bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemisorption and the Distribution of Acid Y Zeolite Cumene Cracking Products
Authors: Patrylak Lyubov 
Published: October 2002

The results obtained for the pulse cracking of cumene in the presence of zeolite-containing acidic catalysts were analyzed taking into account data complications arising because of the chemisorption of the components of the reaction mixture on the acid sites of the catalyst samples. The propene/benzene (P/B) molar ratios in the reaction mixtures, which amounted to 0.60–2.7, deviated considerably from the expected stoichiometry depending on the nature of the samples, their mode of preparation, their preliminary thermal treatment and steaming as well as on the experimental conditions employed. At the same time, the total yields of cracking products and non-converted cumene were, as a rule, 1.5–3-times less than the amounts of cumene fed into the system. The infringement of the stoichiometry and the considerable material imbalance observed may be attributed to the chemisorption of both cumene and the final conversion products on Lewis acid sites, i.e. coordinatively unsaturated aluminium atoms and zeolite cations, present on the catalyst surface. Chemisorption of the intermediates — phenyl carbocations — on Brönsted acid sites, as well as coke formation as a result of propene polymerization on these sites, must also be taken into consideration. The balance between these various processes and interactions leads to the overall reaction situation observed, thereby enabling conclusions to be drawn regarding both the nature of the catalyst surface and the individual processes, which appear to depend on the strength, amount and correlation between the Brönsted and Lewis acid sites on the samples studied.
Some Physicochemical, Surface and Catalytic Properties of the MoO3/Al2O3 System
Authors: Amin Nabil H. 
Published: October 2002

The effects of MoO3 doping on the solid–solid interactions, surface and catalytic properties of Al2O3 solid were investigated using DTA, TG and XRD methods, N2 adsorption at −196°C and the catalytic conversion of isopropanol at 150–400°C using a flow technique under atmospheric pressure. The nominal composition of the mixed solid was 0.5MoO3:Al2O3. Pure and Mo oxide-treated solids were subjected to thermal treatment at 500–1000°C prior to surface and catalytic measurements. The results showed that the Al2O3 support material when precalcined at 500°C exhibited the highest catalytic activity and selectivity towards isopropanol conversion (100% selective towards propylene formation). Moreover, loading MoO3 on Al2O3, followed by precalcination at 500°C, resulted in the formation of an active catalyst towards dehydration and dehydrogenation, especially for the reaction carried out below 200°C. Further increase in the precalcination temperature of Al2O3 from 500°C to 900°C resulted in a dramatic decrease in its dehydration activity due to the decrease in its surface area and surface acidity. The solids precalcined at 1000°C showed a maximum dehydrogenation activity for the catalytic reaction when the latter was carried out at 400°C.
Surface and Catalytic Properties of MoO3-Treated Co3O4/Al2O3 Solids
Authors: Ghozza A.M. , El-Shobaky G.A. , Mohamed G.M. 
Published: October 2002

The surface and catalytic properties of Co3O4/Al2O3 solids treated with different proportions of MoO3 were investigated, the extent of MoO3 added varying between 0.50 mol% and 5.00 mol% (0.63–5.9 wt%). The pure sample was prepared by thermal decomposition at 600°C of aluminium hydroxide impregnated with a calculated amount of Co(NO3)2 dissolved in the least amount of distilled water. The MoO3-treated samples were prepared by thermal decomposition at 600°C of aluminium hydroxide treated with different proportions of ammonium molybdate followed by treatment with Co(NO3)2 solution. The crystalline phases produced by thermal treatment of the pure and treated samples precalcined at 600°C were characterized using an XRD technique. The surface and catalytic properties of the various catalysts were studied using nitrogen adsorption at −196°C and CO oxidation by O2 at 100–150°C. The results obtained revealed that molybdena treatment of the Co3O4/Al2O3 solids followed by precalcination at 600°C resulted in a decrease in the degree of crystallinity of the Co3O4 phase produced. This treatment effected a progressive small increase in the specific surface area of the treated solids (ca. 10%). However, the catalytic activity was found to be increased considerably by increasing the amount of MoO3 added (184%), reaching a maximum limit at 1.00 mol% MoO3. The activation energies of the catalytic reaction calculated for both the pure and MoO3-treated solids suggested that MoO3 treatment did not modify the energetic nature of the active sites (surface cobalt species) but increased their concentration.
The Effects of Li2O Doping on the Surface and Catalytic Properties of CuO/Al2O3 Solids
Authors: El-Shobaky Gamil A. , Radwan Farouk M. , Turky Abd. El-Mohsen , El-Moemen Ayman Abd. 
Published: October 2002

