Denayer Joeri F M, Ocakoglu Refik A, Thybaut Joris, Marin Guy, Jacobs Pierre, Martens Johan, Baron G V
Dienst Chemische Ingenieurstechniek, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium.
J Phys Chem B. 2006 May 4;110(17):8551-8. doi: 10.1021/jp060657s.
Low-coverage adsorption properties (Henry constants, adsorption enthalpy, and entropy) of linear and branched alkanes (C3-C8) on zeolite MCM-22 were determined using the chromatographic technique at temperatures between 420 and 540 K. It was found that adsorption enthalpy and entropy of linear alkanes vary in a nonmonotonic way with carbon number. The adsorption behavior of alkanes was rationalized on the basis of the pore geometry. Short molecules prefer to reside in the pockets of the MCM-22 supercage, where they maximize energetic interaction with the zeolite. Longer molecules reside in the larger central part of the supercage. For carbon numbers up to six, singly branched alkanes are selectively adsorbed over their linear counterparts. This preference originates from the entropic advantage of singly branched molecules inside MCM-22 supercages, where these species have high rotational freedom because of their small length.
采用色谱技术在420至540K的温度范围内测定了直链和支链烷烃（C3 - C8）在沸石MCM - 22上的低覆盖度吸附特性（亨利常数、吸附焓和熵）。结果发现，直链烷烃的吸附焓和熵随碳原子数呈非单调变化。基于孔几何结构对烷烃的吸附行为进行了合理化解释。短分子倾向于驻留在MCM - 22超笼的口袋中，在那里它们与沸石的能量相互作用最大化。较长的分子驻留在超笼较大的中心部分。对于碳原子数为6及以下的情况，单支链烷烃比其直链对应物更易被选择性吸附。这种偏好源于MCM - 22超笼内单支链分子的熵优势，由于其长度较短，这些分子具有较高的旋转自由度。
