Isabel García

Influence of the reaction conditions and catalytic properties on the liquid-phase hydrodebromination of bromobenzene over palladium supported catalysts: activity and deactivation

The liquid-phase hydrodebromination of bromobenzene with molecular hydrogen over palladium supported catalysts was studied. The reaction was found to be structure-sensitive as regards both the initial activity and the final conversion (deactivation). The influence of the palladium content and the catalytic support effect on the initial activity were negligible in catalysts of similar metal dispersion. The supports tested, viz. SiO2/AlPO4, ZrO2 and MgO, significantly affected the catalyst deactivation. On the other hand, the addition of NaOH to the reaction medium had no effect on the initial activity, but clearly helped the reaction to be completed and avoided passivation of the catalyst. In summary, the activity of the catalyst depends almost solely on its metal particle size, whereas the deactivation of the active phase is decisively influenced in addition to metal particle size, by the nature of the catalyst support and the presence of a base in the reaction medium.

The effect of the addition of sodium compounds in the liquid-phase hydrodechlorination of chlorobenzene over palladium catalysts

Abstract The hydrodechlorination of chlorobenzene over supported palladium catalysts has been studied. The palladium catalysts deactivate as the reaction proceeds due to the HCl formed as by-product. The effect of the addition of sodium compounds has been analysed for the neutralisation of HCl. When NaOH was added to the reaction mixture, no beneficial effect was observed due to the detrimental effect of the alkaline medium on the textural and metallic properties of the catalysts. Doping the support with NaOH prior to impregnation with the metal precursor leads (after calcination and reduction) to catalysts with better activity and tolerance to deactivation, especially those obtained when using PdCl 2 as the metal precursor. Low metal dispersion and the capture of chloride by forming NaCl are the main factors contributing to the improved catalytic properties. Finally, doping the catalysts with NaOH or NaNO 3 , after reduction of the metal precursor leads to a moderate increase in initial activity and final conversion, although NaOH impregnation also gave rise to support corrosion and metal dispersion modification.

Liquid-phase hydrodehalogenation of substituted chlorobenzenes over palladium supported catalysts

Abstract The liquid-phase hydrodehalogenation of substituted chlorobenzenes has been carried out over palladium supported on AlPO4–SiO2. The hydrodehalogenation of the p-chlorobromobenzene undergo a consecutive reaction starting with the CBr hydrogenolysis. For the other substituted chlorobenzenes, the reaction proceeds through the hydrogenolysis of the CCl bond. The reaction rate obtained for the substrates with electron-withdrawing substituents is lower than that of chlorobenzene while for the substrates with electron-releasing groups it is higher. This is related to a modification of the adsorption strength of the molecule and the surface reaction trough the inductive and mesomeric effects of the substituents. The Taft equation is used to correlate the hydrodechlorination catalytic activity of the p-substituted chlorobenzenes with inductive and mesomeric parameters of the substituents. These results seem to indicate that the reaction proceeds through an electrophilic attack.

Comparison of different organic test reactions over acid–base catalysts

Abstract Three test reactions were studied: transformations of 1-phenylethanol (R 1 ), 2-propanol (R 2 ), and 2-methyl-3-butyn-2-ol (R 3 ) over several oxide catalysts. Results were correlated to acid–base properties in these solids, calculated by using temperature programmed desorption–mass spectrometry (TPD–MS) techniques with pyridine, 2,6-dimethylpyridine and carbon dioxide as probe molecules described elsewhere. The three reactions lead to concordant results on acid–base characteristic of catalysts. R 1 and R 2 test reactions are less complicated (less products) than R 3 . However, the latter follows specific ways depending on our catalyst having acid, basic or acid–base pair sites, whereas R 1 and R 2 are less specific.

