Insights on a Hierarchical MFI Zeolite: A Combined Spectroscopic and Catalytic Approach for Exploring the Multilevel Porous System down to the Active Sites

The hierarchization of zeolites to overcome the major drawbacks related to molecular diffusion limitation in micropores is a popular concept in heterogeneous catalysis. Despite the constant increase of new synthesis strategies to produce such hierarchical systems, the deep knowledge of their structural arrangement and how the zeolitic lattice is organized in a multilevel porous system is often missing. This information is essential to design a structure, tuning the porosity and the distribution of easily accessible active sites, and successively controlling the catalytic properties. In the present work, the synthesis of one of the most sophisticated forms of the hierarchical ZSM-5 zeolite has been reproduced, obtaining two multilevel porous materials with different crystallinity degrees, with the final aim of investigating and clarifying the finest features of their active sites. For this purpose, an extended characterization step by means of a unique multitechnique approach has been performed, thus revealing the active site nature, abundance, and distribution. IR spectroscopy with different molecular probes and a targeted catalytic test based on the hydroconversion reaction of n-decane were the toolbox for disclosing how the MFI lattice takes part in the hierarchical structure and how it, working in synergy with the mesoporous system, confers to this material a totally new shape-size selectivity. Merging the information obtained for the synthesized hierarchical zeolite with the characterization results of two reference materials (a mesoporous aluminum-containing MCM-41 and a microporous commercial ZSM-5), it was possible to define an internal and external map of the pore network of this complex and unique molecular sieve, where strong Bronsted acidic sites are located at the mouth of the MFI micropores and, at the same time, exposed at the surface of the mesoporous channels. Hence, the possibility of easily releasing bulky products is ensured and the application possibilities of the MFI lattice are expanded beyond cracking reactions

Photocatalytic degradation of acetone, acetaldehyde and toluene in gas-phase: Comparison between nano and micro-sized TiO2

Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. The photocatalytic degradation could be an interesting method to degrade them. This paper reports the photoactivity study of two classical nano-sized and two micro-sized commercial TiO2 powdered samples. Photocatalytic tests have been performed following the degradation of acetone, acetaldehyde and toluene in the gas phase under UV light. An accurate study of the intermediate oxidation products was performed. XPS and FTIR analyses allowed to highlight the relationship between TiO2 surface properties and reactivity toward VOCs explaining the different behavior of the photocatalyst in case of hydrophilic and hydrophobic pollutants

Trial policentrico multidisciplinare paritetico Radiologia-Endoscopia sul rendimento diagnostico dell'esame a d.c. di superficie dello stomaco

In extens

Epidural plus general anesthesia vs general Anesthesia alone for elective aortic surgery: effects on gastric electrical activity and serum gastrin secretion.

BACKGROUND: The aim of this study was to evaluate differences in electrogastrographic activity and serum gastrin secretion in patients subjected to general anesthesia (GA) vs blended anesthesia (BA = GA plus epidural analgesia) for abdominal aortic surgery. METHODS: Thirty-four patients (all males: 28 with abdominal aorta aneurysm, 6 with obstructive aorto-iliac disease; mean age: 68+/-7 years) were randomly assigned either to GA (N.=17) or to BA (N.=17) for abdominal aortic surgery. Each patient was evaluated for serum gastrin secretion at the time of electrogastrography (EGG) 24 h before and after surgery, using ambulatory equipment. Gastrin levels were tested under fasting conditions and after a standard meal. EGG shows gastric electrical activity that parallels gastric motor activity. RESULTS: Before surgery, no significant difference was found for any of the EGG parameters or the serum gastrin integrated value (area under the curve [AUC]) between the two groups of patients. After surgery, an increased frequency of electrical waves (tachygastria) was observed in 22% of those undergoing GA and in 5% of patients undergoing BA. The power ratio (postprandial/fasting total power) was exceedingly high (>4) in 53% of the GA patients and in 11% of the BA patients (P<0.05). The gastrin AUC was 263+/-58 pg/mL in the GA group and 179+/-92 pg/mL in the BA group (P<0.01). CONCLUSIONS: An excess of EGG activity and serum gastrin secretion was observed in patients undergoing GA vs those submitted to BA. Thus, the latter procedure seems to affect gastric function less than GA alone