Monomolecular Cracking Rates of Light Alkanes over Zeolites Determined by IR Operando Spectroscopy

The coverage of H-MFI zeolite acid sites by light alkanes (C3–C7) at monomolecular cracking reaction conditions was determined using infrared operando spectroscopy. Under such conditions, alkane adsorption through H-bonding leads to a fully reversible perturbation of the zeolite νOH band at 3600 cm–1. This was used to assess the coverage at various temperatures and pressures, allowing for the determination of the adsorption thermodynamic parameters at reaction conditions. The simultaneous determination of apparent monomolecular cracking rate constants allowed for the direct determination of the intrinsic cracking rate constants, activation energies, and activation entropies. These results show that while the coverage of the active sites increases with the alkane size, the differences tend to decrease at high temperature because of entropic effects. The intrinsic activation energy was constant for all alkanes investigated in this study (∼190 kJ mol–1), lying in the lower range of the values usually derived...

[1]  T. Bučko,et al.  Monomolecular cracking of propane over acidic chabazite: An ab initio molecular dynamics and transition path sampling study , 2011 .

[2]  Arnaud Travert,et al.  Effective bulk and surface temperatures of the catalyst bed of FT-IR cells used for in situ and operando studies. , 2013, Physical chemistry chemical physics : PCCP.

[3]  Guy Marin,et al.  Adsorption of C2−C8 n-Alkanes in Zeolites† , 2011 .

[4]  A. Bell,et al.  Effects of Si/Al ratio on the distribution of framework Al and on the rates of alkane monomolecular cracking and dehydrogenation in H-MFI. , 2013, Journal of the American Chemical Society.

[5]  T. Degnan,et al.  Applications of zeolites in petroleum refining , 2000 .

[6]  E. Iglesia,et al.  The roles of entropy and enthalpy in stabilizing ion-pairs at transition states in zeolite acid catalysis. , 2012, Accounts of chemical research.

[7]  J. Bokhoven,et al.  Observation of a compensation relation for n-hexane adsorption in zeolites with different structures: implications for catalytic activity , 2005 .

[8]  R. Snurr,et al.  An explanation for the differences in catalytic hydrocarbon cracking activity between steam and chemically dealuminated Y zeolites , 2000 .

[9]  B. Smit,et al.  Combined Density Functional Theory and Monte Carlo Analysis of Monomolecular Cracking of Light Alkanes Over H-ZSM-5 , 2012 .

[10]  J. Lercher,et al.  Alkane sorption in molecular sieves: The contribution of ordering, intermolecular interactions, and sorption on Brønsted acid sites , 1997 .

[11]  W. Haag.  Catalysis by Zeolites – Science and Technology , 1994 .

[12]  J. Lercher,et al.  The influence of extraframework aluminum on H-FAU catalyzed cracking of light alkanes , 1996 .

[13]  B. Gil,et al.  In situ thermogravimetry in an infrared spectrometer: an answer to quantitative spectroscopy of adsorbed species on heterogeneous catalysts , 2004 .

[14]  A. Bhan,et al.  Entropy considerations in monomolecular cracking of alkanes on acidic zeolites , 2008 .

[15]  Li-Chiang Lin,et al.  Effects of Zeolite Structural Confinement on Adsorption Thermodynamics and Reaction Kinetics for Monomolecular Cracking and Dehydrogenation of n-Butane. , 2016, Journal of the American Chemical Society.

[16]  F. Maugé,et al.  IR study of hydrotreating catalysts in working conditions : Comparison of the acidity present on the sulfided phase and on the alumina support , 1999 .

[17]  Enrique Iglesia,et al.  Effects of partial confinement on the specificity of monomolecular alkane reactions for acid sites in side pockets of mordenite. , 2010, Angewandte Chemie.

[18]  M. Boudart,et al.  Experimental criterion for the absence of artifacts in the measurement of rates of heterogeneous catalytic reactions , 1982 .

[19]  M. Bettahar,et al.  Reaction mechanisms and kinetics in the n-hexane cracking over zeolites , 1997 .

[20]  Li-Chiang Lin,et al.  Adsorption Thermodynamics and Intrinsic Activation Parameters for Monomolecular Cracking of n-Alkanes on Brønsted Acid Sites in Zeolites , 2015 .

[21]  Z. Sobalík,et al.  Determination and properties of acid sites in H-ferrierite: A comparison of ferrierite and MFI structures , 1998 .

