Physico-Chemical Features and Catalytic Activity of Sulfated Zirconia Prepared by Sol–Gel Method. The Role of the Solvent Evaporation Step

ZrO₂–SO₄ powders have been prepared by following a single-step sol–gel preparative route using zirconium propoxide as the starting compound. Sulfuric acid was employed both as the sulfating agent and as the catalyst of the polycondensation reaction in the gel formation. Two different series of dried precursors were obtained by either evaporating the solvent in an oven at 100°C (xerogels) or in supercritical conditions (aerogels). All the samples were calcined at three temperatures (470, 550, and 630°C) for the same time length (5 h). The powders were characterized for phase composition–crystallinity, surface area–porosity, sulfur content and surface state (XPS). The catalytic activity of the calcined samples was tested in the isomerization of n-butane in a continuous system at 150°C in absence of H₂ and 250°C in presence of H₂. The role played by the conditions of the solvent elimination, at the end of the sol–gel reaction, in affecting the physico-chemical and catalytic properties of the powders is discussed.     

An FT-IR and flow reactor study of the conversion of propane on γ-Al2O3 in oxygen-containing atmosphere

The conversion of propane in the presence of oxygen over alumina has been studied using a fixed bed flow reactor. The interaction of the same catalyst with propane, propene, isopropanol and acetone has also been investigated, with additional gas-phase monitoring, in an FT-IR cell. Alumina looks active in the catalytic conversion of propane to propene, with the production of CO₂, CO, ethylene, methane as the main by-products, depending on the reaction temperature. Higher hydrocarbons such as butenes, butadiene, benzene and toluene are also found.

This reactivity is mainly attributed to the weak but not negligible Brønsted acidity of the surface OH’s of alumina, possibly activating propane in the form of isopropoxides and allowing oligomerization of propene. This shows the detrimental effect of the uncovered alumina support in the case of alumina-supported catalysts for propane oxydehydrogenation and explains the positive role of doping with basic neutralizing agents such as potassium.     

Analysis of the behaviour of a 4-stroke Si engine fuelled with ammonia and hydrogen

The use of hydrogen as fuel represents a possible solution to reduce greenhouse gas emission from vehicles. Although proper engine running with hydrogen has been widely demonstrated, hydrogen storage onboard of the vehicle is a major problem.     

Use of NOAA-AVHRR NDVI images for the estimation of dynamic fire risk in Mediterranean areas

Wildfires are a major cause of land degradation in the Mediterranean region due to their frequent recurrence in the same areas. The evaluation of fire risk is therefore of high practical importance, particularly during the summer arid season, when fires are most frequent and harmful. Recent studies have demonstrated that the evaluation of dynamic fire risk can be carried out by the use of remotely sensed images, and specifically of NOAA-AVHRR Normalized Difference Vegetation Index (NDVI) data. This use relies on the sensitivity of the index to vegetation dryness, which is a major predisposing factor for fire occurrence. Several problems, however, remain linked to the spatial variability of the risk in environmentally heterogeneous areas, which requires the application of suitable processing techniques to the low-resolution imagery.The current work reports on the development and testing of different methodologies for estimating dynamic fire risk by the use of NOAA-AVHRR data. The investigation was conducted in Tuscany (Central Italy) using a large archive of fires that occurred in the region and NOAA-AVHRR NDVI data of 16 years (1985-2000). Relying on previous methodological achievements of our group and other research groups, several procedures were tested to extract information related to fire risk from the remotely sensed images. These trials led to define an optimum method which is based on the identification of pixels where the accordance between interyear variations in fire probabilities and NDVI values is maximum. The accuracy of the risk estimates from this optimum method was finally evaluated by a leave-one-out cross-validation strategy. In this way, the performance of the methodology was assessed, together with its potential for operational fire risk monitoring and forecasting in Mediterranean areas.     

