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Applied Catalysis A, General (v.328, #1)
Etherification of glycerol and ethylene glycol by isobutylene by Katarína Klepáčová; Dušan Mravec; Alexander Kaszonyi; Martin Bajus (pp. 1-13).
The influence of catalyst, solvent and temperature on the etherification of glycerol and ethylene glycol with isobutylene in the liquid phase catalysed by strong acid ion-exchange resins of Amberlyst type (Amberlyst 15 and 35), p-toluenesulfonic acid and by two large-pore zeolites H-Y and H-Beta was studied. Reactions were carried out in the temperature range from 50 to 90°C at autogenous pressure in solvent (dioxane, dimethyl sulfoxide and sulfolane). The basic kinetic parameters for complex of 11 equilibrium reactions for glycerol and 5 equilibrium reactions for ethylene glycol were estimated. The highest conversion of glycerol was achieved on H-Beta, but on this catalyst the formation of tri- tert-butyl glycerol was sterically hindered. The highest amount of di- and tri-ethers was formed over Amberlyst 35. Over H-Y the reaction was slower due to its lower acidity, and final concentration of di- and tri-ethers was not achieved in monitored reaction time. p-Toluenesulfonic acid provides satisfactory results only when sulfolane was used as a solvent. The solvent plays an essential role because it can affect the investigated etherification reaction with its polarity and homogenization of reaction mixture. The concentration of glycerol and ethylene glycol higher ethers in end product can decrease as temperature increases showing that the side reaction of isobutylene dimerisation is more sensitive to temperature.
Keywords: Abbreviations; G; glycerol; IB; isobutylene; TBA; tert-; butyl alcohol; DIB; diisobutylene; TTBG; tri-; tert; -butyl ether of glycerol; DTBG1; 1,3-di-; tert; -butyl ether of glycerol; DTBG2; 1,2-di-; tert; -butyl ether of glycerol; MTBG1; 1-mono-; tert; -butyl ether of glycerol; MTBG2; 2-mono-; tert; -butyl ether of glycerol; EG; ethylene glycol; MEEG; mono-; tert; -butyl ether of ethylene glycol; DEEG; di-; tert; -butyl ether of ethylene glycol; A; Amberlyst; p; -TSA; p; -toluenesulfonic acid; X; conversionEtherification; tert; -Butylation; Glycerol; Ethylene glycol; Ion-exchange resin; Amberlyst; Zeolites; p; -Toluenesulfonic acid; Kinetics
Low temperature water–gas shift: The effect of alkali doping on the CH bond of formate over Pt/ZrO2 catalysts by John M. Pigos; Christopher J. Brooks; Gary Jacobs; Burtron H. Davis (pp. 14-26).
Addition of alkali dopants (e.g., Li, Na, and K) to Pt/ZrO2 low temperature water–gas shift catalysts led to an important weakening of the formate CH bond, as indicated by a shift to lower wavenumbers in infrared spectroscopy. Formate CH bond breaking is suggested to be the rate-limiting step of the mechanism, and enhanced WGS rates and formate decomposition rates are can be explained by formate CH bond weakening. ▪Using combinatorial methods, doping Pt/ZrO2 with alkali cations such as Li, especially Na, and K, was found to have a positive impact on the low temperature water–gas shift rate. In this investigation, DRIFTS results indicate that the alkali cation significantly shifts the formate CH band positions toward lower wavenumbers in the order K (2774cm−1)−1)−1)−1). Not only were the bands shifted, but the overall intensities were found to be higher with the addition of alkali promoter. Three separate tests were conducted to probe the stability of formates, including (1) steady state experiments at 225°C; (2) transient formate decomposition studies at 130°C in steam; and (3) dry hydrogen–deuterium exchange tests at 225°C. In each case, the alkali significantly impacted the formate decomposition rate, due to the weakening of the formate CH bond. The results suggest a new direction in water gas shift catalyst design.
Keywords: Zirconia (ZrO; 2; ); Platinum; Lithium (Li); Sodium (Na); Potassium (K); Alkali; Promoter; Dopant; Doping; Water–gas shift; Fuel processor; Hydrogen; Formate; Carbonate
Activity and selectivity control by niobium for the preferential oxidation of co on pt supported catalysts by S. Guerrero; J.T. Miller; E.E. Wolf (pp. 27-34).
