Citrate route

Nd2Ni04+5 powder was prepared by nitrate-citrate route as described by Courty, et a1. (1973). Stoichiometric amounts of neodymium and nickel oxides were dissolved in diluted nitric acid. After addition of a large excess of citric acid, the solution was dehydrated and heated until self-combustion of the precipitate to obtain submicronic precursor particles (Boehm, 2005). The final annealing was performed at 1000°C for 12 hours to obtain a single crystalline phase. The particles were then ball milled to obtain an average grain size (d0 5) of about 0.8 pm. A terpineol-based slurry was prepared from this powder and this was deposited on the electrolyte by screen printing and then sintered at 1100°C for three hours in air (Lalanne, 2008). 

A new citrate route for the synthesis of catalysts easy to scale-up and environmentally friendly. 

A new method was developed, based on the original citrate route, which allows to synthesize perovskites with different incorporated metallic cations. Various catalysts based on the barium zirconate were prepared by this method. Perovskites were obtained containing either noble (Pd, Rh) or other metals (K, Cu, Mn). These systems were tested for several catalytic reactions, giving promising results. 

In 2001, we proposed a variation of the original citrate route, more widely applicable and less hazardous, in which 1) nitrates are not used as starting salts, and 2) the decomposition is carried out under milder conditions, involving a lean oxygen gas flow (1,5% O2), and lower temperatures (T 350°C). 

The modified citrate route developed at the University of L Aquila is a new, versatile and easy technique to synthesize perovskitic systems ABO3 in which different metallic cations can be incorporated both in A and B sites. 

Again significant expansion of the perovskite lattice (a = 5.44A) was observed. LaCo03 prepared via the citrate route, as can be inferred from the sharpness of the peaks, exhibit a large increase in the degree of crystallinity when compared with those prepared via both the co-precipitation and the thermal evaporation route. Similar results were also seen at lower temperatures, namely 600°C and 700°C, again an observation not seen for the other two preparation routes. However this time the lattice expansion was less significant (a = 5.41A). 

The citrate route to colloidal Au, first described by Hauser and Lynn [164], is a popular method to prepare Au hydrosols. Synthesis by the citrate method involves the addition of chloroauric acid to a boiling solution of sodium citrate [144]. A wine red color indicates the onset of reduction. The average diameter of the nanoparticles can be varied over a range of 10-100 nm by varying the concentration ratio between chloroauric acid and sodium citrate (see Fig. 2.4). Turkevich [165] proposed that the reaction involved the formation of acetone dicarboxylate. Subsequent reduction occurs by the dicarboxy-late species. The citrate method has been extended to synthesize of Pt and Ag nanoparticles [166-168]. Turkevich and coworkers [169] prepared Au-Pt... 

The role of support on the performance of noble metals-based catalysts for the total oxidation of aromatic hydrocarbons is essential [38]. Although with a smaller surface area than the typical supports, perovskites also demonstrate good properties as carriers for noble metals. Thus, perovskites of type LaBOs (B = Co, Mn, Fe, Ni) synthesized using the citrate route were used as support for noble metals in total oxidation of toluene [39]. The performances of these catalysts varied in the order Fe>Mn>Co>Ni, and the superior behavior of iron was attributed to the low temperature of calcination and the high stability of the perovskite lattice irrespective of the nature of the stream it was exposed to. The dispersion of palladium at the different stages of the process remained unchanged. 

Yue Z, Zhou J, Wang X, Gui Z, Li L (2001) Low temperature sintered Mg-Zn-Cu ferrite prepared by auto-combustion of citrate-nitrate gel. J Mater Sci Lett 20 1327-1329 Du K, Zhang H (2003) Preparation and performance of spinel LiMn O, by a citrate route... 

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