Nanoscale bimetallic catalysts: are they really bimetallic?

The existence of bimetallic particles (and their reducibility and location on/or in the support) in Ru–Co/NaY and Pt–Co/NaY samples has been studied by in situ X-ray adsorption spectroscopy (XAS). It is established that in Ru–Co/NaY the monometallic clusters maintain their identity, whereas in Pt–Co/NaY the existence of small bimetallic particles can be established. In both cases the results are supported by other techniques, such as XPS and temperature-programmed reduction. Copyright © 2002 John Wiley & Sons, Ltd.     

Lowering reaction temperature: Electrochemical ammonia synthesis by coupling various electrolytes and catalysts

Ammonia is a vital emerging energy carrier and storage medium in the future hydrogen economy, even presenting relevant advantages compared with methanol due to the higher hydrogen content(17.6 wt% for ammonia versus 12.5 wt% for methanol). The rapidly growing demand for ammonia is still dependent on the conventional high-temperature and high-pressure Haber–Bosch process, which can deliver a conversion rate of about 10%–15%. However, the overall process requires a large amount of fossil fuels,resulting in serious environmental problems. Alternatively, electrochemical routes show the potential to greatly reduce the energy consumption, including sustainable energy sources and simplify the reactor design. Electrolytes perform as indispensable reaction medium during electrochemical processes, which can be further classified into solid oxide electrolytes, molten salt electrolytes, polymer electrolytes, and liquid electrolytes. In this review, recent developments and advances of the electrocatalytic ammonia synthesis catalyzed by a series of functional materials on the basis of aforementioned electrolytes have been summarized and discussed, along with the presentation and evaluation of catalyst preparation, reaction parameters and equipment.     

On the path to catalysts for the low-temperature ammonia synthesis

A nontraditional approach to the development of catalysts for low-temperature ammonia synthesis is considered. The approach is characterized by application of catalysts representing heterogeneous analogs of the known homogeneous nitrogen-fixing systems based on transition metal compounds and strong electron donors. The use of this approach led to the development of catalysts that considerably surpass in their activity (at atmospheric pressure) the industrial catalyst for the ammonia synthesis. Some of the developed catalysts are active in the formation of ammonia from dinitrogen and dihidrogen even at 110–150°C. The mechanisms of activation and hydrogenation of dinitrogen over these new catalysts are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 796–806, May, 1998.     

Isodiagonality in the periodic table

Diagonal relationships in the periodic table were recognized by both Mendeléev and Newlands. More appropriately called isodiagonal relationships, the same three examples of lithium with magnesium, beryllium with aluminum, and boron with silicon, are commonly cited. Here, these three pairs of elements are discussed in detail, together with evidence of isodiagonal linkages elsewhere in the periodic table. General criteria for defining isodiagonality are proposed.     

Interaction between catalysts for ammonia synthesis and oxygen

Reversible poisoning of the catalysts for ammonia synthesis by oxygen has been used to eliminate the pyrophoric nature of the reduced catalysts via their treatment by the mixtures of nitrogen, hydrogen or helium with oxygen at catalysis temperatures. Kinetic studies of oxygen sorption, catalyst structure, activity and stability to the secondary oxidation of the samples partially oxidized at various temperatures have revealed that the optimum temperatures to eliminate the pyrophoric effect are 673–773 K.

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Nitrogen forms on supported catalysts for ammonia synthesis

Nitrogen chemisorption on supported Fe–Co, Fe–Mo and Co–Mo catalysts for ammonia synthesis has been studied. No considerable effect of carrier (carbon fibers) on nitrogen chemisorption has been found. It is shown that for these samples chemisorbed nitrogen has various dissociative forms.

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Mechanism of ammonia synthesis over iron catalysts in the equilibrium region

It is shown that the mechanism proposed by Temkin and Pyzhev for ammonia synthesis does not correspond to the experimental data on the properties of the catalyst surface and the stages of the process. A three-stage mechanism is discussed: 1) N₂+ Z = ZN₂; 2) 2ZN + 3H₂ = 2NH₃ + 2Z; 3) 2ZN₂ + Z 2ZN (2 and 3 are equilibria, 3 being displaced to the right, 1 is the limiting stage), based on simple Langmuir concepts, which leads to a kinetic equation which agrees with the data of Winter on the kinetics of NH₃ decomposition and the data of Benton on the retardation of the NH₃ synthesis reaction by the product. An equation is derived for dissociative adsorption on a uniform surface involving the adsorption of each adatom at two adsorption sites; the equation corresponds to the same dependence of on P as the logarithmic adsorption isotherm.Published for purposes of discussion.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 213–221, March–April, 1989.     

