Applied Catalysis A, General (v.466, #C)

Contents (iii-xii).

Efficient and reusable Co/nitrogen doped hollow carbon sphere catalysts for the aerobic oxidation of styrene by Isaac Nongwe; Vilas Ravat; Reinout Meijboom; Neil J. Coville (1-8).
Display OmittedMonodispersed hollow carbon spheres (HCSs) were made by decomposition of gaseous CH3CN over silica Stöber spheres in a CVD reaction. The nitrogen doped HCSs (N  = 8.7%) were used as support for well dispersed Co3O4 nanoparticles (7–8 nm; 1% and 2% Co). The Co/N-HCS samples were calcined at various temperatures. The materials calcined at 300 °C for 3 h were found to oxidize styrene to styrene oxide (styrene epoxidation) using dry air as oxidant (120 °C/DMF) with 99% styrene conversion and 85% selectivity to styrene oxide; they could also be reused in repeat catalytic reactions.
Keywords: Nitrogen doped carbons; Hollow carbon sphere; Cobalt oxide; Nanoparticles; Styrene oxidation;

Structural characterisation of Ni/alumina reforming catalysts activated at high temperatures by Cristina Jiménez-González; Zouhair Boukha; Beatriz de Rivas; Juan José Delgado; Miguel Ángel Cauqui; Juan Ramón González-Velasco; Jose Ignacio Gutiérrez-Ortiz; Rubén López-Fonseca (9-20).
This paper is devoted to the characterisation of Ni/alumina reforming catalysts. A special attention was paid to the control of the catalytic properties by the synthesis route of bulk and supported catalysts. In this sense it was shown that the massive formation of NiAl2O4 phase, associated with low NiO/NiAl2O4 molar ratios on the catalyst surface, due to a calcination step at high temperatures was notably beneficial for obtaining highly dispersed nickel catalysts (with a Ni crystallite size of 6 nm) after severe reduction at 850 °C. This activation procedure did not affect textural and acidic properties to a large extent. Thus, among the investigated nickel catalysts the 70%NiAl2O4/Al2O3 sample exhibited the best performance in the steam reforming of methane.
Keywords: Nickel aluminate; Alumina supported nickel catalyst; Characterisation; Methane steam reforming;

Two alternative routes for 1,2-cyclohexanediol synthesis by means of green processes: Cyclohexene dihydroxylation and catechol hydrogenation by Claudia Antonetti; Anna Maria Raspolli Galletti; Pasquale Accorinti; Stefano Alini; Pierpaolo Babini; Katerina Raabova; Elena Rozhko; Aurora Caldarelli; Paolo Righi; Fabrizio Cavani; Patricia Concepcion (21-31).
In this paper we compare two different reactions, aimed at the synthesis of 1,2-cyclohexanediol. Specifically: (a) the direct epoxidation and hydrolysis (dihydroxylation) of cyclohexene to trans-1,2-cyclohexanediol, with an aqueous solution of hydrogen peroxide, and (b) the hydrogenation of catechol to a mixture of cis and trans-1,2-cyclohexanediol, in an attempt to establish green protocols for the synthesis of diols. Both reactions, the dihydroxylation of cyclohexene and the hydrogenation of catechol, were carried out without organic solvents. In the former case, an unprecedented 97.4% yield to the glycol was obtained, by selecting proper reaction conditions and using a tungstic acid/phosphoric acid catalyst, in a biphasic system with a phase-transfer agent. In the second approach, a heterogeneous alumina-supported Ru(OH) x catalyst was used, and a 90% yield to the glycol was obtained. A comparison of the two processes allowed to show the lower environmental impact of the catechol hydrogenation route.
Keywords: Cyclohexene dihydroxilation; 1,2-Cyclohexanediol; Catechol hydrogenation; Tungstate catalyst; Supported ruthenium hydroxide;

Solvent-free hydrothermal synthesis of anatase TiO2 nanoparticles with enhanced photocatalytic hydrogen production activity by Ayad F. Alkaim; Tarek A. Kandiel; Falah H. Hussein; Ralf Dillert; Detlef W. Bahnemann (32-37).
TiO2 nanoparticles exhibiting large surface area were synthesized by the hydrothermal treatment of the water soluble titanium(IV) bis(ammoniumlactato) dihydroxide (TALH) complex in the presence of aqueous ammonia. The obtained powders were characterized by X-ray diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, and nitrogen adsorption. Their photocatalytic activities were assessed by the photocatalytic hydrogen evolution from aqueous EDTA solutions. The effects of Pt- and photocatalyst loading, EDTA concentration, light intensity, pH, and temperature on the H2 evolution rate were studied in detail. The highest reaction rate was obtained for the TiO2 photocatalyst loaded with 0.4–0.5 wt.% Pt at pH 5 and this was found to be 18 and 34% higher than that of TiO2 P25 and TiO2 UV100, respectively. The reaction rate increased substantially with increasing the temperature from 5 °C to 45 °C.
Keywords: TiO2; Photocatalytic hydrogen production; EDTA; Photocatalysis; Anatase nanoparticles;

The NaOH-cationic micellar system was employed for selective cross aldol condensation of benzaldehyde with n-heptanal in equimolar amount to synthesize jasminaldehyde (90%).The efficiency of NaOH-cationic micellar systems was demonstrated for selective cross aldol condensation of benzaldehyde with n-heptanal (as model reaction, which involves cross and self condensation reactions) in equimolar amount to synthesize jasminaldehyde (cross product) with high selectivity. In comparison of biphasic reactions in NaOH aqueous solution (in absence of surfactant), the aldol reactions in NaOH-micellar solution were faster and selective to cross product without consumption of NaOH. The reaction rate and jasminaldehyde selectivity was observed to be influenced by surfactant concentration and reaction temperature. The equimolar reaction of both aldehydes in NaOH-cetyltrimethyl ammonium bromide (CTAB: 200 mM) aqueous solution resulted to highest conversion of n-heptanal (99%) with 90% selectivity to jasminaldehyde within 4 h. The reusability of NaOH-CTAB system was examined for five reaction cycles.
Keywords: Cross aldol condensation; Base catalysis; Jasminaldehyde; Cetyltrimethyl ammonium bromide; Micelles; Micellar catalysis; Reuse of micellar solution and NaOH;

