Donato A.G. Aranda

Study of Soybean Oil Hydrolysis Catalyzed by Thermomyces lanuginosus Lipase and Its Application to Biodiesel Production via Hydroesterification

The process of biodiesel production by the hydroesterification route that is proposed here involves a first step consisting of triacylglyceride hydrolysis catalyzed by lipase from Thermomyces lanuginosus (TL 100L) to generate free fatty acids (FFAs). This step is followed by esterification of the FFAs with alcohol, catalyzed by niobic acid in pellets or without a catalyst. The best result for the enzyme-catalyzed hydrolysis was obtained under reaction conditions of 50% (v/v) soybean oil and 2.3% (v/v) lipase (25 U/mL of reaction medium) in distilled water and at 60°C; an 89% conversion rate to FFAs was obtained after 48 hours of reaction. For the esterification reaction, the best result was with an FFA/methanol molar ratio of 1:3, niobic acid catalyst at a concentration of 20% (w/w FFA), and 200°C, which yielded 92% conversion of FFAs to soy methyl esters after 1 hour of reaction. This study is exceptional because both the hydrolysis and the esterification use a simple reaction medium with high substrate concentrations.

Comparison between several methods of total lipid extraction from Chlorella vulgaris biomass

The use of lipids obtained from microalgae biomass has been described as a promising alternative for production of biodiesel to replace petro-diesel. It involves steps such as the cultivation of microalgae, biomass harvesting, extraction and transesterification of lipids. The purpose of the present study was to compare different methods of extracting total lipids. These methods were tested in biomass of Chlorella vulgaris with the solvents ethanol, hexane and a mixture of chloroform:methanol in ratios 1:2 and 2:1. The solvents were associated with other mechanisms of cell disruption such as use of a Potter homogenizer and ultrasound treatment. The percentage of triglycerides in the total lipids was determinated by the glycerol-3-phosphate oxidase-p-chlorophenol method (triglycerides monoreagent K117; Bioclin). Among the tested methods, the mixture of chloroform:methanol (2:1) assisted by ultrasound was most efficient, extracting an average of 19% of total lipids, of which 55% were triglycerides. The gas chromatographic analysis did not show differences in methyl ester profiles of oils extracted under the different methods.

A study of the promoting effect of noble metal addition on niobia and niobia alumina catalysts

The catalytic activity of Nb 2 O 5 and Nb 2 O 5 /Al 2 O 3 -supported metal catalysts was evaluated in the n-heptane conversion, CO hydrogenation and butadiene hydrogenation. After high temperature of reduction (HTR), the metal adsorption capacity decreases on all the samples, due to the reduction of Nb 2 O 5 with subsequent blocking of metal atoms and bimetallic effect. It was also observed that the activity decay caused by metal-support interaction was remarkably inhibited on the bimetallics with respect to the monometallics by comparing reaction rates after HTR. Thus, the addition of Rh to Co, Cu to Pd and Sn to Pt on niobia catalysts significantly altered the product distribution in Fischer-Tropsch synthesis (FTS) and in the hydrogenation and dehydrogenation of hydrocarbons, respectively. In addition, an unusual bifunctional effect was obtained in Pt/Nb 2 O 5 /Al 2 O 3 catalyst.

The promoting effect of noble metal addition on niobia-supported cobalt catalysts

Abstract The promoting effects of a noble metal (Pd, Pt, Rh) added to Co/Nb 2 O 5 catalysts were studied by varying the Me/Co atomic ratios. Acid niobium was calcined to niobium pentoxide. The surface and bulk structures of the calcined materials were characterized by XPS and TPR techniques. The catalytic performance was obtained with CO hydrogenation. The addition of a noble metal promoted the reduction of Co 3+ and Co 2+ phases at the surface. XPS results revealed that Co 2+ species are well dispersed as a thin layer around the niobium support together with Co 3 O 4 crystallites islands. The CO 3 O 4 /Co 2+ ratio depends on the surface area of the support. XPS measurements also revealed that PdO, Rh 2 O 3 and PtO 2 are the main phases in the mono and bimetallic catalysts. The activity of the bimetallic catalysts increased and the stability was already attained. The selectivities towards C 5 + and oxygenates increased with the addition of Rh up to an atomic ratio of 0.5 and decreased beyond that. This behavior is similar for both temperatures of reduction at 573 and 773 K.

