黄土高原22万年来的黑碳记录和古火灾害历史重建

The term black carbon is used to describe a relatively inert and ubiquitous form of carbon, comprising a range of materials from char and charcoal to element or graphite carbon produced by the incomplete combustion of fossil fuels and biomass. Due to its inertness, the BC in soils, lacustrine and marine sediments and ice can persist over a long period of time. So BC signatures in geological deposits can be used as evidence of natural fires happened in their surroundings. To study the temporal and spatial changes in paleofires over the Chinese Loess Plateau, black carbon concentrations were analyzed on the loess-paleosol samples from three sections including Lijiayuan, Lingtai and Weinan along a north-south transect. Using the orbitally-tuned time-scales of the sections, the black carbon sedimentation rates (BCSR) were calculated. Meanwhile, with objective to document fine resolution fire history during late Pleistocene and Holocene periods, we measured BC concentrations of loess-paleosol samples at dense sampling intervals since 28 ka BP. in Lijiayuan section. The BCSR of the samples were also calculated. In addition, we also conducted observation on black carbon morphologies to examine their sources. Based on the results, the following remarks can be concluded: 1. In the last two glacial cycles, the BCSR values in glacial periods are 2-3 times higher than in interglacial periods, and the BCSR variability has a relatively strong precession-associated 23 kyr period, suggesting that the glacial cold-dry climate conditions were apt to induce natural fires over the Loess Plateau, 2. Comparison of the BCSR records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern and interglacial periods. 3. Pollen records and carbon isotope analyses of organic matter have shown that the Loess Plateau was covered by an Artemisia-dominated grassland vegetation both during glacial and interglacial periods, So grassland fires were the dominant fire types in the Plateau, which is also corroborated by the observation of black carbon morphology. In addition, statistics and comparison of BC particle sizes among the sections demonstrated that BC records probably reflected local fires. 4. According to previous studies about the effect of fires on vegetation changes, we considered that the fires might play an important role in the expansion of grassland during glacial periods, besides the control of climate changes. 5. The high resolution black carbon record in Lijiayuan section has shown that the BCSR series well documented Younger dryas (YD) and Heinrich (HI和H2) events, suggesting that natural fires in the northwestern part of Chinese Loess Plateau could regularly respond to the millennial scale climate oscillation.

