Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Catalysis A, General (v.364, #1-2)
Promotion of carbon nanotube-supported Pt catalyst for methanol and ethanol electro-oxidation by ZrO2 in acidic media by Huanqiao Song; Xinping Qiu; Fushen Li (pp. 1-7).
The electrochemical activity of ZrO2-modified Pt/CNT catalyst was studied in terms of methanol, ethanol and CO electro-oxidation. The results demonstrated that the promotion of catalytic activity was different for methanol and ethanol oxidation at the catalyst with the same Pt/ZrO2 molar ratio. A reason was proposed on the basis of the structural analysis of the catalyst nanoparticles.Carbon nanotube-supported ZrO2 and Pt (Pt–ZrO2/CNT) catalysts with various Pt/ZrO2 molar ratios were prepared by sol–gel and ethylene glycol reduction methods. X-ray diffraction and transmission electron microscopy showed that ZrO2 nanocrystallites tend to grow gradually with the increase of ZrO2 ratio, whereas the size of Pt crystallites decreases and they disperse uniformly on the surface of carbon nanotube-supported ZrO2. The composite catalyst activities were examined by cyclic voltammetry, potentiostatic polarization and CO stripping voltammetry in acidic solutions. The results demonstrated that the addition of ZrO2 significantly increased the catalytic activity of Pt for methanol and ethanol oxidation. However, the promotion degree varied with the increase of ZrO2 content. The maximum catalytic activity for methanol and ethanol oxidation was observed at Pt–ZrO2/CNTs (1:1) and Pt–ZrO2/CNTs (1:3), respectively. This difference was ascribed to the dissimilar catalytic mechanism of Pt–ZrO2/CNTs for methanol and for ethanol electro-oxidation.
Keywords: Carbon nanotube-supported ZrO; 2; and Pt; Anode catalysts; Promotion of catalytic activity; CO stripping; Direct alcohol fuel cell
Highly enantioselective Ru-catalyzed asymmetric hydrogenation of β-keto ester in ionic liquid/methanol mixtures by Eva Öchsner; Karola Schneiders; Kathrin Junge; Matthias Beller; Peter Wasserscheid (pp. 8-14).
The enantioselective hydrogenation of methyl acetoacetate (MAA) was studied in detail using a ruthenium-monodentate binaphthophosphepine complex in a homogeneous solution formed by different ionic liquids and methanol. Remarkably, ionic liquid additives did not only open an attractive way for catalyst recycling in repetitive batch-mode but also led to significantly increased catalytic activity compared to pure methanol. Enantioselectivities up to 95% have been achieved in mixed ionic liquid/methanol systems which are comparable to the values obtained in pure methanol.A group of ionic liquids, which increase the activity of a ruthenium-phenyl-4,5-dihydro-3H-dinaphtho[2,1-c;1′2′-e]phosphepine complex, was identified, synthesized and applied as co-solvent in the asymmetric hydrogenation of MAA in methanol. In these systems the enantioselectivities were found to be in the same range like for pure methanol reaching typical values of 90–96%.
Keywords: Asymmetric catalysis; Hydrogenation; Ketones; Keto ester; Ionic liquid
Evaluation of reactor and catalyst performance in methane partial oxidation over modified nickel catalysts by Bjørn Christian Enger; Rune Lødeng; Anders Holmen (pp. 15-26).
The process of catalytic partial oxidation (CPO) of methane was investigated at moderate furnace temperatures (500–973K) and 1atm over a series of modified Ni catalysts. By exposing the catalysts to different GHSV (15–600NlCH4/gh), the conditions ranged from approaching equilibrium at bed exit gas temperatures to oxygen break-through with associated effects on methane conversion and product composition.The process of catalytic partial oxidation (CPO) of methane was investigated at moderate furnace temperatures (500–973K) and 1atm over a series of modified Ni catalysts. By exposing the catalysts to different GHSV (15–600Nl CH4/gh), the conditions ranged from approaching equilibrium at bed exit gas temperatures to oxygen break-through with associated effects on methane conversion and product composition.By modifying Ni catalysts we illustrate that the expected availability of reducible oxygen species influence the combustion activity of the catalyst. This is reasoned from observations of stronger temperature gradients and a higher maximum gas temperature with modifiers such as Co, Mo, Pt, Pd, Rh and to some degree Cr, as compared to a pure Ni catalyst. Modifiers which are generally difficult to reduce, such as oxides of W, Fe and Mn did not increase combustion activity at the bed entrance.At conditions where oxygen break-through was observed, the formation of coupled products, in particular ethane was promoted. It is reasoned that hetero-homogeneous coupling may be involved. The pure Pt and Pt-modified Ni catalysts were found to promote ethane formation even at 100% oxygen conversion.Interestingly, we here report results suggesting a direct route to synthesis gas over Rh, most likely working in parallel to a combustion reforming mechanism at high GHSV. This is argued based on an evaluation of water-gas-shift and the H2/CO ratio at low bed exit gas temperatures. The conclusion appears reasonable even when accounting for a potentially higher surface temperature than gas temperature.
Keywords: Synthesis gas; Hydrogen; Partial oxidation; Methane; Nickel; Alumina
Synthesis and characterization of a novel multi-site phase transfer catalyst and a kinetic study of the intramolecular cyclopentanation of indene by P.A. Vivekanand; T. Balakrishnan (pp. 27-34).
An easy access to a hitherto unknown novel multi-site catalyst viz., 1,3,5-tris(benzyltriethylammonium bromide)benzene (TBTABB) is delineated from low cost starting materials. The potentiality of the new multi-site phase transfer catalyst was demonstrated by following the kinetics of the cyclopentanation of active methylene compounds under identical conditions. Based on the experimental results, a suitable mechanism is proposed.An easy access to a hitherto unknown novel multi-site catalyst viz., 1,3,5-tris(benzyltriethylammonium bromide)benzene (TBTABB) is delineated from low cost starting materials. The structures of the synthesized MPTC's and spiro indene derivative were evidenced by1H NMR,13CNMR, IR and elemental analysis. The potentiality of the new multi-site phase transfer catalyst was demonstrated by following the kinetics of the cyclopentanation of indene under pseudo-first order conditions by employing aqueous sodium hydroxide and 1,4-dibromobutane in excess. The kinetics of cyclopentanation of indene was carried out at low temperature (40°C) and was monitored by gas chromatography. Further, the catalytic efficiency of the TBTABB was compared with those of the disite and single-site catalysts by investigating the kinetics of various cyclopentanation reactions. In examining six kinds of phase transfer catalyst, we found TBTABB to be highly efficient. The investigation considered the effects of various experimental parameters and conditions, including agitation speed, concentration of catalyst, concentration of substrate, concentration of sodium hydroxide and temperature on the rate of the reaction. The effect of multi-site phase transfer catalysts on the reaction rate is studied. From the Arrhenius plot, the activation energy was found to be 14.18kcalmol−1. Thermodynamic parameters such as Δ S#, Δ G# and Δ H# were also evaluated. Utilizing the kinetic and thermodynamic results, we have proposed an interfacial mechanism for the cyclopentanation of indene. From the different experiments it can be concluded that TBTABB has great potential as a multi-site phase transfer catalyst.