The effects of doping CuO/Al2O3 solids with Li2O on their surface and catalytic properties were investigated using nitrogen adsorption at −196°C, the decomposition of H2O2 at 20–40°C and the oxidation of CO by O2 at 175°C. The pure solids were prepared by wet impregnation of finely powdered solid Al(OH)3 which had been precalcined at 400°C; the resulting material was then dried and calcined at 500°C with copper nitrate dissolved in the least amount of distilled water. The amount of copper oxide in such solids was fixed at 13.5 wt% while the amounts of Li2O added varied between 0.19 wt% and 3.80 wt%. The results obtained showed that such Li2O doping enhanced the crystallization of the CuO phase to an extent proportional to the amount of dopant added and increased the concentration of surface OH groups. This treatment led to a progressive small increase in the BET surface areas (SBET) of the treated solids, which attained a maximum limit at 0.76 wt% Li2O but decreased upon increasing the dopant concentration above this limit. The addition of 0.76 wt% Li2O effected an increase of 14.6% in the SBET values of the treated solids while the addition of 3.80 wt% Li2O led to a corresponding decrease of 38.5% in this value. Doping with Li2O resulted in a progressive decrease in the catalytic activity of the solids towards CO oxidation by O2 while the presence of 3.80 wt% Li2O effected a decrease of 72.5% in the value of the reaction rate constant measured at 175°C. In contrast, such treatment of CuO/Al2O3 solids with Li2O brought about a progressive increase in their catalytic activity towards H2O2 decomposition, which reached a maximum limit in the presence of 1.90 wt% Li2O and then decreased when the amount of Li2O added was increased above this limit, falling to values which were smaller than those measured for the pure catalyst samples. The doping process did not modify the activation energy of the catalyzed H2O2 reaction but modified the concentration of the catalytically active constituent present in the system.
Effect of MgO Addition on the Surface and Catalytic Properties of the CuO/Al2O3 System
Authors: Deraz Nasr-Allah M. 
Published: October 2002

The effect of MgO on the solid–solid interactions, surface and catalytic properties of CuO/Al2O3 solids was investigated using XRD methods, nitrogen adsorption at −196°C and oxidation of CO by O2 at 150–300°C. The nominal composition of the pure mixed solid was 0.20CuO:Al2O3 and the amounts of MgO added varied between 0.43 wt% and 3.30 wt%. The pure and MgO-treated solids were subjected to precalcination (thermal treatment) at 600°C and 800°C, respectively. The results obtained revealed that CuO underwent solid–solid interactions with pure and doped alumina at temperatures of 600°C and above to yield a poorly crystalline copper aluminate (CuAl2O4) phase. The amount of copper aluminate produced increased on increasing the precalcination temperature to 800°C. Magnesium oxide inhibited the formation of CuAl2O4 at 600°C but enhanced this reaction at 800°C, the inhibiting and enhancing effects depending on the amount of MgO present. Doping with MgO effected a measurable increase in both the specific surface areas and catalytic activities of the solids precalcined at 600°C. The reverse effect was observed for the doped solids preheated in air at 800°C. Doping at 600°C and 800°C modified the concentration of catalytically active constituents involved in chemisorption and catalysis of the CO oxidation reaction.
Physicochemical and Catalytic Properties of Vanadia/Titania Catalysts. II. Textural Properties
Authors: El-Nabarawy Th. , Alaya M.N. , Ahmed S.A. Sayed , Youssef A.M. 
Published: October 2002

