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Applied Catalysis A, General (v.327, #2)
Evolution of the properties of PtGe/Al2O3 reforming catalysts with Ge content by Rafael Mariscal; José L.G. Fierro; Juan C. Yori; José M. Parera; Javier M. Grau (pp. 123-131).
The current interest in reforming products is in the production of isoparaffins that have high octane numbers and low environmental pollution. It is well known that isoparaffin selectivity is controlled by the acid function, which can be altered by the promoter content and at the same time, an improvement of stability can be achieved by decreasing the deactivation by coke formation. Thus, the optimization of the Pt/Ge atomic ratio on the catalytic activity of PtGe/Al2O3 catalysts used in n-heptane reforming has been studied. ▪The effect of the Pt/Ge atomic ratio on the catalytic activity of PtGe/Al2O3 catalysts used in n-heptane reforming was studied. The samples were prepared by the coimpregnation method on chlorinated alumina. The platinum content was 0.5wt.%, and Ge-loading was varied to obtain Pt/Ge atomic ratios of 0.3, 0.7, 1.4, 2.1 and 3.5. Pt/Al2O3 and Ge/Al2O3 catalysts were also prepared as references. Characterization was carried out by temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD), Fourier transform IR spectroscopy (FTIR) with CO as the probe molecule, X-ray photoelectron spectroscopy (XPS), cyclohexane (CH) dehydrogenation, and n-heptane reforming. The preparation method followed in this work revealed a decrease in the metallic activity of Pt due to the presence of Ge. The Ge2+ and Ge4+ species, after reduction at 500°C, were detected on the surface of PtGe catalysts. The increase in the Ge content led to a decrease in hydrogenolysis activity and the formation of aromatics; an increase in the formation of isomers and cycloparaffins, and a reduction in the production of gas and in deactivation by coke, thereby improving catalyst stability. The results show that the maximum isoparaffin yield of all catalysts tested was obtained for a Ge-loading of 0.27wt.% (Pt/Ge atomic ratio=0.7). These changes in the performance of the PtGe catalysts may be attributed to the modifications occurring in the metallic and in the acid function of Pt/Al2O3 due to the introduction of Ge. The metallic catalytic activity of Pt is modified by the geometrical effect (dilution of Pt ensembles) and changes in the electronic properties of platinum. Ge addition produces a weakening of Pt/Al2O3 acid strength and an increase in the acid sites total density by the presence of Ge oxides.
Keywords: n; -Heptane reforming; Isoparaffin selectivity; Pt/Ge atomic ratio optimization; Electronic effect
Wet milling of H-ZSM-5 zeolite and its effects on direct oxidation of benzene to phenol by S. Gopalakrishnan; S. Yada; J. Muench; T. Selvam; W. Schwieger; M. Sommer; W. Peukert (pp. 132-138).
ZSM-5 catalyst (original; crystal size −5.5μm) was wet milled for 30min and 3h to obtain catalysts of different crystal sizes (crystal sizes −440nm and 220nm). The original and milled catalysts were subjected to benzene to phenol oxidation. The smaller the crystals the lesser the catalyst deactivation. ▪The direct oxidation of benzene to phenol with N2O over ZSM-5 catalysts suffers from the problem of rapid catalyst deactivation mainly due to the secondary transformation of phenol into heavier hydrocarbon compounds leading to the catalyst coking. In order to investigate the deactivation behavior of the ZSM-5 catalysts during this reaction, a comparative study was performed over ZSM-5 catalysts having different crystal sizes. The original catalyst was milled to two different periods of time to obtain catalysts having various crystal sizes. The original and the milled catalysts were tested for the benzene to phenol reaction to get an insight into the effect of crystal size on the catalyst deactivation. There was a decrease in catalyst deactivation with a decrease in crystal size. An indirect dependence of catalyst deactivation with total acidity was observed.
Keywords: Benzene oxidation; Nitrous oxide; Phenol; ZSM-5; Crystal size; Microreactor
Influence of support on catalytic behavior of nickel catalysts in oxidative steam prereforming of n-butane for fuel cell applications by Katsutoshi Nagaoka; Katsutoshi Sato; Hiroyasu Nishiguchi; Yusaku Takita (pp. 139-146).
Oxidative steam reforming of n-butane over supported Ni catalysts at relatively low temperature, 723K, is reported. Catalytic performance was investigated not only after H2 treatment at 1073K “reductive treatment” but also after subsequent O2/Ar treatment at the reaction temperature “oxidative treatment” to mimic the shutdown and startup of the domestic fuel cell system. After the reductive treatment, n-butane conversion attained 100% for all the catalyst at a lower space velocity (SV) of 67L(hg)−1. Differences in catalytic activity were emphasized at a higher SV of 667L(hg)−1, and were attributed to corresponding differences in metal surface area. Since a fraction of Ni in some catalysts was oxidized during the reaction at the higher SV, the reaction at the higher SV was indicated to be kinetically more oxidative condition. Although Ni/Al2O3 was inactive at the lower SV after the oxidative treatment, n-butane conversion of the other catalysts attained 100%. In contrast, only Ni/MgO was able to convert n-butane at the higher SV after the oxidative treatment. Therefore it was revealed that nickel oxide species on the catalyst were reduced by n-butane in the reactant even under severe oxidative conditions.