Keywords: Phase transfer catalysis; Catalytic activity; Cyclopentanation; Indene; Kinetics; Multi-site; Interfacial mechanism
Coke analysis by temperature-programmed oxidation: Morphology characterization by Bárbara Sánchez; Martín S. Gross; Bruno Dalla Costa; Carlos A. Querini (pp. 35-41).
Temperature-programmed oxidation technique may provide useful and unique information regarding coke morphology and kinetics parameters, as long as the experiment is carried out up to intermediate final temperature. This experimental design makes it possible to distinguish how the coke reaction order changes as a function of coke conversion, and replicate complex kinetics behavior such as those found in catalyst with high level of coke, e.g. 14wt%, as shown in the figure.Temperature-programmed oxidation (TPO) profiles obtained using high final temperature are usually very similar in shape and it is not possible to easily distinguish among different kinetic models. Typically, statistical criteria are used to select the one that best fits the experimental TPO profile. In this work, we show that using final temperatures selected in such a way that the coke is still reacting with oxygen, relevant information can be obtained from the experimental profile. Coked naphtha reforming catalysts, obtained from an industrial reactor, are characterized by running TPO analyses using intermediate temperatures. Results clearly show that the coke reaction order changes as the coke conversion increases. When the initial coke content is approximately 5wt% or higher, coke has a tridimensional structure that leads to a low reaction order, close to 0.2. At high conversion levels, approximately 80%, the coke reaction order starts increasing until reaching a value of 1 at conversion close to 1. This information is easily obtained by plotting the experimental coke reaction order using the data at constant temperature. In this way, it is possible to easily distinguish among different models, and to replicate the experimental results.
Keywords: Temperature-programmed-oxidation; Coke characterization; Coke morphology
Shape and size controlled α-Fe2O3 nanoparticles as supports for gold-catalysts: Synthesis and influence of support shape and size on catalytic performance by Guang-Hui Wang; Wen-Cui Li; Kun-Ming Jia; Bernd Spliethoff; Ferdi Schüth; An-Hui Lu (pp. 42-47).
Shape and size controlled α-Fe2O3 single crystals were synthesized by a hydrothermal method in the presence of amino acids. When gold colloidal nanoparticles were deposited on the surfaces of the synthesized α-Fe2O3 nanoparticles, Au/α-Fe2O3 catalysts display remarkable differences in catalytic activities in CO oxidation for the differently shaped and sized α-Fe2O3 nanoparticles used as supports.Synthesis of shape- and size- controlled α-Fe2O3 nanoparticles was performed through a hydrothermal method assisted with amino acids. The products were characterized by transmission electron microscopy and X-ray diffraction. It was found that the type of amino acids has significant impact on the shape and size of the obtained α-Fe2O3 nanoparticles. The use of acidic amino acids typically leads to the formation of α-Fe2O3 nanoparticles with spindle shape. However, rhombohedrally shaped α-Fe2O3 nanoparticles were formed in the case of basic amino acids. When gold colloidal nanoparticles were deposited on the surfaces of α-Fe2O3 nanoparticles, Au/α-Fe2O3 catalysts display substantial differences in catalytic activities in CO oxidation for the differently shaped α-Fe2O3 nanoparticles used as supports. In general, spindle shaped Au/α-Fe2O3 shows higher catalytic activity than catalysts based on rhombohedral iron oxide. Under our catalytic test conditions, for spindle shaped Au/α-Fe2O3 catalyst, large hematite crystals induce higher catalytic activity than smaller ones, whereas for rhombohedral Au/α-Fe2O3 catalysts, medium-sized α-Fe2O3 nanocrystals show high catalytic activity for CO oxidation.
Keywords: Hematite; Amino acids; Hydrothermal method; Gold catalysts; CO oxidation
Effect of SAPO-34's composition on its physico-chemical properties and deactivation in MTO process by Ali Izadbakhsh; Fatholah Farhadi; Farhad Khorasheh; Saeed Sahebdelfar; Musa Asadi; Yan Zi Feng (pp. 48-56).
Crystallinity of SAPO-34 samples with different Si/Al ratio (0.05–0.5) of synthesis gel showed a maximum at low to medium range of Si/Al ratio around 0.13. Interestingly, NH3-TPD, FTIR and TG results did not show any significant change in the number of the strong acid sites. Performing reactor tests indicated that SAPO-34 samples with higher crystallinity led to a longer life time in the reactor.Several SAPO-34 samples with different Si/Al ratio (0.05–0.5) of synthesis gel were prepared hydrothermally at crystallization temperature of 190–215°C. The products were characterized by XRD, SEM/EDX, NH3-TPD, FT-IR and nitrogen adsorption techniques. EDX data showed a deviation of elemental composition of products with respect to the Al, Si, and P from that of the gel mixture, but the increasing trend of Si/Al ratio of the products was confirmed. According to XRD and SEM results, crystallinity of samples increased with Si/Al ratio up to the low to medium range of ca. 0.13. However, a reduction in the crystallinity was observed with further increase of the silicon content of the synthesis gels. Interestingly, temperature programmed desorption of ammonia results did not show any significant change in the number of the strong acid sites which was re-confirmed by Fourier transformed infrared and thermo gravimetery results. These results along with those of reactor performance tests at reaction temperature of 400°C and methanol flow of WHSV=1h−1 indicated that SAPO-34 crystallinity, a factor influenced by the Si/Al ratio, is an important parameter for the coking behavior in the methanol to olefin conversion. The samples with higher crystallinity (Si/Al=0.13–0.22) led to a longer life time (100% activity) in the reactor of up to 3h instead of 1h for those with lower crystallinity.
Keywords: MTO; Acidity; Life time; SAPO-34; Silicon content
Hydrogenation of 2-pentyne over Pd/Al2O3 catalysts: Effect of operating variables and solvent selection by J.A. Bennett; R.P. Fishwick; R. Spence; J. Wood; J.M. Winterbottom; S.D. Jackson; E.H. Stitt (pp. 57-64).
