Current Catalysis - Volume 3, Issue 2, 2014

Our research Center called “Centro de Investigación y Desarrollo en Ciencias Aplicadas - Dr. Jorge Ronco, CINDECA” celebrated 40 years of its foundation. Our research Institute is devoted to heterogeneous and homogeneous catalysis, reactors design, green chemistry, bio-catalysis, design and synthesis of new catalytic materials between others. In this context, the research topics are oriented towards the technological application in the field of catalyzed chemical processes. Our research Center organized a series of events such as invited conferences from worldwide researchers and poster sessions. In fact, 150 participants mostly P.h.D students along with researchers from all over Argentina gathered for three days to discuss their research and debate new and exciting ideas. In the present special issue eighteen manuscripts on different subtopics such as, new synthetic material, homogeneous catalysis heterogeneous catalysis, bio-catalysis, green chemistry, organic clean procedures and environmental remediation have been subjected to consideration. I would like to take this opportunity to thank Bentham Science Publishers for appointing us as Editor-in-Chief of the journal, and to acknowledge supporting staff for their enthusiasm, dedication and continual support. I also thank authors and reviewers for their positive contribution and wish the journal will have a great success.

H3PW12O40 in bulk form presents suitable properties to be used as catalyst in the selective oxidation of sulfides with 35% aqueous hydrogen peroxide, and sulfoxides or sulfones were obtained as products in high to excellent yields and selectivity. We found that sulfides were oxidized to the corresponding sulfoxides, with near stoichiometric 35% w/V aqueous hydrogen peroxide, at room temperature (20°C) and with a catalytic amount of bulk H3PW12O40. Similarly, sulfides were transformed to the corresponding sulfones using excess of 35% w/V aqueous hydrogen peroxide and a temperature of 70°C. In both cases acetonitrile was used as reaction solvent.

The commercial biocatalyst Novozym ® 435 was used for the kinetic resolution of (R/S)-ibuprofen through the esterification with short chain alcohols (ethanol, 1-propanol and 2-propanol) in the absence of organic co-solvent. The best enzymatic performance was obtained by employing ethanol as reagent and solvent. Due to the deleterious effect of this alcohol on the integrity of the commercial biocatalyst previously reported different organic co-solvents (isooctane, nhexane, carbon tetrachloride, ethyl acetate, acetonitrile and tetrahydrofuran) were screened in order to minimize the volume of ethanol to be used. Thus, the effect of the chemical nature of the co-solvent on enantioselective esterification of (R/S)-ibuprofen with ethanol was evaluated. The results show that the best performance was obtained with the reaction system without co-solvent added. Additionally, this investigation demonstrated the need to address multiple physicochemical properties of the solvents to analyze their effects on biocatalysis.

Diphenyilsulfide oxidation by H2O2 as oxidant was studied through the structural effect of the isomorphous W-Mo systems, Anderson type, with [Ni(II)Mo(VI)6-xW(VI)xO24H6]-4 composition. These phases were proved as alternative catalysts instead of W and Mo conventional systems. The characterization of the substituted phases was carried out by different physico-chemical techniques (AAS, DRS, micro-Raman, XRD, TPR). The catalytic evaluation for the phase NiW6 revealed that the process was selective to the sulfone formation (selectivity ~ 81-88 %) while the Ni-Mo bi-metallic system (NiMo6) was only selective to the sulfoxide production (selectivity 98 %). The activity was 90 % at 60 and 180 min for the NiMo6 and NiW6 respectively, whereas the substituted phases presented intermediate values. The observed differences can be related to the strength of the bridge bonds (Mo-O…Ni and W-O…Ni) associated to the higher electronegativity and ionic potential of Mo with respect to W. Hence, the W-O bond is more reactive by the inductive effect of Ni, which produces a higher oxidation of diphenyilsulfide to give sulfone, considering the electronic mobility in the redox processes.

