Mechanism of selective benzene hydroxylation catalyzed by iron-containing zeolites
Mechanism of selective benzene hydroxylation catalyzed by iron-containing zeolites
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DOI：
10.1073/pnas.1813849115
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发表时间：
2018-11
期刊：
影响因子：
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通讯作者：
Benjamin E. R. Snyder;Max L. Bols;Hannah M. Rhoda;Pieter Vanelderen;Pieter Vanelderen;Lars H. Böttger
中科院分区：
文献类型：
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作者：
Benjamin E. R. Snyder;Max L. Bols;Hannah M. Rhoda;Pieter Vanelderen;Pieter Vanelderen;Lars H. Böttger
意义铁沸石是一种多相催化剂，在许多重要的工业应用中显示出潜力，包括在室温下甲烷选择性部分氧化为甲醇，以及苯选择性转化为苯酚。存在与Fe-沸石催化剂相关的实际限制，这些限制可以通过机械见解来解决;然而，关于Fe沸石的可靠实验数据是有限的。本研究明确了Fe分子筛催化苯选择性羟基化反应的机理，阐明了活性中心结构与催化性能（活性、选择性）之间的关系。从这项研究的机制洞察代表了重要的一步，在选择性烃氧化催化功能的合成控制。苯直接催化转化为苯酚将产生广泛的经济影响。铁沸石在这种转化中表现出高活性和选择性的显著组合，导致它们过去在中试工厂水平上的实施。然而，存在与该方法的催化剂失活相关的问题。机理的洞察力可以解决这些问题，也提供了一个蓝图，实现高性能的选择性氧化催化。最近，我们发现在Fe分子筛中选择性氧化烃类的活性中心（α-O）是一种异常活泼的Fe（IV）= O物种。在这里，我们采用先进的光谱技术，以确定该Fe（IV）= O中间体与苯的反应，事实上再生还原Fe（II）的活性位点，使催化营业额。同时，一小部分Fe（III）-酚盐中毒的活性位点形成，定义了催化剂失活的机制。密度泛函理论计算提供了进一步深入了解实验定义的机制。α-O的极端反应性显著降低（消除）了芳族羟基化的限速屏障，导致扩散限制反应坐标。这有利于快速扩散的苯底物的羟基化，而不是缓慢扩散的（但更具反应性的）含氧产物，从而提高选择性。这定义了一种同时获得高活性（转化率）和选择性的机制，使得惰性烃底物能够有效地氧化升级。
Significance Fe zeolites are heterogeneous catalysts that show potential in a number of important industrial applications, including the selective partial oxidation of methane to methanol at room temperature, and the selective conversion of benzene to phenol. There are practical limitations associated with Fe-zeolite catalysts that may be resolved with mechanistic insight; however, reliable experimental data on Fe zeolites are limited. This study defines the mechanism of selective benzene hydroxylation catalyzed by Fe zeolites, clarifying the relationship between active site structure and catalytic performance (activity, selectivity). Mechanistic insight from this study represents an important step toward synthetic control over function in selective hydrocarbon oxidation catalysis. A direct, catalytic conversion of benzene to phenol would have wide-reaching economic impacts. Fe zeolites exhibit a remarkable combination of high activity and selectivity in this conversion, leading to their past implementation at the pilot plant level. There were, however, issues related to catalyst deactivation for this process. Mechanistic insight could resolve these issues, and also provide a blueprint for achieving high performance in selective oxidation catalysis. Recently, we demonstrated that the active site of selective hydrocarbon oxidation in Fe zeolites, named α-O, is an unusually reactive Fe(IV)=O species. Here, we apply advanced spectroscopic techniques to determine that the reaction of this Fe(IV)=O intermediate with benzene in fact regenerates the reduced Fe(II) active site, enabling catalytic turnover. At the same time, a small fraction of Fe(III)-phenolate poisoned active sites form, defining a mechanism for catalyst deactivation. Density-functional theory calculations provide further insight into the experimentally defined mechanism. The extreme reactivity of α-O significantly tunes down (eliminates) the rate-limiting barrier for aromatic hydroxylation, leading to a diffusion-limited reaction coordinate. This favors hydroxylation of the rapidly diffusing benzene substrate over the slowly diffusing (but more reactive) oxygenated product, thereby enhancing selectivity. This defines a mechanism to simultaneously attain high activity (conversion) and selectivity, enabling the efficient oxidative upgrading of inert hydrocarbon substrates.