Titania gels, Ta and Tb, were precipitated from aqueous solutions of titanium tetrachloride at pH values of 3.0 and 9.0, respectively. Calcination products were obtained from these gels by thermal treatment at 300–1000°C. Vanadia/titania catalysts were obtained by impregnating Ta and Tb with ammonium vanadate to give products containing 4–12 wt% V2O5. These products were calcined at 400°C or 600°C, respectively. The adsorption of nitrogen at −196°C was followed and the isotherms thus obtained analyzed to enable the determination of the textural characteristics of the catalysts through the use of conventional methods of textural analysis. The specific surface area and total pore volume of titania decreased and its mean pore radius increased on increasing the calcination temperature from 400°C to 1000°C. Titania precipitated at pH 3.0 and calcined at 1000°C exhibited non-porous characteristics as indicated by the absence of hysteresis in the corresponding adsorption isotherm. The textural changes were attributed to the anatase → rutile transformation and also to the sintering of rutile. The specific surface area and porosity of vanadia/titania catalysts changed with increasing calcination temperature and with increasing vanadia content. However, the effect of calcination temperature was more pronounced.
Catalytic Conversion of Ethanol and Isopropanol on γ-Irradiated Co3O4/Al2O3 Solids
Authors: Doheim M.M. , El-Boohy H.A. , El-Shobaky G.A. 
Published: October 2002

The catalytic conversion of ethanol and isopropanol was conducted over Co3O4/Al2O3 solids (19.3 wt% Co3O4) precalcined at 400°C and subjected to different doses of γ-radiation. The reaction was studied at different temperatures in the range 250–400°C and monitored using nitrogen as a carrier gas flowing at a rate of 18 cm3/min. The γ-ray doses employed were 0.2, 0.4, 0.8 and 1.6 MGy, respectively. The results obtained indicated that γ-irradiation effected a progressive decrease in the catalytic activity of the solids towards alcohol conversion, reaching a minimum value after 0.8 MGy irradiation. The irradiation process also effected a measurable decrease in the dehydration selectivity towards the alcohols investigated and an increase in their dehydrogenation selectivity. These results were discussed in terms of an effective decrease in the concentration of sites exhibiting Brönsted acidity brought about by γ-irradiation, which also generated a small decrease in the particle size of the Co3O4 crystallites and a measurable increase in the specific surface areas of the solids investigated.
Dye Adsorption by Modified Cotton. Steric and Energetic Interpretations of Model Parameter Behaviours
Authors: Khalfaoui M. , Baouab M.H.V. , Gauthier R. , Lamine A. Ben 
Published: October 2002

The variations of the three parameters, viz. anchorage number, receptor site density and half-saturation concentration, as determined theoretically (Khalfaoui et al. 2002) and related to the adsorption energy, exhibited different behaviours when examined in terms of the adsorption of various dyes on to modified cotton. When plotted against the percentage nitrogen content of these cottons, variations in the effective receptor site density and the inverse of the adsorbed molecules anchorage number allowed the adsorption process to be described topographically in terms of the parallel or perpendicular adsorption of the dye molecule on to the adsorbent surface. The presence of ionic or van der Waals forces in such adsorption was also considered. The values of the model parameters were found to be related to the magnitude of the steric hindrance arising from the anchorage geometry of the dye molecule. Where the site density was high, a form of dimerization of the dye molecules was favoured. The best conditions for obtaining a high adsorption capacity, necessary for textile dyeing and wastewater depollution, were considered. Through the use of the half-saturation capacity, c1/2, it was possible to determine the change in the adsorption energy when the receptor site spacing was decreased and to relate such variation to the rate of steric hindrance, τ.
Adsorption of Mercury(II) Ions on Procion Blue MX-3G-attached Magnetic Poly(Vinyl Alcohol) Gel Beads
Authors: Denizli Adil , Arpa Çiğdem , Bektas Sema , Genç Ömer 
Published: October 2002

