Synthesis Of Aurichalcite And Rosasite And Analysis Of Preparation Process

Aurichalcite and rosasite are the main active phases in Cu/ZnO catalyst precursor. During the coprecipitation progress, mixed Cu2+ and Zn2+ react with CO32- and OH-, then subcarbonate precipitation formed. Crystal nucleus in the mother liquor grow into crystals gradually during the aging time. Because of the similar ionic radius and the electronic environment of Cu2+ and Zn2+, both of them could have isomorphous substitution reaction with subcarbonate, and then form aurichalcite (Cu,Zn)5(CO3)2(OH)6 and zincian malachite (Cu,Zn)2CO3(OH)2.(Cu>Zn)5(CO3)2(OH)6 and (Cu,Zn)2CO3(OH)2 could become CuO-ZnO solid solution after calcination. After reduction, Cu embedded in ZnO lattice and is able to be a very great interaction with ZnO. Moreover, it could prevent the loss and sintering of Cu and thus enhance the activity and stability of the catalyst effectively. Therefore, it’s of significant importance to increase the content of (Cu,Zn)5(CO3)2(OH)6 and (Cu,Zn)2CO3(OH)2 in catalyst precursor in order to prepare highly active, more stable Cu/ZnO catalyst.The catalyst precursor prepared by coprecipitation is a mixture of (Cu,Zn)5(CO3)2(OH)6, (Cu,Zn)2CO3(OH)2, carbonate and subnnitrate, therefore, it’s hard to know the accurate content of Cu and Zn in subcarbonate and at the same time to form CuO-ZnO and make it the most out of it.In this essay, we prepared single phase (Cu,Zn)5(CO3)2(OH)6 and (Cu,Zn)2CO3(OH)2 in two new ways. Based on this, We we investigated the effect of species of metal salts, Cu/Zn ratios, substitution temperature and time as well as microwave radiation on isomorphous substitution process to choose the best conditions and methods of preparation. Then we analysed the change of phase transformation, the crystal structure and the effect of microwave radiation on Cu2+, Zn2+ somorphous substitution process.Main conclusions after researches:(1). The preparation of (Cux,Zn1-x)5(CO3)2(OH)6 with Cu2+ isomorphous substitution method is different from coprecipitation method that product is single phase (Cux,Zn1-x)5(CO3)2(OH)6 The optimistic condition to synthesis (Cux,Zn1-x)5(CO3)2(OH)6 with Cu2+ isomorphous substitution method:Cu(CH3COO)2 as the copper source of isomorphous substitution and lasting 1.5 h at 60 ℃. The structure and size of crystal we get is appropriate. When Cu/Zn=35:100, the maximum amount of Cu in (Cux,Zn1-x)5(CO3)2(OH)6 is 29.5%.(2). The preparation of (Cu1-x,Znx)2CO3(OH)2 with Zn2+ isomorphous substitution method is different from coprecipitation method that product is single phase (Cu1-x,Znx)2CO3(OH)2. The optimistic condition to synthesis (Cu1-x,Znx)2CO3(OH)2 with Zn2+ isomorphous substitution method:Zn(NO3)2 as the zinc source, lasting 1.5h between 40℃～80℃. The shape and size of crystal we get is appropriate. When Zn/Cu=90:100, the content of Zn in (Cu1-x,Znx)2CO3(OH)2 is 49.7%, much higher than reported.(3). Microwave irradiation does not affect the composition of isomorphous substitution product. But compared with the samples made under water bath conditions, microwave irradiation accelerate the reaction rate of isomorphous substitution. Besides, microwave radiation can control the size of crystal, crystallite size of (Cu,Zn)5(CO3)2(OH)6 get bigger, whereas, (Cu,Zn)2CO3(OH)2 get smaller. Meanwhile, both of them change in the range of 20-3 Onm. This is probably an essential reason that microwave irradiation contributes to the enhancedt activity and stablity of Cu/ZnO catalyst for methanol synthesis.