CYCLIZATION OF ACETYLENE OVER PD(111) - A THEORETICAL-STUDY OF REACTION-MECHANISMS AND SURFACE INTERMEDIATES

被引:79
作者
PACCHIONI, G
LAMBERT, RM
机构
[1] UNIV MILAN, DIPARTIMENTO CHIM INORGAN MET ORGAN & ANALIT, VIA VENEZIAN 21, I-20133 MILAN, ITALY
[2] UNIV CAMBRIDGE, DEPT CHEM, CAMBRIDGE CB2 1EW, ENGLAND
关键词
D O I
10.1016/0039-6028(94)90766-8
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
We have investigated the elementary steps of the cyclization reaction of acetylene to benzene on Pd(111) by means of ab initio cluster model wave functions. The geometry of reactants, intermediates and final products has been fully optimized by total energy calculations. A vibrational analysis of some of the adsorbed species has been performed. We have identified the structure of a stable surface intermediate, C4H4, which results from the combination of two acetylene molecules. This surface species, which has already been characterized by several surface techniques, is reminiscent of metallopentacycles in organometallic chemistry; in C4H4 the two C atoms directly bonded to the surface are sp3 hybridized, while the other two C atoms assume an sp2-like coordination; the C4H4 is tilted by congruent-to 40 degrees from the surface normal. By the addition of one acetylene molecule to C4H4 one obtains benzene; once formed, C6H6 easily desorbs from the surface. An alternative route for benzene formation has also been considered. It implies the reaction of two C4H, units to form C8H8, cyclo-octatetraene, which easily splits off to give benzene plus an acetylene molecule. On the basis of the present calculations, however, the two routes appear to be associated to a similar thermodynamic stabilization.
引用
收藏
页码:208 / 222
页数:15
相关论文
共 38 条
[1]  
BADDELEY CJ, IN PRESS
[2]   CALCULATION OF SMALL MOLECULAR INTERACTIONS BY DIFFERENCES OF SEPARATE TOTAL ENERGIES - SOME PROCEDURES WITH REDUCED ERRORS [J].
BOYS, SF ;
BERNARDI, F .
MOLECULAR PHYSICS, 1970, 19 (04) :553-&
[3]   STRUCTURE OF CHEMISORBED ACETYLENE AND ETHYLENE ON NI, PD AND PT SURFACES [J].
DEMUTH, JE .
SURFACE SCIENCE, 1979, 84 (02) :315-328
[4]  
DUPUIS M, 1991, MOTECC MODERN TECHNI
[5]   THERMAL EVOLUTION OF ACETYLENE AND ETHYLENE ON PD(111) [J].
GATES, JA ;
KESMODEL, LL .
SURFACE SCIENCE, 1983, 124 (01) :68-86
[6]   HARTREE-FOCK-SLATER-LCAO STUDIES OF THE ACETYLENE-TRANSITION METAL INTERACTION .1. CHEMISORPTION ON NI SURFACES - CLUSTER-MODELS [J].
GEURTS, P ;
VANDERAVOIRD, A .
SURFACE SCIENCE, 1981, 102 (01) :185-206
[7]   HARTREE-FOCK-SLATER-LCAO STUDIES OF THE ACETYLENE-TRANSITION METAL INTERACTION .2. CHEMISORPTION ON FE AND CU - CLUSTER-MODELS [J].
GEURTS, P ;
VANDERAVOIRD, A .
SURFACE SCIENCE, 1981, 103 (2-3) :416-430
[8]  
HAY PJ, 1985, J CHEM PHYS, V82, P270, DOI 10.1063/1.448799
[9]   SIZE DEPENDENCE OF SURFACE CLUSTER-MODELS - CO ADSORBED ON CU(100) [J].
HERMANN, K ;
BAGUS, PS ;
NELIN, CJ .
PHYSICAL REVIEW B, 1987, 35 (18) :9467-9473
[10]  
Herzberg G., 1950, SPECTRA DIATOMIC MOL