Carboxylic acids are valuable chemical products, which can be produced efficiently by catalytic oxidation of various organic compounds using vanadium-based catalysts. Degradation resistance of carboxylic acids under applied reaction conditions is an important factor influencing selectivity of such reactions. This paper addresses the oxidative and non-oxidative gas phase degradation of formic, acetic and propionic acids over V2O5/TiO2 and MoVTeNb mixed oxides. Formic acid has been found to undergo mainly acid catalyzed decarbonylation, regardless the presence or absence of oxygen in the feed. Both acetic and propionic acids underwent oxidation (in aerobic conditions) through one-carbon degradation steps until CO and CO2 were produced. The mechanistic aspects of these transformations are discussed. The key intermediacy of 2-(hydro)peroxy carboxylic acids is suggested, based on the nature of primary reaction products. The catalytic activity of MoVTeNb mixed oxides toward oxidative and non-oxidative degradation of acetic and propionic acids appeared notably lower compared to that of V2O5/TiO2. This may be linked to the enhanced efficiency of the former catalyst in selective oxidation of organic substrates to carboxylic acids.
Keywords: V2O5/TiO2; Mo–V–Te–Nb mixed oxides; Formic acid; Acetic acid; Propionic acid; Degradation; Oxidative degradation;

The photocatalytic activities of several Bi2WO6 and TiO2/Bi2WO6 materials with different activated carbon (AC) contents were studied for Rhodamine B (RhB) (and Phenol) photodegradation under UV–vis and vis illumination. A wide characterization of the materials was carried out. The addition of AC strongly affected the Bi2WO6 morphology although not the crystalline phase. Even in the material with the lowest AC content (2 wt% nominal content) a structure with hierarchical porosity was formed. AC presence increased the initial reaction rates in the degradation of RhB. An important improvement in the photoactivity under both UV–vis and vis illumination conditions was obtained with the lowest AC content (2 wt%) when compared to the pristine material Bi2WO6 or to the systems with higher AC additions. AC/TiO2/Bi2WO6 materials were also improved in comparison to the TiO2/Bi2WO6 heterostructure without carbon. The improvement cannot be only ascribed to adsorption capability and surface area effects. A mechanism explaining the role of AC on the photocatalytic activity improvement is proposed.
Keywords: Photocatalysis; Rhodamine B; Bismuth tungstate; Sunlike;

Clay entrapped Cu(OH) x as an efficient heterogeneous catalyst for ipso-hydroxylation of arylboronic acids by Bashir Ahmad Dar; Prince Bhatti; A.P. Singh; Anish Lazar; Parduman R. Sharma; Meena Sharma; Baldev Singh (60-67).
A remarkably active, selective and stable montmorilonite-KSF entrapped Cu(OH) x catalyst, has been prepared for the ipso-hydroxylation of arylboronic acids under ambient conditions without requirement of any ligand or base. This catalyst shows excellent reusability without leaching and any significant loss in catalytic activity. The catalyst was characterized using, XRD, SEM, TPR, IR, XPS and BET surface area measurement techniques.
Keywords: Phenols; Heterogeneous catalysis; Clay; Copper; Water chemistry;

Water-resistant Fe–Ca–O x /TiO2 catalysts for low temperature 1,2-dichlorobenzene oxidation by Xiaodong Ma; Jinshan Shen; Weiya Pu; Hongwen Sun; Qin Pang; Jie Guo; Ting Zhou; Huiqin Cao (68-76).
Fe–Ca–O x /TiO2 composite catalysts were synthesized to develop a low-temperature and water-resistant technology for the catalytic oxidation of 1,2-dichlorobenzene (o-DCB), as a model of chlorinated volatile organic compounds. The composite catalysts were characterized by XRD, TEM, N2 adsorption/desorption and H2-TPR. Activity measurements were conducted in the range of 200–500 °C, in both the presence and absence of water. It was found that the incorporation of FeO x on TiO2 could significantly improve the catalytic activity, but the activity was remarkably inhibited over a broad temperature range centered at 300 °C due to the existence of water. Simultaneous incorporation of Fe and Ca oxide (Fe–Ca–O x ) on TiO2 could not only further improve the catalytic activity but also enhance the performance of water-resistance in the wet reaction. Among the tested catalysts, the catalyst with Fe–Ca–O x loading of 7 wt% showed the highest catalytic activity. The total conversion of o-DCB could be obtained at 350 °C, in both the dry and wet reaction. The catalytic oxidation of o-DCB over TiFeCa-7 followed first-order kinetics with an apparent activation energy of 32 kJ/mol. The surface acidity of the catalyst and the intermediate species in the reaction were investigated by in situ FTIR spectroscopy. It is proposed that o-DCB molecule should be preferentially adsorbed on the Lewis acid sites, forming partial oxidation products, which could be subsequently oxidized to form final products.
Keywords: Chlorinated volatile organic compounds; 1,2-Dichlorobenzene; Catalytic oxidation; Water-resistance; Fe–Ca–O x /TiO2;

Cu-based catalysts are often used for the production of C2 oxygenates or hydrocarbons from syngas, although numerous studies have been reported, the exact mechanism remains in debate, and presents a major challenge in catalysis. In this study, the preference mechanism for C―C chain formation of C2 oxygenates and the role of promoters in syngas conversion on Cu(2 1 1) and metal-doped MCu(2 1 1) (M = Rh, Ni) surfaces, including CH x (x  = 1–3) hydrogenation, dissociation and coupling, as well as CO or CHO insertion into CH x (x  = 1–3), have been systematically investigated by using density functional theory method. Our results show that pure Cu(2 1 1) surface shows a better catalytic activity to C2H4 formation rather than C2 oxygenates. However, promoters Rh and Ni-doped Cu(2 1 1) surfaces show a better activity and selectivity to C2 oxygenates rather than hydrocarbons, in which CH2 species is responsible for C2 oxygenates formation by CHO insertion. In addition, the difference between CO and CHO insertion into CH x (x  = 1–3) to form C2 oxygenates is mainly attributed to the HOMO–LUMO gap of CH x ―CHO and CH x ―CO, the smaller HOMO–LUMO gap greatly facilitates the charge transfer and hybridization between adsorbed species and catalysts.
Keywords: C2 oxygenates; Mechanism; Cu(2 1 1); Metal-doped Cu(2 1 1); Density functional theory;

