63 resultados para Steam reforming


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Social work in the UK is currently undergoing a process of major reform and a wide range of recommendations have been made aimed at improving practice and education. This paper focuses on the Social Work Reform Board's proposals for improving practice learning in qualifying level social work education. It examines how recommendations for better partnership working between Higher Education Institutions and employers and developing critical reflection in agencies are likely to impact on student learning. Drawing on experience of social work education in Northern Ireland it considers the potential of the Reform Board's proposals for improving the quality of practice learning and enhancing students' preparedness for employment. The paper concludes that differences in educational aims and priorities, resistant practice cultures and cut-backs in resourcing could present major obstacles that must be overcome if this potential is to be realised.

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Ni/K-MgO-ZrO catalysts for dry reforming of methane, with a range of Mg/Zr ratios and each containing about 10 wt% Ni, were prepared via Ni nitrate impregnation on MgO-ZrO supports synthesized by co-precipitation using KCO. It was found that a proportion of the potassium of the precipitant remained in the samples and improved the stability of the catalysts in the reaction. It was also shown that reduction of the catalysts at 1,023 K without calcination in air is necessary for stable and high activity; calcination in air at 1,073 K gives a deterioration of the catalytic properties, leading to rapid deactivation during the reaction. The order of the CH conversions of the reduced catalysts after 14 h on stream was as follows: Ni/K-MgZr ~ Ni/K-Mg ≥ Ni/K-MgZr Ni/K-Zr. A catalyst with 0.95 wt% K on MgO-ZrO with a Mg:Zr mole ratio of 5:2 showed the best resistance to deactivation. Experiments in a microbalance system showed that there was only negligible coke deposition on the surface of this sample. This behaviour was attributed to the presence of Ni nanoparticles with a diameter of less than 10 nm located on a MgO/NiO solid solution shell doped by K ions; this in turn covers a core of tetragonal ZrO and/or a MgO/ZrO solid solution. This conclusion was supported by EDS/TEM, XPS, XRD and H chemisorption measurements. © 2013 Springer Science+Business Media New York.

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The aqueous phase reforming (APR) of xylitol was studied in a continuous fixed bed reactor over three catalysts: Pt/Al2O3, Pt/TiO2 and Pt-Re/TiO2. The data obtained in the case of the monometallic Pt catalysts was compared to the bimetallic Pt-Re sample. The effect of Re addition on the catalyst stability, activity, product formation and selectivity toward hydrogen and alkanes was studied. The bimetallic catalyst demonstrated a higher selectivity to alkanes compared to the monometallic samples. The monometallic catalyst was more selective toward hydrogen formation. A plausible reaction scheme explaining differences in selectivity toward hydrogen and alkanes was proposed and discussed.

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Gas-to-liquid processes are generally used to convert natural gas or other gaseous hydrocarbons into liquid fuels via an intermediate syngas stream. This includes the production of liquid fuels from biomass-derived sources such as biogas. For example, the dry reforming of methane is done by reacting CH4 and CO2, the two main components of natural biogas, into more valuable products, i.e., CO and H2. Nickel containing perovskite type catalysts can promote this reaction, yielding good conversions and selectivities; however, they are prone to coke laydown under certain operating conditions. We investigated the addition of high oxygen mobility dopants such as CeO2, ZrO2, or YSZ to reduce carbon laydown, particularly using reaction conditions that normally result in rapid coking. While doping with YSZ, YDC, GDC, and SDC did not result in any improvement, we show that a Ni perovskite catalyst (Na0.5La0.5Ni0.3Al0.7O2.5) doped with 80.9 ZrO2 15.2 CeO2 gave the lowest amount of carbon formation at 800 °C and activity was maintained over the operating time.

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Highly reactive radicals play an important role in high-temperature gasification processes. However, the effect of radicals on gasification has not been systematically investigated. In the present study, the formation of carbon-radical precursors using atomic radicals such as OH, O, and H and molecules such as H2 and O2 was characterized, and the effect of the precursors on the adsorption step of steam char gasification was studied using quantum chemistry methods. The results revealed that the radicals can be chemisorbed exothermically on char active sites, and the following order of reactivity was observed: O > H2 > H > OH > O 2. Moreover, hydrogen bonds are formed between steam molecules and carbon-radical complexes. Steam molecule adsorption onto carbon-O and carbon-OH complexes is easier than adsorption onto clean carbon surfaces. Alternatively, adsorption on carbon-O2, carbon-H2, and carbon-H complexes is at the same level with that of clean carbon surfaces; thus, OH and O radicals accelerate the physical adsorption of steam onto the char surface, H radical and O2 and H2 molecules do not have a significant effect on adsorption. © 2010 American Chemical Society.