中国煤中22种环境敏感微量元素的地球化学研究

本论文按照统一的采样和统一的分析测试方法对全国煤中22种环境敏感微量元素及全硫含量进行了系统的研究。通过统计学的方法不仅给出了中国煤炭部分环境敏感微量元素的分布范围、算术均值、标准差、几何均值、几何偏差，中位数，而且首次给出了95％置信度下算术均值、几何均值以及元素含量分布的置信区间等，并与前人大量样品的统计结果进行比较。还通过统计分析了部分环境敏感微量元素在我国煤中的主要赋存状态，以及选煤对这部分微量元素的脱除机理和脱除效果等，得到以下几点认识： 1. 通过与前人大量样品统计所得到的结果进行比较，进一步证明了论文中使用的这批样品是中国煤炭平均化学成分的良好代表。本次所分析的23种元素中，As、Be、Co、Cr、Cu、Hg、Pb、Se、Th、Tl、U、F、S等13元素与前人数10年研究的统计结果在分布范围、均值含量等上非常一致，但本次的结果更为可信，更接近中国煤炭平均化学成分的真实状况。此外，本次对这B、Sn这2种元素的分析数据也是目前反映我国煤中分布最具有代表性的数据。 2. 根据样品的无偏性，对平均值的置信区间进行计算。首次给出了全国煤中各元素在95％置信度下的算术均值的置信区间、几何均值的置信区间以及元素含量分布的置信区间等。可以为后人研究各元素在绝大多数煤中的含量及均值情况时作为参考。同时统计分析表明，按照95％置信度计算，16元素的真实平均值在我们所得到的平均值±11％范围之内，最大偏差为硒，在±20％之间。 3. 平均值作为最常用的统计量之一，中国煤中不同元素的不同均值之间有一定的差异，反映了元素在煤中不同的分布状态。论文中通过对23种元素在全国煤中的5种不同的均值比较，一般元素的产量加权均值与总体样品均值之间都比较接近；绝大多数元素的储量加权均值比较低，这与西北、华北地区未开采利用的煤炭资源量大，煤质好有关。 4. 通过与Swaine（1990）给出世界煤中元素的分布范围进行比较，22种环境敏感微量元素在我国煤中的分布处于世界煤的有限范围之内。其中，Cr、Cu、Mn、Mo、Se、Sn、Th、Tl、U、V、F等微量元素在我国煤中的分布与世界煤比较接近，而As、B、Ba、Be、Cd、Co、Cl、Hg、Ni、Pb、Sb等微量元素在我国煤中较世界煤低很多。 5. 与世界主要煤炭资源大国和Swaine（1990）给出的世界煤元素均值含量的比较显示，大部分环境敏感微量元素在我国煤中的均值含量与世界主要煤炭资源大国煤中的均值含量也比较接近。其中，我国煤中B、Co、Cu、Hg、Pb、U等6种元素含量均值与美国煤比较接近，As、Cd、Sb、Tl等4种元素含量均值与澳大利亚煤比较接近，Ba、Cr、Mo、Ni、V等4种元素含量均值与前苏联煤比较接近，Be、Mn、Se、Th、F等5种元素含量均值与世界煤比较接近。 6. 随着煤炭变质程度的增高，各元素均值含量没有表现出明显规律性的增高或降低。但22种环境敏感微量元素在褐煤、弱粘煤、不粘煤、气煤等较低变质程度煤中的含量整体水平不高，绝大多数微量元素主要在中高变质程度煤中较为更为富集。不同成煤时期以及不同聚煤区煤中各种环境敏感微量元素不同的富集程度，从总体上反应了绝大部分环境敏感微量元素在华南煤中更为富集，而占全国储量3/4的华北和西北煤中的总体水平相对较低。 7. 通过对环境敏感微量元素与灰分及主要灰成分之间的关系进行分析，初步了解了它们在煤中的主要赋存状态。煤中绝大部分环境敏感微量元素还是具有非常明显的无机亲和性，在煤中主要以矿物无机形态存在。主要与粘土矿物、黄铁矿及硫化物相结合，而与碳酸盐矿物关系不大。 8. 脱除率的分析显示，15种元素的脱除率与灰分的脱除率之间具有显著的正相关性，说明煤中绝大部分环境敏感微量元素主要以无机形态存在，因此提高原煤入洗率，降低原煤灰分的同时也可以在很大程度上降低环境敏感微量元素的燃煤排放。 9. 部分环境敏感元素的脱除率受到其在煤中的赋存状态、矿物形态、煤级以及选煤厂洗选工艺等诸多因素的影响，在不同样品中脱除率的差异较大。某些样品中微量元素的脱除率较高，最高脱除率可达到70％以上。从平均脱除率来看，灰分、硫分及绝大多数环境敏感微量元素处于30％－70％之间，只有少数几个元素不到20％。

The chemical nature of carbonaceous deposits and their role in methane dehydro-aromatization on Mo/MCM-22 catalysts

Various carbonaceous deposits are formed during the course of methane dehydro-aromatization (MDA) under non-oxidative conditions on Mo/MCM-22 catalysts. These carbon species were investigated by various temperature-programmed techniques such as TPH and TPCO2, combining with TPO and TGA results in order to reveal their chemical nature and determine their amounts. The TPO profiles recorded from coked Mo/MCM-22 catalysts show two temperature peaks: one at about 756 K and the other at about 876 K. The coke amounts related to these two peaks were determined on the basis of the corresponding corrected and deconvoluted TPO profiles, combining with the TGA profiles concerned.

An investigation of the roles of surface aluminum and acid sites in the zeolite MCM-22

Ammonia adsorption studies reveal that the observed Lewis acidity in the zeolite MCM-22 is derived from at least two types of framework aluminum sites (Al(F)), that is, octahedral Al(F) and three-coordinate Al(F). Comparative ammonia or trimethylphosphine (TMP) adsorption experiments with MCM-22 confirm that octahedral Al species gives rise to the signal at delta(ISO) approximate to 0 in the (27)Al NMR spectrum; this is a superposition of two NMR signals from the different Al species on the water-re constructed zeolite surface. A sharp resonance assigned to framework Al reversibly transforms on ammonia adsorption to delta(ISO) (27)Al approximate to 55 from tetrahedral Al(F), while the broad peak is assigned to nonframework aluminium which results from hydrothermal treatment. This study also demonstrates the effectiveness of (27)Al magic angle spinning (MAS) and multiple quantum (MQ) MAS NMR spectroscopy as a technique for the study of zeolite reactions.

Oriented growth of MCM-22 zeolite films

MCM-22 zeolite films have been grown with layers vertical to the substrate under hydrothermal synthesis conditions, and characterized by X-ray diffraction and scanning electron microscopy.

PRINCIPAIS INDICADORES: AGRÍCOLAS, v. 3, n. 22, 2010.

2010

PRINCIPAIS INDICADORES: LEITE E DERIVADOS, v. 3, n. 22, 2010.

2010