An in situ methylation of toluene using syngas over bifunctional mixture of Cr2O3/ZnO and HZSM-5 by Seulah Lee; Donguk Kim; Jihye Lee; Yeseul Choi; Young-Woong Suh; Changq Lee; Tae Jin Kim; Seong Jun Lee; Jung Kyoo Lee (90-97).
The in situ methylation of toluene using syngas (in situ methylation hereafter) was studied to produce xylenes over bifunctional catalysts comprising Cr2O3/ZnO (CrZ) and HZSM-5 (SiO2/Al2O3  = 30) in a fixed-bed down-flow reactor at 460 psig. In this study, three basic aspects in the in situ methylation were investigated: (1) the catalytic activity of CrZ as the methanol synthesis catalyst with respect to the equilibrium conversion, (2) the evaluation of catalytic synergies in the in situ methylation over bifunctional catalyst, and (3) the effect of the ratio of catalytic functions regarding the ratio of methanol synthesis catalyst to HZSM-5, and their intimacy. The CrZ catalyst exhibited very low CO conversion to methanol in the methanol synthesis reaction, which is controlled by the equilibrium. However, the bifunctional mixture of CrZ and HZSM-5 catalysts exhibited significant catalytic synergies in the in situ methylation in terms of catalytic activity and product selectivities, with about a 10-times-higher CO conversion rate, and 2- to 3-times-higher toluene conversion and xylene production rates compared to the monofunctional catalysis of methanol synthesis and toluene disproportionation, respectively. The in situ methylation also gave rise to higher catalytic performance than in typical toluene methylation conducted with a molar feed ratio of methanol/toluene of 0.5. The catalytic synergy was manifested when both metallic and acidic functions were brought into close intimacy with a weight ratio of CrZ/HZSM-5 close to one in the in situ methylation.
Keywords: Syngas; Toluene methylation; Methanol synthesis catalyst; Cr2O3/ZnO; HZSM-5; Bifunctional catalyst; Xylenes production;

A series of MOF-based catalysts, metal-salen complexes incorporated into amino-functionalized MIL-101 matrices by salicylaldehyde condensing to amino group and coordinating metal ion through one pot method, have been prepared and characterized. The successful preparation of catalysts demonstrates that postsynthetic modification (PSM) is a practical and powerful route to generate MOF-based catalyst with multiple active sites. The catalytic performances of prepared catalysts were investigated via selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA-oil) by molecular oxygen in the absence of solvent. It was found that NH2-MIL-101(Cr)-Sal-Co, as a typical case, behaves as cooperative catalyst for cyclohexane selective oxidation. That is, salen-Co(II) attached to framework of MOF is able to assist in the generation of new radicals from peroxides via a Haber–Weiss catalytic cycle to promote conversion of cyclohexane while framework Cr ion is able to catalyze the dehydration of intermediate product cyclohexyl hydroperoxide (CHHP) to improve KA-oil selectivity. Furthermore, this catalyst exhibits good recyclability and behaves as truely heterogeneous catalyst.
Keywords: Metal-organic framework; Postsynthetic modification; Metal-salen; Cooperative catalyst; Cyclohexane selective oxidation;

Effects of Si/Al ratio and Pt loading on Pt/SAPO-11 catalysts in hydroconversion of Jatropha oil by Ning Chen; Shaofeng Gong; Hisakazu Shirai; Toshitaka Watanabe; Eika W. Qian (105-115).
A series of Pt/SAPO-11 catalysts were prepared with various Si/Al ratios and Pt loadings and characterized by using BET, XRD, XRF, and CO pulse adsorption, as well as 29Si NMR and NH3-TPD techniques. Their catalytic performances in hydroconversion of Jatropha oil were tested with a fixed-bed flow reactor system. The isomerization activity increased with the Si/Al ratio because there were more medium acidic sites on the SAPO-11 supports. Pt/SAPO-11 catalysts with a Si/Al ratio of 0.4 demonstrated high activity for both deoxygenation and isomerization among catalysts with the same Pt loading. The deoxygenation, isomerization and cracking activities strongly depended on the Pt loading. The best activity was observed for the sample with a 3 wt% Pt loading, which generated an 83% yield of iso-C15-18 hydrocarbons under the LHSV of 0.5 h−1. Based on the mechanistic study of hydroconversion of methyl oleate, a reaction network for the hydroconversion of Jatropha oil was suggested.
Keywords: SAPO-11; Si/Al ratio; Pt loading; Jatropha oil hydroconversion; Methyl oleate;

Efficient conversion of levulinic acid into alkyl levulinates catalyzed by sulfonic mesostructured silicas by J.A. Melero; G. Morales; J. Iglesias; M. Paniagua; B. Hernández; S. Penedo (116-122).
Sulfonic mesoporous silicas have demonstrated an outstanding catalytic performance in the esterification of levulinic acid with different alcohols to produce alkyl levulinates, a family of chemicals considered to be excellent oxygenated fuel extenders for gasoline, diesel and biodiesel. Catalyst screening indicated that propylsulfonic acid-modified SBA-15 material was the most active one, among tested materials, due to a combination of moderately strong sulfonic acid sites with relative high surface hydrophobicity. Under optimized reaction conditions (T  = 117 °C, ethanol/levulinic acid molar ratio = 4.86/1 and catalyst/levulinic acid = 7 wt%) almost 100% of levulinic acid conversion was achieved after 2 h of reaction, being negligible the presence of levulinic acid by-products or ethers coming from intermolecular dehydration of alcohols. The catalyst has been reused, without any regeneration treatment, up to three times keeping almost the high initial activity. Interestingly, a close catalytic performance to that achieved using ethanol has been obtained with bulkier alcohols.
Keywords: Sulfonic acids; Levulinic acid; Alkyl levulinates; Fuel formulation; Acid catalysis;

Carbonaceous deposits (hard coke) were studied by various solid state 13C nuclear magnetic resonance (NMR) techniques after demineralization of the spent and regenerated fluid catalytic cracking (FCC) catalysts obtained from Indian refineries. A number of structural parameters such as aromaticity, H/C ratio, fraction of protonated ( f a P ) and non-protonated ( f a NP ) aromatic carbons, number of pericondensed rings per average molecule (N peri), and aromatic condensation index (γ ar) are derived from the NMR data. Findings of thirty-two and thirty-nine aromatic rings in coke from regenerated catalysts and five and nineteen rings in coke from spent catalysts are rationalized by various parameters such as feed, temperature and process conditions of FCC reactor on the basis of condensation. The coke are found more condensed in regenerated catalysts compared to spent catalysts revealing that the temperature has a marked effect in the evolution of coke structure whereas feeds and other process conditions govern the nature and composition of coke.
Keywords: FCC catalysts; Hard coke; 13C NMR; Pericondensed aromatics;

