20 research outputs found
Probing the Local Structure of Na in NaNO₃-Promoted, MgO-Based CO₂ Sorbents via X-ray Absorption Spectroscopy
Full text linkISSN:0897-475
Development of Zn- and V-based Catalysts for Nonoxidative and Oxidative Dehydrogenation of Propane and the Role of Oxidative Pyrolysis
No full textPhotoelectrochemical glycerol oxidation on Mo-BiVO(4) photoanodes shows high photocharging current density and enhanced H(2) evolution
No full textMo-doped BiVO(4)'s lower efficiency can be attributed in part to exciton recombination losses. Recombination losses during photoelectrochemical water oxidation can be eliminated by using glycerol as a hole acceptor. This results in an enhanced photocurrent density. In this research, we present the synthesis of a Mo-doped BiVO(4) photoelectrode with a greater photocurrent density than a traditional pristine photoanode system. Increased photon exposure duration in the presence of glycerol leads to 8 mA cm(−2) increase in photocurrent density due to the creation of a capacitance layer and a decrease in charge transfer resistance on the photoelectrode in a neutral-phosphate buffer solution thus confirming the photo charging effect. Glycerol photooxidation improves the photoelectrode's rate of hydrogen evolution. Research into the effects of electrolyte and electrode potential on photoelectrodes has revealed that when the applied potential increases, the light absorbance behaviour changes following its absorption distribution over the applied potential. Under a transmission electron microscope (TEM), a unique dynamical crystal fringe pattern is found in the nanoparticles scratched from the photoelectrode
Correlating the Structural Evolution of ZnO/Al2O3 to Spinel Zinc Aluminate with its Catalytic Performance in Propane Dehydrogenation
No full textZn-based Al2O3-suported materials have been proposed as inexpensive and environmentally friendly catalysts for the direct dehydrogenation of propane (PDH), however, our understanding of these catalysts’ structure and deactivation routes is still limited. Here, we correlate the catalytic activity for PDH of a series of Zn-based Al2O3 catalysts with their structure and structural evolution. To this end, three model catalysts are investigated. (i) ZnO/Al2O3 prepared by atomic layer deposition (ALD) of ZnO onto γ-Al2O3 followed by calcination at 700 °C, which yields a core-shell spinel zinc aluminate/γ-Al2O3 structure. (ii) Zinc aluminate spinel nanoparticles (ZnxAlyO4 NPs) prepared via a hydrothermal method. (iii) A reference core-shell ZnO/SiO2 catalyst prepared by ALD of ZnO on SiO2. The catalysts are characterized in detail by synchrotron X-ray powder diffraction (XRD), Zn K-edge X-ray absorption spectroscopy (XAS), and 27Al solid state nuclear magnetic resonance (ssNMR). These experiments allowed us to identify tetrahedral Zn sites in close proximity to Al sites of a zinc aluminate spinel phase (ZnIV–O–AlIV/VI linkages) as notably more active and selective in PDH relative to the supported ZnO wurtzite phase (ZnIV–O– ZnIV linkages) in ZnO/SiO2. The best performing catalyst, 50ZnO/Al2O3 gives 77% selectivity to propene (gaseous products based) at 9 mmol C3H6 gcat−1 h−1 space time yield (STY) after 3 min of reaction at 600 °C. On the other hand, the core-shell ZnO/Al2O3 catalyst shows an irreversible loss of activity over repeated PDH and air-regeneration cycles, explained by Zn depletion on the surface due to its diffusion into subsurface layers or the bulk. ZnxAlyO4 NPs gave a comparable initial selectivity and catalytic activity as 50ZnO/Al2O3. With time on stream, ZnxAlyO4 NPs deactivate due to the formation of coke at the catalyst surface, yet the extend of coke deposition is lower than for the ZnO/Al2O3 catalysts, and the activity of ZnxAlyO4 NPs can be regenerated almost fully using calcination in air.<br /
El manuscrito persa sobre tiro con arco Izá (Revelación) por Tāher Māwarā al-Nahri
Full text linkThe current article contains a discussion and translation of an undated Persian manuscript on archery titled Izāh (Revelation) written by Tāher Māwarā al-Nahri. Internal references suggest an early date for parts of the text. The author, Tāher Māwarā al-Nahri, is presently unknown and his birth and death dates are uncertain. The author presents himself and his opinions confidently and is very sure of the correctness of his master’s teachings. This master, Ja’far Māwarā al-Nahri, is likewise unknown at the moment though the epithet, Māwarā al-Nahri, applied to both of them and meaning «from beyond the river» suggests they were either Transoxanian or descended from people from that area. Therefore it is possible this manual is a unique survival of Central Asian archery traditions.En este artículo se traduce y comenta un manuscrito persa sin fecha sobre el tiro con arco titulado Izá (Revelación), escrito por Tāher Māwarā al-Nahri. Las referencias internas sugieren que algunas partes del texto fueron escritas en épocas tempranas. El autor, Tāher Māwarā al-Nahri, es actualmente desconocido y las fechas de su nacimiento y muerte son inciertas. El autor presenta sus argumentos, y a sí mismo, con seguridad, y está convencido de la corrección de sus enseñanzas magistrales. Este maestro, Ja’far Māwarā al-Nahri, es igualmente desconocido actualmente, aunque el epíteto, Māwarā al-Nahri, aplicado a ambos, significa «desde más allá del río». Este epíteto sugiere que provenían de Transoxania o fueron descendientes de personas de esa zona. Por tanto, es posible que este manual sea el único que ha sobrevivido en relación a las tradiciones de tiro con arco de Asia Central
