Influence of the synthetic procedure on the properties of three Ziegler-Natta catalysts with the same 1,3-diether internal donor

Being the main responsible for the huge production of polyolefins, heterogeneous Ziegler-Natta catalysts are among the most important catalysts in the chemical industry and they have been optimized over the years since their discovery in 1953 crossing many different generations. Lastly, catalysts of the 5th generation are characterized by the introduction in the pre-catalyst of 1,3-diether compounds as internal electron donors, which are stable in the presence of AlR3 activators and do not require the further addition of external donors during the following steps of the catalytic process to control the activity and selectivity. In this work, we synthetized and systematically investigated by a multi-technique approach three Ziegler-Natta catalysts characterized by the same 1,3-diether donor, but differing in the synthesis route. We found that the synthetic route influences the MgCl2 particle size, as well as the properties of the Ti species. In particular, the reprecipitation method brings the smallest MgCl2 particles and the most positive Ti4+ sites in the pre-catalyst, but also the largest amount of accessible Ti3+ sites after TEAl activation. These structural and spectroscopic data correlate pretty well with the kinetic of gas-phase propylene polymerization in very mild conditions

Electronic Properties of Ti Sites in Ziegler-Natta Catalysts

Although Ziegler-Natta (ZN) catalysts play a major role in the polyolefin market, a true understanding of their properties at the molecular level is still missing. In particular, there is a lack of knowledge on the electronic properties of Ti sites. Theoretical calculations predict that the electron density of the Ti sites in the precatalysts correlates with the activation energy for olefin insertion in the Ti-alkyl bond generated at these sites after activation by Al-alkyls. It is also well known that the effective charge on the Ti sites in the activated catalysts affects the olefin π-complexation. In this contribution, we exploit two electronic spectroscopies, UV-vis and Ti L2,3-edge near-edge X-ray absorption fine structure (NEXAFS), complemented with theoretical simulation to investigate three ZN precatalysts of increasing complexity (up to an industrial system) and the corresponding catalysts activated by triethylaluminum (TEAl). We provide compelling evidence for the presence of monomeric 6-fold-coordinated Ti4+ species in all of the precatalysts, which however differ in the effective charge on the Ti sites. We also unambiguously demonstrate that these sites are reduced by TEAl to two types of monomeric 5-coordinated Ti3+, either alkylated or not, and that the former are involved in ethylene polymerization. In addition, small TiCl3 clusters are formed in the industrial catalyst, likely due to the occurrence of severe reducing conditions within the catalyst pores. These data prove the potential of these two techniques, coupled with simulation, in providing an accurate description of the electronic properties of heterogeneous ZN catalysts

Anomalous exothermic and endothermic data observed by Nano-Ni-composite samples

This is an experimental paper summarizing the observations of anomalous data on excess heat, D(H)-loading and abrupt desorption with endothermic heat sink in Ni-nano-composite samples under D(H)-gas charging at both room and elevated temperatures, done by Kobe-Technova group in 2012-2013. Referring to our JCF12 paper (Y. Miyoshi et al., JCF-12-1) on Pd1Ni7/ZrO2 samples, experimental procedure and results reported for Ni/ZrO2, Cu0.21Ni0.21/ZrO2 and Cu0.08Ni0.36/ZrO2 samples (partially reported in our JCF13-15 paper by Sakoh et al.) will be summarized. We have reanalyzed time-dependent data for speculating heat releasing mechanisms during the long (several weeks) lasted phase of D(H)-loading-into-nano-metal. It seems that competing process of D(H)-gas sorption and desorption at the surface of nano-powders would be attributed to the mechanism. Burst-like heat peaks of η-values (in unit of eV per D(H)-take-in/out) were observed with anomalously high values reaching 600 eV/H-sorption, and with smaller [eta]-values for isotopic Dsorption than H-sorption, at 573K. Integrated heat values for several-week runs were reached at the levels of ca. 800eV/atom-Ni for Cu0.08Ni0.36/ZrO2 samples, which were about 10 times larger than those of Ni/ZrO2 samples and about 4 times larger than those of Cu0.21Ni0.21/ZrO2 samples, at temperatures of 523 to 573K