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Minneapolis, MN, United States

Ga/HZSM-5 catalysts, synthesized by the incipient wetness impregnation technique, showed a steady decline in Brønsted acidity with gallium addition. A maximum in propane conversion and aromatics selectivity at a Ga/Al ratio of about 0.5 suggests synergy between proton and gallium sites. A microkinetic model using 312 elementary steps and 25 rate and equilibrium parameters to describe the aromatization of propane over HZSM-5 with Si/Al of 16 is the base case against which the effects of Ga are compared. Kinetic models based on two different Ga active sites, including GaH2+ and GaH2 +, were first used individually to describe the diverse dataset that includes conversion to 10 different products as a function of temperature (510-540 °C), space time (2-8 gcat h/mol), and Ga/Al (0-1) variations. An evaluation of these models based on an assigned catalytic functionality for these sites and the associated parameters showed that both sites are required to provide a unified description of the catalytic behavior across gallium content with monohydridic Ga-sites being predominantly prevalent at low Ga/Al ratio and dihydridic Ga-sites at high Ga/Al ratios. In this paper, we address the ability to discriminate between the models and their implications for the primarily dehydrogenation nature of the Ga active sites. © 2010 Elsevier Inc. All rights reserved.

Knutson T.R.,University of Minnesota | Hanson P.J.,University of Minnesota | Aydil E.S.,421 Washington Avenue SE | Penn R.L.,University of Minnesota
Chemical Communications | Year: 2014

Copper zinc tin sulfide (CZTS) thin films were deposited from homogeneous solutions of precursors and directly onto conductive films via selective thermolysis by microwave heating. Microwave energy is absorbed strongly by conductive films, which enables preferential heating to a sufficiently high temperature for the deposition of CZTS exclusively on the conductive layer without homogeneous nucleation of CZTS in the liquid phase or heterogeneous nucleation of CZTS on uncoated portions of substrates. This journal is © the Partner Organisations 2014.

Yue X.-F.,Jining University | Cheng J.,Jining University | Li H.,Jining University | Zhang Y.-Q.,Jining University | Wu E.L.,421 Washington Avenue SE
Chinese Physics B | Year: 2010

The product polarizations of the title reactions are investigated by employing the quasi-classical trajectory (QCT) method. The four generalized polarization-dependent differential cross-sections (PDDCSs) (27π/σ) (dσ00/dωt), (27π/σ) (dσ20/dωt), (2π/σ) (dσ22+/dωt), and (2π/σ) (dσ21-/dωt) are calculated in the centre-of-mass frame. The distribution of the angle between k and j', P(θr), the distribution of the dihedral angle denoting k-k'-j' correlation, P(r), as well as the angular distribution of product rotational vectors in the form of polar plots P(θr, r) are calculated. The isotope effect is also revealed and primarily attributed to the difference in mass factor between the two title reactions. © 2010 Chinese Physical Society and IOP Publishing Ltd.

Khare A.,421 Washington Avenue SE | Wills A.W.,University of Minnesota | Ammerman L.M.,University of Minnesota | Norris D.J.,421 Washington Avenue SE | Aydil E.S.,421 Washington Avenue SE
Chemical Communications | Year: 2011

Starting with metal dithiocarbamate complexes, we synthesize colloidal Cu2ZnSnS4 (CZTS) nanocrystals with diameters ranging from 2 to 7 nm. Structural and Raman scattering data confirm that CZTS is obtained rather than other possible material phases. The optical absorption spectra of nanocrystals with diameters less than 3 nm show a shift to higher energy due to quantum confinement. © 2011 The Royal Society of Chemistry.

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