Effect Of Surface Microstructure Regulation Of Sulfated Solid Acid Superacid On Its Reactivity And Stability

Sulfated solid superacid(SO₄^2-/M_xO_y)is one of the most representative solid acids.Sulfated solid superacid(SO₄^2-/M_xO_y),distinguished from conventional liquid acids,has significant advantages of high catalytic activity,rapid separation,easy recycling and low corrosivity.However,when such materials are used for industrial applications,there are still many problems such as reactivity and stability.With regards to this,the academic community has proposed a variety of solid acid improvement strategies,including introducing various transition metals and noble metals such as Pt,Pd,Ir,Fe,Mn,etc.into the SO₄^2-/M_xO_y catalyst for modification.Alternatively,Ni O,Al₂O₃,molecular sieves,rare earths and the like are introduced into the carrier to form a multi-component composite carrier,which exhibits strong acidity and excellent catalytic activity after being sulfated.The starting point of these work is to adjust the interaction between the sulfur species and the carrier by introducing new components into the solid super acid to form a new acid center.Thereby improving the reactivity and stability of the solid super acid.At present,the method for improving the reactivity and stability of solid superacids still mainly follows this research idea.Different from previous research ideas,this paper takes sulfuric acid-promoted solid acid superacid as research object,and finds that surface microstructure regulation can effectively enhance its reactivity and stability.By regulating the bonding mode of the atoms on the surface of titanium dioxide,the coordination of the atoms can be affected.After the sulfating,the acidity of the solid super acid is effectively improved and the catalytic activity is enhanced.In addition,by adjusting the surface hydrophobicity of the sulfuric acid-supported titanium dioxide,the stability is effectively enhanced.In addition,it is also extended to the synthesis of dimethyl silicone oil.The specific research contents and conclusions of this paper are as follows:Firstly,mesoporous Ti O₂（B）whisker was firstly applied as a support for synthesizing the novel sulfated solid superacid(SO₄^2-/Ti O₂（B）).According to NH₃-TPD,TG and Py-IR characterization results,it was found that the similar amount of sulfate group on Ti O₂（B）and anatase showed significantly different acid characteristics and catalytic performances.The total acid amount of SO₄^2-/Ti O₂（B）was about 1.8 times as anatase-supported sulfated solid superacid(SO₄^2-/Ti O₂).Simultaneously,the SO₄^2-/Ti O₂（B）possessed higher percentage of Br（?）nsted acid and more weak-medium acid strength than SO₄^2-/Ti O₂.These acidic properties endowed SO₄^2-/Ti O₂（B）with the increased esterification reaction rate and decreased alkylation byproduct selectivity compared with that of SO₄^2-/Ti O₂.Analysis exhibited that there were more bridged bidentate sulfate groups coordinated to the Ti O₂（B）in SO₄^2-/Ti O₂（B）,which could induce more Ti cations to form Br（?）nsted acid sites than that of the chelating one.This was the key factor to be responsible for the unique acid characteristics of SO₄^2-/Ti O₂（B）.Secondly,this paper studies a strategy of facile coating a thick-tunable hydrophobic layer over the SO₄^2-/M_xO_y,which can significantly improve the water tolerance with negligible inhibition on the catalytic performance of SO₄^2-/M_xO_y.Even after being directly immersed in water,the hydrophobic SO₄^2-/M_xO_y can still maintain above 90%of original catalytic activity whereas pristine SO₄^2-/M_xO_y and control samples are almost completely deactivated.Additionally,both ³¹P MAS NMR and Hammett results adequately demonstrate that the superacidic property of solid sueracid can be maintained under the OTS layer.Finally,the above mentioned self-made SO₄^2-/Ti O₂ solid super acid was applied to the application system of synthesizing dimethyl silicone oil from octamethyl cyclotetrasiloxane（D4）and hexamethyldisiloxane（MM）.In the synthesis of dimethyl silicone oil,SO₄^2-/Ti O₂ solid super acid not only has good catalytic activity but also excellent stability,and the activity of 7 cycles is not obvious.However,the fatal disadvantage of solid-liquid separation is difficult in high viscosity liquids.To solve this problem,the activity and recovery performance of the shaped catalyst were preliminarily studied.