Kinetic study of transesterification of methyl acetate with ethanol catalyzed by 4-(3-methyl-1-imidazolio)-1-butanesulfonic acid triflate by Yanmei Peng; Xianbao Cui; Ying Zhang; Tianyang Feng; Zheng Tian; Lexing Xue (131-136).
The chemical equilibrium and reaction kinetics for transesterification of methyl acetate with ethanol to form ethyl acetate and methanol catalyzed by an ionic liquid 4-(3-methyl-1-imidazolio)-1-butanesulfonic acid triflate ([HSO3-bmim]CF3SO3) were studied. The reaction enthalpy was obtained experimentally and theoretically. The effects of temperature, initial molar ratio of ethanol to methyl acetate and catalyst concentrations to the reaction rate were investigated. The reaction mechanism of transesterification catalyzed by ionic liquids is proposed. Based on the reaction mechanism, an ideal-solution model (IM) and a non-ideal-solution model (NIM) were used to correlate the reaction kinetics data. The NIM was more reliable to describe the reaction kinetics. Compared with sulfuric acid, the ionic liquid catalyst was more active.
Keywords: Transesterification; Reaction kinetics; Ionic liquid catalyst; Ethyl acetate; UNIQUAC;

Development of gallium incorporated mesoporous silica catalysts for the selective removal of BTX by Azhagapillai Prabhu; Ahmed Al Shoaibi; Chandrasekar Srinivasakannan (137-141).
Three-dimensional mesoporous gallium KIT-6 with different Si/Ga molar ratios have been prepared by using P123 as a structure directing agent under acidic medium in hydrothermal conditions. The synthesized Ga-KIT-6 materials were characterized using small angle X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), nitrogen sorption analyzer, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FT-IR) and thermo gravimetric analysis (TGA). The developed mesoporous gallium KIT-6 material possesses a high surface area of 892 m2  g−1 and pore volume of 1.24 cm3  g−1. The mesoporous structure of the catalyst together with the presence of gallium in the silica framework, which confers acidity for better adsorption. Adsorption of BTX over the different Si/Ga molar ratios of cubic Ia3d (Ga-KIT-6) materials were studied and found that the better adsorption on Ga-KIT-6 (5). Interestingly, this material showed excellent adsorption capacity of BTX in aqueous solution.
Keywords: Mesoporous silica; Ga-KIT-6; Adsorption of BTX compounds; Surface acidity; Surface area;

Optimisation of alkene epoxidation catalysed by polymer supported Mo(VI) complexes and application of artificial neural network for the prediction of catalytic performances by Misbahu Ladan Mohammed; Dipesh Patel; Rene Mbeleck; Debdarsan Niyogi; David C. Sherrington; Basudeb Saha (142-152).
A greener and efficient alkene epoxidation process using heterogeneous molybdenum (Mo) based catalysts and tert-butyl hydroperoxide (TBHP) as an oxidant has been developed. A polybenzimidazole supported Mo(VI) complex, i.e. PBI.Mo and polystyrene 2-(aminomethyl) pyridine supported Mo(VI) complex, i.e. Ps.AMP.Mo catalysts have been successfully prepared and characterised. The catalytic activities of the polymer supported Mo(VI) catalysts have been tested for epoxidation of 1-hexene and 4-vinyl-1-cyclohexene in a jacketed stirred batch reactor. Batch experiments have been conducted to study the effect of different types of catalysts, catalyst loading, feed mole ratio (FMR) of alkene to TBHP and reaction temperature on the yield of epoxide for both alkenes, i.e. 1-hexene and 4-vinyl-1-cyclohexene. The long-term stability of PBI.Mo and Ps.AMP.Mo catalysts has been evaluated by recycling the catalyst several times for batch experiments using conditions that will form the basis of a continuous epoxidation process. The extent of Mo leaching from each polymer supported catalyst has been investigated by isolating any residue from reaction supernatant solutions after the removal of the heterogeneous catalyst and using the residue as potential catalyst for epoxidation. An artificial neural network (ANN) model has been employed to predict the catalytic performance of PBI.Mo and Ps.AMP.Mo catalysts for all batch experimental results. The ANN predicted values are in good agreement with the batch experimental results. The results obtained from batch experiments and ANN modelling provided useful information for conducting continuous epoxidation experiments in multi-functional reactors such as FlowSyn and reactive distillation column (RDC).
Keywords: Alkene epoxidation; Artificial neural network (ANN); tert-Butyl hydroperoxide (TBHP); Heterogeneous catalysis; Polymer supported Mo(VI) catalyst; 1-Hexene; 4-Vinyl-1-cyclohexene;

Novel ZnO-carbon and ZnO nanofibers were fabricated by electrospinning of polymer precursor followed by subsequent annealing in nitrogen and air, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) indicated the smooth and beadless nanofibers with wurtzite crystal structure. X-ray photoelectron spectroscopy (XPS) showed the presence of oxygen vacancies (VO) and chemisorbed O2 on the surface of the samples. Band gap narrowing of the ZnO-carbon nanofibers in comparison to ZnO were measured by diffuse reflectance spectroscopy (DRS). Photo-degradation of azo dye under the UV and visible light was evaluated and ZnO-carbon showed an enhancement in photocatalytic activity due to the presence of carbonaceous species and oxygen vacancies. Formation of hydroxyl radical during the photocatalytic process was verified by the formation of carbon using photoluminescence (PL) analysis. The photocatalytic mechanism was investigated by measuring the degradation rate in the presence of tert-butyl alcohol (t-BuOH) and I anion as •OH radical and hole (h +) scavenger. The results indicated photo-generated electrons are the main photo-oxidation pathway.
Keywords: Electron–hole recombination; Carbon doped ZnO; Zn―O―C; Electrospinning; Photosensitization;

