Semi-Hydrogenation Of 2-Methyl-3-Butyn-2-Ol On PdCu Alloy Catalysts With Ultralow Pd Loading

Vitamin E,an antioxidant with good physiological activity and pharmacological value,has been widely used in modern clinical medicine.The production and application of vitamin E have aroused widespread concern in the field of both academy and industry.In the chemical industry,the semi-hydrogenation reaction of relevant alkynols such as 2-methyl-3-butyn-2-ol（MBY）is a key step in the synthesis of vitamin E,but some reactions such as over-hydrogenation（to 2-methyl-2-butanol（MBA））and/or oligomerization of C=C bonds usually occur simultaneously under the reaction conditions.The state-of-the-art catalysts generally contain poisonous additives such as quinoline and heavy metal lead,leading to environmental concern and decrease of product quality.Therefore,the development of high-performance catalysts for the semi-hydrogenation of alkynols has important scientific and industrial significances.Aiming at this research goal,the major findings of this dissertation are as following.In chapter 3,we first introduced the second metal（mainly Group IB metals:Cu,Ag,Au）to prepare Pd/ⅠB group metal alloy catalysts.Under the identical reaction conditions,the selective hydrogenation performance of alkynols over these Pd-IB alloy catalysts was compared.The results suggested that group IB metals affected the semi-hydrogenation activity of Pd particles in different ways.Au did not significantly poison the Pd active sites,and over-hydrogenation reaction tends to occur on this catalyst.Ag showed significant poisoning effect on Pd particles and Pd Ag was almost inert in MBY hydrogenation.The introduction of metal Cu selectively poisoned the active sites towards over-hydrogenation,thus effectively enhancing the selectivity of the catalytic hydrogenation reaction.Among several copper salts investigated,copper nitrate seemed to be an ideal Cu precursor.In chapter 4,then the influence of the preparation methods of Pd Cu catalysts on the structure and performance of the active center of the catalysts was systematically studied.Combined with a series of characterization techniques,the influence of the p H value of Pd deposition,the composition of the catalysts,the interaction between the metal and the support on the performance of MBY semi-hydrogenation was investigated in detail.The author changed the p H value of the Pd-deposited H₂Pd Cl₄solution,deposited trace amount of Pd（500 ppm）on the 0.5Cu O/Si O₂ support,prepared two low-cost 0.05Pd-0.5Cu O/Si O₂ catalysts via deposition-reduction method,and systematically investigated the catalytic performance of the MBY selectivity hydrogenation under mild conditions.The obtained catalysts were characterized by several techniques including XRD,TEM,H₂-TPR,etc.The results showed that the p H value of H₂Pd Cl₄ solution can significantly change the structure of Pd Cu catalysts.In the case of p H value of 5,the Cu O was partially dissolved in acidic Pd²⁺solution,and then co-reduced with Pd²⁺by Na BH₄,forming Pd Cu alloy structure in sub-nanometer;In contrast,no Pd Cu alloy strucutre was observed when p H value was7.Finally,the kinetics of the MBY semi-hydrogenation reaction over both catalysts were compared,and we found that the presence of Cu/Cu O species changed the adsorption strength of MBY on the catalyst surface,leading to its low activity in hydrogenation of C=C bond in 2-methyl-3-buten-2-ol（MBE）.Therefore,the semi-hydrogenation selectivity of 0.05Pd-0.5Cu O/Si O₂-5 catalyst is the best among all the catalysts.