载体对其负载的Cu-Co双金属催化剂上5-羟甲基糠醛氢解选择性生成2,5-二甲基呋喃的影响

碳-氧键氢解是生物质呋喃基化合物制备交通燃料常见的模型反应,其中5-羟甲基糠醛(HMF)转化为汽油添加剂2,5-二甲基呋喃(DMF)尤为引人关注.本文采用CeO2,ZrO2和Al2O3负载的Cu-Co双金属催化剂用于HMF选择性氢解制DMF的反应中.采用X射线衍射、N2吸附-脱附、投射电镜、H2-程序升温还原、氨-程序升温脱附和元素分析表征了新鲜的和使用过催化剂的结构,并将其与催化活性相关联.Cu-Co/CeO2催化剂通过在大的Cu颗粒上还原C=O键生成了最多的2,5双(羟甲基呋喃)(BHMF).但Cu-Co/Al2O3催化剂具有高度分散的Cu,Cu-Co复合氧化物和大量的弱酸位,因而生成DMF的选择性最高.Cu-Co/ZrO2催化剂则由于存在强酸位,DMF选择性较低,生成了各种过度氢解产物,如2,5而甲基四氢呋喃和5,5-二(亚甲基)双(2-甲基呋喃).因此,考察了Cu-Co/Al2O3催化剂上的反应路径,以及温度、氢气压力和时间等操作条件的影响,使其具有较优的HMF转化率和DMF选择性.     

Eco-friendly synthesis of jasminaldehyde by condensation of 1-heptanal with benzaldehyde using hydrotalcite as a solid base catalyst

The catalytic activity of hydrotalcite ([M(II)_1−xM(III)_x(OH₂)]^x+(CO₃²⁻)_x/n·mH₂O; where M(II) = Mg, Ni, Zn and M(III) = Al) was evaluated for the synthesis of jasminaldehyde by solvent free condensation of 1-heptanal with benzaldehyde. The effect of activation of as-synthesized Mg-Al hydrotalcite samples of varied Mg/Al molar ratio on its catalytic activity was studied and correlated with their basicity as determined from the model test reaction. The effect of reaction parameters such as, amount of catalyst, benzaldehyde to 1-heptanal molar ratio and reaction temperature on conversion of 1-heptanal and selectivity of jasminaldehyde was studied in detail. Maximum selectivity of jasminaldehyde (86%) with 98% conversion of 1-heptanal was observed using as-synthesized Mg-Al hydrotalcite of Mg/Al molar ratio of 3.5 as a catalyst. The kinetics of the reaction was measured and reaction rate and order of reaction were determined under optimum reaction conditions. The catalyst was re-used upto three cycles without significant loss in its activity. The base catalyzed reaction mechanism for condensation of 1-heptanal with benzaldehyde is proposed.     

Calculations of the giant dipole resonance for sd-shell nuclei in the open-shell random phase approximation

The systematics of the giant dipole resonance have been calculated in the open-shell RPA for all the self-conjugate sd-shell nuclei, using (i) a phenomenological Rosenfeld interaction, (ii) Barret, Hewitt and McCarthy G-matrix elements and (iii) Kuo G-matrix elements. The excitations are based on shell model ground states for all nuclei except ²⁸Si for which a projected Hartree-Fock ground state was used.     

Minimization of energy variance for a determinantal state as a useful variation on the hartree-fock theme

It is suggested that a single determinantal state in the neighbourhood of the Hartree-Fock state, having the minimum energy variance might be a ‘better’ intrinsic state for describing some of the low energy states of a nucleus. At higher excitation energies the resulting orbitals may provide a suitable single-particle basis for describing the nuclear level density at that energy.     

Measurements of total and positronium-formation cross sections for the scattering of positrons by alkali atoms

We present a review of our recent measurements of total cross sections (Q _T's) for the scattering of positrons by Na, K, and Rb, and positronium-formation cross sections (Q _Ps's) for Na and K. For our total cross section measurements, a beam transmission technique has been used. For ourQ _Ps measurements, our approach involves setting upper and lower limits onQ _Ps using a combination of (1) measuring the transmission of the positron beam with the angular discrimination of the apparatus made as poor as possible, and (2) measuring the 511 keV annihilation gamma rays in coincidence produced by the decay of para-Ps formed in the scattering cell. Comparison with theoretical calculations shows that our measuredQ _T's andQ _Ps's for Na and K agree reasonably well with a close coupling approximation (CCA) calculation which takes into account the formation of Ps in then=1 andn=2 states. In the 3–10 eV energy range, this calculation predicts a peak in theQ _T's andQ _Ps's for K which also appears in our measurements. The absence of such a peak in our measuredQ _T's andQ _Ps's (preliminary) for Na in this energy range is also consistent with the same theory. Comparisons with five-state CCA calculations ofQ _T which do not take Ps-formation into account also show good agreement with our positron-Na, K, and RbQ _T measurements for energies above 20 eV, but show dramatic departures from our measurements below 10 eV for K and Rb.     

Collective mechanism for nuclear stopping and transverse flow in heavy-ion collisions

The role of filamentation instability of quark-gluon plasma, in explaining collective phenomena in relativistic heavy-ion collisions, has been analyzed. Using equations of SU(2) two fluid color hydrodynamics it is shown that this instability can significantly enhance nuclear stopping and might contribute to collective sideward flows.     

Collective thermalization in quark gluon plasma

A very important question in ultrarelativistic heavy ion collisions is that of thermalization of the high energy density quark gluon plasma forud in the central rapidity region. Different approaches have been adopted by various authors to study this thermalization problem. These include phenomenological string and capacitor plate models, perturbative QCD based parton cascade models and the classical non-perturbative approach. In this paper we briefly review the earlier studies and discuss our work which emphasizes the role of non-perturbative collective effects (classical chaos) in the thermalization of the plasma. In particular, using classical equations of motion of a coloured parton in self-consistent colour fields, we have carried out a 1+1 dimensional simulation of coloured partonic matter. We find that in certain parameter domains, the system exhibits chaotic behaviour in non-abelian plasma oscillations, which then leads to thermalization of the plasma.     

Unitary group decomposition of hamiltonian operators. II. SU (4) irreducible tensors,norms and their energy variation and symmetry breaking

SU(6) ? SU(4) tensor decomposition of effective interactions in the 2s-1d shell has been carried out to examine the relative importance of the various irreducible tensors in many-particle spaces. For this purpose norms of the irreducible tensors are evaluated in many-particle spaces. Variation of the expectation value of the square of the irreducible tensor parts with excitation energy has also been examined using the polynomial expansion method. A new measure of symmetry breaking that is theoretically more sound is derived which includes in its definition partial width as well as internal width. This is used to study SU(4) symmetry mixing in nuclei.