Hydrogenation of 2-pentyne over 1wt.% Pd/Al2O3 was studied in a 2.65L baffled stirred vessel. The effects of stirring speed, hydrogen pressure, concentration of substrate, catalyst loading, solvent selection and catalyst preparation method upon the rate and selectivity were investigated. A solvent mixture of 1:1 heptane/2-propanol gave optimal cis/trans and pentene/pentane selectivities of 25.39 and 49.41 respectively.Hydrogenation of 2-pentyne over 1wt.% Pd/Al2O3 was studied in a 2.65L baffled stirred vessel. The effects of stirring speed, hydrogen pressure, concentration of substrate, catalyst loading, solvent selection and catalyst preparation method upon the rate and selectivity were investigated. It was shown that increasing the stirring speed from 445 to 1100rpm and crushing the particles from >150 to 45–75μm led to increases in the reaction rate, confirming the existence of mass transfer resistances. Catalyst preparation method (Type A: crushing followed by impregnation or Type B: impregnation followed by crushing) had a strong effect on reaction behaviour, with Type B particles showing a much higher metal dispersion and consequently faster reaction rate than Type A. Solvent selection was found to have a very strong effect upon reaction rate and selectivity and in heptane the reaction rate was faster than isopropanol. In a 50/50 mixture of heptane and isopropanol the rate of alkyne hydrogenation was intermediate to that observed in the solvents individually while selectivities were up to 5 times greater. The most favourable conditions in terms of selectivity were 2bar of hydrogen, a stirring speed of 445rpm and a solvent mixture of 1:1 heptane/isopropanol, where the highest cis/trans pentene ratio was 25.39, and the highest pentene/pentane ratio was 49.41.
Keywords: Catalysis; Hydrogenation; 2-Pentyne; Selectivity; Palladium/alumina
Dry reforming of methane using Ni–Ce catalysts supported on a modified mineral clay by Carlos Enrique Daza; Alain Kiennemann; Sonia Moreno; Rafael Molina (pp. 65-74).
Ni–Ce catalysts supported on delaminated clay were used in the CO2 reforming of methane between 500 and 800°C without reduction pre-treatment. The catalysts showed high catalytic activities and yields during two temperature cycles with molar ratios between 0.6 and 1.2. Ce showed a beneficial effect on the activities and selectivities and in the diminution of coke.Ni–Ce catalysts supported on mineral clay modified with Al and PVA (polyvinylic alcohol) were synthesized in the presence of microwave radiation. The effect of the nominal quantity of Ce (3, 5 and 10wt.%) was analyzed. The catalysts calcined at 800°C were characterized by elemental chemical analysis, XRD, TPR-H2, TPO and TEM, and evaluated in the reaction of CO2 reforming of methane between 500 and 800°C, using a mixture of reacting agents of 5/5/40 CH4/CO2/Ar (50mLmin−1) without reduction pre-treatment. The XRD showed that the structure of the catalyst is thermally stable while the TPR-H2 suggested the formation of two types of main reducible species that are related with the different environments that Ni may adopt on the surface of the support. The catalysts showed high catalytic activities during two temperature cycles (increase and decrease) and high yields towards CO and H2 with molar ratios between 0.6 and 1.2. The active phase of the catalyst is stable under the conditions of the reaction since sintering was not observed. Ce showed a beneficial effect on the activities and catalytic selectivities of the solids and in the diminution of the production of coke, depending on the nominal quantity. With the increment of the quantity of Ce an increment in the conversions and catalytic selectivities was obtained. The catalyst with 3wt.%. of Ce showed the lowest levels of coke production. After the catalytic process the main formation of nanotubes of coke on the surface of the catalyst was established.
Keywords: Mineral clay; Reforming of methane; Delamination; Cerium; Nickel; Syngas
Phosphorus effect on Co//Mo and Ni//Mo synergism in hydrodesulphurization catalysts by M. Villarroel; P. Baeza; F. Gracia; N. Escalona; P. Avila; F.J. Gil-Llambías (pp. 75-79).
In the conventional hydrodesulphurization (HDS) catalysts type Co(or Ni)Mo/γ-Al2O3, including commercial catalysts, the effect of phosphorus on HDS activity can be well explained by an increase of synergism (Fso) Co//Mo and Ni//Mo caused by the increased mobility of spillover hydrogen on theOH phosphorus surface structure separating the crystallites CoSx or NiSx and MoS2 sulphides.The influence of P concentration on the synergism between Co/γ-Al2O3 or Ni/γ-Al2O3 and Mo/γ-Al2O3 stacked beds separated by a 3-mm stack of P x/γ-Al2O3 is studied in the hydrodesulphurization of gasoil under operating conditions similar to those of industry. The results shown increased Co//Mo and Ni//Mo synergism related to changes in zero point of charge (ZPC), acid strength, and band intensities of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy due to the incorporation of P into the γ-Al2O3 used as separator.
Keywords: Hydrodesulphurization; Phosphorus; Hydrogen spillover; Synergism CoMo and NiMo
Ring opening and kinetics study of hydrotreated LGO on Ni-Mo carbide supported on HY and H-Beta catalysts by K. Chandra Mouli; A.K. Dalai (pp. 80-86).
Pt-Ir/HY, Ni-Mo carbide/HY and Ni-Mo carbide/H-Beta catalysts were used to improve the fuel quality of Hydrotreated Light Gas Oil (HLGO). All the catalysts are well characterized by using BET, Elemental, TPR, TPD and XRD analyzers. Screening of the catalysts were done and observed that Ni-Mo carbide/HY is an effective catalyst for improvement in cetane index of HLGO. A 12 unit increase in cetane index was observed on Ni-Mo carbide/HY at 325°C, whereas Ni-Mo carbide/H-Beta could not improve the cetane index effectively. The Pt-Ir/HY deactivates in three days even though its activity is comparable with that of Ni-Mo carbide/H-Beta. NMR analysis showed that the Ni-Mo carbide/HY catalyst improves the cetane index of the fuel by selectively converting the naphthenes to paraffins in the temperature range of 300–325°C. Low cetane index was observed above 325°C due to the dominance of dehydrogenation and secondary cracking reactions. Simulated distillation results indicated the presence of high percentage of naphtha fraction above 325°C, which decrease the fuel quality due to their low cetane values. A first order kinetic model was proposed and the model was well fit with the experimental values. Arrhenius activation energies of 111, 89 and 42kJ/gmol were observed for dehydrogenation, aromatic saturation and cracking reactions, respectively.Environmental concerns and regulations require severe upgrading of gas oils to get clean-burning transportation fuels. Fuel quality improvement of hydrotreated LGO was studied on Pt-Ir/HY and Ni-Mo carbide catalysts supported on HY and H-Beta. 12 unit increase in the cetane index was observed at 325°C on Ni-Mo carbide/HY. High cetane ring opening products formation was observed at 300–325°C on Ni-Mo carbide/HY which was also confirmed by NMR and boiling point distribution results.
