Controllable Preparation Of Cobalt-based Nanosheets And Their Performance In The Styrene Epoxidation Reaction

With the increasing demand for fine chemicals such as drugs,perfumes,and cosmetics,efficient synthesis of fine chemicals has become an urgent problem to be solved.As an intermediate in the synthesis of fine chemicals,styrene oxide plays a very important role both in industry and life.Styrene oxide is mainly synthesized by the styrene epoxidation reaction,so how to catalyze the styrene epoxidation in a green and efficient manner has become an urgent problem to be solved.Heterogeneous catalysts,especially cobalt-based nanomaterials,have been favored due to their facile separation,low cost,and good activity.To this end,we first selected the most stable structure Co₃O₄ in cobalt oxides as the model,and controllably prepared an anisotropic Co₃O₄ nanosheets with（111）as the dominant exposed surface by co-precipitation method.This nanosheet can efficiently catalyze styrene epoxidation reaction,and its catalytic performance is 5.69 times higher than that of commercial isotropic Co₃O₄in enhancing the styrene oxide yield.It is known that the better performance of Co₃O₄nanosheets is due to the exposure of more tetrahedral Co²⁺through various characterization methods.Thus,we prepared Co Al₂O₄ nanosheets containing only tetrahedral Co²⁺by the same synthetic method,and verified that tetrahedral Co²⁺is the dominant active site for Co₃O₄ nanosheets to catalyze the styrene epoxidation reaction.In addition,we further confirmed the superiority of tetrahedral Co²⁺in catalytic kinetics by combining the epoxidation mechanism of styrene.Therefore,the exposure of more tetrahedral Co²⁺on the surface of Co₃O₄ nanosheets is the reason for the efficient catalytic styrene epoxidation.In the Co₃O₄spinel structure,tetrahedral Co²⁺can promote the production of styrene oxide.In order to explore whether Co²⁺still maintains its superiority in other catalytic systems,we controllably prepared Co-Ti O₂ nanosheets by a process method.In the styrene epoxidation reaction,the Co-Ti O₂ nanosheets maintained high activity,and the styrene oxide yield increased by nearly 1/3 when the doping amount of Co²⁺was nearly doubled.This indicates that Co²⁺is one of the reasons for the good catalytic performance of Co-Ti O₂ nanosheets.Therefore,Co²⁺still maintains a high activity after being separated from the Co₃O₄ spinel system.This dissertation mainly studies the promoting effect of Co²⁺on the styrene epoxidation reaction,and also provides some theoretical guidance for the further synthesis of efficient styrene epoxidation catalysts and the design of other catalysts.