Analysis On Surface Acidity And Catalytic Esterification Activity Of Solid Superacid SO₄～(2-)/MoO₃-TiO₂

Solid acid can be regarded as a solid that changes the color of basic indicator, and solid superacid can be defined as a solid acid whose acidity is stronger than that of 100% H2SO4 (H0=-11.92). Since the early 1980s, the preparation and application of solid superacid SO2-4/MxOy have been becoming an active area of research, because such a superacid has many appealing advantages: It has diversified classes, very strong acidity, no corrosive halogen irons, and it is suitable for various acid-catalyzed reactions with multiple reutilization and easy regeneration. Moreover, it offers the possibilities of circumventing the drawbacks associated with conventional liquid inorganic acid such as corrosion to the reactor, difficulty in separation from the reaction mixture, complicated post-treatment, and environmental pollution.A new type of solid superacid SO2-4/MoO3-TiO2(SMT)was prepared and its possible surface structure,surface acidity and catalytic esterification activity were analyzed in this paper.First, with (NH4)6Mo7O24 as the source of molybdenum, SO2-4 as the accelerant and Ti(OH)4 prepared by aging methods at low temperature as the precursor of TiO2, SMT was obtained via calcination at high temperature. The process parameters of SMT preparation were optimized using the catalytic synthesis of n-butyl propanoate as a probe reaction. The optimum process conditions for preparing SMT were pH 8 for Ti(OH)4 deposition, 20% MoO3, 0.5mol/L H2SO4 and 773K for calcinating.Second, the influence of adding Mo into SO2-4/TiO2 on crystallizing temperature, crystal phases, possible surface structure and specific area was studied by DTA,XRD,FT-IR and BET. Experimental results have demonsrated that addition of MoO3 into SMT decreased the crystallizing temperature of TiO2 that is beneficial for the crystallization of TiO2 surface, increased the specific area and controlled the reduction of the specific area on calcination. Compared with SO2-4-TiO2, SMT, however, showed a declined thermostability. Both SMT and SO2-4/TiO2 was anatase crystalline phases. The acid sites on SMT surface exhibited a chelating biligand structure that was characteristic of a superacid.Third, qualitative or quantitative analysis of the acid species were carried out using FT-IR spectra of pyridine adsorbed on the catalyst surface, Hammett indicator and n-butylamine titratio. The results demonsrated that SMT was Br?nsted acid. The...