Dawson-type heteropolyoxometalate compounds (HPC) P2M18O62 -6 (M= Mo, W) have received increasing attention in the catalytic field due to the combination of redox and acidic properties in the same structure. It has been proved that the introduction of vanadium into the Keggin framework is beneficial for redox catalysis, shifting its activity from acid to redox-dominated. In this work we prepared and characterized vanadium (V) substituted Wells-Dawson heteropolysalt (WDKV). Fresh solid samples were characterized by 31P MAS-NMR, FTIR, SEM, XRD, TGA and Potentiometric titration measurements. Also, we performed the oxidation of a 1,4-dihydropyridine using WDKV as catalyst in acetonitrile media, with H2O2 as oxidant agent. The optimal procedure is the following: 1 mmol% of WDKV, a ratio 1,4-DHP: H2O2 (1:214) at reflux of acetonitrile. It must be noted that along all reactions, no secondary products were observed.

This paper presents a rational strategy to purify the lipase B of Candida antarctica of the commercial extract Lipozyme® through size exclusion coupled with anionic exchange chromatography using a non conventional, easy to remove buffer system such as ammonia-ammonium. In this context, each step of the purification was followed through the determination of the protein content, esterase activity measurements, SDS-PAGE, agarose electrophoresis, UVspectroscopy and isoelectric focusing. The purification of the commercial extract afforded a sample that retains 47% of the proteins (being CALB the major enzymatic component of the purified sample) with a hydrolytic activity higher than the starting crude extract.

Different Fe2O3/Al2O3 catalysts (4 wt% Fe) were prepared and characterized by N2 physisorption, SEM-EDX, TGA and XRD. The systems were tested for the oxidation of high concentration phenol solutions (5 g/L) in a batch reactor at 50 °C, using H2O2 as oxidant. In order to enhance the catalyst stability two strategies were combined: an elevated temperature of calcination (900 °C) and pre-treatments with different organic acids (acetic, oxalic acid). The stability of the catalyst was improved significantly (leaching levels were reduced by up to 70%), with a good performance over the global oxidation process: mineralization levels of ca. 50% with oxidant consumption efficiencies of around 75%.

Five MnOx-CeO2 samples with a molar ratio Mn-Ce between 0 and 100% were obtained by coprecipitation. The samples, which were called 10/0, 7/3, 5/5, 3/7, 0/10, were characterized by XRD, FTIR, XPS, specific surface area and TPR. Phenol was selected as pollutant. The adsorption of phenol from aqueous solution on Mn-Ce samples was carried out in a batch reactor at 25 and 50° C. The adsorption isotherms were described by Langmuir and Freundlich isotherm models and both model fitted. The characterization results showed the formation of solid solution where Mn3+ replaces Ce4+. The most active solid was Mn-Ce 7/3. The results showed that the adsorption process is a function of the Mn- Ce composition. Thermodynamics parameters ΔG0, ΔH0 and ΔS0 were calculated. These parameters indicated that the adsorption of phenol onto Mn-Ce was spontaneous and exothermic at 25 and 50 °C.

MoOx-ZrO2 based catalysts were prepared by equilibrium adsorption in basic (pH 8) or in acid (pH 2) conditions with molybdenum content up to 3 wt.% (pH 8) and up to 8 wt.% (pH 2) using hydrous zirconium oxide, designated as ZrO2(383), as support. The samples were characterized by textural analysis (BET), X-ray diffraction (XRD), Raman and X-ray photoelectron (XPS) spectroscopies. The catalytic behavior was analyzed for the selective oxidation of diphenylsulfide (DPS) to diphenylsulfone (DPSO2) or diphenylsulfoxide (DPSO) using H2O2 as oxidizing agent. The results show that the pH of the contacting solution affects the uptake of the Mo species and the molecular state of the adsorbed species. Raman spectroscopy identified polymolybdate structures at pH 2 and molybdate aggregates at pH 8. XRD analysis revealed that at increasing molybdenum concentration the interaction between the supported species and the zirconia surface favored the tetragonal volume fraction of zirconia at the expense of the thermodynamically stable monoclinic phase in all series of samples. High conversion of DPS (88%) and selectivity to diphenylsulfone (DPSO2) (60%) was obtained for the pH 2 series of catalysts. These results suggest that the acid environment was the most efficient synthesis parameter leading to the formation of polymolybdates species which are considered the active phases in this reaction.