[22]  Enrique Iglesia,et al.  Catalytic consequences of spatial constraints and acid site location for monomolecular alkane activation on zeolites. , 2009, Journal of the American Chemical Society.

[23]  D. Tzoulaki,et al.  On the location, strength and accessibility of Brønsted acid sites in hierarchical ZSM-5 particles , 2012 .

[24]  Paul M. Zimmerman,et al.  Hexane Cracking on ZSM-5 and Faujasite Zeolites: a QM/MM/QCT Study , 2015 .

[25]  F. Ribeiro,et al.  Determination of the Au active site and surface active species via operando transmission FTIR and isotopic transient experiments on 2.3 wt.% Au/TiO2 for the WGS reaction , 2012 .

[26]  J. Lunsford,et al.  Intrinsic Catalytic Cracking Activity of Hexane over H−ZSM-5, H−β and H−Y Zeolites , 1999 .

[27]  Paul M Zimmerman,et al.  Ab initio simulations reveal that reaction dynamics strongly affect product selectivity for the cracking of alkanes over H-MFI. , 2012, Journal of the American Chemical Society.

[28]  B. Gates,et al.  Monomolecular and bimolecular mechanisms of paraffin cracking: n-Butane cracking catalyzed by HZSM-5 , 1992 .

[29]  Bin Xu,et al.  Catalytic activity of Brønsted acid sites in zeolites: Intrinsic activity, rate-limiting step, and influence of the local structure of the acid sites , 2006 .

[30]  A. Bhan,et al.  A link between reactivity and local structure in acid catalysis on zeolites. , 2008, Accounts of Chemical Research.

[31]  S. Khadzhiev,et al.  A kinetic model for the hexane cracking reaction over H-ZSM-5 , 1994 .

[32]  A. Corma,et al.  Can macroscopic parameters, such as conversion and selectivity, distinguish between different cracking mechanisms on acid catalysts? , 1997 .

[33]  Paul M. Zimmerman,et al.  Insights into the Kinetics of Cracking and Dehydrogenation Reactions of Light Alkanes in H-MFI , 2013 .

[34]  Arnaud Travert,et al.  Probing zeolites by vibrational spectroscopies. , 2015, Chemical Society reviews.

[35]  S. A. Hashimi,et al.  Catalytic Behavior of Brønsted Acid Sites in MWW and MFI Zeolites with Dual Meso- and Microporosity , 2011 .

[36]  R. Snurr,et al.  Monomolecular cracking of n-hexane on Y, MOR, and ZSM-5 zeolites , 1999 .

[37]  J. Bokhoven,et al.  Observation of a compensation relation for monomolecular alkane cracking by zeolites: the dominant role of reactant sorption , 2004 .

[38]  A. Savara.  Standard States for Adsorption on Solid Surfaces: 2D Gases, Surface Liquids, and Langmuir Adsorbates , 2013 .

[39]  Berend Smit,et al.  Theoretical Simulation of n-Alkane Cracking on Zeolites , 2010 .

[40]  W. Vermeiren,et al.  Impact of Zeolites on the Petroleum and Petrochemical Industry , 2009 .

[41]  G. Seo,et al.  Catalytic cracking of n-octane over alkali-treated MFI zeolites , 2005 .

[42]  R. Lobo,et al.  High‐Temperature Produced Catalytic Sites Selective for n‐Alkane Dehydrogenation in Acid Zeolites: The Case of HZSM‐5 , 2011 .

[43]  R. A. Santen,et al.  Carbonium ion formation in zeolite catalysis , 1994 .

[44]  J. Lercher,et al.  Monomolecular conversion of light alkanes over H-ZSM-5 , 1995 .

[45]  M. Stockenhuber,et al.  Bronsted acid and pore controlled siting of alkanes sorption in acidic molecular sieves , 1997 .

[46]  J. Bokhoven,et al.  An Explanation for the Enhanced Activity for Light Alkane Conversion in Mildly Steam Dealuminated Mordenite: The Dominant Role of Adsorption , 2001 .

[47]  F. Guerzoni,et al.  Roles of Brønsted and Lewis sites during cracking of n-octane on H-mordenite , 1992 .

[48]  P. Sautet,et al.  Effect of Temperature on the Adsorption of Short Alkanes in the Zeolite SSZ-13—Adapting Adsorption Isotherms to Microporous Materials , 2014 .