Keywords: H; 2; production; Oxidative steam prereforming; n; -Butane; Activity after oxidative treatment; Fuel cell
Pulse CH4/D2O reaction on a Ni/YSZ anode in SOFC by Zhiqiang Yu; Steven S.C. Chuang (pp. 147-156).
The activity and coking characteristics of a nickel/yttrium stabilized zirconia (Ni/YSZ) anode in a YSZ electrolyte/LSM cathode fuel cell have been investigated by steady state H2 as well as pulse CH4 and D2O/CH4 reactions. Pulse CH4 reaction produced H2, CO and carbon deposits (i.e., coke); pulse D2O/CH4 reaction led to the formation of H2, HD, D2 and CO under the open circuit condition where O2− was not able to diffuse across the YSZ membrane. Closing the circuit allowed O2− to diffuse across the YSZ membrane from the lanthanum strontium manganate (LSM) cathode to the Ni/YSZ anode, leading to oxidation of HD/D2 for electric power generation at 750 and 850°C. The observed preferential electrochemical oxidation of HD/D2 over H2 suggests that (i) the reaction of D2O/CH4 (i.e., reforming of CH4 with D2O) occurs at the sites in the vicinity of the three phase boundary (i.e., the Ni–YSZ interface) where the electrochemical oxidation of HD/D2 takes place; (ii) the production of H2 from the dissociation of CH4 occurs on the Ni surface sites which is far from the three phase boundary. Build-up of coke has a more significant inhibition effect on the electrochemical oxidation reaction for electric power generation than the CH4 dissociation reaction on the Ni/YSZ anode at 750 and 850°C. Coking could be attributed to the inability of O2− to diffuse on the Ni surface to initiate electrochemical oxidation.▪The activity and coking characteristics of a nickel/yttrium stabilized zirconia (Ni/YSZ) anode in a YSZ electrolyte/LSM cathode fuel cell have been investigated by steady state H2 as well as pulse CH4 and D2O/CH4 reactions. Pulse CH4 reaction produced H2, CO and carbon deposits (i.e., coke); pulse D2O/CH4 reaction led to the formation of H2, HD, D2 and CO under the open circuit condition where O2− was not able to diffuse across the YSZ membrane. Closing the circuit allowed O2− to diffuse across the YSZ membrane from the lanthanum strontium manganate (LSM) cathode to the Ni/YSZ anode, leading to oxidation of HD/D2 for electric power generation at 750 and 850°C. The observed preferential electrochemical oxidation of HD/D2 over H2 suggests that (i) the reaction of D2O/CH4 (i.e., reforming of CH4 with D2O) occurs at the sites in the vicinity of the three phase boundary (i.e., the Ni–YSZ interface) where the electrochemical oxidation of HD/D2 takes place; (ii) the production of H2 from the dissociation of CH4 occurs on the Ni surface sites which is far from the three phase boundary. Build-up of coke has a more significant inhibition effect on the electrochemical oxidation reaction for electric power generation than the CH4 dissociation reaction on the Ni/YSZ anode at 750 and 850°C. Coking could be attributed to the inability of O2− to diffuse on the Ni surface to initiate electrochemical oxidation.
Keywords: Solid oxide fuel cell; Nickel; Methane reforming; Coking; Deuterium transient
Partial differentiation of neural network for the analysis of factors controlling catalytic activity by Tadashi Hattori; Shigeharu Kito (pp. 157-163).
It was attempted to identify factors controlling catalytic activity by applying the numerical partial differentiation of trained neural network to several examples of experimentally established correlations of catalytic activities with properties of catalyst components. In all the examples, the primary factors that had been proposed in experimental studies were successfully identified by the method. ▪In order to examine the possibility for identifying the factors controlling catalytic activity by neural network, the numerical partial differentiation of trained neural network was applied to several examples of experimentally established correlations of catalytic activities with primary factors: oxidation of propene on oxide catalysts, oxidation of butane on lanthanide oxides, decomposition of formic acid on metal catalysts, oxidation of methane on lanthanide oxides, and support and additive effects on low temperature combustion of propane over Pt catalyst. The relative importance of the given factors including dummy parameters were estimated from the numerical differentiation of trained artificial neural network, and they were compared with those obtained by previously proposed methods using the weightings of connecting links of trained neural network. In all the examples, the primary factors that had been proposed in experimental studies were successfully identified by the numerical differentiation of trained neural network. As for the connecting weight-methods examined for the comparison, only the method proposed by Olden et al. and us gave satisfactory results to identify the primary factors. Further, it was demonstrated that the partial differentiation method could be used to obtain local information, that is, the partial derivatives for individual catalyst, which would enable us to know the method how each catalyst can be improved.
Keywords: Neural network; Partial differentiation; Sensitivity analysis; Controlling factor; Catalytic activity
Hydrogen generation from methanol oxidation on supported Cu and Pt catalysts: Effects of active phases and supports by Yu-Chuan Lin; Keith L. Hohn; Susan M. Stagg-Williams (pp. 164-172).
