49,375 research outputs found
High-Quartz solid solution phases from xerogels with conposition 2MgO·2Al2O3·5SiO2 (cordierite) and Li2O·Al2O3·nSiO2 (n=2 to 4) (β-eucriptite) characterization by XRD, FTIR and surface measurements
No full text[100714.EG "beta". SAPERI.ALTRE_INFORMAZIONI:] Si riferisce sulla preparazione di xerogeli amorfi di composizioni pari a quella della cordierite (Mg2Al4Si5O18) e della eucriptite (Li2O·Al2O3·n SiO2 dove n= da2 a 4). Questi interessanti materiali, ad elevatissimo sviluppo superficiale (fino a 900 m²/g) furono caratterizzati mediante diffrazione RX, FTIR e misure di superficie. Caratteristica peculiare di questi materiali è anche lo distribuzione monomodale del diametro dei pori, centrata attorno a 40
“Stopped-Flow Desorption” Analysis of the Nature of Strongly Adsorbed Species During n-Butane Oxidation in a Flow Reactor
No full textThe presence and the evolution as a function of time of strongly adsorbed species during n-butane oxidation in a flow reactor was studied by "stopped-flow desorption" experiments and by thermogravimetric and Fourier-transform infrared analyses on a (VO)2P2O 7 catalyst highly active/selective in the conversion of n- butane to maleic anhydride. In particular, the presence of an adsorbed species was found which desorbs as crotona1dehyde only at temperatures around 100 K higher than the reaction temperature (573 K). The parallel increase in the amount of this species formed with the change in catalytic behavior (a decrease in the rate of n-butane depletion with a parallel increase in the rate of maleic anhydride formation) suggests that due to the reduced turnover number, the formation of strongly adsorbed species causes catalyst deactivation by site blocking, but at the same time allows controlled reactivity of the surface which prevents the consecutive oxidation of maleic anhydride to carbon oxides. © 1987 Elsevier Science Publishers B.V
A study of molybdena catalysts in ethanol oxidation. Part 1. Unsupported and silica-supported MoO3
No full textBackground: Acetaldehyde is a main organic intermediate for manifold chemical products. In the near future, its production using renewable raw materials is rapidly becoming highly desirable. In this paper, investigations on pure and silica-supported molybdenum oxide (MoO3) as catalysts for the ethanol oxidative dehydrogenation process to acetaldehyde are reported. Results: Acicular pure α-MoO3 crystals and silica-gel supported MoO3 (1, 5 and 12% wtMoO3/wtsupport) were prepared by the thermal decomposition method and by incipient wetness impregnation, respectively. Catalysts were studied and extensively characterized assessing structural, morphological and chemical properties. The samples were tested in ethanol oxidative dehydrogenation through Temperature Programmed Surface Reaction (TPSR) and steady-state measurements. MoO3/SiO2 samples were constituted by MoO3 particles weakly interacting with the support, but also by some molybdate species entering the silica framework and significantly modifying the silica morphology. High catalyst acidity limits oxydehydrogenation yield, catalyzing the competitive dehydration reaction to ethylene. Thus, the highest obtained acetaldehyde yield was ≈60%. Molybdenum loss by MoO3 volatilization was found on MoO3/SiO2. Conclusion: The produced and characterized catalysts are active, and allow quite a high yield to acetaldehyde. Slight deactivation was observed and also investigated. © 2021 Society of Chemical Industry (SCI)
A study of molybdena catalysts in ethanol oxidation. Part 2. Alumina-supported and silica-doped alumina-supported MoO3
No full textBACKGROUND: γ-Al2O3 and silica-doped aluminas are largely used supports for industrial catalysts. The addition of silica to alumina modifies its acid–base properties, also affecting its dispersion ability of supported species. In this paper, investigations on the silica doping effect in alumina-supported MoO3 catalysts, developed for the oxidative dehydrogenation process of ethanol to acetaldehyde, are reported. RESULTS: MoO3 (1÷12% wtMoO3/wtsupport) supported over pure γ-Al2O3, SiO2 (1 and 5 wt.%) doped γ-Al2O3 were prepared by incipient wetness impregnation. Catalysts were studied and extensively characterized structurally, morphologically, and chemically. All samples were tested in ethanol oxidative dehydrogenation in Temperature Programmed Surface Reaction conditions. Best performing catalysts were also tested in steady-state and time-on-stream experiments. At 573 K, the best acetaldehyde yield (60% in steady state conditions) was found on 12 wt.% MoO3 over 1 wt.% SiO2 on alumina. The slight deactivation after 8 h on stream (10% activity loss) is attributed to a limited MoO3 loss by volatilization. CONCLUSION: The investigated catalysts are active and allow quite a high yield to acetaldehyde. The addition of silica to alumina increases both the conversion of ethanol and the selectivity to acetaldehyde, and reduces MoO3 volatilization, due to the higher activity of monomeric molybdates with respect to polymeric ones. The high acidity of the catalysts limits oxydehydrogenation yield, catalyzing competitive reaction to ethylene. © 2021 Society of Chemical Industry (SCI)
