%0 Journal Article
%T Rate Parameter Distributions for Isobutane Dehydrogenation and Isobutene Dimerization and Desorption over HZSM-5
%A Trevor C. Brown
%A David J. Miron
%A Abdullah K. Alanazi
%A Cam Le Minh
%J Catalysts
%D 2013
%I MDPI AG
%R 10.3390/catal3040922
%X Deconvolution of the evolved isobutene data obtained from temperature-programmed, low-pressure steady-state conversion of isobutane over HZSM-5 has yielded apparent activation energies for isobutane dehydrogenation, isobutene dimerization and desorption. Intrinsic activation energies and associated isobutane collision frequencies are also estimated. A combination of wavelet shrinkage denoising, followed by time-varying flexible least squares of the evolved mass-spectral abundance data over the temperature range 150 to 450 ¡ãC, provides accurate, temperature-dependent, apparent rate parameters. Intrinsic activation energies for isobutane dehydrogenation range from 86 to 235.2 kJ mol £¿1 (average = 150 ¡À 42 kJ mol £¿1) for isobutene dimerization from 48.3 to 267£¿kJ mol £¿1 (average = 112 ¡À 74 kJ mol £¿1) and for isobutene desorption from 64.4 to 97.8£¿kJ mol £¿1 (average = 77 ¡À 12 kJ mol £¿1). These wide ranges reflect the heterogeneity and acidity of the zeolite surface and structure. Seven distinct locations and sites, including Lewis and Br£¿nsted acid sites can be identified in the profiles. Isobutane collision frequencies range from 10 £¿0.4 to 10 22.2 s £¿1 and are proportional to the accessibility of active sites, within the HZSM-5 micropores or on the external surface.
%K isobutane dehydrogenation
%K isobutene dimerization
%K isobutene desorption
%K HZSM-5 catalysis
%K wavelet shrinkage denoising
%K time-varying flexible least squares
%U http://www.mdpi.com/2073-4344/3/4/922