Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

Isolated transition metal ions/oxides in molecular sieves and on surfaces are a class of active sites for selective oxidation of hydrocarbons. Identifying the active sites and their coordination structure is vital to understanding their essential role played in catalysis and designing and synthesizing more active and selective catalysts. The isolated transition metal ions in the framework of molecular sieves (e.g., TS-1, Fe-ZSM-5, and V-MCM-41) or on the surface of oxides (e.g., MoO3/Al2O3 and TiO2/SiO2) were successfully identified by UV resonance Raman spectroscopy. The charge transfer transitions between the transition metal ions and the oxygen anions are excited by a UV laser and consequently the UV resonance Raman effect greatly enhances the Raman signals of the isolated transition metal ions. The local coordination of these ions in the rigid framework of molecular sieves or in the relatively flexible structure on the surface can also be differentiated by the shifts of the resonance Raman bands. The relative concentration of the isolated transition metal ion/oxides could be estimated by the intensity ratio of Raman bands. This study demonstrates that the UV resonance Raman spectroscopy is a general technique that can be widely applied to the in-situ characterization of catalyst synthesis and catalytic reactions. (C) 2003 Elsevier Science (USA). All rights reserved.

Mn-containing AlPO-11 and SAPO-11 catalysts for simultaneous isomerization and dehydrogenation of n-butane

MnAPO-11 and MnAPSO-11 were synthesized hydrothermally, and supported Mn-AlPO-11 and Mn-SAPO-11 were also prepared for comparison. Characterization results showed that there were differences in acidity and reducibility caused by the different incorporation methods of manganese. The manganese species in the samples also weakened the metallic properties of the palladium particles when the latter was added into the catalysts. Catalytic testing results for dehydroisomerization of n-butane indicated that incorporation of manganese increased the selectivity toward isomerization products. The highest isobutene selectivity (34.86%) could be obtained over a Pd/MnAPO-11 catalyst. When a combined catalyst system containing Pd/SAPO-11 and MnAPSO-11 was used in a single bed of two layers, the isobutene selectivity could be greatly improved, as compared to the single catalyst alone.

腐殖质对白浆土中Fe、Mn、Al形态转化及磷生物有效性的影响

在三江平原布置长期试验，研究连年施用有机肥后土壤腐殖质变化及其对白浆±Fe、Mn、Al形态转化及磷生物有效性的影响。结果表明，施用牛粪后土壤腐殖质含量升高，且以松结态腐殖质的增长为主；土壤的DTPA提取态和有机络合态Fe、Mn、Al含量上升，使土壤有效态磷含量上升。因此，生物措施是治理白浆土，促进土壤磷素养分有效性上升，增大土壤缓冲容量和抗逆性的有效措施。

Influence of iron promoter on catalytic properties of Rh-Mn-Li/SiO2 for CO hydrogenation

The effect of iron promoter on the catalytic properties of Rh-Mn-Li/SiO2 catalyst in the synthesis Of C-2 oxygenates from syngas was investigated by means of the following techniques: CO hydrogenation reaction, temperature-programmed reduction (TPR), temperature-programmed desorption and reaction of adsorbed CO (CO-TPD and TPSR) and pulse adsorption of CO. The results showed that the addition of iron promoter could improve the activity of the catalysts. Unexpectedly, the yield of C-2 oxygenates increased greatly from 331.6 up to 457.5 g/(kg h) when 0.05% Fe was added into Rh-Mn-Li/SiO2 catalyst, while no change in the selectivity to C-2 oxygenates was observed. However, the activity and selectivity Of C-2 oxygenates were greatly decreased if the Fe amount exceeded 1.0%. The existence of a little iron decreased the reducibility of Rh precursor, while the reduction of Fe component itself became easier. CO uptake decreased with increasing the quantity of Fe addition. This phenomenon was further confirmed by CO-TPD results. The CO-TPD and TPSR results showed that only the strongly adsorbed CO could be hydrogenated, while the weakly adsorbed CO was desorbed. We propose that Fe is highly dispersed and in close contact with Rh and Mn; such arrangements were responsible for the high yield Of C-2 oxygenates. (C) 2002 Elsevier Science B.V. All rights reserved.