The promotional effect of Nb on Pt supported on alumina or on niobia, was studied for the preferential oxidation of CO (PROX) in hydrogen. The results show a unique effect of Nb as a promoter to Pt. At low Nb loadings on Pt/alumina, the CO oxidation activity and selectivity are significantly increased. The CO selectivity is 100% at conversions up to about 60%. For Pt supported on Nb2O5, however, the CO oxidation activity is strongly suppressed with low CO conversion but high H2 oxidation activity. Pt on niobia, therefore, is poorly selective for the PROX reaction, but is an active hydrogen oxidation catalyst, resistant to CO poisoning. For Pt supported on highly loaded Nb-alumina or Nb2O5, XPS indicate an increase in the Pt and Nb oxidation states. These surface changes also correlate with changes in the DRIFTS spectra suggesting that CO is more weakly adsorbed on Pt/Nb2O5 compared to Pt/Al2O3, or Pt/Nb-Al2O3.The activity of niobia supported platinum catalysts have been studied during the preferential oxidation of CO (PROX) in a hydrogen rich flow. The results reported here show a unique effect of niobium as a catalyst, which can either acts as a promoter or as inhibitor depending on niobia content. Increasing the niobia content increases the oxidation states of Pt and Nb affecting also their binding energies.▪
Keywords: PROX reaction; Pt supported catalyst; Nb promoter
Theoretical study of methane reforming on molybdenum carbide by Hiroyuki Tominaga; Masatoshi Nagai (pp. 35-42).
The adsorption of methane and the subsequent reaction of two dissociatively adsorbed CH3 species on a β-Mo2C (001) slab to form either ethylene or ethane were studied using density functional theory (DFT) calculations. Four methane-adsorption models of β-Mo2C (001) with different methane adsorption profiles were investigated. Following structural optimization for adsorption, methane was dissociated into CH3 and H at the three-fold site for the surface Mo atoms, without the underlying carbon atoms of the second layer and the two-fold site position for the surface Mo atoms before optimization. For the two adsorption positions, the adsorption energy of methane was identical at 289kJ/mol. The other two adsorption positions were unstable relative to these two positions. After optimization of the two methanes for dissociation into 2CH3 and 2H, with one CH3 approaching the another CH3, C2H5 (Intermediate 2) was formed, together with the formation of ethylene through the release of one hydrogen. The first principle molecular dynamics (MD) of Intermediate 2 produced ethylene with one hydrogen, while the MD of Intermediate 2 with the addition of two hydrogen molecules produced ethane following the restricted attack of one hydrogen on the C2H5 species at approximately 2Å from the surface after its desorption.▪The adsorption of methane and the subsequent reaction of two dissociatively adsorbed CH3 species on a β-Mo2C (001) slab to form either ethylene or ethane were studied using density functional theory (DFT) calculations. Four methane-adsorption models of β-Mo2C (001) with different methane adsorption profiles were investigated. Following structural optimization for adsorption, methane was dissociated into CH3 and H at the three-fold site for the surface Mo atoms, without the underlying carbon atoms of the second layer and the two-fold site position for the surface Mo atoms before optimization. For the two adsorption positions, the adsorption energy of methane was identical at 289kJ/mol. The other two adsorption positions were unstable relative to these two positions. After optimization of the two methanes for dissociation into 2CH3 and 2H, with one CH3 approaching the another CH3, C2H5 (Intermediate 2) was formed, together with the formation of ethylene through the release of one hydrogen. The first principle molecular dynamics (MD) of Intermediate 2 produced ethylene with one hydrogen, while the MD of Intermediate 2 with the addition of two hydrogen molecules produced ethane following the restricted attack of one hydrogen on the C2H5 species at approximately 2Å from the surface after its desorption.
Keywords: DFT; Ethane; Ethylene; First principle molecular dynamics; Methane; Reforming
Synthesis and characterization of mesoporous silica-supported nano-crystalline sulfated zirconia catalysts prepared by a sol–gel process: Effect of the S/Zr molar ratio by R. Akkari; A. Ghorbel; N. Essayem; F. Figueras (pp. 43-51).
