Styrene Epoxidation And Oxidative Carboxylation Of Styrene Reactions Over Supported Gold-based Catalysts

In the development of humen society, the remarkable utilize of petrifation and fuel, such as coal and petroleum, cause increase of the amount of the carbon dioxide discharge. This greatly affects the balance of atmosphere and biosphere. As a result, it lead to"green house"and a series of problems which are related to our living environment. How to solve the current problems becomes a serious problem for sientist in the whole world. By another way, the carbon resourse like petroleum, coal and natural gas is limited. Then, it will be anoher serious problem for humen that the resourse will dry up one day. However, CO2 abroadly exists in atmosphere and water, in which the amount of carbon is ten times more than that of the petroleum, coal and natural gas. So if we can successfully reuse, converse, and fix CO2, it will be one way to solve the above problems. Nowadays, the chemical fixation of carbon dioxide is a hot topic and challenge because of the inertness of carbon dioxide.The most effective route for carbon dioxide chemical fixation is to synthesize five-membered cyclic carbonate via the coupling of CO2 with epoxides. Since 1969 Inoue et al. first reported cyclic carbonate can be prepared by cycloaddition of CO2 to epoxides, numerous catalysts such as alkali metal halides, organic bases, metal oxides, zeolites, smectites and metal complexes have been investigated. However, activity, stability and recovery of the catalysts still remains to be improved. Besides another way to synthesize cyclic carbonate, is via oxidative carboxylation of olefin, which couples two sequential reactions of epoxidation of olefin and CO2 cycloaddition to epoxide formed. Synthesis of cyclic carbonate from olefin and CO2 gives a simple route that avoids the preliminary synthesis and isolation of epoxides. Furthermore, easily available and low-priced chemicals of olefins may be reused to produce valuable chemicals as compared with epoxide as substrates. This direct synthesis route for cyclic carbonate from olefin is not only energy saving but also simple and economic. Despite the usefulness of this reaction, little efforts have been made so far, in contrast to extensive study on the coupling reaction of CO2 with epoxide.Arai et al. reported, Au/SiO2-ZnBr2/Bu4NBr catalyst system is active for the direct synthesis styrene carbonate (SC) from styrene. In this system, supported metallic Au is active for the epoxidation of styrene, and ZnBr2/Bu4NBr cooperatively catalysing the subsequent CO2 cycloaddition to epoxide. Moreover, the efficiency of the SC one-pot synthesis would be determined mostly by the catalytic performance of the gold catalyst. Hence, if more active and selective catalysts for the epoxidation reaction were to be explored, more effective catalyst system for the one-pot synthesis would be realized.The supported gold-base catalysts are a kind of new materials developed recently and may be used widely in chemical industry, environmental protection and automobile industry because of their special properties. Particularly, the supported gold-based catalysts exhibit excellent catalytic performance for CO oxidation and low temperature water-gas shift reaction. Recently, Choudhary et al report novel high active(67.0%) and selective(66.1%) catalysts by homegeneous deposition-precipation using urea in the epoxidation of styrene to styrene epoxide by t-butyl hydroperoxide (TBHP).In the former work, we made a study for the epoxidation of styrene by t-butyl hydroperoxide (TBHP) over the catalyst Au/Fe(OH)3 prepared by co-precipitation method, and the results showed better convesion and selectivity. Later, we conbine Au/Fe(OH)3 and ZnBr2/ Bu4NBr to catalyze CO2 and styrene to directly synthesize styrene carbonate. Moderate yield of desired product- styrene carbonate was obtained. The influence of chemical state of catalyst support and gold on activity is studied in detail. The catalysts were characterized by XPS and Fe M?ssbauer spectra. The synergistic effect of Au3+ and Fe(OH)3 is responsible for its good activity for styrene epoxidation. When the above supported gold catalyst was combined with ZnBr2/ Bu4NBr catalysts, Au/Fe(OH)3 is active for the epoxidation of styrene and ZnBr2/ Bu4NBr are active for the CO2 cycloaddion to styrene epoxide.