Magnetic poly(vinyl alcohol) (mPVAL) gel beads (150–200 μm in diameter) carrying Procion Blue MX-3G (122 μmol/g) were used for the removal of different amounts (50–650 mg/l) of Hg(II) ions from aqueous solutions. The mPVAL gel beads were characterized by swelling tests, electron spin resonance (ESR), elemental analysis and scanning electron microscopy (SEM). The swelling ratio of the mPVAL gel beads, which had a spherical shape and porous structure, was 76%. The presence of magnetite particles in the polymeric structure was confirmed by ESR spectroscopy. The capacity of the beads towards Hg(II) ions increased with time during the first 10 min of adsorption and then levelled off towards an equilibrium adsorption capacity. The adsorption of Hg(II) ions on the plain beads was very low (0.57 mg/g) but increased substantially (to 69.2 mg/g) on beads to which Procion Blue MX-3G had been attached. The Langmuir adsorption isotherm was applicable to the description of Hg(II) ion adsorption by Procion Blue MX-3G-attached mPVAL gel beads. Such adsorption increased with increasing pH of the aqueous medium and reached a plateau level at ca. pH 6.0. The optimal pH range for Hg(II) ion adsorption was 6.0–7.0. More than 95% of the adsorbed Hg(II) ions was desorbed within 15 min when 0.1 M HNO3 was used as an elution agent. Regeneration of the Procion Blue MX-3G-attached mPVAL gel beads under these conditions was also reasonable.
How Valid are the Biological and Ecological Principles Underpinning Global Change Science?
Authors: Makarieva Anastassia , Gorshkov Victor G. , Mackey Brendan , Gorshkov Vadim V. 
Published: October 2002

The prevailing scientific approach to investigating and understanding the environmental consequences of human-induced global change is underpinned by two basic biological principles. First, the principle that species genetically adapt to changing environment conditions. Second, the principle that nutrients present in the environment in the smallest relative concentrations limit biological productivity. We contend that both principles have been formulated based on the results of investigations into either artificially selected organisms, or anthropogenically perturbed landscapes. In both these cases, organisms are studied outside their natural ecological niche. We argue that natural ecosystems do not conform to the above two principles. Non-perturbed biota of natural ecological communities form and maintain optimal environment conditions by buffering the flux of primary environmental resources that would otherwise randomly fluctuate as the result of purely physical processes. In such a biotically-mediated environment the availability of nutrients does not limit biological productivity. Critically, the capacity of the biota to regulate local environment conditions obviates the need for species to continually adapt to random environmental fluctuations. We illustrate how the failure to distinguish between the functioning of perturbed and unperturbed biota prevents the development of policies and strategies that will lead to the long term resolution of the global ecological crisis.
Population Growth the Scapegoat? Rethinking the Neo-Malthusian Debate
Authors: Collins Patrick 
Published: October 2002

In the last thirty years of the twentieth century we saw a resurrection of the writings of Matlhus. In their new guise we are told that instead of war, pestilence and famine, the earth has decreasing biodiversity, loss of species, loss of natural resources and water shortages, to name but a few, to look forward too. Population growth today, as it was two hundred years ago, is portrayed as Public Enemy number one. There is little doubt that the Neo-Malthusian argument has made an impact on policy, indeed, probably moreso than did its namesake. The newly clad argument shares much with its namesake, not least, its significant faults. The argument is two hundred years old, and the inaccuracies share that age. Malthus' predictions never reigned true because he made the fundamental error of not taking account of technical progress, or the ability of human ingenuity to adapt to change. This paper looks at the evolution of both sides of the population argument, and argues that this year's World Summit in Johannesburg should not fall foul to the dangerous generalisations invoked by the Neo-Malthusian school of thought. This paper is an attempt to lay the blame for environmental degradation not on the increasing population of the Third World, but on the consumption patterns and lifestyles of the First World. Affluence consumes energy and produces waste at a far higher rate than poverty. In looking at the environmental debate only an integrated approach, and not one that is concerned solely with ‘demonising’ population growth, can result in success.
Field Measurement and Criteria for Sound Insulation between Dwellings in Europe
Authors: Sheridan Linda , Maluski Sophie 
Published: October 2002

