215
[39]. It can be concluded that the key to the butene selectivity depended on the
relative stability of radical intermediates over metal surfaces. This could explain
why Pt surfaces always show poor selectivity for the formation of butene rather than
it always exhibited high selectivity towards butanes.
2.4 Influence of the Support on Hydrogenation
of 1,3-Butadiene
The different metal surfaces clearly showed various mechanisms and selectivities;
further, the presence of support can influence the reaction pathway and selectivity
towards butenes. There have been a number of studies carried out at investigating
the support effects [56–61]. Primet et al. [60] investigated various supported
platinum catalysts with low metal loading (<1 wt%) for the hydrogenation of
1,3-butadiene. It was found that the acidic sites presented on the support can cause
an electron shift through the interface between meta-support interfaces.
Consequently, the bond strength between unsaturated hydrocarbons and the metal
active sites can be altered, thus changing the selectivity and reaction rate. In addition,
the catalyst deactivation can also be affected by the other properties such as acidity
of the support and the pore diffusion. Recent work by Pattamakomsan et al. [62]
also revealed that the Pd/Al 2 O 3 catalytic performance was improved when the mixed
Al 2 O 3 structure support consists of 80% θ- and 20% α-Al 2 O 3 rather than pure Al 2 O 3 .
The relatively high acidity and BET surface area of Al 2 O 3 yielded higher dispersion
of Pd and significantly enhanced rate of hydrogenation. Moreover, the bimodal pore
distribution of the mixed-phase θ/α Al 2 O 3 promoted butene desorption products to
obtain a much lower formation of butane when compared to the pure θ-Al 2 O 3 that
had only small pores. It can be concluded that Al 2 O 3 support with different phase
compositions effected the selectivity towards 2-butene. Moreover, Hou et al. [63]
investigated the influence of various supports such as Al 2 O 3 , SiO 2 , CeO 2 , ZrO 2 , and
TiO 2 on Pd-Ni surfaces for the selectivity butadiene hydrogenation towards different
products. As discussed in Fig. 5, each support favoured different selectivity for the
butenes. Among the expected products (1-butene, cis-2-butene, and trans-2-butene),
alumina support showed highest selectivity towards 1-butene. The following is the
order of selectivity towards 1-butene: Al 2 O 3 > SiO 2 > CeO 2 ∼ ZrO 2 > TiO 2 . It can be
concluded that the strong metal-support interaction between Pd-Ni and alumina
played a key role on 1-butene selectivity over other supports. Furthermore, Cukic
et al. [56] used high-throughput experimentation for Pd/Al 2 O 3 catalyst with different
variables such as stirring rate, calcination temperature, the solution pH, and the time
taken for impregnation, and heating rate. It was found that these parameters
influenced the conversion of 1,3-butadiene significantly. For example, during the
impregnation process, the use of excess solution caused a decrease in activity when
compared to the incipient wetness impregnation. On the other hand, the ramping
rate for drying, and the holding time for (both drying and calcination) did not show
Selective Hydrogenation of 1,3-Butadiene to 1-Butene: Review on Catalysts, Selectivity…
[39]. It can be concluded that the key to the butene selectivity depended on the
relative stability of radical intermediates over metal surfaces. This could explain
why Pt surfaces always show poor selectivity for the formation of butene rather than
it always exhibited high selectivity towards butanes.
2.4 Influence of the Support on Hydrogenation
of 1,3-Butadiene
The different metal surfaces clearly showed various mechanisms and selectivities;
further, the presence of support can influence the reaction pathway and selectivity
towards butenes. There have been a number of studies carried out at investigating
the support effects [56–61]. Primet et al. [60] investigated various supported
platinum catalysts with low metal loading (<1 wt%) for the hydrogenation of
1,3-butadiene. It was found that the acidic sites presented on the support can cause
an electron shift through the interface between meta-support interfaces.
Consequently, the bond strength between unsaturated hydrocarbons and the metal
active sites can be altered, thus changing the selectivity and reaction rate. In addition,
the catalyst deactivation can also be affected by the other properties such as acidity
of the support and the pore diffusion. Recent work by Pattamakomsan et al. [62]
also revealed that the Pd/Al 2 O 3 catalytic performance was improved when the mixed
Al 2 O 3 structure support consists of 80% θ- and 20% α-Al 2 O 3 rather than pure Al 2 O 3 .
The relatively high acidity and BET surface area of Al 2 O 3 yielded higher dispersion
of Pd and significantly enhanced rate of hydrogenation. Moreover, the bimodal pore
distribution of the mixed-phase θ/α Al 2 O 3 promoted butene desorption products to
obtain a much lower formation of butane when compared to the pure θ-Al 2 O 3 that
had only small pores. It can be concluded that Al 2 O 3 support with different phase
compositions effected the selectivity towards 2-butene. Moreover, Hou et al. [63]
investigated the influence of various supports such as Al 2 O 3 , SiO 2 , CeO 2 , ZrO 2 , and
TiO 2 on Pd-Ni surfaces for the selectivity butadiene hydrogenation towards different
products. As discussed in Fig. 5, each support favoured different selectivity for the
butenes. Among the expected products (1-butene, cis-2-butene, and trans-2-butene),
alumina support showed highest selectivity towards 1-butene. The following is the
order of selectivity towards 1-butene: Al 2 O 3 > SiO 2 > CeO 2 ∼ ZrO 2 > TiO 2 . It can be
concluded that the strong metal-support interaction between Pd-Ni and alumina
played a key role on 1-butene selectivity over other supports. Furthermore, Cukic
et al. [56] used high-throughput experimentation for Pd/Al 2 O 3 catalyst with different
variables such as stirring rate, calcination temperature, the solution pH, and the time
taken for impregnation, and heating rate. It was found that these parameters
influenced the conversion of 1,3-butadiene significantly. For example, during the
impregnation process, the use of excess solution caused a decrease in activity when
compared to the incipient wetness impregnation. On the other hand, the ramping
rate for drying, and the holding time for (both drying and calcination) did not show
Selective Hydrogenation of 1,3-Butadiene to 1-Butene: Review on Catalysts, Selectivity…