Characterization and dehydrogenation activity of Pt/Nb2O5 catalysts

Pt/Nb2O5 catalysts were prepared with different loadings of Pt and characterized by TPR, DRS, H2 and CO chemisorption and H2/O2 titration. Higher metal content catalysts presented an increasing SMSI effect related to a lower adsorption capacity. The Pt blocking by NbOx species causes the formation of new interfacial active sites. After a high temperature reduction, the catalysts were highly selective towards dehydrogenation products and total inactive for hydrogenolysis in the case of n-heptane conversion.

Characterization of Pt-Sn bimetallic catalysts supported on alumina and niobia

Abstract Alumina and niobia Pt-Sn supported bimetallic catalysts were characterized by TPR, hydrogen chemisorption and cyclohexane dehydrogenation. The TPR profiles of niobia supported Pt-Sn catalysts showed the presence of different precursors from the ones obtained on alumina. Furthermore, the hydrogen uptakes indicated that the amount of metallic tin formed in the niobia supported catalysts was higher than in the alumina supported catalysts. After reduction at 773 K, the platinum/niobia catalyst displayed a strong metal-support interaction (SMSI) effect, with the creation of new interfacial active sites. The addition of a small tin content led to a suppression of the SMSI. Increasing the amount of tin, however, induced a marked poisoning of the platinum.

Effect of preparation method on the properties of Nb2O5 promoted platinum catalysts

Abstract Pt/Nb2O5 catalysts were prepared on a reducible support by ion exchange and incipient wetness of different platinum salts. The Pt/Nb2O5/Al2O3 catalysts were prepared with several loading of niobium oxide over alumina, aiming different surface coverages and platinum dispersions. These catalysts were characterized by using different techniques: TPR, DRS, chemisorption of H2, CO, CO2 and pyridine. The catalytic activity was evaluated in the n-heptane conversion. Platinum oxide was the main surface precursor on the Nb2O5 supported catalysts, while a oxychloroplatinum surface complex was the precursor for Pt/Nb2O5/Al2O3 catalysts. These different precursors promote the formation of different platinum particle sizes, being the Pt/Nb2O5/Al2O3 samples more disperse. After high temperature of reduction, the platinum adsorption capacity decrease on all the samples, due to the reduction of Nb2O5, and subsequent blocking of surface platinum atoms. Nb2O5 and Nb2O5/Al2O3 supported catalysts are very selective to olefins in the n-heptane conversion. Furthermore, Bronsted acidic sites are formed on Pt/Nb2O5/Al2O3 catalysts with higher Nb2O5 loading, leading to a better stability of the catalysts.

The nature of metal oxide on adsorptive and catalytic properties of Pd/MeOx/Al2O3 catalysts

Abstract The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO 3 /Al 2 O 3 catalyst than on the Pd/CeO 2 /Al 2 O 3 and Pd/Nb 2 O 5 /Al 2 O 3 catalysts. The explanation for the very high N 2 production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Me δ + stoichiometric reaction. The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N 2 selectivity.

Oxidation and reduction effects of propane-oxygen on Pd-chlorine/alumina catalysts

Pd–chloride precursor salt was used to prepare Pd/Al2O3 catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was related to the Pd2+ sites observed on Pd/Al2O3 through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H2, the IR spectra showed the linear and bridge adsorbed CO species on the Pd0 surface. After propane reaction, a new band at 2130 cm-1 related to CO adsorption on Pd2+ species was noted. Carbon monoxide species adsorbed on Pd0 were also observed in all samples after reaction. Our results suggest surface ratios of Pd0/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However, the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible formation of palladium hydroxide (Pd–OH) at the surface, diminishing the number of active surface sites. Dynamic fluctuations into the reaction conditions supported the idea that a pseudo‐equilibrium adsorption–desorption of water was reached. After water removal or increasing in the reaction temperature the equilibrium was shifted to the direction of OH–Pd decomposition. This behavior suggests that the inhibitory effect of water is a reversible phenomenon, being a function of the amount of water and the reaction temperature.

Activity and selectivity of Pt-Sn/Nb2O5 in n-heptane conversion

Abstract The catalytic properties of niobia and alumina supported platinum and platinum-tin catalysts were evaluated at the conversion of n-heptane at 773K. Over a niobia supported platinum catalyst the reaction proceeded via a monofunctional path, with a high selectiviy for oleflns. This was explained by the formation of a SMSI state, leading to the coverage of platinum particles by NbO x and the formation of metal-support interfacial sites. The presence of tin inhibited the formation of a SMSI state, causing a decrease in the olefins/toluene ratio.