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首页> 外文学位 >Microcalorimetric study of adsorption processes on microporous carbons: Characterization of surface functional groups and gasification catalysts.
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Microcalorimetric study of adsorption processes on microporous carbons: Characterization of surface functional groups and gasification catalysts.

机译：微量量热法研究微孔碳的吸附过程：表面官能团和气化催化剂的表征。

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A microcalorimetric study was undertaken in order to gain new insight regarding the surface chemistry of various carbonaceous materials. The initial phase of the study identified two distinct types of active sites associated with complex formation on acid treated chars prepared from a proprietary phenol-formaldehyde resin. It appeared that one type of site (heat of oxygen adsorption around 75 kcal/mol) is created by decomposing CO{dollar}sb2{dollar} bound groups, while a second site type (heat of oxygen adsorption around 50 kcal/mol) created by decomposing CO surface complexes is only formed at outgassing temperatures above 600{dollar}spcirc{dollar}C. These findings were also consistent with total surface area measurements for the materials studied.; A second phase of the study indicated that physical mixtures of alkaline-earth metal carbonates and coal chars are not effective in creating a significant number of new active sites for char gasification, whereas the opposite conclusion was reached for alkali metal carbonates. In particular, differential heats and rates of oxygen adsorption support a redox mechanism for sodium and potassium catalyzed char gasification. However, the data suggest a mechanism involving reduced metallic sodium and mixed oxides for sodium carbonate catalysis, while only a mixture of oxides is apparent in the case of potassium carbonate catalysis.; Finally, a model was developed, based on the mechanistic concept of chemical reactions, to explain batch-type differential calorimetric data. This basic model is capable of describing both differential heat and rate versus coverage behavior for gas adsorption on microporous solids at low temperatures. Two extreme mechanisms were investigated: (1) kinetically controlled adsorption; and (2) adspecies equilibrium adsorption. It was clearly shown that when surface equilibrium is achieved, the differential heat of adsorption declines in monotonic or "stepwise" fashion as a function of surface coverage. Conversely, it was found that when kinetics dominate the adsorption process, the differential heat may increase, decrease, or fluctuate as a function of surface coverage while the differential rate of adsorption monotonically declines. These findings are in excellent agreement with the oxygen adsorption on all the carbonaeous materials studied.
机译：为了获得有关各种含碳材料表面化学的新见识，进行了微量量热研究。研究的初始阶段确定了两种不同类型的活性位点，这些活性位点与由专有的酚醛树脂制备的酸处理焦炭上的复合物形成有关。似乎是通过分解CO {dollar} sb2 {dollar}的结合基团产生了一种类型的位点（大约75 kcal / mol的氧吸附热），而第二种类型的位点（大约50 kcal / mol的氧吸附热）产生了。通过分解CO表面配合物仅在排气温度高于600℃时形成。这些发现也与所研究材料的总表面积测量结果一致。研究的第二阶段表明，碱土金属碳酸盐和煤焦的物理混合物不能有效地产生大量新的活性炭气化活性位，而碱金属碳酸盐却得出相反的结论。特别是，不同的热量和氧气的吸附速率支持钠和钾催化的焦炭气化的氧化还原机理。然而，数据表明了一种机制，其中涉及还原的金属钠和混合氧化物用于碳酸钠催化，而在碳酸钾催化的情况下，仅氧化物混合物是明显的。最后，基于化学反应的机理概念，开发了一个模型，以解释批处理类型的量热数据。该基本模型能够描述在低温下气体吸附在微孔固体上的差热和速率与覆盖率的关系。研究了两种极端机理：（1）动力学控制的吸附； （2）形态平衡吸附。清楚地表明，当达到表面平衡时，吸附的差热根据表面覆盖率以单调或“逐步”方式下降。相反，发现当动力学主导吸附过程时，差热可能会随表面覆盖率的增加，减少或波动，而吸附的差速则单调下降。这些发现与所研究的所有碳质材料上的氧吸附极为吻合。

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