n-Butane selective oxidation on vanadium-based oxides : Dependence on catalyst microstructure
No full textProcess of ammonia removal from anaerobic digestion and associated ammonium sulphate production: Pilot plant demonstration
No full textA process for the continuous extraction of ammonia from anaerobic digesters is proposed. In this process, a portion of the sludge treated in the digesters is continuously withdrawn and transferred to a thin film evaporator (TFE) unit, where the ammonia is stripped through a biogas stream. The ammonia-rich biogas is treated with a sulfuric acid/water solution in a reactive absorption unit, with production of ammonium sulphate. The chemistry of a CH4/CO2/NH3 gas phase in thermodynamic equilibrium with a liquid sulfuric acid/water solution is investigated theoretically, with focus on the simultaneous absorption of CO2 and NH3 into the liquid phase. Pilot plant experimental data confirm the theoretical results. Further pilot plant experimental results obtained during on-off cycles of the stripping equipment demonstrate that, when the TFE unit is off, ammonia concentration in the digestate rises quickly, while, when the stripping equipment is turned on again, ammonia concentration drops down. On average, during the 180 days of pilot plant experimentation, 4.1 g N–NH4 per kg of sludge fed to the digester, i.e. 19.3 g N–NH4 per kg of total solids (TS) fed to the digester, are stripped from digestate and recovered as ammonium sulphate, demonstrating the feasibility of the proposed concept
Surface acidity of vanadyl pyrophosphate, active phase in n-butane selective oxidation
No full textThe surface acidity of two (VO)2P2O7 catalysts with similar specific activities per square meter of surface area in 1-butene selective oxidation, but different specific activities in n-butane selective oxidation, was studied by ammonia, pyridine, acetonitrile, CO, and CO2 adsorption, by ammonia temperature-programmed desorption, and by 2-propanol oxidation. The results for both catalysts indicate the presence of strong Brønsted sites attributed to surface P-OH groups and of medium strong Lewis sites attributed to V(IV) coordinatively unsaturated ions exposed on the surface. The presence of these centers was related to the (VO)2P2O7 structure itself and is fairly independent of the (VO)2P2O7 preparation method. However, in the (VO)2P2O7 prepared in an organic medium and to a lesser extent in the (VO)2P2O7 prepared in an aqueous medium, the presence of very strong Lewis sites also was observed. The enhancement of the rate of n-butane activation in the (VO)2P2O7 prepared in an organic medium was attributed to the presence of these sites. The role of the preparation method in the formation of such very strong Lewis sites also is discussed. © 1986 American Chemical Society
Surface Reactivity of Coals Toward Water and N-hexane - An Adsorption Microcalorimetric Study
No full textIllinois and Polish fine coal samples, previously characterized by conventional chemical analyses, have been separated by densimetric centrifugation. Both sink and float fractions have been analyzed by X-ray photoelectron spectroscopy and by adsorption microcalorimetry in contact with water and n-hexane vapors. The surface reactivity of Illinois coals (refractory to oil agglomeration processes) is higher than Polish ones (very easily agglomerable) toward both water and n-hexane. This different behavior has been attributed predominantly to the nature of the surface inorganic sites, having an acidic character in the case of Illinois coal, and a more pronounced basic character in the case of Polish coal
Beyond Cultural Aphasia.
No full textA Conversation between Rossella Ciocca and the scholar and cultural activist G. N. Devy, author of the People's Linguistic Survey of India, about nomadic communities and their endangered languages and cultures
On the activity and stability of Pt-K/Al2O3LNT catalysts for diesel sootand NOx abatement
No full texttDPNR Pt-K/Al2O3catalyst has been studied for the simultaneous removal of soot and NOx, in the presenceof both water and carbon dioxide. In particular, the effect of soot on the NOxstorage activity and onthe stability of Pt-K/Al2O3catalyst has been addressed. It has been found that: (i) the presence of sootdecreases the NOxstorage activity at any temperature in the range 250–350◦C; (ii) the stability of theadsorbed species is lower in the presence of soot; (iii) nitrates ad-species directly interact with soot andparticipate to the soot combustion; (iv) aged catalyst shows a lower storage capacity and a lower sootoxidation activity attributed to loss of K-active species
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