1,721,129 research outputs found
Catalytic materials based on silica and alumina: Structural features and generation of surface acidity
No full textThe structural, surface chemical and catalytic properties of the materials belonging to the SiO2-Al2O3 system are reviewed critically. In particular, amorphous silicas, transitional aluminas, different silica-aluminas (silica-rich and alumina-rich) and protonic zeolites are taken into consideration. The nature of the acid sites, of the Lewis and of the Bronsted type, over these surfaces is discussed and rationalized, based on the fundamental chemistry and structural chemistry of silicon and aluminum compounds
Silica-alumina catalytic materials: A critical review
No full textThe applications of silica-aluminas in industrial catalytic processes are briefly reviewed. The literature data on the surface chemistry and structural chemistry of silica-aluminas are summarized. The Al-stuffed amorphous silica model is proposed for fully amorphous materials, and described. The reasons for the versatility of these materials as acid or acido-basic catalysts as well as tunable supports for metal and sulphide catalysts are also discussed
Critical Aspects of Energetic Transition Technologies and the Roles of Materials Chemistry and Engineering
No full textThe perspectives of technological advances needed for short term energetic transition are briefly reviewed and discussed critically. In particular, the technologies for the greenhouse gas emission-free production of electrical energy, its storage and transport, the production, transport, storage and use of hydrogen, and the use of biomass derived technologies are shortly and critically reviewed. Critical aspects are emphasized. The role of chemistry, and in particular materials chemistry and engineering, in short-term developments are underlined
Statistical pattern recognition approach for long-time monitoring of the G.Meazza stadium by means of AR models and PCA
No full textIn recent years, the interest for the automatic evaluation of the state of civil structures is increased. The development of Structural Health Monitoring is allowed by the low costs of the hardware and the improving of the computational capacity of computers that can analyze considerable amount of data in short time. A Structural Health Monitoring (SHM) system should continuously monitor structures, extracting and processing relevant information, to efficiently allocate the resources for maintenance and ensure the security of the structure. Considering the latest developments in this field, great attention has been paid to data-based approaches, especially to autoregressive models; these econometric models, born in the field of finance, are usually used to analyze the vibration time series provided by the sensors applied on the monitored structures. Indexes based on these autoregressive models can be used as features by which the structural integrity can be assessed. This work proposes the application of a multivariable analysis, Principal Component Analysis (PCA), to the set of the autoregressive model parameters estimated on the vibration responses of a real structure under operational conditions. This approach reduces a complex set of data to a lower dimension, by representing the behavior of the structure through the few variables. This work uses the principal components of the autoregressive model parameters as indicators that can effectively describe different operational levels and some important environmental effects. The strategy is applied for the first time on the data collected by the long-time monitoring system installed on the stands of the G. Meazza stadium in Milan. The results will show that this procedure is effective in representing the status of the structure and can be used in a structural health monitoring prospective
Adsorption and oligomerization of isobutene on oxide catalyst surfaces. A Fourier-transform infrared study
No full textThe F.t.i.r. spectra of isobutene adsorbed at 170-300 K on the pure oxides silica, alumina, magnesia and titania, as well as on the phosphated samples prepared by impregnation of these pure oxides and of silica-alumina with phosphoric acid have been recorded. At low temperatures (170-220 K), molecularly adsorbed species are observed on pure oxides, with a spectrum similar to that of liquid isobutene, although with specific perturbations of the modes primarily involving the vinylidene moiety. Isobutene is transformed only on titania even at low temperatures into a new compound identified as its dimer 2,4,4-trimethylpent-1-ene. On phosphated samples oligomerization occurs at 293 K, producing oligomeric species identified as 5-10 monomeric unit cationic polymers
From Surface Science to Industrial Heterogeneous Catalysis
No full textThe different types ofindustrial heterogeneous catalysis heterogeneous catalyst currently applied in the chemical industry are described. The catalytic activity is correlated to their main surface properties, which are the object of investigation based on surface science and theoretical calculations. Acidic, basic, oxidation, hydrogenation, and dehydrogenation catalysts are described. Metal, oxide, sulfide, and halide catalytic materials are considered. The practical need for promoters and stabilizers is underlined, frequently resulting in multicomponent and multiphasic catalytic systems. The complexity and multidisciplinarity of the field of heterogeneous catalysis research are emphasized, where collaboration among chemical engineers, material scientists, physical, inorganic, and organic chemists, and surface and material physicists is needed to fully understand phenomena and develop technologies. As a case study, the steam reforming process for producing hydrogen from natural gas is considered. The available data make it clear that knowledge on the molecular phenomena for most industrial processes is still largely incomplete and subject to debate. It is emphasized that surface science and surface chemistry, as well as computational studies, are needed to further improve existing technologies and to apply heterogeneous catalytic processes in the new era of industrial chemistry based on renewables
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Reutilization of silicon- and aluminum- containing wastes in the perspective of the preparation of SiO2-Al2O3 based porous materials for adsorbents and catalysts
No full textThe waste materials available as sources of silicon and aluminum for producing porous materials like amorphous silicas, aluminas, amorphous silica-aluminas, and zeolites, to be used as catalyst and adsorbents, are briefly summarized. The procedures for preparing these materials from wastes are also taken into account. The limits of this approach in terms of economy and environmental protection are also briefly considered. It is concluded that mesoporous materials can be prepared from wastes, but care to product quality and to overall process efficiency is needed
Study on the thermal decomposition of plastic residues
No full textThe use of plastics in the last decades significantly increased, thus plastic recycling processes are needed. Generally, mixtures of plastic materials are disposed together, hence the recovery of the polymeric material is difficult and expensive. Plastic residues could be valorized by thermal degradation processes aimed at recovering energy and/or valuable compounds for chemical industry. The main technologies used for this purpose are gasification and pyrolysis. The latter is a thermal degradation process that occurs in the absence of oxygen at moderate temperature (300-700°C), that could be used to recover the thermal power of biomasses. The reaction products are bio-oil, biogas and biochar. The aim of this work was to employ pyrolysis to energetically exploit different pure plastic materials, namely polyethylene terephthalate (PET), polyamide (Nylon-6), polyvinyl chloride (PVC) and polyurethane (PU), as well as a complex one such as end of life tyres (ELT). The reaction was performed at 400 °C for 90 min. The pyrolysis system was composed by a tubular quartz reactor heated with a tubular vertical oven. An integrated condenser was used to separate the liquid reaction products, while the incondensable gases were collected in a latex balloon. The reaction products were quantified gravimetrically and, in order to evaluate the functional groups, characterized by FTIR analysis. The reaction gases were also analyzed by GC-MS to determine the composition of this fraction. Results obtained from the different plastics were significantly different in terms of distribution and composition. In particular, PET produced a biogas consisting mainly of acetaldehyde and hydrocarbons, while the liquid fraction was composed of benzoic and terephthalic acids. Nylon-6 degraded producing a large amount of reaction gas (65 g/100g) composed of ammonia and light hydrocarbons, while the reaction liquid was mainly caprolactam. Around 53 g/100g of PVC reaction products were gaseous, mainly hydrochloric acid, followed by toluene and benzene at high concentrations. The degradation of PU produced a reaction gas, mainly composed by formic and acetic aldehydes. ELT pyrolysis was responsible for the production of high amounts of solid residue, while reaction gas and liquid seemed to be mainly constituted by hydrocarbons. In general, the study of pure plastic pyrolysis could help to better understand the thermal decomposition of complex plastic residues such as ELT
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