Surface Organometallic Chemistry on Zeolites: Synthesis of Group IV Metal Alkyls and Metal Hydrides on Hierarchical Mesoporous H-ZSM-5

Abstract

Surface organometallic chemistry (SOMC) has mainly been devoted to the reaction of organometallics with surfaces comprising highly divided and dehydroxylated oxides. The field has been extended to SOMC on metal nanoparticles. However, to the best of our knowledge, SOMC has not been extended to hierarchical fibrous zeolites, although zeolitic materials are a particular class of oxides. Zeolite catalysis is important in hydrocarbon industrial chemistry. However, having an optimum balance between the activity and selectivity of the zeolitic catalysts remains a major challenge in the field. The main difficultly is the plethora of surface sites, only some of which are catalytically active. Given that the acido–basic properties and porosity of zeolites are especially important to the refining and petrochemical industries, we decided to explore this rather unexplored area. Here, three novel well-defined single-site materials [(Np)3M@ZSM-5, M = Ti, Zr, and Hf] supported on a hierarchical mesoporous H-ZSM-5 material (1) are reported. They are prepared using the concepts and tools of SOMC. They are further converted to their corresponding metal hydride [(H) n M@ZSM-5, M = Ti, Zr, and Hf, (n = 1–2)] materials (5–7) through controlled hydrogenolysis of [(Si–O−)­M­(Np)3, M = Ti, Zr, and Hf] materials (2–4) under H2 (1 atm) at 150 °C for 16 h. All these surface catalysts are characterized by various spectroscopic techniques including Fourier transform infrared spectroscopy, elemental analysis, solid-state NMR spectroscopy, powder X-ray diffraction, Brunauer–Emmett–Teller surface area measurements, and scanning electron microscopy and high-resolution transmission electron microscopy analyses and are supported by density functional theory calculations. The catalytic activity of these well-defined single-site novel materials will be tested for the catalytic applications in petrochemistry for refinery processes such as hydrocracking of distillates from crude oil or intermediate refinery process streams to useful petroleum value-added products for the society.