Catalytic partial oxidation (CPO) of methanol was studied over Cu/ZnO and Pt/ZrO2 catalysts. These catalysts gave different results, with Cu/ZnO producing more CO2 and Pt/ZrO2 producing more CO. To explain this difference, the kinetics of four reactions (CPO, methanol decomposition (MD), methanol steam reforming (MSR), and water-gas shift (WGS)) were measured and used in a packed-bed model of the experimental reactor. For both catalysts, oxidation reactions were much faster than other reactions, so oxidation dominates the process until all of the oxygen is consumed. Once oxygen was depleted, MD dominated on Pt/ZrO2, keeping selectivity of CO high. On Cu/ZnO, however, MD was much slower, so MSR and WGS were dominant after oxygen had been consumed. In addition, deactivation of Cu/ZnO was investigated and it can be attributed to the existence of CH3O species or formate ions on the catalyst's surface. The effect of catalyst support was studied by adding ceria to Pt/ZrO2. While ceria addition appeared to enhance the importance of WGS, increased ceria loading led to higher selectivities of CO2 and H2O.Catalytic partial oxidation (CPO) of methanol was studied over Cu/ZnO and Pt/ZrO2 catalysts. The differences between these two are attributed to the reaction rates of CPO and methanol decomposition (MD). A packed-bed model was derived to predict the catalytic behaviors. In addition, deactivation of Cu/ZnO may be ascribed as deposition of methoxy species or formate ions on the catalyst's surface. ▪
Keywords: Hydrogen; Methanol oxidation; Copper zinc; Platinum; Ceria; Kinetics
Effect of calcination temperature on the structural characteristics and catalytic activity for propene combustion of sol–gel derived lanthanum chromite perovskite by K. Rida; A. Benabbas; F. Bouremmad; M.A. Peña; E. Sastre; A. Martínez-Arias (pp. 173-179).
A study of a sol–gel prepared lanthanum chromite perovskite catalyst following in detail the structural evolution as a function of the calcination steps between 200 and 1000°C in correlation with the catalytic activity for propene combustion of the system at selected temperatures in such range is presented. ▪The perovskite type lanthanum chromite LaCrO3 has been synthesized by a sol–gel method. Its bulk structural and surface characteristics have been examined by X-ray diffraction (XRD), SEM, SBET measurements, Fourier Transform Infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) as a function of the calcination treatment performed between 200 and 1000°C over the precursor powder and in correlation with information achieved from TG-DTA thermal analysis. The characterization results are employed to rationalize the catalytic behaviour of the system towards propene complete oxidation. It is shown that the catalytic activity becomes optimized when a single perovskite LaCrO3 phase is achieved upon calcination at T>ca. 700°C. In contrast, coexistence of perovskite LaCrO3 and monazite LaCrO4 at lower calcination temperatures appears detrimental to the combustion activity of the system.
Keywords: LaCrO; 3; –LaCrO; 4; Perovskite; Sol–gel; Calcination temperature; C; 3; H; 6; combustion; SOFC
Steam reforming of ethanol with co-fed oxygen and hydrogen over Ni on high surface area ceria support by N. Laosiripojana; S. Assabumrungrat; S. Charojrochkul (pp. 180-188).
Ni on high surface area CeO2 support (Ni/CeO2 (HSA)) provides considerably higher ethanol steam reforming reactivity (with/without co-fed oxygen and hydrogen) with excellent resistance toward carbon deposition compared to Ni/Al2O3 and Ni on conventional ceria (Ni/CeO2 (LSA)). The additional of O2 (as oxidative steam reforming) and H2 significantly reduced the degree of carbon deposition. The presence of both reactants also promoted the conversions of hydrocarbon presented in the system (i.e. CH4 and C2H4) to CO and H2. Importantly, the major consideration of these adding is the suitable co-fed reactant/C2H5OH ratio.Comparison of the conversion and product distributions (EtOH (×), H2 (●), CO (○), CO2 (♢), CH4 (♦), C2H6 (▵), and C2H4 (▴)) from steam reforming (small symbols with dot lines) (4kPa C2H5OH, and 12kPa H2O) and autothermal reforming (large symbols with solid lines) (4kPa C2H5OH, 12kPa H2O, and 1.6kPa O2) of ethanol over Ni/CeO2 (HSA). ▪Ethanol steam reforming with/without co-fed oxygen and hydrogen over Ni on high surface area (HSA) CeO2 support, synthesized via a surfactant-assisted method, (Ni/CeO2 (HSA)) was studied under solid oxide fuel cell (SOFC) operating conditions for later application as an in-stack reforming catalyst. The catalyst provides considerably higher reforming reactivity and excellent resistance towards carbon deposition in comparison with Ni/Al2O3 and Ni on conventional ceria (Ni/CeO2 (low surface area; LSA)). At the temperature above 800°C, the main products from the reforming processes over Ni/CeO2 (HSA) were H2, CO, and CO2 with some amount of CH4 depending on the inlet steam/ethanol and co-fed reactant (i.e. O2 and H2)/ethanol ratios, whereas high hydrocarbon compound i.e. C2H4 was also observed from the reforming of ethanol over Ni/CeO2 (LSA) and Ni/Al2O3. An addition of O2 (as oxidative steam reforming) and H2 significantly reduced the degree of carbon deposition. The presence of both reactants also promoted the conversions of hydrocarbon presented in the system (i.e. CH4 and C2H4) to CO and H2. The major consideration of these additions is the suitable co-fed reactant/C2H5OH ratio. The presence of too high oxygen concentration could oxidize Ni particles to NiO, which resulted in a lower reforming reactivity, and also combusts H2 to H2O. The suitable O2/C2H5OH molar ratio for the oxidative steam reforming of Ni/CeO2 was 0.4, which is less than that of Ni/Al2O3. An addition of too high hydrogen content slightly decreased the catalyst activity, which could be due to the active site competition of nickel particle and the inhibition of gas–solid redox reactions between the gaseous hydrocarbon components with the lattice oxygen (OO x) on the surface of CeO2 support in the case of Ni/CeO2.