The catalytic behavior of a series of cobalt catalysts supported on zirconia in the selective catalytic reduction (SCR) of NO has been studied using propane as reducing agent. The catalysts were characterized by Raman Spectroscopy, Temperature Programmed Reduction (TPR), Diffuse Reflectance Spectroscopy UV-Vis (DRS) and X-ray Photoelectron Spectroscopy (XPS) to assess the physicochemical properties of cobalt species. Results for SCR of NO indicate that the activity is substantially related to the cobalt concentration and consequent nature of supported cobalt species. The formation of segregated oxidic phases on the catalytic surface produces an activity decrease. The most active catalyst contains Co(II) ions, interacting with the support, in tetrahedral coordination.

This paper focuses on the preparation, characterization and analysis of the catalytic activity of a series of alumina- supported Cu and Pt catalysts modified with different amounts of cerium, in order to employ them in the carbon monoxide preferential oxidation (CO-PROX) reaction. The catalysts containing only copper as metallic phase allowed us to obtain very good conversion of CO to CO2, reaching a maximum of 70% conversion for the catalyst with higher concentration of Cu supported on the alumina modified with the highest concentration of Ce (0.54 wt% Cu, 25 wt% Ce). For catalysts containing both Cu and Pt the conversions achieved were reasonably good, although lower than for the monometallic catalysts, but at lower temperature. All the catalysts were characterized by different physicochemical techniques: temperature-programmed reduction, X-ray diffraction, UV-VIS diffuse reflectance spectroscopy and surface area. The presence of ceria in these catalysts is pointed as one of the main reasons for their good activity, mainly because the CeO2 increases the availability of O2 to be used in this oxidation reaction.

The combination of both infrared and Raman spectroscopy are powerful tools to obtain information of catalytic materials at a molecular level. The present investigation shows, a systematic study “in situ” about the effects of the temperature in the molecular structure of the supported phosphotungstic Wells-Dawson heteropolyacid (HPA). The infrared and Raman analyses of the samples were performed under in situ conditions from RT to 500 ^oC range in flowing helium. The oxide supported heteropolyacid was synthesized through a conventional impregnation method (in aqueous) at theoretical monolayer coverage. These studies provided evidences on the dehydration of the HPA upon in situ calcination. Moreover, the in situ investigation allows establishing the surface molecular structure or the thermal stability of the HPA. Additionally, the presence of crystals of HPA over TiO2 suggests that the “theoretical” monolayer loading should be re-evaluated.

In this study, the sulfur tolerance and hydrothermal stability of Cu-KNO3/ZrO2 catalysts in catalytic diesel soot oxidation were investigated. Supported alkaline nitrate catalysts have shown excellent activity for soot oxidation in the presence of O2 or NO/O2. High-temperature water vapor treatments do not affect the catalytic activity, suggesting a good hydrothermal stability of the catalysts. Treatments performed at high SO2 concentration lead to a partial deactivation of the catalysts for the combustion reaction in the presence of O2. The presence of copper improves the sulfur tolerance of the KNO3/ZrO2 catalyst for the combustion of soot in the presence of NOx. NO/O2 present in the feed flow of the reactor can regenerate in situ nitrate anions that provide the redox cycles required for the reaction.

This paper deals with the computational modeling of the chiral modifier/substrate interaction for chiral modifiers studied in our laboratory, different from those conventionally used in enantioselective hydrogenation reactions. (S)- (+)-1-aminoindane and (R)-(-)-1-aminoindane were chosen as chiral modifiers and the selected substrates were methyl pyruvate, ethyl pyruvate and 1-ethyl-4,4-dimethyl-pyrrolidinae-2,3,5-trione. The geometry of each of the chiral modifier/substrate complexes was optimized using DFT calculations and a BLYP functional. The theoretical enantiomeric excess was calculated from the energy of each of the proposed complexes. The calculations were carried out considering different reaction solvents through the use of COSMO program. It was found that this simple model allows predicting the experimental values of both the sense of enantiodifferentiation and the enantiomeric excess with a good approximation. It was also able to predict the inversion of configuration when using the (S)-(+)-1-aminoindane as chiral modifier in polar solvents such as acetic acid and 2-propanol.