Hydrogenolysis of cellulose into polyols over Ni/W/SiO2 catalysts by Su Jin You; In Gu Baek; Eun Duck Park (161-168).
The direct conversion of cellulose into polyols in the presence of hydrogen was examined over Ni/W/SiO2 catalysts to establish the effects of average pore size of support and reduction temperature on the catalytic performance. The crystalline particle size of W, determined by X-ray diffraction (XRD), generally increased with increase in the average pore size of support and reduction temperature for Ni/W/SiO2. The yield of polyols such as sorbitol, mannitol, erythritol, ethylene glycol, and 1,2-propanediol increased on decreasing the crystalline particle size of W in Ni/W/SiO2. The individual catalytic activity of Ni/W/SiO2 was much better than that of the combined catalyst systems, i.e., Ni/SiO2  + W and Ni/SiO2  + WO3. The oxidation state effect of nickel and tungsten in Ni/W/SiO2 catalyst on the catalytic performance was also investigated. The reduced and oxidized Ni/W/SiO2 catalysts were found to be effective in forming polyols and organic acids, respectively.
Keywords: Cellulose; Ethylene glycol; Hydrogenolysis; NiW; Silica;

Enhanced activity of sol–gel prepared SnO x –TiO2 in photocatalytic methanol reforming by Katalin Majrik; Emília Tálas; Zoltán Pászti; István Sajó; Judith Mihály; László Korecz; Eszter Drotár; András Tompos (169-178).
In this contribution a simple method is elaborated for the preparation of Pt/SnO x –TiO2 catalysts which are active in the photocatalytic reforming of methanol. The region of low tin content (Sn/Ti atomic ratio: 0–0.015) is explored. Tin content related activity changes of the catalysts are discussed in terms of the results of structural characterization.Tin-modified anatase TiO2 samples were obtained from sol–gel method by use of Ti-isopropoxide, SnCl4 or Sn(OBu)4 and citric acid in absolute ethanol solution followed by calcinations at 400 °C in air. After loading Pt by impregnation the catalytic activity has been tested irradiating the slurry of the catalysts suspended in mixture of water and methanol by means of two different light sources, one working exclusively in the visible region and one in a broader spectral range including a UV-component, respectively. Hydrogen production activity has been correlated with structural data obtained from different characterization techniques such as ESR spectroscopy, XRD, XPS, SEM and Raman spectroscopy as well as diffuse reflectance UV–Vis spectrophotometry.According to ESR spectroscopic measurements the presence of oxygen vacancies was responsible for the slight visible light absorption. XRD, XPS, SEM and Raman spectroscopic results indicated that highly dispersed SnO x accumulated in the surface region of TiO2, no tin incorporation into the lattice was observed. The fundamental band gap was not influenced by the presence of tin. Loading of the tin-modified samples by 0.5 wt% Pt increased the hydrogen production in comparison to 0.5 wt% Pt/TiO2 samples.The improvement in the catalytic activity was explained by formation of new tin related charge carrier traps leading to (i) prevention of electron–hole recombination and (ii) additional modification of the adsorption of reactants. Details of the two different working mechanisms are described.The increased hydrogen production over the tin modified samples provides a promising step toward practical usage of light for hydrogen production.
Keywords: TiO2; SnO2; Sol–gel method; Hydrogen production; Methanol; Photocatalytic reforming;

The activity of single and two-component catalyst systems consisting of a partial oxidation catalyst and a reduction catalyst (Ag/Al2O3), were investigated for selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with n-decane (HC) as a reductant. The single component Ag/Al2O3 catalyst showed a maximum NO x conversion of 28% at 400 °C and formation of minor amounts of hydrocarbon cracking products. Co-presence of partial oxidation catalyst, especially metal/ZSM-5, along with Ag/Al2O3 enhanced the NO x conversion of the composite catalysts. Among the composite catalysts, Zn/ZSM-5–Ag/Al2O3 combination led to the most increase in NO x conversion. It was identified that the n-decane can be more effectively converted, on Zn/ZSM-5, to smaller hydrocarbons (such as ethene, propane and propene) intermediates. These in situ generated intermediates were found to enhance the NO x conversion of Zn/ZSM-5–Ag/Al2O3 composite catalysts. Catalyst optimization showed that the NO x conversion increased with increase in zinc loading of up to 5 wt% in ZSM-5 and by increasing Zn/ZSM-5 content in the composite mixture catalyst. A combination of 17 mg of Ag/Al2O3 and 33 mg of 5%Zn/ZSM-5 led to the most active catalyst showing a maximum NO x conversion of about 67% at 400 °C.
Keywords: Ag/Al2O3; HC-SCR; Zn/ZSM-5; Partial oxidation; Oxygenated hydrocarbons;

A facile approach to improve the quality of diatomite as sulfuric acid catalyst support by Min Wang; Yubin Xiang; Guilong Zhang; Jimei Song; Dongqing Cai; Zhengyan Wu (185-189).
High-energy electron beam (HEEB) irradiation, a facile modification approach, was applied to modify the pore size distribution of diatomite and improve the quality of diatomite as a catalyst support. The results demonstrated that HEEB irradiation modified the pore size distribution of diatomite due to etching, Coulomb explosion and thermal effects. The BET specific surface area, X-ray diffraction and catalytic performance results indicated that pore structure modification improved the micro-properties of diatomite and the catalytic efficiency of catalysts prepared from treated diatomite.
Keywords: Diatomite; High-energy electron beam irradiation; Pore size distribution; Catalytic efficiency;

In situ IR study for elucidating reaction mechanism of toluene steam reforming over Ni/La0.7Sr0.3AlO3−δ catalyst by Daiki Mukai; Yuki Murai; Takuma Higo; Satoshi Tochiya; Takashi Hashimoto; Yukihiro Sugiura; Yasushi Sekine (190-197).
Steam reforming of toluene as a model compound of biomass tar was conducted on supported Ni catalysts. The Ni catalyst supported on perovskite oxide (La0.7Sr0.3AlO3−δ : LSAO) showed the highest toluene conversion (58%) and lowest coke formation (57 mg g-cat−1) at 873 K thanks to the smaller Ni particle size and larger perimeter between Ni and perovskite support, confirmed by XRD, BET, STEM and XAFS. In this paper, adsorption of toluene on Ni/LSAO catalyst was investigated using FT-IR method to estimate the reaction mechanism. IR spectra during temperature programmed desorption revealed that strong adsorption of toluene was observed only on LSAO and Ni/LSAO. The decomposition of adsorbate to CO or CO2 was promoted by supported Ni metal. Lattice oxygen of perovskite support contributed to the oxidation of the intermediate at the interface of Ni and perovskite. In addition, the oxidation of intermediate was promoted by introducing steam. Investigating adsorptions of various probe molecules (benzene, n-heptane, ethylene and benzaldeyde) revealed that decomposition of aromatic ring proceeded on Ni/LSAO.
Keywords: Steam reforming of toluene; Ni catalyst; Perovskite support; FT-IR; Adsorbed species;