Keywords: Ethanol; Steam reforming; Hydrogen; Oxidative steam reforming; Ceria
Chabazite supported NiMo catalysts: Activity and sulfur poisoning by B.R. Greenhalgh; S.M. Kuznicki; A.E. Nelson (pp. 189-196).
Bimetallic clusters of nickel and molybdenum on the surface of chabazite (CHA), show novel activity and resistance to sulfur poisoning in hydrogenation catalysis. Characterization studies of Ni-CHA, Mo-CHA, and NiMo-CHA support the observed catalytic properties of bimetallic NiMo-CHA, indicating a synergistic effect between nickel and molybdenum on chabazite. ▪This paper reports recent findings on nanostructured mixed metal clusters of nickel and molybdenum on the surface of chabazite (CHA) which show novel activity and resistance to sulfur poisoning in hydrogenation catalysis. Three systems, Ni-CHA, Mo-CHA, and NiMo-CHA, were prepared by ion-exchange and characterized by instrumental neutron activation analysis (INAA), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and NH3 temperature programmed desorption (TPD) in order to give insight into the structure of the supported phases. Ethylene hydrogenation was used as a probe reaction, in both the presence and absence of H2S, as a measure of the activity, selectivity and deactivation characteristics of these systems. The findings of the characterization studies support the observed catalytic properties of bimetallic NiMo-CHA, which shows unique selectivity and resistance to sulfur poisoning relative to the monosmetallic (Ni-CHA and Mo-CHA) systems. These findings indicate a synergistic effect between nickel and molybdenum on chabazite.
Keywords: Zeolite; Chabazite; Nickel; Molybdenum; Ethylene; Methane; Hydrogenation; Dispersion; Nanocluster
Steam reforming of ethanol on supported nickel catalysts by J.W.C. Liberatori; R.U. Ribeiro; D. Zanchet; F.B. Noronha; J.M.C. Bueno (pp. 197-204).
The catalytic behavior of Ni/Al2O3 catalysts modified with La and Ag was investigated in the steam reforming of ethanol. The coking cannot be suppressed by Ag promotion. Inversely, the La has a positive effect to decreasing coking on Ni catalysts in steam reforming of ethanol. A scheme for ethanol reactions with H2O on Ni surfaces is proposed on basis of activity tests. ▪The catalytic behavior of Ni/Al2O3 catalysts modified with La and Ag was investigated in the steam reforming of ethanol. The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and Fourier transform infrared spectroscopy (FTIR) of CO adsorption. The reaction rate for noncatalytic decomposition of ethanol in the homogeneous gas phase becomes significant only at high temperatures ( T≥890K). FTIR results revealed that Ag strongly modifies the Ni surface, decreasing the intensity ratio of the bands for adsorbed CO in the bridging mode at low frequency (LF) and the linear mode at high frequency (HF). Similar but smaller effect was observed in the La-containing catalyst. The activity and stability against carbon depostion for steam reforming of ethanol of Ni/Al2O3 catalyst was only slightly sensitive to Ag but the activity was strongly dependent on the presence of La. The reaction data suggest that at temperatures lower than 650K the Ni/Al2O3 catalyst was active for decomposition of ethanol via the acetaldehyde intermediate, showing high selectivity to methane and CO. The rate of steam reforming of ethanol became significant at temperature higher than 650K. Comparing Ni/Al2O3 and Ni/La–Al2O3 catalysts the results pointed out that the Ni became more susceptible to modification by water in La-containing Ni catalyst. The Ni/La–Al2O3 catalysts become inactive at low temperatures, and the activity could be regenerated with reduction of NiO by ethanol on raising the reaction temperature. Differently from the steam reforming of methane, the coking cannot be suppressed by Ag promotion in the case of steam reforming of ethanol. Inversely, the La has a positive effect to decreasing coking on Ni catalysts. A scheme for ethanol reactions with H2O on Ni surfaces is proposed based on reaction tests.
Keywords: Steam reforming of ethanol; Hydrogen production; Ni-supported catalysts
Synthesis, characterization and catalytic activity of a new peroxomolybdenum(VI) complex-based coordination polymer by M. Afsharpour; A.R. Mahjoub; M.M. Amini (pp. 205-210).
A new form of polymeric compound of molybdenum, [MoO(O2)2.4,4′-bipy] n, was synthesized and characterized by infrared, ultraviolet, and nuclear magnetic resonance spectroscopes and thermal analysis, and have been used as a heterogeneous catalyst for the epoxidation of cyclohexene and cyclooctene at room temperature. Results showed that this catalyst has significant potential as an oxidant in oxygen atom transfer reactions. ▪A new form of polymeric compound of molybdenum, [MoO(O2)2.4,4′-bipy] n, was synthesized by a simple and inexpensive route and characterized by infrared, ultraviolet, nuclear magnetic resonance spectroscopes and thermal analysis. The prepared catalyst was used for the epoxidation of cyclohexene and cyclooctene in a heterogeneous system at room temperature. Results showed that the new form of MoO5 complex has significant potential as an oxidant in oxygen atom transfer reactions. This reagent oxidized olefins to epoxides in the presence of hydrogen peroxide with high conversions and selectivity. Effects of temperature, amount of catalyst, hydrogen peroxide and solvent in the epoxidation of substrate have been investigated. The stability of catalyst in epoxidation reactions has been investigated in homogenous system by recovering catalyst and recycling. Results showed that catalyst can be used at least for five consecutive cycles without a significant drop in yield.