Determination of isoflavones using capillary electrophoresis in combination with electrospray mass spectrometry

Various isoflavones were separated on an uncoated fused-silica capillary electrophoresis (CE) column (110 cm × 75 μm I.D.) using 25 mM ammonium acetate buffer and UV and electrospray ionization mass spectrometric (ESI-MS) detection. CE-ESI-MS with negative-ion electrospray ionization has been shown to be a suitable technique for the determination of this type of natural compound. The modest sample loading of the CE technique can be circumvented by coupling it with MS; in addition, the mass-resolving capability and high sensitivity of MS for structural analysis of mixtures can thus be exploited. Furthermore, ESI-MS allows one not only to determine the molecular mass of isoflavones, but also the presence of various functional groups according to observed losses from the [M - H]− ion during collision-induced dissociation by adjusting some MS parameters.

Analyses of phenolic compounds by capillary electrophoresis electrospray mass spectrometry

Several phenolic compounds found in olive mill wastewater were quantitatively and qualitatively analyzed on an uncoated fused-silica capillary electrophoresis column (67 cm × 75 µm i.d.) using 30 mM aqueous ammonium acetate buffer/methanol (90:10) and negative electrospray mass spectrometry detection. Quantitative analysis, with p-chlorophenol as the internal standard, was carried out by single ion monitoring Limits of detection ranged from 1 pg for 4-hydroxybenzaldehyde and protocatechuic acid to 386 pg for vanillic acid. Copyright

Qualitative and Quantitative Analyses of Phenolic Compounds by High-performance Liquid Chromatography and Detection with Atmospheric Pressure Chemical Ionization Mass Spectrometry

High-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (APCI-MS) in the negative-ion mode has been succesfully used for qualitative and quantitative determination of fifteen phenolic compounds found in olive mill wastewater. APCI gives information about both the molecular weight of these molecules and about their structure, showing consistent collision-induced dissociation pathways, which have been elucidated to give detailed information about the structure of the fragments. Quantitative analysis, using p-bromophenol as an internal standard, was carried out using calibration graphs for injections in the 0.01–1000 ng range, working both in scanning and selected-ion monitoring data aquisition modes, resulting in correlation coefficients higher than 0.98 for all compounds.

Determination of volatile organic compounds in drinking and waste water from Cordoba (Spain) by closed‐loop stripping analysis in combination with gas chromatography coupled with mass spectrometry

Analyses of volatile organic compounds (VOCs) during the different physical and chemical processes that drinking water undergoes at water‐treatment plants from Cordoba (Andalusia, Spain) have been carried out by closed‐loop stripping (CLSA) in combination with gas chromatography and detection by mass spectrometry and FID. The chloration path within the purification process has shown the formation of some halogenated compounds in the ppb range. However, the most volatile compounds that elute under the gas Chromatographic peak of the extraction solvent (CS2) cannot be determined. Furthermore, this method has been applied to analyse waste water.

Rapid determination of chlorogenic acid and related compounds in sunflower seeds by high‐performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

High-performance liquid chromatography (HPLC) in combination with atmospheric pressure chemical ionization mass spectrometry (APcI-MS) was applied to the determination of the phenolic fraction found in methanolic extracts of sunflower seeds (mainly chlorogenic acid and derived compounds). These extracts were directly separated by HPLC and detected by both negative and positive APcI-MS. Abundant structural information about these compounds can be obtained even at low extraction cone voltages. This method has been shown to be a rapid and effective method for the analysis of crude extracts from sunflower seeds.

A experimental IEEE1588-BASED system for synchronized phasor measurement in electric subestation

The proposed technique synchronizes substation Event for Wide area measurement system (WAMS). Specifically for phasor meters with synchronism needs up to the microsecond range. This Intelligent Electronic Devices (IEDs) experimental PTP-BASED system comprise three main technologies: a PTP slave LM3S8962 microcontroller, a floating point DSP (TMS320C6713) and a six simultaneous channel analog to digital converter (ADP8365) for the three current and voltage signals. For Master task a NI PCI_1588 card and a Symmetricoms XLI IEEE1588 GrandMaster system for test. For the essays we have defined 3 types of experimental systems: for subestation measurements, for laboratory measurements and for high precision Synchronism test.