Effects of Chain Length on the Mechanism and Rates of Metal-Catalyzed Hydrogenolysis of n-Alkanes

被引:61
作者
Hibbitts, David D. [1 ,3 ]
Flaherty, David W. [1 ,2 ]
Iglesia, Enrique [1 ]
机构
[1] Univ Calif Berkeley, Dept Chem Engn, Berkeley, CA 94720 USA
[2] Univ Illinois, Dept Chem & Biomol Engn, Urbana, IL 61801 USA
[3] Univ Florida, Dept Chem Engn, Gainesville, FL 32611 USA
关键词
GENERALIZED GRADIENT APPROXIMATION; INITIO MOLECULAR-DYNAMICS; TOTAL-ENERGY CALCULATIONS; RING-OPENING REACTIONS; C-C BONDS; ETHANE HYDROGENOLYSIS; THERMAL-DECOMPOSITION; SURFACES; ISOMERIZATION; PLATINUM;
D O I
10.1021/acs.jpcc.6b00323
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
C-C cleavage in C-2-C-10 n-alkanes involves quasi equilibrated C-H activation steps to form dehydrogenated intermediates on surfaces saturated with H atoms. These reactions are inhibited by H-2 to similar extents for C-C bonds of similar substitution in all acyclic and cyclic alkanes and, thus, show similar kinetic dependences on H-2 pressure. Yet, turnover rates depend sensitively on chain length because of differences in activation enthalpies (Delta H double dagger) and entropies (Delta S double dagger) whose mechanistic origins remain unclear. Density functional theory (DFT) estimates of Delta H double dagger and Delta G double dagger for C-C cleavage via >150 plausible elementary steps for propane and n-butane reactants on Ir show that hydrogenolysis occurs via alpha,beta-bound RC*-C*R'double dagger transition states (R = H, CxH2x+1) in which two H atoms are removed from each C*. Calculated Delta H double dagger values decrease with increasing alkane chain length (C-2-C-8), consistent with experiment, because attractive van der Waals interactions with surfaces preferentially stabilize larger transition states. A concomitant increase in Delta S double dagger, evident from experiments, is not captured by periodic DFT methods, which treat low-frequency vibrational modes inaccurately, but statistical mechanics treatments describe such effects well for RC*-C*R double dagger species, as previously reported. These findings, together with parallel studies of the cleavage of more substituted C-C bonds in branched and cyclic alkanes, account for the reasons that chain length and substitution influence Delta H double dagger and Delta S double dagger values and the dependence of rates on H-2 pressure and consequently explain differences in hydrogenolysis reactivities and selectivities across all alkanes.
引用
收藏
页码:8125 / 8138
页数:14
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共 70 条
[21]  
GAULT FG, 1957, CR HEBD ACAD SCI, V245, P1620
[22]   MECHANISMS OF SKELETAL ISOMERIZATION OF HYDROCARBONS ON METALS [J].
GAULT, FG .
ADVANCES IN CATALYSIS, 1981, 30 :1-95
[23]   Effect of the Damping Function in Dispersion Corrected Density Functional Theory [J].
Grimme, Stefan ;
Ehrlich, Stephan ;
Goerigk, Lars .
JOURNAL OF COMPUTATIONAL CHEMISTRY, 2011, 32 (07) :1456-1465
[24]   A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu [J].
Grimme, Stefan ;
Antony, Jens ;
Ehrlich, Stephan ;
Krieg, Helge .
JOURNAL OF CHEMICAL PHYSICS, 2010, 132 (15)
[25]   CARBON-CARBON BOND-CLEAVAGE REACTIONS IN DECOMPOSITION OF METALLACYCLES [J].
GRUBBS, RH ;
MIYASHITA, A .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1978, 100 (23) :7418-7420
[26]   Improved adsorption energetics within density-functional theory using revised Perdew-Burke-Ernzerhof functionals [J].
Hammer, B ;
Hansen, LB ;
Norskov, JK .
PHYSICAL REVIEW B, 1999, 59 (11) :7413-7421
[27]   A climbing image nudged elastic band method for finding saddle points and minimum energy paths [J].
Henkelman, G ;
Uberuaga, BP ;
Jónsson, H .
JOURNAL OF CHEMICAL PHYSICS, 2000, 113 (22) :9901-9904
[28]   A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives [J].
Henkelman, G ;
Jónsson, H .
JOURNAL OF CHEMICAL PHYSICS, 1999, 111 (15) :7010-7022
[29]   Role of Branching on the Rate and Mechanism of C-C Cleavage in Alkanes on Metal Surfaces [J].
Hibbitts, David D. ;
Flaherty, David W. ;
Iglesia, Enrique .
ACS CATALYSIS, 2016, 6 (01) :469-482
[30]   SELECTIVITY CONTROL AND CATALYST DESIGN IN THE FISCHER-TROPSCH SYNTHESIS - SITES, PELLETS, AND REACTORS [J].
IGLESIA, E ;
REYES, SC ;
MADON, RJ ;
SOLED, SL .
ADVANCES IN CATALYSIS, VOL 39, 1993, 39 :221-302