Francesco Arena

A characterization study of the surface acidity of solid catalysts by temperature programmed methods

Abstract The surface acidic properties of various solid catalysts (i.e., clay montmorillonite, acid modified smectite clay, HY zeolite, sulphate-promoted ZrO 2 (SO 2− 4 /ZrO 2 ) and Cs-exchanged dodecatungstophosphoric acid (H 0.5 Cs 2.5 PW 12 O 40 )) have been comparatively evaluated by temperature programmed desorption (TPD) measurements of adsorbed NH 3 , C 5 H 5 N and C 6 H 6 . Mathematical analysis of TPD spectra of adsorbed ammonia indicates the presence of weak, medium and strong acid sites in all the catalysts. On the basis of the TPD patterns of NH 3 , C 5 H 5 N and C 6 H 6 , the nature (Bronsted and Lewis) of the acid sites has been ascertained. Catalytic measurements in CH 3 OH dehydration and benzene alkylation indicate that besides the acidic properties, the diffusional phenomena also play a key role on the reactivity of solid acid catalysts. The superior catalytic performance of the H 0.5 Cs 2.5 PW 12 O 40 system in the above reactions has been explained in the light of a pseudo-liquid behaviour.

Highly active screen-printed electrocatalysts for water oxidation based on β-manganese oxide

A versatile screen-printing method is applied for the preparation of efficient water oxidation catalysts based on a nanostructured β-MnO2 material prepared by a redox-precipitation method, and commercial β-MnO2. The catalyst films were tested for activity in water oxidation over a range of neutral to alkaline pH. The onset of water oxidation in case of the nanostructured MnO2 films is found at an overpotential (η) of 300 mV at pH 13.6 (1.0 M NaOH), with current densities reaching 10 mA cm−2 at η = 500 mV. The screen-printed MnO2 (nano) is one of the most active manganese oxide-based catalysts reported to date, despite consisting mostly of the common pyrolusite (β-MnO2) phase, so far generally found inactive in water oxidation. The films prepared from commercial β-MnO2 were found to be moderately active, with an onset of water oxidation at η = 500 mV (pH 13.6), and currents up to 5 mA cm−2 at η = 800 mV. At pH 6, the two samples exhibit similar activity and also match or surpass the performance of recent benchmark manganese oxides. X-ray absorption spectroscopy (XAS) studies suggest that the crystal phase is unchanged after prolonged electrochemical cycling. Scanning electron microscopy (SEM) analysis indicates very little corrosion of the surface morphology after prolonged catalyst operation at alkaline pH. However, high-resolution transmission electron microscopy (HRTEM) analysis shows the formation of a small amount of an amorphous phase on the surface of the nanorods after oxygen evolution over 12 hours in alkaline media.

Structure and redox properties of bulk and supported manganese oxide catalysts

The effects of the oxide carrier (γ-Al2O3, SiO2, ZrO2, TiO2), MnOx precursor (KMnO4 , Mn(NO3)2 and Mn(CH3COO)2), loading (2–17 wt.% Mn) and preparation method on the structure and reduction pattern of MnOx-based catalysts have been systematically evaluated by X-ray diffraction (XRD) and temperature programmed reduction (TPR) measurements in the range 273–1073 K. Oxide precursor and preparation method determine both the structure and average oxidation number (A.O.N.) of the MnOx (1.5<x<2) phase in bulk and supported systems. The reducibility scale, based on the inverse sequence of the onset temperature of reduction (To,red), signals that the reduction pattern of MnOx catalysts depends upon Mn loading and nature of the oxide–support interaction, which control both dispersion and A.O.N. of the active phase.

Hydrogenation of acetylene in ethylene rich feedstocks: Comparison between palladium catalysts supported on pumice and alumina

Abstract The activity–selectivity patterns of Pd/pumice catalysts are compared with industrial and home prepared Pd/Al 2 O 3 catalysts in the hydrogenation of acetylene in ethylene rich feedstocks (front-end and tail-end cuts). The iso-kinetic relationship (IKR) approach and a new mathematical model, surface site evolution model (SSEM), are employed in this comparison. Pumice and alumina supported Pd catalysts show different metal redox properties. A similar reaction mechanism is adequate to describe the reaction pathway independently by the catalysts and the gas mixtures considered. This mechanism involves the formation of surface polymers during the catalytic reactions and different catalytic sites which are discriminated on the basis of the different steric interactions of the reagents with the surface species. Although the surface mechanism appears to be analogous for all the Pd catalysts considered, industrial Pd/Al 2 O 3 and Pd/pumice catalysts show a different activity–selectivity pattern as a consequence of their different electron density and ensemble size.

Prenatal testicular torsion: ultrasonographic features, management and histopathological findings.