To understand the complexity of the reactions involved in the steam reforming of glycerol and with the aim of identifying the contribution of C-C and C-O bonds cleavage, in this work we have studied the steam reforming of C3 alcohols simpler than glycerol such as 1-propanol, 2-propanol, 1,2-propanediol and 1,3-propanediol. A Pt/SiO2 catalyst was employed and were studied the conversion and the product distribution for each alcohol. It was possible to determine the absence of C-O and C-C bonds cleavage in a secondary alcohol such as 2-propanol and 1,2 propanediol. The presence of reaction intermediates with an aldehyde function, deactivates the catalyst due to their strong adsorption on the metal site, moreover, the presence of hydroxyl-aldehydes promotes the C-C bonds cleavage favoring the gas production. The reaction pathway from glycerol to acetol by cleavage C-O bonding or dehydration on metal site is responsible for the subsequent reactions leading to deactivation. The main reaction pathway to obtain gaseous products from glycerol reforming involve C-C bonds cleavage of primary alcohols such as 2,3-dihydroxypropanal, 1,2-ethanediol and 2-hydroxyethanal. In order to confirm the proposed reaction pathways, steam reforming of ethylene glycol was performed, identifying this compound as primary intermediates to obtain gaseous products from glycerol.

Various 3-H-1,5-benzodiazepines were prepared from the solvent-free reaction of o-phenylenediamine and substituted 1,3-diphenyl-1,3-propanedione, giving good yields of benzodiazepines. The H6P2W18O62.24H2O solid heteropolyacid, which possesses a Wells-Dawson type structure was used as catalyst both in bulk and silica-supported forms (0.1, 0.2, 0.4 and 0.6 g/g, named 0.1WDSiO2, 0.2WDSiO2, 0.4WDSiO2 and 0.6WDSiO2, respectively). The structure of the synthesized heteropolyacid was confirmed using different characterization techniques (FTIR; 31P-RMN, and potentiometric titration).

The catalytic performance of mesoporous materials with a MCM-41 structure in the reaction of α-pinene oxidation with H2O2 was investigated by a comparative study of Ti-MCM-41and V-MCM-41 catalysts. These materials were prepared by hydrothermal synthesis, from theoretical molar ratios silicon / metal (Si/M) = 20, 60 and 240 in the initial synthesis gel. The results of the catalytic evaluation showed that for a similar molar content of metal in the materials (0.023 mole of metal/100 g of catalyst), Ti-MCM-41 presented the best TON values. Moreover, V-MCM-41 showed a lower efficiency of H2O2 than Ti-MCM-41, which can be attributed to the presence of clusters species (V-O-V)n and nanooxides VxOy which accelerate the decomposition reaction of peroxide to water. On the other hand, it is noteworthy that the polymerization degree of the surface vanadium species and the appearance of VxOy crystallites have a significant effect on the selectivity to the products obtained.

The α-pinene dimerization in liquid phase was studied by using phosphotungstic acid catalysts H3PW12O40, (HPW) supported on commercial silica. These catalysts were characterized by XRD, FT-IR and FT-IR of pyridine adsorbed. Catalyst characterization by XRD showed the presence of HPW crystals on HPWSi catalyst. FT-IR spectra showed only bands assigned to the pyridine adsorption on Bronsted acid sites. The catalytic activity was found to depend on the reaction temperature and the amount of catalyst loaded in the reactor, and the highest selectivity in dimers corresponded to the HPW supported. Under reaction conditions 130ºC and 4% catalyst, the most active catalyst showed 100% α-pinene conversion and 55% selectivity to dimers. The selectivity to dimers increases with the increase of the reaction temperature and the amount of catalyst loaded in the reactor.

In this paper we propose the preparation of a PtSn bimetallic catalyst through techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M) using water as solvent. The system, PtSn0.2ac, was employed in the chemoselective liquid-phase hydrogenation of acetophenone, cinnamaldehyde and benzaldehyde. The results were compared with those obtained with a PtSn catalyst also prepared via SOMC/M, but using a conventional paraffinic solvent. The aqueous medium-prepared catalyst resulted to be as active in and selective to the desired product (unsaturated alcohols) as that obtained from n-heptane. This catalyst has the advantage of being prepared in a solvent compatible with the environment, without losing the superior characteristics of SOMC/M-based systems.