Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Acc Chem Res. 2012 Feb 21;45(2):206-14. doi: 10.1021/ar2001342. Epub 2011 Oct 17.
Supported catalysts, metal or oxide catalytic centers constructed on an underlying solid phase, are making an increasingly important contribution to heterogeneous catalysis. For example, in industry, supported catalysts are employed in selective oxidation, selective reduction, and polymerization reactions. Supported structures increase the thermal stability, dispersion, and surface area of the catalyst relative to the neat catalytic material. However, structural and mechanistic characterization of these catalysts presents a formidable challenge because traditional preparations typically afford complex mixtures of structures whose individual components cannot be isolated. As a result, the characterization of supported catalysts requires a combination of advanced spectroscopies for their characterization, unlike homogeneous catalysts, which have relatively uniform structures and can often be characterized using standard methods. Moreover, these advanced spectroscopic techniques only provide ensemble averages and therefore do not isolate the catalytic function of individual components within the mixture. New synthetic approaches are required to more controllably tailor supported catalyst structures. In this Account, we review advances in supported catalyst synthesis and characterization developed in our laboratories at Northwestern University. We first present an overview of traditional synthetic methods with a focus on supported vanadium oxide catalysts. We next describe approaches for the design and synthesis of supported polymerization and hydrogenation catalysts, using anchoring techniques which provide molecular catalyst structures with exceptional activity and high percentages of catalytically significant sites. We then highlight similar approaches for preparing supported metal oxide catalysts using atomic layer deposition and organometallic grafting. Throughout this Account, we describe the use of incisive spectroscopic techniques, including high-resolution solid state NMR, UV-visible diffuse reflectance (DRS), UV-Raman, and X-ray absorption spectroscopies to characterize supported catalysts. We demonstrate that it is possible to tailor and isolate defined surface species using a molecularly oriented approach. We anticipate that advances in catalyst design and synthesis will lead to a better understanding of catalyst structure and function and, thus, to advances in existing catalytic processes and the development of new technologies.
负载型催化剂，即在基底固相上构建的金属或氧化物催化中心，在多相催化中发挥着越来越重要的作用。例如，在工业中，负载型催化剂被用于选择性氧化、选择性还原和聚合反应。与纯催化材料相比，负载型结构提高了催化剂的热稳定性、分散性和比表面积。然而，这些催化剂的结构和机理表征提出了巨大的挑战，因为传统的制备方法通常会得到结构复杂的混合物，其各个组分无法分离。因此，负载型催化剂的表征需要结合先进的光谱技术，而不同于均相催化剂，后者具有相对均匀的结构，通常可以使用标准方法进行表征。此外，这些先进的光谱技术只能提供整体平均值，因此无法分离混合物中各个组分的催化功能。需要新的合成方法来更可控地调整负载型催化剂的结构。在本报告中，我们回顾了我们在西北大学实验室开发的负载型催化剂合成和表征方面的进展。我们首先介绍了传统合成方法的概述，重点介绍了负载型氧化钒催化剂。接下来，我们描述了使用锚固技术设计和合成负载型聚合和加氢催化剂的方法，这些技术提供了具有优异活性和高比例催化活性位的分子催化剂结构。然后，我们强调了使用原子层沉积和有机金属接枝制备负载型金属氧化物催化剂的类似方法。在本报告中，我们描述了使用高分辨率固态 NMR、紫外-可见漫反射（DRS）、紫外拉曼和 X 射线吸收光谱等敏锐的光谱技术来表征负载型催化剂。我们证明，使用分子定向方法可以对定义明确的表面物种进行剪裁和分离。我们预计，催化剂设计和合成方面的进展将有助于更好地理解催化剂的结构和功能，从而推动现有催化工艺的发展并开发新技术。