Probing the dynamics of the local structure of Na in NaNO3-promoted, MgO-based CO2 sorbents via X-ray absorption spectroscopy
No full textThis work provides insight into the local structure of Na in MgO-based CO2 sorbents that are promoted with NaNO3. To this end, we use X-ray absorption spectroscopy (XAS) at the Na K-edge to interrogate the local structure of Na during CO2 capture (MgO + CO2 ↔ MgCO3). The analysis of Na K-edge XAS data shows that the local environment of Na is altered upon MgO carbonation when compared to NaNO3 in the as-prepared sorbent. We attribute the changes observed in the carbonated sorbent to an alteration in the local structure of Na at the NaNO3/MgCO3 interfaces and/or in the vicinity of [Mg2+···CO32–] ionic pairs that are trapped in the cooled down NaNO3 melt. The changes observed are reversible, i.e. the local environment of NaNO3 was restored after a regeneration treatment to decompose MgCO3 to MgO. The ex situ Na K-edge XAS experiments were complemented by ex situ magic-angle spinning 23Na nuclear magnetic resonance (MAS 23Na NMR), Mg K-edge XAS and X-ray powder diffraction (XRD). These additional experiments support our interpretation of the Na K-edge XAS data. Furthermore, we develop in situ Na (and Mg) K-edge XAS experiments during the carbonation of the sorbent (NaNO3 is molten at the conditions of the in situ experiments). These in situ Na K-edge XANES spectra of molten NaNO3 open new opportunities to investigate the atomic scale structure of CO2-sorbents modified with Na-based molten salts using XAS
Correlating the Structural Evolution of ZnO/Al2O3 to Spinel Zinc Aluminate with its Catalytic Performance in Propane Dehydrogenation
No full textExplain the Discovery Theory in Knowledge
No full textThe human knowledge from the different levels of its being and achieving knowledge from outside world, and the correspondence between human science and world, are among most important issues that have preoccupied the mind of many contemporary thinkers and epistemologists. The author of this paper has tried, based on the principles of Transcendental Theosophy such as Asalat al-wujud, Wahdat al-wujud, and their implications, to show that contrary to what is called Mullasadra’s epistemology (his views on the nature of science and discovery) and regarded as Mullasadra’s ultimate believe, in philosophical circles, the theory is not the Mullasadra’s final position. I, based on my study and contemplation on his ideas want to prove that the Mullasarda doesn’t believe that science is produced by the perfect forms acquisition through Trans-Substantial Motion, rather the essence of discovery is achieved in the process of Trans-Substantial Motio
The Oldest Persian Enigmatic Treatise
No full textRiddle as a figure of speech, which has been popular in Persian poetry for a long time, is divided into two types: nominal and historical riddles (Chronograph). In the 11th-9th lunar centuries, which was the peak period of the riddle writing, several treatises were written to explain the rules of riddles, as well as to record the best riddles. The lack of comprehensive research on enigmatic treatises has led to problems in identifying them, which has caused mistakes and errors in some reference sources. Such mistakes have found their way into other works and have eventually become so prevalent that they are considered scientific truth. This fundamental research, which was carried out using library sources and dealing with numerous manuscripts, revealed that Zabihullah Safa's view that (الاحیاء فی حل المعمّا) “al-Ehyāe Fī Hal al-Moamā” is the oldest Persian enigmatic treatise is not exact and there is no such treatise. The oldest treatise (مطلوب الاحباب) “Matlōb al-Ahbāb” is the work of Rafi Manouchehr, a merchant known as Badie Tabrizi. The author of the treatise "24 Asl" was also identified
Household savings in transition economies
Full text linkDuring the transition from central planning to market economies now under way in Eastern Europe, output levels first collapsed by 40 to 50 percent in most countries, then staged a modest recovery in the last two years. Longer-term revival of growth requires a resumption of investment and thus, realistically, of domestic savings. To explore the determinants of household savings rates in transition economies, the authors studies matching household surveys for three Central European economies: Bulgaria, Hungary, and Poland. They find that savings rates strongly increase with relative income, suggesting that increasing income inequality may play a role in determining savings rates. Savings rates are significantly higher for households that do not own their homes or that own few of the standard consumer durables-possibly because, with no retail credit or mortgage markets, households must save to purchase houses and durables. The influence of demographic factors broadly matches earlier findings for developing countries. Perhaps surprisingly, variables associated with the household's position in the transition process-including either sector of employment (public or private) or form of employment-do not play a significant role in determining savings rates.Environmental Economics&Policies,Services&Transfers to Poor,Economic Theory&Research,Banks&Banking Reform,Payment Systems&Infrastructure,Safety Nets and Transfers,Rural Poverty Reduction,Environmental Economics&Policies,Banks&Banking Reform,Economic Theory&Research
