Regulation Of Surface Acidity And Catalytic Performance Of Ni/SiO₂-Al₂O₃ Catalyst For Hydrogenation Of 1,4-butynediol

1,4-butanediol（BDO）is an important chemical raw materials which are widely used in engineering plastics,textile,medicine,cosmetics and other fields.Currently,1,4-butynediol hydrogenation is the most used synthetic line for synthesizing BDO.Hydrogenation of unsaturated by-products,such as 1,4-butenediol andγ-hydroxybutylraldehyde,is the key step to control the yield and quality of product.On one hand,structure and state of active component Ni have great impact on hydrogenation performance of Ni/Al₂O₃ catalysts.Previously,we had prepared high performance catalysts for 1,4-butynediol hydrogenation.On the other hand,in view of easy hydration of Al₂O₃ supports,we had introduced SiO₂ into Al₂O₃ via impregnation method to improve the hydrothermal stability of catalyst and prolong lifetime of catalyst.Due to its simple preparation method,varied surface acidity and other advantages,SiO₂ doped Al₂O₃ are widely used as supports and catalysts.A lot of studies had shown that SiO₂ introducing way affected the existence state of SiO₂ on Al₂O₃ and the interaction between SiO₂ and Al₂O₃,which could further affect the texture,surface acidity and the performance of the catalysts.Currently,the research on SiO₂ modified Ni/Al₂O₃ catalysts for 1.4-butynediol hydrogenation mainly focused on the hydrothennal stability of catalyst.Whereas,there are rarely reports concerned about regulation of SiO₂-Al₂O₃ surface acidity and the effects on catalytic performance of Ni/SiO₂-Al₂O₃ catalyst for the hydrogenation of 1,4-butynediol.Based on our previous studies,we prepared Si02-Al₂O₃ supports and Ni/SiO₂-Al₂O₃ catalysts with different surface acidity by varying the way of SiO₂ introduction in the present work.The effects of SiO₂ introduction ways on surface acidity and the catalytic performance of catalyst for the hydrogenation of 1,4-butynediol were investigated.The main results are as follows:1.The effects of SiO₂ introduction way on surface acidity of supports of SiO₂-Al₂O₃ and hydrothermal stability were investigated.The results indicated that surface properties of supports showed obvious differences because of SiO₂ existence state.For SA-2,most of SiO₂ presented multilayer or aggregation on the surface of Al₂O₃ and covered some of Lewis acid sites on the surface,which led to the reduction of acid amounts of SA-2.For SA-1,SiO₂ was introduced into the structure of Al₂O₃ in the process of calcination and caused increase of unsaturated Al3+ on the surface of supports,which resulted to the increase of acid amounts of SA-1.No matter what way SiO₂ had been introduced.the formation of Al-O-Si-OH on SiO₂-Al₂O₃ improved the hydrothermal stability of supports.2.Based on the above work,the effects of surface acidity on the catalytic performance of Ni/SiO₂-Al₂O₃ catalyst were investigated.The results showed that Ni/SA-1 catalyst,using Al₂O₃ support prepared by introducing SiO₂ into Al（OH）3 and then calcination,presented high dispersion of active component and rich Lewis acid sites on the surface.Lewis acid sites could accept the lone electron pairs of C=O and promote activaton and adsorption of carbonyl on the surface of catalysts.The synergy of Lewis acid sites and Ni active sites made the catalyst show excellent activity in the hydrogenation for BDO synthesis.3.Stability of Ni/SiO₂-Al₂O₃ catalysts with different surface acidity was studied.The results showed that carbon deposition and active component aggregation were important factors to affect stability of catalysts.In the process of recycling,the degree of active component aggregation of Ni/SA-1 catalyst was smaller than that of Ni/SA-2.Although more carbon species were deposited on surface of Ni/SA-1,it mainly happened on strong acid sites of catalyst and still had large amount of weak and medium strong Lewis acid sites on the surface.The synergy of weak and medium strong Lewis acid sites with Ni active sites made the catalyst show highest hydrogenation activity and stability in the recycling of hydrogenation for BDO synthesis.