Using hot-vapor bypass for pressure control in distillation columns

Distillation column control is widely explored in literature due to its complexity and importance in chemical and petrochemical industries.In this process,pressure represents one of the most important variables to be controlled.However,there are few studies about how pressure affects the dynamic behavior of distillation columns and most research on distillation column control involve direct manipulation of cooling fluid through the condenser.Nevertheless,such an approach demands constant changes in cooling fluid flowrates that are commonly by the order of tons per hour,which can be difficult to work or even unfeasible in a real plant.Furthermore,this strategy is usually avoided,as it can cause fouling and corrosion acceleration.The hot-vapor bypass strategy fits well as a solution for these issues,eliminating the need to dynamically manipulate cooling fluid flowrates in the condensation unit.This work presents the modeling and simulation of a conventional distillation column for the separation of water and ethanol,in which a comparative study between a conventional pressure control and a control using hot-vapor bypass was performed.The main results were obtained through dynamic simulations which considered various disturbances in the feed stream,and demonstrated superior performance by the hot-vapor bypass system over the usual scheme proposed in literature,while evaluating the Integral Absolute Error (IAE) norm as the control performance index.     

Aero-thermo-chemical characterization of ultra-high-temperature ceramics for aerospace applications

Ultra-High-Temperature Ceramic (UHTC) materials, because of their high temperature resistance, are suitable as thermal protection systems for re-entry vehicles or components for space propulsion. Massive UHTC materials are characterized by poor thermal shock resistance, which may be overcome using C or SiC fibers in a UHTC matrix (UHTCMC).The University of Naples “Federico II” has a proven experience in the field of material characterization in high-enthalpy environments. A hypersonic arc-jet facility allows performing tests in simulated atmospheric re-entry conditions. The Aerospace Propulsion Laboratory is employed for testing rocket components in a representative combustion environment. Ad-hoc computational models are developed to characterize the flow field in both facilities and perform thermal analysis of solid samples.Current research programs are related to a new-class of UHTCMC materials, for rocket nozzles and thermal protection systems. The activities include design of the prototypes for the test campaign, numerical simulations and materials characterizations.     

Enhanced Charge Separation Efficiency in DNA Templated Polymer Solar Cells

The insertion of a DNA nanolayer into polymer based solar cells, between the electron transport layer (ETL) and the active material, is proposed to improve the charge separation efficiency. Complete bulk heterojunction donor–acceptor solar cells of the layered type glass/electrode (indium tin oxide)/ETL/P3HT:PC₇₀BM/hole transport layer/electrode (Ag) are investigated using femtosecond transient absorption spectroscopy both in the NIR and the UV–vis regions of the spectrum. The transient spectral changes indicate that when the DNA is deposited on the ZnO nanoparticles (ZnO‐NPs) it can imprint a different long range order on the poly(3‐hexylthiophene) (P3HT) polymer with respect to the non‐ZnO‐NPs/DNA containing cells. This leads to a larger delocalization of the initially formed exciton and its faster quenching which is attributed to more efficient exciton dissociation. Finally, the temporal response of the NIR absorption shows that the DNA promotes more efficient production of charge transfer states and free polarons in the P3HT cation indicating that the increased exciton dissociation correlates with increased charge separation.     

节能的双线、4×4按键键盘接口

可以用带有ADC的微控制器设计一个双线加接地组成的键盘接口。例如,可以用一个电阻分压器判定一个按下的键《参考文献1)。微控制器的整合ADC,其输入电阻一般在数百千欧量级,为了有足够的精度,键盘分压器应该具有相对较低电阻值,一般为数十千欧量级。但是,在电池供电系统中,电阻分压器会消耗数百毫安电流,这迫使设计者选择经典的数字矩阵开关和多条I/O线作替代。此外,便携设备设计通常也限制了元件的数量。     

Roasting and chlorine leaching of gold-bearing refractory concentrate: Experimental and process analysis

This paper deals with gold extraction from a refractory concentrate by chlorine leaching. The process considers a pre-treatment of refractory materials by low temperature oxidation carried out with low oxygen concentration. The oxidized material is treated by leaching with brine. After gold adsorption/reduction onto activated carbon, iron and base metals can be precipitated by NaOH. Roasting tests show the necessity to carry out a thermal pre-treatment at least at 550 °C to obtain a reduction of sulfur and mercury in the material (50% and 90%, respectively). Highest gold extraction yield (around 93%) is obtained in the leaching test performed with material sample treated at 650 °C. This result confirms the necessity to optimize the thermal pre-treatment to improve Au recovery and to reduce chlorine consumption. A comparison with conventional cyanidation confirms that chlorination could be an useful alternative: in fact, gold extraction yield is quite low: 57% in non-pre-treated material and 25% in pre-treatment material.