209
these parameters is discussed in detail; however, it should be noted that all these
factors affect the reaction synergistically to control the activity and selectivity.
Detailed analysis from the reported literature presented in this chapter is organized
as follows.
2.1 Kinetic Study and Reaction Pathway
The selectivity of this hydrogenation reaction is an important parameter, therefore
studying the reaction kinetics of this reaction on various catalysts and establishes a
probable mechanism that can provide the bridge between the experimental results
and theoretical prediction. In this specific heterogeneous catalytic hydrogenation
process, reactants and protects are geometrical isomers, therefore the reaction
kinetics also provide an insight into stereo/regio-selectivity. The adsorption kinetics
of these isomers on the active sites of the catalysts was found to vary with isomer to
isomer, therefore studying the kinetics can provide the information about stereo/
regio-selectivity on each catalyst. Over many years, the stereochemistry of different
heterogeneous catalysts in selective hydrogenation reactions has been a substantially
interesting subject [1, 7–17]. The kinetic investigations reported in the open
literature are usually carried out in the gas phase or liquid phase (usually under
industrial processing conditions: atmospheric pressures and low temperatures). The
alkenes hydrogenation over the heterogeneous catalysts has been investigated for
almost 80 years. In 1934, Horiuti and Polanyi [16] explained the hydrogenation of
1,3-butadiene reaction mechanism, in which 1,2 and 1,4-addition of two conjugated
C=C double bonds produced 1-butene and 2-butene, respectively. In addition, due
to the existence of cis or trans isomers of 1,3-butadiene, the hydrogenation reaction
can produce either cis- or trans-2-butene. Further hydrogenation of the cis or trans
isomer products obviously produces butane [18, 19]. Well et al. investigated initially
the 1,3-butadiene hydrogenation reaction over different metals (Ru, Ir, Fe, Pt, Co,
Rh, Pd, Cu, Os, and Ni) supported by alumina (Al 2 O 3 ) [18, 20–22]. It was proposed
that the reaction mechanism exhibit two types of selective behaviours namely 1,2
and 1,4 addition over alumina-supported metal catalysts (Scheme 1).
As shown, the formation of 1-butene was mainly responsible for 1,2 hydrogenation pathway. Interestingly, 2-butene formation occurred on Pd through a 1,4-addition pathway. Moreover, the relative yields of cis- and trans-2-butene were
dependent on the conformational characteristics of adsorbed precursors. On the
other hand, Boitiaux et al. reported that 1-butene was formed through syn or antiadsorbed 1,3-butadiene on Pd, Pt and Rh metals, in which trans-butene and cisbutene were formed through anti- and cis-configurations [8–10]. Among active
metals, the behaviour of Pt and Rh for the purpose of 1,3-budadiene hydrogenation
was found to be quite similar, and each of them nearly resembles to that of Pd, the
only difference being in the initial butane formation. 1-Butene can undergo several
other consecutive or parallel transformations to generate cis-2-butene, trans-2-butene and butane. Butane formation occurs through a semi-hydrogenated species,
Selective Hydrogenation of 1,3-Butadiene to 1-Butene: Review on Catalysts, Selectivity…
these parameters is discussed in detail; however, it should be noted that all these
factors affect the reaction synergistically to control the activity and selectivity.
Detailed analysis from the reported literature presented in this chapter is organized
as follows.
2.1 Kinetic Study and Reaction Pathway
The selectivity of this hydrogenation reaction is an important parameter, therefore
studying the reaction kinetics of this reaction on various catalysts and establishes a
probable mechanism that can provide the bridge between the experimental results
and theoretical prediction. In this specific heterogeneous catalytic hydrogenation
process, reactants and protects are geometrical isomers, therefore the reaction
kinetics also provide an insight into stereo/regio-selectivity. The adsorption kinetics
of these isomers on the active sites of the catalysts was found to vary with isomer to
isomer, therefore studying the kinetics can provide the information about stereo/
regio-selectivity on each catalyst. Over many years, the stereochemistry of different
heterogeneous catalysts in selective hydrogenation reactions has been a substantially
interesting subject [1, 7–17]. The kinetic investigations reported in the open
literature are usually carried out in the gas phase or liquid phase (usually under
industrial processing conditions: atmospheric pressures and low temperatures). The
alkenes hydrogenation over the heterogeneous catalysts has been investigated for
almost 80 years. In 1934, Horiuti and Polanyi [16] explained the hydrogenation of
1,3-butadiene reaction mechanism, in which 1,2 and 1,4-addition of two conjugated
C=C double bonds produced 1-butene and 2-butene, respectively. In addition, due
to the existence of cis or trans isomers of 1,3-butadiene, the hydrogenation reaction
can produce either cis- or trans-2-butene. Further hydrogenation of the cis or trans
isomer products obviously produces butane [18, 19]. Well et al. investigated initially
the 1,3-butadiene hydrogenation reaction over different metals (Ru, Ir, Fe, Pt, Co,
Rh, Pd, Cu, Os, and Ni) supported by alumina (Al 2 O 3 ) [18, 20–22]. It was proposed
that the reaction mechanism exhibit two types of selective behaviours namely 1,2
and 1,4 addition over alumina-supported metal catalysts (Scheme 1).
As shown, the formation of 1-butene was mainly responsible for 1,2 hydrogenation pathway. Interestingly, 2-butene formation occurred on Pd through a 1,4-addition pathway. Moreover, the relative yields of cis- and trans-2-butene were
dependent on the conformational characteristics of adsorbed precursors. On the
other hand, Boitiaux et al. reported that 1-butene was formed through syn or antiadsorbed 1,3-butadiene on Pd, Pt and Rh metals, in which trans-butene and cisbutene were formed through anti- and cis-configurations [8–10]. Among active
metals, the behaviour of Pt and Rh for the purpose of 1,3-budadiene hydrogenation
was found to be quite similar, and each of them nearly resembles to that of Pd, the
only difference being in the initial butane formation. 1-Butene can undergo several
other consecutive or parallel transformations to generate cis-2-butene, trans-2-butene and butane. Butane formation occurs through a semi-hydrogenated species,
Selective Hydrogenation of 1,3-Butadiene to 1-Butene: Review on Catalysts, Selectivity…