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 °C, provides accurate, temperature-dependent, apparent rate parameters. Intrinsic activation energies for isobutane dehydrogenation range from 86 to 235.2 kJ mol ？1 (average = 150 ± 42 kJ mol ？1) for isobutene dimerization from 48.3 to 267？kJ mol ？1 (average = 112 ± 74 kJ mol ？1) and for isobutene desorption from 64.4 to 97.8？kJ mol ？1 (average = 77 ± 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.
References
[1]
Le Minh, C.; Brown, T.C. Rate parameters from low-pressure steady-state protolytic cracking and dehydrogenation of isobutane over zeolite catalysts. Appl. Catal. A 2006, 310, 145–154, doi:10.1016/j.apcata.2006.05.030.
[2]
Yanping, S.; Brown, T.C. Kinetics of isobutane dehydrogenation and cracking over HZSM-5 at low pressures. J. Catal. 2000, 194, 301–308, doi:10.1006/jcat.2000.2936.
[3]
Kalaba, R.; Tesfatsion, L.C. Time-varying linear regression via flexible least squares. Compt. Math. Appl. 1989, 17, 1215–1245, doi:10.1016/0898-1221(89)90091-6.
[4]
Le Minh, C.; Alanazi, A.K.; Miron, D.J.; Brown, T.C. Carbon-carbon bond cleavage and dehydrogenation of isobutane over HZSM-5 at low pressures and temperatures. Catal. Lett. 2012, 142, 1470–1473, doi:10.1007/s10562-012-0921-2.
[5]
Miron, D.J.; Kendell, S.M.; Munshi, A.M.; Alanazi, A.K.; Brown, T.C. Time-varying flexible least squares for thermal desorption of gases. Int. J. Chem. Kinet. 2013, 45, 374–386, doi:10.1002/kin.20772.
[6]
Nieskens, D.L.S.; van Bavel, A.P.; Niemantsverdriet, J.W. The analysis of temperature programmed desorption experiments of systems with lateral interactions; implications of the compensation effect. Surface Sci. 2003, 546, 159–169, doi:10.1016/j.susc.2003.09.035.
[7]
Budrugeac, P.; Segal, E. Some methodological problems concerning nonisothermal kinetic analysis of heterogeneous solid-gas reactions. Int. J. Chem. Kinet. 2001, 33, 564–573, doi:10.1002/kin.1052.
[8]
Smit, B.; Maesen, T.L. Molecular simulations of zeolites: Adsorption, diffusion, and shape selectivity. Chem. Rev. 2008, 108, 4125–4184, doi:10.1021/cr8002642.
[9]
Zhdanov, V.P.; Kasemo, B. Surface restructuring, thermal desorption and kinetic bistability, and chemical waves. J. Stat. Phys. 1998, 90, 79–101, doi:10.1023/A:1023243432497.
[10]
Percival, D.B.; Walden, A.T. Wavelet Methods for Time Series Analysis; Cambridge University Press: New York, NY, USA, 2006.
[11]
Kulprathipanja, S. Zeolites in Industrial Separation and Catalysis; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2010.
[12]
Stefanadis, C.; Gates, B.C.; Haag, W.O. Rates of isobutane cracking catalyzed by HZSM-5: The carbonium ion route. J. Mol. Catal. 1991, 67, 363–367, doi:10.1016/0304-5102(91)80049-9.
[13]
Liu, D.; Bhan, A.; Tspatsis, M.; Al Hashimi, S. Catalytic behavior of Br？nsted acid sites in MWW and MFI zeolites with dual meso- and microporosity. ACS Catal. 2011, 1, 7–17.
[14]
Narbeshuber, T.F.; Brait, A.; Seshan, K.; Lercher, J.A. Dehydrogenation of light alkanes over zeolites. J. Catal. 1997, 172, 127–136, doi:10.1006/jcat.1997.1860.
[15]
Gounder, R.; Iglesia, E. Effects of partial confinement on the specificity of monomolecular alkane reactions for acid sites in side pockets of mordenite. Angew. Chem. Int. Ed. 2010, 49, 808–811, doi:10.1002/anie.200905869.
[16]
Honkela, M.L.; Krause, A.O.I. Kinetic modeling of the dimerization of isobutene. Ind. Eng. Chem. Res. 2004, 43, 3251–3260, doi:10.1021/ie030842h.
[17]
Honkela, M.L.; Krause, A.O.I. Influence of linear butenes in the dimerization of isobutene. Ind. Eng. Chem. Res. 2005, 44, 5291–5297, doi:10.1021/ie0491903.