Keywords: Ring opening; Molybdenum; Catalysts; Cetane index; Hydrotreating; Carbide
The influence of alkaline metals on the strong basicity of Mg–Al mixed oxides: The case of transesterification reactions by José M. Fraile; Nuria García; José A. Mayoral; Elísabet Pires; Laura Roldán (pp. 87-94).
The strong basic sites of Mg/Al mixed oxides are mainly due to traces of alkaline metals, as shown by the linear correlation between yield and leachable basicity. This effect is more clearly shown when highly demanding reactions, such as transesterification with branched higher alcohols, are carried out.Several Mg/Al mixed oxides, prepared by three different co-precipitation procedures, have been tested in different transesterification reactions. The catalytic activity for sunflower oil transesterification correlates with the leachable basicity, and not with the total basicity, measured by titration methods. The presence of residual alkaline ions after crystallization is the main source for the strong basicity in this kind of solids, and the difficulty in the complete elimination of the alkaline traces are probably the origin of the strong discrepancies in basicity detected along the literature data. The effect of these alkaline traces is more evident with a more demanding reaction, such as that of methyl palmitate with isobutanol. In such case the alkaline-free solids did not show any catalytic activity. The nature of these strong basic sites makes the recovery problematic, given that part of the alkaline cation is lost to the reaction medium, a process favored by an increase in the polarity of the medium. This fact is also a general limitation for the application of this kind of solids to liquid phase reactions requiring high basicity.
Keywords: Transesterification; Biodiesel; Hydrotalcite; Mixed oxide; Basicity; Leachable basicity
Optimising catalytic properties of supported sulfonic acid catalysts by P.F. Siril; N.R. Shiju; D.R. Brown; K. Wilson (pp. 95-100).
Siliceous SBA-15 supported sulfonic acids were prepared by grafting and co-condensation routes and their surface acidities and catalytic activities compared. By including polystyrene sulfonic acids and Nafion in the study, conclusions have been reached about the importance of interactions between neighbouring acid groups in generating high acid strengths and catalytic activities.Siliceous mesoporous molecular sieves (SBA-15) have been functionalised with propylsulfonic acid groups by both co-condensing 3-mercaptopropyltrimethoxysilane with the solid at the synthesis (sol–gel) stage and by grafting the same compound to pre-prepared SBA-15, followed, in both cases, by oxidation to sulfonic acid. The acidic and catalytic properties of the supported sulfonic acids prepared in the two ways have been compared, using ammonia adsorption calorimetry and the benzylation reaction between benzyl alcohol and toluene. Using a combination of X-ray photoelectron spectroscopy and other analytical techniques, the level of functionalisation and the extent of subsequent oxidation of tethered thiol to sulfonic acid, both in the bulk and close to the surface of SBA-15 particles, have been assessed. The research shows that the co-condensing route leads to higher levels of functionalisation than the grafting route. The extent of oxidation of added thiol to acid groups is similar using the two routes, about 70% near the surface and only 50% in the bulk. Comparison is made with polymer supported sulfonic acid catalysts, Amberlysts 15 and 35, and Nafion. Nafion shows the highest acid strength and the highest specific catalytic activity of all materials studied. Amongst the other materials, average acid strengths are broadly similar but there appears to be a relationship between the concentration of acid sites on the catalysts and their specific activity in the benzylation reaction. A model is proposed to explain this, in which clustering of sulfonic acid groups, even to a small extent, leads to disproportionately enhanced catalytic activity.
Keywords: SBA-15; Solid acid catalysts; Flow adsorption calorimetry; Catalytic activity; Structure–activity correlation
Study of porous anodic alumina supported plate-type catalysts during daily start-up and shut-down operation of methane steam reforming by Lu Zhou; Yu Guo; Makoto Sakurai; Hideo Kameyama (pp. 101-107).
A 0.05wt% trace noble metal Ru doped 17.9wt% Ni catalyst was prepared. It was found that trace Ru-doping was effective for suppressing the deactivation, while an excellent catalytic behavior, that is, self-regeneration of this catalyst has been found during the steam-purge DSS SRM.During a steam-purge daily start-up and shut-down operation of methane steam reforming (DSS), the plate-type alumina supported 17.9wt% Ni catalyst showed deactivation, which resulted from the surface oxidation of sintered Ni. As an approach, considering its high resistance against coke, a methane-purge DSS-like SRM was proposed over 17.9wt% Ni catalyst. Although favorable DSS SRM reactivity was shown, such DSS-like SRM mode was not industrially applicable, when referring to its complex operation, especially the coking potentiality. Therefore, as an ultimate measure, a 0.05wt% trace noble metal Ru doped 17.9wt% Ni catalyst was prepared. It was found that trace Ru-doping was effective for suppressing the deactivation, while an excellent catalytic behavior, that is, self-regeneration of this catalyst has been found during the steam-purge DSS SRM.
Keywords: Porous anodic alumina; Daily start-up and shut-down operation; Nickel catalyst; Steam reforming
Alcohol synthesis by hydrogenation of fatty acid methyl esters on supported Ru–Sn and Rh–Sn catalysts by Takanori Miyake; Takahiko Makino; Shin-ichi Taniguchi; Hiroko Watanuki; Tomohiro Niki; Shizuka Shimizu; Yuki Kojima; Makoto Sano (pp. 108-112).
Alcohol synthesis by hydrogenation of methyl laurate or methyl palmitate was studied on binary catalysts such as Ru–Sn and Rh–Sn supported on Al2O3, SiO2, or ZrO2 at 300°C and 6.0MPa of H2 in an autoclave. Choice of support influenced significantly on the selectivity of the intended alcohol; namely, porous supports afforded more by-product formed by non-catalytic ester-exchange reaction between the intended alcohol and the raw ester.Alcohol synthesis by hydrogenation of methyl laurate or methyl palmitate was studied using binary catalysts such as Ru–Sn and Rh–Sn supported on Al2O3, SiO2, or ZrO2. The catalyst was suspended in the neat ester, and the reaction was carried out at 300°C and 6.0MPa of H2 in an autoclave. Binary catalysts were prepared by the conventional impregnation method and characterized by XRD, isothermal nitrogen adsorption–desorption, and CO-adsorption. Among the catalysts studied, supported Rh–Sn catalyst showed the highest alcohol yield, and a major by-product was a lengthy ester formed by an ester-exchange reaction between the original ester and the formed alcohol itself. The molar ratio of noble metal to tin greatly influenced the catalytic performance. Support with a low surface area, for example α-Al2O3, was favorable for the alcohol synthesis compared with that with a high surface area. It was revealed that the ester-exchange reaction occurred without catalyst just by heating at temperatures higher than 200°C. The results showed that to achieve a high alcohol yield, it is important to prepare catalysts of high activity to hydrogenate the lengthy ester formed in situ.
