Controllable Preparationon Of Pd-based Catalyst And It’s Application On Semi-hydrogenation Of Alkynols For Synthesis Of Vitamin E

Vitamin E is a significant nutrients that human body requires but cannot synthesize in sufficient amounts,which plays a significant role in tuning physiological function of human beings.And Vitamin E has become one of the three pillar product of Vitamin series.Currently,industrial synthesis of Vitamin E is mostly conducted by condensation between iso-phytanol and 2,3,5-trimethylhydroquinone(TMBQ).In this route,the synthesis of iso-phytanol is an vital link for producing Vitamin E.Furtherly,the semi-hydrogenation of relevant alkynols plays extremely important parts in the synthesis of iso-phytanol.Therefore,the study and development of high performance catalysts for the semi-hydrogenation of alkynols is of great value for the efficient synthesis of Vitamin E.Pd catalysts are commonly used for alkynols semi-hydrogenation.However,monometallic Pd catalysts usually suffer limited selectivity especially at high conversions.In industry,Lindlar catalysts are commomly utilized in the semi-hydrogenation of alkynols,which employ some poisonous agents such as Pd and quinoline to improve the selectivity to alkenol.Nevertheless,the addition of Pb leads to serious heavy metal pollution which does great harm to the environment,what’s more,Lindlar catalyst would go through deactivation even after the first run in aqueous media.So it is imperative to develop one or several lead-free Pd-based catalysts for selective hydrogenation of alkynol.Based on the above research background and research status,two lead-free Pd catalysts were synthesized for the semi-hydrogenation of alkynol.For the first catalyst,the reductive metal oxide In2O3 is the carrier to support Pd nanoparticles.In reduction gas atmosphere,the hydrogen spillover of Pd makes the carriers which near Pd particles gradually migrate to the surface of the particles to form a coating.By precisely tuning the reduction temperature,the edges and corner sites of Pd particles could be preferentially poisoned without destroying the plane sites.And we could manipulate such a process that edges and corner sites are poisoned selectively by choosing a suitable reduction temperature(It is now widely believed that the plane sites are the main active sites for the transformation of alkynol to alkenol in semi-hydrogenation reaction,and the corner and edge sites are responsible for over-hydrogenation).So our catalyst has high activity and selectivity.Without adding toxic additives such as heavy metal Pb or organic ligand quinoline,the final yield of alkenol could reach above 95%(TOF=1062 h-1).Generally,the selectivity of Pd catalysts are improved by adding the second metal to form alloy with Pd.However,this method of alloying is non-selective,which would lead to dramatically reduce the catalytic activity for semi-hydrogenation due to the loss of surface active sites.The shortcomings of alloying could be made up by our methods.Besides,within at least ten runs the catalyst exhibited excellent stability.When expanding the substrates to other alkynols,this catalyst still displayed satisfactory performance as well.For quantitative analysis of the poisoning degree,a series of bimetallic catalysts with different In/Pd have been prepared,and successfully applied to the semi-hydrogenation reaction of alkynol.By comparing the performance of this series of catalysts,the optimal In/Pd was obtained which equals to 0.3.In contrast to the performance of monometallic catalysts Pd/Al2O3(TOF=2844 h’1),the selectivity of optimal catalysts Pd-In0.3/Al2O3 could be enheanced from 88.8%to 95.3%with a little activity loss(TOF=2398 h-1).Besides,the optimal proportion of Pd and In could also apply to other industrial carriers which commonly used in industry such as SiO2,CeO2 and TiO2.When expanding the substrates to other alkynols,this catalyst still displayed satisfactory performance as well.To sum up,through the edge and corner poisoned selectivity,the first catalyst with high activity and selectivity was obtained withou adding the Pd or quinoline,which successfully applied to the semi-hydrogenation reaction of alkynol.Then,we carried out quantitative analysis about the promoter effect of In by tuning the amount of In with the metal oxide as the carriers commonly used in industry.The preparation of catalysts is all consistent with the idea of sustainable development.Those catalysts open up new designs for high efficient synthesis of intermediates for Vitamin E.