中新世秦安黄土一古土壤序列记录的古气候变化周期

Analysis of periodic oscillations of climate is very important in understanding the behavior of the climate system. Milankovitch hypothesis, which holds that the glacial-interglacial climatic cycles during the Quaternary were primarily driven by variations in orbital parameters, has been supported by substantial geological evidence. Continuous long-term and high-resolution records are crucial to detect how variations of Earth's orbital parameters affected climate before the Quaternary when the boundary conditions were significantly different. Qinan loess formed in the Miocene is nearly continuous aeolian deposit in northern China. Previous study has established a constrained chronology, which provides a basis to examine long-term climatic variations. One of important issues to untangle the mechanisms behind major climate changes is the investigation of climate cycles recorded in Qinan loess. In this paper, two climatic proxies, magnetic susceptibility and redness, are analyzed for QA-I section to evaluate climate cycles using Maximum entropy spectral analysis and Blackman-Tuckey method. Main conclusions are presented as following: Results exhibit significant peaks at periods of 100 ka, 64 ka, 41 ka, 30 ka and 23 ka, but also 1000 ka, 600 ka and 400 ka. These peaks correspond to the dominant periods of the Earth's orbit parameters, which indicates that the formation of the aeolian sediment in northern China might be primarily driven by variations in orbital parameters. Fluctuations with different cycles respectively dominated in different periods. Major shifts in the dominant cycles occurred at 20.3, 19.0, 17.9, 15.2, 12.5 and 11.3 Myr ago. The transition that happened at 17.9 Myr ago was synchronous with the uplift of the Tibetan Plateau, while others at 15.2, 12.5 and 11.3 Myr ago were in good agreement with the timing of the development of Antarctic ice sheet. Therefore we inferred that these shifts might be related to changes in global ice volume and/or the Tibetan uplift. 3. The strong period of 100 ka is observed between 17.9 and 15.2, and 12.5 and 11.3 Myr ago. Ice sheet-climate models that have been used to explain the cause of the 100 ka period since the middle Pleistocene couldn't be responsible for driving the 100 ka climate cycle in the Miocene in Northern China because of the different boundary of climatic conditions between the Quaternary and Miocene. Further investigation is needed to understand how this cycle became dominant in Qinan loess records during these two time segments.

Synthesis of 2-butoxy ethanol with narrow-range distribution catalyzed by supported heteropolyacids

A supported heteropolyacid (HPA), H3PMo12O40/SiO2, calcined in vacuum at 150 degrees C, has been shown to be an efficient solid acid catalyst for the synthesis of 2-butoxy ethanol with high selectivity. (C) 2000 Elsevier Science B.V. All rights reserved.

Oxidative carbonylation of aniline over a polymer-supported palladium-copper catalyst

The polymer-supported bimetallic catalyst FVP-PdCl2-2CuCl(2) (PVP, poly(N-vinyl-2-pyrrolidone), obtained in situ by the addition of CuCl2 to an alcoholic solution of PVP-PdCl2, exhibits high selectivity and activity for the oxidative carbonylation of aniline with carbon monoxide and oxygen to ethyl N-phenylcarbamate in the presence of a base (NaOAc) under atmospheric pressure. The strong synergic effect of Pd-Cu gives rise to a clear increase in the selectivity and activity. (C) 2000 Elsevier Science B.V. All rights reserved.

Comparative study by infrared spectroscopy and microcalorimetry of the CO adsorption over supported palladium catalysts

The adsorption of CO on Al(2)O(3), ZrO(2), ZrO(2)-SiO(2), and ZrO(2)-La(2)O(3) supported Pd catalysts was studied by adsorption microcalorimetry and infrared (TR) spectroscopy. Some interesting and new correlations between the results of microcalorimetry and IR spectroscopy have been found. The CO is adsorbed on palladium catalysts in three different modes: multibonded (3-fold), bridged (2-fold), both on Pd(lll) and (100) planes, and linear (1-fold) adsorbed species. The corresponding differential adsorption heats lie in the field of high (210-170 kJ/mol), medium (140-120 kJ/mol), and low (95-60 kJ/mol) values, respectively. The nature of the support, the reduction temperature, and the pretreatment conditions affect the surface structure of the Pd catalysts, resulting in variations in the site energy distribution, i.e., changes in the fraction of sites adsorbing CO with specific heats of adsorption. Moreover, the CeO(2); promoter addition weakens the adsorption strength of CO on palladium. Based on the exposed results, a correctness factor, which considers the percentages of various CO adsorption states, must be introduced when one calculates the Pd dispersion using CO adsorption data.

A study on reduction behaviors of the supported platinum-iron catalysts

The reduction behaviors of the supported platinum-iron catalysts and their comparison with supported iron catalysts were studied by TPR (temperature-programmed reduction)-in situ Fe-57 MBS (Mossbauer spectroscopy). The results indicated that the TPR processes of all Fe-containing catalysts were different from that of bulk alpha-Fe2O3. There were interactions between Pt, Fe and the gamma-Al2O3 or SiO2 support for the Pt-Fe/gamma-Al2O3 and Pt-Fe/SiO2 catalysts. All the iron-containing catalysts show that Fe3+ was highly dispersed on the support (gamma-Al2O3 and SiO2) before reduction. No Fe-0 was found in the reduction processes. The Fe3+ was reduced to Fe2+ in tetrahedral vacancy first for the reduction of the Pt-Fe/gamma-Al2O3 catalyst. No Fe2+ in octahedral vacancy was found in the reduction of the Pt-Fe/SiO2 catalyst. Adding Pt to Fe/support (gamma-Al2O3 or SiO2) could promote the reduction of the Fe species. (C) 1999 Elsevier Science B.V. All rights reserved.

Polymer-supported palladium-manganese bimetallic catalyst for the oxidative carbonylation of amines to carbamate esters

The polymer-supported bimetallic catalyst PVP-PdCl2-MnCl2 (PVP=poly(N-vinyl-2-pyrrolidone)) exhibits high activity and selectivity for the oxidative carbonylation of amines with carbon monoxide and oxygen to carbamate esters under atmospheric pressure in the presence of a base (NaOAc). This catalyst is prepared by the addition of MnCl2 to the alcoholic solution of PVP-PdCl2 in situ. A remarkable bimetallic synergic effect and the role of PVP in PVP-PdCl2-MXn (MXn=the second transition metal component such as NiCl2, CoCl2, MnCl2 and FeCl3) gives rise to an obvious increase in the conversion and selectivity for the reaction. Among the second metal components tested, Mn-Pd exerts the strongest synergic effect. (C) 1999 Elsevier Science B.V. All rights reserved.