Keywords: Hydrogenation; Ruthenium; Rhodium; Methyl laurate; Methyl palmitate
Deactivation due to sulfur poisoning and carbon deposition on Rh-Ni/Al2O3 catalyst during steam reforming of sulfur-doped n-hexadecane by Satish L. Lakhapatri; Martin A. Abraham (pp. 113-121).
A mechanism of deactivation for steam reforming of sulfur-containing fuel on Rh-Ni/γ-alumina catalyst has been developed. Sulfur poisoning on nickel sites decreases the rate of steam reforming. Eventually, carbon deposition throughout the catalyst causes an accumulation of aromatic/polymeric carbon on the catalyst surface and loss of reforming activity.Deactivation by sulfur poisoning and carbon deposition of steam reforming catalyst used for hydrogen production from diesel or jet fuel creates a significant barrier to commercialization of fuel cell technologies. Steam reforming of n-hexadecane on a rhodium/nickel catalyst supported on γ-alumina, a formulation previously proposed for steam reforming of logistic fuel, was used to study the deactivation mechanisms. The steam reforming activity was measured in terms of H2 yields and showed that the catalysts were stable in the absence of sulfur but deactivated over a period of 10h when sulfur was present at high loading. Stability and activity were higher with higher amounts of Rh content when Ni was kept constant. TEM-EDS of used catalysts revealed preferential adsorption of sulfur on the surface of Ni crystallites; EDS and XRD analysis showed no bulk sulfide formation. Excessive carbon deposition was observed during steam reforming of sulfur-containing fuel. Blocking of reactant species on the surface of the catalyst due to the formation of aromatic/polymeric carbon on the support was also seen, although higher Rh content inhibited this phenomenon.
Keywords: Steam reforming; Sulfur poisoning; Carbon deposition; Ni/Al; 2; O; 3; TEM; Logistic fuels
Partial oxidation of methane on Pt catalysts: Effect of the presence of ceria–zirconia mixed oxide and of metal content by Fabiano de A. Silva; Juan A.C. Ruiz; Katia R. de Souza; José M.C. Bueno; Lisiane V. Mattos; Fabio B. Noronha; Carla E. Hori (pp. 122-129).
The objective of this work was to study the effects of different noble metal loadings on Pt/CeZrO2/Al2O3 catalysts for the partial oxidation of methane. For both Al and CeZrAl series of samples, the decrease of platinum loading resulted in a significant increase of metallic dispersion. Temperature-programmed reduction and oxygen storage capacity analyses revealed that the sample containing 1.5% Pt presented superior redox properties when compared to the other samples. The catalytic tests showed that the use of smaller Pt contents lead to deactivation. X-ray absorption near edge structure experiments showed that all Pt is in the reduced form above 600°C. In addition, there is evidence that the partial oxidation of methane proceeds through a two-step mechanism. The best performance was obtained for the 1.5Pt/CeZr/Al catalyst that has the largest platinum content, the presence of a homogeneous solid solution, good metal dispersion and high BET surface area.This work evaluated the effects of different noble metal loadings on Pt/CeZrO2/Al2O3 catalysts for the partial oxidation of methane. The use of smaller Pt contents leads to deactivation. The best performance was obtained for the 1.5Pt/CeZr/Al catalyst that has the largest platinum content, the presence of a homogeneous solid solution, good metal dispersion and high BET surface area.
Keywords: Partial oxidation of methane; Cerium doped alumina; Pt/CeO; 2; /Al; 2; O; 3; and Pt/CeZrO; 2; /Al; 2; O; 3; catalysts; Syngas production; Gas-to-liquid technology
Ethylene synthesis from the oxidative bromination of ethane by Hai Tao Wang; Dong Ming Lin; Xiao Ping Zhou (pp. 130-136).
Ethylene was synthesized from the oxidative bromination of ethane and the dehydrobromination of bromoethane. In the oxidative bromination of ethane, ethane was oxidized to bromoethane by oxygen in the presence of HBr over catalyst 1.0%LaCl3/5.9%KCl/5.9%FeCl3/SiO2. In the second reaction, bromoethane was converted to ethylene over another catalyst 12.0wt%ZnO–SiO2. ▪Ethylene was prepared from HBr-mediated ethane oxidation. The process includes two catalytic reactions: the oxidative bromination reaction of ethane and the dehydrobromination reaction of bromoethane. In the oxidative bromination reaction of ethane, bromoethane was synthesized by oxidizing ethane in the presence of oxygen and HBr over a catalyst. The second reaction is the dehydrobromination reaction of bromoethane to form ethylene and HBr over a catalyst. An ethane single pass conversion of 33.9% with a bromoethane selectivity of 86.7% was obtained in the oxidative bromination reaction of ethane over catalyst 1.0%LaCl3/5.9%KCl/5.9%FeCl3/SiO2. In the dehydrobromination reaction of bromoethane, a bromoethane conversion of 99.6% with almost 100% of ethylene selectivity was obtained over 12.0wt%ZnO–SiO2 catalyst.
Keywords: Ethane oxidation; Bromoethane; Ethylene; Catalyst
Effect of La2O3 doping on syntheses of C1–C18 mixed linear α-alcohols from syngas over the Co/AC catalysts by Guiping Jiao; Yunjie Ding; Hejun Zhu; Xianming Li; Jingwei Li; Ronghe Lin; Wenda Dong; Leifeng Gong; Yanpeng Pei; Yuan Lu (pp. 137-142).
The α-alcohols (C1–C18) can be directly synthesized from syngas over the La-doped 15Co/AC catalysts. The reducibility of the 15Co– xLa/AC catalyst decreased and the Co dispersion improved due to the strong interaction between Co and La2O3 species. La2O3 can promote the formation of cobalt carbides (Co2C) which are postulated to play an important role in the synthesis of α-alcohols.Activated carbon-supported La-promoted Co catalysts with different La dopings (15Co– xLa/AC) were prepared by the co-impregnation method and investigated by means of CO hydrogenation, XRD, TPR-MS, CO adsorption and TPSR-MS techniques. The results showed that mixed linear α-alcohols (C1–C18) can be directly synthesized from syngas over the La-doped 15Co/AC catalysts under mild conditions and that the selectivity towards alcohols was improved by doping La into the 15Co/AC catalysts. It was found that the reducibility of the 15Co– xLa/AC catalyst decreased and the Co dispersion improved due to the strong interaction between Co and La2O3 species. La2O3 can promote the formation of cobalt carbides (Co2C), which are postulated to play an important role in the syntheses of the mixed linear α-alcohols. On the other hand, high Co dispersion and an appropriate ratio of Co2+/Co0 can enhance the activity of CO hydrogenation.
