Abstract
Morphology control plays a major role in the design of solid catalysts. Since the heterogeneous Ziegler–Natta catalyst (ZNC) is based on the in situ synthesis of MgCl2 support in a top-down manner, the individual control of the exterior and the interior structure of the catalyst macro-particles is challenging. In this study, we successfully prepared a ZNC with a multi-grain interior structure by the spray-drying of MgO nanoparticles, inspired by the fact that the MgO/MgCl2/TiCl4 core–shell catalyst can maintain the morphology of the raw MgO nanoparticles. This catalyst is the first example of the bottom-up preparation of MgCl2-supported ZNC. Here, we report its basic preparation method, characterization results, and performance in the homo-polymerization of ethylene and propylene, and copolymerization with 1-hexene.
Highlights
Morphology influences the performance of solid catalysts through the diffusion of reactants and heat
Spherical macroparticles with a narrow particle size distribution were obtained by the spray-drying of MgO nanoparticles (50 nm in diameter), using methanol as a dispersant
shell catalyst (S-Cat) showed decay-type kinetic curves in the homo-polymerization of both ethylene and propylene, i.e., the catalyst displayed the highest activity at the early stage of polymerization, and its activity dropped to a certain level, which remained constant until the polymerization was stopped
Summary
Morphology influences the performance of solid catalysts through the diffusion of reactants and heat. There are various sizes of pores within a macroparticle, originating from the hierarchical aggregation of primary catalyst particles These primary particles are made of TiCl4 adsorbed on lateral surfaces of MgCl2 nanocrystals with a lateral dimension of about 5–10 nm and a thickness of 1–2 nm [2]. The multi-grain structure of catalyst particles nicely explains the fact that immediately after the start of the polymerization reaction, the catalyst activity is small, but gradually increases as polymerization proceeds, and, remains high for a relatively long period of time (build-up-type kinetics). To study the multi-grain structure of ZNCs, the bottom-up development of a catalyst with TiCl4/MgCl2 as the primary particle is interesting and important in its own right
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