Interdependent lateral interactions, hydrophobicity and acid strength and their influence on the catalytic activity of nanoporous sulfonic acid silicas
Interdependent lateral interactions, hydrophobicity and acid strength and their influence on the catalytic activity of nanoporous sulfonic acid silicas
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DOI：
10.1039/c0gc00045k
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发表时间：
2010-08-01
期刊：
影响因子：
9.8
通讯作者：
Wilson, Karen
中科院分区：
文献类型：
--
作者：
Dacquin, Jean-Philippe;Cross, Hannah E.;Wilson, Karen
丙磺酸系列（MCM-SO（3）H）和辛基共官能化丙磺酸用巯基丙基三甲氧基硅烷（MPTS）对MCM-41进行后修饰，使SO（3）H的表面覆盖率达到0 12-1单层，制备了（MCM-Oc-SO（3）H）系列催化剂。具有亚单层MPTS覆盖的样品进一步用辛基三甲氧基硅烷接枝以覆盖裸露的羟基位点并调节载体的疏水性。对于MCM-SO（3）H系列，NH（3）量热法显示酸强度作为磺酸负载的函数增加，-Δ H（ads）（NH（3））从87增加到118 kJ mol（-1）。相反，MCM-Oc-SO（3）H显示亚单层SO（3）H覆盖率的酸强度显著增强，发现-Δ H（ads）（NH（3））增加到103 kJ mol（-1）。与这些酸强度测量一致，发现MCM-SO（3）H系列在丁醇与乙酸的酯化中的每中心活性随着SO（3）H含量的增加而增加。引入辛基进一步促进MCM-Oc-SO（3）H系列内所有样品的酯化活性，使得具有最低SO（3）负载的样品的翻转频率分子动力学模拟表明，孤立的磺酸基团与孔壁的相互作用是酸减少的主要原因。MCM-SO（3）H系列中亚单层样品的强度和活性辛基的引入导致疏水性增加和相邻磺酸头基之间的横向相互作用的组合，导致酸强度和酯化活性的显著增强
A series of propylsulfonic (MCM-SO(3)H) and octyl co-functionalised propylsulfonic (MCM-Oc-SO(3)H) catalysts have been prepared by post modification of MCM-41 with mercaptopropyltrimethoxysilane (MPTS) to achieve SO(3)H surface coverages spanning the range 0 12-1 monolayer Within the MCM-Oc-SO(3)H series, samples with submonolayer MPTS coverages were further grafted with octyltrimethoxysilane to cap bare hydroxyl sites and tune the hydrophobicity of the support. For the MCM-SO(3)H series NH(3) calorimetry revealed acid strength increases as a function of sulfonic acid loading, with -Delta H(ads)(NH(3)) increasing from 87 to 118 kJ mol(-1) In contrast, MCM-Oc-SO(3)H exhibits a dramatic enhancement of acid strength for submonolayer SO(3)H coverages, with -Delta H(ads)(NH(3)) found to increase to 103 kJ mol(-1). In line with these acid strength measurements the per-site activity of the MCM-SO(3)H series in the esterification of butanol with acetic acid was found to increase with SO(3)H content Incorporation of octyl groups further promotes esterification activity of all the samples within the MCM-Oc-SO(3)H series, such that the turn over frequency of the sample with the lowest loading of SO(3)H more than doubles Molecular dynamic simulations indicate that the interaction of isolated sulfonic acid groups with the pore walls is the primary cause of the decrease in acid strength and activity of submonolayer samples within the MCM-SO(3)H series Incorporation of octyl groups results in a combination of increased hydrophobicity and lateral interactions between adjacent sulfonic acid head groups, resulting in a striking enhancement of acid strength and esterification activity