Deposition-precipitation with urea DPU

Using urea (CO(NH2)2) makes it possible to employ the real procedure of DP as first described.2,3 Urea acts as a delay base since there is no reaction when it is dissolved in a suspension of the support in the aqueous metal salt solution at room temperature hydrolysis only occurs when this is heated above 333 K, according to the equation  

In the first attempt to prepare supported gold catalysts in this way,77,78 HAuCU was added to a suspension of the support in urea solution heated at 353 K, but after calcination at 673 K, quite large gold particles were obtained on titania, silica and alumina. In other work,79 complete deposition of gold onto alumina (5wt.%) was achieved, but particles were again large after calcination. 

In a more extensive study,37,52 it was found that small gold particles could be obtained on titania, alumina and ceria (Table 4.4) providing that the DP time at 353 K was long enough (at least 4 h). Moreover, it was found 

In addition to titania, alumina and ceria supports (Table 4.4), the DPU method has been applied to other supports. Gold particles supported on ferric oxide were quite small (3-7 nm) after thermal treatment is static air at 623 K.80 Another study reported the use of the DPU method to deposit gold onto other supports (MgO, CaO, SrC 2 and BaO).81 After calcination at 673 K, gold particles of moderate size were obtained on magnesia (8 nm) and on calcia (6nm). In all cases, all the gold in solution was deposited on the support. 

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