Web Release Date: October 30,
Kinetic Study of Propylene Epoxidation with H2 and O2 over a Gold/Mesoporous Titanosilicate Catalyst
rez,
and
Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba West, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan, Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004, China, Escuela de Ingeniería Química, Universidad Industrial de Santander, A.A. 678, Bucaramanga, Colombia, and Environmental Catalysis and Nanomaterials Laboratory, Department of Chemical Engineering (0211), Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
Received: June 30, 2007
In Final Form: August 26, 2007
Abstract:
The kinetics of propylene oxidation to propylene oxide (PO) with H2/O2 mixtures on gold supported on the
mesoporous titanium silicate, Ti-TUD, was investigated using Langmuir-Hinshelwood (L-H) models and
power-rate law (PRL) models. The catalyst gave stable activity and was appropriate for the kinetic studies,
giving high selectivity to PO (>95%) at low conversions of propylene (<6%). The best L-H fit, based on
the F test and obtained using nonlinear regression, gave a rate expression of the form, rPO = k[(
(H2)1/2
(O2))/(1 + (H2)1/2(O2))](H2)1/2[
(C3H6)/(1 + (C3H6))], with an F value of 4.50. The PRL model, also analyzed
using nonlinear regression, gave a rate expression, rPO = k(H2)0.60(O2)0.25(C3H6)0.36, which provided a better
fit to the data, with an F value of 2.11. The best model was a hybrid of the form rPO = k(H2)l(O2)m(C3H6)/[kD/
+ (C3H6)], with an F value of 1.76. This hybrid model was also proven as the best model based on a
model probability criterion. The mechanistic origin of these expressions, which include coupled and sequential
cycles, is discussed. Temperature-programmed desorption measurements of propylene, hydrogen, and oxygen
showed that these species were adsorbed on the catalyst at the reaction temperature (423 K). The quantities
adsorbed were consonant with the equilibrium adsorption constants calculated from the fits of the L-H model
with three independent adsorption sites, a Temkin-Frumkin model for a nonuniform surface, and the exponents
in the PRL models.
Download the full text: PDF | HTML