Selective synthesis of acetic acid from hydrogen and carbon monoxide by homogeneous bimetallic catalysts

Alcohols which are the main products of the reaction of hydrogen and carbon monoxide in onium halide promoted ruthenium systems, are changed to acetic acid with the addition of cobalt carbonyl as the second catalyst component. Among Group VIa-VIIIa transition metal complexes, cobalt carbonyl is the only compound which promoted acetic acid formation when combined with ruthenium carbonyl under the conditions studied. The selectivity to acetic acid varied appreciably with the combinations of solvents and promoters, and exceeded 80% with optimal catalyst composition. The effects of solvents and promoters were investigated together with ¹³C tracer experiments from which the roles of halide anions of onium salts were determined.     

Catalytic and adsorption properties of iron-nickel catalysts in ammonia synthesis

Thermal desorption was used to study the state of chemisorbed nitrogen on the surface of iron-nickel ammonia-synthesis catalysts in the region of the solid solution of nickel and iron. It was shown that the ₁ form of nitrogen should be responsible for catalysis.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 616–618, September–October, 1988.     

Microwave-assisted polyol synthesis of carbon-supported platinum-based bimetallic catalysts for ethanol oxidation

High surface area carbon-supported Pt, PtRh, and PtSn catalysts were synthesized by microwave-assisted polyol procedure and tested for ethanol oxidation in perchloric acid. The catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning tunnelling microscopy (STM), TEM, and EDX techniques. STM analysis of unsupported catalysts shows that small particles (～2?nm) with a narrow size distribution are obtained. TEM and XRD examinations of supported catalysts revealed an increase in particle size upon deposition on carbon support (diameter?～?3?nm). The diffraction peaks of the bimetallic catalysts in X-ray diffraction patterns are slightly shifted to lower (PtSn/C) or higher (PtRh/C) 2θ values with respect to the corresponding peaks at Pt/C catalyst as a consequence of alloy formation. Oxidation of ethanol is significantly improved at PtSn/C with the onset potential shifted for?～?150?mV to more negative values and the increase of activity for approximately three times in comparison to Pt/C catalyst. This is the lowest onset potential found for ethanol oxidation at PtSn catalysts with a similar composition. Chronoamperometric measurements confirmed that PtSn/C is notably less poisoned than Pt/C catalyst. PtRh/C catalyst exhibited mild enhancement of overall electrochemical reaction in comparison to Pt/C.     

Chemosorption of nitrogen on the surfaces of iron-cobalt ammonia synthesis catalysts

Thermodesorption with mass spectrometer recording has been used to investigate the condition of chemosorbed nitrogen on the surfaces of iron-cobalt ammonia synthesis catalysts. In the absorption temperature range 570–740 K two molecular and three atomic forms of adsorbed nitrogen have been detected, the mechanism is discussed of formation of chemosorbed forms of nitrogen and of their interrelations with the catalyst activity. The optimum values of the activation energies for nitrogen desorption on the catalysts investigated have been calculated and compared.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 185–190, March–April, 1988.     

From the Mendeleev periodic table to particle physics and back to the periodic table

We briefly describe in this paper the passage from Mendeleev’s chemistry (1869) to atomic physics (in the 1900’s), nuclear physics (in 1932) and particle physics (from 1953 to 2006). We show how the consideration of symmetries, largely used in physics since the end of the 1920’s, gave rise to a new format of the periodic table in the 1970’s. More specifically, this paper is concerned with the application of the group SO(4,2)⊗SU(2) to the periodic table of chemical elements. It is shown how the Madelung rule of the atomic shell model can be used to set up a periodic table that can be further rationalized via the group SO(4,2)⊗SU(2) and some of its sub-groups. Qualitative results are obtained from this nonstandard table.     