Enantioselective hydrogenation of 1-phenyl-1,2-propanedione over Pt on immobilized cinchonidine on γ-Al2O3 catalysts by Cristian H. Campos; Cecilia Torres; José L.G. Fierro; Patricio Reyes (198-207).
Chirally modified γ-Al2O3 containing different amounts of cinchonidine were prepared by the chemical modification of cinchonidine with trimethoxysilane (TMS-CD). These solids were used as support of Pt catalysts containing 1 wt% Pt by chemical reduction of the hexachloroplatinic acid with H2 at 25 °C and 40 bar. The characterization was carried out by elemental analysis of C, H and N, TG, DRIFT, NMR 13C and 29Si on solid state, N2 adsorption–desorption at 77 K, XDR, XPS and TEM. The catalytic activity was evaluated in the hydrogenation of 1-phenyl-propane-1,2-dione in a batch reactor at 298 K and 40 bar. The effect of H2 pressure, concentration substrate, catalyst mass, solvents effect and recycles, of the catalyst with the major enantiomeric excess was studied. It was found that all catalysts were active in the reaction being the enantiomeric excess of the target product, 1-R-phenyl-1-hydroxy-2-propanone in the range 30–44% and the best catalyst is that supported on γ-Al2O3 with a nominal content of 5 wt% TMS-CD. The results obtained in this study confirm that the variation of reaction conditions show a dependence on the activity and enantioselectivity for substrate adsorption in the metal active sites. In the solvent effect, enantiomeric excess decreased non-linearly with an increasing solvent dielectric and we could be attributed to the interactions between solvents and TMS-CD in the surface. In the recycles studies enantiomeric excess was achieved as 40% even after 3rd reuse with a slight loss in activity and enantiomeric excess.
Keywords: Heterogenization; Platinium; Cinchonidine; 1-Phenyl-propane-1,2-dione; Immobilized heterogeneous catalyst;

Rhodium-catalyzed hydroformylation of acyclic monoterpenic compounds, i.e., linalool and β-citronellene, was studied in toluene and ethanol solutions in the presence of PPh3 or P(O-o-tBuPh)3 ligands. Although both substrates have a monosubstituted terminal double bond, they show different behavior under the hydroformylation conditions. In toluene, linalool gave almost quantitatively a cyclic hemiacetal; whereas the hydroformylation of β-citronellene resulted in two isomeric aldehydes also in a nearly quantitative combined yield. The reactions occurred approximately two times faster in ethanol than in toluene giving the corresponding acetals even in the absence of additional acid co-catalysts. In the absence of phosphorous ligands, linalool (differently from β-citronellene) was very resistant to hydroformylation probably due to the binding with rhodium through both the double bond and the hydroxyl group to form stable chelates. The P(O-o-tBuPh)3 ligand exerted a remarkable effect on the reactivity of both substrates accelerating the reactions by 5–20 times as compared to the system with PPh3. Several fragrance compounds were obtained in high yields through a simple one-pot procedure starting from the substrates easily available from natural bio-renewable resources.
Keywords: Acetalization; Citronellene; Hydroformylation; Linalool; Monoterpenes; Rhodium;

Palladium complexes of the type [IL]2[PdCl4] (IL = imidazolium cation) were found to be very active catalysts for the Suzuki–Miyaura reaction of 2-bromotoluene with phenylboronic acid carried out in 2-propanol or 2-propanol/water at 40 °C using normal heating or microwaves as a heating source. In 2-propanol, the highest yields (89% and 85%) were obtained for [dmiop]2[PdCl4] and [dmdim][PdCl4] (dmiop = 1,2-dimethyl-3-propoxymethyl imidazolium cation, dmdim = 3,3′-[1,7-(2,6-dioxaheptane)]bis(1,2-dimethylimidazolium) cation) containing cations substituted at the C2 carbon with a methyl group. In the presence of water, all [IL]2[PdCl4] complexes produced ca. 90% of 2-methylbiphenyl. Very good results were also obtained in the Suzuki–Miyaura reaction of different aryl bromides and chlorides. For example, the conversion of 2-chlorotoluene was 71% at 70 °C. During the catalytic reaction, the formation of Pd(0) nanoparticles was evidenced by TEM. Mechanistic studies, including Hg(0) tests, showed that Pd(0) nanoparticles acted as a source of catalytically active soluble palladium species.
Keywords: Palladium; Ionic liquids; Suzuki–Miyaura reaction; Nanoparticles;

Effect of sulfidation temperature on the catalytic activity of MoO3/CeO2–Al2O3 toward sulfur-resistant methanation by Minhong Jiang; Baowei Wang; Jing Lv; Haiyang Wang; Zhenhua Li; Xinbin Ma; Shaodong Qin; Qi Sun (224-232).
The effect of sulfidation temperature on the catalytic activity of MoO3/CeO2–Al2O3 toward sulfur-resistant methanation was studied. The prepared catalysts were characterized by N2 physisorption (BET), X-ray diffraction (XRD), Raman spectroscopy (RS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The XRD and XPS results indicated that CeO2 was sulfided at sulfidation temperatures above 500 °C. During sulfidation at 500 °C or above, Ce3+ ions diffused into the catalyst, and/or Al3+ ions migrated to the surface of the catalyst. These two changes enhanced catalyst stability and decreased catalytic activity. The initial catalytic activity decreased as the sulfidation temperature increased. This decrease occurred for the following reasons: the decrease in BET surface area, the undesired sulfidation of CeO2 on the surface, and the crystallization of amorphous MoS2 to form MoS2 crystals. Finally, CeO2 and MoO3 sulfidation mechanisms were proposed for temperatures greater than 500 °C.
Keywords: Sulfidation temperature; Catalytic activity; MoO3/CeO2–Al2O3 catalyst; Sulfur-resistant methanation;