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A systematic theoretical study on the adsorption of steam and its thermal decomposition products on carbon both zigzag and armchair surface was performed to provide molecular-level understanding of the reaction activity of all these reactants in biomass steam gasification process. All the calculations were carried out using density functional theory (DFT) at the B3LYP/6-31+g(d,p) level. The structures of carbonaceous surfaces, all reactants and surface complexes were optimized and characterized. Based on the value of adsorption heat been obtained from the calculation, the activity of all reactants can be ordered as: O > O2 >H2 >H >OH >H2O for both zigzag and armchair surface, and the adsorption style is physisorption to water molecule and chemisorption to the other dissociated components.

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Dry reforming is a promising reaction to utilise the greenhouse gases CO2 and CH4. Nickel-based catalysts are the most popular catalysts for the reaction, and the coke formation on the catalysts is the main obstacle to the commercialisation of dry reforming. In this study, the whole reaction network of dry reformation on both flat and stepped nickel catalysts (Ni(111) and Ni(211)) as well as nickel carbide (flat: Ni3C(001); stepped: Ni3C(111)) is investigated using density functional theory calculations. The overall reaction energy profiles in the free energy landscape are obtained, and kinetic analyses are utilised to evaluate the activity of the four surfaces. By careful examination of our results, we find the following regarding the activity: (i) flat surfaces are more active than stepped surfaces for the dry reforming and (ii) metallic nickel catalysts are more active than those of nickel carbide, and therefore, the phase transformation from nickel to nickel carbide will reduce the activity. With respect to the coke formation, the following is found: (i) the coke formation probability can be measured by the rate ratio of CH oxidation pathway to C oxidation pathway (r(CH)/r(C)) and the barrier of CO dissociation, (ii) on Ni(111), the coke is unlikely to form, and (iii) the coke formations on the stepped surfaces of both nickel and nickel carbide can readily occur. A deactivation scheme, using which experimental results can be rationalised, is proposed. 

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The recent global economic and financial crisis has led the economies of many countries into recession, in particular at the periphery of the European Union. These countries currently face a significant contraction of both public investment in infrastructure and private investment in buildings and, as a result, the unemployment is particularly noticeable in the civil engineering and building sectors. Consequently, in all countries in recession the professional development of fresh civil engineering graduates is disproportionate to their high study effort and qualifications, since they rarely have the opportunity to gain experience in practice and their knowledge gradually becomes obsolete. Under these circumstances, it is imperative for the technical universities in countries in recession to plan and implement a substantial reform of the civil engineering studies syllabus. The objective should be to enable graduates to broaden the scope of their professional activity and increase their employability. In this paper, the widening of civil engineering studies curricula is proposed, in particular in the light of the development of the graduates’ potential on project, programme and portfolio management. In this direction, after a thorough literature review, including ASCE's Body of Knowledge for the 21st century and IPMA's Competence Baseline, it is recommended among others: to increase significantly the offered modules on project management and add new modules on strategy management, leadership behavior, delivery management, organization and environment etc; to provide adequate professional training during the university studies five year period; and to promote fresh graduates’ certification by professional bodies. The proposals are exemplified by presenting a reformed syllabus for the civil engineering studies offered currently by the National Technical University of Athens.

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Conventional understandings of what the Westminster model implies anticipate reliance on a top-down, hierarchical approach to budgetary accountability, reinforced by a post–New Public Management emphasis on recentralizing administrative capacity. This article, based on a comparative analysis of the experiences of Britain and Ireland, argues that the Westminster model of bureaucratic control and oversight itself has been evolving, hastened in large part due to the global financial crisis. Governments have gained stronger controls over the structures and practices of agencies, but agencies are also key players in securing better governance outcomes. The implication is that the crisis has not seen a return to the archetypal command-and-control model, nor a wholly new implementation of negotiated European-type practices, but rather a new accountability balance between elements of the Westminster system itself that have not previously been well understood.