Mesoporous silica-supported nano-crystalline sulfated zirconia catalysts were prepared via the sol–gel process using in situ sulfation. The parameter studied was the S/Zr molar ratio. Two gelation mechanisms were evidenced depending on this ratio. Appreciable catalytic properties in the n-hexane isomerization reaction were observed when the sample presents small size of sulfated zirconia crystallites and both Brönsted and Lewis acidities. ▪Mesoporous silica-supported nano-crystalline sulfated zirconia catalysts were prepared via the sol–gel process using an in situ sulfation. The parameter studied in this work was the S/Zr molar ratio. The synthesized solids were characterized using XRD, N2 physisorption, TG-DTA/SM, sulfur chemical analysis and adsorption–desorption of pyridine, and tested in the gas-phase acid-catalysed isomerization of n-hexane. The gelation process is highly affected by the sulfate loadings. Two gelation mechanisms were evidenced depending on the S/Zr molar ratio. The first one observed when 0.15≤S/Zr≤0.5, is characterized by a relatively high gelation rate. This mechanism favours the formation of two types of mesopores and a low percentage of retained sulfur. The second gelation mechanism occurs for higher S/Zr ratios: 0.5≤S/Zr≤1.2. In that case, slower gelation rates are observed. This slower gelation process leads to materials with reduced BET surface area but the amount of retained sulfur is increased. Appreciable catalytic properties were observed for the sample prepared with the highest S/Zr ratio, which presents the smallest size of sulfated zirconia crystallites and shows both Brönsted and Lewis acid sites on its surface.
Keywords: Sulfated zirconia; Nano-crystalline; Silica; n; -Hexane; Acidity
Catalytic oxidative polymerization of aniline by using transition-metal tetrasulfonated phthalocyanine by M.R. Nabid; R. Sedghi; P.R. Jamaat; N. Safari; A.A. Entezami (pp. 52-57).
A new enzymatic approach was developed to synthesize water-soluble conducting polyaniline (PANI) in the presence of sulfonated polystyrene. There exists a need to develop a more robust mimetic catalyst alternative for enzyme. Different water-soluble metallophthalocyanines as a cost-effective and stable catalyst were used for the polymerization of aniline. The catalytic behavior of these phhtalocyanines depends upon different parameters, such as acidity of solvent and concentration of monomer, catalyst, etc.▪This is the first report on the polymerization of aniline by using water-soluble transition-metal tetrasulfonated phthalocyanine (TSPc). The polymerization performed at the presence of the sulfonated polystyrene as a template and water-soluble, conducting polyaniline (PANI) was obtained. The reactions were carried out with different catalysts, such as iron, cobalt and manganese phthalocyanine. For Fe-TSPc, the yield and rate of polymerization of aniline are highest compared to other methallo phthalocyanine. The reactions carried out with different pH, monomer, catalyst, template and initiator concentrations and the best conditions are reported. The formation of conducting and electroactive form of the polyaniline was confirmed through UV–vis and FT-IR spectroscopy, four-point probe conductivity measurements and cyclic voltammetry.
Keywords: Polyaniline; Tetrasulfonated phthalocyanine; Oxidative polymerization; Water-soluble
HDN and HDS of model compounds and light gas oil derived from Athabasca bitumen using supported metal phosphide catalysts by Ibrahim I. Abu; Kevin J. Smith (pp. 58-67).
The HDN and HDS activity of supported Co0.4Ni2P and Ni0.3MoP is reported. Increased support acidity (Al2O32O30.3MoP/Al2O3 had higher activity than a conventional Ni-Mo-S catalyst, whereas the low activity of Co0.4Ni2P/Al2O3 is related to a high S uptake during reaction.▪Co0.4Ni2P and Ni0.3MoP catalysts, supported on Al2O3, fluorinated Al2O3 (Al2O3-F) and Mobil Catalytic Material (MCM-41), have been prepared from metal phosphate precursors by temperature-programmed reduction (TPR) to 1200K. The catalysts have been characterized and their activity determined for the hydrodenitrogenation (HDN) of carbazole, the hydrodesulphurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the HDN and HDS of a light gas oil (LGO) derived from Athabasca bitumen. The formation of metal phosphides after TPR was confirmed by both X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The acidity of the catalysts, as measured by n-propylamine uptake, was determined by the support acidity and increased in the order Al2O32O3-F0.4Ni2P/Al2O3 catalyst promoted the direct desulphurization of 4,6-DMDBT at 583K and 3.0MPa H2 compared to Ni2P/Al2O3, and the Ni0.3MoP/Al2O3 catalyst had the highest selectivity (83%) for bicyclohexyl (BCHX) among the catalysts tested for the HDN of carbazole at the same conditions. The Ni0.3MoP/Al2O3 also had the highest activity for both the HDN and HDS of LGO, compared to Co0.4Ni2P/Al2O3 and a conventional NiMoS/Al2O3 catalyst that also contained P. The low activity of the Co0.4Ni2P/Al2O3 catalyst was attributed to low metal dispersion, a high S uptake and the possible formation of less active phosphosulphide species such as NiPS3, on this catalyst.
