Partial oxidation of toluene to benzaldehyde and benzoic acid over model vanadia/titania catalysts: Role of vanadia species

Pure and K-doped vanadia/titania prepared by different methods have been studied in order to elucidate the role of vanadia species (monomeric, polymeric, bulk) in catalytic toluene partial oxidation. The ratio of different vanadia species was controlled by treating the catalysts in diluted HNO3, which removes bulk vanadia and polymeric vanadia species, but not the monomeric ones, as was shown by FT-Raman spectroscopy and TPR in H2. Monolayer vanadia species (monomeric and polymeric) are responsible for the catalytic activity and selectivity to benzaldehyde and benzoic acid independently on the catalyst preparation method. Bulk V2O5 and TiO2 are considerably less active. Therefore, an increase of the vanadium concentration in the samples above the monolayer coverage results in a decrease of the specific rate in toluene oxidation due to the partial blockage of active monolayer species by bulk crystalline V2O5. Potassium diminishes the catalyst acidity resulting in a decrease of the total rate of toluene oxidation and suppression of deactivation. Deactivation due to coking is probably related to the Brønsted acid sites associated with the bridging oxygen in the polymeric species and bulk V2O5. Doping by K diminishes the amount of active monolayer vanadia leading to the formation of non-active K-doped monomeric vanadia species and KVO3

Influence of Potassium Doping on the Formation of Vanadia Species in V/Ti Oxide Catalysts

The influence of potassium on the formation of surface vanadia species on V/Ti oxide catalysts contg. from 0.2 to 5 monolayers of vanadia (K/V at. surface ratio ?1) has been investigated by temp. programmed redn. in hydrogen and by FT-Raman spectroscopy under dehydrated conditions. In the pure catalysts, monomeric and polymeric (metavanadate-like) species, \"amorphous\" and bulk cryst. V2O5 were detected depending on the surface vanadia loading. In the K-doped catalysts, vanadia species formed on the surface depend also on the K/V at. ratio. Even at small K/V ratios, K inhibits the formation of the polymeric species in favor of the \"K-doped\" and/or \"K-perturbed\" monomeric species. These species possess lengthened V:O bonds with respect to the monomeric species in the undoped V/Ti oxides. At K/V = 1, the \"K-doped\" monomeric species and \"amorphous\" KVO3 are mainly present on the surface. Redn. of vanadia forms in the K-doped catalysts takes place at higher temps. than in the catalysts where potassium was absent. The monomeric and polymeric species, which are the active sites in partial catalytic oxidn., have the lowest redn. temp. Vanadia species formed on the com. titania, contg. K, were also elucidated. The catalysts were characterized via XPS, high-resoln. transmission electron microscopy, and Brunauer-Emmett-Teller surface area measurements. [on SciFinder (R)

Implication of the Acid-Base Properties of V/Ti-oxide Catalyst in Toluene Partial Oxidation

The work presents the effect of K-doping on V/Ti-oxides taking into account: the surface acid–base properties and the structure of surface vanadia species in respect to the catalyst performance and deactivation. The structure of active surface species determines redox properties, which are related to the catalytic performance by the Mars–van Krevelen mechanism. The reducibility of surface vanadia is studied by temperature-programmed reduction (TPR) in H2. The molecular structure of surface vanadia is determined by FT-Raman spectroscopy in a controlled atmosphere. Surface acid–base properties are characterised via temperature-programmed desorption (TPD) of pyridine with mass spectrometric analysis of the products. Transient response techniques with continuous monitoring of the composition of gaseous phase are applied to follow the catalyst surface transformations. Evolution of benzaldehyde (BA) formed during interaction of toluene with the pre-oxidised catalyst (without gaseous oxygen) gives information about the nucleophilicity of surface oxygen. Addition of potassium to surface vanadia leads to an increased oxygen nucleophilicity, resulting in a higher selectivity towards BA formation. In general, increase in surface basicity decreases catalytic activity, but at the same time the catalyst deactivation due to coking is suppressed. This allows catalyst optimisation in view of a better control of the partial oxidation process

Aspetti epidemiologici della calcolosi di calcio in Italia: distribuzione dei fenotipi intermedi nella popolazione italiana

n/

Pathology reporting in neuroendocrine neoplasms of the digestive system: everything you always wanted to know but were too afraid to ask

During the 5th NIKE (Neuroendocrine tumors Innovation in Knowledge and Education) meeting, held in Naples, Italy, in May 2019, discussions centered on the understanding of pathology reports of gastroenetropancreactic neuroendocrine neoplasms. In particular, the main problem concerned the difficulty that clinicians experience in extrapolating relevant information from neuroendocrine tumor pathology reports. During the meeting, participants were asked to identify and rate issues which they have encountered, for which the input of an expert pathologist would have been appreciated. This article is a collection of the most rated questions and relative answers, focusing on three main topics: 1) morphology and classification; 2) Ki67 and grading; 3) immunohistochemistry. Patient management should be based on multidisciplinary decisions, taking into account clinical and pathology-related features with clear comprehension between all health care professionals. Indeed, pathologists require clinical details and laboratory findings when relevant, while clinicians require concise and standardized reports. In keeping with this last statement, the minimum requirements in pathology datasets are provided in this paper and should be a baseline for all neuroendocrine tumor professionals

Commentary: Case Report: Abdominal Lymph Node Metastases of Parathyroid Carcinoma: Diagnostic Workup, Molecular Diagnosis, and Clinical Management

