Mixed oxide method, calcined

The relation between the drying method and the surface area of powders is important. There are many drying methods, such as air, vacuum, and freeze drying. This point is illustrated with the examples of (Bao.2Pbo.8)Ti03. In powder preparation, the surface reactivity, that is, the specific surface area, plays a very important role. Specific surface areas are often determined by the BET (Brunauer, Eminett, and Teller) method. Typical BET plots of the sol-gel, CMO (calcined mixed oxide method), and MSS (molten salt synthesis method) [15] derived powders are shown in Fig. 1. 

Outside of catalyst preparation, reaction of sucrose with metal nitrates has been used to prepare nanocomposite mixed oxide materials. Wu et al. [46] reported the synthesis of Mg0-Al203 and Y203-Zr02 mixed oxides by reaction of nitrate precursors with sucrose. The resulting powders had smaller particles than those prepared without sucrose. Das [47] used a similar method in the presence of poly vinylalcohol to produce nanocrystalline lead zirconium titanate and metal ferrierites (MFe204, M = Co, Ni, or Zn). The materials prepared using sucrose had smaller crystallites than those made without. Both authors observed an exothermic decomposition of the precursors during calcination. 

Most industrial catalysts based on mixed oxides are simply and economically prepared via co-precipitation in aqueous medium.20 For the preparation of hexaaluminates, this method was first reported by S. Matsuda and co-workers.21 La203 xAl203 samples were prepared starting from an aqueous solution of La and Al nitrates. The precipitation was carried out by the addition of NH4OH solution up to pH=8. After it was washed, filtered and dried, the precursor was calcined at different temperatures up to 1400 °C. For a La203/Al203 mole ratio 5/95, the formation of a layered-alumina phase was observed starting from 1000°C and samples with a surface areas of 30 m2/g and 8 m2/g have been obtained upon calcination at 1200 °C and 1400 °C for 2 h respectively. 

Another method of analysis makes use of a subtraction procedure and has been applied to investigate the oxidation state of a series of Ce-Zr mixed oxides during a temperature programmed process [195]. A difference spectrum between the sample at a defined state and the calcined, fully oxidized material displays a positive peak at the position of feature Bo, characteristic of Ce, and a negative peak at the position of feature C, characteristic of Ce. The overall peak-to-peak amplitude is then proportional to the average reduction degree of Ce in the sample. 

Mixed oxide samples were prepared by the co-precipitation from aquatic solutions of the cations ([Ce(IV)] = 0.1 M) by adding equal volume of 1 M NHj solution under controlled conditions. Further calcium cerium mixed oxide samples were prepared by the incipient wetness method, for comparison. The solid phase was heated to dryness, in an oven at 250 C. Samples of magnesium cerium and calcium cerium mixed oxide prepared by co-precipitation were subsequently calcined at 400, 600 and 800 "C. 

Citrate method The preparation procedure consisted in the dissolution of the metal salts, namely Mn(N03)2 4H20 and Ce(N03)3 6H20, in distilled water, the complexation of the metallic cations with citric acid and the rapid concentration of the liquid by evaporation under vacuum. The viscous liquid was dried at 80°C and the amorphous precursor obtained was decomposed in air prior to calcination. Owing to the complexing property of the citrate anion, this procedure leads to the formation of finely dispersed two-phase systems or favours the formation of mixed oxide phases upon calcination, when these exist. Samples were calcined for 5 hours at 200, 300,400 or 500°C. 

PZC/IEP of Al-Ce Mixed Oxide Obtained by Evaporation and Calcination of AI(NO3)3-Ce(NO3)3-Citric Acid Solution Electrolyte T Method Instrument pH Reference... 

PZC/IEP of Al-Fe Mixed Oxide Calcined at 1200°C for 3 h AljOj (mol%) Electrolyte T Method Instrument... 

Titania and titania containing mixed oxides are extensively used as catalysts and supports. Recently, many preparation techniques have been developed to control their pore structure. However, some of them are not suitable for a systematic control of the pore distributions. In addition, pores usually disappear after calcination at high temperature [1]. To avoid this problem, catalysts were calcined at relatively low temperature [2-4] or an extraction method was used to remove organic residues [2]. Under such mild conditions, it is impossible to remove completely the organic residues which are bonded to a titania precursor. 

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