Keywords: Heterogeneous catalysts; Peroxo molybdenum; Epoxidation
Mode of zeolite catalysts deactivation during chlorinated VOCs oxidation by M. Guillemot; J. Mijoin; S. Mignard; P. Magnoux (pp. 211-217).
The catalytic oxidation of tetrachloroethylene (PCE), chosen as model for chlorinated hydrocarbons, was investigated over Pt/HY, Pt/NaY and Pt/NaX under humid conditions at a space velocity of 15,300h−1. PCE is selectively transformed into CO2 and HCl over all catalysts studied in this work. 1.2%Pt/HY exhibits the highest activity with the complete conversion of PCE at 500°C and undergoes no significant deactivation after 4h of reaction. It was also highlighted in this work, that water vapour plays a preponderant role for PCE transformation and to limit catalyst deactivation. On the other hand, Pt/NaFAU catalysts are also active in PCE transformation but it appeared that 1%Pt/NaX underwent a high and rapid deactivation by the formation of NaCl clusters.▪The catalytic oxidation of tetrachloroethylene (PCE), chosen as model for chlorinated hydrocarbons, was investigated over Pt/HY, Pt/NaY and Pt/NaX under humid conditions at a space velocity of 15,300h−1. PCE is selectively transformed into carbon dioxide (CO2) and hydrochloric acid (HCl) over all catalysts studied in this work. 1.2%Pt/HY exhibits the highest activity with the complete conversion of PCE at 500°C and undergoes no significant deactivation after 4h of reaction. It was also highlighted in this work, that water vapour plays a preponderant role for PCE transformation and limits catalyst deactivation. On the other hand, platinum-exchanged sodic faujasites (Pt/NaFAU) are also active in PCE transformation but it appeared that 1%Pt/NaX underwent a high and rapid deactivation by the formation of sodium chloride (NaCl) clusters.
Keywords: Deactivation; Catalytic oxidation; Chlorinated VOCs; Zeolite; FAU
Structural, acidic and redox properties of V2O5/NbP catalysts by Qing Sun; Dongmei Fang; Suming Wang; Jianyi Shen; Aline Auroux (pp. 218-225).
A series of V2O5/NbP catalysts were prepared by the wetness impregnation method. The results showed that V2O5 could be well dispersed on the surface of NbP. The strength of surface acidity of NbP was decreased while the proportion of weak acid sites was increased upon the addition of V2O5 on NbP. The isopropanol conversion reaction and methanol oxidation reaction indicated that NbP possessed only surface acidity and weakened the redox properties of supported V2O5.▪V2O5 supported on niobium phosphate (NbP) with V2O5 loadings from 5 to 25wt% were investigated by using different techniques. The structural properties were characterized by O2 chemisorption, X-ray diffraction (XRD), Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). The surface acidity was determined by the techniques of microcalorimetry and infrared spectroscopy (FTIR) using NH3 as a probe molecule. Isopropanol (IPA) and methanol probe reactions in the presence of O2 were employed to provide the information about the surface acidity and redox property simultaneously. V2O5 is well dispersed on the surface of NbP according to the results from XRD and LRS with a V2O5 loading lower than 15wt%. The vanadium and niobium elements in V2O5/NbP catalysts were present in the +5 oxidization state as observed from XPS. Chemical adsorption of O2 showed that vanadia dispersed on NbP with about 60% dispersion. The results from NH3 adsorption microcalorimetry suggested that the loaded V2O5 weakened the surface acidity of NbP while increased the proportion of weak acid sites. The results from IPA conversion reaction pointed out that IPA only converted to dehydration products (propylene (PPE) and diisopropyl ether (DIPE)) on NbP. The addition of V2O5 on NbP led to an oxidative product acetone (ACE), but not as much as on bulk V2O5. These results indicated that NbP possessed only surface acidity and weakened the redox property of supported V2O5. Accordingly, NbP produced only dimethyl ether (DME) from the dehydration of methanol owing to the lack of redox property, while the V2O5/NbP catalysts produced mainly dimethoxymethane (DMM) due to its acidic-redox bi-functional character. Specifically, methanol was first oxidized on the redox sites of V2O5/NbP to produce formaldehyde (FA) which was then condensed with additional methanol on the acidic sites of V2O5/NbP to form DMM.
Keywords: V; 2; O; 5; /NbP catalyst; Adsorption microcalorimetry; Acidic and redox properties; Isopropanol probe reaction; Methanol probe reaction
Au/PO43−/TiO2 and PO43−/Au/TiO2 catalysts for CO oxidation: Effect of synthesis details on catalytic performance by Zhen Ma; Suree Brown; Steven H. Overbury; Sheng Dai (pp. 226-237).