On the planar periodic table

We reconsider, in this work, the construction of the two‐dimensional (2‐D) periodic table. The two‐dimensional logarithmic Coulomb system is used to generate atomic shells for the 2‐D atoms. A q‐deformed model is developed to explain the ordering of the shells predicted by the 2‐D Madelung rule. Our model, with the value q=1.26 for the deformation parameter, reproduce very well the above rule. We also compute the key function and the address function which, together with our model for the Madelung rule, permit us to give a new format of the 2‐D periodic table. It is shown that this table is different from the one existing in the literature, and we have a new family of elements, the g family. The question of the existence of 2‐D “ions” is briefly discussed. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 206–211, 2000     

Highly active Fe36Co44 bimetallic nanoclusters catalysts for hydrolysis of ammonia borane: The first-principles study

In this paper, Fe₃₆Co₄₄ nanocluster structure is used to catalyze the hydrolysis reaction of ammonia borane to produce H₂. Firstly, we complete the construction of Fe₃₆Co₄₄ cluster structure and calculate the electronic properties of the cluster. By comparing the adsorption process of Ammonia Borane (AB) in active sites of the cluster, which have different Effective Coordination Number (ECN), the qualitative relationship between ECN and the catalytic activation of AB is clarified, and the optimal catalytic active site is obtained. Then, from the perspective of different reaction paths, we study the hydrolysis reaction of AB in multiple paths, and obtain 5 different reaction paths and energy profiles. The calculation results show that in the case of NH bond priority break (path 5), the reaction has the minimum rate-determining step (RDS) barrier (about 1.02 eV) and the entire reaction is exothermic (about 0.40 eV). So, path 5 is an optimal catalytic reaction path. This study will have an important guiding significance for the study of the AB hydrolysis reaction mechanism.     

The periodic table: revelation by quest rather than by revolution

The concept of major scientific advances occurring as a short-term ‘revolutionary’ change in thinking interspersed by long periods of so-called ‘normal’ science seems to be losing ground to more ecological models, which are more inimical of the twists and turns of life. From this idea it is a short step to charting science’s progress against stages used in fictional storytelling, which after all is life-based. This paper explores the development of the periodic table in terms of the achievement of a fictional ‘quest’, and finds the stages of such a story are well represented. While Mendeleev or perhaps Meyer might be considered by some to be the hero of the quest, its first stage—the call—is represented by the Karlsruhe conference in 1860, with an international cast of ‘companions’ and ‘helpers’ who contributed to the Table’s early development. The ‘journey’ may have been frustrated by lack of appropriate data and understanding of concepts, but the ‘arrival’ phase is clearly marked by the award of the Davy medal jointly to Mendeleev and Meyer in 1882, Throughout these stages there are lesser, although still significant contributions made by “little people” of science to the overall progress of the Table. The end of the journey is not the end of the quest: the discovery of new elements—“new ordeals”—and their incorporation into an increasing range of types and styles of periodic table, which—akin to the “life-renewing goal” of the fictional quest—continue.     

Effective bimetallic composite catalysts for the synthesis of arylated furans and thiophenes in aqueous media

Chemistry of Heterocyclic Compounds - N-(4,6-Dimethylpyrimidin-2-yl)-5-phenylisoxazole-3-carboxamide was used as a ligand for obtaining bimetallic boron-containing heterogeneous catalysts...     

The periodic table in flatland

The D-dimensional Coulomb system serves as a starting point for generating generalized atomic shells. These shells are ordered according to a generalized Madelung rule in D dimensions. This rule together with an Aufbau Prinzip is applied to produce a D-dimensional periodic table. A model is developed to rationalize the ordering of the shells predicted by the generalized Madelung rule. This model is based on the introduction of a Hamiltonian, invariant under the q-deformed algebra U_q(so(D)), that breaks down the SO(D + 1) dynamical symmetry of the hydrogen atom in D dimensions. The D = 2 case (Flatland) is investigated in some detail. It is shown that the neutral atoms and the (moderately) positive ions correspond to the values q = 0.8 and q = 1, respectively, of the deformation parameter q. © John Wiley & Sons, Inc.