			Home About us Contact

Cr Catalysts (cr + catalyst)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Ethylene polymerization behavior of Cr(III)-containing montmorillonite: Influence of chromium compounds

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2009
Kazuhiro Yamamoto
Abstract Montmorillonite was treated with Cr(NO3)3, Cr(acetate)3, and Cr(acac)3 to give three catalyst precursors, Cr-MMT-1, Cr-MMT-2, and Cr-MMT-3, respectively. Application of these catalysts to the ethylene polymerization reaction revealed Cr-MMT-1 to be much more reactive than the other two while the molecular weight distributions of the polymers were practically the same. Elemental analysis, XRD, and TEM measurements suggested that chromium occupied the interlayer section in Cr-MMT-1 and mostly the outer surface region for the other two catalysts. Aluminosilicate-supported Cr catalysts exhibited reactivity similar to that of Cr-MMT-2 and Cr-MMT-3. However, more of the low-molecular-weight polymer was formed. These data suggested that there is a relationship between the sites of the Cr ions and catalytic reactivity, and between supporting solid identity and molecular weight distribution of the polymer. The use of n -Bu2Mg and Et2Zn in the place of Et3Al led to lower activity but gave polymers of narrower molecular weight distribution, with more of the high-molecular-weight material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2272,2280, 2009 [source]

A comparative study of multimodal vs. bimodal polyethylene pipe resins for PE-100 applications,

POLYMER ENGINEERING & SCIENCE, Issue 9 2005
Paul J. DesLauriers
In this paper several high density polyethylene pipe resins are compared to polyethylene resins made in the Phillips Loop-Slurry Process (single-reactor), using a catalyst of chromium on modified aluminophosphate (Cr/AlPO4). A brief description of the Cr/AlPO4 system is presented along with polymer chain architecture (i.e., topology) and other structural aspects of polymers made from these catalysts. The physical properties of these resins and their fabricated pipe processing/performance properties were compared to both PE80 and conventional bimodal type PE-100 resins. Results from this study show that high-density polyethylene resins made from Cr/AlPO4 catalysts possess primary structural attributes that are truly unique for chromium-catalyzed resins. These multimodal resins have very high molecular weights (MW; Mw > 400 kg/mol) and exceptionally broad MW distributions (MWD; Mw/Mn > 50). Topologically, these resins were found to have uniform short chain branching distributions across the MWD; as in polymers made from single site metallocene catalysts) and significantly reduced levels (10 times less) of long chain branching when compared to resins made using chromium catalysts on conventional supports. Furthermore, results from rheological, fabricated pipe processing, and performance studies suggest that these resins should be especially well suited for high performance pipe applications. Pipe samples made from these resins were found to meet PE-100 requirements including low temperature impact properties. POLYM. ENG. SCI., 45:1203,1213, 2005. © 2005 Society of Plastics Engineers [source]

Site-selective XAFS spectroscopy tuned to surface active sites of Cu/ZnO and Cr/SiO2 catalysts

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001
Yasuo Izumi
XAFS (X-ray absorption fine structure) spectra were measured by using the fluorescence spectrometer for the emitted X-ray from sample. The chemical shifts between Cu0 and CuI and between CrIII and CrVI were evaluated. Tuning the fluorescence spectrometer to each energy, the Cu0 and CuI site-selective XANES for Cu/ZnO catalyst were measured. The first one was similar to the XANES of Cu metal and the second one was the 5 : 5 average of XANES for CuI sites + Cu metal. The population ratio of copper site of the Cu/ZnO catalyst was found to be Cu metal : Cu2O : CuI atomically dispersed on surface = 70(±23) : 22(±14) : 8(±5). Site-selective XANES for CrIII site of Cr/SiO2 catalyst was also studied. [source]