In the issue of March 2021, Lenschow et al. reported the case of a 46-year-old woman with recurrent, programmed death-ligand-1 (PD-L1) negative, tumor mutational burden (TMB)-high parathyroid carcinoma (PC), who showed stable disease as her best response on imaging, and a three-fold drop in PTH after treatment with intravenous pembrolizumab. Given the remarkable results obtained by Lenschow et al. with the anti-PD-1 agent pembrolizumab in the above-mentioned case, we performed an extensive search for possible further relevant data sources, including a) full published articles in international online databases (PubMed, Web of Science, Scopus, and Embase); b) preliminary reports in selected international meeting abstract repositories (American Society of Clinical Oncology, ASCO; European Neuroendocrine Tumor Society, ENET; European Society for Medical Oncology, ESMO); c) registered clinical trials in the U.S. National Institutes of Health registry of clinical trials (http://clinicaltrials.gov) and in any primary register of the WHO International Clinical Trials Registry Platform (ICTRP)

Transient kinetics and in situ spectroscopic techniques for the characterisation of V/Ti-oxide catalysts in toluene partial oxidation

Development of selective oxidation catalysts is a major concern of modern chemical industry. Among several systems, VTi-oxide based catalysts showed the most promising and versatile, able to catalyse key reactions like oxidation of o-xylene to phtalic anhydride and the abatement of NOx for pollution control. Extensive investigation in the past decades concluded that supported vanadia is present as a layer of molecularly-defined surface compounds VxOy, ("monolayer species") on top of the carrier oxide which are the catalytically active sites. Despite all the efforts to correlate the activity of VTi-oxide with its structure, the catalytic role of the different active species in the selective oxidation of hydrocarbons and how to tune their properties are still open questions. The goal of the present thesis is the in situ characterisation of V/Ti-oxide by transient-response chemical (feed step-response, temperature-programmed analyses) and spectroscopic (infrared and Raman) techniques to answer these important questions by using toluene partial oxidation as test reaction. First, the identification and elucidation of the role of the vanadia species was carried out, using Raman spectroscopy and activity tests. The strongly-bound monolayer species which cannot be dissolved by acid treatment were found to have isolated vanadate structure and be catalytically active in toluene partial oxidation. They have redox properties close to more condensed vanadate ("polymeric") species, which are also active. Vanadium present as crystalline V2O5 is not directly active, but plays a role in the surface reduction mechanism. By in situ DRIFTS, it has been shown that V/Ti-oxide active sites work with a coupled mechanism of product desorption and site reoxidation. Re-oxidation can occur either by reaction with gas-phase O2 or by oxygen spillover from bulk V2O5. Acidity associated with V-O-V bridges in monolayer species is likely responsible for the reversible deactivation of the catalysts caused by strongly held surface coke. Second, the modification of the acid/base catalyst properties by K addition and the formation of surface V oxide species were studied. The presence of K modifies the molecular structure of the vanadia surface species and forms new K-containing ones. These species are difficult to reduce in hydrogen and they are not catalytically active. Their presence causes a diminished catalytic activity. At the same time, Lewis and Brønsted acidity is depressed. This eliminates the phenomenon of deactivation. The excessive basicity caused by potassium addition has a detrimental effect on selectivity in benzoic acid, which is strongly held on the surface because of their intrinsic acidity and undergoes overoxidation to CO2. Finally, the VTi-oxide was supported on structured supports based on woven fibreglass. The use of structured beds is interesting in chemical engineering due to their advantages in terms of increased mass and heat trasfer, reduced pressure drop and optimal flow distribution. In order to reach optimum performance, the rather inert silica surface must be modified by adding an alumina layer on top of the fibres. This modification is essential for an optimal support because of insufficient dispersion of the titania layer on silica due to phase repulsion between the two oxides. The structured catalysts possess comparable activity and identical selectivity to the studied non-structured VTi-oxide catalyst with the same content of vanadia layers

IDENTIFICATION AND INVESTIGATION OF SHALLOW PALEOCHANNELS IN THE CHAMELECON VALLEY (HONDURAS): 1D VS 2D ELECTRICAL RESISTIVITY SURVEYS

Electrical Resistivity Tomography (ERT) and resistivity depth sounding surveys were undertaken at two sites located along the Chamelecòn Valley (Honduras). The objective of the surveys was to determine the occurrence, geometry and lithological properties of the Chamelecòn River’s shallow paleochannels. Following the interpretation of aerial photograms which indicated the likely presence of paleochannels, two sites were selected for the surveys. Resistivity depth soundings were used to achieve electro-stratigraphic sections obtained by interpolating 1D inverted data that would assist with assessing the occurrence of paleochannels at a large scale. The presence of paleochannels at the two sites was assessed through interpretation of the electro-stratigraphic sections. At Site 2, the abundant 1D data, the small distance between the soundings and the shallow target, allowed determining the course of the paleoriver as shown by resistivity and electrical transmissivity maps. The results from the 1D data, although affected by strong heterogeneities, are congruent with the 2D inverted models. ERT surveys confirmed the presence of paleochannels and allowed achieving detailed imaging of the alluvial geological bodies. Paleochannel deposits show resistivity values ranging between 70 and 100 ohm m at Site 1, while resistivity values range between 90 and 120 ohm m at Site 2. The latter resistivity values were affected by the presence of coarser deposits. Resistivity values suggest that at both sites paleochannel deposits have a clay content that is lower than 3 %. Other alluvial deposits in the area show resistivity values that range between 19 and 70 ohm m at Site 1, while resistivity values range between 30 and 90 ohm m at Site 2. These lower values suggest that clay content can be as high as 29 %. The presence of paleochannels assessed by means of 1D surveys and the lithological characterisation assessed by means of 2D surveys were confirmed by logs from boreholes drilled at the sites