A series of acid–base bifunctional CaO-ZrO2 catalysts was prepared simply by the impregnation method and evaluated for the vapour-phase dehydration of 1,4-butanediol (BDO). The effects of CaO content and calcination temperature on the catalytic properties of the CaO-ZrO2 catalysts were investigated. It was found that the catalyst with 12.5 wt% CaO and at a calcination temperature of 650 °C exhibited favorable catalytic performance and good stability for the selective dehydration of BDO to 3-buten-1-ol (BTO). The maximum BTO selectivity and BDO conversion reached 68.9% and 94.6%, respectively. The formation of by-product, THF, was markedly suppressed. These catalysts were characterized by N2 physisorption, XRD, FT-IR spectra, NH3-TPD and CO2-TPD. The results indicated that the CaO-ZrO2 catalysts showed higher basicity density and similar acidity density compared to unmodified ZrO2 due to the formation of Ca–O–Zr Hetero-linkage by CaO introduction. The catalytic performance depended on the coexistence of acidic and basic sites on the surface of catalysts.
Keywords: 1,4-Butanediol; 3-Buten-1-ol; Dehydration; CaO-ZrO2 acid–base bifunctional catalyst; Ca–O–Zr Hetero-linkage;

Path lumping kinetic model for aqueous phase reforming of sorbitol by Farid Aiouache; Lisa McAleer; Quan Gan; Ala’a H. Al-Muhtaseb; Mohammad N. Ahmad (240-255).
This work presents a kinetic model for the aqueous phase reforming of sorbitol that uses a lumping scheme of intermediates and approximates the complex path to gas products via a reforming route and liquid oxygenate route including hydrodeoxygenation, decarbonylation and dehydrogenation reactions. The model was tested at temperatures ranging from 473 K to 523 K, using monometallic Ni and bimetallic Ni-Pd catalysts supported on γ-Al2O3, ZrO2 and CeO2. The model revealed that the relevant competing paths were a function of the composition of catalyst and the conversion to the carbon gaseous products. Paths of reforming and CO2 methanation were more important than decarbonylation and hydrodeoxygenation at small conversions for all catalysts whereas the hydrodeoxygenation–decarbonylation towards alkanes release was more competitive than the reforming at high conversions with Ni/Al2O3 and Ni-Pd catalysts supported on ZrO2 and CeO2 but was still less competitive with Ni-Pd catalyst supported on γ-Al2O3.
Keywords: Sorbitol; Kinetics; Aqueous phase reforming; Lumping scheme; Catalyst; Biofuel;

Co/SiO2-based catalysts for Fischer Tropsch synthesis (FTS) were prepared by a high-temperature super-critical drying (HT-SCD) method, and the effects of the drying method on the catalytic properties were investigated. X-ray diffraction analysis (XRD) of the calcined catalysts revealed that the cobalt species formed in the HT-SCD catalysts is mainly a less-reducible cobalt silicate (Co2SiO4-like species), whereas that formed in catalysts prepared by a conventional thermal drying (TD) is mainly the easily reducible Co3O4 species. Moreover temperature programmed reduction (TPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and H2 chemisorption measurements revealed that the addition of rhenium or ruthenium to the HT-SCD catalysts improves the reducibility of the cobalt species and the cobalt dispersion, and partially suppresses the covering cobalt particles with SiO2 layer. The type of cobalt precursors used for catalyst preparation also had an effect on the cobalt species formed in the calcined catalysts. The HT-SCD catalysts with cobalt silicate exhibited higher olefin selectivities for FTS than the Co3O4-based catalysts prepared by TD, whereas the C11+ selectivities of the TD catalysts were higher than those of the HT-SCD catalysts. On the other hand, turn over frequency (TOF) estimated from the amount of H2 chemisorbed was constant without depending on the drying method and the type of cobalt precursors.
Keywords: Fischer Tropsch synthesis; High-temperature super-critical drying; Co-Re/SiO2;

Electrocatalytic oxidation of methanol on Ni(II)Salen complex encapsulated with type-Y zeolite by Rong Zhang; Weike Zhang; Lizhen Gao; Jing Zhang; Ping Li; Wenyang Wang; Ruifeng Li (264-271).
Type-Y zeolite modified electrode was prepared with the mixture of high pure graphite and the zeolite-encapsulated Ni(II)(Salen) [Salen: N, N′-bis(salicylidene)ethylenediamine] complex as modifier by physical absorption method on the substrate of glassy carbon (GC). The electrochemical characterization of this modified glassy carbon electrode (Ni(Salen)Y/GCE) shows good redox behavior of Ni(III)(Salen)OOH/Ni(II)OH(Salen) couple from cyclic voltammetric experiments. Moreover, electrocatalytic oxidation of methanol at the surface of the Ni(Salen)Y/GCE was studied in a 1.0 M NaOH solution. Compared to bare GCE, Graphite/GCE, NaY/GCE, NiY/GCE, the Ni(Salen)Y/GCE significantly enhanced the anodic current for catalytic oxidation of methanol. The effects of both scan rate and methanol concentration on the anodic peak height of the methanol oxidation were discussed. Also, the mechanism of electrocatalytic methanol oxidation on this modified electrode was proposed to be ECE’ process, which changes from diffusion control at low concentration to a catalytic reaction between the methanol and Ni(III)(Salen)OOH at higher methanol concentration. In addition, the catalytic current is proportional to the concentration of methanol from 0.005 M to 0.3 M. The detection limit and the sensitivity were obtained to be 9.92 mM and 7.27 μA mM−1 form cyclic voltammetry. Finally, using a chronoamperometric method, the catalytic rate constant (k cat) value for electrocatalytic methanol oxidation was found to be 5.48 × 104  cm3  mol−1  s−1.
Keywords: Type-Y zeolite; Encapsulated Ni(II)(Salen) complex; Zeolite-modified electrode; Methanol oxidation; Electrocatalyst;