Multiphoton ionization of pyrrole-water mixed clusters

Multiphoton ionization of the hydrogen,bonded pyrrole-water clusters (C4H5N)(n)(H2O)(m) is studied with a reflectron-time of flight mass spectrometer at 355 mn. With increasing partial concentration of pyrrole in a gas mixture source, a series of poly-pyrrole-water binary-mixed cluster ions can be observed, including unprotonated cluster ions [(C4H5N)(x)(H2O)(y)](+), protonated cluster ions [(C4H5N)(x)(H2O)(y)](+) and dehydrogenated cluster ions [(C4H4N)(C4H5N)(x)(H2O)(y)](+). Ab initio calculations of their structures, bond strengths, charge distributions and reaction energies are carried out. Stable structures of these clusters are obtained from the calculations. A probable formation mechanism of the cluster ions [(C4H5N)(x)(H2O)(y)](+), [(C4H5N)(x)(H2O)(y)]H+ and [(C4H4N)(C4H5N)(x) (H2O)(y)](+) is supposed to be the ionization of clusters followed by dissociation.

Binding of metal ions with protein studied by a combined technique of microdialysis with liquid chromatography

A method has been developed for the determination of interactions of metal ions and protein by using microdialysis sampling technique combined with pre-column derivation and reversed-phase ion-pair liquid chromatographic (HPLC analysis. Cu(II), Zn(II) and human serum albumin (HSA) were chosen as model metal ions and protein, respectively. The mixed solutions of metal ions and HSA with different molar ratios buffered with 0.1 M Tris-HCl containing 0.1 M NaCl at pH 7.43 were sampled with a mirodialysis probe by keeping perfusion rate at 1 mul/min and the temperature at 37 degreesC. The free concentrations of metal ions in microdialysates were assayed by precolumn derivatization with meso-tetra(4-sulfophenyl)-porphyrin (TPPS4) followed ion-pair HPLC analysis. The recovery (R) of microdialysis sampling was measured in vitro under similar conditions as 65.74% for Cu(II), 70.45% for Zn(II) with R.S.D. below 3.2%. The primary binding constants and number of binding site estimated by the Scatchard plot analysis are 5.04 x 10(6) M-1 and 0.85 for Cu(II), and 9.87 x 10(6) M-1 and 1.10 for Zn(II), respectively. The competition of Cu(II) and Zn(II) at the second binding site on HSA was investigated, and it was observed that there is a second site on HSA to bind Cu(II) and Zn(II), the affinity of Cu(II) is stronger than that of Zn(II) to this second site of HSA. (C) 2001 Elsevier Science B.V. All rights reserved.

Competing binding of metal ions with protein studied by microdialysis

A method has been established to study the competing binding of metal ions with protein by a combined technique of microdialysis with high performance liquid chromatography (HPLC). Ni2+, Cd2+, Zn2+, Cu2+ and human serum albumin (HSA) were chosen as model metal ions and protein. The experimental results show that Ni2+ and Cu2+ share a common primary binding site on HSA, and Zn2+ and Cd2+ share a different common primary binding site from them, but there is a common multi-metal binding site for all of those four metal ions. This method show advantages of fast sampling, easily to be operated and especially to be useful when ideal spectroscopic probes are not available for the study of interaction between protein and metal ions.

Novel Potentiometric Membrane Sensor for the Determination of Trace Amounts of Chromium(III) Ions

A plasticized Cr3+ ion sensor by incorporating 2,3,8,9-tetraphenyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene (TTCT) ionophore exhibits a good potentiometric response for Cr3+ over a wide concentration range (1.0×10-6-1.0×10-1 M) with a slope of 19.5 mV per decade. The sensor response is stable for at least three months. Good selectivity for Cr3+ in comparison with alkali, alkaline earth, transition and heavy metal ions, and minimal interference are caused by Li+, Na+, K+, Co2+, Hg2+, Ca2+, Pb2+ and Zn2+ ions, which are known to interfere with other chromium membrane sensors. The TTCT-based electrode shows a fast response time (15 s), and can be used in aqueous solutions of pH 3 - 5.5. The proposed sensor was used for the potentiometric titration of Cr3+ with EDTA and for a direct potentiometric determination of Cr3+ content in environmental samples.