223
[58,100–102]. It can be concluded that the bimetallic catalysts showed highest
selectivity when compared to monometallic catalyst; however, Pd-Au and Pd-Ag
supported on SiO 2 showed less selectivity when compared to Al 2 O 3 support.
To summarize, for the selective hydrogenation reaction on metal surfaces, the
selectivity towards 1-butene is tremendously dependent on the electronegativitysupported metal catalyst system, and hence, can be regulated either by modulating
the properties of supported metal (by another metal/or promoter species?). Moreover,
carbonaceous deposits formed on the surface of a catalyst during the reaction/
process under prevailing reaction/operation conditions (ratio of reactants,
temperature, etc.) alter the catalyst surface characteristics, e.g. dispersion of
metal(s), Promoters further modify the surface and disturb the electronic properties
of Pd or metals. Additives affect the adsorption of reactants and formation of surface
residues, as well. This knowledge facilitates one to have a better expertise of the
overall process to improve the selectivity, by appropriately selected combination of
catalysts, additives/promoters and fine tuning the reaction conditions.
3 Summary and Future Outlook
The major findings from the detailed literature review on 1,3-butadiene selective
hydrogenation with heterogeneous catalysts are: (a) selectivity in this reaction relies
upon the different adsorption strengths of the unsaturated reactants and products.
Butadiene tends to be preferentially adsorbed on all active sites blocking the access
of n-butenes, when it was present in excess. 1-Butene hydrogenation to butane and
its isomerization to cis-butene was found to occur only, when butadiene concentration
becomes low during the course of the reaction; (b) the acidity of the support plays a
critical role in mediating electron transfer through the metal-support interface, that
ultimately changes the bond strength between unsaturated hydrocarbons and the
metal active sites which results in changing the selectivity and reaction rate; (c)
changing the dispersion and the metal particle size may affect both activity and
selectivity. Their role in tuning the activity and selectivity are attributed to their
geometric and electronic effects; (d) hydrogenation of butadiene over metal
catalysts, the selectivity for 1-butene formation is governed by the electronegativity
of the catalyst. Hence, selectivity may be affected either by changing the supported
metal and/or by the additive species; (e) the use of bimetallic catalysts has been
proved that it is right approach for improved selectivity as well as minimizing the
undesirable side-reactions of full isomerization and hydrogenation of the desired
alkene. These observations foster the interest to develop bimetallic nanoparticles
with well-defined geometric shapes and dimensions and are still continuing with the
desire to regulate their performance for selective hydrogenation of 1,3-butadiene.
The role of second metal in bimetallic catalysts, various additives and acidity of the
supports in controlling the selectivity needs to be studied to gain further insight into
the underlying mechanism.
Selective Hydrogenation of 1,3-Butadiene to 1-Butene: Review on Catalysts, Selectivity…
[58,100–102]. It can be concluded that the bimetallic catalysts showed highest
selectivity when compared to monometallic catalyst; however, Pd-Au and Pd-Ag
supported on SiO 2 showed less selectivity when compared to Al 2 O 3 support.
To summarize, for the selective hydrogenation reaction on metal surfaces, the
selectivity towards 1-butene is tremendously dependent on the electronegativitysupported metal catalyst system, and hence, can be regulated either by modulating
the properties of supported metal (by another metal/or promoter species?). Moreover,
carbonaceous deposits formed on the surface of a catalyst during the reaction/
process under prevailing reaction/operation conditions (ratio of reactants,
temperature, etc.) alter the catalyst surface characteristics, e.g. dispersion of
metal(s), Promoters further modify the surface and disturb the electronic properties
of Pd or metals. Additives affect the adsorption of reactants and formation of surface
residues, as well. This knowledge facilitates one to have a better expertise of the
overall process to improve the selectivity, by appropriately selected combination of
catalysts, additives/promoters and fine tuning the reaction conditions.
3 Summary and Future Outlook
The major findings from the detailed literature review on 1,3-butadiene selective
hydrogenation with heterogeneous catalysts are: (a) selectivity in this reaction relies
upon the different adsorption strengths of the unsaturated reactants and products.
Butadiene tends to be preferentially adsorbed on all active sites blocking the access
of n-butenes, when it was present in excess. 1-Butene hydrogenation to butane and
its isomerization to cis-butene was found to occur only, when butadiene concentration
becomes low during the course of the reaction; (b) the acidity of the support plays a
critical role in mediating electron transfer through the metal-support interface, that
ultimately changes the bond strength between unsaturated hydrocarbons and the
metal active sites which results in changing the selectivity and reaction rate; (c)
changing the dispersion and the metal particle size may affect both activity and
selectivity. Their role in tuning the activity and selectivity are attributed to their
geometric and electronic effects; (d) hydrogenation of butadiene over metal
catalysts, the selectivity for 1-butene formation is governed by the electronegativity
of the catalyst. Hence, selectivity may be affected either by changing the supported
metal and/or by the additive species; (e) the use of bimetallic catalysts has been
proved that it is right approach for improved selectivity as well as minimizing the
undesirable side-reactions of full isomerization and hydrogenation of the desired
alkene. These observations foster the interest to develop bimetallic nanoparticles
with well-defined geometric shapes and dimensions and are still continuing with the
desire to regulate their performance for selective hydrogenation of 1,3-butadiene.
The role of second metal in bimetallic catalysts, various additives and acidity of the
supports in controlling the selectivity needs to be studied to gain further insight into
the underlying mechanism.
Selective Hydrogenation of 1,3-Butadiene to 1-Butene: Review on Catalysts, Selectivity…