Keywords: Mixed linear α-alcohols; La doping; Fischer–Tropsch synthesis; Co–; x; La/AC catalysts; Co; 2; C species
Structures and CO oxidation activities of size-selected Au nanoparticles in mesoporous titania-coated silica aerogels by Yutaka Tai; Wataru Yamaguchi; Koji Tajiri; Hiroyuki Kageyama (pp. 143-149).
We have prepared Au/Titania-coated silica aerogel catalysts from Au nanoparticles (AuNPs) having well-regulated sizes in the range 1.4–6.4nm, through heat-treatment of thiol-capped AuNPs, size-separation through fractional precipitation, and adsorption of the AuNPs on the support in a nonpolar solvent. The Au particle size was preserved during calcination of the catalyst samples at 673K and subsequent CO oxidation. The turnover frequency for CO oxidation of the catalysts changed drastically when their sizes varied from 4 to 5nm, but it did not change appreciably in other size regions. X-ray absorption spectroscopy and X-ray diffraction measurements revealed that lattice contraction and structural changes become prominent at Au diameters of less than 4–5 nm. Thus, the structural changes that occurred in the AuNPs in this diameter region are consistent with the enhanced catalytic activity.We have prepared Au/Titania-coated silica aerogel catalysts from Au nanoparticles (AuNPs) having sizes in the range 1.4–6.4nm. The turnover frequency for CO oxidation mediated by the catalysts changed drastically when their sizes changed over the range from 4 to 5nm, but did not change appreciably over other size regions. X-ray absorption spectra and X-ray diffraction measurements revealed that lattice contraction and structural changes became prominent when the Au diameters were less than 4–5nm.
Keywords: Supported gold catalyst; Au nanoparticle; Aerogel support; Size-dependence; CO oxidation; TEM; EXAFS; XRD
Coke formation during CO2 reforming of CH4 over alumina-supported nickel catalysts by A.S.A. Al–Fatish; A.A. Ibrahim; A.H. Fakeeha; M.A. Soliman; M.R.H. Siddiqui; A.E. Abasaeed (pp. 150-155).
Carbon dioxide reforming of methane to synthesis gas over Ni supported alumina catalysts was investigated at atmospheric pressure. Influences of Ni loading, catalyst stability, coke deposition and synthesis gas ratios(H2/CO ratio) were studied. It was observed that, increasing Ni loading increases the formation of carbon. For high surface area catalyst, at low Ni loading, no coke formation on the catalyst was obtained.Carbon dioxide reforming of methane to synthesis gas over Ni supported alumina catalysts was investigated at atmospheric pressure. Two supports: high surface area γ-Al2O3 (SA-6175) and low surface α-Al2O3 (SA-5239) were used for the preparation of catalysts by the wet impregnation method. The reforming reactions were carried out using (CO2:CH4) feed ratio of 1:1, and reaction temperatures 500, 600, 700 and 800°C. Influences of Ni loading, catalyst stability, coke deposition and synthesis gas ratio (H2/CO) were studied. Spent and fresh catalysts calcined at 900°C were characterized by XRD, SEM and TGA techniques. It was observed that increasing Ni loading increases the formation of carbon. For high surface area catalyst, at low Ni loading, no coke formation on the catalyst was obtained. Similarly, no carbon formation was observed for low surface catalyst at 800°C reaction temperature with feed ratio of 1.3/1.0.
Keywords: CO; 2; reforming; CH; 4; activation; Supported catalysts; Coke; Ni loading; Stability
Comparison of water–gas shift reaction activity and long-term stability of nanostructured CuO-CeO2 catalysts prepared by hard template and co-precipitation methods by Petar Djinović; Jurka Batista; Janez Levec; Albin Pintar (pp. 156-165).
Characterization and water–gas shift reaction (WGSR) activity of CuO-CeO2 catalysts synthesized by hard template (HT) and co-precipitation (CP) methods was studied. CO conversions up to 62% were attained, with H2 selectivity above 99%. Superior BET surface area and CuO dispersion of CuCe HT samples with an ordered mesoporous structure, are decisive factors contributing to higher WGS activity.This study focuses on the characterization and water–gas shift reaction (WGSR) activity of CuO-CeO2 catalysts containing 10, 15 and 20mol% CuO synthesized by hard template method (HT) with KIT-6 silica acting as a template and co-precipitation method (CP). The obtained solids were characterized by SEM/TEM microscopy, N2 adsorption/desorption, XRD, H2-TPR/TPD, N2O decomposition and NH3 chemisorption/TPD methods. The preparation techniques yield fundamentally different products despite the same nominal chemical composition. Catalysts prepared by the HT method exhibited ordered mesoporous structure, which was identified as the negative replica of the KIT-6 silica pore system. Considerable differences in BET surface area (147–166m2/g for CuCe HT samples compared to 22–54m2/g for CuCe CP solids, respectively) were measured. CuO dispersion values between 28% and 40% were determined for CuCe HT solids, in case of CuCe CP samples, these values were in the range of 8–20%. H2-TPR/TPD experiments revealed facile and extensive CeO2 reduction in all tested samples, which increased with CuO loading. Very similar density of surface acidic sites was determined for both CuCe HT and CuCe CP catalyst samples at each CuO loading, with CuCe CP solids exhibiting the absence of strong acidic sites. WGS reaction activity was tested at the stoichiometric CO/H2O ratio and low contact times in the temperature range from 250 to 450°C. Despite rigorous reaction conditions, CO conversions up to 62% and 54% were attained for CuCe HT and CuCe CP samples, respectively, with H2 selectivity above 99% over the entire temperature range. Superior BET surface area and CuO dispersion of CuCe HT samples are decisive factors contributing to higher activity in the investigated WGS reaction, compared to the ones synthesized by the co-precipitation method.
Keywords: CuO-CeO; 2; catalysts; Co-precipitation; Hard template method; Water–gas shift reaction; Stability; Activity
Deposition of Al-Fe pillared bentonites and gold supported Al-Fe pillared bentonites on metallic monoliths for catalytic oxidation reactions by L.M. Martínez T; M.I. Domínguez; N. Sanabria; W.Y. Hernández; S. Moreno; R. Molina; J.A. Odriozola; M.A. Centeno (pp. 166-173).
Al-Fe pillared bentonite and gold supported on Al-Fe pillared bentonite catalysts deposed on Fecralloy monoliths have been prepared, characterized and tested in two oxidation reactions: gaseous oxidation of CO and phenol oxidation in aqueous medium. The deposition of the solid on the metallic substrate does not alter its structural characteristics. The use of monoliths improves the activity in both reactions and offers the additional advantage to facilitate the separation of the catalyst from the reaction medium.Al-Fe pillared bentonite and gold supported on Al-Fe pillared bentonite catalysts deposed on Fecralloy monoliths have been prepared, characterized and tested in two oxidation reactions: gaseous oxidation of CO and phenol oxidation in aqueous medium. The deposition of the solid on the metallic substrate does not alter its structural characteristics. The use of monoliths improves the activity in both reactions and offers the additional advantage to facilitate the separation of the catalyst from the reaction medium.
