Preparation, Characterization And Catalytic Applications Of Solid Superbases KOH/SnO₂

Solid superbases are substances that possess basic sites higher than26(H_corresponding to the pKa value of the indicator). Compared with the traditional liquidalkali catalyst, there are some advantages of using solid superbase as the catalyst suchas extremely high activity and selectivity, mild reaction conditions, easy to beseparated from the products, simple post-processing, few corrosion to the reactor,recyclable, less waste liquid and residue. Due to the excellent characteristics of solidsuperbase catalysts, solid superbase catalysts are a class of promising industrialcatalyst in the green industry. They are expected to replace existing catalyst andcatalytic process in the future, and become a new generation of environment-friendlyfunctional catalytic materials.Herein, the support SnO2was prepared by using graphene oxide as templateunder reflux-digestion. Then, a series of solid superbase material KOH/SnO2wereobtained by thermal treatment of SnO2which modified with different quanlity ofKOH at550oC under N2. The structure and surface properties of these catalysts werestudied in detail by XRD, SEM, N2adsorption-desorption method, FT-IR, CO2-TPDand Hammett indicators method. Furthermore, its catalytic performances in theKnoevenagel condensation reaction and one-pot synthesis of polyfunctionalized4H-pyrans from condensation of aldehydes, malononitrile and an active methylenecompound were investigated. We also studied the effects of the KOH loading as wellas the relationship between the superbasicity and the catalytic activity. The obtainedmain research results are illustrated as follow:(1) The regular SnO2-based solid superbase nanoarchictures with specificmorphology and uniform pore structure were synthesized by using graphene oxide astemplate. It is found that the catalyst peforms the most superbasic sites and thehighest base strength, and it shows base strength in the range of26.5-33.0withsuperbasic sites up to1.362mmol/g, when the KOH loading was20%. This studyprovides a new carrier for the preparation of solid superbase, and may open up a routefor the design and synthesis of new functional superbase materials.(2) The obtained solid superbase material inhibited excellent catalytic activityand selectivity in Knoevenagel condensation reaction and one-pot synthesis ofpolyfunctionalized4H-pyrans from condensation reaction of aldehydes, malononitrile and an active methylene compound under mild reaction conditions. The relationshipbetween the superbasicity and the catalytic activity was disclosed. The resultsindicated that stronger base strength and more superbasic sites could result in thebetter catalytic activity.