A reusable and highly active heterogeneous catalyst of the type Mg1+x Ca1−x O2 has been developed and thermally treated at 850 °C for 6 h. The catalytic activity was investigated during the transesterification of glycerol with dimethyl carbonate to synthesize the valuable glycerol carbonate. A typical Mg1.2Ca0.8O2 mixed oxides catalyst was characterized by BET surface area, surface base amount, CO2-TPD, XRD and FTIR, and its microstructure was studied by the aid of scanning and transmission electron microscopy. The investigated characteristics gave a clear insight into the catalytic performance of the catalyst. Over 0.30 g of this catalyst, glycerol conversion was almost complete and the yield of glycerol carbonate was 100% under atmospheric pressure. The best reaction conditions are: molar ratio of glycerol/DMC of 1:2, reaction temperature of 70 °C and 90 min of reaction time. The transesterification results showed that the synergism interaction between Ca and Mg species in the catalyst structure was the reason for its high activity.
Keywords: Glycerol; Glycerol carbonate; Mixed oxide catalyst; Fuel additives;

The selective oxidation of ethylbenzene and cyclohexene to acetophenone and 2-cyclohexene-1-one using N-hydroxyphthalimide (NHPI) under oxygen atmosphere in the presence of an SiO2/Al2O3-supported cobalt catalyst occurs with conversions of 83 and 75% and selectivities of 99%. The supported cobalt is also a suitable and efficient catalyst for the oxidative deprotection of oximes to the corresponding carbonyl compounds. The reaction conditions have been optimized considering the effect of various parameters such as reaction time, amount of catalyst, temperature and reusability of the catalyst after several runs. Moreover, some possible mechanisms for the oxidation of ethylbenzene, cyclohexene and oximes have been proposed.
Keywords: Cobalt supported catalyst; Oxidation, Ethylbenzene; Cyclohexene; Oxime;

The doping effect of rare earth (RE) elements La, Nd and Yb on the acidity and metal function of Pt/HBEA catalysts was investigated, as well as its influence in the hydroisomerization of n-hexane. HBEA zeolite was submitted to ion exchange with increasing amounts of RE using nitrate solutions, followed by Pt introduction. The samples were characterized by powder X-ray diffraction, chemical analysis and low temperature N2 adsorption. The acidity of the samples was study through pyridine adsorption followed by FTIR spectroscopy and the model reaction of n-heptane cracking. The influence of RE elements on the metal function was studied by magnetic susceptibility measurements, model reaction of toluene hydrogenation and H2 chemisorption analysis. The characterization methods showed that the presence of very small amounts of RE elements increases the strength and density of the acid sites due to the appearance of new Lewis acid sites that are detected upon RE loading. The electronic properties and metal dispersion of Pt were also improved. In n-hexane hydroisomerization reaction an increased catalytic activity and selectivity into dibranched isomers is detected in the presence of very low contents of La and Nd (less than 0.4 wt.%). For higher amounts and also in the case of Yb doped samples, where the amounts introduced were higher, a decrease in catalytic activity as well as a higher selectivity in cracking products is noticed as a result of stereochemical limitations inside the zeolite pore structure.
Keywords: Rare earth elements; Bifunctional catalysis; Pt/HBEA; n-Hexane hydroisomerization;

Highly efficient Ni-ZrO2 catalyst doped with Yb2O3 for co-methanation of CO and CO2 by Yan-Hui Huang; Ji-Jie Wang; Zhi-Ming Liu; Guo-Dong Lin; Hong-Bin Zhang (300-306).
A type of highly efficient Ni-ZrO2 catalysts doped with Yb2O3 for co-methanation of CO and CO2 was developed, and displayed excellent activity and thermal stability. Over the Ni6Zr2Yb2 catalyst under the reaction conditions of 0.1 MPa and 573 K, the observed total conversion of CO and CO2 (denoted as X(CO and CO2)) maintained continuously at a high level of ∼97.4% during 25–126 h after the reaction started, with the corresponding STY(CH4) reaching ∼9.11 g h−1  g−1. The results of heat-resisting test showed that, over the Ni6Zr2Yb2 catalyst after undergoing 24 h of the methanation operation at 1073 K followed by going down to 573 K, the X(CO and CO2) still maintained stable at the level of 89%; whereas X(CO and CO2) observed on the other two reference systems, Ni6Zr4 and Ni6Zr2Sm2, which both underwent the similar heat-resisting test at 923 K and 1023 K, respectively, fell to 2.8% and 2.4%, respectively. The results of the catalyst characterization demonstrated that the high activity, and especially the extremely high thermal stability, of the Ni6Zr2Yb2 catalyst for CO and CO2 methanation were associated with the formation of (Zr-Yb)O y oxide with c-ZrO2 structure. The pronounced promoter action of Yb2O3 may be due to the high solubility of Yb2O3 in ZrO2 lattice as the ionic radius of Yb3+ (0.087 nm) is quite close to that of ZrIV (0.079 nm). Solution of a considerable amount of Yb3+ in the ZrO2 host resulted in the formation of (Zr-Yb)O y oxide with simple c-ZrO2 structure. It is the major factor for the high activity and high thermal stability of the Ni6Zr2Yb2 catalyst.
Keywords: Ni-ZrO2 catalyst; Yb2O3-doped Ni-ZrO2 catalyst; CO and CO2 co-methanation;

A lanthanide-containing polyoxometalate of Na7H2LaW10O36·32H2O (LaW10) have been chemically anchored to the amino-modified mesoporous silica through an organic linker. The catalysts have been characterized by ICP-ES, FT-IR, N2 sorption measurements, UV–vis, MAS-NMR, and HR-TEM. It is found that the LaW10 nanoparticles are highly dispersed on mesoporous silica, and the resulting catalysts show highly efficient deep desulfurization in only 35 min with almost 100% conversion of dibenzothiophene by using (SiO2/NH3 +/LaW10)/[bmim]BF4 (bmim = 1-butyl-3-methylimidazolium) in the presence of H2O2 as oxidant. Furthermore, deep desulfurization proceeds smoothly in model oil with S content as low as 100 ppm. A scaled-up experiment, in which the volume of model oil increases from 5 to 1000 mL with S content of 1000 ppm, indicates that almost 100% sulfur removal can be achieved in 45 min. Additionally, the catalyst could be recycled and reused at least ten times without any decrease of the catalytic efficiency. To the best of our knowledge, the (SiO2/NH3 +/LaW10)/[bmim]BF4 catalyst system with H2O2 as oxidant exhibits great potential for practical application as desulfurization systems reported so far.
Keywords: Polyoxometalates; Desulfurization; Lanthanides; Mesoporous silica;