Keywords: Al-Fe pillared bentonite; Gold catalysts; Metallic monoliths; CO oxidation; Phenol oxidation
ZnO activation by using activated carbon as a support: Characterisation and photoreactivity by E. Pulido Melián; O. González Díaz; J.M. Doña Rodríguez; G. Colón; J. Araña; J. Herrera Melián; J.A. Navío; J. Pérez Peña (pp. 174-181).
Activated carbon loaded ZnO materials were synthesised, characterised and evaluated in the photocatalytic decomposition of phenol and 2,4-dichlorophenol. Changes in the FTIR vibration bands of the surface hydroxyl groups were recorded. Laser scattering studies showed that AC loading leads to smaller ZnO particles. BET and SEM analysis showed agglomeration of ZnO particle pores in the AC structure.The effect of the mixing ZnO with different portions of activated carbon (AC) has been studied. The resulting catalysts were characterised and evaluated in the photocatalytic decomposition of aqueous pollutants. Changes in the catalyst colour and in the FTIR vibration bands of the surface hydroxyl groups were recorded. νOH vibrations were shifted to lower wavenumbers as AC loading increased, demonstrating modification of the acid-base character of the catalysts. Laser scattering studies showed that AC loading leads to smaller ZnO particles. BET surface area measurements and scanning electron micrograph (SEM) analysis showed agglomeration of ZnO particle pores in the AC structure.Results showed that in addition to a synergistic effect of the AC-ZnO combination, AC content modifies the ZnO particle properties and consequently photocatalytic behaviour. This was evident in phenol degradation experiments where changes in the concentration profiles of the catechol and hydroquinone degradation intermediates, were observed. However, the AC-ZnO catalysts were less efficient than pure ZnO in the degradation of 2,4-dichlorophenol (DCP). This seems to be due to the strong adsorption of the DCP molecule on AC, resulting in lower diffusion to the catalytic ZnO and thus a lower rate of photocatalysis.
Keywords: Photocatalytic degradation; ZnO; Activated carbon; Phenol; 2,4-Diclorophenol
Photocatalytic performance of alumina-incorporated titania composite nanoparticles: Surface area and crystallinity by Chung-Sung Yang; Ya-Jen Wang; Mong-Shian Shih; Ya-Ting Chang; Chia-Chi Hon (pp. 182-190).
The time-evolved photo-degradation curves for the removal rates of salicylic acid, derived from the PL intensity, over P-25 (0.0057min−1), AIT-4 (0.0142min−1), AIT-6 (0.0158min−1), and AIT-7 (0.0173min−1) are in the ratio of 0.33:0.82:0.91:1.00. The degradation rate for binary AIT nanoparticles is 2.5–3.0 times as large as that of P-25.Alumina-incorporated titania (AIT) nanoparticles, a TiO2-based binary photocatalyst with tunable Al/Ti ratio, can be prepared via an one-pot non-aqueous synthetic route. The adjustable Al/Ti atomic ratio (from 4.4% to 11.85%) offers a needed opportunity to elucidate the optimal incorporation level for AIT to attain the maximum photocatalytic efficiency, and to study the effect of incorporated alumina on the crystallinity of the nanocomposite photocatalyst. The nanoparticles with highest Al/Ti ratio (AIT-4, Al/Ti=11.85%) reveal the largest specific surface area (SSA) of 370.89m2g−1, which is 4.7% larger than that of the one with lowest Al/Ti ratio (AIT-7, Al/Ti=4.4%, 353.66m2g−1). Nevertheless, AIT-4 is about seven times larger than Degussa P25 (53.25m2g−1) in SSA. The phase composition of AIT was monitored by powder X-ray diffraction (P-XRD). The gradual changes in composition of nanoparticle and surface area accompanying crystallinity were evaluated by EDX of HR-TEM and by BET analysis. The characterization data show that the crystallinity of AIT photocatalysts decreases as the atomic ratio of Al/Ti increases from 4.4% to 11.85%. In the photocatalytic degradation of salicylic acid (SA) by UV lamp ( λ=254nm, 18W), the degradation rate constants of SA over P25 (0.0057min−1), AIT-4 (0.0142min−1), AIT-6 (Al/Ti=7.88%, 0.0158min−1), and AIT-7 (0.0173min−1) are in the ratio of 0.33:0.82:0.91:1.00. The experimental data show that the highest catalytic efficiency is achieved with the sample having the lowest SSA (i.e. AIT-7). Therefore, the optimal incorporation amount of Al2O3 in AIT is Al/Ti=4.4%, suggesting that the effects of crystallinity prevail over those of the surface area, when the difference of SSA among the photocatalysts is less than 5%.
Keywords: Photocatalyst, Crystallinity, Surface area, TiO; 2; , Al; 2; O; 3
Mesoporous ZSM-5 zeolite catalysts prepared by desilication with organic hydroxides and comparison with NaOH leaching by Sònia Abelló; Adriana Bonilla; Javier Pérez-Ramírez (pp. 191-198).
Hierarchical porous zeolites are prepared by desilication of ZSM-5 in aqueous solutions of tetraalkylammonium hydroxides (TPAOH and TBAOH). The treatment in organic hydroxides is compared with conventional NaOH leaching. The TPAOH-treated zeolite displays improved performance in the liquid-phase benzene alkylation with ethylene with respect to the parent and NaOH-treated zeolites.Hierarchical zeolites combining micro- and mesoporosity were prepared by desilication of ZSM-5 (Si/Al=42) in aqueous solutions of tetraalkylammonium hydroxides (TPAOH, TBAOH). Similarities between the treatment mediated by organic hydroxides and the conventional NaOH leaching comprised (i) the requirement to work with a starting zeolite in the optimal Si/Al window of 25–50 and (ii) the minor influence of the counter-cation (H+, NH4+, Na+) on the degree of mesoporosity developed. However, both desilication media presented distinctive kinetic and mechanistic characteristics. The use of organic hydroxides directly produced the protonic form of the mesoporous zeolite upon calcination, simplifying the final ion exchange with NH4NO3 characteristic of the NaOH treatment. Silicon dissolution in TPAOH (or TBAOH) was much slower than in NaOH, making the demetallation process highly controllable. The treatment in the organic base was less selective for silicon extraction, i.e. a higher amount of aluminum was leached to the solution compared to the NaOH treatment. The differences in porosity development and chemical composition of the final solid can be assigned to the effect of the bulky tetraalkylammonium cation. The optimal hierarchical ZSM-5 zeolite (treated in 1M TPAOH at 338K and 8h) had a mesopore surface area of 160m2g−1 and the intrinsic zeolite properties were largely preserved. This sample displayed improved catalytic performance in the liquid-phase benzene alkylation with ethylene compared to the parent and NaOH-treated zeolites.
