The metal-catalyzed polymerization of simple olefins, such as ethylene and propylene, has been one of the transformational discoveries in chemistry of the 20th century. It is difficult to imagine today’s civilization without ubiquitous plastics, such as polyethylene and related polymers. Although often attributed to Karl Ziegler and Giulio Natta, the winners of the 1963 Nobel Prize in Chemistry...

Mesoporous alumina with narrow pore size distribution centered in the range of 4.4-5.0 nm and with a specific surface area as high as 270 m²·g-1 was prepared via the nanocasting approach using a CMK-3 carbon replica as a hard template. Based on this support, a series of catalysts containing 1, 5, 10, 20 and 30 wt % of chromium was prepared by incipient wetness impregnation, characterized, and s...

Both metallocene and Phillips chromium catalysts are used in the commercial manufacture of polyethylene. Unlike most other systems, Chevron Chemical (CPC) platform does not use methylaluminoxane or fluoroorganic boranes. Instead, support itself serves to activate (ionize) metallocenes, which then polymerize ethylene at high activity. Most these solid acid supports can also be anchor Cr make a c...

Unveiling the nature and distribution of surface sites in heterogeneous catalysts, for Phillips catalyst (CrO3/SiO2) particular, is still a grand challenge despite more than 60 years research. Commonly used references Cr K-edge XANES spectral analysis rely on bulk materials (Cr-foil, Cr2O3) or molecules (CrCl3) that significantly differ from actual sites. In this work, we built library spectra ...

Delley et al. (1) propose a new proton transfer mechanism to explain the mysterious initiation mechanism (2) of the Phillips polymerization catalyst. The authors’ mechanism invokes dormant (D) sites and active Si(OH)CrR sites, as summarized in Fig. 1. A combination of transition state theory, Delley et al.’s (1) density functional theory (DFT) results, and standard microkinetic modeling techniq...

We study the behavior of the cuspidal spectrum of T\^, where %? is associated to Gln(i?) and V is cofinite but not compact. By a technique that modifies the Lax-Phillips technique and uses ideas from wave equation techniques, if r is the dimension of JP, Na{k) is the counting function for the Laplacian attached to a Hilbert space Ha, Ma(X) is the multiplicity function, and Ho is the space of cu...

1. Coronary Artery Disease (C4D) Genetics Consortium. A genome-wide association study in Europeans and South Asians identifies five new loci for coronary artery disease. Nat Genet. 2011;43:339–344. 2. Musunuru K, Strong A, Frank-Kamenetsky M, Lee NE, Ahfeldt T, Sachs KV, Li X, Li H, Kuperwasser N, Ruda VM, Pirruccello JP, Muchmore B, Prokunina-Olsson L, Hall JL, Schadt EE, Morales CR, Lund-Katz...