Airborne and structure-borne sound transmission are the dominant noise paths in terraced, semi-detached houses and in multi-storey buildings, often causing annoyance when heard. They usually are controlled by applying building regulations before, during and after the construction of the dwellings. As part of a comparative study of the control and promotion of quality in housing in Europe, the acoustic quality in dwellings have been investigated for France, Norway, Sweden, the Netherlands, Germany, Switzerland, Italy and the United Kingdom. The study highlights many differences in regulations, criteria and methods of measurement. The conclusion drawn from this comparison is that there is no uniformity in the regulations for the acoustic quality of dwellings in Europe and much work is needed to establish uniformity.
A Computer Investigation of the Performance of Virtual Reflectors: Part 1 - Development of the Method
Authors: Oldham D J , El-Zeky L 
Published: October 2002

In a companion paper [1] a technique for improving acoustic conditions in open stage auditoria by means of virtual reflectors has been proposed. Possible methods of testing the application of a virtual reflector system were discussed and it was concluded that computer simulation was the most appropriate. However, before employing a commercially available package it was necessary to devise suitable procedures. The need for both a directional loudspeaker and a directional microphone is an essential requirement for the virtual reflector system but most computer simulation packages only allow for source directivity. Hence a method of incorporating the effect of microphone directivity using the principle of reciprocity was developed. The basis of establishing the gain factor has been devised and it is proposed that the convolution of echograms rather than the convolution of true impulse responses can be employed to predict system performance. The action of the virtual reflector system has been investigated using a model of an open stage theatre. Both system microphone and system loudspeaker were selected from a catalogue of available modern commercial sound equipment. The resulting STI contours demonstrated that the effect of the virtual reflector over the audience area to the rear of a human speaker was to raise the speech intelligibility to be approximately equal to that to the front of the speaker. It has been shown that the STI at the rear of a speaker with the virtual reflector system in operation does not increase significantly with gain. This is due to the Modulation Transfer Functions which determine the STI value being determined by the convolution of two impulse responses multiplied by a gain factor and added to a third impulse response. The resulting impulse response therefore consists of many ‘reflections’ and hence the MTF's and STI values will be adversely affected if excess gain is applied.
Frequency and Time Numerical Solutions of 3D Sound Propagation in Open and Closed Spaces
Authors: Tadeu António , António Julieta , Godinho Luís 
Published: October 2002

Problems in acoustics can often be solved with the aid of formulas or expressions known as Green's functions. These functions, or fundamental solutions, relate the field variations (such as pressures) in an acoustic medium caused by sound sources placed elsewhere in the medium. The two fundamental solutions most often used are for harmonic point loads in a three-dimensional, infinite, homogeneous space, and for a harmonic line load acting within two-dimensional spaces. These are chosen because their solutions are known in closed-form and they are relatively simple in structure. This paper presents a set of three-dimensional solutions applied when the space domain is modeled with plane barriers placed together to reproduce spaces that vary from a simple half-space to a parallelepiped closed space. It is assumed that the homogeneous three-dimensional space is subjected to 3D point sources and spatially sinusoidal, harmonic line sound loads. The resulting expressions are implemented to evaluate the field inside a rectangular space, whose walls allow different absorption coefficients. The time responses are obtained by means of Inverse Fourier Transforms. Complex frequencies are used to attenuate the response at the end of the time window. The effect of this attenuation is taken into account by re-scaling the time response.
Impact Sound Insulation of Timber Floors: Interaction between Source, Floor Coverings and Load Bearing Floor
Authors: Scholl W. , Maysenhölder W. 
Published: October 2002

It is well known that prediction of impact sound of timber floors contains large uncertainties. They partly originate from the dynamic interaction of impact sources and floor elements which makes it difficult to characterise the performance of the elements of a floor in the right way. First results of a project recently started at the Fraunhofer-Institut für Bauphysik on this subject are presented. Calculations reveal strong influences of impact source and load bearing floor on the acoustical performance of the floor coverings. There are considerable deviations between concrete and timber floors. The standard ISO tapping machine and human walkers interact quite differently with floors and coverings, thus modifying the impact sound improvement “of the floor covering”. To clearly separate performance of the floors, floor coverings and impact sources detailed information about their dynamic properties is necessary. Non-linear effects are expected especially with carpets. The results of the project should be helpful to design a laboratory measuring method for the impact sound improvement on lightweight (timber joist) floors and to design floors with a better impact sound insulation.