Keywords: Hierarchical zeolites; Mesoporous ZSM-5; Desilication; Organic base; Tetraalkylammonium hydroxide; NaOH; Benzene alkylation
Anomalous diffusion during isopropanol decomposition on (ZrO2)1− x (CeO2) x catalysts by A. Iosifidis; D.E. Petrakis; P.J. Pomonis (pp. 199-210).
In this work the effect of composition of (ZrO2)1− x (CeO2) x catalysts on the ratio γ= Ec/ Ed between the activation energies for the isopropanol decomposition, estimated in the chemical reaction ( Ec) and the diffusion ( Ed) controlled regimes, was studied. The solid catalysts with x=0.0; 0.2; 0.5; 0.8 and 1.0 were prepared by heating the precursors at 400, 600 and 800°C and characterized by N2 porosimetry, X-ray diffraction, SEM/EDS analysis and NH3/TPD. Their catalytic activity for the decomposition of isopropanol in the temperature range 200–400°C was probed in a tubular flow reactor. The estimated Arrhenius plots showed a distinct and well-defined change of slopes corresponding to alternation from the chemical to the internal diffusion-controlled regime of the process. The ratio γ= Ec/ Ed of the corresponding activation energies was found equal to γ≈1 for x=0.0, meaning total lack of diffusion limitations, and converges to γ≈2 for x=1.0, corresponding to classical internal diffusion control. For 0< x<1 the values of 1< γ<2 signify anomalous diffusion related linearly to some compositional property of the (ZrO2)1− x (CeO2) x catalysts. The origin of this phenomenon is discussed in relation to the variable binding strength and friction of movement of the isopropanol species on the more active ZrO2 and the less active CeO2 nanoparticles of the solid catalysts.The decomposition of isopropanol on (ZrO2)1− x (CeO2) x catalysts shows anomalous diffusion effects related linearly to their composition x. The origin of this phenomenon is related to the variable friction of the reacting species along their path from the inactive CeO2 particles (dark) to the active ZrO2 particles (white).
Keywords: Anomalous diffusion; (ZrO; 2; ); 1−; x; (CeO; 2; ); x; catalysts; Isopropanol decomposition; Activation energy
Selective oxidation of styrene to benzaldehyde catalyzed by Schiff base-modified ordered mesoporous silica materials impregnated with the transition metal-monosubstituted Keggin-type polyoxometalates by Jianglei Hu; Kexin Li; Wei Li; Fengyan Ma; Yihang Guo (pp. 211-220).
Schiff base-modified ordered mesoporous silica materials impregnated with the transition metal monosubstituted Keggin-type polyoxometalates, K10− nX n+MW11O39-Schiff-SBA-15, were prepared via the coordination of transition metal centers in the Keggin units with nitrogen atoms of Schiff base modified silica supports. The composites exhibited high catalytic reactivity, selectivity, and stability toward the reaction of oxidation of styrene to produce benzaldehyde by H2O2.A series of Schiff base-modified ordered mesoporous silica materials impregnated with the transition metal-monosubstituted Keggin-type polyoxometalates (mono-TMSPs), K10− nX n+MW11O39-Schiff-SBA-15, (X=P/Si, M=Co/Ni/Cu/Mn), was prepared using successive grafting procedures of SBA-15 silica with 3-aminopropyl-trimethoxysilane, benzaldehyde, and mono-TMSP. The composite materials were well-characterized by spectroscopy methods, X-ray diffraction analysis, transmission electron microscopy, and nitrogen sorption analysis to confirm the structure integrities of the Keggin unit and Schiff base ligand after the incorporation, to evidence formation of the coordination binding between the starting Keggin units and the Schiff base-modified silica matrix, and to investigate the morphology and surface textural properties of the composite catalysts. These materials were subsequently utilized as efficient and selective catalysts in the reaction of oxidation of styrene to benzaldehyde using H2O2 as an oxidant. For comparison, an amine-modified SBA-15 silica material impregnated with mono-TMSP (K10− nX n+MW11O39-NH2-SBA-15) and the neat Keggin unit (K10− n[X n+M(H2O)W11O39]) was also tested. The influences of key reaction parameters, including the molar ratios of H2O2 to styrene, compositions and loadings of the neat mono-TMSPs, solvents, the catalyst amount, and reaction temperatures on the reactivity and selectivity, were also studied. Finally, the reusability of the catalysts was evaluated.
Keywords: Selective oxidation; Benzaldehyde; Supported polyoxometalate; Ordered mesoporous material; Schiff base
Au–Pd/AC as catalysts for alcohol oxidation: Effect of reaction parameters on catalytic activity and selectivity by Alberto Villa; Nikolina Janjic; Paolo Spontoni; Di Wang; Dang Sheng Su; Laura Prati (pp. 221-228).
The oxidation of different alcohols with molecular oxygen in water has been investigated using a range of activated carbon-supported Au–Pd bimetallic catalysts. The effect of the Au–Pd ratio on the conversion and selectivity was observed and a synergistic effect is present in a large range of the Au–Pd ratio, being maximized for Au80–Pd20 composition instead of Au90–Pd10 shown in glycerol oxidation [A. Villa, C. Campione, L. Prati, Catal. Lett. 115 (2007) 133]. Moreover the enhancement of conversion observed by adding a base resulted greater for gold-rich catalysts rather than for palladium-rich ones.The effect of the alcohol concentration and the metal/substrate ratio in the presence or the absence of the base was also studied revealing substantial differences in terms of both activity and selectivity. At 1M concentration under biphasic conditions benzyl alcohol has been selectively oxidized to benzaldehyde (S90=98%) even in the presence of NaOH with a TOF of 18,000h−1 using Au60–Pd40/AC as the catalyst.The oxidation of different alcohols with molecular oxygen in water has been investigated using a range of activated carbon-supported Au–Pd bimetallic catalysts. The effect of the Au–Pd ratio was observed on the conversion and selectivity and a synergistic effect is present in a large range of Au–Pd ratio. Moreover the enhancement of conversion observed by adding a base resulted higher for gold-rich than for palladium-rich catalyst. Under controlled conditions, even in the presence of the base, a high selectivity to aldehyde was obtained using Au60–Pd40/AC as the catalyst.
Keywords: Gold–palladium alloy; Alcohol oxidation