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Gas-to-liquid processes are generally used to convert natural gas or other gaseous hydrocarbons into liquid fuels via an intermediate syngas stream. This includes the production of liquid fuels from biomass-derived sources such as biogas. For example, the dry reforming of methane is done by reacting CH4 and CO2, the two main components of natural biogas, into more valuable products, i.e., CO and H2. Nickel containing perovskite type catalysts can promote this reaction, yielding good conversions and selectivities; however, they are prone to coke laydown under certain operating conditions. We investigated the addition of high oxygen mobility dopants such as CeO2, ZrO2, or YSZ to reduce carbon laydown, particularly using reaction conditions that normally result in rapid coking. While doping with YSZ, YDC, GDC, and SDC did not result in any improvement, we show that a Ni perovskite catalyst (Na0.5La0.5Ni0.3Al0.7O2.5) doped with 80.9 ZrO2 15.2 CeO2 gave the lowest amount of carbon formation at 800 °C and activity was maintained over the operating time.

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The comparison of three ionic liquid-mediated catalytic processes for the benzoylation of anisole with benzoic anhydride is presented. A detailed understanding of the mechanism by which the zeolite and metal triflate reactions in bis{trifluoromethanesulfonyl}imide-based ionic liquids has been reported previously, and these routes are considered together with an indium chloride-based ionic liquid system. Solvent extraction and vacuum/steam distillation have been assessed as possible workup procedures, and an overall preliminary economic evaluation of each overall process is reported. Although the predominant activity is associated with the in situ formation of a homogeneous acid catalyst, the low cost and facile separation of the zeolite-catalysed process leads to this route being the most economically viable overall option. The results of a continuous flow miniplant based on the zeolite catalyst are also presented and compared with the reaction using a small plug How reactor.

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The kinetics of the water-gas shift reaction Were Studied on a 0.2% Pt/CeO2 catalyst between 177 and 300 degrees C over a range of CO and steam pressures. A rate decrease with increasing partial pressure of CO was experimentally observed over this sample, confirming that a negative order in CO can occur under certain conditions at low temperatures. The apparent reaction order of CO measured at 197 degrees C was about -0.27. This value is significantly larger than that (i.e, -0.03) reported by Ribeiro and co-workers [A.A. Phatak, N. Koryabkina, S. Rai, J.L. Ratts, W. Ruettinger, R.J. Farrauto, G.E. Blau, W.N. Delgass, F.H. Ribeiro, Catal. Today 123 (2007) 224] at a similar temperature. A kinetic peculiarity was also evidenced, i.e. a maximum of the reaction rate as a function of the CO concentration or possibly a kinetic break, which is sometimes observed in the oxidation of simple molecules. These observations support the idea that competitive adsorption of CO and H2O play an essential role in the reaction mechanism. (C) 2008 Elsevier B.V. All rights reserved.

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The aim of this research is to compare the adsorption capacity of different types of activated carbons produced by steam activation in small laboratory scale and large industrial scale processes. Equilibrium behaviour of the activated carbons was investigated by performing batch adsorption experiments using bottle-point method. Basic dyes (methylene blue (MB), basic red (BR) and basic yellow (BY)) were used as adsorbates and the maximum adsorptive capacity was determined. Adsorption isotherm models, Langmuir, Freundlich and Redlich-Peterson were used to simulate the equilibrium data at different experimental parameters (pH and adsorbent particle size). It was found that PAC2 (activated carbon produced from New Zealand coal using steam activation) has the highest adsorptive capacity towards MB dye (588 mg/g) followed by F400 (476 mg/g) and PAC 1 (380 mg/g). BR and BY showed higher adsorptive affinity towards PAC2 and F400 than MB. Under comparable conditions, adsorption capacity of basic dyes, MB, BR and BY onto PAC 1, PAC2 and F400 increased in the order: MB <BR <BY. Redlich-Peterson model was found to describe the experimental data over the entire range of concentration under investigation. All the systems show favourable adsorption of the basic dyes with 0 <R-L <I (C) 2007 Elsevier B.V. All rights reserved.