In Situ Preparation And Performance Of Quasi-TS-1 On Silica Surface

TS-1 molecular sieve is a widely used catalyst,and the main synthesis method is the classical hydrothermal synthesis method.In view of the situation that a large number of active structures in the classic TS-1 molecular sieve are embedded in the interior and cannot effectively play a catalytic role,in this paper,the adsorption phase reaction was used to prepare quasi-TS-1 on the surface of silica gel in situ,and the relevant process parameters and influence laws were explored.The paper firstly verifies the feasibility of the research scheme through experiments.Experiments without loading SiO2 show that it is difficult to synthesize highly active catalytic substances without the adsorption layer on the surface of SiO2,and there is no characteristic absorption peak of TS-1 in the UV-vis spectrum;by separating the supernatant and reacting,it is further proved It is difficult to synthesize highly active catalytic species in bulk.The adsorption process analysis showed that the template agent tetrapropylammonium hydroxide(TPAOH)could be enriched in the adsorption layer,which was beneficial to the in situ reaction on the silica surface.Studies have shown that when the water content does not exceed 2.0 g,quasi-TS-1 is mainly formed in the adsorption layer on the surface of silica gel,and subsequent experiments are based on this.The main conclusions are as follows:When the quasi-TS-1 was prepared by the adsorption phase reaction process,the optimal TPAOH/TBOT(molar ratio)was 1.11-1.34,while the typical value in the literature was greater than 10.This is because the enrichment of TPAOH in the adsorption layer can ensure the reaction to occur.Its concentration is high enough to meet the needs of quasi-TS-1 synthesis.When the quasi-TS-1 was prepared by the adsorption phase reaction process,the optimal range of Si/Ti molar ratio was 4.9-6.5,which was lower than the literature value of 15-30.This may be because the Si in the silica gel can participate in the synthesis of quasi-TS-1,thereby reducing the demand for Si in the raw material.This guess is supported by experiments measuring Si concentration in solution.A method for reducing the amount of expensive TPAOH during the adsorption phase reaction was found:when the amount of TPAOH was reduced by 40%,equal amount of TPABr and half amount of tetramethylguanidine were supplemented to synthesize quasi-TS-1 with higher activity.