Gold supported on titania (Au/TiO2) is a highly active catalyst for low-temperature CO oxidation, but high-temperature deactivation is a shortcoming that may constrain its use in car-emission control and organic combustion. Here, we attempted to address this problem using phosphate-doped Au/TiO2. Control experiments were performed to obtain an explicit picture on the impact of synthesis details.▪Supported gold catalysts are active for CO oxidation, but the high-temperature deactivation is a shortcoming that may constrain their applications. Herein, we attempted to address this problem by using phosphate-doped Au/TiO2 synthesized via two routes. In route I, Au/PO43−/TiO2 catalysts were prepared by treating TiO2 (Degussa P25) with diluted H3PO4, followed by loading gold via deposition-precipitation. In route II, PO43−/Au/TiO2 catalysts were prepared by treating H2-reduced Au/TiO2 with diluted H3PO4. These catalysts were systematically pretreated at 200 or 500°C before reaction testing. The overall CO conversion on 200°C-pretreated Au/PO43−/TiO2 or PO43−/Au/TiO2 was always lower than that on 200°C-pretreated Au/TiO2. However, the advantage of the phosphate addition became apparent after thermal treatment at a higher temperature. Both Au/PO43−/TiO2 and PO43−/Au/TiO2 pretreated at 500°C retained significant activities at room temperature, whereas 500°C-pretreated Au/TiO2 lost its activity. Control experiments and catalyst characterization were performed to investigate the impact of synthesis details on catalytic performance.
Keywords: Gold catalysis; CO oxidation; Titania; Phosphate; Dopant; Sintering; Deactivation
Pd–LaMnO3 as dual site catalysts for methane combustion by S. Cimino; M.P. Casaletto; L. Lisi; G. Russo (pp. 238-246).
Novel Pd–LaMnO3 combustion catalysts were developed which possess unique features: their dual site nature with matching operating ranges (low+mid/high temperature) makes them promising candidates for the development of fully catalytic or hybrid premixed radiant burners for both domestic and industrial applications with improved thermal efficiency and characterised by strongly discontinuous operation.▪Dual site Pd–LaMnO3 monolithic catalysts with different Pd loadings were prepared and tested in the high temperature lean premixed combustion of methane. It was shown that the novel catalysts effectively combine low and high temperature oxidation activity within a single system, which in turn has a wider operating window than Pd or LaMnO3 alone. In particular, evidence was found of a self-regenerative thermal activation process which restores Pd sites responsible for light-off at low temperature.Morphological and chemical analysis (SEM–EDS, BET, ICP-MS, XPS) of Pd–LaMnO3 catalysts were correlated to the results of extensive isothermal and self-sustained (steady state and transient) combustion tests in order to shed light on the nature of the catalytic species acting at different temperature levels, and on the reversible synergic interactions occurring between Pd and perovskite upon controlled thermal treatments or reaction ageing.
Keywords: Catalytic combustion; Palladium; Perovskite; Structured catalysts; Methane; Catalyst self-regeneration; Steady-state multiplicity
Non-sulfided nickel supported on silicated alumina as catalyst for the hydrocracking of n-hexadecane and of iron-based Fischer-Tropsch wax by R. de Haan; G. Joorst; E. Mokoena; C.P. Nicolaides (pp. 247-254).
Nickel(II) was introduced by wet impregnation onto a commercial silicated alumina (Siralox 40). TPR showed that the nickel oxide species was predominantly associated with the alumina phase present in the Siralox support. Hydrocracking of a model compound, n-hexadecane, and of iron-based Fischer-Tropsch was carried out over the non-sulfided Ni/Siralox 40 catalysts. The product selectivities obtained at different metal loadings, crystallite sizes and calcination temperatures are described. The results are also compared with those obtained with a commercial sulfided NiMo/SiO2-Al2O3 catalyst.▪Nickel(II) was introduced by wet impregnation onto a commercial silicated alumina (Siralox 40®, SiO2/Al2O3 mole ratio=1.1) and the physico-chemical properties of the calcined Ni/Siralox samples were determined by BET, H2 chemisorption, O2 back-titration and TPR. The latter technique showed that the nickel oxide species was predominantly associated with the alumina phase present in the Siralox support. Hydrocracking of a model compound, n-hexadecane, was carried out over the non-sulfided Ni/Siralox 40 catalysts at 345–360°C, WHSV=2.2h−1 and 55bar. At an average conversion of 41.3% and up to 144h on-stream, the 3.0% Ni/Siralox 40 catalyst (calcined at 300°C) gave a product spectrum that closely resembled “ideal hydrocracking” and produced low C1–C2 selectivities (∼1.8wt%). Increasing the metal loading to 4.5% resulted in an increase in the average metal crystallite size, and consequently, in higher C1–C2 selectivities of 11.5wt%. Calcination of the catalyst precursor at 500°C, however, afforded lower C1–C2 selectivies (3.1wt%), but the extent of secondary cracking was higher. In the hydrocracking of the iron-based Fischer-Tropsch wax over the 4.5% Ni catalyst (at 360°C, WHSV=2.8h−1, 70bar, and using an H2/feed (l/l) ratio of 8.0×102), a diesel selectivity of 74.9% was obtained at a conversion of 51.6%. These results compare favourably with those obtained with a commercial sulfided NiMo/SiO2-Al2O3 catalyst at 380°C. The non-sulfided Ni/Siralox catalyst, however, exhibited a higher hydrogenolysis activity.
Keywords: Non-sulfided; Nickel; Silicated alumina; Hydrocracking; n; -Hexadecane; Iron-based Fischer-Tropsch wax
Highly selective synthesis of acetylferrocene by acylation of ferrocene over zeolites by Martina Bejblová; Stacey I. Zones; Jiří Čejka (pp. 255-260).