Keywords: Transition metal phosphide; Catalyst; Hydrodesulphurization; Hydrodenitrogenation; Carbazole; 4,6-Dimethyldibenzothiophene; Athabasca bitumen
SILCA—Supported ionic liquid catalysts for fine chemicals by Jyri-Pekka T. Mikkola; Pasi P. Virtanen; Krisztian Kordás; Hannu Karhu; Tapio O. Salmi (pp. 68-76).
Various ionic liquids (ILs), together with Pd-metal species were immobilized on a high-surface area, structural active carbon cloth. The resulting SILCA (supported ionic liquid catalyst) catalysts were studied in the production of fine chemicals, i.e. in the hydrogenation of unsaturated aldehydes, citral and cinnamaldehyde. In this paper we illustrate the feasibility of altering the selectivity profiles, not only by means of altered reaction conditions but also by variation of the nature of the IL present in the catalytic layer. ▪Various ionic liquids (ILs), together with Pd-metal species were immobilized on a high-surface area, structural active carbon cloth. The resulting SILCA (supported ionic liquid catalyst) catalysts were studied in the production of fine chemicals, i.e. in the hydrogenation of unsaturated aldehydes, citral and cinnamaldehyde. These model molecules are challenging ones, due to the possibility of several parallel and consecutive reactions that can occur, depending on the experimental conditions and the nature of the catalyst. In this paper we illustrate the feasibility of altering the selectivity profiles, not only by means of altered reaction conditions but also by variation of the nature of the IL present in the catalytic layer. The catalysts were characterized by means of, e.g. nitrogen physisorption, XPS as well as FESEM and EFTEM. The results revealed that Pd derived from a Pd(acac)2-precursor, initially dissolved into the ionic liquid, undergoes a change of oxidation state from Pd2+ to Pd4+, regardless of the ionic liquid in question. However, upon decomposition of the precursor, at 373K, under H2-flow, a transition to either Pd+ or Pd0 occurred, indicating the formation of catalytically active Pd complexes or nano particles, respectively.
Keywords: Supported ionic liquids; Heterogeneous catalysis; Fine chemicals; Hydrogenation
Monolithic microfibrous nickel catalyst co-modified with ceria and alumina for miniature hydrogen production via ammonia decomposition by Ye Liu; Hong Wang; Jianfeng Li; Yong Lu; Haihong Wu; Qingsong Xue; Li Chen (pp. 77-82).
Non-woven microfibrous nickel catalysts modified with trace alumina and/or ceria were fabricated and examined in ammonia decomposition. The modification treatments could provide a 2-fold promotion of ammonia conversion compared with the neat microfibrous nickel. Roughly 20W power output hydrogen (∼220mL/min) could be achieved with >99% ammonia conversion in a bed volume of 0.9mL at 650°C.▪A non-woven microfibrous structure with 15vol% 8μm diameter nickel fibers was built using wet-lay papermaking and sintering processes. Surface of the sinter-locked nickel fibers was then chemically modified with Al2O3 and CeO2, by immersing this novel microfibrous metallic media in a 65°C aqueous solution containing each of Al(NO3)3·6H2O and Ce(NO3)3·6H2O or both of them for 2 or 4h at a constant metal ion concentration of 0.5mol/L. Chemical modifications provided a significant increase of the surface nickel atoms per gram catalyst but obviously suppressed the activity of the metallic nickel sites as indicated by the lowered TOF values. The chemical modification with a mixture solution with the optimal Al3+/Ce3+ ratio of 9 resulted in a 10-fold increase of the surface nickel atoms per gram catalyst but a 3-fold decrease of the TOF of ammonia, compared with the neat microfibrous nickel substrate. This chemically modified catalyst was capable of producing roughly 20W power hydrogen with >99% ammonia conversion at 650°C in a bed of 0.9mL throughout a 100h continuous test. Activation energies ( Ea) for microfibrous nickel catalysts were all alike in range from 103 to 105kJ/mol, suggesting that the active site nature was not changed by the chemical modification treatments.
