12O40 (PW) was supported on Si-MCM-41. They were characterized using powder X-ray diffraction (XRD), FT-IR, BET and TEM. The catalytic activity of these materials were tested for the acetalization of carbonyl compounds with 2,2-bis(hydroxymethyl)propane-1,3-diol at refluxing temperature using a Dean–Stark apparatus. The hydrophobic properties of catalyst and alcohols, and the steric properties of carbonyl compounds were suggested to play important roles in the acetalization. Fifteen weight percent PW/MCM-41 was found to be more active than other catalysts used and to have similar activity to that of HPA. TEM studies show that the high dispersion of HPA units, which was maintained through out the reaction, was lost when recycled even for shorter reaction cycle. The reaction was also studied over commercially available heteropolyacids, and zeolites (Hβ, HY, HM and ZSM-5). Occurrence of the reaction mainly within the pores was confirmed by running the reaction over the HPA loaded on an as-prepared catalyst that provides less product yield than the calcined material.
Keywords: Acetalization; Acetals; Al-MCM-41; Pentaerythritol; Hydrophobicity
Inhibition effect of nitrogen compounds on CoMoP/Al2O3 catalysts with alkali or zeolite added in hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene by Hiroshi Mizutani; Hideki Godo; Takayuki Ohsaki; Yoshinori Kato; Takashi Fujikawa; Youssef Saih; Takako Funamoto; Kohichi Segawa (pp. 193-200).
The inhibition effects of nitrogen compounds on CoMoP/Al2O3 catalysts due to doping with Li or USY-zeolite in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) have been studied. Quinoline was selected as the model nitrogen compound. Changes in the HDS rate, conversion and selectivity were investigated. The acidity of the oxidic catalysts was studied using Fourier-transformed infrared spectroscopy (FT-IR), pyridine adsorption, and ammonia temperature-programmed desorption (NH3-TPD). The catalysts were studied in both oxidic state and sulfidic state by X-ray photoelectron spectroscopy (XPS).The HDS of DBT as a reference probe molecule is thought to proceed first through direct desulfurization pathways, then to hydrogenolysis. A significant amount of benzene was detected in the case of CoMoP/zeolite-Al2O3. The HDS of 4,6-DMDBT over CoMoP/zeolite-Al2O3 in the absence of quinoline proceeds through a very complex mechanism that involves several other reactions, such as isomerization, alkylation, and hydrocracking. This can probably be attributed to the acidic properties of zeolite. In the presence of quinoline, a strong inhibition effect was observed for all the catalysts. The inhibition effects of quinoline on CoMoP/Al2O3-Li were smaller than its effects on the other catalysts; this fact resulted in the enhancement of HDS activity. Moreover, from the XPS investigations we can conclude that CoMoP/Al2O3-Li showed a relatively higher sulfidation degree for both Mo and Co. Thus, it seems to have a relatively higher catalytic activity.
Keywords: Inhibition effects of nitrogen compounds; CoMoP/Al; 2; O; 3; Li; USY-zeolite; DBT; 4,6-DMDBT; XPS
Effect of moisture on the active species in Cu–CeO2 catalyst by W.J. Zhang; S. PalDey; S. Deevi (pp. 201-208).
The influence of moisture present in air on the CO oxidation activity of 10% Cu–CeO2 catalysts was studied, and the active Cu species in the catalyst were examined by high-resolution transmission electron microscopy (HRTEM). It was found that the catalyst is highly sensitive to the moisture in air. The fresh oxidized catalyst was deactivated after exposure to air with the light-off temperature increasing from 30 to 70°C. A large amount of small Cu(OH)2 nanocrystals in the size of 1–4nm were observed in the exposed catalyst in this study, rather than the copper oxide clusters proposed in the literature. The transformation of the active CuO x nanocrystals to Cu(OH)2 nanocrystals is believed to be the cause of catalyst deactivation when moisture is present. The driving force for this transformation is the lower surface energy of Cu(OH)2 as compared to copper oxides. The results highlight the important role of surface energy in the stability and reactivity of the active cluster species in the catalysts.
Keywords: Cu–CeO; 2; CO oxidation; Moisture; Deactivation
Tungstosilicate salts as catalysts in phenol tetrahydropyranylation and depyranylation by Gustavo P. Romanelli; Juan Carlos Autino; Mirta N. Blanco; Luis R. Pizzio (pp. 209-215).
The catalytic behavior of water-insoluble cesium or rubidium tungstosilicates was studied in phenol tetrahydropyranylation and depyranylation reactions.The salts were synthesized and characterized using Fourier transform infrared spectroscopy, BET surface area measurements, thermogravimetric and differential thermal analysis and acidity evaluation by potentiometric titration with n-butylamine. Solids with high specific surface area, high thermal stability, and undegraded Keggin structure of the anion were obtained. The cesium salts showed a higher acidity than the rubidium salts.Both reactions were carried out at room temperature, using toluene in the tetrahydropyranylation and methanol in the depyranylation as solvents. It was observed that there is an influence of the acid strength of the different catalysts on the yields obtained in both reactions, although the textural properties of the salts must also be taken into account. The cesium salts were more active than rubidium salts, the latter being only active in the depyranylation reaction.
Keywords: Tungstosilicic acid; Salts; Tetrahydropyranylation; Depyranylation; Phenol
Comparison of ion-exchange resin catalysts in the dimerisation of isobutene by Maija L. Honkela; Andrew Root; Marina Lindblad; A. Outi I. Krause (pp. 216-223).
Seven ion-exchange resin catalysts were compared in the dimerisation of isobutene with tert-butyl alcohol (TBA) as the selectivity enhancing component. Experiments were also carried out with sodium exchanged resins to study the order of the reaction and the effect of sodium components in the feed. The dimerisation of isobutene was confirmed to be a second-order reaction with respect to the amount of active sites. Ion-exchanged sodium was found to decrease the selectivity for di-isobutenes and thus behave differently than the polar components. The average acidities of the acid groups of the resins treated with various polar components and of the resins ion-exchanged with sodium were obtained by NMR measurements. The results suggested that the effect of TBA and of the ion-exchanged sodium on the acidity is similar. Their different behaviour in the dimerisation of isobutene can be explained by the participation of TBA in the chain scission and by the blocking of the sites by the ion-exchanged sodium. Experiments with the different catalysts showed that the surface sulphonated catalysts are the most active in the dimerisation of isobutene. Furthermore, good selectivities for di-isobutenes are obtained with the medium crosslinked resins (12–20 DVB%).
Keywords: Abbreviations; DIB; di-isobutenes (2,4,4-trimethyl pentenes); DVB; divinylbenzene; IB; isobutene (2-methyl propene); IP; isopentane (2-methyl butane); MTBE; methyl; tert; -butyl ether (2-methoxy-2-methyl propane); TAME; tert; -amyl methyl ether (2-methoxy-2-methyl butane); TBA; tert; -butyl alcohol (2-methyl-2-propanol); TETRAB; tetraisobutenes; TRIB; tri-isobutenesIon-exchange resins; Isobutene dimerisation; Acid capacity