Large-pore zeolites, particularly zeolite Beta, catalyze ferrocene acylation with acetic anhydride in a liquid phase with extremely high selectivity to mono-acetyl product. ▪Zeolites with different structure and concentration of acid sites were investigated in a liquid phase acylation of ferrocene with acetic anhydride. It was found that the conversion of ferrocene increased in the order: medium pore zeolites<1D large pore zeolites<3D large pore zeolites. Zeolite SSZ-33 with interconnecting 10 and 12-membered rings exhibited a slightly lower conversion compared with mordenite. The increase in the conversion of ferrocene was observed with decreasing Si/Al ratio for the given zeolite structure. Both Broensted and Lewis acid sites contribute to the catalytic activity of zeolites in ferrocene acylation. Mono-acylated ferrocene (acetylferrocene) was synthesized by this reaction with almost 100% selectivity.
Keywords: Acetylferrocene; Acylation; Zeolites; Structural types
Manganese oxide catalysts for NOx reduction with NH3 at low temperatures by Min Kang; Eun Duck Park; Ji Man Kim; Jae Eui Yie (pp. 261-269).
Manganese oxide catalysts were investigated for the low temperature selective catalytic reduction (SCR) of NOx with NH3. The active MnOx catalysts, precipitated with sodium carbonate and calcined in air at moderate temperatures such as 523K and 623K, have the high surface area, the abundant Mn4+ species, and the high concentration of surface oxygen on the surface. ▪Manganese oxide catalysts prepared by a precipitation method with various precipitants were investigated for the low temperature selective catalytic reduction (SCR) of NOx with NH3 in the presence of excess O2. Various characterization methods such as N2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and X-ray absorption near edge structure (XANES) were conducted to probe the physical and chemical properties of MnOx catalysts. The active MnOx catalysts, precipitated with sodium carbonate and calcined in air at moderate temperatures such as 523K and 623K, have the high surface area, the abundant Mn4+ species, and the high concentration of surface oxygen on the surface. The amorphous Mn3O4 and Mn2O3 were mainly present in this active catalyst. The carbonate species appeared to help adsorb NH3 on the catalyst surface, which resulted in the high catalytic activity at low temperatures.
Keywords: NO reduction; Manganese oxides; NH; 3; -SCR; Precipitation method; Calcinations
Characteristics and catalytic properties of [ t-BuNSiMe2Flu]TiMe2/dMMAO catalyst dispersed on various supports towards ethylene/1-octene copolymerization by Chanintorn Ketloy; Bunjerd Jongsomjit; Piyasan Praserthdam (pp. 270-277).
In the present study, the characteristics and catalytic properties of [ t-BuNSiMe2Flu]TiMe2/dMMAO catalyst dispersed on various supports towards ethylene/1-octene copolymerization were investigated. First, the dMMAO was impregnated onto various supports such as SiO2, SiO2–TiO2, and TiO2. Then, copolymerization of ethylene/1-octene was conducted with and without the presence of supports in different solvent mediums. It revealed that the SiO2–TiO2 support exhibited the highest activity among the other support. The high activity observed for the SiO2–TiO2 support can be attributed to fewer interactions between the support and dMMAO as confirmed by XPS and TGA results. It can be proposed that the different solvents can possibly alter the nature of catalyst in two ways; (i) changing the interaction between the support and cocatalyst and/or (ii) changing the form of active species i.e., active ion-pair and solvent-separated ion-pair as seen in the homogeneous system. However, there was no effect with regards to activity of the solvent mediums employed for the homogeneous system. It is worth noting that the Ti-complex rendered pronouncedly high incorporation of 1-octene having the triblock (OOO) and diblock (EOO) copolymers. The properties of copolymer by means of GPC, DSC, and 13C NMR were further discussed in more details.▪In the present study, the characteristics and catalytic properties of [ t-BuNSiMe2Flu]TiMe2/dMMAO catalyst dispersed on various supports towards ethylene/1-octene copolymerization were investigated. First, the dMMAO was impregnated onto various supports, such as SiO2, SiO2–TiO2, and TiO2. Then, copolymerization of ethylene/1-octene was conducted with and without the presence of supports in different solvent mediums. The SiO2–TiO2 support exhibited the highest activity among all the supports. The high activity observed for the SiO2–TiO2 support can be attributed to fewer interactions between the support and dMMAO, as confirmed by XPS and TGA results. The different solvents can alter the nature of the catalyst in two ways: (i) changing the interactions between the support and cocatalyst and/or (ii) changing the form of active species i.e., active ion-pair and solvent-separated ion-pair, as seen in the homogeneous system. However, there was no effect with regards to activity of the solvent mediums employed for the homogeneous system. It is worth noting that the Ti-complex made possible high incorporation of 1-octene having the triblock (OOO) and diblock (EOO) copolymers. The properties of copolymers by means of GPC, DSC, and13C NMR were further discussed in more detail.
Keywords: Metallocene catalyst; Copolymerization; Ti complex; Silica; Titania; Supports
Control of selectivity in phenol hydroxylation using microstructured catalytic wall reactors by Kunio Yube; Masashi Furuta; Nobuaki Aoki; Kazuhiro Mae (pp. 278-286).