[18]
Talwalkar, S.; Chauhan, M.; Aghalayam, P.; Qi, Z.; Sundmacher, K.; Mahajani, S. Kinetic studies on the dimerization of isobutene with ion-exchange resin in the presence of water as a selectivity enhancer. Ind. Eng. Chem. Res. 2006, 45, 1312–1323, doi:10.1021/ie050922g.
[19]
Talwalkar, S.; Chauhan, M.; Katariya, A.; Aghalayam, P.; Ivanova, M.; Sundmacher, K.; Mahajani, S. Selectivity engineering with reactive distillation for dimerization of C4 olefins: Experimental and theoretical studies. Ind. Eng. Chem. Res. 2007, 46, 3024–3034, doi:10.1021/ie060860+.
[20]
Hauge, K.; Bergene, E.; Chen, D.; Fredriksen, G.R.; Holmen, A. Oligomerization of isobutene over solid acid catalysts. Catal. Today 2005, 100, 463–466, doi:10.1016/j.cattod.2004.08.017.
[21]
Gounder, R.; Iglesia, E. Catalytic hydrogenation of alkenes on acidic zeolites: Mechanistic connections to monomolecular alkane dehydrogenation reactions. J. Catal. 2011, 277, 36–45, doi:10.1016/j.jcat.2010.10.013.
[22]
Milas, I.; Nascimento, M.A.C. The dehydrogenation and cracking reactions of isobutane over the ZSM-5 zeolite. Chem. Phys Lett. 2003, 373, 379–384, doi:10.1016/S0009-2614(03)00611-0.
[23]
Zheng, B.; Blowers, P. Reactivity of isobutane on zeolites: A first principles study. J. Phys. Chem. A 2006, 110, 2455–2460, doi:10.1021/jp056707v.
[24]
Mota, C.J.A.; Bhering, D.L.; Ramirez-Solis, A. Activation of alkanes on zeolites: A DFT study of hydride abstraction and dehrydrogenation on extra-framework aluminium species. Int. J. Quantum Chem. 2005, 105, 174–185, doi:10.1002/qua.20668.
[25]
Milas, I.; Silva, A.M.; Nascimento, A.C. A density functional study on the nature of the adsorption complex between isobutane and H-ZSM5 and its implication for the mechanism of activation of alkane molecules over H-ZSM5. Appl. Catal. A 2008, 336, 17–22, doi:10.1016/j.apcata.2007.08.034.
[26]
Weitkamp, J.; Hunger, M. Acid and base catalysis on zeolites. In Studies in Surface Science and Catalysis; ？ejka, J., van Bekkum, H., Corma, A., Schüth, F., Eds.; Elsevier: Amsterdam, The Netherlands, 2007; Volume 168, pp. 787–835.
Hufton, J.R.; Ruthven, D.M.; Danner, R.P. Adsorption and diffusion of hydrocarbons in silicalite at very low concentration: Effect of defect sites. Microporous Mater. 1995, 5, 39–52, doi:10.1016/0927-6513(95)00034-7.
[29]
Saravanan, C.; Auerbach, S.M. Modelling the concentration of diffusion in zeolites. 1. Analytical theory for benzene in Na-Y. Chin. J. Chem. Phys. 1997, 107, 8120–8131, doi:10.1063/1.475075.
[30]
Truitt, M.J.; Toporek, S.S.; Rovira-Truitt, R.; White, J.L. Alkane C–H bond activation in zeolites: Evidence for direct protium exchange. J. Am. Chem. Soc. 2006, 128, 1847–1852, doi:10.1021/ja0558802.
[31]
R Core Team. R: A Language and Environment for Statistical Computing; R Foundation for Statistical Computing: Vienna, Austria, 2012.
[32]
Nason, G. Wavethresh: Wavelet Statistics and Transforms. R package version 4.6.2. Available online: http://cran.r-project.org/web/packages/wavethresh/index.html (accessed on 2 April 2013).
[33]
Kalaba, R.; Tesfatsion, L. A Multicriteria approach to model specification and estimation. Comput. Stat. Data Anal. 1996, 21, 193–214, doi:10.1016/0167-9473(94)00030-1.
[34]
Montana, G.; Triantafyllopoulos, K.; Tsagaris, T. Flexible least squares for temporal data mining and statistical arbitrage. Expert Syst. Appl. 2009, 36, 2819–2830, doi:10.1016/j.eswa.2008.01.062.
