The Preparation And Properties Of Zeolite-Based Solid Superacid Catalysts

Liquid acid catalysts such as H₂SO₄and HF are widely used in the industrialchemical processes, but they have serious drawbacks in handling, corrosiveness,toxicity and difficult separation. As environmentally benign catalysts, solid superacidcatalysts can solve these problems effectively. Because of unique shape-selectivity,large surface area, structural stability, strong resistance to toxicity as well as moderateacidity, zeolite-based solid superacid catalysts compared with other solid superacidcatalysts have been attractive for many acid catalyzed reactions, therefore they holdthe most promise.In this paper, the solid superacid catalysts were prepared with ZSM-38,SAPO-34and MCM-41molecular sieves as carrier and Zr （SO4）2（ZS）, H₃PW₁₂O₄₀（HPW） and H₂SO₄as active component. XRD, FT-IR, SEM, EDS, TG and laserparticle size analyzer were applied in the test of catalyst composition and structure.The effect of treatment conditions on the catalytic performance for esterification ofacetic acid （AA） with ethanol reaction had been studied. XRD analysis proves that ZSis highly dispersed on the zeolite surface by amorphous state. IR spectra show that Lacidity will be enhanced as the calcination temperature increasing, while B acidityimproves with the increment of ZS loading amount. From SEM and EDS analysis, wecan draw that the treatment of calcination and the addition of organic substances canimprove the sulfur content as well as Zr content, thereby increasing acid amount, acidstrength and catalytic performance in esterification reaction. TG analysis shows thatthe weight loss of ZS/SAPO-34catalyst can be divided into three stages, namely, at102.9,345.7and543.3oC, corresponding to the removal of free water accompanywith template agent in the catalyst, crystal water as well as the release of SO3from ZSdecomposition respectively; as ZS decomposition temperature is much higher than theexperimental reaction temperature, the catalyst can well maintain high stability during reaction process.Compared catalytic property of different zeolite-based solid superacid catalysts,we can conclude that the catalytic performance is associated with acid amount andstrength. Under suitable conditions, the conversion of AA is up to90.6%and theselectivity of ethyl acetate approaches to100%. The mechanism of zeolite-based solidsuperacid catalysts catalyze esterification had also been explored in this paper.Experimental results showed that catalysts mainly maintained B acid sites treated withlow temperature, and L acid sites with high temperature. Meanwhile, superacid centeris the corelation of B acid sites with L acid sites, within the scope of study, the greaterthe total acid strength and amount, the more beneficial to esterification reaction.