Keywords: Microfibrous catalyst; Nickel; Hydrogen production; Ammonia; Fuel cells
Hydroformylation of higher olefin in halogen-free ionic liquids catalyzed by water-soluble rhodium–phosphine complexes by Qi Lin; Weidong Jiang; Haiyan Fu; Hua Chen; Xianjun Li (pp. 83-87).
The biphasic hydroformylation of higher olefins catalyzed by water-soluble rhodium complexes has been efficiently performed in halogen-free ionic liquids [Rmim][ p-CH3C6H4SO3]. The catalytic system shows high activity and chemoselectivity for aldehyde and the ionic liquid containing catalyst can be reused several times without a significant decrease in the activity and selectivity. The reaction rate is strongly dependent on the cation and anion of ionic liquids used.▪The biphasic hydroformylation of higher olefins was performed efficiently in the halogen-free ionic liquids 1- n-alkyl-3-methylimidazolium p-toluenesulfonate ([Rmim][ p-CH3C6H4SO3]) using Rh-TPPTS [TPPTS: trisodium salt of tri( m-sulphonylphenyl)phosphine] complexes as catalyst. The catalytic system offers high activity and chemoselectivity for aldehyde with a good retention of the catalyst in ionic liquid phase. The ionic liquid containing catalyst can be easily separated and reused several times without a significant decrease in the activity and selectivity. The results indicated that the cation and anion of ionic liquids strongly influenced the reaction rate. Furthermore, the reaction rate was markedly accelerated when the chain-length of alkyl in ionic liquids was comparable with that of olefin. A “matching effect” between the chain-length of alkyl in ionic liquids and that of olefins was firstly reported.
Keywords: 1-; n; -alkyl-3-methylimidazolium; p; -toluenesulfonate; Ionic liquid; Hydroformylation; Water-soluble rhodium–phosphine complexes
Structure and catalytic properties of molybdenum sulfide nanoplatelets by Nora Elizondo-Villarreal; Rodrigo Velázquez-Castillo; Donald H. Galván; A. Camacho; Miguel José Yacamán (pp. 88-97).
A nanostructured form of molybdenum disulfide/dioxide was prepared by a two-step hydrothermal/gas phase reaction carried at high-temperature sulfidation of molybdenum in H2S/H2. Image of HAADF-STEM shows that the lines of contrast appear with a saw tooth contrast. The number of adsorption sites is incremented by the presence of kinks at the edges of the nanoplatelets.▪A nanostructured form of molybdenum disulfide/dioxide was prepared by a two-step hydrothermal/gas phase reaction carried at high-temperature sulfidation of molybdenum in H2S/H2 for 2h. The material was composed of a solid MoO2 core with MoS2+ x crystallites nucleating on its surface. Most of the MoS2+ x have the shape of a single stacked platelet, which are 12–30nm long and are about one MoS2 unit cell wide. High-resolution electron microscopy (HREM), energy-dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM), in high-angle annular dark-field (HAADF). Electron diffraction (EDX) in the transmission electron microscope and X-ray diffraction were used to characterize the structure of the catalysts. It is found that the sample consists of MoS2+x nanoplatelets with unit cell thickness which are exfoliated and are free to rotate along the basal plane. In addition, the edges of the platelets become very rough increasing the number of adsorption sites. The structure–catalytic properties of MoS2+ x for hydrogenation over sulfur removal were observed in the hydrodesulphurization (HDS) reaction of dibenzothiophene (DBT). It was found that nanoplatelets have a very high catalytic activity for HDS. The number of adsorption sites is incremented by the presence of steps and kinks at the edges of the nanoplatelets.
Keywords: Electron microscopy; Molybdenum sulfide nanoplatelets; Hydrodesulphurization