The effects of phenol hydroxylation on the regioselectivity (the molar ratio of hydroquinone to catechol) using catalytic microreactors were investigated. The regioselectivity depends on the characteristics of the microreactor, such as catalyst placement and sizes of microchannels, and could be arranged linearly as a function of Sh number, expressed by the velocity u, microchannel height H, and microchannel length L.▪Selective hydroxylation of phenol to benzenediols with hydrogen peroxide aqueous solution over titanium silicalite-1 (TS-1) catalyst was performed using microstructured catalytic wall reactors. We investigated effects on the reaction results of various reaction conditions, such as reactant conversion and product selectivities were investigated. The regioselectivity of the parallel reactions, i.e., the molar ratio of para-diol (hydroquinone) to ortho-diol (catechol), is known to be dependent on the reaction parameters, such as temperature and reactant concentrations. In this study, we found that the selectivity also depends on the characteristics of the microreactor, such as catalyst placement and sizes of microchannels, which contributed significantly to the reactant concentrations on the catalyst surface. Especially, the selectivities changed markedly with increases in the height of microchannels. The results indicated that the regioselectivities could be arranged linearly as a function of Sh number, expressed by the velocity u and the design parameters of the microreactor, i.e., microchannel height H and microchannel length L.
Keywords: Microreactors; Heterogeneous catalyst; Selective oxidation; Hydroxylation of phenol
Catalytic oxidation of highly concentrated real industrial wastewater by integrated ozone and activated carbon by Lecheng Lei; Li Gu; Xingwang Zhang; Yaling Su (pp. 287-294).
A comparison among individual ozonation, GAC adsorption and their integration shows the significant synergistic effect occurs in the integrated process at basic pH conditions. No synergistic effect occurs at acid pH conditions. The pH value affects the reaction mechanism. The primary reaction mechanism at acidic conditions is adsorption–ozonation regeneration, while the primary mechanism at basic conditions is catalytic oxidation.▪Integration of ozone and granular activated carbon (GAC) was applied to treat highly concentrated real wastewater from chemical industry. The results revealed that the integrated process had more advantages than the individual ozonation and GAC adsorption. The integrated process enhanced COD removal, increased ozone utilization and avoided frequent GAC regeneration. The pH value was found to exert a great effect on COD removal; a positive effect on COD removal was more pronounced at basic conditions than at acidic conditions. Furthermore, there were some differences in reaction mechanisms at different pH conditions, as confirmed by FTIR and SEM analysis. At the acidic conditions, the primary reaction mechanism was adsorption–ozonation regeneration, while at the basic conditions, GAC adsorption ability was restrained, and the primary mechanism was catalytic oxidation.
Keywords: Industrial wastewater; Ozonation; GAC adsorption; Catalytic ozonation
Oxidation of mono- and bicyclic aromatic compounds with hydrogen peroxide catalyzed by titanium silicalites TS-1 and TS-1B by Daniele Bianchi; Rino D’Aloisio; Rossella Bortolo; Marco Ricci (pp. 295-299).
The hydroxylation of a series of mono- and bicyclic aromatic substrates with hydrogen peroxide was investigated using titanium silcalite TS-1 and a new catalyst (TS-1B) obtained by post-synthesis modification of TS-1. In most cases, TS-1B showed a better selectivity to the corresponding phenols, with respect to the conventional TS-1. ▪The hydroxylation of a series of oxygenated aromatic compounds (phenols and ethers) with hydrogen peroxide, catalyzed by titanium silicalite TS-1 and a new catalyst TS-1B, was investigated operating in a biphasic reaction medium.In several cases, the reaction afforded phenols with fairly good selectivity. TS-1B is often a better catalyst than the conventional TS-1, displaying higher selectivity on hydrogen peroxide and also higher shape selectivity. So it appears to have some potential in the direct synthesis of selected phenols, in alternative to the conventional multi-step methods.
Keywords: Arenes; Oxidation; Hydrogen peroxide; Titanium; Zeolites
The evaluation of the stability of Ni/MgO catalysts for the gasification of lignin in supercritical water by Takeshi Furusawa; Takafumi Sato; Masanari Saito; Yasuyoshi Ishiyama; Masahide Sato; Naotsugu Itoh; Noboru Suzuki (pp. 300-310).
The deactivation of catalyst during reuse test with Ni/MgO catalyst occurred regardless of regeneration treatments, and the reasons of deactivation were due to the presence of char-like carbonaceous products, the formation of Mg(OH)2 phase and the decrease in Ni metal surface area.▪The lignin gasification in supercritical water with 20wt.% Ni/MgO catalyst showed high catalytic performance, however, the deactivation of catalyst was observed when this catalyst was reused successively three times. The used catalyst was characterized by BET, XRD, TPR, CO chemical adsorption techniques, TPO and TEM observation, and the reasons of deactivation were discussed in detail. When the mixture of Ni/MgO catalyst and THF insolubles obtained in the previous run was used as a catalyst for the next run, the carbon yield of gas products considerably dropped due to the presence of char-like carbonaceous products and the formation of Mg(OH)2 phase. Moreover, the deactivation of catalyst was also observed even after used catalyst was regenerated by oxidation at 1023K for 1h and reduction at 1173K for 1h. The decrease in Ni metal surface area of catalyst treated by oxidation and reduction probably caused catalyst deactivation. The deactivation of catalyst during reuse test with Ni/MgO catalyst occurred regardless of regeneration treatments.
Keywords: Nickel catalyst; Gasification; Lignin; Reuse; Deactivation