Aim:  To highlight the ultrasonographic features of prenatal torsion of the testis in utero (IUTT) at presentation, the neonatal management and the histological findings postorchiectomy or biopsy.

Thoracoscopy versus thoracotomy for esophageal atresia and tracheoesophageal fistula repair: review of the literature and meta-analysis.

INTRODUCTION The thoracoscopic approach to esophageal atresia (EA) with tracheoesophageal fistula (TOF) represents a challenging procedure whose real benefits remains unclear. Our purpose is to identify, through a meta-analysis, clinical evidence of the reliability of the thoracoscopic repair (TR) for EA/TOF compared with the open repair. MATERIALS AND METHODS Defined PubMed search, with analysis of intraoperative and postoperative complications after open or thoracoscopic primary anastomosis for EA/TOF. RESULTS Five articles met the criteria of meta-analysis, being comparative studies between TR and conventional open repair (COR), although they were retrospective. One article was excluded because it was available only in Japanese. We observed a slight prevalence, statistically insignificant, of the intraoperative and postoperative complication rate for TR: odds ratio (OR) 1.29. Excluding the conversion rate, the meta-analysis between the complication rate for TR and COR did not show a significant difference (OR 0.64). Anastomosiss leaks and strictures considered together did not show a significant difference between the two techniques, p = not significant and OR of 0.56. Similar results were observed analyzing the single outcome of leaks and strictures; the meta-analysis did not show any significant differences with an OR, respectively, of 1.05 and 0.43. CONCLUSIONS The effectiveness of the endoscopic technique for EA/TOF repair is indicated with outcomes not different from open surgery. A randomized controlled trial is needed in this field to indicate which procedure is superior, open or TR.

Late hormonal function after testicular torsion

INTRODUCTION Testicular torsion may be an important cause of male infertility. We aimed to investigate the late hormonal function in patients with testicular ischemia/reperfusion injury of the testis after orchidectomy or detorsion. METHODS Twenty patients (mean age, 13.6 years) were prospectively evaluated at a mean of 5 years after testicular torsion. The serum follicle-stimulating hormone, luteinizing hormone (before and after gonadotropin-releasing hormone stimulation), testosterone, and inhibin B were measured. Fifteen age-matched adolescents without evidence of endocrine disease were used as controls for inhibin B values. Data are quoted as mean +/- SEM. RESULTS Twelve patients were treated with detorsion and orchidopexy, and 8 underwent orchidectomy. Serum follicle-stimulating hormone, luteinizing hormone, and testosterone were all within the reference range. Inhibin B levels were significantly reduced in the 2 groups compared with the controls (34.5 +/- 5.2 vs 63.9 +/- 12.8 pg/mL, P = .02), but were not significantly different between the orchidectomy group and the group that underwent detorsion (41.3 +/- 9.7 vs 30.4 +/- 5.9 pg/mL, P = .41). CONCLUSION Hormonal testicular function can be compromised after testicular torsion, although the type of surgery (orchidectomy or orchidopexy) does not seem to change the effect of this ischemia/reperfusion injury.

How oxide carriers affect the reactivity of V2O5 catalysts in the oxidative dehydrogenation of propane

The catalytic pattern of several oxide carriers (MgO, Al2O3, ZrO2, TiO2, SiO2, HY zeolite) and supported V2O5 (4.7–5.3 wt%) catalysts in the oxidative dehydrogenation of propane to propylene (PODH) has been comparatively investigated. The fundamental role of the oxide support on both reducibility and reactivity of vanadia catalysts has been assessed. A direct relationship between the specific surface activity of oxide carriers and that of vanadia catalysts is discussed. The inverse relationship between the specific activity and the onset temperature of reduction marks the prevailing redox behaviour of V2O5 catalysts in the PODH reaction.

FTIR spectroscopic investigation of the active sites on different types of silica catalysts for methane partial oxidation to formaldehyde

Several commercial silica samples showing different catalytic activities in the partial oxidation of methane (MPO) to formaldehyde have been investigated using FTIR technique. Two IR absorption bands at 893 and 909 cm−1, observed upon dehydroxylation of the silica catalysts and assigned to reactive siloxane sites on the surface (“strained siloxane bridges”), were found to disappear upon heating in methane at high temperature. The catalytic activity increases together with the intensity of the bands due to such “strained” sites in the different SiO2 samples.

Gastrointestinal sequelae in survivors of congenital diaphragmatic hernia

Background: Gastrointestinal sequelae have been sporadically reported in survivors of congenital diaphragmatic hernia (CDH). The aim of the present paper was to evaluate the gastrointestinal morbidity in infant, adolescent and adult patients who had undergone repair of CDH.